Variable-Rate Irrigation Uniformity Model For Linear-Move Sprinkler Systems

Variable-rate irrigation (VRI) can vary the application rate by either changing the amount of water flowing through sprinkler nozzles (zone control) or varying the speed of a moving irrigation system across parts of a field, referred to as speed/sector control. The uniformity of sprinkler irrigation in each management zone under VRI directly affects crop growth and yield. The use of different nozzle diameters on a linear-move sprinkler irrigation system is a simple and affordable method for achieving VRI. There are few studies on modeling the uniformity of VRI on linear-move sprinkler irrigation systems. In this study, a cubic spline difference-value model was used to simulate the variable-rate water distribution and uniformity of a linear-move system. Nine tests were designed to evaluate VRI uniformity with different nozzle diameters. A simulation and corresponding field experiments were carried out. The application rate of the simulation model was higher than the experimental values because of wind drift. The uniformity coefficients of the simulation with nozzle diameters of 1.98, 2.97, and 4.17 mm in tests 1, 2, and 3 were 86.56%, 85.24%, and 79.94%, respectively. The uniformity coefficients of the VRI simulations with combinations of nozzle diameters in tests 4 through 9 were 76.89%, 80.70%, 76.67%, 69.58%, 76.64%, and 81.87%, respectively. The smallest error between the simulation and experiment was 1.6%, and the largest error was 13.0%. The simulation model and prediction method can be applied to other sprinkler irrigation systems.