EVALUATING THE IMPORTANCE OF SOIL
MOISTURE AVAILABILITY (AS A LAND QUALITY)
ON SELECTED RAINFED CROPS IN SEROWE AREA,
BOTSWANA
Esther Mweso
March 2003
Evaluating the importance of soil moisture availability (as a
land quality) on selected rainfed crops in Serowe area,
Botswana
By
Esther Mweso
Thesis submitted to the international Institute for Geo-information Science and Earth Observation
in partial fulfilment of the requirements for the degree of Master of Science in Geo-information
Science and Earth Observation, Soil Information Systems for Sustainable Land Management
Degree Assessment Board
Assoc. Prof. Dr. D.G. Rossiter (ITC)
Drs. S. de Bruin (University of Wageningen)
Dr. A. Farshad (ITC)
Dr. M. Lubczynski (ITC)
(Chairman/Second supervisor)
(External Examiner)
(First supervisor)
(Internal Examiner)
I
Disclaimer
This document describes work undertaken as part of a programme of study at the
International Institute for Geo-information Science and Earth Observation. All
views and opinions expressed therein remain the sole responsibility of the author,
and do not necessarily represent those of the institute.
II
Abstract
The main objective of this research was to evaluate land with emphasis on soil moisture
availability for rainfed maize and sorghum in Serowe area in Botswana.
To accomplish this, hydraulic properties such as actual soil moisture content, infiltration
rate and hydraulic conductivity measurements were measured and examined verses soil
properties in space. Interviews with farmers and agricultural extension staff helped to
formulate land utilisation types (LUTs), land use requirements (LURs) and land
characteristics (LCs). PS2 water limited production potential was used to evaluate the
effect of soil moisture on yield of the selected crops, namely maize and sorghum.
Automated Land Evaluation System (ALES) was employed to classify land into
suitability classes, considering also the management.
The PS2 water limited potential revealed that increase in initial matric suction (PSIinti.)
leads to yield reduction of 53% for maize and 57% for sorghum implying that reduction
in soil moisture leads to decline in yield. The difference in yield at different levels of
PSIint was significant (99%). There is positive relationship between moisture availability
and yield of the crops. Late planting leads to low yield.
The negative relationship between actual soil moisture and infiltration rate as well as
hydraulic conductivity on landscape basis does not give any meaningful results but the
positive relationship on the basis of soil type, clearly declare the importance of soil and
its variability.
The area has different soil types, which are spatially variable. The main soil types are
Ferralic Arenosols (mainly in plateau), Calcic Luvisols, Pellic Vertisols, Eutric Nitosols
(mainly in peneplain) and Endoleptic Regosols (mainly in hilland). The spatial variability
of soil types influences soil moisture distribution.
Distribution of farmlands is mainly on clay loam and sandy clay loam soils which are
found on the middle and lower terraces.
Evaluation results show that different map units have different suitability classes, and that
soils of the hilland and plateau are not suitable for the land utilisation types currently
practised in the area.
III
Acknowledgements
My deepest and profound gratitude go to Dr A Farshad, my main supervisor for his
guidance, expert advices, encouragement and valuable comments. I am indebted for his
assistance during fieldwork.
I am grateful to Dr D.G Rossiter, my second supervisor for his advice, comments and
willingness to assist even during his vacations.
Bart Krol and Dr. Shrestha for their suggestions and advice during proposal writing.
To the Government of Malawi, The Director of Land Resources Department, Mr J.N
Mlenga, for giving me an opportunity to pursue this course, and The Deputy Director for
Training, Mr J.J. Mussa for all the logistics made.
Dr W. Siderius for his insights about the study area.
I am sincerely grateful to my colleagues Ermias Betemariam, Enver Mapanda and Dennis
Tembo with whom pleasant and hard times were shared, my colleagues from Soil Science
Division, to my M.Sc. colleagues Ki Hwan Cho, Haig Sawasawa, Micheal Mwangangi,
Amos Situma, Phoebe Luwum for their invaluable help in enhancing my computer skills.
The people at Setekwane camp in Serowe, Botswana for good company-you really made
our stay comfortable.
I am especially grateful to my husband Sanless, and my children Chimango and Zenani
for enduring my eighteen months absence and incessantly offering encouragement
throughout the period.
To my brothers, sisters, nephews and nieces for their prayers and moral support.
To the Almighty God for seeing me through the programme
IV
V
Table Of Contents
Disclaimer .................................................................................... II
Abstract .......................................................................................III
Acknowledgements..................................................................IV
Table Of Contents .....................................................................VI
List of tables..................................................................................IX
List of figures................................................................................. X
List of Plates .................................................................................XI
Chapter 1: Introduction ............................................................. 1
1.1 IMPORTANCE OF AGRICULTURE IN THE SOUTHERN AFRICA DEVELOPMENT
COMMUNITY (SADC) REGION ........................................................................................ 1
1.2 PROBLEM FORMULATION ........................................................................................... 2
1.3 RESEARCH OBJECTIVES .............................................................................................. 2
1.3.3 Overall objective ................................................................................................ 2
1.3.2 Specific objectives .............................................................................................. 3
1.3.3 Research questions............................................................................................. 3
1.3.4 Hypotheses ......................................................................................................... 3
1.4 CONCEPTUAL FRAMEWORK ........................................................................................ 3
1.5 THESIS OVERVIEW...................................................................................................... 6
Chapter 2: A Literature review on soil water ...................... 7
2.1 SOIL MOISTURE ..................................................................................................... 7
2.1.1 Definition and importance ................................................................................. 7
2.1.2 Some concepts of soil moisture .......................................................................... 7
2.1.3 Soil water relations............................................................................................ 8
2.1.4 Infiltration .......................................................................................................... 8
2.1.5 Hydraulic conductivity....................................................................................... 9
2.2 MODELLING SOIL WATER ......................................................................................... 10
2.2.1 WOFOST.......................................................................................................... 10
2.2.2 PS123 ............................................................................................................... 10
2.2.3 Hydrus.............................................................................................................. 11
2.2.4 Water balance .................................................................................................. 11
2.2.5 Loss of water by plants .................................................................................... 12
2.2.6 Optimum availability of soil moisture.............................................................. 12
2.4 SOIL VARIABILITY .................................................................................................... 13
2.5 LAND EVALUATION .................................................................................................. 13
Chapter 3 Study area ............................................................... 17
VI
3.1 LOCATION ................................................................................................................ 17
3.2 CLIMATE .................................................................................................................. 17
3.2.1 Rainfall............................................................................................................. 18
3.2.2 Temperature..................................................................................................... 18
3.2.3Relative Humidity.............................................................................................. 19
3.2.4 Evapotranspiration .......................................................................................... 19
3.2.5 Wind ................................................................................................................. 20
3.2.6 Sunshine ........................................................................................................... 20
3.3 GEOLOGY................................................................................................................. 20
3.4 GEOMORPHOLOGY ................................................................................................... 21
3.5 VEGETATION ............................................................................................................ 23
3.6 HYDROLOGY ............................................................................................................ 24
Chapter 4 Materials and Methods ........................................ 26
4.1 MATERIALS .............................................................................................................. 27
4.2 RESEARCH METHODS AND TECHNIQUES ................................................................... 27
4.2.1 Data exploration and Aerial photo interpretation........................................... 27
4.2.2. Soil survey...................................................................................................... 27
(A) Pit description..................................................................................................... 27
(B) Infiltration........................................................................................................... 28
(C) Hydraulic conductivity ....................................................................................... 28
(D) Soil moisture measurements............................................................................... 29
(E) Particle size distribution..................................................................................... 29
4.2.4 Land evaluation ............................................................................................... 30
(A) Interviews............................................................................................................ 30
(B) Climatic data access ........................................................................................... 30
(C) Production potential PS-2 .................................................................................. 31
(D) Selection of Land use requirements (LURs)....................................................... 33
(F) Building model in Automated Land Evaluation System (ALES) for Land
Suitability Evaluation................................................................................................ 34
4.3 DATA PROCESSING AND ANALYSIS ........................................................................... 35
4.3.1 Statistical analyses........................................................................................... 35
(A) Hydraulic properties........................................................................................... 35
(B) PS-2 Production Potential water –limited production ....................................... 36
4.3.2 Geostatistical analysis ..................................................................................... 36
4.3.3 Remote Sensing ................................................................................................ 36
4.4 LIMITATIONS............................................................................................................ 36
Chapter 5 Soils ............................................................................. 37
5.1 SOIL AND SOIL FORMATION ...................................................................................... 37
5.1.1 Climate............................................................................................................. 37
5.1.2 Erosion............................................................................................................. 37
5.1.3 Vegetation ........................................................................................................ 39
5.1.4 Parent material ................................................................................................ 39
5.2 GENERAL DESCRIPTION OF LANDFORMS AND SOILS ................................................. 39
5.3 SOILS OF THE STUDY AREA ....................................................................................... 44
VII
Chapter 6 Land use .................................................................. 48
6.1 LAND USE DEFINITON AND KINDS OF LAND USE ....................................................... 48
6.2 LAND UTILISATION TYPES IN THE SEROWE AREA ..................................................... 49
Description of land utilisation types (LUTs) ............................................................ 50
LUT1 Maize-based.................................................................................................... 50
LUT2 Sorghum-based ............................................................................................... 51
Chapter 7 Results and Discussion ...................................... 54
7.1 HYDRAULIC PROPERTIES .......................................................................................... 54
7.1.1 Infiltration rates ............................................................................................... 54
7.1.2 Actual moisture content ................................................................................... 57
7.1.3 Hydraulic conductivity (k) ............................................................................... 59
7.1.4 Relationship of the hydraulic properties.......................................................... 62
7.2 SOIL MOISTURE MAP ................................................................................................ 70
7.3 SPATIAL VARIABILITY .............................................................................................. 71
7.3 WATER-LIMITED PRODUCTION POTENTIAL PS2 ....................................................... 75
7.4 PHYSICAL LAND EVALUATION................................................................................. 81
SUMMARY ...................................................................................................................... 85
Chapter 8 Conclusion and recommendations........................... 86
References..................................................................................... 88
APPENDIX A: SOIL HYDRAULIC PROPERTIES RESULTS ................................................... 91
APPENDIX B: SOIL PROFILE DESCRIPTION ...................................................................... 93
APPENDIX C: CLIMATIC FILE ....................................................................................... 108
APPENDIX D (A): GENERIC DATA VALUES FOR MAIZE AND SORGHUM ......................... 113
APPENDIX D(B): GENERIC DATA VALUES .................................................................... 113
APPENDIX E: GROWTH CYCLE FOR MAIZE AND SORGHUM ........................................... 114
APPENDIX F: GLOSSARY .............................................................................................. 114
APPENDIX G: QUESTIONNAIRE .................................................................................... 115
APPENDIX H: RESULTS OF PARTICLE SIZE DISTRIBUTION ANALYSIS ............................ 121
APPENDIX I: DECISION TREES ...................................................................................... 122
VIII
List of tables
Table 4- 1 The crop indicative values............................................................................ 32
Table 4- 2 LURs for maize ............................................................................................. 33
Table 4- 3 LURs for sorghum ........................................................................................ 34
Table 6- 1 Crop calendar................................................................................................ 49
Table 6- 2 Yield gap for LUT1 in 1999/2000 ................................................................ 51
Table 6- 3 Yield gap for LUT2 in 1999/2000 growing season ..................................... 51
Table 6- 4 Yield gap for late planting for LUT1 .......................................................... 52
Table 6- 5 Yield gap for late planting for LUT2 .......................................................... 52
Table 7- 1 Descritpive statistics for infiltration between landscapes ......................... 55
Table 7- 2 ANOVA for infiltration between landscapes.............................................. 55
Table 7- 3 ANOVA for infiltration between soil types ................................................ 56
Table 7- 4 Differences between pairs of means of soil types ....................................... 56
Table 7- 5 ANOVA for moisture content between the landscapes ............................. 57
Table 7- 6 Descriptive statistics for moisture between landscapes............................. 57
Table 7- 7 ANOVA for differences between pairs of soil types .................................. 58
Table 7- 8 Means and standard deviations of the soil types........................................ 58
Table 7- 9 The confidence intervals of the soil types ................................................... 59
Table 7- 10 ANOVA for hydraulic conductivity based on landscapes...................... 60
Table 7- 11 Descriptive statistics for saturated hydraulic conductivity..................... 60
Table 7- 12 Means and standard deviations of soil types ............................................ 61
Table 7- 13 The ANOVA for the means of saturated hydraulic conductivity........... 61
Table 7- 14 Differences in the means of saturated hydraulic conductivity of different
soil types................................................................................................................... 62
Table 7- 15 Correlation of hydraulic properties across the area................................ 62
Table 7- 16 Correlation of hydraulic properties by landscape ................................... 64
Table 7- 17 Correlation of hydraulic properties for soil types ................................... 67
Table 7- 18 The water limited yield of LUT1 for cropping year 1999/2000 .............. 75
Table 7- 19 water limited yield of LUT2 in the cropping year 1999/2000 ................. 75
Table 7- 20 LUT1 yield with different levels of PSIint ................................................ 76
Table 7- 21 ANOVA for water-limited yield of LUT1................................................. 76
Table 7- 22 ANOVA for water-limited yield of LUT2................................................. 77
Table 7- 23 The crop water functions at PSIint 500 and 2000cm for LUT1 ............. 77
Table 7- 24 The crop water functions at PSIint 500 and 2000cm for LUT2 ............. 78
Table 7- 25 Physical suitability for LUT1 and LUT2 .................................................. 83
IX
List of figures
Fig 1- 1 A generalised flow chart of the conceptual frame work.................................. 5
Ψ-Ψ
Ψ relations of soils of different texture ................ 9
Fig 2- 1 Some characteristic SMΨ
Fig 2- 2Water fluxes that condition the volume of moisture in the rooting zone and
availability of water for uptake by roots............................................................... 12
Fig 3- 1 Location of Serowe the study area in Botswana............................................. 17
Fig 3- 2 The variation in rainfall distribution within years ........................................ 18
Fig 3- 3 Variations in rainfall amount between years ................................................. 18
Fig 3- 4 Temperature ranges of the study area. ........................................................... 19
Fig 3- 5 The relative humidity of the area. ................................................................... 19
Fig 3- 6 Sunshine hours over the year........................................................................... 20
Fig 3- 7 The Kalahari basin with the fault line running northwest to southeast ...... 21
Fig 3- 8 The geological map of Serowe.......................................................................... 21
Fig 3- 9 The stereogram depicting part of the study area. .......................................... 22
Fig 3- 10 The cross section of the study area ................................................................ 23
Fig 4- 1 Flow diagram of research activities................................................................. 26
Fig 4- 2 Theta probe........................................................................................................ 29
Fig 5- 1 Study area showing the sample blocks and pit profile points ....................... 41
Fig 5- 3 The geopedological map of Serowe.................................................................. 42
Fig 5- 4 The soil map of Serowe..................................................................................... 45
Fig 6- 1 Land use map of Serowe................................................................................... 48
Fig 7- 1Basic infiltration rates ....................................................................................... 54
Fig 7- 2 Saturated hydraulic conductivity at SVD 081................................................ 60
Fig 7- 3 Hydraulic properties across the area .............................................................. 63
Fig 7- 4 Relationship of hydraulic properties in hilland ............................................. 65
Fig 7- 5 Relationship of hydraulic properties in peneplain......................................... 66
Fig 7- 6 Relationship of hydraulic properties per soil type......................................... 68
Fig 7- 7 Soil moisture distribution map at 10cm depth ............................................... 71
Fig 7- 8 Soil moisture distribution map at 30cm depth ............................................... 71
Fig 7- 9 Moulded variogram parameters for AMC at 10 and 30 cm depths............. 72
Fig 7- 10 Soil moisture at 10cm depth (ordinary kriging ............................................ 73
Fig 7- 11 The error map at 10cm depth ........................................................................ 73
Fig 7- 12 Soil moisture map at 30cm depth (ordinary kriging) .................................. 74
Fig 7- 13 The error map for 30cm depth ...................................................................... 74
Fig 7- 14 Yield response to PSIint applied for LUT1 .................................................. 79
Fig 7- 15 Yield response to PSIint applied for LUT2 .................................................. 80
Fig 7- 16 Physical land suitability for LUT1 ................................................................ 84
Fig 7- 17 Physical land suitability for LUT2 ................................................................ 84
X
List of Plates
Plate 3- 1 Part of the study area, depicting plateau and hilland................................. 23
Plate 3- 2 One of the vegetation types in the study area.............................................. 25
Plate 3- 3 Gully erosion in some parts of the study area ............................................. 25
Plate 5- 1 A gully showing layers of depositional materials around Sokwe area in
Serowe ...................................................................................................................... 38
Plate 5- 2 Gully formation due to water erosion .......................................................... 38
Plate 5- 3 Ferralic Arenosols and Pellic Vertisols profiles .......................................... 42
XI
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Chapter 1: Introduction
1.1 Importance of agriculture in the Southern Africa development
Community (SADC) Region
Food security is a global concern as it affects the quality of life for both present and future
generations. But the environmental degradation poses a challenge to the scientific world since it
affects the agricultural production in terms of climatic changes and land degradation. This calls
for proper land use information at various levels of planning.
In many developing countries, agriculture, more especially crop production, is the major source
of livelihood. This is true in the Southern Africa Development Community (SADC) region.
Increasing the productivity of marginal rainfed agriculture is the key for many countries to
radically improve food security and reduce rural poverty.
As observed by Voortm (1985) increased agricultural production can be achieved by more
intensive use of land and by bringing additional land to cultivation both of which imply
substantial changes in land utilisation. Reliable predictions and recommendations can be made if
there is sound planning of changes in land use that requires a thorough knowledge of the natural
resources and reliable estimates of what they are capable of producing.
Despite the marginal ecological suitability, farmers in semi-arid areas depend on rainfed
agriculture. In countries of SADC alone, over two million people are estimated to live in areas
with average annual rainfall of around 500mm. The vast majority of these are at least partially
dependent on rainfed cropping for their subsistence (Gollifer, 1990) . Farmers in this zone face
high risk of crop failure due to variability of rainfall within and between years (Singh and Reddy,
1988; Tersteeg et al., 1992); In bad years, the harvest is very poor to suffice farmers demand.
Botswana is one of the countries in southern Africa that faces similar problems. Tersteeg et al,
(1993) further explain that in order to adapt to such an environment, farmers have typically
adopted strategies to spread and minimise risks like rearing livestock and small-scale commercial
activities. Parry et al, (1988) conclude that crop yields in these regions are very sensitive to the
amount of seasonal rainfall. Therefore, it is necessary to derive the relationship between average
yield decrease and relative evapotranspiration deficit as yield response factor in order to quantify
the effect of water stress (Landon, 1984). In agricultural production, climate is one of the factors
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
that are considered critically. The most important parameters within climate are rainfall,
temperature and radiation (Sys et al., 1991).
Today, many developing countries like Botswana are trying to improve on agricultural production
with the aim of attaining food security.
1.2 Problem formulation
Drought is a major drawback in agricultural production and has become a worrisome situation in
the SADC region. Serowe area in Botswana, which is the study area for this research, experiences
long droughts. In some years farmers plant seeds without harvesting due to a number of factors,
such as poor rainfall distribution, use of late maturing crop varieties and poor choice of land for
agricultural production as more land is devoted to livestock production followed by settlement
(D. O. S. M, 2001). This calls for better planning of land for maximum productivity. Land
evaluation provides a set of data on potentials and constraints that can contribute to decisions on a
sustainable land use.
The suitability map (FAO, 1990c) available for rainfed agriculture in Botswana was conducted at
a national scale (Tersteeg et al., 1992) making the map generic. This map cannot give detailed
information of soils in a specific area but can be instrumental for further research. It is assumed
that there are some variations within an area for soil characteristics. This makes the suitability
map weak tool for planning because it can only evaluate production systems based on standard
level of inputs.
Therefore, some studies are needed to focus on smallholder farmer level. Some
studies have been conducted in the area especially looking at the groundwater flow and recharge
for domestic use (SGC, 1988). These studies focussed on improvement of water supply to the
residents and livestock of the area. So far little has been done in Botswana on the role of soil
moisture availability in relation to crop yield. With no surface water resources, farmers rely on
rainfall for crop production yet this rainfall is not enough. Therefore there is need to establish the
water balance model for the area that can be used as a reference point for production of some
cereal crops. It is against this background that the study is going to evaluate land in Serowe area
in Botswana with emphasis on soil moisture availability.
1.3 Research objectives
1.3.3 Overall objective
The overall objective is to evaluate the effect of available soil moisture on yield of rainfed maize
and sorghum in Serowe area in Botswana.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
1.3.2 Specific objectives
1. To determine the theoretical water-limited yield of grain crops (maize and sorghum)
2. To examine variations in distribution of different soil types
3. To analyse the relationship between soil types and hydraulic properties (actual
water content (AWC), hydraulic conductivity (k) and infiltration rate)
4. To evaluate soil moisture availability with respect to soil type and spatial variability
5. To describe principle land use types for rainfed smallholder grain products
6. To carry out land suitability evaluation with emphasis on soil moisture availability.
using PS123 and ALES softwares.
1.3.3 Research questions
1. What is the theoretical water limited yield for sorghum and maize?
2. Does the area have different soil- geomorphic units?
3. What are the different types of soil in the study area?
4. What are the factors that influence soil moisture availability?
5. Does spatial variability affect soil moisture distribution?
1.3.4 Hypotheses
1.Different soil types have different soil hydraulic properties.
2.Soil moisture distribution is controlled by spatial variability.
3.There is a spatial dependency between soil moisture and soil variability.
4.Soil properties can be used to infer the land quality moisture availability in the land
suitability evaluation process.
1.4 Conceptual framework
In carrying out a research, all activities and procedures have to be laid and followed properly in
order to succeed with that work. Similarly, there is a conceptual framework that was laid which
acted as a guide and provided links to different activities within the research life cycle. Referring
to the diagram (fig 1-1) of this conceptual framework a brief explanation is given.
The central point is the moisture availability, which is explained by different tools. The aim is to
find out the effect of soil moisture availability on the crop production (yield), for which maize
3
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
and sorghum were selected. Each tool comes into play at different stage and one tool can be an
input to another tool. The major tools are PS2, which is a production potential programme for
estimating yield, and Automated Land Evaluation System (ALES), which is used to evaluate
land.
The entry point is the aerial photo and image interpretation leading to the establishment of map
units, which can be described after fieldwork, that is, when the soil contents of the units become
known. On top of the newly collected information, historical data are also used in different stages
of the study. Then soils are examined for their hydraulic properties.
Furthermore, interviews were conducted to the farmers and agriculture extension workers to get
data on agronomic, management, land use requirements and land characteristics. Apart from
getting data from interviews, LURs and LCs were developed based on environmental conditions
of the area. Climatic data was also accessed. These data were used to run PS2 (of PS123) and
ALES. The results of PS-2 programme and the LURs and LCs were put in ALES to build a model
to classify land into suitability classes. This final product can be used in land use planning.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
API
Topographic map
Landsat
Prefield
work
Geomorphology
Land cover units
Geopedological
units
Fieldwork
Land qualities
Interviews
LUTs
LUR/LC
Post fieldwork
Climatic data
PS2
ALES
Land suitability
classes
Fig 1- 1 A generalised flow chart of the conceptual frame work
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
1.5 Thesis overview
This research work is concerned with land evaluation with emphasis on soil moisture availability
as a land quality. The water limited production potential model is used to come up with
theoretical crop yield for the area. The model considers climatic conditions, crop attributes, soil
attributes and management practices in the study area.
Chapter 1 gives the introduction of research with its problem formulation, research objectives,
research questions, hypotheses and conceptual framework.
Chapter 2 is reviewing soil moisture and soil water related concepts, the empirical crop modelling
that simulates the ideal situation of the crop environment and land evaluation concepts which
deals with matters on what resources are available, the demands of the crop and how these match
to each other to come up with the suitability class.
Chapter 3 describes the study area in terms of location, that is, the geographical position of the
area, climate as it relates to the performance of the selected crops, geomorphology which gives
the picture on the terrain of an area, geology as it reveals the parent material of soils in the area,
vegetation and hydrology that is, all relevant environmental parameters.
Chapter 4 gives the research methods as well as the materials used in this research and problems
faced during the research work.
Chapter 5 discusses the soils in terms of factors that influence soil formation, description of
geomorphological units, soil profiles and description of soils occurring in the area.
Chapter 6 is on Land use/cover. This chapter covers land use and land cover in general, the land
utilisation types (LUTs) in the area, the LUTs being researched and their key attributes and the
differences in yield between actual and potential.
Chapter 7 presents the results and discussion on the sample sites, soil profiles, description of soil
map units, hydraulic properties and their relationship, soil moisture maps, the water limited
production potential and land evaluation.
Chapter 8 gives the conclusion and recommendations.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Chapter 2: A Literature review on soil water
There is a relationship amongst soil, climatic factors and biotic factors. In this relationship, the
crop is the beneficiary. The soil water does interact with the above-mentioned factors.
2.1 Soil moisture
2.1.1 Definition and importance
Soil moisture is the water held in pores in the soil in liquid and vapour phases(Scott and Maitre,
1998). Soil moisture is the source of water for plant use in particular, in the rainfed agriculture.
There are a number of factors that affect the growth and performance of crops like soil, water and
evapotranspiration (ET). Water serves four general conditions in plants: the major constituent of
the physiologically active tissue; As a reagent in photosynthetic and hydrolytic processes; as a
solvent for salts, sugars and other solutes and water is essential for the maintenance of turgidity
necessary for cell enlargement and growth. Therefore, It is vital to check at which crop growth
stage is moisture critical so as to take mitigation measures like timely planting and soil and water
conservation practices (Kamoni, 1985). In the development of a crop, the annual mean figures as
well as their distribution during the year are important.
2.1.2 Some concepts of soil moisture
Available water capacity (AWC) is the amount of water that the soil can store; that is available
for use by plants expressed as volume fraction or percentage (USDA, 1997).
Field capacity (FC) is the maximum water content that the soil holds following free drainage. It
represents the condition of each individual soil after the large pores have drained freely under
gravity (Landon, 1984). This in practice is usually taken as the moisture content of a soil, which
has drained freely for two days after saturation.
Wilting point (WP) is the condition at which the plant loses turgor and is commonly estimated
by measuring the 15-bar percentage of a soil (wilting point).
Permanent wilting point (PWP) is defined as soil moisture content at which the leaves do not
recover their turgor if subsequently placed in a saturated atmosphere. PWP is taken as the lower
limit of available water so that water in drier soils is assumed to be not available to plants.
Water in unsaturated soils is held in thin films on soil particles or pore surface or as wedges
where the particle or pore surfaces lie sufficiently close together (Landon, 1984). In practice,
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
water uptake by the roots is affected by the depth and density of rooting, gradients in water
potential and hydraulic conductivity of both soil and roots.
