Developing optimal drip irrigation schedule for alfalfa production in desert using the HYDRUS-1D model

Abstract

【Objective】 Soil water is one of the most important abiotic factors influencing plant growth in arid areas. This paper aims to develop an optimal drip irrigation schedule for alfalfa production in desert farmlands in Northwestern China. 【Method】 The study was based on the HYDRUS-1D model . It compared four irrigation schedules: intensive irrigation (LH-I), moderate intensity irrigation (MH-I), and low intensity irrigation (SM-I). Without irrigation was the control (CK). Each irrigation schedule was associated with five initial volumetric water contents in the 0-20 cm soil layer: 4% (S1), 6% (S2), 8% (S3), 10% (S4) and 12% (S5). Overall, there were 20 combinations. In the simulation for each treatment, we “measured” the time for soil water in the root zone to reach the wilting point, as well as the soil water content at the wilting point. We also measured the time-period during which the soil water content in the root zone remained above the wilting point. These enabled us to find the optimal irrigation schedule. 【Result】 The effect of SM-I and CK on the above criteria was more sensitive to change in the initial soil water content in the top 0-20 cm of soil. The plant roots were able to take up water even without irrigation when the initial soil water content in the 0-20 cm of soil was greater than10%. When the initial soil water content was less than 20%, the majority of irrigated water in the LH-I treatment remained in the topsoil. With an appropriate initial moisture content, the topsoil had a positive effect on retaining the irrigation water from MH-I in the root zone. The retention time of water in the root zone was positively correlated with the topsoil water content in SM-I. The water content in the deep soil was greater in LH-I irrigation than in other treatments. Soil water content remained above the withering point for 5.7 days in MH-I, the longest among all treatments. 【Conclusion】 When initial volumetric water content in the 0-20 cm soil layer was less than 4%, LH-I was optimal, when the initial topsoil water content was higher than 4%, MH-I worked the best.

Keywords

• desert farmland
• alfalfa
• drip irrigation
• moisture content
• irrigation scheduling