EU Soil Protection Strategy
Working Group on Soil Erosion
Task 3.2. Development of criteria and indicators to assess soil sustainable use
Task 4.1. Concrete measures to combat soil erosion in agriculture
Restrictions of agricultural zones and identification of soil
protection practices by using soil quality decision support tools.
With special reference to the Mediterranean region*
D. de la Rosa, E. Diaz-Pereira, F. Mayol
Consejo Superior de Investigaciones Científicas (CSIC)
Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS)
Avda. Reina Mercedes 10, 41012 Sevilla.
diego@irnase.csic.es
1. Introduction
Impacts of soil erosion on soil functioning and soil quality …
The results of exploiting agricultural systems without consideration of the
consequences on soil quality have been environmental degradation. It is evident the
importance of soil quality in achieving sustainable farming systems, which balance
productivity and environmental protection. The impact of agricultural use and management
must be analyzed not only on crop yield but also on soil quality/degradation.
Agricultural management systems located on the most suitable lands, according to
their agro-ecological potentialities and limitations, is the best way to get the sustainability.
Land use planning and soil management recommendations
based on traditional land
evaluation analysis allows to develop this task. Also, the new concept of soil quality as “the
capacity of a specific kind of soil to function with its surroundings, sustain plant and animal
productivity, maintain or enhance soil, water and air quality and support human health and
habitation” (Karlen et al., 1997) must be considered. The soil quality evaluation framework,
identifying key soil quality attributes or indicator among the nearly infinite list of soil
properties, and developing methods for evaluating and monitoring it with respect to the
numerous soil functions (e.g. soil erosion) is an evolving process. Soil quality indicators
refer to measurable soil attributes that influence the capacity of soil to perform crop
production or environmental functions.
________________________
(*) Contribution to the first step in the process of formulate an EU Soil Protection Strategy, as
adaptation and enlargement of the paper presented by D. de la Rosa in the Alicante SCAPE
Workshop (14 – 16 June 2003). Sevilla, 29 July 2003.
Soil quality encompasses physical and chemical besides biological soil properties.
Table 1 shows a set of soil quality indicators of specific relevance to soil erosion. Most of the
physical/chemical indicators (e.g. texture, stoniness, clay content, pH or cation exchange
capacity) are very fix and permanent in the time. On the contrary, the biological indicators
are very dynamic and exceptionally sensitive to changes in soil conditions such as those
produced by soil management practices. For example, enzyme activities has been found to be
very responsive to different agricultural practices such as no-tillage (Dick 1992). Likewise,
Garcia et al. (1998) found that restoration practices of degraded arid soils in marginal areas
strongly influenced by soil enzyme activities.
Table 1. Major soil quality indicators of specific relevance to soil erosion.
______________________________________________________________________
Soil attributes
______________________________________________________________________
Soil physical/chemical indicators
Growing season length, Slope, Useful depth, Texture, Stoniness, Clay content,
Organic matter, Carbonate content, Structure, Salinity, Sodium saturation, pH,
Cation exchange capacity, Bulk density, Infiltration rate, Porosity, Water retention,
Hydraulic conductivity, Surface roughness, Surface crusting, Workability status,
Topsoil pulverization, Subsoil compaction, Contamination risk
Soil biological indicators
Micro-organism population, Microbial biomass and respiration, Mycorrhizal association,
Nematode communities, Enzyme activities, Organic matter characterization
______________________________________________________________________
Unlike water and air quality, simple standards for individual soil quality indicators do
not appear to be sufficient because numerous interactions and trade-offs must be considered.
Soil quality evaluation tries to predict the natural ability of each soil to function, and land
evaluation tries to predict land behavior for each particular use. Land evaluation is not the
same as soil quality evaluation, basically because land refers not only to soil but to the
combined resources of soil terrain, climate, water and land use.
Also, the biological
parameters of the soil are not considered by land evaluation.
In this contribution, concrete measures to combat soil loss in agricultural lands,
with special reference to the Mediterranean region, are analyzed within two major topics: i)
land use planning, and ii) soil management recommendations. Also, soil quality decision
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support systems (DSS) are discussed as major tools to formulate for each particular soil the
sustainable land use and management system. By using these DSS systems (e.g. MicroLEIS;
De la Rosa et al., 2003) is the best way for compilation of measures of “good agricultural
practices” for prevention of soil erosion according to the within-region variability of soils,
climate, land use and socio-economic conditions.
2. Land use planning: Location of agricultural land and crop diversification
Criteria for restrictions to agricultural practices …
2.1. General land capability
Land use changes from native vegetation to intensively tilled agricultural
cultivation are one of the first reasons for soil degradation. Within a particular area, it is very
important the positive correlation between present land use and potential land suitability.
