The degraded sandy soil poses severe threat
Studies have shown that the soils of the Sudanian-Savannah in the semi-arid zones have low organic carbon and nitrogen contents because of low biomass production and the high rate of organic matter decomposition. However, phosphorus deficiency in these soils has been identified as the most serious constraint to crop production. Apart from low phosphorus stocks, the low-activity clay of these soils has a relatively low capacity to retain added phosphorus. The textures are predominantly sandy to sandy loams. The dune soils in the Sahel have very high hydraulic conductivity and therefore rapid internal drainage, and high loss of plant nutrients by leaching. In the Sudanian-Savannah zones, the formation of a surface crust reduces internal drainage, and water erosion becomes a more serious problem than in the Sahel. The sandy soils in the Sahel are ready victims of wind erosion, especially during the dust storms that occur at the beginning of the rainy season. Crop seedlings are damaged by sand abrasion and burial during these storms. In Africa nutrient outputs exceed inputs. An FAO (Food and Agriculture Organization) study on the nitrogen, phosphorus, and potassium balances for 35 crops in 38 sub-Saharan countries between 1982 and 1984 showed that annually 22 kg nitrogen, 2.5 kg phosphorus, and 15 kg potassium were lost from each hectare. There was a net loss of 49 kg per hectare or 9.3 million tonnes of plant nutrients removed from the system in sub-Saharan Africa in 1983. Furthermore, these quantities of annual nutrient removal are projected to increase to a rate of 60 kg per hectare or 13.2 million tonnes of plant nutrients by 2000 AD. These figures are alarming, especially when one realizes that the productivity of these soils in their native state is already low because of low inherent levels of plant nutrients. Sub-Saharan Africa consumes fertilizer at the lowest rate in the world-- - roughly 10 kg nutrients per hectare. In this context, any effort to improve and maintain soil fertility through an integrated approach will be a boon, not only to sustain food grain production, but also for the conservation of the natural resource base. |
The resource-poor pearl millet farmers of Sahelian
Africa are beleaguered by the twin maladies of nutrient-starved sandy soil, and low,
erratic rainfall. This low soil fertility has been found to be the factor seriously
limiting crop production. The acidic sandy soils, which spread over a good portion of
Sahelian Africa, are weakly structured and are prone to water and wind erosion. Mainly
composed of quartz, they have low water-holding capacities and nutrient contents. The
fertilizer-use efficiency in such soils is hampered by severe leaching.