Under irrigation conditions, the relationship between crop yield and water supply can be
determined when the crop water requirements and crop water deficits on one hand and maximum
and actual crop yield on the other hand are quantified. Doorenbos and Kassam (1979) describe
that there is relationship between yield and evapotranspiration and that in general, the decrease in
yield is proportionally greater with increase in water deficit.
2.1.3 Soil water relations
In irrigated maize, cumulative pan evaporation ratio of 1.0 gives high yield as well as maximum
efficiency of water use as compared to ratios of 1.4, 1.2, 0.8 and 0.6 (Prasad et al., 1997). This
suggests that there is a threshold of moisture that the crop requires to perform economically other
factors remaining constant. Maximum available moisture can be defined as the amount of water
present at field capacity diminished by the amount, which is present at permanent wilting point.
Crop water use (also known as evapotranspiration (ET)) is influenced by prevailing weather
condition, available water in the soil, crop species and growth stages (Al-Kaisi and Broner, 1992).
After the rain or irrigation, actual ET is higher than when the soil or crop surface is dry. However,
not all the available water capacity can be considered as equally available to plants. It is this
readily available water held in at low tension within the larger soil pores, which is particularly
affected by soil structural conditions. In many cases crops must rely on water that is stored in the
soil (residual moisture) at the end of the rainy season (Landon, 1984). In crop production, there
are a number of factors needed like solar radiation nutrients and moisture but the availability of
soil moisture is the key to plant growth and to the net production of crops.
Tersteeg et al., (1993) cite (Pike 1971) that in Botswana, rainfall varies spatially from 250mm to
700mm that is erratically distributed between years. The soil moisture availability is also affected
by the farming system in the area.
2.1.4 Infiltration
Infiltration refers to the vertical intake of water into a soil usually at the soil surface. The larger
the pore size the greater the infiltration rate. The infiltration rate determines a soils water
adsorption capacity that reveals the likely behaviour of soil under precipitation. It is the rate of
this process, relative to the rate of water supply that determines how much water will enter the
unsaturated soil zone, and how much if any, will runoff (Hillel, 1982). The infiltration rate of a
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soil remains the same for a very long time unless the soil itself is changed. After infiltration,
percolation takes place which is a general term for downward flow of water in the unsaturated
zone (Dingman, 1993)
2.1.5 Hydraulic conductivity
The soil moisture availability is related to soil hydraulic properties. Hydraulic conductivity (k) is
the rate at which water moves through a porous medium under a unit potential gradient. It is also
called permeability (Dingman, 1993). Knowledge of the hydraulic properties is indispensable for
addressing many soil, hydrological, environmental, ecological and agricultural problems (USDA,
1997). These hydraulic properties are influenced by texture, structural characteristics and organic
matter content of the soil (Landon, 1984; Lascano, 1997; Ward and Robinson, 1989). In general
there is rapid decrease of K with decrease in water content in unsaturated soils due to rapid
draining of larger pores (Landon, 1984). Kosta (1994) further explains that soil water in
unsaturated zone is of special importance at the partitioning of water in form of precipitation.
There is a relationship between soil moisture retention curve and hydraulic conductivity (k).
Different methods are used to measure k and these should give similar results. Fig 2-1 below
shows some characteristic matric suction relations of soils of different textures.
Ψ-Ψ
Ψ relations of soils of different texture
Fig 2- 1 Some characteristic SMΨ
Source: Landon (1984)
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2.2 Modelling soil water
There are several empirical models in soil water that are used to predict the yield of crops in
various situations. Such empirical models are useful as they forewarn the future in terms of
agricultural production.
2.2.1 WOFOST
This is an empirical modelling tool that explains crop growth on the basis of the underlying
processes such as photosynthesis and respiration, and how these processes are affected by
environmental conditions. The model describes crop growth as biomass accumulation in
combination with phonological development. It stimulates the crop life cycle from sowing to
maturity. The basis for calculation of dry matter production and yield is the rate of gross carbon
dioxide (CO2) assimilation by the green canopy, determined by the level of irradiance, the green
area of the crop capable of intercepting the incoming radiation, the photosynthetic characteristics
of the crop species and the prevailing temperature. A part of assimilates is used by crop for
respiratory processes to provide energy for its own maintenance. The remainder of assimilates is
available for the increase in structural dry matter. The increase in total weight is partitioned over
the roots, stem and storage organs (Wokabi, 1994).
2.2.2 PS123
This is a procedure that assumes the ideal situation of a crop. All factors that affect the growth
and performance of a crop are considered to run the model. The PS123 programme is a crop
growth simulation model. The basis for calculating the biophysical (crop) production potential
(yield) is the capability of green plants to reduce atmospheric CO2 to carbohydrates. As the intake
of atmospheric CO2 takes place through the stomata, which also forms the defence system of the
plant against moisture stress, there is a strong correlation between the rate of transpiration and the
rate of assimilation of CO2 (Driessen and Konijn, 1992). The PS-1 production situation represents
the least possible analytical complexity, as only solar radiation and temperature during the
growing period and the biophysical characteristics of the crops are taken into account. All other
land qualities are assumed to be optimum. The PS-2 simulates the water limited production
potential. Production possibilities are determined by irradiance of photosynthetically active
radiation temperature and availability of water (Driessen and Konijn, 1992). Crops have different
response to the total received radiation and how much can be converted to growth and yield.
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2.2.3 Hydrus
This is a programme that simulates two-dimensional variably saturated water flow, heat
movement and transport of solutes involved in sequential first order decay reactions. The
programme numerically solves the Richard’s equation for saturated-unsaturated water flow and
convection dispersion type equations for heat and solute transport. The flow equation
incorporates a sink term to account for water uptake by plant roots. The programme may be used
to analyse water and solute movement in unsaturated, partially saturated or fully saturated porous
media (Simunek et al., 1999).
2.2.4 Water balance
Water transport and retention processes in the soil are complex. The soil surface is exposed
continuously to changing radiation fluxes, which create diurnal cycles of temperature, relative
humidity, and even water vapour fluxes caused by temperature gradients. Plants take up water
from the soil through their roots and lose it through transpiration. This water uptake is controlled
by soil matric suction in the rooting zone, which partly controls the rate of infiltration and
sorptivity, which is the combined influences of capillary action and adhesive forces to soil and
solid surfaces. The status of the plant influences the rate of carbon dioxide (CO2) supply because
the stomatal openings are affected by the water potential in the plant (Van Keulen and Wolf,
1986).
The crop water requirements vary considerably with the crop, crop development stages and their
length, and with the evaporative demand of the atmosphere. The water balance can be described
as follows:
RMS = [UPFLUX=(CR+D)-TR]/RD
(2-1)(Van Keulen and Wolf, 1986)
Where,
RSM is the rate of change of volume fraction of moisture in the rooting zone (cm d -1)
UPFLUX is the net of water vapour flow through the upper boundary of the rooting zone (cm d-1)
(CR+D) is the net rate of water flow through the lower boundary of the rooting zone (cm d-1)
TR
is the actual rate of transpiration (cm d-1)
RD
is equivalent depth of the rooting zone (cm).
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Fig 2- 2Water fluxes that condition the volume of moisture in the rooting zone and
availability of water for uptake by roots
Source: Driessen and Konijn (1992)
2.2.5 Loss of water by plants
Uptake of water by crops is almost equal to the rate of transpiration. Plants can produce to their
biophysical potential only if the availability of water is optimum. Plants curb their consumption
of water if supply is constrained; actual transpiration becomes less than maximum and production
becomes less than the biophysical potential (Driessen and Konijn, 1992).
2.2.6 Optimum availability of soil moisture
Most of the times water stress in plants is associated with shortage of water in the soil. However,
shortage of air (oxygen) in the soil interferes with uptake of water by the plant. Some plants are
adapted to such conditions because of the development of some tissues (Aerenchyma) through
which oxygen diffuses easily from the tissues of the leaves into the shoot axis and roots(Larcher,
1980) . Plants that are not equipped with aerenchyma in their roots have difficulties in taking up
water in waterlogged environments; they show symptoms of drought and close their stomata.
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There are two critical boundary values in the range of moisture in the soils. One is associated with
wetness and low matric suction and another one with drought and high suction.
2.4 Soil variability
Soils from different areas behave differently (spatial and temporal variability of soils) for
example in water holding capacity, infiltration rate, drainage and erosion risk. This implies that
different management practices are also applied for sustainable management. According to
Wilding and Drees (1983) spatial studies of soil properties and the nature of soil variability
depend largely on the scale of observation and properties in question. Despite the economic and
cultural importance of soil maintenance, detailed international surveys suggest that soils under
agricultural use are in danger of losing capacity to fulfil their economic, cultural and ecological
functions (Jazairy, 1993)
Soil characteristics vary in time and space (Parry et al., 1988). Models can be developed to
explain these variations. There are a number of models that are used depending on the purpose of
the project. Soil surveys are one type of the models that are carried out to obtain information
about the distribution of soil characteristics of an area. This can be detailed or semi-detailed soil
survey based on the geopedological approach (Zinck, 1988/89) that emphasises the strong
integration of geomorphology and pedology. It is based on hypothesis that boundaries drawn by
landscape analysis separate most of the variation in the soils and sample areas are representative
(Girma, 2001). This is not a complete approach as we assume that soils within the landscape can
have variations as well hence the application of geostatistical approach is employed to
supplement the information gaps in the variations of soils in time and space. The Continuous
Model of Spatial Variation (McBratney and Gruijter, 1992) can be used to assess the variations
of soil within the soil map unit that is homogeneous so as to come up with detailed information of
that soil map unit and interpolate to the unvisited points.
2.5 Land evaluation
Environmental attributes such as land and topography play controlling roles in the spatial
distribution of soil moisture content (Qiu et al., 2001). This necessitates the usefulness of land
evaluation in order to come up with a sound land use planning. Land evaluation can be defined as
the assessment of land performance when used for specified purposes (FAO, 1983). Land
evaluation predicts how each land area would behave if it were used according to each system. In
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order for the evaluation to be meaningful it should take into account the economics of the
proposed alternative enterprises, the social and the environmental implications of such
enterprises. However, most land evaluation methods have been focussed on assessing the
potential of land without considering the economic part. Carrying out area specific land
evaluation can provide good guidance for planners at local level.
Automated Land Evaluation System (ALES)
Land evaluation mostly deals with demand side of the resources (land use requirements) and the
supply side (land qualities). The two are matched to come up with the land suitability class.
Automated Land Evaluation System (ALES) is a programme that is used by land evaluators to
build expert systems to evaluate land (Rossiter and Van Wambeke, 1993). It should be noted that
the system is an empty shell that requires knowledge from the expert.
The entities evaluated by ALES are map units which may be defined either broadly (as in
reconnaissance surveys and general feasibility studies) or narrowly (as in detailed surveys and
farm scale planning (Rossiter and Van Wambeke, 1997).
The system has also the format of an expert system based on the FAO framework for land
evaluation. It allows the user to build decision trees, containing ratings for land qualities and
requirements for land utilisation types. The four major components are:
•
A knowledge base (the actual expert system), containing descriptions of different land
uses in both physical and economic terms
•
A data base containing, information on the natural resources
•
An inference algorithm, allowing matching of land and land uses
•
An explanation facility, which permits the analysis of results
The knowledge base is specified by the user and contains the relations between land and land use
requirements, in which land use can either, be a single crop or a crop rotation. Land use
requirements are defined in the system in terms of levels of limitation. Similar levels of
limitations may originate from different combinations of land characteristics as derived from the
decision trees.
The database to be developed by the user contains information from natural resource surveys.
Both discrete and continuous information can be handled by the system, which provides
possibilities to generate missing information through decision tress.
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In the inference algorithm, matching of land qualities and land use requirements takes place
according to user defined procedures, which results in an evaluation matrix, that allows easy
selection of the best land for a particular land use. Suitability is expressed quantitatively,
according to the framework principles, and in relation to a non-constrained yield or ‘nominative’
yield for use in economic evaluation.
The explanation facility allows the user to analyse the results through a backward chain in the
system. Interactive procedure is possible to improve the evaluation procedure.
ALES is able to evaluate land in physical terms only, or both physical and economic terms. Each
evaluation consists of land utilisation types like proposed land uses and a set of land mapping
units. In physical evaluation, map units are assigned physical suitability classes, which indicate
the relative suitability: s1, s2 s3/nl and n2. ALES can also compute an economic evaluation
following the computation of a physical evaluation. All components of economic model have to
be present otherwise evaluation will not be possible. One of the limitations of ALES is that it has
no input or output for maps.
It is important for evaluators to construct decision trees to infer each land quality from its set of
diagnostic characteristics. These are hierarchical multi-way keys, in which values of the
diagnostic land characteristics (LCs) are the diagnostic criteria and the result is the severity level
of the land quality to be evaluated (Rossiter, 2001b). This is where the expert knowledge of the
evaluator has to be put into systematic form.
Certain concepts and definitions are needed to form a basis of land evaluation. These concern the
land quality, land characteristics, diagnostic factors and land requirements. The following
definitions are from the FAO (1983):
Land quality (LQ) is an attribute of land that acts in a distinct manner in its influence on the
suitability of the land for a specific kind of use like temperature regimes, soil moisture
availability and drainage. It directs attention towards the way in which the land affects suitability
for use.
Land characteristic (LC) is an attribute of land that can be measured or estimated, and that can
be employed as a means of describing land qualities or distinguishing land units of differing
suitabilities for use.
Diagnostic factor is a variable that is used to estimate land qualities in land evaluation. In some
cases a land quality can be satisfactorily described on the basis of a single land characteristic or a
combination of a number of land characteristics.
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Land use requirement (LUR) is the conditions of land necessary or desirable for the successful
and sustained practice of a given land utilization type. It considers crop requirements,
management requirements and conservation requirements.
Land utilization type (LUT) is a specific manner of occupying and using the land, with
specified management methods in a defined technical and socio-economic setting. In the context
of rainfed agriculture, it can refer to a crop, crop combination or cropping system.
Land mapping units (LMU) as defined by Rossiter (2001b) is a specific area of that land that
can be delineated on a thematic map and whose land characteristics can be determined. These are
sets of maps delineations designated by a single name, and representing a single legend category.
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Chapter 3 Study area
3.1 Location
The study area is a part of the Serowe area in Botswana located 300km northwest of Gaborone,
which is the capital (fig 3-1). The elevation of Serowe ranges from 1060 to 1240m above sea
level. The geographical position is within the range of 16o 07’37” to 26o 54’10” East and 22o
14’10” to 22o 30’33” South (UTM coordinates of 410000, 7650000 and 49000, 7510000)
covering an area of about 244048ha.
Fig 3- 1 Location of Serowe the study area in Botswana
Reasons for selecting Serowe area:
1. Semi-arid area with rainfall range of 450-470mm/annum
2. Subsistence agriculture is predominant
3. High erosion potential due to topography and sealing
3.2 Climate
Serowe area in Botswana is characterized by semi-arid climate with cool dry winters and hot
moist summers.
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3.2.1 Rainfall
The mean annual rainfall is 477mm as reported by Swedish Geological Survey (1988). The
rainfall is highly variable in time and space with growing period starting from November to April
(Fig 3-2 and Fig 3-3). Botswana in general falls under ustic regimes based on the available
climatic data (De Wit and Nachtergaele, 1990). During the rainy season and indeed all the year
round , monthly totals are consistently exceeded by the potential evaporation for the same period.
Rainstorms are frequently intense and of short duration and localised. An entire month’s total can
fall within the space of a few hours over a small area (SGC, 1988).
Rainfall (mm)
Rainfall distribution within years
150
100
50
0
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
Time (months)
Fig 3- 2 The variation in rainfall distribution within years
Rainfall (mm)
Rainfall variations between years
1000
500
0
1986 1988 1990 1992 1994 1996 1998 2000
Time (Years)
Fig 3- 3 Variations in rainfall amount between years
3.2.2 Temperature
The temperature goes as high as 30 or more before rainy season in October whilst in winter
period (May to August) the area experiences low temperatures of minimum of 12 oC. This period
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is also characterised by low wind speed and long hours of sunshine. The radiation and
evaporation are at their lowest levels. Fig 3-4 below shows the daily temperature for the year
2000.
Temperature
Temperature
40.00
30.00
20.00
10.00
0.00
Jan Feb Mar Apri May Jun
Jul
Aug Sep Oct Nov Dec
Time (months)
Fig 3- 4 Temperature ranges of the study area.
3.2.3Relative Humidity
The area experiences low relative humidity during winter (May to August) with
minimum of 45% but start increasing in late August and reach a maximum of 70%. Refer
to fig 3-5
Relative Humidity
(%)
Relative Humidity
80
60
40
20
0
Jan Feb Mar Apri May Jun
Jul Aug Sep Oct Nov Dec
Months
Fig 3- 5 The relative humidity of the area.
3.2.4 Evapotranspiration
As a semi-arid area, Serowe experiences high evapotranspiration rates in summer when
temperatures are high and moisture is available. Low evapotranspiration occurs during winter
when soils become drier. Soil moisture of <0.05cm3/cm3 were recorded to a depth of 1.80m near
the ADAS station in mid August (Timmermans and Meijerink, 1999) indicating very dry soils.
Evapotranspiration rates varying from 0.2 to 10mm/d have been estimated by different methods
during different previous studies carried out in the area.
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3.2.5 Wind
Wind can be described as air in motion. It moves in circuits and is powered by unequal heating of
large masses of air. Wind plays an important role in rain formation. Since the earth is warmed
differently, the air above these surfaces absorbs different amounts of heat. Warm air rises while
cool air sinks which creates the environment for flowing air movement. This movement ends up
in the formation of clouds and eventually rain is formed. The average wind speed in the study
area is 1.22m/s.
Windspeed
Windspeed
2.00
1.50
1.00
0.50
0.00
Jan Feb Mar Apri May Jun Jul Aug Sep Oct Nov Dec
Months
Figure 3-6 Wind speed graph
3.2.6 Sunshine
Sunshine is a form of measuring solar radiation. The World Meteorological Organisation defines
sunshine hours as the sum of the time intervals during which the direct solar irradiance exceeds a
threshold of 120Wm-2 . In crop production, this amount of solar irradiance plays a major role in
photosynthetic process. The area receives an average of 8.6 sunshine hours per day.
15.00
10.00
5.00
ec
D
Ju
l
Au
g
Se
p
O
ct
N
ov
Ju
n
M
Fe
b
ar
Ap
ri
M
ay
0.00
Ja
n
Sunshine
Sunshine hours
Months
Fig 3- 6 Sunshine hours over the year
3.3 Geology
There is a fault line running from northwest to southeast that led to the formation of a bed-like
feature in the Kalahari (Fig 3-7). The sandveld (see 3.4) consists of sandstone of different nature
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in terms of colour (red, yellowish and whitish). There are some intrusions of sand in the hardveld
(see section 3.4). Around Mogorosi area, there is occurrence of ironstone of the plinthic groups.
Some calcium carbonate concretions also appear in some parts of Mabeleapodi that is in the
northeast of the study area and around Sokwe hill. In the hardveld there are Andesite deposits that
were cooled under water. Fig 3-8 shows the geology of the study area.
Fig 3- 7 The Kalahari basin with the fault line running northwest to southeast
Fig 3- 8 The geological map of Serowe
3.4 Geomorphology
Following the geopedological approach (Zinck, 1988/89) three main physiographic units have
been distinguished, namely Sandveld, escarpment and hardveld. The escarpment stretching along
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the plateau edge is not of the same breadth throughout the unit. From the escarpment going to the
east, there is a stretch of undulating to rolling land where there is existence of some rock
outcrops. In general, the escarpment outlines the eastern limit of the stormberg basalt despite the
fact that basalt also occurs extensively to the east of the escarpment line between Serowe and
Mogorosi village (Wellfield Consulting Services, 1998).It should be noted that it is difficult to
come up with geopedological terms for Sandveld and Hardveld, the terms which are used by the
local researchers. The sandveld matches the term plateau, and the hardveld is a peneplain, with a
few terrace levels which can be termed as glacis terraces resulted from peneplanation (Zinck,
1988/89).
This is also approved by occurrence of the inselbergs that are exposed in the area. In between the
plateau and the peneplain, there is a hilly area. Keeping that in mind, three landscapes were
adopted and identified namely Plateau, Hilland and Peneplain. The elevation ranges from 1000m
to 1250m from the hardveld to the sandveld Figure 3-9 shows the stereogram depicting the study
area; plate3-1 showing an overview of the area and figure 3-10 presents the cross section from
west to east.
Fig 3- 9 The stereogram depicting part of the study area.
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Plate 3- 1 Part of the study area, depicting plateau and hilland
Cross section
Pu111
Height (m)
1250
Hi111
1200
Hi112
1150
Pe114
1100
Pe111
1050
Pe113
1000
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
50000
Distance (m)
Fig 3- 10 The cross section of the study area
3.5 Vegetation
The sandveld is covered by variable dense of trees, shrub and grass (D. O. S. M, 2001). Denser
and taller vegetation is generally along the strip of the escarpment contrary to the shallowness of
the soils in this area. However, from field observations, it was noted that the escarpment soils
have high moisture retention capabilities. The common species are Terminalia sericea,
Dichrostachys cinerea, Ochna pulchra and Burkea Africana on sandveld whilst Accacia
mellifera, Ziziphus mucrotana, Accaci tortillas and Accacia luederitzii on the hardveld.
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3.6 Hydrology
The area has seasonal rivers which means they flow for only part of the year. Sometimes they
may only flow for a few hours after heavy rains in summer (SGC, 1988). The drainage network is
more pronounced in the east of the escarpment. The rivers are deeply incised due to gully erosion
as observed around the Sokwe area (Plate3-3) whilst in the escarpment the river course mostly is
in the bedrock. The water table lies between 10 to 40m in the hardveld and 40 to 60m in the
sandveld (D. O. S. M, 2001).
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Plate 3- 2 One of the vegetation types in the study area
Plate 3- 3 Gully erosion in some parts of the study area
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Chapter 4 Materials and Methods
Climatic data
Literature review
Aerial photographs
Landsat TM
Problem definition, research
objectives, research questions
Image
interpretation
Develop
questionnaire
Pre-fieldwork
Geopedological
units for sampling
Sampling: pits,
mini pits, soil
Conduct
interviews
Run PS2
programme
Fieldwork
LUTs,LQs,
LURs, LCs,
Post fieldwork
Build computer
model in ALES for
land evaluation
Compute the
evaluation
Laboratory analysis
Statistical and
geostatistical
Land suitability
classes
Presentation of results
Fig 4- 1 Flow diagram of research activities
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4.1 Materials
The existing aerial photographs at scale of 1:50000
Satellite images of Landsat TM (August 2000) and IKONOS covering 10*10km in the western
part of Serowe.
Existing soil maps of scales: 1:250000 (De Alwis, 1985) and 1:1000000 (FAO, 1990b)
Field documents (FAO, 1990c; Joshua, 1991; Nampad, 2000)
ILWIS 3.1 software
PS123 software
ALES software
Climatic data: Rainfall (1986-2000), Relative humidity, Wind speed, Evapotranspiration and
Temperature for some of the years.
4.2 Research methods and techniques
4.2.1 Data exploration and Aerial photo interpretation
The research work was divided into three phases namely pre-fieldwork, fieldwork and postfieldwork. The first stage was research proposal writing that comprised literature review and
collection of general information of the study area. Then preparation for filed work was followed.
Due to missing of some of the aerial photographs, it was not possible to produce a complete aerial
photo interpretation to develop a base map. Rather, a combination of the aerial photos and
information extracted from the Landsat image were used to come up with a temporary base map.
Three strata were produced, one on the sandveld, another one on the hardveld and the last one
cutting across sandveld and the hardveld on the north-eastern part of the study area. This was
corrected in the field and finally came up with two blocks (see fig 5-1).
4.2.2. Soil survey
A reconnaissance survey was carried on the first day to get an overview of the area. The main aim
was to get acquainted with the area, infrastructure and to figure out where to make pits for soil
profile description and also the position of the farmlands. The base map was corrected in the field
to suit the reality of the study area.
(A) Pit description
Full pit and mini-pits were studied on the main mapping units. Apart from soil description, other
tests like infiltration; hydraulic conductivity and moisture measurements were conducted. Pits
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were dug to a depth of 120m and continue with auguring down to a depth of 180m. Auger hole
observations were made subjectively on some of the sample points. Soils were described
according to the 3rd edition (Revised) (FAO, 1990a).
(B) Infiltration
This was measured using double ring infiltrometer (Eijkelkamp, 1998). Only two sets were used
due to the lack of floaters. The test points were selected and prewetted the previous day. The
rings were pushed ten (10) cm into the soil followed by pouring water into the ring to a depth of
10cm. The drop in water surface (depth) was recorded at every minute until a base saturation was
reached (Plate 4-1). These tests were done on random points as well as on the pit description
sites. The whole procedure was taking about two hours for the sandy soils but longer in heavy
soils.
Plate 4- 1 Conducting infiltration test on one of the sites
(C) Hydraulic conductivity
The inverse auger hole method applied. The test was done after the infiltration test has taken
place. The site where rings were placed was augured to a depth of 100cm, with ten cm diameter
and water was poured into the auger hole. The drop in water depth was measured every 60
seconds for a period of ten minutes. It should be noted that for heavy soils (mainly vertisols) in
some instances, this test was a failure because of development of cracks in the shrinking soils
such that water poured in the auger hole was drained within few seconds.
28
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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(D) Soil moisture measurements
The soil moisture measurements was done in two different ways:
(i)
Gravimetric method: Samples were taken at two different depths of 0-10cm and 2030cm. The samples were weighed and placed in the oven at 105oC for 12hours. After oven
drying, the samples were reweighed to get actual moisture on date of sampling.
(ii) Volumetric method: Theta probe is an instrument used to measure volumetric soil
moisture θv, in the soil instantly (fig 4-2). Volumetric soil moisture content is the ratio
between the volume of water present and the total volume of the sample. This is expressed as
percentage (%vol), or a ratio (m3/m3) (Eijkelkamp, 1998). The probes were inserted into the
soil and a reading was taken after 8 seconds to give room for stabilisation of the instrument.
The theta probe was not reliable in the sense that at some sites (especially sandy soils) it
would give negative readings hence it was abandoned.
Fig 4- 2 Theta probe
(E) Particle size distribution
Soils from different soil horizons from a number of profiles and auger holes were brought to
I.T.C and laboratory analysis on particle size distribution was performed using pipette method.
The following is the procedure for pipette: 15ml of water and 15ml of H2O2 30% were added to
each 20g of soil samples. The samples were left on water bath at temperature of 80oC for
overnight. Then 300ml of water were added and boiled for one hour. After cooling, the samples
were centrifuged and 5mls of 1M CaCl2 solution was added. The samples were then placed on a
shaker for 16hours. Sand was separated with a 50µ sieve. The suspension of clay and silt were
transferred into 1000ml cylinder. The clay and silt were determined by pipetting. The pipette
29
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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suspensions and sand were oven dried at 105oC for 12hours. A blank sample was also prepared to
check the error committed during the procedure.
