An Approach to Estimate Optimal Cut-off Time under Deficit Irrigation

Abstract

The use of deficit irrigation technique has become inevitable due to the lack of water resources in many parts of the world. The goal of this study is to improve the performance of border irrigation under deficit strategy by determining the optimal cutoff time (Tco). For this purpose, field experiments and simulation modeling were carried out. The experimental borders were different in terms of inflow discharge, soil texture and length. 1024 combinations included different physical and management factors were analyzed by the WinSRFR software. By determining the optimal Tco for each combination, fifteen regression equations were extracted for three irrigation levels and five advance times (Ta) (times when water advanced to 30 to 70% of the border lengths). Two indexes including Y (combination of efficiency and uniformity indices) and Y′ (combination of efficiency, uniformity, and requirement efficiency) were used to evaluate border irrigation performance. Based on the validation results, the relationship between Tco and Ta at the 70% of the border length was introduced as a suitable option. The performance of the selected equation was evaluated using the field data. The results illustrated that the calculated values of Y and Y′ from the proposed method was in high agreement with theses from the common optimization method. Tco obtained from the proposed relationship improved the Y and Y′ indices by 9.4 and 6.6%, respectively, compared to the field conditions. The proposed relationship will guarantee application efficiency above 60%, uniformity and requirement efficiency above 80%.