Modelling wheat yield responses to soil and climate variability at the regional scale

We present a study on the impact of soil and climatic variability on the yield of winter wheat in the Hérault-Libron-Orb Valley in southern France. The study was based on the use of a crop simulation model (Euro-ACCESS), run at 63 individual sites throughout the study area, for the current climate (1976 to 1984) and for potential future changes in temperature and precipitation (2047 to 2054). Three climate scenarios were selected to represent low, mid and high changes, although significant winter wheat yield decreases were only observed for the climate scenario with the largest change. In general, the influence of climate change on yields was small (less than 0.1 t ha–1 over the whole simulation period), but strong inter-annual variation was found, which is typical of the Mediterranean climate. Soil variability within the study region was the most important source of spatial variability for the simulated yields, and the soil available water capacity was identified as a good indicator of yield change for large climatic change. Soil variability was important in this study because of the small size of the study region and because of the strong influence of water limitation on crop growth in Mediterranean areas. Statistical relationships were established between crop yields, yield changes and the soil available water capacity. These relationships were used to extrapolate the crop simulation results from individual sites to the whole region using data from soil maps at a scale of 1:250 000. This modelling exercise demonstrated the importance of explicit consideration of soil as well as climatic variability in crop-climate impact studies.