Spatial distribution and simulation of soil moisture and salinity under mulched drip irrigation combined with tillage in an arid saline irrigation district, northwest China

Hetao Irrigation District, a large irrigation district in arid area, northwest China, is suffering from the decreasing water supply and increasing soil salinization. Mulched drip irrigation is widely used for agricultural production in arid area, and tillage management affects soil environment variously. This study aimed to explore combined effects of tillage and mulching modes on soil water and salt transfer under drip irrigation. The experiment included 4 treatments: ridge tillage with full film mulching (RFM), ridge tillage with partial film mulching (RPM), flat tillage with full film mulching (FFM) and flat tillage with partial film mulching (FPM). The results showed that RFM increased soil moisture in root zone (0-40 cm). Soil salt was pushed to the edge of soil wetting front and, RFM and FFM reduced salt accumulation in 0-70 layer significantly than RPM and FPM, indicating that full film mulching could retard the upward movement of soil salt more effectively. Furthermore, the performance of HYDRUS-2D was calibrated and evaluated by comparing the simulated values with observed values, and further verified model by another year dataset, to simulate the spatial distributions of soil water and salt in the two directions under mulched drip irrigation with different irrigation quantity. The simulation showed that the wetted region was expanded to the middle position of the film and the uniformity of irrigation increased with the increasing irrigation amount. In addition, the increasing of assumed irrigation amount induced soil desalination and make soil salinity spatial movement meet a discipline that the direction parallel to the drip line was lower than that perpendicular to the line at the same distance. In all, RFM could be adopted for optimizing soil water-salt regulation under drip irrigation in Hetao Irrigation District, and the model presented here is an efficient approach for investigating the regulation mechanisms of root-zone water and salt dynamics under mulching and/or tillage.