Hole irrigation process simulation using a soil water dynamical model with parameter inversion method

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 (R-2 > 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.

Automated summary

Soil water dynamics are crucial in agricultural irrigation evaluation and water-saving research. A mathematical model was developed using the Richards equation for hole irrigation, showing that single-hole irrigation results in higher soil moisture content than double-hole irrigation. While double-hole irrigation can evenly infiltrate soil in a short time, it does not stimulate long-term crop root growth, which can be achieved through alternating single-hole irrigation.