Analysis of coupling degree between crop water requirement of aerobic rice and rainfall in Beijing areas

Based on the field experimental data in four years, crop water requirement of aerobic rice at every growth stage was determined by soil water balance method. The rainfall amounts in growing season of aerobic rice were calculated under different precipitation probabilities using the weather data in Beijing from 1971 to 2000. For the analysis of the coupling degree between crop water requirement of aerobic rice and rainfall, the guaranteed rates 25%, 50%, 75% and 95% were chosen as typical humid, normal, droughty and extremely droughty year styles, respectively. Using the coupling degree, the supplemental irrigation amount at every growth stage was estimated under four precipitation year styles. Results show that mean value of crop water requirement on aerobic rice was 596.1 mm and the mean ET_c intensity was 4.3 mm/d during entire growing season. The peak values of ET_c intensity occurred at booting ~ earing stage. Under four precipitation year styles, the coupling degrees between crop water requirement and rainfall were 0.82, 0.71, 0.50 and 0.39, respectively. The supplemental irrigation amounts under four precipitation probabilities were 106.6 mm, 171.1 mm, 296.0 mm and 363.9 mm, respectively.