Fertilizer Use Efficiency and Profitability of Irrigated Rice in Mali and Niger.

Rice is a strategic for food security in Africa. Maximizing profitability of fertilizer use requires determination of nutrient response functions. Three and two trials were conducted in Niger and Mali, respectively, in the Niger River valley. The objectives included determination of response functions for N, P and K applied to irrigated rice, and diagnosis of other nutrient deficiencies. Average grain yields were 3.07, 4.09 and 5.49 Mg ha^-1 in Niger and on Danga and Moursi soil types in Mali, respectively. Nitrogen response was curvilinear to plateau in all cases except for a linear response for the Danga soil in Mali. Yield increases with up to 150 kg ha^-1 N ranged from 0.5 to 1.7 Mg ha^-1. Responses to P were also curvilinear with grain yield increases of approximately 0.3 and 1.7 Mg ha^-1 in Niger and Mali, respectively, with 30 kg ha^-1 P. The economically optimal rate (EOR) for N when fertilizer use cost was 4.5 times the value of rice grain (kg kg^-1) ranged from 62 to > 150 kg ha^-1. The EOR of P ranged from 27 to 33 kg ha^-1 and from 12 to 16 kg ha^-1 in Mali and Niger, respectively, depending on the relative cost of fertilizer P. Agronomic efficiency of N varied from <10 to 20 kg kg-1, and of P with 10 kg ha-1 P from 50 to 118 kg kg-1, depending on location. This information can be applied in fertilizer use decision tools oriented to farmer profitability in Mali and Niger.