Simulation of CO2 Exchange and Plant Growth in Temperate European Grasslands: Some Lessons
for Modeling Carbon Sequestration in Tropical Ecosystems
S.G.K. Adiku, J. Tenhunen and M. Reichstein
A canopy flux-growth model, PIXGRO, is described that combines recent advances for observation and
modeling of net ecosystem CO2 exchange with classical approaches in crop growth modeling. The model is
applied to temperate European grassland ecosystems, utilizing data from two sites in Austria and one in
Finland for parameterization and five sites in Austria and Germany for model validation. The model
responded sensitively to management measures, and it simulated GPP, biomass accumulation, and LAI
development well for intensively managed meadows. The correct pattern in seasonal change was obtained
for extensive meadow sites, but output variables were overestimated, demonstrating the need for reparameterization to account for lower canopy nitrogen.
Simultaneous examination of the field data and simulated change in carbon pools with PIXGRO calls
attention to a critical need for appropriate sampling of aboveground and below ground carbon pools in
ongoing studies of NEE at long-term grassland observation sites, and emphasizes the need for improved
time resolution in these observations as well as quantification of spatial heterogeneity. With such
documentation, grasslands provide an opportunity for improving our capacity for up-scaling of results from
plot studies by linking aboveground structural changes to remote sensing indices and for understanding
agricultural impacts by linking belowground development of root systems to hydrological models. The
validated coupling of canopy processes and growth in PIXGRO will aid in analyzing climate change and
management influences on inputs of carbon to soils and on grassland carbon balances. Validating this
approach for tropical ecosystems should enable the assessment of various plant management on carbon
sequestration under tropical conditions.
Economic Potential for Soil Carbon Sequestration
in the Nioro Region of Senegal’s Peanut Basin
J. Antle, B. Diagana, J. Stoorvogel, K. Gray
This paper presents preliminary results from an analysis of the economic potential for soil carbon
sequestration in the Nioro region of Senegal’s Peanut Basin. This analysis was based on the integration of
bio-physical models and economic simulation models using the Tradeoff Analysis System software.
Available soils and climate data were used to implement the DSSAT/Century models to estimate crop
yields and changes in soil carbon stocks under scenarios of increased fertilizer use and increased
incorporation of crop residues in a peanut-millet rotation. Data from the 2001 farm survey conducted by
the Ecole Nationale d’Economie Applique were used to parameterize an econometric-process simulation
model for the peanut-millet production system. These data showed that more than half the farmers are
using low fertilizer application rates. The economic simulation model was designed to simulate a carbonpayment scheme that requires farmers to apply higher fertilizer rates and/or incorporate additional crop
residues into the soil. The results show that increasing fertilizer use alone would result in a low potential
for soil carbon sequestration, but that the combination of increased fertilizer use and crop residue
incorporation could result in the sequestration of marketable quantities of carbon. The paper concludes
with a discussion of the farm-level economic constraints and institutional factors that need to be addressed
to further assess the potential for carbon sequestration in the region.
1
Analyzing Potential Increases in Productivity and Soil Carbon Using Rotational Grazing
O. Badini, C. Stockle, A. Kodio, J.W. Jones, M. Keita
It is hypothesized that rotational grazing will increase both soil carbon and pasture biomass production.
Preliminary data from Mali indicate that soil carbon levels are higher under pastures than croplands. By
allowing more biomass to grow during periods (weeks) with no livestock grazing, plants will grow more
roots and more aboveground mass will be added to the soil. A rotational grazing area (150 ha) has been
established in Torokoro, Mali to test that hypothesis. However, it could take several years to experimentally
evaluate whether soil carbon levels are indeed increasing as hypothesized. Therefore, a simulation analysis
was performed to evaluate the potential changes in production and soil carbon to assess critical factors that
might affect the performance of this community-based management practice. The CROPSYST model was
adapted for simulating pasture in the Torokoro area. Data from pasture sampling in Mali and Burkina Faso
were used to establish pasture production parameters. The detailed soil map and weather database
developed under the SANREM project for the Madiama area was used as inputs to the model. Management
consisted of continuous grazing, no grazing, and different frequencies of grazing return periods to the 150
ha area. Simulated results compared were total area biomass productivity per year, livestock grazing
capacity, and soil carbon changes over a 25-year period of simulation. Results are presented as scenarios
that could be used in discussions with community leaders relative to implications of different grazing
practices on short and long term productivity as well as soil carbon.
Long-term Effects of Crop Rotations with Groundnut or Fallow on Soil N Availability, N Fertiliser
Use Efficiency, Soil Organic Carbon and Crop Yields in the Guinean Zone of West Africa:
B.V. Bado, A. Bationo; F. Lompo; M.P. Cescas; M.P. Sedogo
The effects of annual fallow and groundnut (Arachis hypogea) on soil N fertility, N fertiliser recovery and
subsequent sorghum (Sorghum bicolour) and cotton (Gossypium sp) yields were studied using an 11 years
old (1993-2003) field experiment, curried out in the agronomic research station of Farakô-Ba (4o 20’ West,
11o 6’ North and 405 m altitude), located in the in the Guinean zone of Burkina Faso. A factorial 4x8
design in a split plot arrangement was used. Three sequences of rotation were used as first factor. CottonGroundnut-Sorghum, Groundnut-Cotton-Sorghum and Fallow-Sorghum rotations were compared to
continuous cultivation of sorghum. Each main plot was split in 8 sub plots and 8 fertilizer treatments
(mineral NPK fertilizer, NPK+Crop Residues, NPK+Dolomite, PK+Crop Residues, PK+Manure,
PK+Compost, PK and Control) were applied as second factor.
Crop yields were significantly affected by fertiliser and crop rotations but interaction was not observed
between the two factors. Mean annual yields of succeeding sorghum increased from 547 kg ha -1 in
continuous sorghum to 912 and 1021 kg ha-1 in Fallow-Sorghum and Cotton-Groundnut-Sorghum rotations
respectively. Soils of Fallow-Sorghum and Cotton-Groundnut-Sorghum rotations provided more nitrogen
to sorghum and increased fertilizer N fertiliser use efficiency from 13, and 32 units respectively compared
to continuous sorghum. Soil organic carbon was also affected by crop rotations. Soil organic carbon
increased from 0.36% in continuous sorghum to 0.39 and 0.54% in Cotton-Groundnut-Sorghum and
Fallow-Sorghum rotations respectively. Compared to the original soil, continuous sorghum and CottonGroundnut-Sorghum rotations decreased soil organic carbon. However, only Fallow-Sorghum rotation
maintained soil organic carbon at same lever like that of the original soil.
2
Carbon and Communities: The use of analytical hierarchies
in the assessment of community viability in the application of soil carbon sequestration efforts
P. Bartel
Soil carbon sequestration offers an opportunity to link natural resource management to rural economic
livelihoods. The primary benefit from such an effort will result from increases in productivity derived from
enterprises related to natural resource management and agricultural production. The potential for carbon
offset trades may offer a means to overcome opportunity costs from the implementation of sustainable
practices.
Experience in Senegal indicate that emerging carbon offset trading mechanisms require significant levels of
social organization in order to aggregate sufficient carbon stocks to be attractive for trade agreements. A
tool is presented demonstrating the causal factors for consideration in community organization for
participation in such an effort. Examples from Senegal are used to demonstrate the utility of such an
approach. This approach will provide an assessment tool for targeting suitable communities as well as a
management tool for tracking the strengths and weaknesses of programs as they are implemented.
