Irrigation water depth control targets under different combination of irrigation technique elements for border irrigation

Abstract: Studying surface irrigation feedback control technology and strengthening the control and management of the irrigation process is a key to improve the surface irrigation technology. Surface irrigation feedback control methods usually include an accurate estimation of surface irrigation control parameters by field observational data, irrigation time, and appropriate adjustment of the flow rate to achieve a finer control for the whole process of irrigation. In this paper, three irrigation water depth control targets were proposed based on the results of previous studies in combination with irrigation experiences. The irrigation target was to determine the time stopping irrigation using irrigation model so as to control the quantity of irrigation water. Based on large numbers of field measured data, BI1D, a one dimensional hydrodynamic model of border irrigation based on the hybrid numerical method, was used. This study combines field experiment and numerical simulation to analyze the response of irrigation performance index under treatments of irrigation water depth control targets to different combinations of irrigation technique elements such as soil texture, topography, border length, unit inflow rate, and other factors, thereby determining the suitable irrigation water depth control target. The results showed that: 1) Irrigation depth control targets had an significant effect on the irrigation performance index, which were related with soil texture, slope, the length of border and land leveling precision. So, it could improve irrigation performance effectively by reasonable selection of irrigation depth control objectives. The influence of the irrigation water depth control target on irrigation performance was most obvious when length of border changes, followed by the surface slope, finally by land smooth precision. When the border length was 50 m and the soil texture was sandy loam or clay loam, the best target was that the irrigation water depth of quarter field length was equal to minimum irrigation water depth; When the border length was 100 m and slope was 0, the best target was that the minimum irrigation water depth higher than 0; When the border length was 100 m and slope was higher than 0, the best target was that the irrigation water depth of quarter field length was equal to minimum irrigation water depth; When the border length was 150 m, the best target was that the irrigation water depth of quarter field length was equal to minimum irrigation water depth except for clay loam with good field smooth accuracy (the best target was that the minimum irrigation water depth higher than 0); The best target was that the minimum irrigation water depth higher than 0 for the other combinations of irrigation technique elements. The results provide valuble information for formulating border irrigation feedback control scheme.