The laboratory results were used to cross check field description on soil texture.
Plate 4- 2 Particle size distribution procedure in the laboratory
4.2.4 Land evaluation
(A) Interviews
A main objective of this research was to carry out an evaluation of land in the study area hence
interviews were conducted. Arrangements were made with the Agricultural District Officer to
conduct interviews with smallholder farmers as well as the technical assistants and Soil surveyor
at District level.
Semi-structured questionnaire were prepared during prefield phase (appendix G). Individual
farmers were interviewed at their farmlands. Agricultural extension workers were interviewed to
get information on land use types, land characteristics and severity levels. This information has
been integrated with results from the water balance model and processed using ALES
programme.
(B) Climatic data access
Climatic data for the study area was accessed from Water Resources Programme of ITC. The data
covers a period of 15 years (1986-2001). The data comprised of rainfall, maximum temperature,
minimum temperature, relative humidity, wind speed and sunshine. From this data, only rainfall
30
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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covered the stated period whilst the rest of parameters were from April 1998 to 2001 for Paje and
Mokongweng stations. The data had some missing variables and this posed a problem in running
PS123 programme.
Due to this problem, parameters from Paje and Mokongweng (stations surrounding Serowe) were
regressed and interpolated to fill gaps in Serowe’s climatic data. In some instances, it was not
possible to regress, as only one set of data was available. This was another hiccup. In order to
solve this problem, another set of climatic data was obtained from FAOCLIM. FAOCLIM is a
set data file that stores climatic data for most of the worlds’ meteorological stations. However,
this FAOCLIM data does not indicate the year for which the data was recorded. From this set of
data, maximum and minimum temperatures of Mahalapye station were extracted and used to fill
in the gaps. The latitude difference between Serowe and Mahalapye is 0.6o so it was assumed that
there would be no major climatic differences.
In addition to this data, another set of data was obtained from Gaborone, Botswana. This data
contained rainfall, relative humidity, maximum and minimum temperature of different stations
from 1998 to 2000. From this data, rainfall was for Serowe, maximum and minimum temperature
for Mahalapye and the rest for unknown stations. Some variables from Serowe and Mahalapye
were used to fill in the gaps. Through this rather complex procedure a climatic file was created.
(C) Production potential PS-2
The PS123 programme requires daily climatic data, generic characteristics of the crop and soil
data. The climatic parameters required are maximum and minimum temperature, rainfall, relative
humidity, potential rate of evaporation, sunshine hours and rate of evapotranspiration.
The files for crop and soil were created based on the crop varieties grown in the area and soil
properties. The model was run from Julian day 306 to Julian day 61 using five different levels of
initial matric suction (PSIint.). The planting date was hypothetically chosen from the information
that was derived from interviews. The PSIint used were 500cm, 1000cm, 1500cm, 2000cm,
2500cm and 3000cm. The surface storage capacity of water was calculated based on the surface
roughness of the farmland and the position on the landscape. The following formula was used for
calculation of surface water storage.
31
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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SSC = 0.5 * dr *
sin 2( SIG − PHI ) cot an( SIG + PHI ) + cot an( SIG − PHI )
*
sin( SIG )
2 * cos(SIG ) * cos( PHI )
(4-1)
Where
SSC is equivalent to surface storage capacity (cm)
dr
is surface roughness or furrow depth (cm)
SIG is clod angle or furrow angle (degree)
PHI is average slope of the land (degree)
(Driessen and Konijn, 1992)
It should be noted that only Pe111 (Tread/Riser on higher terrace), Pe112 (Tread/riser on middle
terrace), Pe113 (Tread/Riser on Lower terrace) and Pe115 (Slope floor complex of the Vale) were
evaluated in this programme of PS123 because that is where the farmlands are located.
Apart from running the programme using different initial matric suctions, another scenario was
run that considered late planting by two weeks. The reason behind this was to find out if there
would be differences in yield between early and late planting since most of the farmers plant late.
This was revealed during farmer interviews.
Below are crop characteristics that represent the crop indicative values.
Table 4- 1 The crop indicative values
Characteristic
Photosynthetic mechanism
SLA
TO oC
Tsum
ke
Tleaf
Root depth
Maize
C4
14-35
10
1600
0.6
1000
100-170
Sorghum
C4
11-21
10
1600
0.6
975
100-120
SLA is specific leaf area, m2 kg-1
TO is threshold temperature of development (oC d)
Tsum is heat requirement for full development (oC d)
Ke is the extinction coefficient for visible light
Tleaf is heat sum for full development of leaf tissue (oC d)
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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(D) Selection of Land use requirements (LURs)
Set of LUR were selected which suits the environmental conditions of the area as well as the land
use types according to the list published by FAO (1984) of the suggested land use requirements.
These LURs were based on the following criteria:
• Importance (relevance) for use
• Spatial variations in the corresponding land quality in the study area
• Availability of knowledge with which to evaluate the corresponding land quality
• Availability of data with which to evaluate the corresponding land quality
The LURs and LCs were chosen and crosschecked using the information acquired through
interviews from the farmers and agricultural extension staff. (See Table 4-2)
Table 4- 2 LURs for maize
Land
quality
Diagnostic
factor
Factor rating
Erosion
hazard
Soil
workability
Highly
suitable s1
Total rainfall in >600
growing season
(mm)
Textural class
SC, VFS, CL
Yield Kg ha
>6000
Soil
effective >120
depth (cm)
Textural class
SL, SC, LS,
S
Soil
effective >120
depth (cm)
Soil drainage
Excessively
drained, well
drained
Slope %
<3
Erosion class
None
Wet consistence
class (stickness) Non-sticky
Sealing
hazard
Texture class
Crusts (mm)
Moisture
availability
Rooting
conditions
Oxygen
availability
S, LS, SL
None
33
Mod.
Marginally
Suitable s2 suitable s3
400-600
300-400
Not suitable
n
<300
FS, SL
S
4000-6000 2000-4000
50-120
30-50
C
<2000
<30
SCL, L
SiCL,
C
50-120
30-50
<30
Mod.well
drained
Imperfectly
drained
Poorly
drained
3-8
Moderate
9-16
Severe
>16
very severe
Slightly
sticky
SCL
<5
Sticky
Very sticky
L, CL
5-10
_
>10
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Table 4- 3 LURs for sorghum
Land
quality
Diagnostic
factor
Moisture
availability
Total rainfall in
growing season
(mm)
Textural class
Yield Kg -ha
Soil
effective
depth (cm)
Textural class
Rooting
conditions
Factor rating
Highly
suitable S1
>500
Mod.
Suitable
S2
400-500
SL, LS
3000
>170
FS, CL
S, SCL
2000-3000 1500-2000
50-170
50-70
C, S
<1500
<50
SL, LS, S
SCL, L
CL
C
50-70
<50
Imperfectly
drained
Poorly
drained
9-16
Severe
>16
Very
severe
Sticky
Very sticky
Si, SiL,
C
2-5
>5
Erosion
hazard
Soil
effective >170
70-170
depth
Soil drainage
Excessively
Mod.well
drained, well drained
drained
Slope %
<3
3-8
Erosion class
Slight
Moderate
Soil
workability
Wet consistence
class (stickness) Non-sticky
Sealing
hazard
Texture class
Oxygen
availability
Crusts (mm)
S, LS,
SiC, SC
<1
Slightly
sticky
C, SL, SCL
1-2
Marginally
suitable S3
Not suitable
N
250-400
<250
(F) Building model in Automated Land Evaluation System (ALES) for Land
Suitability Evaluation
The data obtained through interviews during fieldwork was processed and fed into ALES. A
single model called “Botswana Suitability Land Evaluation” was built for both LUTs.
This is the stage by which ALES can assess the suitability of each land-mapping unit. This
involves construction of decision trees for each LUR based on expert knowledge. Each LUT has
different LURs. The LURs and their diagnostic factors as shown in tables 4-2 and 4-3 were the
inputs for construction of decision trees. In this procedure, one land quality would be determined
by more than one land characteristic to come up with the severity levels.
The decision trees were constructed by matching the LURs and LCs for example; decision tree
for land quality moisture availability was determined by considering diagnostic factors total
34
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
rainfall in the growing season, the soil depth, the textural class and yield. The major factor is total
rainfall, therefore was at the top of the tree but the amount of water a soil can hold also depends
on soil depth hence soil depth was the second branch. Soil texture plays a role in the moisture
holding capacity of the soil, this factor came at the third branch and then the yield came on the
last branch. These factors were matched against each other to determine the severity level of land
quality soil moisture availability. Below is an example of a decision tree.
LUT 2,Erosion hazard
> Slp (Slope)
<3 (none) [0-3 %]....... : 1 (none)
3-8 (slight) [3-8 %] > Txc (Textural class)
FS (Fine sand) [3-10 c : 2(slight)
SL (Sandy loam) [10-15 c : 3 (moderate)
LS (Loamy sand) [15-20 c : =2
CL (Clay loam) [20-50 c : =3 (moderate)
SCL (Sandy clay loam) [5 : 2 (slight)
9-16 (moderate) [8-16 %] : 3 (moderate)
>16 (severe) [16-25 %].. : 4 (severe)
The last step was to enter all the map units into database where the severity level was determined
based on the decision trees, which had already been created. At this point, the model was now
ready to compute the evaluation. After computation, the results were reviewed to check for
irregularities and improve the evaluation procedure
Since ALES is not GIS based, the map units were classified using Integrated Land and Water
Information System (ILWIS) programme, a geographical information system. Columns were
added to the histogram of the Geopedological map using the suitability class domain. The
suitability maps were created from attribute map of the geopedological map.
4.3 Data processing and analysis
4.3.1 Statistical analyses
(A) Hydraulic properties
The measurements from field were statistically analysed using Excel, SPSS and R programme (R
Development Core Team, 2002) softwares in order to examine the differences in the strata and
also to evaluate the relationship between them. Parameters like descriptive statistics, correlation
and regression analysis were performed.
35
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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(B) PS-2 Production Potential water –limited production
The results from PS-2 were regressed using Excel software in order to establish the relationship
between moisture availability and yield. The independent variable (x-axis) was the initial matric
suction and dependent variable (y-axis) was yield (See fig 7-3 –7-6).
Furthermore, the yield was classified into suitability classes and used as a diagnostic factor in
ALES programme. The reason for using two evaluation tools is that PS2 evaluates land based on
water-limited only whilst ALES considers environmental aspects, managerial aspects and soil
characteristics.
4.3.2 Geostatistical analysis
This operation was done in order to examine the spatial variability of soils and soil moisture
distribution as well as producing the soil map. The operation used the Ordinary krigging. The lag
spacing was set at 2000m for both moisture at 10cm depth and 30cm depth. The range was
1700m with a limiting distance of 14000m for moisture at 10cm depth. In case of 30cm depth, the
lag was 2000m, a range of 4000m with limiting distance of 16000m.
Although the sample size was small (56points) the analysis went further to do krigging
to examine the spatial variability.
4.3.3 Remote Sensing
This technique was employed to produce a land use map using ILWIS software. Initially, a map
list of bands 1,2,3,4,5 and 7 from Landsat image was created. From this map list, a sample set
was produced that stores the relevant data regarding input bands, land use classes and background
image for selecting the training areas. A false colour composite (FCC) map was produced from
bands 4,3,2 (4-red, 3-blue and 2-green) and was used as a background image to train the sample
set. A training phase was performed whereby six classes were defined and these are bare sand,
dense vegetation, farmland, Savanna shrub, Savanna trees and settlement. Classification of the
image was done using Minimum Mahalanobis Distance Classifier algorithm.
4.4 Limitations
•
The climatic data sets had a lot of gaps.
•
With system of operating from three different settlements (cattle post, farmland and
village) it was time consuming to get access to some of the farmers for interviews.
36
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Chapter 5 Soils
5.1 Soil and soil formation
Soils are one of the major natural resources that life depends on. Dumanski (1993) describes soil
as a natural body in relation to the factors of soil formation. Soil formation is induced by a
number of factors such as climate, parent material, biological activity and topography (Jenny,
1941).
Development of soil is materialised in the formation of horizons. The soil horizons are layers of
soil or soil material approximately parallel to the land surface and differing from adjacent
genetically related layers.
5.1.1 Climate
Botswana, in particular Serowe area is under semi-desert area, hence climatic factor plays a major
role in soil formation. Daily and seasonal variations coupled with low and irregular rainfall are
responsible for the type of weathering and profile development in general. However, rainfall
effectiveness in terms of infiltration /runoff, temperature and wind are important parameters to
consider when discussing soil formation in the study area.
Wind plays a role more especially in the sandveld where it blows the sands from one place to
another making some depositional aeolian dunes. Despite the strong winds on the sandy material,
a dense vegetation of the area (Savannah bush land with good grass cover) has led to minimal
wind erosion except in the open spaces where vegetation is very scanty or no vegetation at all.
5.1.2 Erosion
Water erosion has played a major part in the peneplain. Soil materials move from the eroded
terrace to the lower glacis of the area resulting in the stratification of horizons as they get
deposited at different time. These materials are unconsolidated which undergo further weathering
(see plates 5-1 and 5-2).
37
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Plate 5- 1 A gully showing layers of depositional materials around Sokwe area in
Serowe
Plate 5- 2 Gully formation due to water erosion
38
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
5.1.3 Vegetation
Although the area is densely vegetated, its role in soil formation is very minimal (subverting wind
erosion). This is due to the small leaf nature of vegetation. The organic matter content is low
ranging from 0.39% top (10cm) in sandveld to 0.65% (Betemariam, 2003) in the hardveld. The
soil structure is not well developed because of the low organic content as explained by Farshad
(1997) that organic matter content of less than 1% is insufficient to promote good soil structure
and cohesion between soil particles, hence, leading to higher susceptibility to soil erosion.
5.1.4 Parent material
The major parent material in the area is sand derived from sandstone and stormberg
Basalt. However, some lime does occur in the peneplain. Most of the soils are formed insitu. Alluvial deposits are common in the lower part of the peneplain.
5.2 General description of landforms and soils
A geopedological map (fig 5-2) of the study area was developed with the corresponding legend
upon inferring the available aerial photographs and image interpretation. The area has three main
landscapes (see 3.4) upon which landforms were distinguished. Fig 5-1 shows the points of soil
profile pits within the two blocks.
Pu111 Summit
This is the highest point in the study area. It lies on the bed of Kalahari basin with elevation
ranging from 1200 to 1260m.The map unit is limited by abrupt descent to the lower plains. The
soils are deep to very deep, well to somewhat excessively drained. Three different soils occur in
this landform. The yellowish and grayish soils are on the western part of the plateau where they
are found in strips in the direction of the wind. These soils are formed on aeolian deposits. The
third type occurs near the escarpment and these are yellowish brown (with chroma more than 4)
to yellowish red fine sands. The pH ranges between 4 and 4.5. There is not much distinction in
horizons of the soil profile (see plate 5-3 for soil profiles in the study area). It is flat to
undulating.
Hi111 Slope facet complex
This map unit divides the sandveld and the hardveld and stretches northeast to southwest. The
soils are shallow, somewhat excessively drained, yellowish red to yellowish or dark reddish
brown sands and loamy sands. The area is hilly with slope of 10-30%.
39
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Hi112 Talus-hillock-complex
The map unit is on the lower part of Hi111 with slope of 0-5%. The soils are moderately deep to
shallow, well to somewhat excessively drained, light yellowish brown to dark grayish brown fine
sands to loamy fine sands (non calcareous between 50-100cm). It is flat to undulating.
Pe111 Tread/riser of Lower terrace
In this map unit, the soils are deep to very deep, poorly to imperfectly drained, dark grayish
brown to very dark gray clay. The slope is within the range of 0-5%. It is the lowest part of the
study area with elevation of 1000m. The area is undulating. It is used for arable cropping. The
soils are compound and have abrupt boundaries. Some lime concretions occur in some parts of it.
Pe112 Middle terrace
The map unit has deep, moderately well drained reddish brown to dark yellowish brown sandy
clayloam to sandyclay. These are alluvial deposits that come from the eroded terrace. They show
lamellae of clay accumulation. The soil is a consociation of Calcic Luvisol. It has a slope of 0-2%
with pH of 7.5. They are used for arable cropping.
Pe113 Tread/riser of Higher terrace
The soils in this map unit are deep to very deep, well to excessively drained, red to yellowish red
loamy fine sands over sand loams. The slope is within the range of 0-5%. The area is flat to
undulating.
Pe114 Tread/riser of Eroded terrace
The map unit is in the centre of the study area. It is highly eroded. The soils are moderately deep
to shallow, moderately well to well drained, dark brown to reddish brown clayloam to clay. It lies
on the basalt basement complex with a few rock outcrops. It is undulating to rolling. This is used
for settlement and commercial purposes.
Pe115 Slope floor complex of the vale
These are incisions that occur at the bottom of the middle terrace. The soils are deep to very deep,
moderately to imperfectly drained, dark grayish brown-to-brown clayloam to clay. The slope is 05%. It is flat to undulating.
40
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Pe116 Slope facet complex of the Inselbergs
These are rocky hills that occur on hardveld. They are steep-sided residual hills rising abruptly
from the surrounding erosional peneplain. They occur mostly on the granitic gneiss basement
complex.
Fig 5- 1 Study area showing the sample blocks and pit profile points
41
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Plate 5- 3 Ferralic Arenosols and Pellic Vertisols profiles
Fig 5- 2 The geopedological map of Serowe
42
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Table 5-1 The geopedological legend
Landscape
Relief
Type
Lithology
Landform
Plateau
Mesa
Sand with Silcretes and
ferricretes
Summit
Hilland
Hill
Sandstone
Peneplain
Map
unit
symbol
Pu 111
Slope
(%)
Major soils
0-5
Arenosols
(Orthoeutric
Arenosol
Hypoluvic Dystric
Arenosol, etc)
Slope
facet
complex
Hi111
10-30
Eutric Arenosol
Arenic
Luvic
Xerosol
Ferralic Arenosol
Arenic
Ferric
Luvisol
Arenic
Ferric
Luvisol
Calcic Luvisol
Orthic Luvisol
Chromic Luvisol
13885
Sandstone
Talus-hillock
complex
Hi 112
0-5
Orthic Luvisol
Ferralic Arenosol
Arenic
Ferric
Luvisol
Luvic Arenosol
Chromic
Calcic
Luvisol
Calcic
Eutric
Nitosol
4020
Higher
Terrace
Residual/unconsolidated
Tread/Riser
Pe113
0-5
Calcic Luvisol
Ferralic Arenosol
Arenic
Ferric
Luvisol
Calcic Cambisol
Orthic Luvisols
Eutric Nitosols
Chromic Nitosol
Chromic
Calcic
Luvisol
Calcic Gleysol
18124
Middle
terrace
Residual/unconsolidated
Tread/Riser
Pe112
0-5
Ferralic Arenosol
Chromic Luvisol
Arenic
Calcic
Luvisol
Eutric Nitosol
Calcic
Eutric
Nitosol
18124
Lower
terrace
Residual/unconsolidated
Tread/Riser of
Pe113
0-5
Pellic Vertisol
Ferric Arenosol
Chromic Vertisol
Calcic Cambisol
Orthic Luvisol
Chromic
Calcic
Luvisol
10977
Eroded
terrace
Sandstone
Eroded terrace
Pe114
0-5
Chromic
Calcic
Luvisol
Ferralic Arenosol
4637
43
Area
(ha)
163826
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Vale
Residual/unconsolidated
Slope
floor
complex
Pe115
Inselbergs
Basalt/Sandstone
Slope
facet
complex
Pe116
0-5
Arenic
Ferric
Luvisol
Calcic cambisol
Ferralic Arenosol
Orthic Luvisol
Pellic Vertisol
Chromic
Calcic
Luvisols
Rock outcrops
14975
221
5.3 Soils of the study area
The study area has four groups of soils (Driessen et al., 1998) namely Arenosols, Regosols,
Luvisols, and Vertisols.
The dominant group is the Arenosols. They are inherent, yellowish red to reddish brown single
grain materials. They are predominantly structureless, non-stick and non-plastic when wet and
loose when dry. These are deep to very deep sands predominantly of Aeolian nature (D. O. S. M,
2001), and excessively to somewhat excessively well-drained soils with an average pH of 4.5.
There are some patches where the soils are just yellowish fine sands. The profiles are quite
uniform throughout the depth. The total fine sands are generally more than 50 percent. Clay and
silt are less than 10 percent (laboratory results).
One strange thing about these sandy soils is the growth of small plants (with shallow rooting
depth) during the hot months yet the moisture content is very low. This suggests that there is
some moisture kept within 10-20cm of the soil profile. In most cases the subsurface horizons are
completely dry. After rains most moisture is available up to 10m deep (D. O. S. M, 2001).
The Luvisols are characterised with crusting which impedes water infiltration. This results in
widespread of sheet erosion in arable fields. They have a pH of 5.5 on average and are well to
somewhat excessively drained. They are occur on the young land surfaces on the lower parts of
the landscapes, in some cases are associated with vertisols.
The Regosols are shallow soils with uncompleted weathered parent material with low infiltration
rates. They are prone to erosion. Regosols form a hard surface early in dry season that (this crust)
hinders emergence of seedlings and infiltration of rain. In general the surface horizon is thin with
very low organic matter content. The soil pH is 7.0. They occur on the peneplain and are used for
grazing livestock.
44
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
The Vertisols are deep soils characterised by high clay content, usually more than 50% with poor
drainage. Results from particle size distribution analysis indicate a range of 48 to 51% clay
content.
Fig 5-3 shows the soil map of the study area.. It should be noted that the soil map has been
adopted from the original map (De Alwis, 1985). Although some differences were noted in the
field especially in the western part of Pu111 and in map unit Pe111, these could not be added on
the map because data gathered from the field was not enough to effect the change.
Fig 5- 3 The soil map of Serowe
45
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Table 5-2 Correlation table between the FAO soil map and geopedological map
(presented in this thesis)
Symbol
Soil Description
Classification
Landform
A1
Deep to very deep, poorly to imperfectly drained, dark grayish brown to
very dark gray clay. Flat to almost flat
Deep to very deep, poorly to imperfectly drained, dark grayish brown to
reddish brown clay loam to clay
Flat to slightly undulating
Pellic vertisol, partly
sodic
Chromic Vertisol
Lower terrace
(Pe113)
Lower terrace
(Pe113)
Deep to very deep, imperfectly drained dark grayish brown sandy
clayloam to clay. Flat to slightly undulating
Mod. deep to very deep. Imperfectly to mod. Well drained, dark grayish
brown to brown sandy loam to sandy clay
Flat to slightly undulating
Vertic Cambisol
Middle terrace
(Pe112)
Vale
(Pe115)
A4b
Mod. deep to very deep imperfectly to mod. Well drained. Dark grayish
brown to brown clay loam to clay
Flat to undulating
Calcic Cambisol
A4c
Mod. deep to very deep, mod. Well-drained grayish brown-to-brown
sandy loam to sandy clayloam. Flat to undulating
Deep to very deep, imperfectly to mod. Ell drained, dark brown sandy
clay loam to clay
Flat to slightly undulating
Calcic cambisol
A10
Deep to very deep, mod. Well-drained, strong brown to yellowish red
sandy loams to sandy clayloams. Flat to undulating
Chromic Calcic Luvisol
partly petrocalcic
High terrace
(Pe111)
A12
Mod. Deep to deep, well drained, brown to yellowish red loamy sands
to sandy loams
Almost flat to undulating
Arenic Ferric Luvisol
Middle terrace
(Pe112)
A13
Mod. deep to deep mod. Well to well drained, dark red to strong brown,
sandy loam to sandy clayloam. Almost flat to undulating
Chromic Luvisol
Middle terrace
(Pe112)
A14
Mod. deep to very deep, mod well to well drained. Dark brown to
yellowish sandy loam to sandy clay
Flat to undulating
Orthic Luvisol
Middle terrace
(Pe112)
A16
Very deep., mod. Well to well drained, dark red to strong brown, sandy
loam to sandy clayloam. Almost flat to undulating.
Eutric Nitosol
A16a
Very deep, imperfectly to mod. Well-drained, dark red to dark brown
sandy clayloam to clay strongly calcareous and often with dark grayish
brown top layer. Flat to almost flat.
Deep to very deep well to somewhat excessively drained, dark red to
brown sands to loamy sands
Almost flat to slightly undulating
Calcic Nitric Nitosol
Middle terrace
(Pe112)
High terrace
(Pe111)
Middle terrace
(Pe112)
A2
A3
A4
A9
A19
Calcic Cambisol
Calcic Luvisol
Lower terrace
(Pe113)
Vale
(Pe115)
Vale
(Pe115)
Middle terrace
(Pe112)
Ferralic Arenosol
Lower terrace
(Pe111)
Deep to very deep imperfectly to poorly drained (very) dark gray sandy
clay to clay. Flat
Very shallow to shallow, well to somewhat excessively drained, reddish
brown to dark brown sandy loam to clay loam
Undulating to hilly
Calcaric Gleysol Sodic
High terrace
(Pe111)
Slope-facet
complex
Hi111
B5
Mod. deep to deep, mod well to well drained, reddish brown to strong
brown sandy clay loam to clay
Undulating to rolling on basalt
Chromic Luvisol
Slope-facet
complex
B5a
Shallow t mod deep, well drained reddish brown to strong brown sandy
clay loam to sandy clay
Undulating to rolling (mainly on basalt)
Chromic Luvisol
Partly petric, some lithic
Vale
(Pe115)
B6
Mod. deep to deep, mod. well to well drain, dark brown to reddish
brown clayloam to clay. Undulating to rolling (basalt)
Calcic Luvisol
Eroded terrace
(Pe114)
A30
B1
46
Eutric Regosol
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
D9
Deep, mod, well drained, reddish brown to dark yellowish brown sandy
clay loam to sandy clay
Flat to undulating
Calcic Luvisol
Middle terrace
(Pe112)
S1
Very shallow to shallow, excessively drained yellowish red to yellowish
brown sands and loamy sands
Undulating to hilly
Ferralic Arenosol
Lithic
Slope-facet
complex
Hi111
S1a
Moderately deep, somewhat excessively drained, yellowish red to
yellowish or dark reddish brown sands and loamy sands. Undulating to
hilly
Ferralic Arenosol
Slope
complex
(Hi111)
S3
Deep to very deep, well to somewhat excessively drained, yellowish
brown (but with chroma of more than 4) to yellowish red fine sands.