Soil Organic Carbon Dynamics, Functions and Management in West African Agro-ecosystems
A. Bationo, B.Vanlauwe, J. Kihara , and J. Kimetu
Soil fertility depletion (mainly N, P and carbon) has been described as the single most important constraint
to food security in West Africa. Over half of the African population is rural and directly dependent on
locally grown crops, 28% of the population is chronically hungry and over half of people is living on less
than US$ 1 per day as a result of soil fertility depletion.
Soil organic carbon (SOC) is simultaneously a source and sink for nutrients and plays a vital role in soil
fertility maintenance. In most parts of West Africa agro-ecosystems (except the forest zone), the soils are
inherently low in SOC. The low SOC content is due to the low shoot and root growth of crops and natural
vegetation, the rapid turnover rates of organic material with high soil temperatures and fauna activity
particularly termites and the low soil clay content. With kaolinite as the main clay type, the cation exchange
capacity of the soils in this region often less that 1 cmol kg-1, depends heavily on the SOC. There is a rapid
decline of SOC levels with continuous cultivation. For the sandy soils, average annual losses may be as
high as 4.7% whereas with sandy loam soils, losses are lower, with an average of 2%. To maintain food
production for a rapidly growing population application of mineral fertilizers and the effective recycling of
organic amendments such as crop residues and manures are essential.
Crop residue application as surface mulch can play an important role in the maintenance of SOC levels and
productivity through increasing recycling of mineral nutrients, increase in fertilizer use efficiency, and
improvement in soil physical and chemical properties and a decrease in soil erosion. However, organic
materials available for mulching are scarce giving the low overall production levels of biomass in the
region and their competitive use as fodder, construction material and cooking fuel. Animal manure has
similar role as residue mulching for the maintenance of soil productivity but it will require between 10 and
40 ha of dry season grazing and between 3 and 10 ha of rangeland of wet season grazing to maintain yields
on one hectare of cropland. The potential of manure to maintain SOC levels and maintain crop production
in thus limited by the number of animals and the size and quality of the rangeland. The potential livestock
transfer of nutrients in West Africa is 2.5kg N and 0.6kg P per hectare of cropland.
Scarcity of organic matter calls for alternative options to increase its availability for improvement of SOC
stock. Firstly, the application of mineral fertilizer is a prerequisite for more crop residues at the farm level
and the maintenance of soil organic carbon in West African agro-ecosystems and therefore most research
should focus on the improvement of nutrient use efficiency in order to offer to the small-scale farmers costeffective mineral fertilizer recommendations. Secondly, recent success story on increasing crop production
and SOC at the farm level is the use of the dual purpose grain legumes having ability to derive large
proportion of their N from biological N fixation, a low N harvest and substantial production of both grain
3
and biomass. Legume residues can be used for improvement of soil organic carbon through litter fall, or for
feeding livestock with manure being returned to the crop fields.
In the decision support system for organic matter management, recommendation for appropriate use of
organic material was made based on their resource quality, expressed as a function of N, polyphenol and
lignin content. High quality organic materials release a high proportion of their N quickly. The impact of
organic resource quality on SOC is less clear. Low quality organic resources contain substantial amounts of
soluble polyphenols and lignins that may affect the longer-term decomposition dynamics and contribute to
build up of SOC. Future research need to focus more on whether the organic resource quality concept is
also useful for predicting different degrees of stabilization of applied organic C in one or more of the
organic matter pools.
ACdN Technology Development and Adoption/Diffusion in Southern Mali: Approaches Used,
Lessons Learned and Perspectives
A. Berthé, M.Doumbia, C. Roncoli, R. Kablan, R. Yost and C. Neely
In the past, technological progress in Sub-Saharan Africa was not sufficient to meet the rapidly increasing
demand for food. Although innovations developed by research may have a high technical performance they
are either not adopted or are not properly used by the African smallholders. Apart from their complex
farming systems, structural deficits within the national extension and research system and the poor farmer
responsiveness of agricultural research are mentioned as major reasons for the poor success.
This paper discusses different ways use by a National Agricultural Research Systems (NARS) to make
farmers more responsive to research and development action on “Amenagement en Courbes de Niveau
(ACdN)” a natural resource management technology. To begin with, direct and indirect benefits of ACdN
for farmers and the state are discussed. It is explained that agricultural research can only create a positive
impact when its results are adopted by the target group. Following on this, different ways are discussed to
make NARS more farmer-responsive. The discussion refers to the participation of farmers in governance,
financing and evaluation of agriculture research and priority setting. The advantages and disadvantages of
the different mechanisms are discussed and challenges for technical assistance derived.
In future, technical assistance should engage more in the strengthening smallholders’ organizations. These
should be supported in their efforts to acquire the technical knowledge, management skills and political
influence necessary to represent the interests of smallholder farmers appropriately. A further challenge is to
establish incentive systems within NARS which encourage co-operation with farmers. This would imply
that the researchers’ performance is measured against the relevance of their work for the target group and
impact achieved at the farm level. Finally, technical assistance should concentrate on the promotion of
partnerships between the different stakeholders. In this respect, NARS should be supported in their efforts
to become more attractive for potential partners.
4
ACdN Technology Research and Adoption/Diffusion in the Dry Savannah of Mali
A. Berthé, M.Doumbia, C. Roncoli, R. Kablan, R. Yost and C. Neely
In the past, technological progress in Sahel Africa was not sufficient to meet the rapidly increasing demand
for food. Although innovations developed by research may have a high technical performance they are
either not adopted or are not properly used by the African smallholders. Apart from their complex farming
systems, structural deficits within the national extension and research system and the poor farmer
responsiveness of agricultural research are mentioned as major reasons for the poor success.
This paper focus on a case study on technology development and transfer of “Amenagement en Courbes de
Niveau (ACdN) in Southern Mali. The potential effects of ACdN based on farmers’ and scientists’ criteria
are discussed. Constraints to the adoption and diffusion of ACdN are also analyzed and recommendations
are made to foster participatory technology development and transfer involving stakeholders. It is explained
that agricultural research can only create a positive impact when its results are adopted by the target group.
Following on this, different ways are discussed to make NARS more farmer-responsive. The discussion
refers to the participation of farmers in governance, financing and evaluation of agriculture research and
priority setting. The advantages and disadvantages of the different mechanisms are discussed and
challenges for technical assistance derived.
Amenagement en Courbes de Niveau” or Ridge Tillage Increases Soil C
Through Increased Soil Moisture Capture and Storage in Mali: Part 2.
