Potential impacts of climate change on the grain yield of maize for the midlands of KwaZulu-Natal, South Africa

The increase in atmospheric carbon dioxide concentration and changes in associated climatic variables will likely have a major influence on regional as well as international crop production. This study describes an assessment of simulated potential maize (Zea mays) grain yield using (i) generated weather data and (ii) generated weather data modified by plausible future climate changes under a normal planting date and dates 15 days earlier and 15 days later using CropSyst, a cropping systems simulation model. The analysis is for maize production at Cedara, a summer rainfall location within the midlands of KwaZulu-Natal, South Africa. Baseline weather data input series were generated by a stochastic weather generator, ClimGen, using 30 years of observed weather data (1971-2000). The generated baseline weather data series was similar to the observed for its distributions of daily rainfall and wet and dry day series, monthly total rainfall and its variances, daily and monthly mean and variance of precipitation, minimum and maximum air temperatures, and solar radiant density. In addition, Penman-Monteith daily grass reference evaporation (ET nu) calculated using the observed and generated weather data series were similar except that the ET nu values between 2 and 3 mm were less for the observed than for the corresponding generated values. Maize grain yields simulated using the observed and generated weather data series with different planting dates were compared. The simulated grain yields for the respective planting dates were not statistically different from each other. However, the grain yields simulated using the generated weather data had a significantly smaller variance than the grain yields simulated using the observed weather data series. The generated baseline weather data were modified by synthesized climate projections to create a number of climatic scenarios. The climate changes corresponded to a doubling of carbon dioxide concentration to 700 mu l(-1) without air temperature and water regime changes, and a doubling of carbon dioxide concentration accompanied by mean daily air temperature and precipitation increases of 2 degrees C and 10%, 2 degrees C and 20%, 4 degrees C and 10%, and 4 degrees C and 20%, respectively. The increase in the daily mean minimum air temperature was taken as three times the increase in daily mean maximum air temperature. Input crop parameters of radiation use and biomass transpiration efficiencies were modified for maize in CropSyst, to account for physiological changes due to increased carbon dioxide concentration. Under increased carbon dioxide concentration regimes, maize grain yields are much more affected by changes in mean air temperature than by precipitation. The results indicate that analysis of the implications of variations in the planting date on maize production may be most useful for site-specific analyses of possible mitigation of the impacts of climate change through alteration of crop management practices. (c) 2006 Elsevier B.V. All rights reserved.