In West Africa, rice (Oryza sativa L. and Oryza glaberrimaI Steud) production is not meeting current demand. Low yields are attributed to diverse biotic and abiotic constraints including nutrient deficiencies, inadequate agronomic practices, and socio-economic constraints. This study quantified yield and profit responses of rainfed rice produced in the Sudan Savanna of Burkina Faso and Mali to fertilizer N, P, K, and Mg-S-Zn-B treatment. The mean yields were 2.2 and 2.4 Mg ha-1 for upland rice in Finkolo and for lowland rice in Longorola in Mali, respectively, and 1.5 and 2.2 Mg ha-1 for upland rice at Boni and Karaba in Burkina Faso. Lowland rice grain yield was not affected by nutrient application at Longorola. The grain yield increases with 30 and 60 kg ha-1 N were, respectively, 0.30 and 0.48 Mg ha-1 at Karaba, 0.21 and 0.34 Mg ha-1 at Boni, and 0.32 and 0.41 Mg ha-1 at Finkolo indicating similarity in response. Grain yield response to P was observed only at Karaba. If fertilizer were applied at 50% rather than 100% of the economically optimum rate, as might be the case for financially constrained farmers, the mean yield increase was 36% less but agronomic efficiency was 23% higher and the profit cost ratio was 66% higher. There was no response to K or to Mg-S-Zn-B. The results, therefore, indicate high potential for profitable response of rainfed upland rice production for Sudan Savanna to fertilizer N but little potential for other fertilizer nutrients. These results should, however, be considered together with other field research results in making fertilizer use decisions.
Key words: Agronomic efficiency, economically optimal rate, response function, yield.
EOR, Economically optimal rate of nutrient application or the rate expected to maximize net return per hectare to nutrient application; Mg-S-Zn-B, a diagnostic treatment containing NPK plus 15 kg ha-1 S, 2.5 kg ha-1 Zn, 10 kg ha-1 Mg, and 0.5 kg ha-1 B; PCR, profit to cost ratio, or the net return divided by the cost of fertilizer nutrient use.