Soil fertility management in irrigated rice systems in the Sahel and Savanna regions of West Africa: Part I. Agronomic analysis

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Yield, input use, productivity and profitability of irrigated rice systems were analyzed based on surveys in Senegal (Thiagar and Guédé), Mali (Office du Niger) and Burkina Faso (Kou Valley). The objective was to determine agronomic factors contributing to farmers' fertilizer-use efficiency and productivity, given current farmer practices. (A second paper addresses profitability and risk issues). Grain yields were highly variable, within and across sites. Minimum grain yield was 0.2 t ha −1 (Thiagar), maximum recorded grain yield was 8.7 t ha −1 (Office du Niger). The yield gap between actual farmers' yield and simulated potential or maximum attainable farmers' yield ranged from 0.6 to 5.7 t ha −1 (Kou), 1.8 to 8.2 t ha −1 (Thiagar), 0.3 to 6.3 t ha −1 (Office du Niger), 0.8 to 5.7 t ha −1 (Guédé), indicating considerable scope for improved yield. Physiological nitrogen efficiency (δ grain yield/δ N uptake) was mostly between 40 and 80 kg grain kg −1 plant N. Apparent recovery of fertilizer N was highly variable (average: 30–40% of applied N). Timing of N fertilizer application by farmers was extremely variable and often did not coincide with critical growth stages of the rice plant. Other agronomic constraints included: use of relatively old (>40 days) seedlings at transplanting (Kou, Office du Niger), P and/or K deficiency (Office du Niger), unreliable irrigation water supply (Kou, dry season), delayed start of the wet growing season resulting in yield losses of up to 20% due to cold-induced spikelet sterility (Kou, Guédé, Office du Niger), weed problems (Thiagar), and late harvesting (Thiagar). Discussions during meetings with farmers at the survey sites revealed that farmers lacked knowledge on (i) optimal timing, dosage and mode of fertilizer application, (ii) optimal sowing dates to avoid yield loss due to cold- or heat-induced sterility, and (iii) the importance of N as the main limiting factor to yield. Possibilities to achieve a sustainable increase in rice productivity and profitability in West African irrigation systems are discussed.