K. Brannan* R. Kablan, R. Yost, A. Yorote, Y. Toloba, S. Sissoko, M. Vaksman, M.Doumbia
Soil moisture data from a field study was used to investigate the effect of the “amenagement en courbes de
niveau aka ACN” practices on soil moisture storage, runoff and deep percolation. Two treatments were
applied in two locations (Siguidolo and Fansirakoro) including ACN and control. Thirty two Diviner 2000
PVC access tubes were installed vertically from 10cm up to 160cm in two replications of 6 and 4 tubes per
plot, in Siguidolo and Fansirakoro, respectively. In each of the ACN treatments, 4 access tubes at random
distances across the slope but at equal distances above the ADOs. In Siguidolo two additional tubes were
installed at both the lower and upper slopes of the ADOs. Readings were taken regularly over the growing
season from June 27 to September 19 for a total of 36 readings of soil profile water content. Tipping-bucket
rain gages were installed at each location for monitoring of rainfall. Soils data were also collected at each
site for characterization of soil carbon and moisture. Finally, meteorological data from nearby stations were
used for calculation of evapotranspiration. The observed data was used to estimate a simplified water
balance for fields with and without ACN. Preliminary results of this study will be presented and methods
will be discussed in this paper. Since this is the first season of the multi-year study, only qualitative
information is presented. The main focus of this qualitative analysis is the estimation of deep-percolation
for the fields at Siguidolo with and without ACN. Generally, the fields with ACN had a larger amount of
deep percolation than the fields using conventional management. The deep percolation for the fields was
estimated using a form of Darcy’s equation and the soil moisture readings from the Diviner 2000
instrument. Future work will include a complete water balance for each field and runoff will be compared
for fields with and without ACN. Increasing deep percolation on agricultural fields is important for both
local water resource management and carbon sequestration. The increase in deep percolation will increase
the recharge of local groundwater resources, which villagers rely on through wells as their sole drinking
water source. Also, reductions in surface runoff and the re-direction of that water into the ground will
reduce the potential disturbance and loss of soil-carbon from the soil surface. The potential benefits of the
ACN with respect to both soil carbon sequestration and water resource management may be great and
through this work we hope to provide quantitative evidence of these benefits.
5
Enhancing Integrated Soil Fertility Management Through C-sequestration to Combat Resource
Degradation in Overpopulated Sahelian Countries
H. Breman, A. Mando and M. Wopereis
The present and potential above and below ground carbon stocks in Sahelian countries, and conditions and
processes of change are known well enough to quantify potential C-sequestration levels. Socio-economic
and policy environments are in general such that farmers’ practices lead to resource degradation and
decreased carbon stocks, as they are (in short and medium term) more profitable than sustainable practices.
Enhancing integrated soil fertility management through C-sequestration could be a solution for this
problem. Overpopulation being a crucial element of the Sahelian conditions, the use of mineral fertilizers is
required. However, in extended regions and for many crops, in particular for the staples of the poor,
fertilizer use is not profitable (enough) for farmers’ adoption and is not environmentally sustainable.
Integrated soil fertility management, i.e. combined use of locally available organic resources and judicious
use of mineral fertilizer) can change this, leading to rapid improvement of fertilizer use efficiency and
profitability through improved soil organic matter status. IFDC is effectively promoting it in Sahelian
countries and in West Africa as a whole, working through stakeholder platforms organized at all levels,
from villages to supra-national.
The unfavorable socio-economic and policy environments limit the use to regions and crops for which
fertilizer use is already profitable. IFDC developed strategic site selection to identify such conditions, and
promotes integrated soil fertility management as a tool to enlarge such regions and to extend the
profitability of fertilizer use to more crops.
Combined use of C-sequestration and integrated soil fertility management will enhance this tool, enabling
to tackle resource degradation by profitable use of fertilizer for still larger regions and more crops. Benefits
from C-sequestration will make it easier for small holders to take the risk of replacing soil mining practices
by more sustainable integrated soil fertility management technologies.
The optimal organic matter quality for maximum C-sequestration differs from the optimum quality for
integrated soil fertility management. A compromise has to be defined; each of the processes on its own has
limited recommendation domains, which shrink to almost zero if poverty reduction and environmental
stability on marginal land are added as criteria.
Small holders and farmers on marginal land cannot take risks. Prudence is called for when promoting
alternative agricultural practices among them. Trial and error approaches are unacceptable in view of their
limited resources and of the limited speed of processes leading to increased above and belowground carbon
stocks. Scientific evaluation of potentials and modeling and simulation are therefore indispensable tools for
the participatory identification, development and validation of likely options for change.
The paper will summarize the potential for above and belowground C-sequestration in Sahelian countries.
It will present IFDC’s insight in integrated soil fertility management, e.g. the analysis of results of long
term soil managements trials, in which different organic sources and fertilizers are used on their own and in
combination. Another element concerns the use of modeling and simulation, linking soil organic matter
dynamics and agricultural development.
6
Assessing, Measuring, and Monitoring Carbon Sequestration from Changes in Land Management
S. Brown
Through changes in land management, humans have the potential to change the direction and magnitude of
the flux of carbon dioxide between the land and atmosphere while at the same time providing multiple
benefits to meet environmental and socioeconomic goals of sustainable development. One of the first steps
that needs to be considered by interested parties is an assessment of the potential for carbon sequestration
(considering both biophysical and socioeconomic factors) for a given suite of activities being considered to
meet development goals; such an approach will be presented for Guinea. A key aspect for implementing
carbon sequestration projects is then to accurately and precisely measure and monitor project-level carbon
benefits. Winrock has developed and tested a toolbox of methods for measuring individual carbon pools in
land-use and forestry projects. In this presentation, I will demonstrate how these tools and techniques have
been applied to forestry projects in a variety of tropical environments to estimate the carbon stocks to
within less than 10% of the mean with 95% confidence at modest costs. I will also show how advances in
very-high resolution digital imagery systems are showing promise for providing a cost-efficient means for
monitoring carbon in a variety of forest project types.
Remote Sensing and Ecological Modeling for Assessing C Sequestration
in Semiarid Grassland Soils
R.T. Conant, R.B. Boone, and M.K. Ngugi
A key component for sustaining production in grassland ecosystems is the maintenance of soil organic
matter (SOM), which can be strongly influenced by management. Many management techniques intended
to increase forage production may increase SOM, thus sequestering atmospheric C. Likewise, SOM losses
can potentially be reversed, and atmospheric C sequestered, with adoption of improved range management
practices. Further, conversion from either cultivation or native vegetation into managed grassland could
also sequester atmospheric C. Assessing C sequestration rates requires (1) information about past and
current land use/management practices and (2) the means to translate range management information into
estimates of CO2 fluxes. We have developed such as system within the central North American Great
Plains using a mechanistic biogeochemical model driven by remotely sensed data. Our system consists of a
production efficiency model that estimates plant CO2 uptake and is linked to a SOM model derived from
the Century model. The production efficiency model is driven by frequently available moderate resolution
(MODIS) satellite data. The plant primary production sub-model dynamically allocates C to above- and
belowground structures based upon foliage removal rates by grazers and plant water and nutrient demand.
Field-level model validation in the US will be completed during the 2004 growing season and region-wide
assessments will then be carried out. The global availability of MODIS data coupled with our model-based
approach ensures that US results are applicable to other semiarid regions. We discuss how integrated
assessments in East Africa inform grassland managers, and potential applications in the Sudan-Sahelian
region.
7
Modeling Soil Spatial Variability for C Stocks Estimation
at the Field Level and Considerations for Scaling Up.
L. Delisle, S. Traore, A. Ballo, M. Doumbia, R.Yost*.
Quantification of soil organic C for the field surface is a critical step in developing a soil C accounting
system to make soil C available for the C offset trading market. This calculation requires several steps
including the efficient sampling of soil C, determining area and volume of the field as a preliminary step
before scaling up to a regional level. Geostatistical techniques of kriging and spatial analysis were used to
convert point samples to area and volume estimates of C. Three questions were addressed: 1) What
differences does it make to consider the spatial variability of soil C? 2) How much difference does it make
to consider the effect of slope on the soil C tonnage calculations? and 3) What software tools appear most
suitable for the calculation? The results indicate that considering the spatial variability was not particularly
significant. This indicates that simple measures of soil C such as the mean may be sufficient to estimate C
tonnages. The effect of slope seems to make only a minor difference unless the land is extremely steep.
Several software packages are available for automatic area and volume estimation, that fit particular
computational needs at the field level and beyond. While grid based interpolators such as Surfer excel in
the representation of continuous surfaces characteristic of random variability within fields, ArcGIS and
similar vector software are preferred to scale up estimates at landscape scales where systematic variability
is predominant.
