Simulating Water and Nitrogen Dynamics in Drip-irrigated Soil Based on the HYDRUS-2D Model

【Objective】 Water flow and solute transport in soil is important not only for plant acquisition of resources from soil but also for soil and water environment. In terrestrial ecosystems, they are impacted by numerous factors. The objective of this paper is to investigate the effects of drip irrigation amount on spatiotemporal change in water and nitrogen in Hetao Irrigation District, Inner Mongolia. 【Method】 A field experiment was conducted to measure the movement of water, nitrate and ammonium in soils, with the irrigation amount controlled at 6 mm (D1) or 60 mm (D2). The measured data was used to calibrate the HYDRUS-2D model, and the calibrated model was then used to elucidate how increasing the irrigation amount to 120 mm would affect water and nitrogen movement. 【Result】 Irrigation increased soil water content in all growth stages. Following irrigation and fertilization, ammonium and nitrate contents both increased rapidly and then decreased. On average, ammonium and nitrate in the 0~10 cm soil layer decreased by 60.0%~62.0% and 40.0%~46.7%, respectively, after the D1 and D2 irrigations, with the decreasing rate varying with growing stage. Compared to D2, D1 increased soil water content at jointing, heading and filling stage by 5.9%, 8.0% and 6.7%, respectively. Soil ammonium and nitrate both decreased along the soil depth. Nitrate accumulation decreased gradually when the crop grew from jointing stage to filling stage. The simulated soil water content and nitrogen agreed well with the measured data. 【Conclusion】 Experimental data and simulated results showed that irrigating the maize by 120 mm of water can effectively reduce accumulation of nitrate in the 0~60 cm soil layer, and that increasing irrigation frequencies can further curtail nitration accumulation in the 60~100 cm soil layer. These results provide guidance for improving irrigation and fertigation for maize production in Hetao Irrigation District.