Comparison of strategies for optimizing management parameters and estimation of optimal cutoff time for furrow irrigation

Furrow irrigation has been one of the most commonly used approaches for crops, but with the low yield of irrigation water. In this study, 45 sets of experiments were conducted to further improve the performance of furrow irrigation in the Guanzhong Plain of Shaanxi province, China. Three optimization strategies of management parameters were quantitatively compared (Strategy 1: only optimize the cutoff time; Strategy 2: only optimize the inflow discharge; Strategy 3: simultaneously optimize the inflow discharge and cutoff time). A simplified method was proposed to estimate the optimal cutoff time for the closed-end furrow irrigation. The results show that Strategy 3 presented the best performance of the irrigation, followed by Strategies 1 and 2. The application efficiency, distribution uniformity, and storage efficiency for Strategy 3 increased by 20.5%, 10.6%, and 3.3%, respectively, and these increased by 13.8%, 4.1%, 1.1% and 6.8%, 9.3%, 0.4% for Strategies 1 and 2, respectively, compared with the measured. More importantly, Strategy 3 was recommended only from the perspective of irrigation performance, but Strategy 1 was recommended when considering the practicability of the optimization strategy at the same time. A linear function was used to characterize the optimal cutoff time, optimal cutoff time, and the time when water advanced to 0.75 length of the furrow (T0.75L), where the determination coefficient of the function was 0.920, according to the different capacities of soil infiltration and the combinations of irrigation elements. The mean absolute percentage error was 16.71% between the simulated and estimated optimal cutoff time values. The Tcop values of Strategy 1 and 3 were estimated by T0.75L, indicating fully consistent with the simulation using WinSRFR software. The mean absolute percentage errors of all furrow irrigation experiments were 10.88% and 12.00%, respectively. The indicators of irrigation performance were simulated with the optimal cutoff time under Strategies 1 and 3. It was found that the optimization values were lower than those in the simulation. But there were small declines of the application efficiency, distribution uniformity, and storage efficiency values, which were 1.0%, 4.0%, 3.5% and 4.0%, 4.8%, 4.1% for Strategies 1 and 3, respectively. In addition, the estimated optimal cutoff time values of Strategies 1 and 3 were used to simulate the irrigation performance, where the comprehensive irrigation performance indicator not less than 85.0%, accounting for 77.3% and 90.2% of the effective experiments, respectively, indicating an outstandingly higher than the current condition (64.4%). Therefore, this approach can be used to reliably estimate the optimal cutoff time values for the closed-end furrow irrigation, according to the time when water advanced to 0.75 length of the furrow, T0.75L. The finding can provide a strong basis to develop a real-time feedback control system in surface irrigation.