Flat to undulating
Ferralic Arenosol
Summit
(Pu111)
S5
Deep to very deep, well to somewhat excessively drained, red to strong
brown fine sands to loamy fine sands
Flat to undulating
Ferralic Arenosol
S5a
As S5, but showing lamellae of clay accumulation
Luvic Arenosol
S6
Deep to very deep, somewhat excessively to excessively drained, red to
yellowish brown fine sands and loamy fine sands. Undulating to rolling
dunes
Ferralic Arenosol
Middle terrace
(Pe112)
High terrace
(Pe113)
Middle terrace
(Pe112)
Middle terrace
(Pe112)
S7
Deep to very deep, well to somewhat excessively drained, red to strong
brown loamy fine sand. Flat to undulating
Arenic Ferric Luvisol
Middle terrace
(Pe112)
S10
Deep to very deep, well to excessively drained, red to yellowish red
loamy fine sands over sand loams
Flat to undulating
Arenic Ferric Luvisol
High terrace
(Pe111)
S16
Deep to very deep, somewhat excessively drained, light yellowish
brown to dark grayish brown fine sands to loamy fine sands
Flat to undulating
Dystric Arenosol
Vale
(Pe115)
S17
Deep to very deep, well to somewhat excessively drained, light
yellowish brown to dark grayish brown fine sands to loamy fine sands
(non calcareous between 50 and 100cm)
Eutric Arenosol
Talus-hillock
complex
(Hi112)
Note: Ks= soils on coarse-grained sedimentary rocks
R = very shallow soils on steep hills, ridges and escarpments
Adopted from: Soil Mapping and Advisory Service Project BOT/80/003
47
facet
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Chapter 6 Land use
6.1 Land use definiton and kinds of land use
Land use is the activity that is carried out on a piece of land for a certain period of time. It may
change with time from one land use to another. However the concept of land use is too wide to be
useful except in very general analyses(Driessen and Konijn, 1992).The major kinds of land use
are rainfed agriculture and grazing whilst irrigated agriculture is at a very small scale. Land use in
Serowe is also influenced by settlement. The major settlements are found along the base of the
scarp. The concentration here, according to senior residents, owes much to the existence of
ephemeral springs in the former years. Although these no longer flow, abandoned spring
discharge points can still be seen at Serowe and Paje (SGC, 1988). Fig 6-1 shows the land
use/land cover for the area.
Fig 6- 1 Land use map of Serowe
48
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
6.2 Land utilisation types in the Serowe area
As “land use” is too wide a concept to be useful in land evaluation, land utilisation type (LUT)
was introduced which is more specific. It is characterised by its key attributes like biological,
socio-economic and technical aspects of land use that are relevant to functioning of it (Driessen
and Konijn, 1992)
In Serowe area, there are a number of LUTs that are practised and these are as follows;
traditional rainfed maize, traditional rainfed sorghum, traditional millet, traditional,
mechanised rainfed maize, irrigated vegetables, orchards and traditional cattle ranching.
A cattle rearing is the biggest enterprise in the area. The land parcels are commonly called cattle
posts. There are no paddocks to limit mobility of cattle during grazing. The herdsmen have to
drive cattle to the drinking places that are improvised by borehole at the cattle posts.
As the interest of this research was on smallholder farmers who grow rainfed crops, LUTs
traditional rainfed maize and traditional rainfed sorghum were chosen, as they are major cereal
foods in the area and in Southern region as a whole. The two LUTs are sometimes grown under
mixed cropping but majority of the farmers that were interviewed practise single cropping
systems.
The area of farmland ranges from 4ha to 10ha. For those with greater than 4ha do not use the
whole land at one growing season due to problems of acquiring farm inputs such that part of the
land remains idle. This indirectly leads to fallowing of the land although it is not their intention to
do so. All the farms are well fenced to protect the crops from destruction by grazing animals. The
rains start in November and end in April and harvesting is done in May/June when crops have
completely dried (see table 6-1). This crop calendar was captured during the interviews with
farmers in the study area. The hypothetical dates for planting were chosen based on this calendar.
Table 6- 1 Crop calendar
Activity
Land
preparation
& seeding
Weeding
Harvesting
Months
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
49
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
There are specific varieties that are grown for one main reason of early maturity, as the rains are
very erratic. The varieties for maize are Kgalagadi, Porch pearl and R201, all mature within the
range of 120-125 days. Farmers use a seed rate of 7kg -ha (calculated from the results of farmers
interviews) yet the recommended rate is 10kg -ha for row planting and 20kg -ha for broadcasting.
As for sorghum, the varieties are Phofu (red in colour) and Segaolane (white in colour). Phofu
takes 115 to 125 days and Segaolane matures within the range of 125 to 130 days.
According to results of the farmers’ interviews, the management of the farms is generally poor.
Land preparation and planting are done simultaneously as the farmers wait until the rains come.
The seed is mostly recycled from the previous harvest.
Description of land utilisation types (LUTs)
The selection of land use types depends on the local resources situation. The land use types in the
area are maize, sorghum, millet, cowpeas and cattle raise-based. Obviously the climatic condition
of the area is an important and decisive factor why these types are practised.
The selected land use types in this study are rainfed maize and sorghum under traditional
management. Since these LUTs are traditionally managed, the inputs are low with low degree of
management. For these low inputs, the farmer does not apply anything to improve the quality of
land therefore; it is not strange that farmers in the area experience low yields.
LUT1 Maize-based
This is a rainfed traditionally managed land use type. The family members provide labour but
during peak periods of weeding, casual labour is employed. It should be noted that only those
families that can afford to pay for casual labour do employ it. Main source of power is animal
draught except for a few farmers who use tractors for ploughing and planting only. The seed is
broadcasted on the same day of ploughing the field, at rate of seven kilograms per hectare. The
farmers have access to reasonable agricultural services. The main variety grown is Kgalagadi,
which takes 125 days to reach maturity with plant population of 10,000per hectare. In all the
farmlands visited no fertiliser is applied to the crops.
Sometimes the crop is attacked by stalkborers but there is no control measure. Farmers do not
practice any soil and water conservation measures.
50
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
LUT2 Sorghum-based
This is also rainfed traditionally managed land use type. The family members provide labour but
during peak periods of weeding, casual labour is employed. Main source of power is animal
drought except for a few farmers who use tractors for ploughing and planting only. The seed is
broadcasted on the same day of ploughing the field, at rate of five kilograms per hectare. The
farmers have access to reasonable agricultural services. The preferred variety is Phofu (red
sorghum), which takes 115 to 125 days to reach maturity with plant population of 40,000 per
hectare. In all the farmlands visited no fertiliser is applied. Crickets, aphids and birds mainly
attack sorghum. The birds are the most serious pests of sorghum and if left unattended to, the
production is drastically reduced to zero. There is no control for crickets and aphids but scaring
them away controls birds.
Below are tables showing the differences in yield between the actual and potential for both early
and late planting. The actual yields are calculated from the yields obtained during interviews with
farmers whilst the potential yields are the results from PS2 water- limited production potential
(see tables 6-2 to 6-5).
Table 6- 2 Yield gap for LUT1 in 1999/2000
Mapping units
Actual yield
Water-limited yield
Yield gap
Pe111
96
6072
5976
Pe112 & Pe113
219
5754
5535
Pe115
317
1606
1289
Table 6- 3 Yield gap for LUT2 in 1999/2000 growing season
Mapping units
Actual yield
Water-limited yield
Yield gap
Pe111
305
1420
1115
Pe112 & Pe113
219
1268
1049
Pe115
105
1115
1050
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Table 6- 4 Yield gap for late planting for LUT1
Mapping units
Actual yield
Water-limited yield
Yield gap
Pe111
96
5853
5757
Pe112 & Pe113
219
5455
5236
Pe115
317
1257
940
Table 6- 5 Yield gap for late planting for LUT2
Mapping units
Actual yield
Water-limited yield
Yield gap
Pe111
96
1219
914
Pe112 & Pe113
219
1021
802
Pe115
317
1008
903
The yield gap is very wide due to a number of reasons:
Late land preparation as the farmers wait for the rains to come. The seed rate used by farmers is
too low to produce good yield since plant population is also reduced. The recommended seed
rates are 20kg –ha for maize and 10kg –ha for sorghum. Farmers never apply fertilizer to their
crops to boost plant growth. Although nutrient test was not conducted in the area during
fieldwork, the soils are not fertile enough to produce good yield. Literature on crop production in
the area indicates that fertilizing the crops either in organic form or inorganic form is necessary
for better output (Gibbon and Pain, 1985; Nampad, 2000)
Weeding is done only once, which gives chance for the weeds to compete favourably with the
crops.
Farmers do not practise soil and water conservation measures that would assist in minimising
water runoff and encourage infiltration as revealed from interviews. Since some farms are on
sloping areas this water runoff also carries away fertility of the soil.
Control of pests is minimal especially for sorghum, which is highly susceptible to attack by birds.
Labour to scare these birds are rarely found as it used to be in the past years when children were
used. Nowadays, children are encouraged to go to school hence there is no one to attend to the
crops.
52
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
As observed from tables 6-2 to 6-5, the yields are too low to offset the cost of growing these
crops. The currency is in Pulas (P). The cost of maize seed is P3 per 10kg bag. On average the
area planted is 4ha and making a total of P12. Casual labour is P5 per day per person and on
average one employs 3casual labourers, which gives a total of P45. Total expenditure is P57. This
gives a negative gross margin of P57 since the yield is not sold but rather consumed by the family
members.
53
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Chapter 7 Results and Discussion
7.1 Hydraulic properties
This section describes the results got from measurements of hydraulic properties and their
relationships.
7.1.1 Infiltration rates
Below is fig 7-1 showing the infiltration rates over time that was measured in the field.
60
60
Infiltration
Infiltration
80
40
20
0
40
20
0
0
5
10
15
20
0
Time
(a)
5
10
Time
(b)
EPT 01
SVD 081
Fig 7- 1Basic infiltration rates
In some sites, at first the water intake was high (7-1a) and dropped with time until the base
infiltration rate was reached whilst in other sites, the initial intake was low (7-1b) but increased
with time, then dropped until it reached the base infiltration rate. This can be attributed to the
status of the surface features of the sites. In cases where there was leaf litter and a lot of cow dung
on the surface, initial intake was high as opposed to surfaces without any litter.
It should be noted that the graphs are not smooth and this is probably due to the fact that in the
process of infiltration, the water intake is not always in the order of decreasing at a decreasing
rate but rather it fluctuates as water enters the soil until it stabilises. (See appendix A for the
results of measurements)
54
15
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Table 7- 1 Descritpive statistics for infiltration between landscapes
STRATUM
Sandveld (Plateau)
Escarpment (Hilland)
Hardveld (Peneplain)
Variable
Infiltration rate
Infiltration rate
Infiltration rate
Minimum Maximum Mean
18.5
47.5
22.99
8.3
36.2
18.37
6
18
14.43
Std.
Deviation
8.9
7.25
8.3
Results from descriptive statistics indicate that soils from plateau area have highest infiltration
rates and those of peneplain have the lowest rates. There are variations in all the three landscapes
and the widest variations occur in the peneplain. This can be attributed to different soil types
found in the landscape. There are Arenosols, Luvisols, Regosols and vertisols, which have
different infiltration rates. Another reason could be due to different position in the landscape as
soils on the plateau are different from soils on the slope facet complex due to soil forming factors.
Variations in the plateau area can be attributed to fine sands as well as very fine sands occurring
in the area. Also the clay percent in these soils is different. The clay percent ranges from 3% to
8% of the first 10 to 20 cm of the soil profiles. Joshua (1991) explains that infiltration rates can be
variable for a textural class. In his findings, the Arenosols had a range of 18.5 to 54.3cm/hr from
the same study area.
There are differences in these rates and to see the significance of their differences an ANOVA
table was calculated (see table 7-2 below). The proportion of different soil particle size fractions
influences the pore size distribution, which in turn determines the infiltration rates.
Table 7- 2 ANOVA for infiltration between landscapes
Infiltration rate
SS
df
Between landscapes 979.2219
Within landscapes
Total
6870.286
7849.508
MS
2
489.6109
98
100
70.10496
F
Sig.
6.98397
0.000
The differences between the landscapes and within each landscapes are highly significant
(P=0.000).
The analysis went further to look at differences in soil type. Table 7-3 shows the
ANOVA table for differences between point pairs of the soil types.
55
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Table 7- 3 ANOVA for infiltration between soil types
Soil type
Residual
Df
4
48
SS
1687.57
2773.75
MS
421.89
57.79
F-value
7.3009
P
0.000112
The ANOVA for differences between pairs of soil types indicate that there is high
significant difference between the means of the pairs of soil types.
Table 7- 4 Differences between pairs of means of soil types
Soil type
VC
PV
OL
FA
CL
Mean
9.757143
12.74444
26.875
22.40385
13.9875
Stdev
4.238261
6.389271
10.62022
8.459432
5.736708
FA-CL
OL-CL
PV-CL
VC-CL
OL-FA
PV-FA
VC-FA
PV-OL
VC-OL
VC-PV
Infiltration rates
Difference L-limit
-2.6297
-6.7791
-2.4393
-8.5471
6.0634
1.1153
2.1428
-3.0660
0.1904
-5.0434
8.6932
4.9243
4.7725
0.6230
8.5028
2.6468
4.5822
-1.5257
-3.9206
-8.8316
U-limit
1.5198
3.6686
10.9744
7.3517
5.4242
12.4619
8.9220
14.3587
10.6900
0.9903
Note: FA is Ferralic Arenosols; OL is Orthic Luvisols; CL is Chromic Luvisols; PV is Pellic Vertisols and
VC is Vertic Cambisols.
The means between Pellic Vertisols and Calcic Luvisols, Pellic Vertisols and Ferralic
Arenosols, Vertic Cambisols and Ferralic Arenosols and Pellic Vertisols and Orthic
Luvisols are significantly different (95%) (Tukey HSD) but there is no significant
difference between Vertic Cambisols and Chromic Luvisols and Vertic Cambisols and
Orthic Luvisols. Considering the upper and lower limits of these differences, an overlap
that includes a zero between the lower and upper limits indicates that the means are
significantly different.
These results imply that there are variations in the soil properties that led to such
differences in behaviour. These variations are probably due to the texture of soils and
organic matter as Dingman (1993) explains that soil texture and organic matter are some
of the factors that influence infiltration of fluids in the soil.
56
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
7.1.2 Actual moisture content
The moisture results are not due to rainfall differences since the area did not receive any rains
during the period of moisture measurements. Below is analysis of variance table (table 7-5) for
the measurements of actual moisture content based on landscape.
Table 7- 5 ANOVA for moisture content between the landscapes
AMC at 10cm
SS
Between landscapes 456.2632
df
2
MS
228.1316
98
100
2
18.39074
AMC at 30cm
Within landscapes
1802.292
Total
2258.555
Between landscapes 350.2463
Within landscapes
Total
98
100
1604.67
1954.917
175.1232
F
12.4047
Sig.
0.000
10.69507
0.000
16.37419
There is high significant difference in the moisture content between the landscapes (99%
level). The differences are higher at 10cm depth than at 30cm depth. The F-values are
high (12.4 and 10.69) meaning that there are high variations in the moisture content
between the landscapes. Table 7-6 shows the descriptive statistics.
Table 7- 6 Descriptive statistics for moisture between landscapes
STRATUM
Sandveld (Plateau)
Escarpment (Hilland)
Hardveld (Peneplain)
Variable
AMC at 10cm
AMC at 30cm
AMC at 10cm
AMC at 30cm
AMC at 10cm
AMC at 30cm
Minimum Maximum
0.72
7.45
0.22
5.11
1.06
20.92
1.19
13.56
0.38
9.6
0.44
13.56
Mean
3.23
2.12
8.55
7.08
5.00
6.61
Std.
Deviation
2.03
1.33
5.77
4.66
3.05
4.18
Soils in the hilland had the highest moisture content at both depths of 10cm and 30cm followed
by peneplain and the last being plateau area. The standard deviation is also high in the hilland,
which implies that there is a wide variation in the soil properties.
The field measurements were further analysed based on soil type as shown in table 7-7
57
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Table 7- 7 ANOVA for differences between pairs of soil types
Actual moisture at 10cm depth
Df
SS
Soil type
4
565.25
Residual
48
567.46
MS
141.31
11.82
F-value
11.953
P
0.000
Actual moisture at 30cm depth
Df
SS
Soil type
4
647.26
Residual
48
314.93
MS
161.81
6.56
F-value
24.663
P
0.000
There is high significant difference between the means in soil types (table 7-7). The Fvalues are high signifying wide variations in the actual moisture content between the soil
types. Below is table 7-8 showing the means and standard deviations of these soil types.
Table 7- 8 Means and standard deviations of the soil types
At 10cm depth
Soil Type
Mean STDEV
At 30cm depth
Soil Type
Mean STDEV
Ferralic Arenosol 3.058 2.187
Ferralic Arenosol
2.073 1.642
Chromic Luvisol 6.829 2.308
Chromic Luvisol
8.614 4.432
Vertic Cambisol 11.01 5.306
Vertic Cambisol
10.07 1.316
Pellic Vertisol
7.911 0.998
Pellic Vertisol
11
3.693
Orthic Luvisol
3.775 3.197
Orthic Luvisol
1.6
0.271
The Vertic Cambisols had highest mean (11.01) as well as standard deviation (5.306) at 10cm
depth whilst Pellic Vertisols had highest (11) with Calcic Luvisols having the highest standard
deviation (4.432) at 30cm depth. These variations indicate that the soils have different properties
and behaviour.
In order to examine the differences in pairs of soil types, the confidence intervals were calculated
for each pair (table 7-9).
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Table 7- 9 The confidence intervals of the soil types
Moisture at 10cm depth
Soil type Difference Lower limit
FA-CL
-2.6296
-6.7791
OL-CL
-2.4393
-8.5471
PV-CL
6.0634
1.1526
VC-CL
2.1428
-3.0660
OL-FA
0.1904
-5.0434
PV-FA
8.6932
4.9244
VC-FA
4.7725
0.6230
PV-OL
8.5028
2.6469
VC-OL
4.5821
-1.5257
VC-PV -3.9206
-8.8316
Moisture at 30cm depth
U-limit
1.5198
3.6686
10.9744
7.3517
5.4242
12.4619
8.9220
14.3587
10.6900
0.9903
Soil type
FA-CL
OL-CL
PV-CL
VC-CL
OL-FA
PV-FA
VC-FA
PV-OL
VC-OL
VC-PV
Difference
-6.1390
-7.2428
1.0016
1.0571
-1.1038
7.1406
7.1961
8.2444
8.3000
0.0556
L-limit
U-limit
-9.2302 -3.0478
-11.7930 -2.6927
-2.6569 4.6601
-2.8233 4.9375
-5.0029 2.7952
4.3330
9.9482
4.1049 10.2874
3.8819 12.6069
3.7498 12.8502
-3.6029 3.7140
There is significant difference (99%) confidence interval (Tukey HSD) between means for soil
type pairs Pellic Vertisols and Chromic Luvisol, Pellic Vertisols and Ferralic Arenosols, Vertic
Cambisols and Ferralic Arenosols and Pellic Vertisols and Orthic Luvisols at 10cm depth whilst
at 30cm depth, they are Ferralic Arenosols and Chromic Luvisols, Orthic Luvisols and Chromic
Luvisols, Pellic Vertisols and Ferralic Arenosols, Vertic Cambisols and Ferralic Arenosols and
finally Vertic Cambisols and Orthic Luvisols. The difference between Orthic Luvisols and
Ferralic Arenosols is not significant.
7.1.3 Hydraulic conductivity (k)
The inverse auger hole measurements were calculated and below is an example of the saturated
hydraulic conductivity over time. Amongst the soil types occurring in the area, Arenosols had the
highest hydraulic conductivity. This owes to the fact that large continuous pores have a lower
resistance to flow (and thus a higher conductivity) than or discontinuous pores (Irvine et al.,
2001).
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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[h+r/2] (log)
INVERSE AUGER METHOD
1.90
1.85
1.80
1.75
1.70
0
200
400
600
Time [sec]
Kshat=397.4cm -d
Fig 7- 2 Saturated hydraulic conductivity at SVD 081
The calculated results were further analysed to find out the differences between the landscapes
and also between the soil types. Table 7-10 shows the ANOVA for hydraulic conductivity
between the landscapes
Table 7- 10 ANOVA for hydraulic conductivity based on landscapes
SS
Hydraulic conductivity Between landscapes 657237.5
Within landscapes
Total
2711456
3368694
df
MS
F
Sig
2
328618.7
11.88
0
98
100
27667.92
There is significant difference between the landscapes (99%). But to have a better understanding
of this variable, the computed means are displayed in table 7-14.
Table 7- 11 Descriptive statistics for saturated hydraulic conductivity
STRATUM
Variable
Minimum Maximum
Sandveld (Plateau) Hydraulic conductivity 99.4
844.6
Escarpment (Hilland) Hydraulic conductivity
9.9
695
Hardveld (Peneplain) Hydraulic conductivity
9.9
397.4
Mean
301.65
193.49
82.71
Std.
Deviation
232.50
176.92
108.02
The descriptive statistics indicate that hydraulic conductivity in the plateau area is highest
followed by hilland and the least being the peneplain. The standard deviation follows the same
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trend. There is wide variation of saturated hydraulic conductivity in the plateau area due to
different particle size of the sands in the area. There are fine sands as well as very fine sands and
in some instances, there are loamy sands.
The means and standard deviations were calculated for the soil types in the area table 7-12.
Table 7- 12 Means and standard deviations of soil types
Soil type
Mean
Pellic Vertisols
75.2
Vertic Cambisols 104.85
Orthic Luvisols
188.8
Ferralic Arenosols 291.88
Calcic Luvisols
77.3
STDEV
151.98
119.26
173.51
224.44
84.37
The Ferralic Arenosols have highest mean (291.8) and standard deviation (224.4) and these are
significant (99%) as shown in table 7-13. The reason for this high standard deviation can
probably be due to the variation of the size of the sand particles in this soil. In some cases there
are very fine sand to fine sand whilst in other cases there are fine sandy loam. This is supported
by Irvine (2001) who came into conclusion that hydraulic conductivity is a highly variable soil
property.
The ANOVA was calculated for the means of the soil types (table 7-13) whilst table 7-14 shows
the confidence intervals.
Table 7- 13 The ANOVA for the means of saturated hydraulic conductivity
Soil type
Residual
Df
4
48
SS
515440
1687981
MS
128860
35166
F-value
3.6643
Although the F-value is low (3.66) the difference is significant.
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Table 7- 14 Differences in the means of saturated hydraulic conductivity of different
soil types.
Soil type
FA-CL
OL-CL
PV-CL
VC-CL
OL-FA
PV-FA
VC-FA
PV-OL
VC-OL
VC-PV
Hydraulic conductivity
Difference L-limit
U-limit
214.584 -11.7285 440.8977
133.85 -199.274 466.9739
27.555 -240.286 295.3972
-2.1
-286.189 281.989
-80.7346 -366.186 204.7169
-187.029 -392.578 18.5195
-216.685 -442.998 9.6285
-106.294 -425.675 213.0864
-135.95 -469.074 197.1739
-29.6556 -297.497 238.1861
Although the means show differences, these are not significant. The lower and upper limits
overlap each other and include a zero, which implies that they are not significantly different.
7.1.4 Relationship of the hydraulic properties.
In order to evaluate the relationship of these hydraulic properties, correlation was done based on
all observations, landscapes and soil type. Table 7-15 shows the correlation of hydraulic
properties across the area.
Table 7- 15 Correlation of hydraulic properties across the area
Infiltration
AMC at 10cm AMC at 30cm Hydraulic (k) rate
AMC at 10cm Pearson Correlation
1
Sig. (2-tailed)
AMC at 30cm Pearson Correlation
0.6757**
1
Sig. (2-tailed)
8.43E-16
Hydraulic (K) Pearson Correlation
-1.96E-01*
-0.3622**
1.0000
Sig. (2-tailed)
4.96E-02 0.00019721
Infiltration rate Pearson Correlation -2.74E-01**
-0.5374**
0.5368**
1.0000
Sig. (2-tailed)
5.54E-03 6.74023E-09
0.0000
AMC is Actual Moisture content
** Correlation is significant at the 0.001level (2-tailed)
* Correlation is significant at the 0.05 level (2-tailed)
The results show that AMC at 10 and 30cm are highly correlated (0.001 level), hydraulic
conductivity and AMC at 10 and 30cm depth are correlated (0.05level), infiltration and AMC at
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10 and 30cm depth; infiltration and hydraulic conductivity are highly correlated (0.001level)
(table 7-15). Based on these correlations, the analysis went further to perform regression analysis.
Figure 7-3 shows the results of regression analysis across the area.
Across the area
y = -0.6103x + 21.85
2
R = 0.1008
Infiltration cm-hr
Infiltration cm-hr
Across the area
60
40
20
0
0
5
10
15
20
25
y = -1.1189x + 24.572
R2 = 0.2972
50
40
30
20
10
0
0
5
10
AWC at 10
15
20
25
AWC at 30
(a)
(b)
1000
500
0
0
5
10
15
20
y = -17.763x + 289.39
R2 = 0.1516
Across the area
y = -10.805x + 252.51
R2 = 0.064
Hydraulic
conductivity
Hydraulic
conductivity cm-d
Across the area
1000
500
0
25
0
5
10
15
AWC at 30
AWC at 10
(c)
(d)
Hydraulic
conductivity cm-d
Across the area
y = 10.848x - 8.3023
R2 = 0.2382
1000
800
600
400
200
0
0
10
20
Infiltration cm-hr
(e)
Fig 7- 3 Hydraulic properties across the area
63
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40
50
20
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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There is weak negative relationship between AMC at 10 and 30cm respectively (7-3a and
b) and infiltration with R2=0.29. Again there is a weak negative relationship between
AMC at 10 and 30cm and hydraulic conductivity (7-3 c and d). But the relationship is
significant (0.001 and 0.05 levels) as observed in table 7-15. As for infiltration and
hydraulic conductivity, the relationship is positive. In all the cases, the R2 is not
explaining much of the relationships, which means that there are other factors that come
into play.
Correlation of hydraulic properties between landscapes was calculated and presented in
table 7-16 and regression was calculated based on the significance of the correlation (fig
7-4)
Table 7- 16 Correlation of hydraulic properties by landscape
Landscape
Plateau
(Sandveld)
Hilland
(Escarpment)
Peneplain
(Hardveld)
Variable
AMC at 10
AMC at 10 AMC at 30 Hydraulic Infiltration rate
Pearson Correlation
1.00
Sig. Level
AMC at 30
Pearson Correlation
0.04
1.00
Sig.level
0.86
Hydraulic (k) Pearson Correlation
-0.29
-0.14
1.00
Sig. level
0.22
0.58
Infiltration rate Pearson Correlation
-0.02
-0.24
0.19
1.00
Sig. level
0.94
0.32
0.44
AMC at 10
Pearson Correlation
1.00
Sig. level
AMC at 30
Pearson Correlation
0.61*
1.00
Sig.level
0.00
Hydraulic (k) Pearson Correlation
-0.11
-0.17
1.00
Sig. level
0.48
0.29
Infiltration rate Pearson Correlation
-0.20
-0.50
0.43*
1.00
Sig.level
0.20
0.00
0.00
AMC at 10
Pearson Correlation
1.00
Sig. level
AMC at 30
Pearson Correlation
0.91*
1.00
Sig. level
0.00
.