Soil Carbon Sequestration and Rural Livelihoods in Drylands: A Pilot Study from Senegal
D. Diouf and P. Tschakert
This paper documents the results of a two-year pilot project in the Old Peanut Basin of Senegal, assessing
real project opportunities for both carbon investors and local smallholders. Total system carbon, measured
in 2001 on cultivated fields and land under fallow, varied between 12.7 t ha -1 and 59.3t ha-1. Carbon
simulations with CENTURY suggest potential sequestration rates ranging from 0.06–0.43tC ha-1 yr-1 under
various land use and soil management scenarios. Highest annual carbon gains can be expected from longterm improved fallow, tree plantations with Faidherbia albida, and agricultural intensification. However,
results from a farmer-centered cost-benefit analysis indicate that the majority of farmers, especially those
with low resource endowment, are most likely not able to implement these practices, due to lacking
investment capital. Net present values varied between -2,000 $ ha-1 and +2,500 $ ha-1, also showing less
possibilities for poorer households.
Focusing on household assets and existing adaptive responses of smallholders to an uncertain environment
provides a practical entry point for carbon sequestration projects, by linking stakeholders’ concerns, more
sustainable land use and management practices, and potential financial and livelihood gains in the future.
Coupled carbon-development projects should offer baskets of management choices and technologies from
which farmers can choose depending on their needs and capacities. Together with carefully designed costsharing mechanisms, such an approach is more likely to assure local interest and participation. It may
strengthen flexible, diverse, and adaptive livelihood strategies, and, thus, enhance the resilience of local
resource management systems in the long run.
8
Remote Sensing and Modeling of Soil Carbon Sequestration in Agricultural Lands of Mali.
P. Doraiswamy, G. McCarty, E. Venteris, M. Doumbia,
R. Hunt and A. Franzluebbers
Agriculture in sub-Saharan Africa is a low-input low-output systems of agriculture which maintained
Africa at subsistence levels but is no longer able to feed the people. In addition, there are the associated
problems of land degradation accelerated by low-input systems which in some instances has exceeded the
resilience threshold of soils. The Carbon from Communities Project in Mali was carried out in several sites
to study the potential for increasing levels of soil carbon and the potential for increasing soil quality to
improve crop production. The objective of this research was to use satellite remotely sensed imagery for
mapping current landuse and to assess impact of different land management on soil productivity and crop
yields. High resolution imagery from Quickbird in combination with lower resolution SPOT HRV and
Landsat ETM imagery were used to develop a landuse classification for a study area (8x 8 km) near
Konobougou. Ground truth data was acquired from site visits. Field sizes were small and the best
available combination of temporal, spatial and spectral resolution imagery was utilized to develop a landuse
map. Based on the classification, and available climate, soil texture, in-situ soil carbon measurements and
crop statistics data, a soil carbon sequestration model was used to map the current and potential levels of
soil carbon for the various landuse. Spatial parameters derived from remotely sensed data were integrated
in models for crop yield and soil carbon simulations. Modeling techniques provide an opportunity to
optimize production levels by adapting alternate management practices and predicting future crop yields
and potential levels of soil carbon sequestration.
Capturing Water for Food and Carbon Sequestration
M. Doumbia*, R. Yost, J. Gigou, H. Coulibaly, A. Yoroté, A. Berthé, A. Bagayoko,
Y. Toloba, P.C.S. Traoré, R. Kablan, and K. Brannan
The loss of rain water is one the key constraints to food security, combating desertification, and
environmental rehabilitation in Mali as well as in many other countries of the Sahel region of West Africa.
In addition to low crop yields, losses of soil and water, specifically runoff, takes away about 40% of
nutrients applied to soil, costing the farmer an annual average of US$20. Losses to soil degradation in Mali
have been estimated to be about US$1.84 millions in 1988. These losses will reach US$12.4 millions in
year 2005 if proven technologies are not widely used. An emerging technology, known as ‘aménagement
des champs en courbes de niveaux’ (ACN) or ridge-tillage along contour lines is being adopted by farmers
(+ 10,000 ha) to alleviate these effects. The purpose of this paper is to review ACN and its impact on
carbon sequestration.
Capturing water through ACN has increased crop yields by 30% (cotton, maize, sorghum and millet). Yield
increases have reached 50% when the practice was combined with the appropriate fertilizers. Yield
increases have essentially been attributed to reduced runoff (20 to 40% reduction) and a deeper wetting
front (increasing from 1.2 to 2.0 m). In addition, native plant species, which may have disappeared due to
water stress, are emerging in plots under ACN. Furthermore, ACN is believed to increase drinking water
through infiltration of more water to the ground water table (as indicated by the rise of the water level in
wells). Furthermore, ACN is believed to increase the oil production from the ‘shea butter’ tree (Vitellaria
paradoxa).
Research is being conducted to determine the effects of ACN on soil organic carbon (SOC) content under
various conditions (soil fertility, cropping systems, rainfall, duration of the ACN, reduced tillage, crop
residues management, etc.). There are strong tendencies of ACN to increasing SOC. SOC increased from
0.23% (in 2000) to 0.28% (2002) in Zan Diarra’s fields at Konobougou. SOC increased from 0.22 to 0.30%
in four years of cotton-cereal cultivation under ACN at Konobougou.
9
In order to assist farmers with the implementation of ACN, and the adoption of ‘C-4 technologies’,
community organization and development is needed. The community-level effects of ACN on food
production, rural income, and environmental rehabilitation should be quantified.
Shea Butter Tree (Vitellaria paradoxa) Stocks Carbon and Improves Soil Fertility
J Gigou , K. Traoré, R. Oliver, F. Ganry
In farmer’s field, trees (mainly shea butter trees) are associated with crops and then constitute a landscape
of “shea butter tree parkland”. In the region of Fana, on a slope of 1-4 %, trees are numerous at the bottom
of the catena. In this position, the parkland is dominated by the shea butter trees (23 trees ha -1 out of 24)
that cover 8% of the area. At the top and middle of the catena, trees are less numerous and derived from
several species of which there are fewer shea butter trees.
Consequently, at the bottom of the catena trees restore an important quantity of nutrients to the soil: 35 kg
CaO ha-1, 8 kg MgO ha-1, 4,5 kg K2O ha-1 et 9 kg N ha-1. These contributions are similar to those from
mineral fertilisers, mainly CaO and MgO that can prevent soil acidification.
These trees sequestrate about 15 t ha-1 of C in their aerial biomass. The  13C study showed that organic
matter from the shea butter tree influences the soil at 2.5 times the radius of the tree canopy. But the global
increase of soil carbon due to trees is not higher than 1 t ha -1.
So, the shea butter trees improve soil fertility in cultivated land and stocks carbon at the bottom of the
catena. Is it possible to improve the tree parkland with other species when ensuring rain water conservation
in order to obtain comparables effects at the top and middle of the catena ?
10
A Farm-level Analysis For Carbon Sequestration in Ghana Using IMPACT
Linked with the DSSAT-Century, Household and Ruminant Models
E. González-Estrada, V.K. Walen, J. Naab, P.K. Thornton and M. Herrero
The paper describes a preliminary study on potential effects of alternative management practices for carbon
(C) sequestration at the farm level. In 2003, data were collected from three farms in the Upper West region
of Ghana, to produce a farmscale characterization with biological, social and economic elements. This was
carried out using a generic tool for data collection on crop-livestock systems called IMPACT (Integrated
Modelling PlAtform for Crop-livestock systems in the Tropics). IMPACT was used to produce a base-line
analysis of current C balances for each farming system and an assessment of the households’ economics
and nutrition. These data were subsequently linked to the Household optimization model that quantified C
balances under an “optimal management” scenario in which income is maximized and food security
achieved. Further analyses were carried out linking the DSSAT-Century cropping system model and the
Ruminant performance simulation model to study the effects within the farm from alternate strategies.
