Modeling maize yield responses to improvement in nutrient, water and cultivar inputs in sub-Saharan Africa

Maize yields in sub-Saharan Africa (SSA) are at the lower end of the global range of yields since decades. This study used the large-scale agricultural crop growth model GEPIC to simulate maize yield responses to different management scenarios concerning: (a) level of nutrient supply; (b) extent of irrigated areas; and (c) low- or high-yielding cultivars. The results show that extending irrigation or planting an improved cultivar produced little effect on maize yield at the current level of nitrogen (N) and phosphorus (P) application rates. Increasing nutrient supply to the level commonly applied in high-input regions would allow for a tripling of maize yields from the current 1.4-4.5 Mg ha−1 and could increase yields even to 7 Mg ha−1 in combination with an improved cultivar. Irrigation was found to be especially effective for lifting very low yields concomitant to improved nutrient supply and cultivar. The highest yields when combining all the three improved management practices were predicted for East and Southern Africa with mostly 8-10 Mg ha−1, and West Africa with 7-9 Mg ha−1. The lowest yield potentials were found for the Western parts of Central Africa where they often reached only about 4-6 Mg ha−1, due to low solar radiation and low nutrient availability on highly weathered soils. The inputs required for reaching these high yield levels would be very costly. Nevertheless, the simulation shows that with a supply of only 50 kg N ha−1 and 18 kg P ha−1, which is less than one third of the current level in high-input countries, the maize yield could be doubled for most areas in SSA. The resulting increase in maize production would be about 10 times of the amount currently imported to the sub-continent including food aid.