Agricultural marginal lands used to be the ideal scenario for soil erosion.
Normally,
increasing agricultural land capability correlates with a decrease in the soil erosion process.
The case of a Mediterranean region: Andalucia,
as shown in Tables 2,
the
relationship between present land use (current use) and agricultural capability land (potential
use) is clearly unbalanced (AMA, 1987). About 1 million of hectares of rainfed agricultural
lands must be changed to forestry, grazing or natural lands in order to get a better equilibrium
in comparation with the moderately or clearly marginal lands.
Table 2. Present land uses and land capability classes in Andalucia region.
______________________________________________________________________
Category
Estimated extension
Percentage
(103 ha)
(%)
______________________________________________________________________
Present land use
Irrigation agricultural lands
592
7
Rainfed agricultural lands
3,165
36
Forestry, grazing and natural lands
4,007
46
Others
936
11
Land capability class
S1 Excellent agricultural lands
535
6
S2 Good agricultural lands
1,735
20
S3 Moderately marginal lands
2,311
27
N Marginal and nule
4,073
47
______________________________________________________________________
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Secondly, the land use for settlement purposes: housing, commercial, industrial and
transport, is one of the main process causing irreversible loss of agricultural soils. In the
Mediterranean region, this loss affects mainly to the best agricultural lands of the river valleys
with traditional irrigated systems (“huertas”; Martinez, 2003). In order to change these land
use decisions, policy instruments must be developed which help achieve the soil protection
objective. For example, in Germany the federal government declared that by the year 2020 the
current land use for settlement purpose of 130 hectare per day should be lowered to 30 hectare
per day (Bizer, 2003). Also, precise measurements of restoration of the horizon sequence of
soil profile for subterranean conductions (e.g. gas pipelines and water infrastructures) would
be interesting to preserve the soil individuals.
2.2. Relative soil suitability
Within the agricultural lands, all soils can be used for almost all crops if sufficient
inputs are supplied. The application of inputs can be such that it dominates the conditions in
which crops are grown, such as it can be the case in greenhouse cultivation. However, each
soil unit has its own potentialities and limitations (soil suitability), and each crop its
biophysical requirements. In order to minimize the socio-economic and environmental costs
of such inputs, the second major objective of land use planning is to predict the inherent
suitability of a soil unit to support a specific crop for a long period of time. This kind of
studies provides a rational basis to diversify agricultural soil system considering all the
possible crops (De la Rosa and Van Diepen, 2002).
The soil key attributes used in land use planning for soil erosion, through the land
evaluation analysis, are mainly soil physical/chemical indicators (Table 1). Most of these
indicators (e.g. texture, stoniness, clay content, pH or cation exchange capacity) are very fix
and permanent in the time. The soil biological indicators are not used in land evaluation.
Therefore, the first land use decisions such as the identification of the marginal and
the best agricultural lands, can be really based on knowledge and information following the
traditional land evaluation analysis. In this sense, land use planning policy should relate
major land use to soil capability and soil suitability, for each particular site and socioeconomic context (Figure 1).
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3. Soil management recommendations: Formulation of tillage intensity
Identification of mechanical soil protection practices …
Soil tillage is need to prepare suitable seedbed to grow crops, to control weeds, and to
incorporate manures, fertilizers, pesticides and other amendments. At the same time, the
negative consequences of tillage practices strongly accelerate soil erosion process, by
destroying soil organic matter and soil structure. Inappropriate tillage practices accelerate the
soil degradation processes, especially soil erosion and compaction. To formulate the tillage
type and intensity for each particular soil is a critical point to combat the soil erosion problem
in the agricultural lands (De la Rosa el al., 1999).
In general terms, tillage systems can range from full width intensive tillage to zero
tillage (i.e. conventional tillage, reduced tillage, ploughless tillage, minimum tillage and
no-tillage). The most common intensive tillage system of dry farming consists of i) burning
the straw or stubble after harvest, ii) mouldboard ploughing to break the hardened soil
surface, and iii) many successive disking and harrowing to reduce soil clod size. This
conventional repeated tillage system accelerates decomposition of organic matter thus
affecting soil physical, chemical and biological attributes of soil quality. It is clearly
inappropriate for the most of the soils and must be avoided to combat soil erosion.
On the contrary, with the no-tillage system (direct showing), several studies show that
continuous organic matter increases and soil structure improves, restoring and improving soil
quality, crop yields increase, and soil erosion is controlled (e.g. Tebrugge and During, 1999).