These two models produced response curves that described a range of possible interactions between
management of crop residue, manure and livestock. In general, increased manure application to crops
improved both soil C and grain yields. Retaining crop residues in the field had a greater effect on C
sequestration but optimal results were related to a reduction of herd sizes due to limited biomass
availability. Special attention should be paid to the consequences that changes in resource allocation could
have on the overall functioning of the farm. Future work will involve assessing the impacts of management
changes on household well-being indicators (food security and income).
Ridge Tillage for Carbon Sequestration in the Gambian Cropping Systems
A.K Jarju, B. Jobe, F.S. Fatajo, M.N Faye, A. Bittaye
C. Yamoah, R. Kablan, R. Yost
Organic matter content in the Gambian farmlands is Low and generally less than 1%. Increased oil carbon
has been unequivocally proven to be beneficial to the Sahelian zone cropping systems because of its
moisture and nutrient retention properties. Based on this, an experiment was set up in the Gambia to test
the hypothesis that, ridge tillage, noted for its water conservation features plus modest fertilization,
increases crop yield. The experiment was a split plot design with three replications. Main plots were ridge
tillage and conventional tillage. Subplots were four fertilizer rates: 1) check with no fertilizer, 2) half the
national recommended rate, 3) full the national recommended rate, and 4) double the national
recommended rate. Abnormality of the weather pattern in 2002 delayed planting to mid August and
resulted in partial crop failure. Results in 2003, showed that fertilizer significantly increased maize yields
(P<0.0001) but not tillage. Averaged across fertilizer rates, maize yields were 940 kg ha -1in ridge tillage
and 920 kg ha-1 in the conventional tillage (P>0.05). Interaction between fertilizer and tillage was
significant at the 10% probability level (P=0.08), meaning that tillage partly influenced fertilizer positively.
It was calculated that, if maize stover is incorporated in the soil after harvest, between 0.65 t ha -1 and 3 t ha1
carbon may be sequestered annually. Over 150 farmers, who were linked to the studies, opted for the
lowest fertilizer rate based on economic considerations. From 2004 and beyond, these farmers will serve as
focal points in order to assist their neighbors to implement ridge tillage on their own farms.
11
A Framework for Integrating Remote Sensing, in situ Sampling, and Biophysical Models
for Monitoring Soil Carbon Sequestration
J.W. Jones, S. Traore, J. Koo, M. Bostick, M. Doumbia, J. Naab
Participating in carbon markets could provide farmers in developing countries the incentives they need to
improve land management, however carbon traders need assurances that contract levels of carbon are being
achieved. Thus, methods are needed to monitor and verify soil carbon changes over time and space to
determine whether target levels of carbon storage are being met. Because direct measurement of soil carbon
changes over the large areas needed to sequester contract amounts of carbon is not possible, other
approaches are necessary. An integrated approach is described in which an Ensemble Kalman Filter is used
to assimilate remote sensing data and in situ soil carbon measurements into stochastic biophysical models
to estimate soil carbon changes over time and space. The approach takes into account errors in in situ and
remote sensing data as well as uncertainties in the biophysical models to estimate mean and variance of soil
carbon for each uniform land unit within a larger land area. It also provides estimates of area-wide
aggregate soil carbon mean and variance values at each point in time. The approach requires initial values
of soil carbon over space along with its spatial statistical characteristics. Over time, model predictions are
made, remote sensing and in situ measurements update these predictions using maximum likelihood
methods, and the spatial pattern of soil carbon thus evolves. In this paper, examples are given to
demonstrate the approach for a large, heterogeneous area, emphasizing uncertainties in aggregate estimates
of soil carbon changes over time and information needed to implement this approach.
“Amenagement en courbes de niveau” or Ridge tillage Increases Soil C
Through Increased Soil Moisture Capture and Storage in Mali, Part 1
R. Kablan*, K. Brannan, R.Yost, A. Yorote, Y. Toloba, S. Sissoko, M. Vaksman, M. Doumbia
In the Sahel, the production of food crops takes place despite limited variable and often deficient rainfall on
soils with inherent low organic matter content and low water holding capacity. A field study was initiated
to determine the effect of the “amenagement en courbes de niveau aka ACN” practices on soil moisture
storage, its utilization by crops in relation to yield and soil carbon change. Two treatments were applied in
two locations (Siguidolo and Fansirakoro) including ACN and control. Thirty two Diviner 2000 PVC
access tubes were installed vertically from 10cm up to 160cm in two replications of 6 and 4 tubes per plot,
in Siguidolo and Fansirakoro, respectively. In each of the ACN treatments, 4 access tubes at random
distances across the slope but at equal distances above the ADOs. In Siguidolo two additional tubes were
installed at both the lower and upper slopes of the ADOs. The calibration of the Diviner was carried out
using gravimetric samples. Readings were taken regularly over the growing season from June 27 to
September 19 for a total of 36 readings of soil profile water content.
For both sites, there was soil moisture storage throughout the soil profiles independent of tube locations
where ADOs were present. Soil moisture stored in the ACN system mostly in deeper profiles (>100cm)
was consistently higher than that of control, indicating that in addition to capture of earlier rains, ACN
treatment was effective in capturing water during the season. Similarly, soil moisture stored between
adjacent tubes between ADOs and near the vicinity the ADOs appeared to increase from the lower slope
ADO to the upper slope ADO, indicating soil moisture within two ADOs was most likely controlled by the
ADOs rather than contour ridges created during planting of the crop. Where ADOs were present, the full
160cm of the profile appeared to be full of water, whereas where there was no ADO only about 110cm of
soil contained water. A field capacity of about 25% at Siguidolo and 39% at Fansirakoro was reached after
8 days of rain in the ACN system whereas without ADOs water content for most of the 91 days was less
than 20% at Siguidolo and less than 30% at Fansirakoro, indicating greater rain water runoff.
The measurements confirm farmer observations that they can plant sooner and in a wetter soil where the
ADOs are present. The reasons for 30 to 50% greater yields seem clearly related to greater water capture
and storage, thus the reason for greater C storage becomes clear. The technology also leads to greater water
storage as well as soil C contents increases.
12
Practical Methods of Estimating Soil Organic C in Soils of the Sahel, West Africa
H. Konare, N.V. Hue, R. Yost, G. McCarty, M. Doumbia, H. Coulibaly, and A. Bagayoko
Accurate soil carbon determination is important to the estimation of the reduction of atmospheric CO 2
concentration. However, no satisfactory methods exist especially in the developing countries and the
dynamics of soil carbon is still debatable.
This work is to evaluate Loss On Ignition ( LOI ) as a low technology option to measure soil organic C and
to explore the possibility of future use of a conventional wet method ( Walkley & Black or W & B ) and a
new method of mid-infrared spectroscopy for measuring soil organic C. We also correlated these
measurements with other soil properties. A set of 27 soil samples from Mali at 0-20 and 20-60 cm depth
were collected in different regions and agricultural systems . The clay contents of these samples range from
3% to 60%.
