Optimization of irrigation scheduling considering constraints of surface irrigation technology

Irrigation scheduling should be determined by considering both the crop requirements and the constraints of the irrigation method. In order to research the irrigation scheduling that is appropriate for wheat-maize crop sequence in the North China Plain, different treatments of irrigation experiments were performed in three consecutive years in Xiongxian, Hebei Province. All treatments of the experiments were simulated by the soil water balance model ISAREG. The simulation results showed that the parameters were calibrated and the model was validated well. Several alternative irrigation strategies were simulated with the model for the years corresponding to different probabilities of irrigation requirements. The irrigation times, application depths, water losses both from irrigation and rainfall, and crop yields were compared. The current irrigation scheduling was evaluated. The comparison results show that the current application volumes largely exceed the irrigation requirements. Main reasons were the constraints of the surface irrigation technology, such as uneven basin surface, relative small inflow rate and large basin sizes, which caused difficulty to control the irrigation in a small water volume. In order to get the appropriate application depth for each irrigation that can not only meet the basic crop water requirement, but also lead to minimum water losses, the surface irrigation model SRFR was used to simulate the irrigationships in different crop growing periods. From the simulations, the minimum net irrigation depth and the relationships between the application efficiency and the low-quarter infiltration depth were obtained for each irrigation and different inflow rates. Based on above results, the improved irrigation schedulings for average, dry and severe dry years were proposed by combining improvement of irrigation methods.