However, other studies (e.g. Arshad, 1999) point out how the level of success in no-tillage
system varies with i) crop species, ii) soil type, iii) climatic conditions, and iv) growing
season length. It is clear that no-tillage has gained wide acceptance in Australia and North
and South America but, adoption of this technology has been very slow elsewhere.
In order to rationalize the soil tillage practices, a conservation tillage system,
formulated for each specific site in relation to the operation sequence, implement type and
intensity, would include the set of concrete measures against the soil erosion (Figure 1). In
spite of universal rules must not be done in relation to critical levels of
indicators (Table 1),
soil erosion
the following general comments are made for management
recommendations.
3.1. Soil erosion indicators vs. soil tillage
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Short growing season length (GSL < 250 days; e.g. in Scandinavia or Mediterranean
region) is considered a barrier to adoption of no-tillage system (Arshad, 1999). Growing
season length is determined by the temperature regime and the availability of water for each
soil and crop (FAO, 1978).
Also, high slope gradient ( > 15 %) appears to be a limiting factor to introduce notillage farming systems (Martinez-Raya, 2003).
Conventional implements (e.g. plow moldboard, or disk cultivator) which cause soil
inversion can be especially appropriate for high slope soils due to the elevate surface
roughness (> 30 mm). Increasing the surface roughness decreases the transport capacity and
runoff detachment by reducing the flow velocity. During a rainfall event rough surfaces are
eroded at lower rates than smooth surfaces under similar conditions. The soil workability
status for each tillage operation is very related with the produced surface roughness.
The soil workability status (“tempero”) is considered as the optimum soil water
content where the tillage operation has the desired effect producing the greatest proportion of
small aggregates (Dexter and Bird, 2001). Out of this interval the soil is too wet or too dry,
and therefore the tillage operation alters in an adverse way the soil physical properties and
facilitates the soil erosion. The topsoil pulverization by repeated tillage and under dry soil
conditions appears to have a very negative effect on the erosion. Finely pulverized soils are
usually smooth, seal rapidly and have low infiltration rates, as might be the case for some
rototilling operations or for repeated cultivations of silt loam soils under dry conditions.
These limits can be predicted in terms of soil composition through the use of pedotransfer
functions. In conclusion, the water workability limits for each soil and operation, or the
number of available work days for tillage, must be considered in order to reduce the soil
erosion effects.
With especial reference to Mediterranean region, in those soils with low infiltration
rate and prone to surface sealing the effects of no-tillage can increase runoff generation and
erosion problem (Gomez et al., 1999). For these climatic conditions, soil frequently have low
organic matter content and weak structure resulting in low infiltration rates. The best results
of no-tillage system seem to be obtained on the heaviest clay soils.
The increased density of the soil just beneath the depth of tillage (subsoil compaction)
is one of the most striking effects of management system, very specially ploughless tillage.
Increased soil bulk density reduces the air permeability, the hydraulic conductivity and
sometimes the root development. The subsoil compaction is caused by tillage and traffic with
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increasing weight agricultural machinery. This problem is especially severe in heavy-textured
and poorly drained soils. Subsoiling, deep ploughing, para-ploughing and numerous other
devices have been developed to alleviate the problems created by compaction.
The
compaction risk or vulnerability of agricultural soils, measured by the pre-compression stress,
can be used to give recommendations for site specific farming systems (e.g. implement type,
wheel load, and tire inflation pressure). Also, it can allow the agricultural machine industry to
develop site adjusted machines to support the ideas of good farming practices (Horn et al.,
2002).
Today, the use of new herbicides are drastically changing the methods of crop
production, without to know exactly their impacts on soil quality/degradation. Effective weed
management is identified as other limiting factor in the adoption of zero tillage system. In this
case, soil contamination risk by herbicides must be deeply analyzed because, ironically,
farming practices to remedy eroded soils can increase the soil degradation by contamination.
On the soil biological indicators, which are very dynamic and exceptionally sensitive
to changes in soil conditions, and especially with reference to their effects on soil erosion
much needs to be done. For example, to explore the potentiality of biochemical properties
(e.g. enzyme activities) in the assessment of soil quality, it is desirable to have a database of
these properties in native soils with late-successional vegetation from different ecosystems
around the world (Quilchano and Marañon, 2002).
4. Agro-ecological decision support systems: Soil quality evaluation and monitoring
Programs in training and transfer of technology, especially for farmers …
Emerging technology in data and knowledge engineering provides excellent
possibilities in the land use planning and soil management recommendations analysis. This
analysis basically involves the development and linkage of integrated databases, biophysical
models, computer programs, and optimization and spatialization tools, which constitute
actually the decision support systems (DSS; De la Rosa and Van Diepen, 2002).