Dichromate oxidation (W&B), loss on ignition, and combustion at 1300 ºC were run on the 27 samples to
determine soil organic C contents. Particle size analysis was also determined. The data obtained from the
above methods were compared with the results from combustion and infrared methods determination of
soil C.
Our preliminary results show that LOI data are very high compared to the W&B and combustion at all
combinations of initial ( 105 ºC or 120 oC ) and final temperatures ( 350 ºC or 600 ºC ). In contrast, the
modified W & B and the combustion methods yielded very similar results which range from 0.2 to 2.5 %C.
Ensemble Kalman Filter Simulation of Carbon Dynamics in a Semi-Arid Rotational Grazing System
W. McNair Bostick, O. Badini, J. W. Jones, R. Yost, C. Stockle, and A. Kodio
Increasing atmospheric CO2 has increased interest in enhancing carbon (C) sequestration in land stocks and
given rise to C trading. In C trading, one party offsets a portion of their CO 2 emissions by paying another
party to sequester C. Management of degraded agricultural lands to increase C sequestration can allow land
managers to participate in C trading and improve the productivity of the land. One challenge to
implementing C trading is verifying sequestration over thousands of hectares. The objective of this study
was to test the use of the Ensemble Kalman Filter (EnKF) data assimilation algorithm for estimating spatiotemporal soil C dynamics in a rotational grazing system in the Madiama commune (Mopti region) of Mali.
The study site is approximately 150 hectares and has six rotational grazing parcels. Soil C measurements
from 2003 and a soil survey were used to initialize and parameterize a soil C model. Biomass productivity
trends that resulted in 0, 25, and 50% increases in annual biomass production after 50 years were used with
the model to create scenarios of soil carbon dynamics over a 50-year period. Then, assuming only means
and variances of initial C and model parameters for the entire site were known, a set of hypothetical
“measurements” of soil C during the 50-year period were used to test the ability of the EnKF to combine
model estimates and measurements to estimate spatio-temporal soil C dynamics.
13
Simulating Cropping Systems in Ghana with DSSAT-CENTURY
J. B. Naab, J. Koo, J. W. Jones, K. J. Boote
Cropping system models, which integrate management practices, soil, and weather to predict crop yield and
soil carbon sequestration, are being used in the Carbon from Communities project. However, to provide
useful information to researchers and community decision makers, the models must be capable of
quantifying crop performance in communities where they are to be used. Thus, it is necessary to adapt the
models to soil, climate, and cropping systems of interest and to evaluate predictions from the model relative
to local data. This paper discusses the adaptation of the Decision Support System for Agrotechnology
Transfer (DSSAT) linked with the CENTURY Soil Organic Matter model, DSSAT-CENTURY, to the
cropping systems in two locations in northern Ghana. Minimum datasets for running the model (e.g. soil,
weather, and management) from five years of peanut farming experiments in Tamale, Ghana and three
years of maize rotations in Tamale and Nyankampala were assembled. Model parameters for local cultivars
and soils were calibrated from local data, preliminary simulations, and literature reviews. The accuracy of
the model was evaluated by comparing simulated outputs with measurements. The model was able to
predict peanut growth yield under planting dates, varieties, and leaf spot disease epidemic after calibration.
It also was reasonably accurate in simulating maize yield variability under different nitrogen fertilizer
application rates and years. Further studies will be continued in Ghana to fine-tune critical crop parameters
with more datasets and to evaluate soil carbon model predictions. Preliminary results from long-term
simulations of soil organic carbon evolution under different management scenarios will be presented.
Utilisation de l’observation spatiale pour le suivi de la dynamique de la végétation au Sahel
A. Nonguierma
La connaissance de l’état du couvert végétal et de son évolution saisonnière est importante pour les pays du
Sahel où de nombreuses régions naturelles sont défrichées chaque année pour les besoins agricoles et
domestiques. Ces modifications ont de sérieuses implications sur l’état du couvert végétal et donc sur le
potentiel biophysique pour les activités de séquestration de carbone au Sahel.
Le Centre Régional AGRHYMET a mis en place un dispositif multi-scalaire de surveillance de la
dynamique des couverts végétaux au Sahel, basé principalement sur la caractérisation radiométrique du
rythme biologique de la végétation. Le système s'appuie implicitement sur l'existence de paramètres
spectraux mesurables par observation spatiale (exemple de l’indice de végétation), étroitement conditionnés
par certaines caractéristiques indicatrices de la végétation recouvrant le sol : indice foliaire, quantité de
biomasse, etc....
A chaque étape, les analyses sur plusieurs années permettent de montrer le développement potentiel de la
végétation, de mesurer la nature, l’ampleur et la célérité des modifications qui ont lieu ainsi que de prévoir
les états futurs du couvert végétal. A l’échelle globale, on a pu ainsi mettre en exergue les variations liées à
la longueur des périodes végétatives (à l’intérieur d’une année et entre années) et à l’intensité des
changements de la végétation. A l’échelle locale, on a pu évaluer l’impact de la pression foncière (agricole
et pastorale) sur les zones forestières.
L’expérience tirée du système AGRHYMET montre que les images spatiales combinées à des observations
de terrain dans le cadre d’un système d’information, constituent un bon support pour améliorer la base de
connaissances sur l’état et l’évolution du couvert végétal et par conséquent du potentiel de séquestration du
carbone atmosphérique au Sahel.
14
Indigenous Knowledge in African Drylands and the Kyoto Protocol
L. Olsson
This paper looks into indigenous knowledge in land management in order to address the challenge of
climate change mitigation, as it is expressed in the Kyoto Protocol.
Modifying natural ecosystems for producing food has to a large extent been a process of learning-by-doing
by generations of farmers rather than a scientific one, particularly in developing countries. How can the
concept of carbon sequestration be reconciled with land management practices as they have evolved in
African drylands?
Degraded agricultural soils have been depleted of nutrients and soil organic matter with a declining
agricultural yield as a result. Investments in improved land management (e.g. agro forestry, livestock, crop
rotation, mulching) can increase productivity and at the same time increase the storage of organic carbon.
The paper reports from research in semi-arid Sudan investigating the possibilities to combine improved
land management (based on traditional practices) among peasants with the sequestration of soil carbon.
Even if indigenous knowledge on good land management corresponds with the scientific principles behind
carbon sequestration there is a huge gap between the Kyoto Protocol and the potential implementation of its
mechanisms in rural areas of many developing countries.
Here we report on a systems analysis approach to reconcile the scientific and the indigenous knowledge
necessary for implementation of climate change mitigation in Sudan.
Lessons in Social Learning, Visions of Scaling Out Fostering Institutional Capacity
for Community-Based Land Management in North-Central Mali
C. Roncoli, C. Jost, K. Moore, S. Cissé, A. Ballo
This paper aim to increase understanding of community interest, incentives and capacity to initiate and
implement land management practices with carbon sequestration potential. It synthesizes lessons learned
from efforts by SANREM CRSP to foster the development of local institutional capacity to test, monitor,
and eventually fully implement a pasture management system inspired by Holistic Management TM and
landscape ecology principles in north-central Mali (Madiama Commune). While the agro-ecological
context and local production systems in the research site are representative of the Sahelian region, the area
is also distinctive in that it constitutes an entry point into the Niger inland delta, an important passage for
transhumant cattle in biannual migrations to wetland and dryland pastures. Stakes and claims on natural
resources are shaped by the diverse interests of agriculturalists and pastoralists, the coexistence of multiple
ethnic traditions, and the overlaying of different state structures and policies, including the recent thrust
toward decentralization of governance. The SANREM CRSP experiment hinges on an appreciation of the
centrality of information, skills, networks, and institutions for successful and sustainable community-based
natural resource management. It has focused its efforts on building local capacity for environmental
monitoring, collective decision-making, multi-stakeholder facilitation, conflict resolution, and civil society
participation in governance as well as on developing sustainable resource management technologies. Based
on an analysis of the social learning process in the Madiama Commune, we identify a number of key
lessons relative to the role of human and social capital in supporting the implementation of land use
approaches that can enhance carbon sequestration in a Sahelian environment. Key insights concern the
salience of local contextual specificity and of scientists’ assumptions and agendas in shaping the
perceptions, practice, and the performance of the Holistic ManagementTM model. We also explore some
issues and implications relative to scaling out and up both the institutional mechanisms and the
technological approach beyond the area of project intervention.
