Search

The contribution of Cassia siamea hedgerows and mulch to erosion control was evaluated on a 14% slope of a Lixisol/Alfisol at Machakos, Kenya. The four treatments, in 400 m 2 runoff-plots were: hedgerows with prunings applied as mulch to the crop, hedgerows and crops with prunings removed, mulch only applied to the crop and a control. The hedgerows were planted on the contour, 4 m apart and 0.25 m between plants. Maize and cowpea were planted in sequence. The control plot sustained an average annual water loss over 3 y of 31 mm runoff and soil loss of 19 t ha −1 . The best treatment, hedgerows with mulch, reduced losses to 13% and 2% of the control. Hedgerows without mulch reduced losses respectively to 23% and 7%, while mulch without hedgerows reduced losses to 41% and 17%. Soil loss was considerably influenced by one single storm in April 1990 due to the nature of that storm and to the susceptibility of the soil to erosion at that particular time. Differences in crop yield between treatments were small. The hedgerow treatments depressed cowpea yield slightly in less than normal rainy seasons but improved cowpea yields in wet seasons.

To develop adequate and sustainable land use plans, a clear assessment of the potential of the land and of the existing farming systems, as well as an identification of ways to attain these potentials is required. The agricultural system in the limestone area south of Malang is classified into different land units, land uses and livestock units. Land uses include a further distinction into agro-forestry system and annual crop. Simulation models are used as a tool to explore the production potential of crops and livestock. Existing crop simulation models are used and adjusted to the situation at hand. A new livestock simulation model is developed that includes major farm household influences, particularly the influence of land and land use on the feed resource and on livestock production. The model considers also the seasonality of feed availability; feed is quantified on a monthly basis. Two production orientations, with their specific technologies, were distinguished; low external-input agriculture (relying on manure only) and yield-oriented agriculture (relying on inorganic fertilizers only). The present crop and livestock productions are far below the potentials, as were explored with the simulation models. Constraints to agricultural production in the research area are high erosion, a low soil organic matter and a declining natural soil fertility. Hence options for land use are explored which focus on biophysical sustainability. The latter is defined here as avoiding excessive erosion, at least maintaining the present soil organic matter content of 2% and maintenance of a closed balance of the most limiting resource.Systems with cattle, more perennials and yield-oriented agricultural systems leave more biomass than current cropping thus creating more cover, litter and mulch. An increase in the use of inorganic fertilizers seems the only viable direction towards more biomass production. Increased fertilizer use will improve the quantity and quality of crop yields as well as of crop residues for animal husbandry. Since 100% of crop residues never will be used in animal husbandry, effort should be made to return the left-overs to the soil in order to maintain or increase the soil organic matter content, i.e. better residue management. The extra manure both in terms of quantity and quality will also contribute to the latter goal. Finally, the higher soil organic matter content will improve the physical state of the heavy clay soils thus improving their water holding capacity, it will lower the soil's erodibility and improve nutrient use efficiency. So, use of inorganic fertilizers will trigger a cascade of effects that all point in the direction of a more sustainable use of the natural resources.

Soil erosion by water is the principal cause of land degradation, and a major constraint to agricultural development in developing countries. In semi-arid zones measures have to be taken to reduce on-site soil, water and nutrient losses and in sub-humid mountainous zones the focus should also be on reducing sedimentation of reservoirs and on other downstream effects. Soil conservation and watershed development activities and projects are hard to evaluate, since neither their effects nor their beneficiaries can be easily detected. Methods are developed to identify potential participants and to assess on-site and downstream effects of conservation measures, by using water and nutrient balances and yield response functions. In the evaluation of these projects cost-benefit analysis (CBA) and multi-criteria analysis (MCA) can complement each other. The efficiency of the projects can be conveniently assessed with CBA, when the effects can be quantified and valued. And MCA can be used to assess scores on non-monetary attributes of the efficiency, equity and conservation criteria, and to show how conflicting objectives of different actors affect the scores.

To develop adequate and sustainable land use plans, a clear assessment of the potential of the land and of the existing farming systems, as well as an identification of ways to attain these potentials is required. The agricultural system in the limestone area south of Malang is classified into different land units, land uses and livestock units. Land uses include a further distinction into agro-forestry system and annual crop. Simulation models are used as a tool to explore the production potential of crops and livestock. Existing crop simulation models are used and adjusted to the situation at hand. A new livestock simulation model is developed that includes major farm household influences, particularly the influence of land and land use on the feed resource and on livestock production. The model considers also the seasonality of feed availability; feed is quantified on a monthly basis. Two production orientations, with their specific technologies, were distinguished; low external-input agriculture (relying on manure only) and yield-oriented agriculture (relying on inorganic fertilizers only). The present crop and livestock productions are far below the potentials, as were explored with the simulation models. Constraints to agricultural production in the research area are high erosion, a low soil organic matter and a declining natural soil fertility. Hence options for land use are explored which focus on biophysical sustainability. The latter is defined here as avoiding excessive erosion, at least maintaining the present soil organic matter content of 2% and maintenance of a closed balance of the most limiting resource.Systems with cattle, more perennials and yield-oriented agricultural systems leave more biomass than current cropping thus creating more cover, litter and mulch. An increase in the use of inorganic fertilizers seems the only viable direction towards more biomass production. Increased fertilizer use will improve the quantity and quality of crop yields as well as of crop residues for animal husbandry. Since 100% of crop residues never will be used in animal husbandry, effort should be made to return the left-overs to the soil in order to maintain or increase the soil organic matter content, i.e. better residue management. The extra manure both in terms of quantity and quality will also contribute to the latter goal. Finally, the higher soil organic matter content will improve the physical state of the heavy clay soils thus improving their water holding capacity, it will lower the soil's erodibility and improve nutrient use efficiency. So, use of inorganic fertilizers will trigger a cascade of effects that all point in the direction of a more sustainable use of the natural resources.