Hydraulic (k) Pearson Correlation
-0.70
-0.69*
1.00
Sig. level
0.00
0.00
.
Infiltration rate Pearson Correlation
-0.65*
-0.60*
0.82*
1.00
Sig. level
0.00
0.00
0.00
.
* Correlation is significant at the 0.001 level (2-tailed)
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From table 7-16, hydraulic properties in the plateau area show no significant correlation ;
in hilland, AMC at 10 and 30cm depth (61%) and infiltration rate and hydraulic
conductivity are correlated (43%). In the peneplain , all the hydraulic properties are
highly correlated. Based on those that are significantly correlated, a regression analysis
was performed (see fig 7-4 and 7-5).
40
30
20
10
0
0
Hilland
y = -0.3653x + 22.013
R2 = 0.0829
5
10
15
Infiltration cm-hr
Infiltration cm-hr
Hilland
20
y = -0.8713x + 24.909
R2 = 0.3058
40
30
20
10
0
0
5
AWC at 10
10
AWC at 30
(b)
(a)
Hydraulic cm-d
Hilland
y = 10.943x - 4.0861
R2 = 0.2034
800
600
400
200
0
0
10
20
Infiltration cm-hr
(c)
Fig 7- 4 Relationship of hydraulic properties in hilland
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The relationship between AMC at 10 cm depth and infiltration (7-4a) is negative and very
weak (R2 =0.08), the same with 30cm depth (R2 =0.31) but the relationship is significant
(0.001 level). This implies that the less the moisture the soil has, the higher the
infiltration. There is positive relationship between infiltration and hydraulic conductivity.
The lower the infiltration rates the lower the hydraulic rates.
Peneplain
y = -1.2689x + 19.333
R2 = 0.4443
30
20
10
0
0
5
10
15
Infiltration cm-hr
Infiltration cm-hr
Peneplain
20
y = -0.8093x + 18.298
R2 = 0.3417
30
20
10
0
0
5
10
15
20
AWC at 30
AWC at 10
(a)
(b)
y = -19.143x + 168.05
R2 = 0.4446
400
300
200
100
0
0
5
10
15
y = -11.441x + 131.72
R2 = 0.7209
Peneplain
Hydraulic
conductivity cmd
Hydraulic
conductivity cm-d
Peneplain
20
200
150
100
50
0
0
5
10
AWC at 30
AWC at 10
(c)
(d)
Hydraulic
conductivity (cmd)
Peneplain
y = 9.2968x - 51.775
R2 = 0.4045
400
300
200
100
0
0
5
10
15
Infitration rate (cm-hr)
Fig 7- 5 Relationship of hydraulic properties in peneplain
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Again, the trend is the same as in the hilland; the relationship is negative for AMC and
infiltration at both depths but the R2 improves to 44 and 34% respectively (7-5a and b)
and for AMC and hydraulic conductivity improves to 44 and 72% respectively (7-5 c and
d). This shows that soils in different landscapes have different properties; hence,
landscape has an influence on the relationship of the hydraulic properties.
Finally, the correlation was calculated based on soil type as shown in table 7-17.
Table 7- 17 Correlation of hydraulic properties for soil types
AMC at 10
AMC at 30
Hydraulic k
Infiltration
Pearson Correlation
Sig. (2-tailed)
Pearson Correlation
Sig. (2-tailed)
Pearson Correlation
Sig. (2-tailed)
Pearson Correlation
Sig. (2-tailed)
AMC at 10 AMC at 30 Hydraulic k Infiltration
1
0.6784**
0.000
-0.2514
0.0694
-0.2432
0.0793
1
-0.4643**
0.0005
-0.5585**
0.000
1
0.5301**
0.000
1
From table 7-17, the results show that AMC at 10cm is highly correlated with AMC at
30cm; AMC at 30cm is highly correlated with hydraulic conductivity; AMC at 30cm is
highly correlated with infiltration and hydraulic conductivity is highly correlated with
infiltration. It is from these correlated variables that regression analysis was performed.
Fig 7-6 shows the relationship of the hydraulic properties by soil type.
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60
Orthic Luvisols
y = 3.2917x + 14.449
2
R = 0.982
Hydraulic
conductivity
(cm/d)
Infiltration
(cm/hr)
Orthic Luvisols
40
20
0
0
5
y = 49.612x + 23.865
R2 = 0.6835
600
400
200
0
0
10
5
10
AMC at 10cm
AMC at 10cm
(a)
(b)
y = 16.007x - 219.04
R2 = 0.7851
Infiltration rate
Orthic Luvisols
Hydraulic
conductivity
(cm/d)
600
500
400
300
200
100
0
0
20
40
60
Infiltration (cm /hr)
(c)
Pellic Vertisolsy = 0.9434x + 2.4825
2
R = 0.8826
30
20
10
0
0
Hydraulic
conductivity
(cm/d)
20
AMC at 10cm
(d)
Pellic Vertisols
10
y = 14.86x - 84.53
R 2 = 0.6338
400
300
200
100
0
0
10
20
30
Infiltration (cm/hr)
(e)
(c)
Fig 7- 6 Relationship of hydraulic properties per soil type
Referring to fig 7-6,in Orthic Luvisols, there is a strong positive relationship between
AMC at 10cm depth and infiltration (R2=0.98); a mild relationship between AMC at
10cm depth and hydraulic conductivity (R2=0.68) and a good relationship between
infiltration and hydraulic conductivity (R2=0.785). These relationships are highly
significant (99%). As for Pellic Vertisols, the relationship between AMC at 10cm is very
strong (R2=0.88) and good relationship between infiltration and hydraulic conductivity
68
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(R2=0.63). These high values of R2 are explaining more of the relationship implying that
they affect each other and the remainder could be factors that were not dealt with in this
research.
It should be noted that the sample size for observation per soil type was not adequate to
make concrete conclusion, however, it was worth analysing it to examine their
relationship.
General summary
The results from regression of actual moisture content and infiltration rate indicate that there is a
weak negative relationship since the correlation is very low. But the relationship is significant
(99%) level. This implies that when a soil is moist, infiltration is lower than when the soil is dry.
Since infiltration is influenced by a number of factors like texture, crust, organic matter content,
porosity, compaction and structure apart from moisture content ((Dingman, 1993; USDA, 1998)
this explains the reason why the R2 is low in all categories. It is explaining only 10 and 29% (at
10cm and 30cm respectively) across the study area (fig 7-3), 8 and 31% in hilland (fig 7-4) and
44 and 34% in the peneplain (fig 7-5). However, the relationship is positive in the category of soil
type 98 and 68% for Orthic Luvisols and 88 and 63% for Pellic Vertisols (fig 7-6). The remainder
is explained by other factors, which were not dealt with during this research such as porosity,
compaction and structure.
The relationship between actual moisture content and hydraulic conductivity is also negative with
R2 of 6% and 15% respectively across the area (fig 7-3) but it is significant at 99% implying that
the less the moisture in the soil the higher the saturated hydraulic conductivity. The relationship
improves in the peneplain (7-5) where the R2 is 44% and 72% respectively. There is an increase
in the saturated hydraulic conductivity as moisture of the soil is reduced since water fills the pore
spaces in the soil. Soils with light texture (Arenosols) had higher hydraulic conductivity values
than those with heavy texture (Vertisols).
There is a positive relationship between infiltration rate and hydraulic conductivity with R2 of
23% across the area (fig 7-3) but higher in peneplain 40% (fig 7-5) which is significant (99%).
This implies that the more the water enters the soil the faster it is drawn to the lower horizons of
the soil profile. Since the R2 is explaining less of the relationship, it shows that there are other
factors that influence these two variables like texture, crust, organic matter content, porosity,
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compaction and structure as already mentioned in the first paragraph. The Arenosols showed
highest values of both hydraulic properties amongst the soil types.
7.2 Soil moisture map
In this section, the soil maps are shown that are resulting from geostatistical approach at
depth of 10cm and another at depth of 30cm. The operation assumed the Continuous
model of spatial variation (CMSV) that soil forming factors vary continuously in space
and that there is spatial dependency between them, therefore the soil properties also are
spatially variable. (See fig 7-7 and 7-8)
The results show the soil moisture distribution at depth of 10cm (fig 7-7) whilst the one
below shows distribution of soil moisture at depth of 30cm (fig 7-8). The highest values
fall in Pellic Vertisols, Calcic Luvisols and Vertic Cambisols for the depth of 10cm but at
30cm depth the highest values fall in the Vertic Cambisols and Pellic vertisols only.
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Fig 7- 7 Soil moisture distribution map at 10cm depth
Fig 7- 8 Soil moisture distribution map at 30cm depth
7.3 Spatial variability
Although the sample size (56 points) was not adequate to reliably estimate a variogram,
we attempted it nonetheless. Results should be considered indicative rather than
definitive. This aimed at assessing the variability of soils in the area. Using soil moisture
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as one of the hydraulic properties, ordinary kriging was performed using lag distance of
2000m for both depths with maximum point pairs of 16. The Continuous model of spatial
Variation (McBratney and Gruijter, 1992) was assumed. Fig 7-9 shows the moulded
variogram for the parameters.
AMC at 10cm
Nugget
Sill
Range
AMC at 30cm
Nugget
Sill
Range
3
32.5
4000
2
20
4000
Fig 7- 9 Moulded variogram parameters for AMC at 10 and 30 cm depths
The moulded variograms show that there is long-range dependence in the soil moisture at
both depths. The range is the same (4000m) but differ in the sill and nugget (2 and 32.5
for AMC at 10cm and 2 and 20 for AMC at 30cm). After 4000m, which is a point of
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inflection, thereafter, the points are no longer related. Fig 7-10 to 7-13 show the maps
using ordinary kriging with their error maps.
Fig 7- 10 Soil moisture at 10cm depth (ordinary kriging
Fig 7- 11 The error map at 10cm depth
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The Error maps show the deviation of the estimated values from the actual values that
were calculated in the field. The further you go away from the point the greater the error.
The lower values indicate less deviation and the higher values indicate greater deviation
from the true value.
Fig 7- 12 Soil moisture map at 30cm depth (ordinary kriging)
Fig 7- 13 The error map for 30cm depth
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The results show that there is spatial variability of soils. There is spatial dependency of
the variables up to a distance of 4000m. These results also show that soil moisture spatial
distribution is related to soil type. These results also agree with Kosta (1994) who came
to the same conclusion; spatial distribution of moisture is related to soil type, vegetation
type, relative height, slope and distance from water streams.
7.3 Water-limited production potential PS2
The results from production potential situation PS2 have been tabulated in table 7-18 and 7-19 for
LUT1 and LUT2 with the growing cycle starting from Julian day 306 and ending on Julian day
61.
Table 7- 18 The water limited yield of LUT1 for cropping year 1999/2000
Mapping units
Growing cycle
Storage yield (SSO)
Total dry matter
Pe111
306-61
6072
11691
Pe112 & Pe113
306-61
5754
9537
Pe115
306-61
1606
6485
Note: These yields are for initial matric suction (PSIint also symbolised by Ψ) at 500cm.
Table 7- 19 water limited yield of LUT2 in the cropping year 1999/2000
Mapping units
Growing cycle
Storage yield (SSO)
Total dry matter
(TDM)
Pe111
306-61
1234
10611
Pe112 &Pe113
306-61
1544
9352
Pe115
306-61
1206
13964
In order to evaluate the relationship of available moisture and yield, different levels of initial
matric suction were applied and table 7-20 and 7-21present the results for both LUTs.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Table 7- 20 LUT1 yield with different levels of PSIint
LUT1
Mapping units
Pe111
Pe112 &Pe113
Pe115
LUT2
PSIint levels (cm)
500
1000
1500
2000
2500
3000
500
1000
1500
2000
2500
3000
500
1000
1500
2000
2500
3000
Yield kg/ha
6072
5069
4957
4421
4494
4327
5754
5768
5814
5719
5823
5823
1606
1476
1488
1456
1365
1338
PSIint levels (cm)
500
1000
1500
2000
2500
3000
500
1000
1500
2000
2500
3000
500
1000
1500
2000
2500
3000
Yield kg/ha
1420
1234
1174
1157
1018
1013
1268
1544
2069
1951
2039
2072
1155
1097
1090
1073
1056
1051
Analysis of variance was calculated to compare the differences in the yield between the
PSIint. See tables 7-22 and 7-23
Table 7- 21 ANOVA for water-limited yield of LUT1
ANOVA
Source of Variation
SS
df
Between Groups
62425452
2
31212726 252.6198
Within Groups
1853342
15
123556.1
Total
64278794
17
MS
F
P-value
0
The ANOVA for yield of LUT1 shows that there is significant difference in yield (95%
level) at different levels of matric suction within the land units as well as between the
land units. That is successive increase in matric suction results in significant difference in
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
yield. Comparing between mapping units, it also shows that the yields are significantly
different (95)% level.
Table 7- 22 ANOVA for water-limited yield of LUT2
ANOVA
Source of Variation
SS
df
Between Groups
1956145
2
978072.4 21.16624
Within Groups
693136.2
15
46209.08
Total
2649281
17
MS
F
P-value
0.000
In sorghum the results also indicate that there is significant difference in the yield at 95 % level as
the matric suction is increased. The striking thing in sorghum is that in land unit Pe112 and Pe113
yield increases with increase in matric suction up to 1500 where it drops then picks up again at
2500 up to 3000. This can be attributed to the soil physical characteristics of clayloam in that land
unit.
Table 7- 23 The crop water functions at PSIint 500 and 2000cm for LUT1
PSIint at 500cm
Day
LAI
Cfwater
306
0
1
316
0.01
1
326
0.07
1
336
0.29
1
346
1.06
1
356
2.53
1
1
3.81
1
11
3.59
0.59
21
2.7
0.13
31
1.25
0.22
41
0
0
51
0
0
53
0
0
Day
306
316
326
336
346
356
1
11
21
31
41
51
53
PSIint at 2000cm
LAI
Cfwater
0
1
0.01
1
0.07
1
0.29
1
1.06
1
2.53
1
3.81
0.89
3.56
0.3
2.63
0.11
0.46
0.22
0
0
0
0
0
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Table 7- 24 The crop water functions at PSIint 500 and 2000cm for LUT2
PSIint at 500cm
Day
LAI
Cfwater
306
0
1
316
0.02
1
326
0.15
1
336
1.2
0.92
346
5.27
0.51
356
6.27
0.45
1
5.91
0.47
11
4.44
0.71
21
0.47
0.4
31
0
0
41
0
0
50
0
0
Day
306
316
326
336
346
356
1
11
21
31
41
50
PSIint at 2000cm
LAI
Cfwater
0
1
0.02
1
0.15
1
1.2
0.83
4.72
0.5
5.79
0.46
5.57
0.49
4.21
0.73
0.65
0.8
0
0
0
0
0
0
In LUT1, with initial matric suction of 500,1000 and 1500cm, the water stress develops at 70th
day after planting (table 7-23) with crop water factor of 0.59 and keeps on reducing to 0.11 but it
improves again on 90th day. At this period in the growing cycle of maize, this is the flowering and
ripening stage which requires enough water to produce yield (Doorenbos and Kassam, 1979).
This implies a reduction in the yield, as the activity is not carried out accordingly. Yield reduction
is in the range of 49 to 53%.
However, as initial matric suction increases from 1500 to 3000cm, the water stress develops even
earlier at 60th day (table 7-23) with crop water factor of 0.89 which means from late vegetative
growth, flowering and yield formation are affected which eventually reduces the number of grains
on the cob as well as the weight. This event coupled with poor ripening of grains leads even to
high yield reduction (57%). The differences in yield from different land units are probably due to
soil inherent properties.
In sorghum, the story is slightly different in the sense that water stress develops quite early at 30th
day of planting (table 7-24) but this improves from 70th up to 90th day. This implies that flowering
is taking place under moisture stress but ripening coincides with improvement of moisture. Yield
reduction in sorghum is in the range of 83.5 to 90%.
The yield results were regressed with the level of initial matric suction (PSIint) applied and fig 714 and 7-15 show the relationship of yield and PSIint applied.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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8000
6000
4000
2000
0
y = -0.5858x + 5890.6
R2 = 0.835
Yield response Pe112 &113
Yield kg/ha
Yield kg/ha
Yield response for Pe111
0
1000
2000
3000
y = -0.0442x + 5860.8
R2 = 0.9157
5850
5800
5750
5700
4000
0
1000
2000
3000
4000
PSIint (cm)
PSIint (cm)
Yield response Pe115
y = -0.0974x + 1625.3
R2 = 0.9004
Yield kg/ha
2000
1500
Fig 7-12 Yield response1000
for maize at different initial matric suction
500
0
0
1000
2000
3000
4000
PSIint (cm)
Fig 7- 14 Yield response to PSIint applied for LUT1
The yield response to levels of matric suction applied shows that there is a positive relationship
between the moisture available in the soil and the crop yield. The R2 is good ranging from 83 to
91% (fig 7-14) which means that moisture availability, explains more of this relationship and the
remainder is explained by other factors which were not dealt with in this research but make a
contribution to the growth and development of the crop.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Yield responsePe111
y = -0.1543x + 1439.3
R 2 = 0.9093
+ 1285.1
Yield response Pe112 &113y = 0.3078x
2
R = 0.7255
Yield kg/ha
Yield kg/ha
1500
1000
500
0
0
1000
2000
3000
4000
2500
2000
1500
1000
500
0
0
1000
PSIint (cm)
2000
3000
4000
PSIint (cm)
y = -0.0377x + 1153
2
R = 0.866
Yield response Pe115
Yield kg/ha
1500
1000
500
0
0
1000
2000
3000
4000
PSIint (cm)
Fig 7- 15 Yield response to PSIint applied for LUT2
Similarly, the yield response to levels of matric suction applied shows that there is a positive
relationship between the moisture available in the soil and the crop yield. The R2 is also good
ranging from 72 to 91% (fig 7-15) which means that moisture availability, explains more of this
relationship and the remainder is explained by other factors which were not dealt with in this
research but make a contribution to the growth and development of the crop.
The yield can be interpolated from the regressed graphs (fig 7-14 and 7-15). However, taking into
account of the problem faced in the data input (section 4.2.4(B)) to running of this model, one
cannot comfortably claim that these results are reliable to be used in the estimation of yield as
explained. In this case, potential yield are greater than experimental yields from the study area.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Nonhebel (1994) Nonhebel came into a conclusion that the averaged data input overestimated the
yields in Netherlands.
7.4 Physical Land Evaluation
The suitability class orders followed the ones published by FAO (1976) (see table below).
Order
S1
S2
S3
N
Suitability class
Highly suitable
Moderately suitable
Marginally suitable
Not suitable
The suitability in general shows that there are differences in ratings of the mapping units
depending on the requirements of the LUTs. One mapping unit is rated moderately suitable, three
are marginally suitable and five are not suitable for maize production whilst three are marginally
suitable and six are not suitable for sorghum. The ratings of individual mapping units are
discussed below. (See fig 7-13 and 7-14 for suitability maps)
Hi111 (Slope facet complex)
The mapping unit is rated unsuitable for both LUTs (sorghum and maize). The physical
suitability subclass is 4Erhz. This map unit is a scarp with slope of >16% and coupled with fine
sand renders it to highly susceptible to erosion. This map unit is not used for arable cropping.
Hi112 (Talus-hillock complex)
This map unit is rated marginally suitable and not suitable for sorghum. The unit has two
different ratings because it is an association of two different soils occurring in the same mapping
unit. The physical suitability subclass is 3Erhz and 4Moav. This map unit is hilly with slope of
10% with shallow soil depth of 50-120cm. In case of maize, the unit is rated marginally suitable
with maximum limiting factors as erosion and moisture availability (3Erhz/Moav). Although the
area gets rainfall within the range of 400-600mm per year, the soil depth is shallow. This coupled
with erosion means that much of this water does not infiltrate into the soil but rather go as runoff.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Pe111 (Tread/Riser of the higher terrace)
The map unit is rated marginally suitable and moderately suitable for sorghum. The physical
suitability subclass is 3Erhz &2Moav/Oxav/Rtco/se/Sowo.This map unit is a compound unit.
One of the components has a slope of 10% and erosion is high. In other components, the soil is
clayloam with shallow depth (60cm) impeding root proliferation. Besides that, it contains some
gravel throughout the soil profile of the 60cm. Germination of seeds is affected by sealing as
reported by farmers during interviews.
As for maize, it is rated moderately suitable with maximum limiting factors of 2Erhz /Rtco/Sowo
for one component, 2Oxav/Rtco for the second and 3Rtco for the third component. This implies
that the third component has rooting depth as a maximum limiting factor.
Pe112 (Tread/Riser of the middle terrace)
This has been rated marginally suitable and not suitable for sorghum. The physical suitability
subclass is 4Moav and 3Erhz for both components, which constitute Pe112. Field interviews
revealed that even though farmers grow sorghum on this unit, the yields are very low.
In case of maize, it is rated not suitable and marginally suitable due to oxygen availability as
maximum limiting factor (4Oxav) meaning that the soils are poorly drained and also rated
moderately suitable due to erosion as a limiting factor (3Erhz). This implies that there are
problems of oxygen availability and erosion.
Pe113 Tread/Riser in the lower terrace
This map unit is rated not suitable for sorghum. The maximum limiting factor is oxygen
availability (4Oxav). A particle size distribution analysis result indicates 51% clay and is poorly
to imperfectly drain. For maize, it is marginally suitable (3Oxav). During interviews with farmers
from this unit, it was learnt that if it rained heavily, the soils get waterlogged for almost two
weeks. This is an indication of poor drainage.
Pe114 Tread/Riser of the Eroded terrace
The map unit is rated as marginally suitable for sorghum but marginally for maize. The maximum
limiting factor is 2Erhz whilst 3Erhz for maize. The map unit is characterised with runoff as the
area is undulating to rolling. From field observations, the area has some surface stones. It is used
for settlement.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Pe115 Slope floor complex of the Vale
It is rated marginally suitable for sorghum and not suitable for maize. This rating coincides with
results from PS-2 where the lowest yields are from this unit for both LUTs. The physical
suitability subclass indicates maximum limiting factors of 3Oxav for sorghum and 4Oxav for
maize. This implies that the land unit has poor drainage that renders oxygen unavailable hence the
crops cannot assimilate CO2. This is supported by infiltration results of 6cm/hr for the area
(appendix A).
Pe116 Inselberg
The map unit is rated unsuitable for both LUTs (4Rtco). The physical suitability subclass
indicates rooting conditions being the maximum limiting factor. Since this are has shallow soil
effective depth (30cm) coupled with slope of 9-16%, such soils cannot support crop growth as
root proliferation is hindered.
Pu111 Summit
The map unit is rated not suitable for both LUTs. Pu111 is a compound unit with association of
three components. The first component that contributes 5% of the map unit is not suitable with
maximum limiting factor of moisture availability (4Moav). It has medium to fine sands that are
excessively drained. This implies that it cannot support growth of these crops. This map unit is
used for livestock grazing.
Table 7- 25 Physical suitability for LUT1 and LUT2
Land
Mapping
units
Hi111
Hi112
Pe111
Pe112
Pe113
Pe114
Pe115
Pe116
Pu111
Physical
Suitability subclass
4Erhz
3Erhz & 4Moav
2Erhz/Rtco/Sowo
&2Oxav/Rtco/Sowo&2Rtco
4Oxav & 3Erhz
2Oxav
3Erhz
4Oxav
4Rtco
4Moav
Note:
Erhz is Erosion hazard
Rtco is rooting condition
Suitabili
ty class
LUT1
S4
s3
s2
n &s3
s3
s3
n
n
n
Physical
Suitability subclass
Suitability class
LUT2
4Erhz
3Erhz/Moa
3Erhz&2Moav/Oxav/Rtco/Se/
Sowo & 2Moav/Rtco
4Oxav
4Oxav
3Erhz
4Oxav
4Rtco
4Moav
n
S3&n
s3&s2
Oxav is oxygen availability
Se
is sealing
83
S4&s3
n
S3
n
n
n
Sowo is soil workability
Moav is moisture availability
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Fig 7- 16 Physical land suitability for LUT1
Fig 7- 17 Physical land suitability for LUT2
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Summary
There is relationship between the hydraulic properties and the nature of relationship is in
two ways as observed across the area (7-3), landscapes (7-4) and soil type (7-5). Actual
moisture content exhibits negative relationship with infiltration and hydraulic
conductivity based on the overall area and landscapes but has a positive relationship on
the basis of soil type. Infiltration rate has a positive relationship with hydraulic
conductivity in all scenarios. The infiltration rate, hydraulic conductivity and texture
affect the soil moisture availability in the soil.
There is spatial dependence of soils in the area and the soils are spatially variable. The
spatial variability of soils affects soil moisture distribution as these soils have different
properties.
The water-limited production potential has revealed that increase in initial matric suction
(PSIint) leads to yield reduction implying that reduction in soil moisture especially at
reproductive stage leads to decline in yield.
The major factors leading to low yield realised by farmers (chapter6.2) in the area are
poor farm management (revealed from interviews) and low erratic rainfall.
The land evaluation ratings show that soils of hilland and plateau are not suitable for the
land utilisation types currently practised in the area mainly due to poor moisture
availability.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Chapter 8: Conclusion and recommendations
The findings emanating from this research are presented in this chapter on the basis of the
objectives and research questions.
There is a positive relationship between soil moisture availability and yield as observed from PS2 that as the moisture in the soil decreases the yield also decline due to moisture stress hence low
yield. The best initial matric suction (PSIint) to be applied is 500cm.
The area has three major landscapes namely Plateau, Hilland and Peneplain (corresponding with
Sandveld, escarpment and Hardveld units of FAO soil map). There are different geomorphic units
that have different soil types. The geopedological units affect the land utilisation types apart from
the precipitation received in the area. The main soils in the area are Ferralic Arenosols (mainly in
the plateau), Calcic Luvisols, Pellic Vertisols, Eutric Nitosols (mainly in peneplain), and
Endoleptic Regosols (mainly in hilland).
There is a relationship between the hydraulic properties. There is a negative relationship between
soil moisture and infiltration rate (see fig 7-3 and 7-4), a negative relationship between soil
moisture and hydraulic conductivity (see fig 7-3 and 7-4) and positive relationship between
infiltration rate and hydraulic conductivity (see fig 7-3 and 7-4). The relationship of these
hydraulic properties based on soil types is also positive (see fig 7-5).