15
Effects of Ados en courbes de niveau on Soil Water Conservation for a Sustainable Crop Yield
Increase and Soil Carbon Content in Sudano-Sahelian Zone of the Peanut Basin of Senegal.
Preliminary results.
M. Sène, A. B. Niane, M. Khouma, K. Brannan, R. Kablan and R. Yost
Storing carbon (C) in the soil plant residue or manure through amendment or increased biomass production
in cultivated land while improving and sustaining agricultural production is one way of mitigating the
greenhouse effect of increased atmospheric C. In the drought-prone, yet highly susceptible to rain water
loss due to runoff Sudan-Sahelian zone of West Africa, ridge tillage across the slope not only can help
control runoff but also is a means of securing the organic matter amendment for improved crop water and
nutrient uptake. For the peanut or sorghum based cropping system of Senegal, well adapted ridge tillage,
referred to as ados en courbes de niveau combined with a bedding operation was compared to farmer
practices, with no tillage, in terms of impact on soil water use efficiency, crop yield, and soil organic
content changes. On-farm trials starting in 2003 in the Nioro area in the peanut basin consists of three
peanut, and sorghum fields, respectively. For each of the 2 crops, three representative farmers fields of
about 1.5 ha were chosen in the Nioro area. Each field is equally divided in 2 plots; with and without ridge
tillage . Site characteristics include mapping of topography, waterways, roads and trees, soil physical and
chemical properties, as well as climatic data ( mainly rainfall ). Monitored parameters include soil water
profile (wetting front, water content), crop growth, biomass and grain yield, and soil carbon content. The
preliminary results indicate that early in the growing season, ridge tillage promotes a rapid downward
movement of the wetting front and permits greater topsoil water content right after a rainfall event. This
proves to be an appropriate way of reducing rain water loss through runoff. As for crop maturation date,
peanut is positively affected by tillage as opposed to sorghum for which root damage during the bedding
operation induces a delay of growth and flowering. Overall, positive effects on total biomass and grain
yield were observed for both crops. The improved biomass production is a basis for increased potential for
crop residue application, thus for an increased soil carbon content.
Le Karité (Vitellaria paradoxa) Stocke Du Carbone
et Améliore la Fertilité des Champs Cultivés
K. Traoré K., J. Gigou , R. Oliver, F. Ganry
Dans les champs des paysans, des arbres (karités principalement) sont associés aux cultures, et forment un
paysage de “ parc à karités ”. Dans la région de Fana, sur un versant en pente faible (1 à 4%), les arbres
sont nombreux en bas de toposéquence. Alors le karité domine largement (23 arbres ha -1 sur 24) et les
arbres couvrent environ 8% de la surface. Au milieu et en haut de la toposéquence, les arbres sont moins
nombreux et appartiennent à de nombreuses espèces, dont peu de karités.
En conséquence, en bas de toposéquence les arbres restituent des quantités importantes d’éléments
minéraux au sol : 35 kg CaO ha-1, 8 kg MgO ha-1, 4,5 kg K2O ha-1 et 9 kg N ha-1, apports comparables à
ceux des engrais. Surtout CaO et MgO permettent d’éviter l’acidification du sol.
Ces arbres participent à la séquestration du carbone. Environ 16 t ha -1 de C sont stockés dans les parties
aériennes des arbres et 8 t ha-1 de C dans les racines. L’étude du  13C a permis de vérifier que la matière
organique du karité influence le sol sur 2,5 fois le rayon du houppier. Mais l’augmentation globale du
carbone du sol due aux arbres ne dépasse pas 1 t ha-1.
Les karités améliorent donc la fertilité des terres cultivées et stockent des quantités importantes de carbone
en bas de toposéquence. Est-il possible d’améliorer le parc arboré, avec d’autres espèces et en conservant
mieux l’eau de pluie, pour obtenir des effets comparables en milieu et en haut de toposéquence ?
16
Enhanced Photoperiod Response Modeling for Improved Biomass Simulation in a Sudanian Carbon
Accounting Framework
P.C.S. Traoré, A. Folliard, M. Vaksmann, C. Porter, M. Kouressy, J.W. Jones
Participation of selected farming communities to future carbon trade contracts is conditioned by the
availability of accurate soil carbon monitoring and verification protocols. To reduce the high uncertainty
inherent to time projections of soil C content, existing coupled soil/plant C models need to be adapted to
local conditions. Sometimes simple model calibration and/or re-parameterization is not enough, and
modification is required.
That is the case for the CERES family of models which governs the computation of cereal growth and
development within the coupled DSSAT-Century simulation environment. Previous studies showed that a
threshold-hyperbolic response to daylength greatly improves predictions of the vegetative phase duration
(VPD) for photoperiod sensitive sorghum varieties of West Africa. There, underestimation of VPD can
have significant impact on estimates of biomass production by major staple crops, including millet for
which a 1-month shorter VPD cuts in half the biomass production.
Field work conducted during the 2003 cropping season in cotton-based production systems near Koutiala
(Mali) revealed that millet and sorghum accounted for about 1 in every 3 of 424 surveyed farmers fields
(millet alone : 1 in 4). With 2003 a year of widespread cotton cultivation, these figures highlight the
important contribution of millet and sorghum to the carbon cycle in these sudanian agricultural
communities, and the subsequent need to improve estimates of biomass production for these crops in a
carbon accounting framework.
Upscaling Carbon Model Predictions Using Very High Resolution Imagery : Evaluation of
Contextual Approaches to Land Cover Classification and Crop Identification
P.C.S. Traoré, W.M. Bostick, A. Yoroté, J. Jones, M.Doumbia
Carbon sequestration in soils is a lengthy process, explaining why large contract areas are required to meet
tradeable carbon quantities over limited time periods. A reliable accounting protocol must therefore be
capable of embracing the variability of conditions that determine differential accretion rates and resulting
stocks inside the contract region. This is particularly challenging in sudanian farming systems of West
Africa, where natural pedo-climatic variability combines with intricate land tenure and management
surfaces to create patchy, heterogenous landscapes.
Classification of visible/NIR satellite imagery is now routinely used for land cover studies, and new very
high spatial resolution (VHSR) sensors feature metric locational accuracy adequate for precision
agriculture. Of particular interest is the ability to discriminate between natural and agricultural vegetation
and to identify individual crops as it relates to various levels of biomass production, a key determinant of C
accretion. Preliminary results using VHSR imagery revealed unprecedented potential for leaf area index
estimation and ridge tillage detection, but highlighted limitations that arise with the application of classical
techniques to VHSR imagery classification.
