Crop rotation and N application rate affecting the performance of winter wheat under deficit irrigation

Deficit irrigation to winter wheat is gradually adopted in the North China Plain (NCP) for conservation of groundwater resources. N application to winter wheat should be decided based on the irrigation water availability. Under deficit irrigation, yield of winter wheat was also related to the water use characters of its previous crops. Field studies were conducted from 2013 to 2016 at Luancheng station in the NCP to evaluate the addition of soybean to the conventional annual double cropping system (winter wheat-summer maize) and reducing N input on the performance of winter wheat under deficit irrigation. Summer maize was either replaced by soybean or inter-planted with soybean. The subsequent winter wheat was applied with six nitrogen rates (0, 135, 216, 270, 324 and 405 kg/ha) with one irrigation or two irrigation applications. The results showed that the average seasonal water use of single soybean (SS), intercropping of maize and soybean (IMS) and single maize (SM) was 359.1 mm, 336.3 mm and 309.6 mm from 2013 to 2016, respectively. The inclusion of soybean as single or inter-planted crop increased the water use during the summer rainy season, which was related to the increase in leaf area index. As compared with the SM, the soil water stored in the 2 m soil profile at the summer crops harvesting was reduced by 24.7 mm and 94.7 mm in 2014, 15.9 mm and 95.6 mm in 2015, respectively, for the IMS and SS, respectively. Due to the dependent of winter wheat on the stored soil water before sowing, the reduction in pre-season soil water content significantly decreased the yield by 1005.4-1878.0 kg/ha. Yield of winter wheat didn't respond to the increase in N application when N rate was over 135 kg/ha. The local N application rate at 270 kg/ha could be reduced up to 50% without apparent effects on crop productivity under deficit irrigation scheduling. The results indicated that for diminishing the reduction in yield of winter wheat under limited water supply, its previous crop with less water use in summer season should be selected. Yield of winter wheat could be maintained with half of its normal N application under limited water supply.