To find out about changes in soil and water conservation technology in eastern Burkina Faso and to avoid the standard answers, the researchers created a platform for communication by giving the villagers the opportunity to create their own village picture book in which their lives and history was documented

Soil erosion by water is the principal cause of land degradation, and a major constraint to agricultural development in developing countries. In semi-arid zones measures have to be taken to reduce on-site soil, water and nutrient losses and in sub-humid mountainous zones the focus should also be on reducing sedimentation of reservoirs and on other downstream effects. Soil conservation and watershed development activities and projects are hard to evaluate, since neither their effects nor their beneficiaries can be easily detected. Methods are developed to identify potential participants and to assess on-site and downstream effects of conservation measures, by using water and nutrient balances and yield response functions. In the evaluation of these projects cost-benefit analysis (CBA) and multi-criteria analysis (MCA) can complement each other. The efficiency of the projects can be conveniently assessed with CBA, when the effects can be quantified and valued. And MCA can be used to assess scores on non-monetary attributes of the efficiency, equity and conservation criteria, and to show how conflicting objectives of different actors affect the scores.

Sahelian rangelands are subject to degradation caused by physical and human factors. This report presents the results of recent research in Burkina Faso on methods for regenerating such rangelands. It begins with an overview of existing regeneration methods. Quantitative ecological field work conducted at two representative sites to understand the regeneration processes, to determine the sustainability of these processes and to understand reasons for success or failure of regeneration technology is described. Water and nutrient (N,P and K) balances as well as vegetation dynamics were studied for different soil and water conservation technologies. A major conclusion is that degraded and crusted soils can only be regenerated by modifying the water balance. Under improved infiltration, subsequent biological processes appear to be able to transform degraded soils into productive soils. However, an improved availability of water often triggers an immediate shortage of nitrogen. Deep infiltration of water stimulates the growth of trees and shrubs which have a stabilizing effect on the overall regeneration process of Sahelian rangelands.

Land degradation by water erosion represents a serious, and fast increasing, environmental threat. Hedgerow barriers control water erosion through the presence of the tree stem and through an increase in infiltration beneath the hedgerow. The infiltration rate beneath hedgerows is 3-8 times higher than in the alley where crops are grown. Soil water content measurements in hedgerow barrier systems indicate that infiltrated water penetrates the soil beneath hedgerows deeper than the soil beneath the alley and the control. An analytical framework for calculating the impact of hedgerows and mulch on infiltration, runoff and soil loss is presented here. The framework was expanded with algorithms to calculate the impact of hedgerows of various densities, ranging from 1-4 rows. The framework was applied on a seasonal basis and the predictions were satisfactory. Extreme events can be explained when dynamic soil and plant conditions are incorporated. A dynamic simulation model called SHIELD has been developed that explains the experimental observations for runoff, soil loss and crop yields using daily time steps. Application of the model illustrates the importance of dynamic soil and plant conditions to the amount of soil being lost and shows that SHIELD can be used to compute the maximum desired distance between hedgerows with respect to tolerable soil loss.

Land degradation by water erosion represents a serious, and fast increasing, environmental threat. Hedgerow barriers control water erosion through the presence of the tree stem and through an increase in infiltration beneath the hedgerow. The infiltration rate beneath hedgerows is 3-8 times higher than in the alley where crops are grown. Soil water content measurements in hedgerow barrier systems indicate that infiltrated water penetrates the soil beneath hedgerows deeper than the soil beneath the alley and the control. An analytical framework for calculating the impact of hedgerows and mulch on infiltration, runoff and soil loss is presented here. The framework was expanded with algorithms to calculate the impact of hedgerows of various densities, ranging from 1-4 rows. The framework was applied on a seasonal basis and the predictions were satisfactory. Extreme events can be explained when dynamic soil and plant conditions are incorporated. A dynamic simulation model called SHIELD has been developed that explains the experimental observations for runoff, soil loss and crop yields using daily time steps. Application of the model illustrates the importance of dynamic soil and plant conditions to the amount of soil being lost and shows that SHIELD can be used to compute the maximum desired distance between hedgerows with respect to tolerable soil loss.

Sahelian rangelands are subject to degradation caused by physical and human factors. This report presents the results of recent research in Burkina Faso on methods for regenerating such rangelands. It begins with an overview of existing regeneration methods. Quantitative ecological field work conducted at two representative sites to understand the regeneration processes, to determine the sustainability of these processes and to understand reasons for success or failure of regeneration technology is described. Water and nutrient (N,P and K) balances as well as vegetation dynamics were studied for different soil and water conservation technologies. A major conclusion is that degraded and crusted soils can only be regenerated by modifying the water balance. Under improved infiltration, subsequent biological processes appear to be able to transform degraded soils into productive soils. However, an improved availability of water often triggers an immediate shortage of nitrogen. Deep infiltration of water stimulates the growth of trees and shrubs which have a stabilizing effect on the overall regeneration process of Sahelian rangelands.

To find out about changes in soil and water conservation technology in eastern Burkina Faso and to avoid the standard answers, the researchers created a platform for communication by giving the villagers the opportunity to create their own village picture book in which their lives and history was documented