High hydraulic conductivity and infiltration rates in sandy soils is an indication that water goes
deep into the soil profiles, and the water table is very deep. This probably feeds the ground water.
There is a wide variation for rate of evapotranspiration (0.2 to 10mm –d) that could have an
influence for the precipitation in the area and indirectly affect the ground water recharge.
There is a spatial dependency of soils in the area. This spatial variability influences soil moisture
distribution since different soils have different properties.
Soil moisture is influenced by infiltration rate, texture of soil, depth of soil profile, organic matter
content and hydraulic conductivity. Soil moisture can be used to infer the land quality moisture
availability in the land suitability evaluation process.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
The distribution of farmlands is mostly on clay loam and sandy clay loam soils as these have a
higher capacity of holding soil moisture.
The land utilisation types considered are traditionally managed rainfed maize and sorghum grown
in single cropping system within the growing cycle of November to May.
Land evaluation reveals that soils in the hilland and plateau are not suitable for the land utilisation
types currently practised in the area. As regards the rainfall pattern in the area, these suitability
classes can be used in the planning of land use. Interviews with farmers revealed that for the past
six years, rainfall distribution has been very poor; sometimes drought develops when the crops
are approaching flowering stage and never came back. This in most cases leads to zero yield.
From these results, maize and sorghum are not suitable for the area, especially at the level of
management practised by farmers.
Recommendations
For further studies, it is recommended to do soil moisture measurements during rainy
season for the following reasons:
•
Time sequence monitoring of soil moisture over entire season to identify critical
periods and assess detailed performance of PS123.
•
Since hydraulic conductivity is a highly variable soil property, a single measured
value is unreliable indicator of hydraulic conductivity of soil; therefore more
measurements should be conducted to come up with a reliable estimate.
•
To enhance understanding of the behaviour of soil hydraulic properties in the
area.
Improvements in terms of cultural practices is needed like early land preparation and
weeding at the right time. Application of fertilizer especially of organic type should be
encouraged since this improves soil structure, nutrient status and water holding capacity.
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
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Tersteeg, J.L., D.J. Radcliff, and P.V. De Wit. 1992. Map of Land Suitability for Rainfed Crop
Production. Soil Mapping and Advisory Services, Gaborone, Botswana.
Tersteeg, J.L., D.J. Radcliff, and P.V. De Wit. 1993. Crop yield simulation and land evaluation at
a national scale, Windhoek.
Timmermans, W.J., and A.M.J. Meijerink. 1999. Remotely sensed actual evapotranspiration:
implications for groundwater management in Botswana 1:222-234.
F. J. Leji (ed.) 1997. Riverside International Workshop on Soil Hydraulic Properties, Riverside,
California. USDA.
USDA. 1998. Soil quality indicators: Infiltration [Online]. Available by National Soil Survey
centre in coopertaion with soil Quality Institute
http://soils.usda.gov/sqi/files/Infiltration.pdf (verified 08/01/03).
Van Keulen, H., and J. Wolf. 1986. Modelling of agricultural production: weather, soils and crops
Centre for Agricultural Publishing and Documentation, Wageningen.
89
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Voortman, R., (ed.) 1985. Guidelines for rainfed agriculture in Mozambique. FAO, Rome.
Ward, R.C., and M. Robinson. 1989. Principles of hydrology. 3rd edition ed. McGraw-Hill Book
Company Europe, Berkshire, England.
Wellfield Consulting Services. 1998. Serowe wellfield 2 extension project (TB10/3/10/95-96,
Main report. Department of Water Affairs, Gaborone, Botswana.
Wilding, L.P., and L.R. Drees. 1983. Spatial variability and pedology. Pedogenesis and soil
Taxonomy: 83-116.
Wokabi, S.M. 1994. Quantified Land Evaluation for maize Yield GAP Analysis at three sites on
the Eastern slope of Mount Kenya. Unpublished Ph.D thesis, University of Ghent, Gent.
Zinck, J.A. 1988/89. Physiography and soils, pp. 156 ITC Lecture notes: SOL.41, Enschede,
Netherlands.
90
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix A: Soil Hydraulic properties results
Site
Moist.
X_ coord Y_coord Infilt.rate 10cm
at Moist.at
30cm
K cm/day
EPT 001 474663
7539777 18
4.03
2.38
347.10
EPT 002 475335
7531980 24
7.45
4.26
248.40
EPT 003 475066
7535877 27
4.85
1.19
198.10
EPT 004 475135
7530185 28.2
4.72
1.46
99.40
ESC 007 473503
7534453 24.5
5.28
0.22
99.40
ESC 027 475317
7531820 12
5.67
2.69
29.80
ESC 051 474197
7529534 26.5
7.91
1.41
149.00
Hard 001 460758
7522868 18
9.66
12.81
29.80
HPT 001 466980
7513874 20.5
1.36
1.69
149.00
HPT 002 466771
7510453 6.1
6.35
9.17
9.9
HPT 003 465347
7507938 20
1.91
0.93
99.4
HPT 004 468575
7513048 12
6.24
8.76
9.9
HPT 005 469774
7518089 6
6.88
9.09
9.9
HPT 006 467215
7517154 6
8.24
7.21
9.9
HPT 007 467604
7519059 18
4.86
8.24
49.7
HPT 008 468601
7518513 17.8
4.58
5.81
99.4
SVD 001 435542
7525186 47.5
0.38
0.44
397.4
SVD 010 434542
7525186 41.3
1.31
2.54
496.8
SVD 200 436542
7527186 27.5
0.77
0.87
447.1
SPT 001 433495
7527033 22.5
0.75
0.83
149
SPT 002 428575
7531451 24.5
1.60
2.12
248.4
SPT 003 444677
7516908 35.2
1.97
1.13
397.4
SPT 004 460780
7525102 18
4.04
1.08
248
Hard 36 466077
7515673 14
1.56
2.60
794.9
Hard 13 466910
7510494 17
8.38
1.67
99.4
Hard 14 475015
7530045 17.5
1.06
1.54
99.4
EST 002 476357
7534631 21.8
20.70
7.99
149
ESC 061 468225
7528791 27.6
6.21
2.14
695
ESC 062 468349
7528318 25.3
6.03
2.82
149
PLT 011 471741
7531685 22.3
20.92
11.84
298.1
PLT 019 470620
7532142 24.5
2.94
5.79
99.4
PLT 024 470047
7532187 21.8
5.06
6.65
397.4
PLN 028 471611
7532947 17.5
15.71
12.90
198.7
PLT 053 471592
7533175 12.5
7.62
6.62
248.4
EPT 021 474564
7539239 18
1.12
1.41
99.4
EPT 012 473645
7539268 18.5
1.12
1.30
844.6
FRM 001 460594
7520848 14.5
3.45
5.11
198.7
FRM 002 463636
7519154 8
9.60
12.07
24.8
FRM 003 464878
7519907 7.3
9.16
11.64
9.9
91
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
FRM 004 463525
7519876 12.5
9.41
10.11
9.9
FRM 005 481118
7537905 8.2
7.49
9.40
9.9
FRM 006 485189
7539910 8.5
6.77
8.99
9.9
FRM 007 484385
7538250 14.3
7.51
11.04
347.8
SVD 081 462000
7527775 36.2
2.40
1.19
397.4
SVD 082 470521
7535305 25.5
0.72
4.63
99.4
SVD 083 464693
7539551 28.3
5.69
1.73
397.4
FRM 008 484223
7538215 8.5
3.19
2.51
9.9
FRM 009 463159
7517322 8.5
10.96
12.22
9.9
ESC 063 471611
7532947 8.3
18.60
12.76
9.9
FRM 010 463153
7517319 8.8
7.15
10.59
447.1
FRM 011 466658
7510188 6
6.30
8.11
9.9
FRM 012 466643
7510139 6
4.01
8.83
9.9
PLN 001 481157
7537855 16.5
1.47
0.69
347.8
Hard 059 461653
7523416 18.8
7.09
13.56
99.4
Hard 071 474783
7530344 15.5
1.39
2.03
99.4
Hard 085 475396
7528069 17.8
1.22
1.70
99.4
EST 003 476642
7535642 18
2.00
2.76
99.4
92
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix B: Soil profile description
Appendix 1: Soil Profile Description
Soil profile SPT 001/2002
A.
Information on soil profile site
B.
General information on the soil profile
Date of examination
25/09/02
Type of observation
mini pit
Authors
Effective soil depth
Location
Ermias
Aynekulu,
Esther Mweso.
433495, 7527033,
Haplic Arenosol
vegetation moderately
disturbed
very deep, >150cm
Drainage class
excessively drained
Altitude
1213 m.a.s.l.
Internal drainage
well drained
Geopedological unit
Pu111
External drainage
neither receiving nor
Topography
flat
Slope
Parent material
Vegetation
0-2%
Aeolian sand
open savannah shrub
land with good grass
cover
open grazing
Land use
C.
Classification (WRB)
Human influence
shedding
Ground water depth
very deep, >150cm
Surface stoniness
none
Rock outcrops
Evidence of erosion
none
none
Soil profile description
Horizon
Depth (cm)
A
0-10
C1
10-40
C2
40-70
C3
70-120
Description
Yellow brown (10YR 5/4) when dry and dark yellowish brown (10YR
4/6) when moist; fine sand; massive structure; medium sub angular blocky;
loose when dry and very friable when moist; non sticky and non plastic;
fine to medium size roots are common; field pH 4.5; gradual boundary
Very brownish yellow (10YR 6/8) when dry and yellow brown (10YR 5/4)
when moist; fine sand; massive structure; loose when dry and very friable
when moist; non sticky and non plastic; few medium roots; field pH 5.0;
gradual boundary
Yellowish brown (10YR 5/8)when dry and when moist; fine sand; massive
structure; loose when dry and very friable when moist; non sticky and non
plastic; few fine roots; field pH 5.5; gradual boundary
Very brownish yellow (10YR 6/8) when dry and yellowish brown (10YR
5/6) when moist; fine sand; weak massive structure; loose when dry and
very friable when moist; non-sticky and non-plastic; few fine roots; field
pH 5.5.
93
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile SPT 002/2002
B.
A.
Classification (WRB)
Human influence
Information on soil profile site
General information on the soil profile
Effective soil depth
Epidystric Arenosol
vegetation moderately
disturbed
very deep, >150cm
Drainage class
excessively drained
Internal drainage
well drained
External drainage
neither receiving nor
Date of examination
25/09/02
Type of observation
Authors
Location
mini pit
Ermias
Aynekulu,
Esther Mweso.
428575,7531451
Altitude
1200 m.a.s.l.
Geopedological unit
Pu111 (Kalahari sand)
Ground water depth
very deep, >150cm
Topography
flat
Surface stoniness
none
Slope
Parent material
Vegetation
Land use
0-2%
Aeolian sand
Savannah
open grazing
Rock outcrops
none
Evidence of erosion
Sealing /crusting
none
none
C.
shedding
Moisture condition
Soil profile description
Horizon
Depth (cm)
Ah
0-15
C1
15-35
C2
35-80
C3
80-140
Description
Very brown (10YR 4/3) when dry and yellowish brown (10YR 5/4)) when
moist; loamy very fine sand; massive structure; slightly hard when dry and
loose when wet; non sticky and non plastic; many very fine, many fine
pores; fine and medium roots are common; field pH 5; gradual boundary
Dark yellowish brown (10YR 3/4) when dry and dark greyish brown
(10YR 4/2) when moist; loamy very fine sand; weak massive structure; soft
when dry and loose when wet; non sticky and non plastic; many fine pores;
medium size roots are common; field pH 6.5; gradual boundary
Very dark yellowish brown (10YR4/4) when dry and dark greyish brown
(10YR4/2) when moist; loamy very fine sand; weak massive structure,
medium to coarse sub-angular blocky; loose when dry and wet ; non sticky
and non plastic; many fine pores; few coarse roots; field pH 7; gradual
boundary
Very yellowish brown (10YR 5/6) when dry and brown (10YR 4/3) when
moist; loamy very fine sand; weak massive structure; loose when dry and
wet; non sticky and non plastic; many fine pores; few coarse roots; field pH
7.0
94
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile SPT 003/2002
A.
B.
Information on soil profile site
General information on the soil profile
Human influence
Effective soil depth
Hypoluvic
Dystric
Arenosol
vegetation disturbed
very deep, >150cm
Drainage class
excessively drained
Pu111
Internal drainage
well drained
Topography
flat
External drainage
neither
Parent material
sand
Slope
Parent material
0-2%
Aeolian sand
Vegetation
Land use
savannah
open grazing
Date of examination
26/09/02
Authors
Location
Altitude
Ermias
Aynekulu,
Esther Mweso.
444677, 7516908
1200 m.a.s.l.
Geopedological unit
C.
Classification (WRB)
receiving
shedding
Ground water depth
very deep, >150cm
Surface stoniness
none
Rock outcrops
none
Evidence of erosion
wind
Sealing /crusting
none
Moisture condition
dry
Soil profile description
Horizon
Depth (cm)
Description
A
0-10
Dark greyish brown (7.5YR 4/4) when moist; fine sand; loose when dry
and wet; non stick non plastic; many very fine pores, fine and medium
roots are common; field pH 6.0
Bt1
10-30
Bt2
30-120
Olive brown (5YR 4.5/4) when moist, loamy fine sand; slightly hard
when dry and loos when wet: non sticky and non plastic; clay bridges;
many very fine pores; few medium size roots; field pH 6.5
Light olive brown (5YR5/4) when moist, loamy fine sand; slightly hard
when dry and loos when wet: non sticky and non plastic; clay bridges;
many fine pores; few medium size roots; field pH 6.5
95
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile SPT 004/2002
A.
Information on soil profile site
B.
General information on the soil profile
Date of examination
24/09/02
Type of observation
mini pit
Authors
Human influence
Effective soil depth
Location
Ermias
Aynekulu,
Esther Mweso.
435542,7525186,
Hypoluvic
Dystric
Arenosol
vegetation disturbed
very deep, >150cm
Drainage class
excessively drained
Altitude
1205 m.a.s.l.
Internal drainage
well drained
Geopedological unit
Pu111
External drainage
neither receiving nor
Topography
flat
Slope
Parent material
Vegetation
0-2%
sandstone
Savannah woodland
Land use
Grazing
C.
Classification (WRB)
shedding
Ground water depth
very deep, >150cm
Surface stoniness
none
Rock outcrops
none
Evidence of erosion
wind
Sealing /crusting
none
Moisture condition
dry
Soil profile description
Horizon
Depth (cm)
Ah
0-15
C1
15-45
C2
45-130
Description
Very dark grey (10YR 6/2.5) when dry dark brown (10YR 4/2.5) when
moist; fine sand; weak massive structure; loose when dry and friable
when moist; non sticky and non plastic; fine roots are common; field pH
5; gradual boundary
Very dark grey (10YR 6/8) when dry and dark brown (7.5YR 5/5) when
moist; Gradual boundary, fine sand; weak massive structure; loose when
dry and very friable when moist; non sticky and non plastic; medium size
roots are common; field pH 5.5; gradual boundary
Very dark grey (10YR 6/3.5) when dry and dark brown (7.5YR 5/4)
when moist; fine sand; weak massive structure; loose when dry and very
friable when moist; non sticky and non plastic; few fine; field pH 6
96
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile EPT 001/2002
A.
Date of examination
Type of observation
Authors
Altitude
Geopedological unit
Topography
13/09/02
mini pit
Ermias
Aynekulu,
Esther Mweso.
474663, 7539777 (300
m from the main road to
Khama
Rhino
sanctuary)
1294m.a.s.l.
Hi111
flat
Slope
Parent material
Vegetation
Land use
0-2 %
Aeolian sand
Savannah woodland
open grazing
Location
C.
B.
Information on soil profile site
General information on the soil profile
Classification (WRB)
Human influence
Effective soil depth
Drainage class
Ferralic Arenosol
vegetation
slightly
disturbed
Very deep, >150cm
Ground water depth
Surface stones
Rock outcrops
Evidence of erosion
Sealing /crusting
somewhat excessively
drained
never saturated (well
drained)
neither
receiving nor shedding
very deep, >150cm
none
none
none
none
Moisture condition
dry
Internal drainage
External drainage
Soil profile description
Horizon
Depth (cm)
A
0-18
C
18 +
Description
Reddish brown (5YR4/4) when dry and yellowish red (5YR4/6) when moist;
fine sand; weak with massive structure; soft when dry and very friable when
moist; non sticky and non plastic; few coarser roots; field pH4.5, smooth
boundary
Reddish yellow (7.5YR 6/8)when dry and strong brown (7.5YR5/8) when
moist; fine sand; weak with massive structure; slightly hard when dry, very
friable when moist; non sticky and non plastic; fine roots are common, field
pH 5.0 smooth boundary
97
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile EPT 002/2002
A.
Date of examination
Authors
Location
Altitude
Geopedological unit
Topography:
Slope
Parent material
Vegetation
Land use
C.
B.
Information on soil profile site
General information on the soil profile
Classification (WRB)
Human influence
15/09/02
Ermias
Aynekulu,
Esther Mweso.
475335, 7531980 (100m
from the military camp
fence
1050m.a.s.l.
Hi112
flat
0-2%
Aeolian sand
savannah woodland
open grazing
Effective soil depth
Drainage class
Internal drainage
External drainage
Ground water depth
Surface stones
Rock outcrops
Evidence of erosion
Arenosol
Slight
vegetation
disturbance
very deep, >150cm
well drained
rarely saturated
slow run-off
Sealing /crusting
very deep, >150cm
none
none
water,
0-5%
area
affected
none
Moisture condition
moist
Soil profile description
Horizon
Depth (cm)
A
0-16
B
16+
Description
Dark greyish brown (2.5Y4/2) when dry and light olive brown (2.5 Y
5/3) when moist; fine sand; weak with massive structure; soft when dry
and loose when moist; slightly sticky and non- plastic; very fine pores are
common; very few fine roots; field pH5.5 abrupt
Reddish yellow (7.5YR 6/8) when dry and strong brown (7.5YR 5/8)
when moist; fine sand; weak massive structure; hard when dry and very
friable when moist; non sticky non plastic; few fine roots; pH 5
98
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile EPT 003/2002
B.
General information on the soil profile
Classification (WRB)
Arenic Acrisol
Human influence
slight
vegetation
disturbance
Effective soil depth
Very deep, >150cm
Drainage class
somehow excessively
drained
Internal drainage
none
External drainage
neither receiving nor
A.
Information on soil profile site
Date of examination
18/09/02
Authors
Ermias
Aynekulu,
Esther Mweso.
Location
475066, 7535877, 6Km
west of Paje village
Altitude
1211m.a.s.l.
Geopedological unit
Hi112
foot
of
the
shedding
escarpment
0-2%
sandstone
savannah woodland
Ground water depth
Surface stones
Rock outcrops
Evidence of erosion
Sealing /crusting
Very deep, >150cm
none
none
vegetation disturbance
none
open grazing
Moisture condition
first 20cm moist, the
Topography
flat
Slope
Parent material
Vegetation
Land use
rest
C.
is
Soil profile description
Horizon
Depth (cm)
Ah
0-15
Description
Reddish brown (7.5YR7/6) when dry and strong brown (7.5YR4/6) when moist; loamy fine sand;
massive structure; loose when dry and moist; non sticky and non plastic; fine pores are common;
very fine roots are common; field pH5; clear boundary
Bt1
15-35
Reddish yellow (7.5YR6/6) when dry and (7.5YR6/4) when moist; loamy fine sand; massive
structure; loose and friable when moist; non sticky and non plastic; fine pores are common; few
medium size roots; field pH5.7; gradual boundary
Bt2
35-54
Pink (7.5YR8/4) when dry and strong brown (7.5YR5/6) when moist; loamy fine sand; massive
structure; soft when dry and friable when moist; non-sticky and non-plastic; very few mottles of
medium size. Common clay cutans ; very fine pores are common; very few fine roots; field
pH5.7; clear boundary
BC
54-60
Pink (7.5YR8/4) when dry and strong brown (7.5YR5/6) when moist; loamy fine sand; massive
structure; soft when dry and friable when moist; non sticky and non plastic; Abundant coarse,
angular, weathered sandstone rock fragments Fine pores; many mottles of medium size grey in
colour. Common clay cutans ; very fine pores are common; few fine roots; field pH5.5; clear
boundary
BC2
60-120
Pink (7.5YR8/4) when dry and strong brown (7.5YR8/4) when moist; loamy fine sand; massive
structure; slightly hard when dry and friable when moist; non-sticky and non plastic; Dominant
stones, angular, weathered sandstone rock fragments Fine pores; many mottles of medium size
grey in colour. Common clay cutans; many very fine pores; few fine roots; filed pH 5.0
99
dry
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 001/2002
A.
Information on soil profile site
B.
General information on the soil profile
Date of examination
Type of observation
20/09/02
mini pit
Authors
Location
Altitude
Ermias
Aynekulu,
Esther Mweso.
465347, 7507938
1025 m.a.s.l.
Geopedological unit
Sd111
Topography
flat
Internal drainage
well drained
Slope
Parent material
Vegetation
0-2%
alluvial material
Savannah bush
External drainage
neither
Land use
open grazing
C.
Horizon
Ah
Classification (WRB)
Human influence
Effective soil depth
Arenic Rhodic Acrisol
slight
vegetation
disturbance
Very deep, >150cm
Drainage class
somehow excessively
drained
receiving
nor
shedding
Ground water depth
Very deep, >150cm
Surface stones
Rock outcrops
Evidence of erosion
Sealing /crusting
none
none
none
none
Moisture condition
dry
Soil profile description
Depth (cm)
0-15
Bt1
15-80
Bt2
80-130
Description
Yellowish red (5YR5/6) when dry and when moist; loamy sand; massive
structure; slightly hard when dry and very friable when moist; non sticky
and non plastic; bridges of sand coated but not strongly cutans; many
medium pores; fine roots are common; biological activities are common;
field pH 6.0; gradual boundary
Yellowish red (5YR6/8) when dry and moist; loamy sand; massive
structure; slightly hard when dry and very friable when moist; non sticky
and non plastic; clay bridges and sand coated, but not strong; many
medium pores; many fine roots; field pH 5.5; gradual boundary
Yellowish red (5YR5/6) when dry and moist; loamy sand; massive
structure; slightly hard when dry and very friable moist; non sticky and
non plastic; clay bridges and sand coated, but not strong; many medium
pores; few medium roots; field pH 5.0
100
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 002/2002
A.
B.
General information on the soil
profile
Classification (WRB)
Arenic
Rhodic
Acrisol
Human influence
vegetation disturbed
Effective soil depth
very deep, >150cm
Information on soil profile site
Date of examination
20/09/02
Type of observation
mini pit
Authors
Ermias
Aynekulu,
Esther Mweso.
466771,
7510453,
Location
15m from the road to
1053 m.a.s.l.
Geopedologic unit
Hi412
Topography
Flat
Slope
Parent material
Vegetation
Land use
C.
0-2%
Alluvial deposits
Shrub
open grazing
Internal drainage
not known
Ground water depth
very deep, >150cm
Surface stones
Rock outcrops
Evidence of erosion
Sealing /crusting
none
none
none
none
Moisture condition
dry
Soil profile description
Horizon
Depth (cm)
Ah
0-22
22-70
Bw1
Bw2
poorly drained
External drainage
sokwe hill
Altitude
Drainage class
70-120
Description
Dark grey (5Y4/1) when dry and very dark grey (5Y3/1) when moist; sandy
clay; very strong structure is coarse and prismatic; hard when dry and very
firm when moist; sticky and plastic; clear slicken sides; fine roots are
common; field pH 8.0; gradual boundary
Dark grey (5Y4/1) when dry and very dark grey (5Y3/1) when moist; sandy
clay; very strong structure which is coarse and prismatic; very hard when
dry and very firm when moist; very sticky and very plastic; clear slicken
sides; few coarse roots; field pH 7.5; gradual boundary
Dark grey (5Y4/1) when dry and very dark grey (5Y3/1) when moist; sandy
clay; excessively hard when dry and very firm when moist; very sticky and
very plastic; clear slicken sides; no roots; field pH 7.0
101
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 003/2002
A.
Information on soil profile site
Date of examination
Type of observation
Authors
B.
Altitude
Geopedological unit
20/09/02
mini pit
Ermias
Aynekulu,
Esther Mweso.
466980, 7513874, near
Sokwe hill
1067m.a.s.l.
Hi412, sand deposit
Topography
Flat
Slope
Parent material
Vegetation
Land use
0-2%
Sandstone
shrub savannah
open grazing
Location
C.
General information on the soil profile
Classification (WRB)
Human influence
Effective soil depth
Arenic Rhodic Arenosol
vegetation disturbed
very deep, >150cm
Internal drainage
well drained
External drainage
neither
receiving
nor
shedding
Ground water depth
very deep, >150cm
Surface stones
Rock outcrops
Evidence of erosion
Sealing /crusting
none
none
none
none
Moisture condition
dry
Soil profile description
Horizon
Depth (cm)
Description
Bt1
0-10
Red (10R4/6) when dry and dark red (10R3/6) when moist; very fine
loamy sand; massive structure; loose when dry and very friable when
moist; non sticky and non plastic; many prominent cutans ; field pH 5.5;
clear boundary
Bt2
10-30
Bt3
30+
Red (10R4/6) when dry and dusky red (10R3/4) when moist; very fine
loamy sand; massive structure; slightly hard when dry and friable when
moist; non sticky and non plastic; Many prominent cutans; field pH 5.5;
clear boundary
Dusky red (10R3/4)) when dry and dark red (10R3/6) when moist; very
fine loamy sand; hard when dry and firm when moist; slightly hard when
dry and very friable when moist; non sticky and non plastic; Many
prominent cutans; field pH 5
102
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 004/2002
A.
Information on soil profile site
B.
Date of examination
21/09/02
Type of observation
Mini-Pit
Authors
Location
Ermias
Aynekulu,
Esther Mweso.
468575,7513048,
Altitude
General information on the soil profile
Classification (WRB)
Human influence
Vertisol
vegetation disturbed
Effective soil depth
Very deep, >150cm
Drainage class
poorly drained
1068 m.a.s.l.
