Impact of climatic variables on the spatial and temporal variability of crop yield and biomass gap in Sub-Saharan Africa- a case study in Central Ghana

We investigated the impact of climate variables on yield and biomass gap variability in two humid topical regions, Brong-Ahafo and Ashanti region, of central Ghana using the crop model LINTUL5 embedded into a general modeling framework, SIMPLACE (Scientific Impact Assessment and Modelling Platform for Advanced Crop and Ecosystem Management). The simulations were run using a late maturity maize variety (Obatanpa) and historical weather data (1992-2007) across the 18 districts of the regions studied. The simulated maize yield and biomass production under water-limited conditions varied spatially which was significantly correlated with the solar radiation and precipitation in the crop growing period (R2 = 0.99; p < 0.05), whereas, associated temporal variability in the simulated maize yield was significantly correlated with the radiation in the crop growing period (R2 = 0.96; p < 0.05). The temporal variability in the simulated potential biomass production was significantly correlated with the solar radiation and average temperature in the crop growing period (R2 = 0.93; p < 0.05), postulating that the solar radiation and the mean temperature are the limiting climatic factor in the study regions. Yield gaps and biomass gaps ranged between 8.8 Mg ha−1 to 10.0 Mg ha−1 and 14.8 Mg ha−1 to 17.1 Mg ha−1 respectively across the districts. Thus average farmer's yield and biomass is only 17% and 13% of the simulated water-limited yield and biomass respectively. The spatial and temporal variability in yield gap was positively correlated with the radiation during the crop growing period. Associated spatial variability in biomass gap was positively correlated with radiation and negatively with the precipitation, whereas temporal variability in the biomass gap was positively correlated with the radiation during the crop growing period. Thus, under the current input intensities in humid, tropical Central Ghana, neither maize grain and biomass yields nor the potential water limited yields are significantly positively related to precipitation during the growing cycle. Closing the large yield gaps will require in the first place adequate supply of nutrients.