Abstract
Soil water dynamics are an important part of agricultural irrigation evaluation standards; therefore, supplying water efficiently has become the focus of agricultural water-saving research, and different soil water movement models have been developed for various water supply models. In this work, a parameter inversion model is coupled with the soil water movement equation (the Richards equation) based on the main variable of the head (h)-based Richards equation to investigate the dynamics of soil moisture under hole irrigation. A mathematical model for hole irrigation with two hole diameters (5 cm or 7 cm) and two hole numbers (one or two) was constructed after verifying the model with field-scale soil water content data from different soil profile depths. The Richards equation based on the Gauss–Newton parameter inversion method was found to accurately simulate the soil moisture dynamics under hole irrigation (R2>0.9). The difference in the water content of the soil profile due to the difference in hole diameter did not exceed 2.7%, and the soil water content under single-hole irrigation was significantly higher than that under double-hole irrigation due to lower evaporation. The infiltration distance of the wetting front under single-hole irrigation, which was mainly distributed on the hole side of the planting ridge, was greater than that under double-hole irrigation at 378 ml irrigation water per plant, and the soil moisture was unevenly distributed at a certain depth. However, the wetting fronts under double-hole irrigation intersected and began to infiltrate the soil evenly within a short time (only 6% of the entire irrigation cycle). The results for wetting front movement under the different hole settings show that double-hole irrigation does not stimulate crop root growth on both sides of the plant in the long term; however, this growth pattern can be stimulated by alternating single-hole irrigation.
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