Internal drainage
not known
Geopedological unit
Sd111
External drainage
Topography
flat
shedding
Slope
Parent material
0-2%
Vegetation
Ground water depth
very deep, >150cm
Alluvial deposits
Surface stoniness
none
Savannah
Rock outcrops
Evidence of erosion
Sealing /crusting
none
none
medium
grassland
with scanty shrubs
Land use
C.
neither receiving nor
Grazing
Moisture condition
dry
Soil profile description
Horizon
Depth
(cm)
Ah
0-20
Bt1
20-50
Bt2
50-90
Bt3
90-130
Description
Dark grey (5Y4/1) when dry and very dark grey (5Y3.1/1) when moist; sandy
clay; very strong structure which is coarse and prismatic; hard when dry and very
firm when moist; sticky and plastic; clear slicken sides; fine roots are common;
field pH 7.5; gradual boundary
Dark grey (5Y4/1) when dry and moist; sandy clay; very strong structure which
is coarse and prismatic; hard when dry and very firm when very sticky and very
plastic; clear slicken sides; few coarse roots; field pH 8.0; gradual boundary
Dark grey (5Y3/1) when dry and black (5y2.5/1) when moist; sandy clay; very
strong structure that is coarse and prismatic; hard when dry and very firm when
moist; very sticky and very plastic; clear slicken sides; no roots; field pH 7.5;
gradual boundary
Dark olive grey (5Y3/2) when dry and dark grey (5Y4/1) when moist; sandy
clay; very strong structure that is coarse and prismatic; hard when dry and very
firm when moist; clear slicken sides; very sticky and very plastic; no roots; field
pH 7.5
103
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 005/2002
A.
B.
Information on soil profile site
General information on the soil profile
Classification (WRB)
Human influence
Vertisol
vegetation
Date of examination
21/09/02
Type of observation
mini-Pit
Authors
Effective soil depth
very deep, >150cm
Location
Ermias
Aynekulu,
Esther Mweso.
469774,7518089,
Drainage class
poorly drained
Altitude
1111 m.a.s.l.
Internal drainage
well drained
Geopedological unit
Pe311
External drainage
neither
Topography
Slope
Parent material
Vegetation
Land use
flat
0-2%
alluvial deposit
savannah bush
open grazing
shedding
C.
slightly
disturbed
receiving
Ground water depth
very deep, >150cm
Surface stoniness
none
Rock outcrops
none
Evidence of erosion
none
Sealing /crusting
medium
Moisture condition
dry
nor
Soil profile description
Horizon
Depth
(cm)
Ah
0-15
Bt1
15-70
Bt2
70+
Description
Black (5Y2.5/1) when dry and moist; sandy clay; very strong structure which is
coarse and prismatic; slightly hard when dry and moist; sticky and plastic; clear
slicken sides; fine roots are common; field pH 7.5; gradual boundary
Black (5Y2.5/1) when dry and dark olive grey (5Y3/2) when moist; sandy clay;
very strong structure which is coarse and prismatic; sticky and plastic; clear
slicken sides; fine roots are common; field pH7.0; gradual boundary
Black (5Y2.5/2) when dry and hen dry and moist; sandy clay; very strong
structure which is coarse and prismatic; sticky and plastic; clear slicken sides; fine
roots are common; field pH 8.5
104
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 006/2002
A.
B.
Information on soil profile site
Date of examination
Type of observation
Authors
Location
Type of observation
Altitude
22/09/02
Mini-Pit
Ermias
Aynekulu,
Esther Mweso.
467215, 7517154
mini pit
1094 m.a.s.l.
Geopedological unit
Sd111
Topography
Flat
Slope
Parent material
0-2%
Alluvial deposits
Vegetation
Land use
Savannah shrub
farmland
General information on the soil profile
Classification (WRB)
Human influence
Endoleptic
Cambisol
none
Vertic
Effective soil depth
very deep, >150cm
Drainage class
poorly drained
Internal drainage
well drained
External drainage
neither
receiving
nor
shedding
Ground water depth
Very deep, >150cm
Surface stoniness
none
Rock outcrops
none
Evidence of erosion
none
Sealing /crusting
very thick
Moisture condition
dry
Remark: A farmland closer to Sokwe hill
C.
Soil profile description
Horizon
Depth (cm)
Ah
0-15
Bw1
15-40
Bw2
40-70
Description
Very dark grey (10YR3/1) when dry and dark brown (10YR3/3) when
moist; sandy clay; strong sub angular structure; extremely hard when dry
and firm when moist; stick and very plastic; fine roots are common; field
pH 7.5; gradual boundary
Very dark grey (10YR3/1) when dry and very dark greyish brown
(10YR3/2) when moist; sandy clay; very strong sub angular structure;
extremely hard when dry and very firm when moist; stick and very plastic;
few medium size roots; field pH 8.0; gradual boundary
Very dark grey (10YR3/1) when dry and very dark greyish brown
(10YR3/2) when moist; sandy clay loam; very strong sub angular structure;
extremely hard when dry and very firm when moist; sticky and very plastic;
field pH 8.0
105
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 007/2002
A.
B.
Information on soil profile site
General information on the soil profile
Classification (WRB)
Human influence
Endoleptic
Luvisol
none
Cutanic
Effective soil depth
very deep, >150cm
Drainage class
somehow
Date of examination
Type of observation
22/09/02
Mini-Pit
Authors
Location
Ermias
Aynekulu,
Esther Mweso.
467604, 7519059
Altitude
1112 m.a.s.l.
Geopedological unit
Sd111
Internal drainage
Rapid
Topography
Flat
External drainage
slow run-off
Ground water depth
Very deep, >150cm
Surface stoniness
none
Rock outcrops
none
Evidence of erosion
none
Sealing /crusting
none
Moisture condition
Dry
Slope
Parent material
Vegetation
Land use
C.
excessively
drained
0-2%
Alluvial deposits
(Andezitic substratum)
Savannah shrub
Grazing
Soil profile description
Horizon
Depth
(cm)
Ah
0-15
Bt1
15-40
Bt2
40-70
Description
Dark greyish brown (10YR3/1or 2) when dry and dark brown (10YR3/3) when
moist; fine sandy loam; weak sub- angular blocky structure; slightly hard when
dry and friable when moist. Slightly sticky and plastic; clay cutans are common;
many fine pores; fine and medium roots are common; field pH 7.5; wavy
boundary
Very dark grey (10YR4/2) when dry and very dark greyish brown (10YR4/4)
when moist; sandy clay loam; weak sub angular blocky structure; slightly hard
when dry and firm when moist; slightly sticky and plastic; many fine pores; few
medium and coarse roots; field pH 7.5; wavy boundary
Very dark grey (7.5YR4/3) when dry and very dark greyish brown (7.5YR3/3)
when moist; sandy clay loam; hard when dry and firm when moist; gravel
sticky; fine pores are common; no roots; field pH 7.5
106
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Soil profile HPT 008/2002
A.
B.
Information on soil profile site
General information on the soil profile
Classification (WRB)
Human influence
Endoleptic
Endoeutic
Regosol
vegetation disturbed
Effective soil depth
35cm
Drainage class
somehow excessively
Date of examination
23/09/02
Type of observation
Authors
Location
Min-Pit
Ermias
Aynekulu,
Esther Mweso.
468601, 7518513
Altitude
1075 m.a.s.l.
Geopedological unit
Sd111
Internal drainage
not known
Topography
Flat
External drainage
slow run-off
Slope
Parent material
2-5%
Sandstone
Ground water depth
Very deep, >150cm
Surface stoniness
none
Vegetation
Woodland
Rock outcrops
none
Land use
Grazing
Evidence of erosion
sheet erosion
Sealing /crusting
none
drained
Moisture condition
C.
Dry
Soil profile description
Horizon
Depth
(cm)
Description
A
0-10
Very dark grey (5YR4/3) when dry and dark brown (5YR3/3) when moist;
sandy clay loam; loose when dry and friable when moist; non sticky and non
plastic; field pH 7.0; wavy boundary
Cr
10-35
Very dark grey (5YR4/3) when dry and dark brown (5YR3/3) when moist;
coarse sandy loam; loose when dry and when moist; non sticky and non plastic;
field pH 7.5
107
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix C: Climatic file
'
Serowe002" -22.16, 26.4, 1040
1
30.5
20
0
0.86 0.637 7.5
0.543
41
28.1
19.2
1.52
0.81
0.635
8.6
0.53
2
30.2
20
0.6
0.76 0.638 7.5
0.544
42
24.4
18.4
2
0.95
0.634
8.6
0.529
3
26
19.4
1.4
0.85 0.64
7.6
0.545
43
27.4
19
0.4
0.91
0.633
8.6
0.528
4
27.9
19.4
0
0.88 0.641 7.6
0.547
44
27.5
20.8
0.4
0.84
0.632
8.6
0.527
5
28.2
20.5
0
0.8
0.643 7.7
0.548
45
28.5
19.8
0
0.94
0.631
8.6
0.526
6
30.5
20.1
0.9
0.8
0.645 7.7
0.549
46
29.3
21.5
5
0.91
0.63
8.7
0.524
7
29.5
21
0.4
0.8
0.646 7.8
0.55
47
28.3
19.5
1.8
0.9
0.627
8.6
0.522
8
32.5
20
0
0.7
0.648 7.8
0.552
48
25.8
17.8
0
0.81
0.623
8.6
0.519
9
27
19.5
0
0.9
0.649 7.9
0.553
49
25.5
16
0
0.56
0.74
8.6
0.516
10
27.7
19.5
0
0.85 0.651 7.9
0.554
50
27.7
17.5
0
0.91
0.616
8.5
0.513
11
29.7
19.1
0
0.79 0.652 8
0.555
51
29.7
17.2
0
0.79
0.613
8.5
0.51
12
30
18.1
0
0.73 0.654 8
0.557
52
28.5
20.4
0
0.94
0.61
8.5
0.507
13
27.5
20.1
0
0.62 0.655 8.1
0.558
53
31
18.8
0
0.83
0.606
8.4
0.504
14
25.6
18
0
0.7
0.657 8.1
0.559
54
28.5
19
0.21
0.86
0.602
8.4
0.501
15
21.3
18
0.3
7.9
0.86
0.56
55
24
17.9
5.4
0.95
0.599
8.4
0.498
16
21.5
17
6.03
0.98 0.658 8.2
0.559
56
21.8
17.5
3.72
0.95
0.595
8.3
0.496
17
22.2
15.4
1.3
0.86 0.657 8.2
0.558
57
24.8
17.5
1.4
0.97
0.592
8.3
0.493
18
20
17
0
0.87 0.656 8.2
0.557
58
26
18.6
1.4
0.92
0.588
8.3
0.49
19
23.5
16.2
0
0.81 0.655 8.2
0.556
59
25.5
19.2
0
0.82
0.585
8.2
0.487
20
24.6
14.5
0
0.8
0.654 8.3
0.555
60
26
17
0
0.86
0.582
8.2
0.484
21
26.8
13.5
0
0.8
0.653 8.3
0.554
61
28.5
17.5
0
0.95
0.578
8.2
0.481
22
28.7
13.8
0
0.7
0.652 8.3
0.552
62
28.5
18.5
0
0.91
0.574
8.1
0.478
23
28.5
14.6
0
0.7
0.651 8.3
0.475
24
28.3
17.2
0
0.55 0.65
25
23.5
18.8
0
26
27.4
19
27
28.1
28
31.7
29
8.2
0.551
63
29.1
19.5
0
0.82
0.571
8.1
0.55
64
29.6
18
0
0.79
0.567
8.1
0.472
0.77 0.649 8.3
0.549
65
29
18.1
0
0.8
0.564
8
0.47
2
0.94 0.649 8.3
0.548
66
27
19
0
0.91
0.56
8
0.467
19.5
0.8
0.95 0.648 8.4
0.547
67
27.2
18
0
0.87
0.557
8
0.464
18.6
0.001 0.93 0.647 8.4
0.545
68
27.2
17.7
0
0.91
0.554
7.9
0.461
32
16.8
0
0.51 0.646 8.4
0.544
69
30.6
17
0
0.82
0.55
7.9
0.458
30
33.2
15.3
0
0.52 0.645 8.4
0.543
70
30.3
15.6
0
0.83
0.546
7.9
0.455
31
35
17.1
0
0.64 0.644 8.4
0.542
71
27.5
18.2
0
0.76
0.543
7.8
0.452
32
32.6
20.1
0
0.76 0.643 8.4
0.541
72
27
17.4
0
0.84
0.539
7.8
0.449
33
33.8
19.5
0
0.74 0.642 8.5
0.54
73
28.6
18.8
0
0.86
0.536
7.8
0.446
34
34.9
19.8
0
0.78 0.641 8.5
0.538
74
30.1
17
0.3
0.95
0.532
7.7
0.444
35
31.1
18.3
0
0.64 0.64
8.5
0.537
75
28
17.5
0
0.83
0.529
7.7
0.441
36
31.1
18
0
0.66 0.64
8.5
0.536
76
28.2
19.4
0
0.96
0.525
7.7
0.438
37
30
18.7
11.9
0.91 0.639 8.5
0.535
77
27
18.4
0
0.94
0.522
7.7
0.435
38
23
19
2.52
0.96 0.638 8.5
0.534
78
24.5
18.5
0
0.96
0.518
7.8
0.432
39
22.5
20
2.9
0.87 0.637 8.6
0.533
79
22.4
19
1.2
0.95
0.515
7.8
0.429
40
26.4
19.1
0.7
0.96 0.636 8.6
0.531
80
26
18.5
4.1
0.95
0.511
7.8
0.426
8.3
108
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
81
26.5
18.5
0.6
0.91 0.508 7.8
0.423
121
21
11.1
0
0.85
0.366
8.2
82
27
17.8
5.4
0.88 0.504 7.8
0.42
122
25.2
8
0
0.84
0.362
8.2
0.301
83
27.8
16.7
0
0.87 0.501 7.8
0.417
123
27
9
0
0.75
0.359
8.2
0.298
84
29
17
0
0.89 0.497 7.8
0.414
124
23.4
11.8
0
0.81
0.355
8.2
0.295
85
30
17
0
0.82 0.494 7.8
0.412
125
24.5
13
0
0.96
0.351
8.2
0.292
86
25.5
16.2
0
0.85 0.49
7.8
0.409
126
25.2
11
2.2
0.89
0.348
8.2
0.289
87
28.2
17
0
0.91 0.487 7.8
0.406
127
24
12
0.9
0.95
0.344
8.2
0.286
88
27.5
16
0
0.9
0.403
128
23.4
6.2
0
0.83
0.341
8.2
0.283
89
25.5
15.6
0
0.85 0.48
0.4
129
22.2
9
0
0.92
0.337
8.3
0.28
90
28.2
18
0
0.89 0.476 7.9
0.397
130
23.5
7.5
0
0.82
0.334
8.3
0.277
91
27
17.5
0
0.87 0.473 7.9
0.394
131
22
10.1
0
0.91
0.33
8.3
0.274
92
23.5
19
0
0.82 0.469 7.9
0.391
132
23
7.5
0
0.84
0.326
8.3
0.271
93
27.5
14
0
0.95 0.466 7.9
0.388
133
21.5
7.3
0
0.9
0.323
8.3
0.268
94
29.5
13
0
0.94 0.462 7.9
0.385
134
18.1
10.5
0
0.83
0.319
8.3
0.265
95
21.3
13.6
0
0.79 0.459 7.9
0.383
135
21.6
3
0.04
0.83
0.322
8.3
0.261
96
23.5
13.5
0
0.9
0.455 7.9
0.38
136
22.5
3.4
0
0.81
0.313
8.3
0.26
97
23.1
14.5
0.13
0.9
0.452 7.9
0.377
137
22
4.5
0
0.78
0.311
8.3
0.258
98
24
13.7
0
0.9
0.448 7.9
0.374
138
22.5
7
0
0.94
0.309
8.3
0.256
99
27
100 25.5
0.483 7.8
7.8
0.304
11
0
0.9
0.445 7.9
0.371
139
24.7
5.7
0
0.8
0.307
8.3
0.254
11.8
0
0.84 0.441 7.9
0.368
140
24.8
6.5
0
0.73
0.304
8.3
0.252
101 25
13.4
0
0.86 0.438 7.9
0.365
141
24.3
6
0
0.77
0.302
8.3
0.25
102 27.5
13.5
0
0.9
0.434 8
0.362
142
24.2
6.6
0
0.75
0.3
8.3
0.248
103 27.8
12
0
0.86 0.431 8
0.359
143
24.8
7.09
0
0.71
0.298
8.2
0.246
104 26.6
13.5
0
0.86 0.427 8
0.356
144
25.5
5.4
0
0.72
0.295
8.2
0.244
105 22
13.4
0
0.87 0.423 8
0.354
145
24.5
5.5
0
0.69
0.293
8.2
0.242
106 22.92
16.6
0
0.97 0.42
0.35
146
25.4
6
0
0.7
0.291
8.2
0.24
107 24.5
10.5
0
0.98 0.416 8
8
0.347
147
26
10.1
0
0.68
0.289
8.2
0.238
108 25.5
11
0
0.97 0.413 8
0.344
148
24.5
3.4
0
0.68
0.287
8.2
0.236
109 26
11.5
2.3
0.86 0.409 8
0.341
149
24.4
6.41
0
0.95
0.284
8.2
0.234
110 24.1
12.7
0
0.76 0.405 8
0.338
150
24
3.6
0
0.74
0.282
8.2
0.232
111 22
13.5
0
0.85 0.402 8
0.335
151
25.7
5
0
0.62
0.28
8.2
0.231
112 24.8
15.4
0
0.91 0.398 8.1
0.332
152
23.1
5
0
0.62
0.278
8.1
0.229
113 27.5
11
0
0.91 0.395 8.1
0.329
153
22.5
2.6
0
0.87
0.275
8.1
0.227
114 30.2
13
0
0.72 0.391 8.1
0.326
154
22.6
2
0
0.73
0.273
8.1
0.225
115 31.5
13
0
0.72 0.388 8.1
0.323
155
21.2
4.1
0
0.84
0.271
8.1
0.223
116 30
11.5
0
0.68 0.384 8.1
0.32
156
16.7
4.6
0
0.99
0.269
8.1
0.221
117 31.5
13.2
0
0.68 0.38
8.1
0.317
157
17.6
4
0
0.94
0.267
8.1
0.219
118 30
0.13
0
0.77 0.377 8.1
0.314
158
18.1
4.5
0
0.94
0.264
8.1
0.217
119 19.5
14.5
0
0.77 0.373 8.1
0.311
159
20
11.2
0
0.87
0.262
8.1
0.215
120 18.5
14.4
0
0.86 0.37
0.307
160
23.9
5.17
2.52
0.91
0.26
8.1
0.213
8.2
109
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
161 24
11
1.4
0.91 0.258 8.1
0.211
201
22.48 6.5
0
0.37
0.29
8.5
0.245
162 22.17
7.6
0.53
0.91 0.255 8
0.209
202
22.58 5.2
0
0.43
0.294
8.6
0.248
163 22.08
7.1
0
0.79 0.253 8
0.207
203
22.67 1
0
0.58
0.298
8.6
0.252
164 21.98
8.6
0
0.82 0.251 8
0.205
204
22.77 3.5
0
0.94
0.302
8.6
0.255
165 21.89
6.5
0
0.88 0.249 8
0.203
205
22.87 3.5
0
0.88
0.306
8.6
0.258
166 21.79
5.6
0
0.9
0.246 8
0.202
206
22.96 5.5
0
0.93
0.31
8.7
0.261
167 21.8
4.9
0
0.84 0.247 8
0.202
207
23.06 3.3
0
0.85
0.314
8.7
0.265
168 21.81
8.5
0
0.84 0.248 8
0.203
208
23.16 2.54
0
0.74
0.318
8.7
0.268
169 21.81
13.5
0
0.87 0.249 8
0.204
209
23.25 3.4
0
0.96
0.322
8.7
0.271
170 21.82
11.6
0
0.89 0.25
8.1
0.205
210
23.35 2.4
0
0.8
0.326
8.7
0.275
171 21.83
8.6
0
0.91 0.25
8.1
0.206
211
23.45 4
0
0.76
0.33
8.8
0.278
172 21.84
12.7
0
0.95 0.251 8.1
0.207
212
23.54 4.5
0
0.69
0.333
8.8
0.281
173 21.84
12.5
0
0.94 0.252 8.1
0.208
213
23.64 5.4
0
0.63
0.337
8.8
0.284
174 21.85
9.5
0
0.98 0.253 8.1
0.209
214
23.74 4.6
0
0.59
0.341
8.8
0.288
175 21.85
9.4
0
0.84 0.254 8.1
0.21
215
23.83 5.4
0
0.84
0.345
8.9
0.291
176 21.86
8.1
0
0.93 0.254 8.1
0.211
216
23.93 6
0
0.79
0.349
8.9
0.294
177 21.87
8.3
0
0.94 0.255 8.2
0.211
217
25.4
8.5
0
0.62
0.353
8.9
0.298
178 21.87
4.5
0
0.95 0.256 8.2
0.212
218
22.9
6.01
0
0.79
0.357
8.9
0.301
179 21.88
3.6
0
0.8
0.257 8.2
0.213
219
23.5
6.1
0
0.96
0.361
9
0.304
180 21.89
4.9
0
0.87 0.258 8.2
0.214
220
23.6
6.19
0
0.91
0.365
9
0.307
181 21.89
5.5
0
0.9
0.259 8.2
0.215
221
24
6.27
0
0.81
0.369
9
0.311
182 21.9
4.5
0
0.9
0.259 8.2
0.216
222
24.8
6.36
0
0.59
0.373
9
0.314
183 21.91
4.5
0
0.9
0.26
0.217
223
27.3
6.45
0
0.5
0.377
9.1
0.317
184 21.92
2.5
0
0.8
0.261 8.3
0.218
224
25.4
6.23
0
0.54
0.381
9.1
0.321
185 21.92
2.8
0
0.82 0.262 8.3
0.219
225
24.4
6.62
0
0.34
0.385
9.1
0.324
186 21.93
5
0
0.95 0.263 8.3
0.219
226
22.2
6.71
0
0.89
0.389
9.1
0.327
187 21.94
3.5
0
0.86 0.263 8.3
0.22
227
21
5.8
0
0.79
0.393
9.1
0.331
188 21.94
3
0
0.86 0.264 8.3
0.221
228
23.5
6.95
0
0.79
0.398
9.1
0.336
189 21.95
4.2
0
0.93 0.265 8.3
0.222
229
25.5
7.11
0
0.82
0.404
9.1
0.341
190 21.95
4
0
0.93 0.266 8.3
0.223
230
26.5
7.27
0
0.61
0.409
9.1
0.347
191 21.96
3.1
0
0.86 0.266 8.3
0.224
231
24.5
7.43
0
0.64
0.415
9.1
0.352
192 21.97
2.5
0
0.68 0.267 8.4
0.225
232
23.5
7.59
0
0.5
0.421
9.1
0.357
193 21.97
5.5
0
0.8
0.268 8.4
0.226
233
24.5
7.74
0
0.75
0.426
9
0.363
194 21.98
9
0
0.88 0.269 8.4
0.227
234
26.3
7.9
0
0.67
0.432
9
0.368
195 21.99
7.3
0
0.94 0.27
8.4
0.228
235
27.5
8.06
0
0.57
0.438
9
0.373
0.27
8.2
196 22
4.09
0
0.8
8.4
0.229
236
26.7
8.22
0
0.53
0.443
9
0.379
197 22.09
7.4
0
0.65 0.274 8.4
0.232
237
27.5
8.38
0
0.73
0.449
9
0.384
198 22.19
3.5
0
0.62 0.278 8.5
0.235
238
26.9
8.53
0
0.58
0.455
9
0.389
199 22.29
2.5
0
0.6
0.282 8.5
0.238
239
27.5
8.69
0
0.6
0.46
8.9
0.395
200 22.38
0.1
0
0.66 0.286 8.5
0.242
240
28.8
8.85
0
0.65
0.466
8.9
0.4
110
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
241 29.8
9.01
0
0.8
0.472 8.9
0.405
281
31
20
0.077 0.43
0.658
8.3
0.575
242 31.8
9.17
0
0.5
0.477 8.9
0.411
282
30.3
19.5
0.08
0.54
0.662
8.3
0.578
243 32.5
9.32
0
0.35 0.483 8.9
0.416
283
36.8
16.5
0.082 0.41
0.666
8.3
0.581
244 33.8
9.48
0
0.33 0.488 8.9
0.422
284
28.1
18
0.084 0.27
0.67
8.3
0.585
245 33.5
9.64
0
0.28 0.494 8.8
0.427
285
23.7
14.6
0.086 0.65
0.674
8.3
0.588
246 34.5
9.8
0
0.53 0.5
8.8
0.432
286
30
11.6
0.089 0.75
0.678
8.3
0.592
247 33.4
9.96
0
0.45 0.505 8.8
0.438
287
32.5
13
0.091 0.77
0.682
8.3
0.595
248 24.5
10.11 0
0.35 0.511 8.8
0.443
288
34
13.6
0.093 0.5
0.685
8.2
0.598
249 31.4
10.3 0
0.72 0.517 8.8
0.448
289
34.2
12.5
0.097 0.31
0.685
8.2
0.597
250 32.64
10.43 0
0.8
0.522 8.8
0.454
290
35.7
15.1
0.102 0.4
0.684
8.2
0.596
251 25.5
10.59 0
0.31 0.528 8.7
0.459
291
34.6
15.4
0.106 0.44
0.683
8.2
0.595
252 29.2
10.75 0
0.67 0.534 8.7
0.464
292
36.5
19.5
0.11
0.682
8.2
0.594
253 35.2
10.9
0
0.6
0.539 8.7
0.47
293
30.5
20
0.115 0.44
0.681
8.2
0.593
254 28.5
11.06 0
0.5
0.545 8.7
0.475
294
32
16.5
0.119 0.61
0.68
8.1
0.592
255 22.2
11.2 0
0.3
0.551 8.7
0.48
295
27.2
17.3
0.123 0.62
0.679
8.1
0.59
256 33.5
11.38 0
0.7
0.556 8.6
0.486
296
29.9
14
0.127 0.73
0.678
8.1
0.589
257 35.6
11.54 0
0.9
0.562 8.6
0.491
297
31.6
16.5
0.132 0.65
0.677
8.1
0.588
258 24.6
11.69 0
0.4
0.568 8.6
0.497
298
34.5
17.9
0.136 0.56
0.676
8.1
0.587
259 22.5
11.83 0
0.6
0.571 8.6
0.5
299
25.5
17.5
0.14
0.55
0.675
8
0.586
260 29.5
11.97 0
0.7
0.575 8.6
0.503
300
20.5
16
0.145 0.93
0.674
8
0.585
261 27.2
12.1
0
0.8
0.579 8.6
0.507
301
23.9
14.5
0.149 0.95
0.673
8
0.583
262 23.2
12.24 0
0.6
0.583 8.6
0.51
302
28.2
13
0.153 0.95
0.672
8
0.582
0.36
263 20
12.38 0
0.7
0.587 8.6
0.513
303
31.6
14.9
0.157 0.69
0.671
8
0.581
264 24.2
12.51 0
0.8
0.591 8.5
0.517
304
26.29 15.4
0.162 0.62
0.67
8
0.58
265 24.9
12.65 0
0.8
0.595 8.5
0.52
305
25
15
0.166 0.94
0.669
7.9
0.579
266 25.7
12.79 0
0.71 0.599 8.5
0.524
306
30.3
14
0.17
0.84
0.668
7.9
0.578
267 27.3
12.93 0
0.72 0.603 8.5
0.527
307
32.2
16.5
0.175 0.88
0.667
7.9
0.576
268 33
13.06 0
0.75 0.607 8.5
0.531
308
34.6
14
0.179 0.6
0.666
7.9
0.575
269 34.7
13.2
0
0.47 0.611 8.5
0.534
309
35
17
0.183 0.72
0.665
7.9
0.574
270 27.5
13.34 0
0.38 0.615 8.5
0.537
310
31.5
20.4
0.188 0.32
0.664
7.9
0.573
271 32
13
0
0.61 0.619 8.5
0.541
311
31
18.5
0.192 0.61
0.663
7.8
0.572
272 34.4
13.7
0
0.68 0.623 8.4
0.544
312
32.6
16.5
0.196 0.61
0.662
7.8
0.571
273 33.5
15.5
0
0.53 0.626 8.4
0.547
313
35.7
16.2
0.2
0.661
7.8
0.569
274 35.5
14.1
0
0.43 0.63
8.4
0.551
314
35
20
0.205 0.44
0.66
7.8
0.568
275 32
18
0
0.33 0.634 8.4
0.554
315
36
17
0.209 0.48
0.659
7.8
0.567
276 29.5
15
0
0.36 0.638 8.4
0.558
316
34.3
15.8
0.213 0.51
0.658
7.7
0.566
277 30.4
12.7
0
0.63 0.642 8.4
0.561
317
33.2
18
0.218 0.67
0.657
7.7
0.565
278 35.1
16
0
0.76 0.646 8.4
0.564
318
31.4
14
0.222 0.3
0.656
7.7
0.564
279 36
16.5
0
0.4
8.4
0.568
319
32.1
14
0.226 0.5
0.65
7.7
0.563
280 36.2
19.4
0.075 0.37 0.654 8.3
0.571
320
30.7
19.5
0.228 0.7
0.654
7.7
0.561
0.65
111
0.53
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
321 31.9
19.1
0.6
0.652 7.6
0.56
322 29.5
18.04 0.232 0.6
0.23
0.651 7.6
0.558
323 24
17.4
0.233 0.7
0.65
7.6
0.557
324 28.5
11
0.235 0.5
0.648 7.5
0.556
325 28
18.16 0.24
0.647 7.5
0.554
326 26.2
18
0.239 0.64 0.645 7.5
0.553
327 28.5
20
0.241 0.71 0.643 7.4
0.552
328 34.4
14.11 0.242 0.61 0.642 7.4
0.55
329 33
15
0
0.54 0.641 7.3
0.549
330 32.5
20.4
0
0.64 0.639 7.3
0.547
331 26.5
18.5
0
0.67 0.638 7.3
0.546
332 32.1
20
0
0.73 0.636 7.2
0.545
0.6
333 31
20.5
0
0.8
0.634 7.2
0.543
334 29.5
18.5
0
0.7
0.633 7.2
0.542
335 26.2
18.5
0
0.79 0.632 7.1
0.541
336 31.2
17.4
0
0.67 0.63
7.1
0.539
337 33.9
15
0
0.46 0.629 7.1
0.538
338 33.8
16
0
0.41 0.627 7
0.537
339 32
17
0
0.59 0.625 7
0.535
340 34.5
18.5
0
0.49 0.624 7
0.534
341 35
19
0
0.48 0.623 6.9
0.532
342 37.3
20
0
0.51 0.621 6.9
0.531
343 26.5
21
0
0.79 0.62
0.53
344 29.1
23
0
0.8
0.618 6.8
0.528
345 28.9
20.43 0
0.83 0.616 6.8
0.527
346 32.5
20.15 0
0.68 0.615 6.8
0.526
347 24.5
18.6
0
0.76 0.614 6.7
0.524
348 31.4
19
0
0.63 0.612 6.7
0.523
349 31.5
14
3
0.46 0.611 6.7
0.522
350 32.5
16.7
3.2
0.57 0.612 6.7
0.523
351 33.4
15.5
0.2
0.47 0.614 6.8
0.524
352 34.5
16.54 0.3
0.49 0.615 6.8
0.525
353 34
18
0.68 0.617 6.9
0.527
0
6.9
354 33
19.5
0
0.54 0.618 6.9
0.528
355 29.6
20.5
0
0.82 0.62
0.529
356 28
19
0
0.91 0.621 7
0.53
357 31
18
0
0.53 0.76
0.532
6.9
7
358 34
17.5
0
0.58 0.624 7.1
0.533
359 32.6
18
0
0.59 0.626 7.1
0.534
360 29
20.5
0
0.66 0.628 7.2
0.535
361 27.3
18.5
0
0.74 0.629 7.2
0.537
362 33.8
19
0.62
0.63 0.631 7.3
0.538
363 37
16
0
0.37 0.632 7.3
0.539
364 34.1
18.5
0
0.57 0.634 7.4
0.54
365 33.3
21
0
0.73 0.635 7.4
0.542
112
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix D (a): Generic data values for maize and sorghum
Photosynthetic mechanism
Threshold temperature
TO
TSUM
Rooting zone RDS
Rooting depth initial
Maximum
Critical leaf water heads
PSI leaf
SLA range
Extinction coefficient visible light ke
Maintenance respiration r(org)
Root
Leaf
Stem
S.O
Maize
C4
Sorghum
C4
10
1600
10
1600
10
100-170
5-10
100-200
17000
14-35
0.6
20000
11-21
0.5
0.010
0.013
0.010
0.010
0.010
0.015
0.010
0.010
0.72
0.72
0.69
0.72
0.72
0.72
0.69
0.74
Heat sum for development tissue EC (org)
Leaf
Root
Stem
s.o
Appendix D(b): Generic data values
RDS
Fr (leaf)
Fr (root)
Fr (stem)
Fr (s.o)
Maize
0
0.60
0.40
0.00
0.00
0.2
0.70
0.30
0.00
0.00
0.3
0.65
0.23
0.12
0.00
113
Sorghum
0
0.22
0.45
0.55
0.55
0.33
0.00
0.01
0.00
0.00
0.34
0.65
0.25
0.10
0.00
0.56
0.25
0.05
0.70
0.00
0.61
0.13
0.00
0.80
0.07
EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix E: Growth cycle for maize and sorghum
Maize
Sorghum
Establishment
15-25
15-20
Vegetative
25-40
20-30
Flowering
15-20
15-20
Yield
35-45
35-40
Ripening
10-15
10-15
Source:(Doorenbos and Kassam, 1979)
Appendix F: Glossary
ASSC is Actual surface storage
SSC
is equivalent to surface storage capacity (cm)
(CR+D) is the net rate of water flow through the lower boundary of the rooting zone (cm d-1)
Dr
is surface roughness or furrow depth (cm)
SIG
is clod angle or furrow angle (degree)
PHI
is average slope of the land (degree)
SLA
is specific leaf area, m2 kg -1
TO
is threshold temperature for development, oC
Tsum is heat requirement for full development, oC d
Ke
is the extinction coefficient for visible light
K
is the hydraulic conductivity
LAI
is leaf area index
LC
is land characteristic
LUR
is land use requirement
PSIint is the matric suction at planting or germination (cm) (ψ)
RD
is equivalent depth of the rooting zone (cm)
RDSroot is reletive development stage.
