Modelling the impact of climate variability and irrigation on winter canola yield and yield gap in Southwest China

Southwest China (SWC) is one of the major canola production areas in China. Due to frequent seasonal drought during the canola growing season, irrigation plays a vital role in improving canola yields. However, the impact of irrigation and climate variations on canola yield and the yield gap (the difference between potential and rainfed yield) has not been properly addressed. Existing experimental data are limited and are not sufficient to answer these questions. A modelling study is therefore warranted to extend the experimental findings. In this study, we used a modeling approach to quantify the yield potential and the yield gap of canola crop, how they are affected by inter-annual climate variability, and how much water is required for irrigation to close the yield gap in southwest China. The APSIM-Canola model was firstly calibrated and validated against experimental data at Yuxi site in SWC from 1981 to 1989. The model was then used to simulate the canola yield under irrigation and rainfed conditions from 1961 to 2010. The simulation results were used to explore the impact of different irrigation scenarios on canola yield. From 1961 to 2010, minimum temperature increased by 0.5 degrees C per decade (p < 0.01) during the canola growing season, whereas daily global radiation decreased by 0.3 MJ m(-2) per decade (p < 0.01). Growing season precipitation ranged from 44.3 to 310.9 mm with a non-significant decreasing trend. The warming and dimming trend from 1961 to 2010 was estimated to reduce the potential yield at the rate of 151 kg ha(-1) per decade (p < 0.01), mainly due to reduced radiation and length of growing period. Simulation results with a single hybrid cultivar showed that the potential canola yield under fully irrigation (3452kg ha(-1)) is about three times the rainfed yield (1215 kg ha(-1)). Improved irrigation increases yield and water productivity, particularly in dry seasons. To achieve similar to 80% of the potential yield, an average amount of 330.1 mm, 302.9 mm, and 265.2 mm irrigation water, were required for canola in wet, medium, and dry seasons, respectively. Longer season canola cultivars may help to mitigate the negative impact of further climate warming in the future.