An Improved Dimensional Model for Calculating the Wetting Pattern in Soil under Drip Irrigation

Abstract

The development of wetting zone in soil under drip irrigation is an important design parameter that is difficult to determine a priori. Using Hydrus-two-dimensional (2D), this paper studied water movement emanating from the drip emitter under different conditions, from which we proposed an improved dimensional model to calculate the radius and depth of the wetting zone using initial soil water content, saturated hydraulic conductivity, irrigation amount, and dripping rate as independent variables. The accuracy of the model was validated against experimental data published in the literature and measured by us. The results show that, compared with experimental data, the root mean square error of the wetting radius and depth estimated using the proposed model are 3.05 cm and 4.76 cm, respectively, with their associated Nash efficiency coefficient being 0.805 and 0.767, respectively. Compared with existing dimensional models that do not consider initial soil moisture prior to irrigation, the proposed model is more accurate and can be reliably used for drip irrigation design. The development of wetting zone and its final shape on the soil surface under drip irrigation is an important parameter to design the distance between emitters but difficult to determine analytically because of the complexity and nonlinearity of soil water flow. Based on previous work, this paper proposes an improved dimensional model to analytically calculate the size of the wetting zone. The model is mathematically simple and uses initial soil moisture content, saturated hydraulic conductivity and irrigation amount as independent variables. The soil physical parameters (saturated hydraulic conductivity and soil matrix potential) in the proposed model can be easily obtained through conventional field experiments. Test against experimental data measured by us and published in the literature for different soils shows that the proposed model is more accurate and robust than existing models and can be used to help design drip irrigation in different soils.