RSM
is the rate of change of volume fraction of moisture in the rooting zone (cm)
SSC
is equivalent surface storage capacity
Tleaf
is heat sum for full development of leaf tissue
TR
is the actual rate of transpiration (cm d-1)
UPFLUX is the net of water vapour flow through the upper boundary of the rooting zone (cm d-1)
ZTint
is depth of phreatic level at planting
is matric suction
Ψ
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RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix G: Questionnaire
Farmer 1 Location: 460594, 7520848
Farm size: 5.3ha
Type of crops grown: maize
Land tenure: customary
Farm operations: Ploughing and planting are done at the same time in Nov /Dec
Weeding is done only once
Fertilizer application: No fertilizer is used
Harvesting: in May when the crop is completely dry
Input acquisition: buys cash
Power: uses animal draught (donkeys)
Labour supply: Family labour
Labour intensity: intensity is high during weeding and harvesting time
Yield: could not disclose the yield
Cropping system: single cropping
Fallowing: no fallowing
Performance of the farm: no variations in the performance
Problems faced: corn crickets
Control: by hand picking
Extension services: access to agriculture extension services
Note: is a model farmer
Farmer 2 Location: 463636, 7519154
Farm size: 7ha but uses only 3ha; the remainder is used for grazing livestock
Type of crops grown: maize and sorghum
Land tenure: customary
Farm operations: land preparation and planting done at the same time when rains come in
November
Weeding is done after two months
Fertilizer application: Does not apply fertilizers
Harvesting; May/June
Input acquisition: Cash
Power: animal draught (donkeys)
Labour supply: family members
Labour intensity: medium intensity
Yield: 7bags of 70kgs maize and 15bags of 70kg for sorghum
Cropping system: Mixed cropping
Fallowing: Does not fallow
Performance of the farm: part of the farm is stony and performance is poor in that area
Problems faced: High winds sooner after emergency of the seedlings and sorghum
Birds attacking sorghum
Sealing of the soil
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Solution: there is no control for wind, as for birds, they are scared and nothing done for the
sealing problem
Extension services: Has access to agricultural extension services
Farmer 3 Location: 464878, 7519907
Type of crops grown: sorghum, maize, cowpeas, and pumpkins
Land tenure: customary
Farm operations: land preparation and planting are done simultaneously
Weeding is done in December
Fertilizer application: no fertilizer application
Harvesting: My/June
Input acquisition: Recycled seed
Power: Animal draught
Labour supply: Family labour for weeding
Labour intensity: high labour intensity
Yield: 10bags of 70kg maize, 15bags of 70kg sorghum
Cropping system: single cropping
Fallowing: No fallowing
Performance of the farm: Eroded area gives low yield
Problems faced: Soil erosion, sealing, birds and aphids on cowpeas
Solution: makes box ridges for soil erosion scaring away birds but no solution for the rest of the
problems
Extension services: gets access to agricultural services
Farmer 4 Location: 481118, 7537905
Farm size: 5.5ha
Type of crops grown: sorghum, maize and cowpeas
Land tenure: customary
Farm operations: land preparation and planting at the same time in Nov/Dec
Weeding is done once
Fertilizer application; no fertilizer applied
Harvesting: June
Input acquisition: Cash (50kg in total for all crops)
Power: animal draught (donkeys)
Labour supply: Family members for weeding
Labour intensity: High
Yield: 13 bags of 70kg sorghum, 8 bags of 70kg
Cropping system: single cropping
Fallowing: no fallowing
Performance of the farm: no variations
Problems faced: wind erosion, aphids on sorghum, sealing
Solution: no solution provided
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Extension services: have access to agricultural services
Farmer 5 Location: 485189, 7539910
Farm size: 10ha
Type of crops grown: sorghum, maize and cowpeas
Land tenure: customary
Farm operations: land preparation and planting at the same time
Weeding is done in December
Fertilizer application
Harvesting
Input acquisition: Uses recycled seed but sometimes buys cash
Power: Donkeys
Labour supply: Family members
Labour intensity: high intensity during weeding
Yield: 41bags of 70kg maize
Cropping system: Mixed cropping
Fallowing: At times 5ha may be fallowed for only one year
Performance of the farm: Experience low yield on sloping side
Problems faced: water and wind erosion
Solution: planted trees to act as wind break but died due to lack of moisture
Extension services: Get access to agricultural extension services
Farmer 6 Location: 484385, 7538250
Farm size: 3ha
Type of crops grown: sorghum
Land tenure: customary
Farm operations: Ploughing and planting simultaneously
Weeding done once when weeds appear
Fertilizer application: no fertilizer application
Harvesting: done in May when the crop is dry
Input acquisition: Uses recycled seed
Power: Uses donkeys
Labour supply: Family members
Labour intensity: Medium intensity
Yield: 70 bags of 70kg each
Cropping system: Single cropping
Fallowing: No fallowing
Performance of the farm: No variations in the performance of the farm
Problems faced: Birds
Solution: No control
Extension services: Get access to agricultural extension services
Farmer 7 Location: 484223, 7538215
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Farm size: 6ha
Type of crops grown: sorghum, maize and cowpeas
Land tenure: customary
Farm operations: Ploughing and planting done simultaneously in November
Weeding is done once
Fertilizer application: No fertilizer is applied
Harvesting: Done in May/June
Input acquisition: Uses recycled seed but sometimes buys using cash
Power: Uses donkeys
Labour supply: Family members but sometimes employ casual labour for weeding
Labour charge: Pays P5 per person per day depending on availability of finances
Labour intensity: Medium intensity
Yield: could not disclose
Cropping system: single cropping
Fallowing: no fallowing
Performance of the farm: Part of the farm has sandy soils and get low yield on that side
Problems faced: birds attacking sorghum
Solution: by scaring the birds away
Extension services: get access to agricultural extension services
Farmer 8 Location: 463159, 7517322
Farm size: 19.5ha but uses only 5ha
Type of crops grown: sorghum and maize
Land tenure: customary
Farm operations: Ploughing and planting done simultaneously
Weeding: done when weeds appear
Fertilizer application: does not apply fertilizer
Harvesting: In May/June
Input acquisition: cash
Power: draught animals (donkeys)
Labour supply: Family members but sometimes employ casual labour for weeding
Labour intensity: medium intensity
Labour charge: P15 per person per day and can employ a maximum of 5
Yield: 11bags of 70kg for sorghum and 17bgas of 70kg for maize
Cropping system: single cropping
Fallowing: Fallow for one year
Performance of the farm: There are some pans in the field where yield is lower than the rest
Problems faced: stalkborers and sealing but is not serious
Solution: No control measure
Extension services: Has access to Agricultural extension services
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RAINFED CROPS IN SEROWE AREA, BOTSWANA
Farmer 9 Location: 463153, 7517319
Farm size: 10ha but uses only 7ha
Type of crops grown: sorghum and maize
Land tenure: Customary
Farm operations: Ploughing and planting done simultaneously
Weeding: done when weeds appear and weeds only once
Fertilizer application: does not apply fertilizer
Harvesting: in June
Input acquisition: Uses recycled and plants 8kg ha-1 for sorghum and 10kg ha-1
Power: Draught animals
Labour supply: prepares traditional beer to people working on the farm
Labour intensity: high labour intensity
Yield: 1bag of 70kg for each crop
Cropping system: single cropping
Fallowing: does fallow for one season
Performance of the farm: part of the farm has cynodon dactylon and competes with crop leading
to low yield
Soil and water conservation: does not practise any
Problems faced: soil erosion, birds and elegant grasshoppers
Scaring them away controls birds, elegant grasshoppers are hand picked and no measure control
for erosion
Extension services: Has access to agricultural extension services
Farmer 10 Location: 466658, 7510188
Farm size: 7ha
Type of crops grown: sorghum, maize and cowpeas
Land tenure: Customary
Farm operations Ploughing and planting done simultaneously
Weeding: done when weeds appear and weeds only once
Fertilizer application: does not apply fertilizer
Harvesting: in June
Input acquisition: buys cash: 10P per 10kg
Power: animal draught
Labour supply: family members
Labour intensity: medium
Yield: 30bags of 70kg for maize and no yield for sorghum due to bird’s attack
Cropping system: single cropping
Fallowing: no fallowing
Performance of the farm: no variations in performance
Problems faced: Cynodon dactylon weed, birds and elegant grasshoppers
Solution: no control
Extension services: Has access to agricultural extension services
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Farmer 11 Location: 466643, 7510139
Farm size: 8ha
Type of crops grown: maize, sorghum and cowpeas
Land tenure:
Farm operations Ploughing and planting done simultaneously
Weeding: done when weeds appear and weeds only once
Fertilizer application: does not apply fertilizer
Harvesting: in June
Input acquisition: cash
Power: animal draught
Labour supply: family members for weeding
Labour intensity: Low
Yield: 5gags of 70kg for each crop
Cropping system: single cropping
Fallowing: no fallowing
Performance of the farm: no variations
Problems faced: the farmland is stony, birds attacking sorghum
Solution: scaring the birds away
Extension services: has access to agricultural extension services
Farmer 12 Location: 467185, 7518324
Farm size: 8ha
Type of crops grown: sorghum and maize
Land tenure: Customary
Farm operations Ploughing and planting done simultaneously
Weeding: done when weeds appear and weeds only once
Fertilizer application: does not apply fertilizer
Harvesting: in June
Input acquisition: cash, buys 3-4 bags of 10kg at 3P/kg
Power: Animal draught
Labour supply: Family labour for weeding
Labour intensity: medium
Yield: 7bags of 70kg of sorghum and 3bags of 70kg of maize
Cropping system: single cropping
Fallowing: fallow for one season
Performance of the farm: no variations in performance
Problems faced: soil erosion, birds attacking sorghum corn cricket attacking maize
Solution: scaring the birds away and no control for corn crickets
Extension services: Does not have access to agricultural services
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix H: Results of Particle size distribution analysis
Code
X_coord
Y_coord
Sand (%)
Silt (%)
Clay (%)
Texture
SPT_002
428575
7531451
95.324
1.306
3.370 Sand
SPT_002
428575
7531451
94.094
1.115
4.791 Sand
SPT_002
428575
7531451
92.929
0.534
6.537 Sand
HARD_13
466995
7514049
93.998
1.414
4.589 Sand
HARD_13
466995
7514049
92.268
1.693
6.039 Sand
HARD_13
466995
7514049
91.757
1.563
6.680 Sand
HPT_001
466980
7513874
91.719
4.983
3.297 Sand
HPT_001
466980
7513874
91.983
1.897
6.120 Sand
HPT_001
466980
7513874
89.443
1.610
8.947 Loamy sand
HPT_003
465347
7507938
91.719
4.983
3.297 Sand
HPT_003
465347
7507938
91.983
1.897
6.120 Sand
HPT_003
465347
7507938
89.443
1.610
8.947 Loamy sand
SPT_003
444677
7516908
94.395
0.872
4.733 Sand
SPT_003
444677
7516908
94.704
0.659
4.637 Sand
SPT_003
444677
7516908
92.371
1.314
6.315 Sand
EPT_002
475066
7535877
87.671
4.110
8.219 Loamy sand
EPT_002
475066
7535877
87.240
3.683
9.078 Loamy sand
HPT_007
467604
7519059
71.099
15.973
12.928 Sandy Loam
HPT_007
467604
7519059
60.365
19.681
19.954 Sandy Loam
HPT_007
467604
7519059
73.317
15.570
11.114 Sandy Loam
HPT_005
469774
7518089
23.544
31.646
44.810 Clay
HPT_005
469774
7518089
22.993
25.571
51.436 Clay
HPT_005
469774
7518089
24.561
26.816
48.623 Clay
HPT_005
469774
7518089
18.324
30.823
50.853 Clay
HPT_06
467215
7517154
56.178
15.084
28.737 Sandy clay loam
HPT_06
467215
7517154
19.969
38.555
41.476 Clay
HPT_06
467215
7517154
68.239
6.646
EPT_01
474663
7539777
88.573
3.809
25.115 Sandy clay loam
7.618 Loamy sand
EPT_01
474663
7539777
88.316
3.372
8.311 Loamy sand
SPT_1
433495
7527033
77.185
12.609
10.206 Sandy Loam
ESC_10
479088
7539915
78.447
12.576
ESC_07
470500
7537503
58.666
17.109
8.977 Sandy Loam
24.225 Sandy clay loam
ESC_11
470089
7534546
58.561
13.760
27.679 Sandy clay loam
ESC_30
473503
7517178
46.700
18.946
34.354 Sandy clay loam
27.375 Sandy clay loam
ESC_14
471662
7532578
56.033
16.592
Sand_17
425914
7534098
96.904
0.888
2.208 Sand
Sand_ 43
431077
7530673
96.953
0.932
2.115 Sand
Sand_ 56
433493
7527033
94.695
1.364
3.941 Sand
Hard_01
460013
7510014
94.138
1.036
4.826 Sand
Hard_32
466630
7513081
91.884
2.977
Hard_11
461741
7511696
26.555
71.998
5.139 Sand
1.447 Silt loam
Hard_54
469767
7518092
22.824
29.453
47.723 Clay
Hard_56
467597
7519066
64.894
16.929
18.177 Sandy loam
Esc_58
474799
7535997
93.815
2.930
3.255 Sand
Farm_01
460594
7520848
87.109
2.902
9.989 Loamy sand
Farm_02
463636
7519154
86.356
2.886
10.758 Loamy sand
Farm_03
464878
7519907
77.430
5.061
17.509 Sandy Loam
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
Appendix I: Decision trees
LUT1 Erosion hazard
> Slp (Slope)
<3 (none) [0-3 %]....... : 1 (none)
3-8 (slight) [3-8 %] > Txc (Textural class)
FS (Fine sand) [3-10 cla : 2 (slight)
SL (Sandy loam) [10-15 c : =1
LS (Loamy sand) [15-20 c : =1
CL (Clay loam) [20-50 cl : 1 (none)
SCL (Sandy clay loam) [5 : =4
9-16 (moderate) [8-16 %] : 3 (moderate)
>16 (severe) [16-25 %].. : 4 (severe)
LUT1,Oxygen availability
> Drg (Soil drainage class)
Wd (Well drained)....... :
Mod (Moderately drained) :
Imp (Imperfectly drained :
Pr (Poorly drained)..... :
1
2
3
4
LUT1,Moisture availability
> TRf (Total rainfall)
250-300 (not adequate) [ : 4 (severe stress)
300-400 (Stress) [300-400 mm] > SEDth (Soil effective depth)
<30 (very shallow) [0-30 : 4 (severe stress)
30-50 ( shallow) [30-50 cm] > Txc (Textural class)
FS (Fine sand) [3-10 class] > Yd (LUT1 Yield class)
ns (not suitable) [1500-] : 4 (severe stress)
ms (marginally suitable) : 3 (stress)
mod.s (moderately suitab) : =2
suit (suitable) [6000-65] : 2 (slightly adequat)
SL (Sandy loam) [10-15 c : =1
LS (Loamy sand) [15-20 c : =1
CL (Clay loam) [20-50 cl : 2 (slightly adequat)
SCL (Sandy clay loam) [5 : =4
50-120 (slightly deep) [ : 3 (stress)
500 (deep) [120-500 cm]. : 2 (slightly adequat)
400-600 (Less adequate) [400-600 mm] > SEDth (Soil effective
depth)
<30 (very shallow) [0-30 : 3 (stress)
30-50 ( shallow) [30-50 : 2 (slightly adequat)
50-120 (slightly deep) [ : 1 (adequate)
500 (deep) [120-500 cm]. : =3
>600 (Adequate) [600-750 mm]>SEDth(Soil effective depth)
<30 (very shallow) [0-30 : 2 (slightly adequat)
30-50 ( shallow) [30-50 : 1 (adequate)
50-120 (slightly deep) [ : =2
500 (deep) [120-500 cm]. : =2
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
LUT1,Rooting Condition
> SEDth (Soil effective depth)
<30 (very shallow) [0-30 : 4 (poor)
30-50 ( shallow) [30-50 cm] > Drg (Soil drainage class)
Wd (Well drained)....... : 1 (very good)
Mod (Moderately drained) : 2 (good)
Imp (Imperfectly drained : 3 (moderate)
Pr (Poorly drained)..... : 4 (poor)
50-120 (slightly deep) [ : 2 (good)
500 (deep) [120-500 cm]. : 1 (very good
LUT1,Soil workability
> Txc (Textural class)
FS (Fine sand) [3-10 cla :
SL (Sandy loam) [10-15 c :
LS (Loamy sand) [15-20 c :
CL (Clay loam) [20-50 cl : =3
SCL (Sandy clay loam) [5 :
1
=1
2
=4
LUT 2,Erosion hazard
> Slp (Slope)
<3 (none) [0-3 %]....... : 1 (none)
3-8 (slight) [3-8 %] > Txc (Textural class)
FS (Fine sand) [3-10 c : 2 (slight)
SL (Sandy loam) [10-15 c : 3 (moderate)
LS (Loamy sand) [15-20 c : =2
CL (Clay loam) [20-50 c : =3 (moderate)
SCL (Sandy clay loam) [5 : 2 (slight)
9-16 (moderate) [8-16 %] : 3 (moderate)
>16 (severe) [16-25 %].. : 4 (severe)
LUT 2,Rooting condition
> SEDth (Soil effective depth)
<30 (very shallow) [0-30 : 4 (poor)
30-50 ( shallow) [30-50 cm] > Txc (Textural class)
FS (Fine sand) [3-10 cla : 1 (very good)
SL (Sandy loam) [10-15 c : =1
LS (Loamy sand) [15-20 c : 2 (good)
CL (Clay loam) [20-50 cl : =3
SCL (Sandy clay loam) [5 : =4
50-120 (slightly deep) [ : 2 (good)
500 (deep) [120-500 cm]. : 1 (very good)
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EVALUATING THE IMPORTANCE OF SOIL MOISTURE AVAILABILITY (AS A LAND QUALITY) ON SELECTED
RAINFED CROPS IN SEROWE AREA, BOTSWANA
LUT 2,Sealing
> Txc (Textural class)
FS (Fine sand) [3-10 cla
SL (Sandy loam) [10-15 c
LS (Loamy sand) [15-20 c
CL (Clay loam) [20-50 cl
SCL (Sandy clay loam) [5
:
:
:
:
:
1 (no problem)
=1
2 (slight prob)
2 (slight prob)
LUT 2,Soil workability
> Txc (Textural class)
FS (Fine sand) [3-10 cla : 1 (Easy)
SL (Sandy loam) [10-15 c : =1
LS (Loamy sand) [15-20 c : 2 (Moderate)
CL (Clay loam) [20-50 cl : =3
SCL (Sandy clay loam) [5 : =4
LUT 2,Oxygen availability
> Drg (Soil drainage class)
Wd (Well drained)....... :
Mod (Moderately drained) :
Imp (Imperfectly drained :
Pr (Poorly drained)..... :
1 (no limitation)
2 (slight limit)
4 (poor)
=3
LUT 2,Moisture availability
> TRf (Total rainfall)
250-300 (not adequate) [ : 4 (severe stress)
300-400 (Stress) [300-400 mm] > Txc (Textural class)
FS (Fine sand) [3-10 cla : 4 (severe stress)
SL (Sandy loam) [10-15 class] > Yd LUT2 (LUT2 yield class)
ns (not suitable) [0-1000] : 3 (stress)
ms (marginally suitable) : 3 (stress)
mod.s (moderately suitab : 2 (less adequate)
suit (suitable) [2000-3000] : 1 (adequate)
LS (Loamy sand) [15-20 c : 3 (stress)
CL (Clay loam) [20-50 cl : =3
SCL (Sandy clay loam) [5 : 2 (less adequate)
400-600 (Less adequate) : 1 (adequate)
>600 (Adequate) [600-750 : =3
124