Nutrient outputs exceed nutrient inputs in many smallholder farming systems in sub-Saharan Africa (hereafter referred to as Africa). This mining of soil nutrients has lead to depletion of soil fertility, which can only be overcome through increased input of nutrients from biological N2 fixation, organic materials and commercial fertilizers. The quantities of organic materials and commercial fertilizers available to smallholders, however, are often limited. The stark realization of continuing soil fertility depletion in many smallholder farming systems in Africa has lead to a call for an alternative approach to nutrient management in which the replenishment of soil fertility is viewed as an investment in natural resource capital. Replenishment of soil fertility with a large, one-time addition of nutrients is (i) more suited to P than N and (ii) suited to external interventions by governments or agencies to invest in soil fertility. The quantity of added nutrient, however, must not exceed the storage capacity of the soil. Nutrient application rates required to replenish soil fertility will be less on sandy than clayey soils. When the supply of organic materials and fertilizers is limited, seasonal application of small to moderate amounts of nutrients to an agricultural area normally results in greater aggregate production for the area than large application of nutrients to only a portion of the area. The challenge is to selectively target applications of commercial fertilizers and organic materials to ensure that limited financial resources and limited amounts of fertilizer and organic resources are effectively used to both optimize crop responses and restore productivity of depleted lands.

English

9906|AGRIS 9902|R98-99ANALY

Jose Juan Caballero

CIMMYT Publications Collection