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Traditional farming systems in Sub-Saharan Africa depend primarily on mining soil nutrients. The African green revolution aims to intensify agriculture through the dissemination of integrated soil fertility management (ISFM). This paper develops a robust and operational definition of ISFM based on detailed knowledge of African farming systems and their inherent variability and of the optimal use of nutrients. The authors define ISFM as a set of soil fertility management practices that necessarily include the use of fertilizer, organic inputs and improved germplasm, combined with the knowledge on how to adapt these practices to local conditions, aimed at maximizing agronomic use efficiency of the applied nutrients and improving crop productivity. All inputs need to be managed in accordance with sound agronomic principles. The integration of ISFM practices into farming systems is illustrated with the dual-purpose grain legume–maize rotations in the savannas and fertilizer micro-dosing in the Sahel. Finally, the dissemination of ISFM practices is discussed.

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We conducted field experiments over 2 years on two acid soils of southern Cameroon to test whether efficient uptake and use of phosphorus (P) from less available sources by grain legume genotypes could benefit subsequent rotational maize. We grew two crops each year. For the first crop we grew 4 genotypes of soybean and of cowpea, plus maize. For the second crop we grew maize. The first crops were fertilized with 0, 90 kg P ha )1 as phosphate rock (PR) or 30 kg P ha )1 as triple super phosphate (TSP). P application highly significantly increased shoot dry matter, P uptake, N 2 fixation and grain yields of the grain legumes with TSP generally more effective than PR. Two of the soybean and two of the cowpea genotypes were more efficient at using P. Only the P-efficient soybean and cowpea genotypes increased subsequent maize yields. Yields of the subsequent maize grown in rotation were significantly correlated with shoot P uptake for which the quantity of P applied with the crop residues of the pre-crop appeared to be a major factor.We also grew the grain legumes in nutrient solutions and measured organic acid-anion exudation from roots, root-surface phosphatase-activity, and root morphological characteristics. Enhanced exudation of organic acid anions from roots of Pdeprived plants might have contributed to the P acquisition efficiency under field conditions of the P-efficient cowpea genotypes and one of the Pefficient soybean genotypes. A higher activity of root-surface acid phosphatase might have been important for the other P-efficient soybean genotype. The results show, that the potential positive rotational effect of cowpea and soybean on the acid, highly P-sorbing soils of southern Cameroon depends on breeding and using P-efficient genotypes when sparingly soluble and suboptimal rates of soluble P fertilizers are used.

teriorate the soil physico-chemical conditions of the often physically and chemically fragile moist savanna soils Nutrient depletion is a major constraint to crop production for in the long term, especially in the case of ammonium moist savanna soils, and inputs of nutrients are required to overcome sulfate [(NH 4 ) 2 SO 4 ] (Pieri, 1992). This observation, tothis constraint. The impact of sole and combined applications of organic inputs (OIs) [fresh tree prunings, Pueraria phaseoloides (Roxb.) Recherche Agronomique, B.P. 1026, Lomé , Togo; J. Diels, N. Sanginga, and O. Lyasse, RCMD, IITA, Ibadan, Nigeria, c/o L.W. Lam-al., 1997), most trials in the West African moist savanna bourn and Co., 26 Dingwall Rd., Croydon CR9 3EE, UK; R. Merckx, deal with manure or crop residues as a source