Establishing optimum irrigation schedules for aerobic rice in Beijing using ORZA2000 model

Optimal irrigation is an important aspect to increase water use efficiency (WUE) in water-saving agriculture. In this study, relationships between yield and irrigation quota, water use efficiency and irrigation quota in different types of annual rainfall were analyzed using the validated ORYZA2000 model and the historical daily weather data from 1971 to 2000 in Beijing. Based on the analysis the optimum irrigation schedules of aerobic rice aimed at the highest irrigation water use efficiency (IWUE) were provided for three yield levels (70%, 80% and 90% of potential yield) and three rainfall year types (dry year, normal year and humid year). Results showed that yield increased with the increase of irrigation quota firstly, but it became stable when irrigation quota reached a certain level. There was a large potential for yield increase in dry and normal years, in which yield could be increased by 3000 kg/hm2 with the irrigation quota of 300 to 500 mm. But yield only could be increased by 1000 kg/hm2 with the irrigation quota of 250 mm in humid years. In the optimum irrigation schedules, soil water content in root zone needed to be kept above 67%, 73% and 83% of field capacity for three yield levels of 70%, 80% and 90% yield potential, respectively, and irrigation amount each time should not be too much, from 50 to 60 mm was best. Irrigation times and irrigation quota need to increase for the increase of yield level. Irrigation times ranged from 3 to 8 in dry years, 2 to 5 in normal years and 1 to 5 in humid years for three yield levels, respectively. WUE for these irrigation schedules ranged from 0.92 to 1.28 g/kg. However, IWUE shifted in a wide range from 1.61 to 7.76 g/kg influenced by precipitation in different types of annual rainfall, and IWUE in humid years was higher than normal and dry years. Highest WUE and IWUE were obtained at 80% potential yield level for all rainfall year types, irrigation quota ranged from 98 to 239 mm in different types of annual rainfall, and generally it equaled to 2 to 5 irrigation times.