Effects of nitrogen fertilization on crop water stress index ofsummer maize in red soil

Available soil water and N fertility are the primary factors limiting dryland crop yield in red soil areas of south China, where N nutrient is usually deficient and seasonal drought occurs frequently during summer and autumn. For the strategy of soil water and N fertilizer management, we investigated the effects of nitrogen fertilization on the crop water stress index (CWSI) in summer maize. The experiments were carried out in the waterproof field plots with sufficient irrigation before and after the soil drying interval of 0, 7, 12, 17, 22, 27 and 32 days in the maize growth period from 30 to 62 days after planting. Nitrogen fertilizer was broadcast as urea at N 0, 140, and 280 kg/ha for each drought treatment. The results show that CWSI is an indicator of maize crop water stress status during the soil drying course. However, the relationship between CWSI and crop yield are changed by increasing the slope of regression equation under the application of N fertilizer. Under slight and moderate soil droughts, N fertilization has less influence on CWSI, while under severe soil drought, the crop yield is decreased under N fertilization and CWSI is increased under high amount N fertilizer, which indicates crop water stress is aggravated by increasing levels of N fertility. The results suggest that the effects of N fertilization on CWSI vary as the fluctuations of soil water stress and amount of N fertilizer.