Review on variable rate irrigation with continuously moving sprinkler machines

With the scale, intensive and modern development of China??s agriculture, it supplies the opportunity for the utilization of continuously moving sprinkler systems. In the large area covered by individually continuously moving sprinkler machine, the spatial variability of crop yield is inevitably caused by soil and crop performance variability. Variable rate irrigation (VRI) has the capability of applying spatially varied water depths to address specific soil, crop, and/or other conditions across the entire field. It has been recognized as an efficient water management practice to enhance water potential productivity for continuously moving sprinkler machines. However, for this emerging irrigation technology, especially in China, we have quite limited knowledge on optional management of VRI systems due to substantially short research history. The advances in VRI research, including the connotation, architecture and construction, identification of management zones, decision support system and economic benefits for VRI system with continuously moving sprinkler machines, are thoroughly reviewed in this article. Moreover, the future research topics are suggested aiming at accelerating the research and application of VRI technology and improving water management for continuously moving sprinkler systems. The study indicates that the theory about the architecture and construction of VRI systems is relatively mature, and it consists of various methods to vary water application depths, a method of position determination, and a microprocessor-based device to control water application amounts from each sprinkler head or groups of sprinkler heads based on location and other management criteria. Besides, the test standard of hydraulic performance for VRI system needs to be further studied. The static delineation of management zones and prescription maps based on soil characteristics is the main water management method for VRI systems, and the dynamic water management based on the continuous monitoring and assessment of climatological and crop data stands for the future of VRI systems. With the development of research about the effects of soil texture on crop potential yield, water use efficiency and crop canopy temperature, the feasibility assessment on static water management and the integrated development of dynamic water management need to be further studied. The decision support system should be developed individually according to the precipitation amount, and the maximum water use efficiency and crop yield should be set as the main objective under dry weather and humid climate conditions, respectively.