Evaluating the effects of texturally distinct soil layers on water flow, solute transport and crop growth with a coupled agro-eco-hydrological model

Soil salinization is one of the key issues in the upper Yellow River basin. Soil capping with capillary barriers is a common practice to hydraulically isolate contaminated soils, which may improve the soil environment for plant growth. To predict the influences of the soil capping on crop yield and soil salinization control in the arid area with shallow groundwater table, a one-dimensional agro-eco-hydrological model, LAWSTAC, capable of simulating water and solute transport in layered soil coupled with crop growth, was applied for simulating sunflower growth in a farmland in Inner Mongolia Autonomous Region of China. The LAWSTAC was calibrated and validated with the experimental data of 2012 and 2013, and the simulation results compared well with the observed soil water content, salt concentration, leaf area index, and sunflower yield. Then this study explored how the soil capping with different thicknesses of top fine layers (10, 15, 18 and 20 cm) and coarse subsoil layers (0, 2, 5 and 10 cm) would influence the soil water and salt dynamics, and yield. Results showed that the soil capping could slightly decrease the water storage in the root zone and rapidly reduce the salt content in crop growth season compared with that in the original soil. The water storages in the root zone showed a negative correlation with the thickness of sand interlayer. The salt contents in the root zone, regardless of thickness of sand interlayer, were all significantly lower than that in the control. A soil capping layer with a thin sand interlayer (about 2-5 cm) was found to be helpful for salt suppression and crop yield increase and can be used to create a low-salt soil environment for seed germination, which will save irrigation water for salt leaching from the root zone before sowing.