Management of acid tropical soils in Africa
1985
Pieri, C. (IRAT/CIRAD. Department of Agronomy | Centre International de Recherche Agronomique pour le Developpement (Paris))
Acid soils cover large areas of Africa and have low productivity due to their low native fertility. Research conducted for many years has proved that such productivity can be markedly increased. However, it is necessary to consider two different cases: the acid soils in the humid tropics and savannas, and the acidified cultivated soils common in western Africa that cover humid, subhumid, and semiarid zones. Application of initial corrective fertilization-using heavy rates of N, P, K-and lime, drastically increases the productivity of the acid soils from Africa. This productivity can be maintained under continuous cropping through annual fertilizer applications that match crop nutrient requirements. This technology-called "investment fertilization" or "maintenance fertilization"-although agronomically sound, is generally not adapted to African conditions, due to the high risks it induces for the small farmer in terms of erosion and potential nonprofitability. This paper presents some low-input technologies and indicates the need for more research on evaluation of lime requirements, availability of P fertilizer in high P-fixing soils, crop tolerance to Al in soil solution, and physical properties of the acid soils. Low fertility sandy soils of western Africa are highly sensitive to acidification, as a consequence of current farming practices that induce nutrient imbalance in the soils. The low levels of fertilization, erosion, leaching, and intense organic-matter mineralization that occur in the semiarid zones are the main causes of soil degradation and acidification. Due to the predominant economic situation, recommended cropping and soil management systems must rely upon intensive use of local resources (crop residues, manures, rock phosphates, nitrogen-fixing legumes) and efficient use of mineral fertilizers, but they must also promote deep socioeconomic changes.
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