Wind erosion is a major contributor to desertification in the Sahel. Although three effective countermeasures for wind erosion (i.e. ridging, mulching with post-harvest crop residue, and windbreaks) have been proposed, they are not practical for Sahelian farmers. Therefore, we designed a new land management practice, termed the ''Fallow Band System,'' which can be used for both controlling wind erosion and improving soil fertility and crop production. This method does not impose additional expense and labor requirements on Sahelian farmers who are economically challenged and have limited manpower. The objective of this study was to evaluate the effects of this system on wind-erosion control and soil-fertility improvement. We conducted field experiments at the International Crops Research Institute for the Semi-Arid Tropics West and Central Africa and showed that (i) a fallow band can capture 74% of wind-blown soil particles and 58% of wind-blown coarse organic matter, which suggests that it can effectively control wind erosion, (ii) the amount of soil nutrients available for crops in a former fallow band was increased by the decomposition of trapped soil materials containing considerable amounts of nutrients, and (iii) the amount of soil water available for crops in a former fallow band was increased by the trapped wind-blown soil materials through improvement of rainwater infiltration into surface soil. These results lead to the conclusion that the ''Fallow Band System'' can be useful for preventing desertification and improving soil fertility in the Sahel, West Africa.
In the Sudan Savanna of West Africa, Plinthosols with a petroplinthic or pisoplinthic horizon at ≤ 50 cm from the surface comprise the major soils. Because these horizons limit the rooting volume and water and nutrient storage capacities of the soils, they should be a major cause of decreased crop yield in the Sudan Savanna. However, the local distribution of Plinthosols is not precisely known, and the relationships between soil classes, effective soil depth, and crop yield, which are considered to be closely related to each other on the Plinthosol soils, are not fully understood. To clarify these relationships, we first reassessed the soil toposequence on a slope at the Institute of Environment and Agricultural Research Saria station in Burkina Faso using the current World Reference Base soil classification system. We then determined the relationships between soil classes and sorghum yield and between the effective soil depth and yield. We also assessed whether ground penetrating radar could predict the position of a petroplinthic horizon. We found (1) that Pisoplinthic Petric Plinthosols were found at the upper slope, Petric Plinthosols were found at the middle slope, and Ferric Lixisols were found at the lower to toe slope; (2) that sorghum yield was significantly larger at the Ferric Lixisols, then at the Petric Plinthosols, and lower at the Pisoplinthic Petric Plinthosols; (3) that sorghum yield was proportional to the effective soil depth at which upper boundary of petroplinthic horizon was found (n = 26, R 2 = 0.78*** exclusion of waterlogged soil); and (4) that ground penetrating radar could predict the effective soil depth and the position of petroplinthic horizons (n = 4, R 2 = 0.99**), suggesting that we could roughly but easily predict sorghum yield and local distribution of Plinthosols having a petroplinthic horizon using GPR. These results may enable us to take more account of the inherent soil conditions when studying soil and water conservation, fertilization methods, and crop breeding, all of which are crucial if sustainable agricultural methods are to be achieved in the Sudan Savanna.
Conservation agriculture (CA) as recommended by the Food and Agriculture Organization of the United Nations consists of three components: minimum soil disturbance, soil cover, and crop rotation/association. CA was expected to become an effective countermeasure against water erosion in the Sudan Savanna, but it has not been adopted by local smallholder farmers. As markets for grain legumes (including cowpea) have not been developed in the Sudan Savanna, crop rotation/association should be considered impractical for these farmers. Therefore, we examined whether legume intercropping as a crop rotation/association component is necessary for preventing soil erosion in the Sudan Savanna. Three-year field experiments were conducted in runoff plots at Institute of Environment and Agricultural Research Saria station. The four treatments were conventional practice (full tillage, no sorghum residue mulching, and no intercropping), two-component CA (minimum tillage (MT) and sorghum residue mulching without intercropping), and three-component CA with velvet bean (VB) or pigeon pea (PP) intercropping. It was revealed that: (1) MT and sorghum residue mulching (without intercropping) effectively reduced the annual soil loss by 54% mainly due to the improvement of soil permeability by the boring of termites and wolf spiders found under the sorghum stover mulch; (2) intercropping in combination with MT and crop residue mulching had no effect on soil erosion control mainly because: (a) PP did not survive the long dry season; (b) VB did not serve effectively as a cover crop since soil loss was concentrated at the beginning of the rainy season when VB was still too small; (c) unexpectedly, in combination with MT and crop residue mulching, intercropping with VB did not increase mulch biomass, especially sorghum biomass which prompts the boring of termites and wolf spiders. These results demonstrate that the third component of CA, namely legume intercropping, is not always necessary; rather, the two remaining componentsminimum soil disturbance and soil coverare sufficient for soil conservation in the Sudan Savanna. This finding lightens the burden of adopting CA and thus facilitates its future promotion to the smallholder farmers in the Sudan Savanna.
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