In order to combat soil erosion, formulating the sustainable soil use and management
for each particular site (taking into account the local situations and the socio-economic
context), a decision support system results to be a basic instrument. Specially, the tillage
sequence and intensity must be specific for local conditions as presented in Figure 1.
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MicroLEIS (Mediterranean Land Evaluation Information System; De la Rosa et al.,
2003),
through its different land evaluation models, analyses the influence of selected
physical indicators on critical soil functions referred to land productivity: agricultural and
forest soil suitability, crop growth and natural fertility; and referred to land degradation: runoff
and leaching potential, erosion resistance, pollutants absorption and mobility, and subsoil
compaction. Therefore, this system appears to be an appropriate approach to develop the soil
physical quality evaluation. Since the lately 1980s, MicroLEIS has evolved significantly
towards an agro-ecological decision support system on Internet (Http://www.microleis.com).
Presently, this system is a set of useful tools for decision-making which can be applied
to a wide range of land productivity and land degradation schemes (Figure 2). The design
philosophy corresponds to a toolkit approach,
where many software instruments are
integrated: databases, statistics, expert systems, neural networks, Web and GIS applications
and other information technologies.
In order to follow the new framework of “soil quality evaluation”, the development
of relationships between all the soil quality indicators and the numerous soil functions (e.g.
soil erosion) is a monumental task. Within this complex contest, the agro-ecological decision
support systems may serve as a first step to develop a soil quality evaluation and monitoring
approach (Figure 3). Following this approach, agro-ecological land evaluation can be an
appropriate procedure for analyzing the soil physical quality from the point of view of the
long-term changes.
Then, a short-term evaluation and monitoring procedure can be
considered mainly for the soil biological quality. Therefore, the soil quality monitoring
would be based exclusively on the most sensitive soil biological indicators, after the
traditional land evaluation analysis by using basically soil physical indicators.
Evaluating and monitoring soil quality is a very complex undertaking. Knowledgebased decision support systems considering separately soil physical quality and soil biological
quality appear to be an appropriate way to formulate, for each unique soil, the best agricultural
practices to minimize land degradation processes such as soil erosion. On this important and
timely topic much needs to be done. The development and use of these computer-based tools
would be one of the major task of a possible EU Soil Conservation Service (e.g. USDA
Natural Resources Conservation Service, Http://www.nrcs.usda.gov).
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5. Main areas where research is needed
Data gaps and research needs related to the above tasks …
There are many unresolved problems referred to the important and timely topics tried
in this contribution. In that way, much more needs to be done by researchers on the impact of
soil use and management systems on soil properties, crop production and environmental
qualities; specially on the following main areas:
-
Sensitive biological indicators of soil quality to evaluate extensive/intensive agricultural
systems.
-
Interactions on soil tillage-soil quality. Possibilities of no-tillage in different ecosystems.
-
Effects of different climate change scenarios on the soil erosion problem.
-
Development and implementation of land use DSS tools to formulate sustainable soil use
and management systems. The use of information technology in agriculture, specially
based on the Internet in order to facilitate the dissemination of the “best agricultural
practices” analysis.
Bibliography cited
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environmental quality in different agroecosystems. Soil & Tillage Research 53: 1-2.
Bizer K. 2003. Economic instruments for protecting soils – a brief introduction. In: C. Boix,
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Dorren and A. Imenson (eds.), Briefing papers of SCAPE, Alicante.
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Imenson (eds.), Briefing papers of SCAPE, Alicante.
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De la Rosa D., Mayol F., Diaz-Pereira E., Fernandez M. and De la Rosa D. Jr. 2003. A Land
Evaluation Decision Support System on Internet (MicroLEIS DSS) for Soil Protection.
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Local conditions
Climate + Terrain + Soil + Water + Land use
and
Socio-economic context
DSS
Soil quality
decision support system
Land use planning
Optimum land uses + Vulnerability areas
Management practices
Crop rotation + Row spacing + Contour tillage
+ Plot size + Residues treatment + Irrigation
+ Operation sequence + Operation number
+ Implement type + Wheel load + Tire inflation
+ Soil workability time
Figure 1. Set of concrete measures against the soil erosion to be formulated for each specific
site by using DSS tools, in order to rationalize the soil tillage practices.
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Figure 2. Conceptual design and components integration of the current status of MicroLEIS
agro-ecological decision support system for sustainable soil use and management
(Http://www.microleis.com)
13
Figure 3. General approach to formulate sustainable soil use and management strategies
developing soil quality assessment on the basis of land evaluation analysis.
14