Climate change impact on water- and nitrogen-use efficiencies and yields of maize and sorghum in the northern Benin dry savanna, West Africa

Abstract

Climate change and variability challenge crop productivity and resource use efficiency in West Africa. Despite abundant research on climate change impact on crop yields and food security, little is known about climate change effects on the resource use efficiencies of the main staple crops in the dry savanna agro-ecological zone of northern Benin, West Africa. This study assessed the impact of climate change on water- and N-use efficiencies, and yields of maize and sorghum in the dry savanna of northern Benin considering three soil fertility management options (return of crop residues, mineral NPK fertilizer application, and combinations of both) and three bias-corrected ensemble mean predictions (BNU-ESM, CanESM2, and MPI-ESM-MR models) of future climate (2080–2099) under Representative Concentration Pathways (RCPs) of 2.6, 4.5, and 8.5. Seasonal rainfall is projected to decrease by 2% under RCP 2.6 and by 4% under RCP 4.5, and to increase by 1% under RCP 8.5 relative to the baseline mean (1986–2005). Increasing trends in minimum temperature of +1.0 °C (RCP 2.6), +2.0 °C (RCP 4.5), +4.7 °C (RCP 8.5) and maximum temperature of +1.1 °C (RCP 2.6), +2.0 °C (RCP 4.5), +4.6 °C (RCP 8.5) are also predicted. Solar radiation was projected to decrease by about 0.4 MJ m−2 d-1. Under these projected climate scenarios, both CERES-Maize and CERES-Sorghum simulated positive responses in aboveground biomass accumulation during the vegetative growth stages. The predicted increase in aboveground biomass growth will be largest under RCP8.5 and smallest under RCP 2.6. This impact can be enhanced by improved soil fertility management, albeit with a crop-specific magnitude. Across the soil fertility management options, CERES-Maize predicted decreases in water-use efficiency by 17–53%, partial factor productivity of nitrogen (N) by 10–47%, and internal N-use efficiency by 5–33% for maize. Similarly, CERES-Sorghum simulated decreases in water-use efficiency (23–51%), partial factor productivity of N (22–49%), and internal N-use efficiency (13–47%) for sorghum. The largest overall loss in resource efficiency and yield were predicted for the RCP 8.5 scenario. The projected climate change for the dry savanna in northern Benin will likely reduce water- and N-use efficiencies as well as grain yields of maize and sorghum considerably but these results should be treated with caution due to shortcomings in the models structure for dealing with effects of enhanced CO2. For reliable assessments of climate change impact on WUE, it is critically important to update parameterization and code of the CERES crop models in DSSAT to have a sufficiently strong effect of CO2 on stomatal conductance and on transpiration.