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Soil nutrient deficiencies can affect rice yield and grain mineral content wherever they occur, but an understanding of their effect on upland rice production in humid forest zone of West Africa is still limited. Therefore, a nutrient omission trial was conducted on foot slope soil in 2003, 2004 and 2005 in Côte d’Ivoire using rice variety WAB 56–104. The effect on rice grain yield (GY) and nutrient content of complete fertilizer (Fc with nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and zinc (Zn)) was compared with Fc from which a specific nutrient was excluded (Fc – N, Fc – P, Fc – K, Fc – Ca, Fc – Mg and Fc – Zn). Before the trial, soil K (0.10 cmol kg−1) and Mg (0.20 cmol kg−1) contents were suitable, but available P-Bray I (4.2 mg kg−1) was found to be deficient. In course of the study, K, Mg and P deficiencies were observed. An antagonistic effect was observed between rice GY and grain concentrations in P, Mg and Ca for treatments Fc – Mg, Fc – P and Fc – K, respectively. Therefore, the use of P, K and Mg fertilizers is recommended for successive cropping seasons in order to rich stable and high rice yield while decreasing of grain concentrations in P, Mg and Ca can be observed. [ABSTRACT FROM AUTHOR]

With the objective of improving rice productivity and generating additional knowledge on rice production in Africa, field experiments were conducted for two consecutive seasons of 2005 and 2006 in Southern Benin. Terre de barre soils at the WARDA experimental station and Niaouli, and the plinthic Ferralsols of Cana were investigated. A complete fertilizer (Fc) composed of N, P, K, Ca, Mg and Zn was used to assess NERICA.4 (upland rice) root development and grain yield (GY). Similar observations were made in treatments with a specific nutrient excluded from Fc (Fc–N, Fc–P, Fc–K, Fc–Ca, Fc–Mg and Fc–Zn). A grain yield of up to 1.4 t ha−1 (Fc–N) and higher root densities for Fc and Fc–Mg at 20–60 cm were attained. Maximum reductions in yield and rooting depth were observed for Fc–P (27%, 27%), Fc–K (30%, 14%) and Fc–Zn (32%, 2%). Drought occurrence, a high C/N ratio and soil acidity influence the effects of nutrients on rice. Removal of N from basal fertilizer was recommended to reduce the effect of mid-season drought. It is suggested that the critical level of K in the soils of West Africa be adjusted to 0.40 cmol kg−1 for upland rice. [ABSTRACT FROM AUTHOR]