One notable difficulty brought by VHSR is that spectral separability traditionally observed between land
cover classes by coarser sensors is lost in the wide spectrum of individual directional reflectance flecks of
smaller soil/vegetation elements. Potential avenues to address this shortcoming may include spatial
aggregation and contextual classification. The latter considers that there is a spectral dependence between
neighboring pixels, and that analysis of resulting image texture can bring complementary information to
improve the performance of pixel-by-pixel classifiers. This work presents results obtained in the
Oumarbougou area (southeast Mali) during the 2003 cropping season.
17
Tracking Environmental Dynamics and Agricultural Intensification in Southern Mali
G.G. Tappan and M. McGahuey
The OHVN Zone (Office de la Haute Vallée du Niger) is a small but very important agricultural production
region in southern Mali. Against a background of environmental degradation including decades of
declining rainfall, loss of vegetation cover and soil erosion, numerous farming communities stand out by
increasing their livelihoods through adoption of soil and water management (SWM) techniques. Field
surveys conducted in 1998 – 2000 indicate that both environmental and agricultural conditions have
improved in the past decade. The adoption of SWM appears to be a catalyst that can lead to improving
livelihoods while better maintaining and even improving the natural resource capital. In an effort to better
quantify environmental trends, we conducted a study using time-series remote sensing analysis of nine
village territories to examine land use and land cover trends from 1965 to 2001. Historical medium and
high resolution satellite images from Landsat and Corona were used to assess land use and land cover
change. The trends show clear indications of agricultural intensification and environmental improvement,
including increased woody vegetation cover as a result of community management of forest resources.
Land Degradation Assessment in Drylands (LADA) and Carbon Sequestration
L. Thiombiano and P Koohafkan
Drylands are characterized by a ratio P/ET comprise between 0,05 and 0,065. Complexity, variability,
resilience, vulnerability, continual transition and severe poverty are the main characteristics of this agroecological zone. 30% of the superficies of sub-Saharan Africa are occupied by drylands where severe land
degradation occurs, and needs to be assessed and monitored. The project on Land degradation Assessment
(LADA) through its 7 steps methodological approach, aims at that end, with the possibility to provide
specific data on hot spots and bright spots.
The presentation emphasis on the significant amount of C loss due to land degradation (hot spots) and the
good potential for carbon sequestration through soil rehabilitation and agricultural intensification (bright
spots). FAO Models for carbon stock assessment are proposed to be used in drylands.
Suggestions on how LADA project could contribute to the estimation of carbon sequestration in drylands
are proposed: (i) accurate evaluation and estimation of land degradation in connection with the evaluation
of carbon stocks; (ii) identification of appropriate techniques for land rehabilitation and enhancement of
carbon stocks; (iii) provision of socio-economic data on dryland for the future development of carbon
market at farmers communities level.
18
SOCSOM (Sequestration of Carbon in Soil Organic Matter) in Senegal
L.L. Tieszen
SOCSOM in Senegal is a project funded largely by USAID and supported by numerous other organizations
to evaluate the opportunities for carbon sequestration in semiarid areas and to both contribute to mitigation
and adaptation to climate change. The framework and specific location developed from extensive
international contributions at two major international workshops at the EROS Data Center (EDC) and in
Dakar. SOCSOM was proposed to “…provide quantitative analyses of the environmental, ecological, and
economic potential for the sequestration of carbon in soil organic matter in spatially explicit sites and to
define the necessary socioeconomic enabling conditions and policies to implement successful projects.”
The project was to emphasize extensive collaboration, site specificity, a bottom-up approach, and
evaluations of the feasibility of “real” projects in real settings. The Mission of SOCSOM is to insure that
the developing countries in semi-arid and sub-humid parts of Africa have the capability to take advantage
of the opportunities to become participants in, and beneficiaries of, international efforts to mitigate climate
change and restore productivity.
The EDC led the multinational team with CSE. A quantitative assessment of the historical patterns of
Carbon changes by ecoregion and based on field data and image interpretation was combined with
additional remote sensing approaches to define degraded and improved areas. Biogeochemical modeling
was used to quantify carbon dynamics and project future impacts of both management decisions and
climate change. Detailed farm and village level economic analyses resulted in a portfolio of possible
management strategies ranging from economically feasible to unrealistic.
All major ecoregions in Senegal experienced dramatic declines in Carbon with 35-year fluxes ranging from
0.1 to 0.9 kg ha-1 yr-1. Only the Northern Coast Ecoregion increased carbon stocks (0.2 kg ha -1 yr-1), an
increase associated with Casuarina plantations established for sand dune stabilization. These large
decreases were clearly associated with land cover conversions but amplified by deceases in woody density
within land cover classes during this period. Modeling suggests that management schemes under current
climate can conserve carbon and fertility or even reverse the degradation. However, this intensification
will require substantial resources both in terms of labor and nutrients and demands capitalization.
Simulations suggest that the 2XCO2 climate projections will severely constrain agricultural production in
Senegal and less seriously continue to deplete carbon stocks. A carbon specialist team evovled in Senegal,
five PINs were prepared for projects in the BioCarbon Fund, and effective training was achieved with
support from FAO-funded participants. We propose a similar extension across the Sahel.
19
Remote Sensing of Soil Carbon in a Semi-Arid Agro-Pastoral System: Initial Results from a K
Nearest Neighbor Classification
R.H. Wynne, P. Doraiswamy, M.S.M. Touré, N. Sengupta, O. Badini, A. Ballo
In our efforts to increase the precision with which remote sensing technology can be utilized to identify
carbon sequestration capacities of various crop and pasture management systems, we are evaluating the
potential of k-nearest neighbor (kNN) estimation. A kNN classifier finds the known k neighbors spectrally
nearest to a sample, then assigns the class label using the class which has a plurality among the nearest
neighbors. Remotely-sensed data include single-date and multitemporal Landsat Enhanced Thematic
Mapper imagery as well as single-date QuickBird multispectral imagery. Soils data, collected in Madiama
by a team led by Oumarou Badini, include a 2002 baseline characterization of soil organic C (108 samples)
and a more intensive 2003 campaign (451 samples). Results using kNN classification in other natural
resource management contexts have been quite robust, leading us to believe that this pilot study has a
reasonable chance of success.
Sustaining Crop Productivity: The Influence of Organic Resource Quality and Quantity
E. Yeboah, B. Vanlauwe, M. K. Abekoe, and C. Gachengo
Increasing concern about long term sustainability and high environmental costs of agro ecosystems in
developed and developing countries supports the need for increased understanding of whole ecosystem
nutrient use efficiency. Application of modern ecosystem concepts to farming systems forms a frontier in
ecosystem science which will benefit both ecosystem theory and agro ecosystem management. Since the
mid-1980s, research on organic resource management has focused on N synchrony and soil organic matter
dynamics. A synthesis of results from this research led to the development of a Decision Support System
(DSS) for organic resource (OR) management. This DSS recommends four OR usage classes based on OR
quality as a function of N, polyphenol and lignin contents. High quality residue (class I) is associated with
relatively high N, low polyphenol and low lignin contents. Medium quality OR are associated with Class II
or Class III. Class II OR have high N and high polyphenol content whereas class III OR have low N and
low lignin content. Low quality OR (class IV) have low N and high lignin content. Two pathways of the
DSS (class II and class III) advise combining OR with mineral resources (MR) which benefits plant
productivity and increases nutrient use efficiency compared to the sole application of OR or MR. These
combined applications form the technical basis of the Integrated Soil Fertility Management paradigm. In
this study, the linkage among organic resource quality, organic resource quantity, mineral application and
soil texture in sustaining crop productivity and N use efficiency in the humid forest zone of Ghana is
reported.
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