Profitable and Sustainable Fertilizer-Management Option in Double Cropping of Irrigated Rice in Senegal River Valley

One of the main factors limiting the yield and productivity of irrigated rice in the Sahel of West Africa is the high cost of fertilizers and inefficient use of nutrients in the cropping systems. A two-year experiment was conducted over four consecutive seasons at Ndiaye (16°11’N, 16°15’W) and Fanaye (16°32’N, 15°11’W) along the Senegal River Valley to investigate alternative fertilizer management options in the double cropping system of rice. Eight fertilizer management options (FMO) were compared to the recommended seasonal application of NPK fertilizer based on yield data, the value-cost ratio (V/C) and the sustainabily of the recommendation. Rice yields increased from 2.5 t/ha without fertilizer application to 8 t/ha under the nine FMOs, which produced similar yields each season at both sites. The V/Cs of the recommended NPK fertilizer (applied each season) varied from 2.3 to 3.7. The V/Cs of FMO that supplied NPK during the hot dry season (HDS) and N during the wet season (WS), or conversely (NPK-N) varied from 3.2 to 5.7. The V/Cs of NPK-NP varied from 2.4 to 4.3. The V/Cs of NPK-NK varied from 2.4 to 4.4. The highest V/Cs ratios (5.2 to 6.3) were obtained by FMOs that supplied NP during the HDS and N during the WS, or conversely. It is concluded that when soil P-Bray1 is above 7 mg P ha, FMOs that supply NPK fertilizer in one season and only N fertilizer in the following season could reduce the cost of fertilization by 26% and improve rice productivity for sustainable management of the double cropping system of rice in the Senegal River Valley.