Abstract:
Abstract: Extensive sand layers are widely distributed over the impact plain of the Yellow River, particularly for Hetao Irrigation Areas in Inner Mongolia of western China. The migration of water and salt under the soil sand layer has posed a great influence on soil water utilization, soil salinization control, and crop growth. In this study, a numerical model of soil water movement was proposed to investigate the field evapotranspiration, crop water consumption, water supply, and deep soil water leakage in the sand layer using the data of field monitoring and laboratory experiments during the growth period of spring maize. Taking the cultivated land of the typical sand layer in the Hetao Irrigation Area as the research object and planting crop as spring corn, two gradients of buried depth were selected: S1 (40-95 cm) and S2 (60-110 cm) of the sand layer in the soils. Three irrigation levels were also set to carry out the field experiment, and then to compare with BWI without sand layer, including W1 (252.5 mm), W2 (315.85 mm), and W3 (378.75 mm). A HYDRUS-1D model was selected to simulate the field evapotranspiration during the growth period of spring maize, deep seepage of soil water, groundwater recharge, and root water absorption. In addition, the temporary water deficit and water productivity were calculated during the whole growth period. Water use in the cultivated land with sand layer was then compared with that without sand layer. The results showed that the soil evaporation loss between grains decreased, whereas, the leaf transpiration water increased, with the increase of buried depth of the sand layer. Specifically, the soil layer above the sand layer was thicker, the soil water storage was larger, the surface soil moisture content was higher, and the soil negative pressure was lower when the buried depth of the sand layer was larger. As such, the deep soil water was less replenished upward through the capillary action. At the same time, there was less leakage to the deep layer below the sand layer after irrigation. Furthermore, the upstream water supply of maize in the field without sand layer increased by 57.01% and 118.53%, respectively, compared with the treatment of shallow (40-95 cm), and deep sand layer (60-110 cm). More importantly, the deep-water leakage of soil under the treatment of sand layer was the least, when the irrigation amount was 315.85mm. Correspondingly, the water absorption of maize roots decreased with the increase in the buried depth of the sand layer, where the largest was found without sand layer during the growth period. Specifically, the shallow (40-95 cm) and deep sand layer (60-110 cm) treatment were 55.51% and 61.31% of evapotranspiration, respectively, whereas, the treatment without sand layer was 66.69%. The irrigation system can be determined for spring maize in the sand layer, according to the sand layer distribution and local conditions. Particularly, the recommended irrigation quota of spring corn can be 315.85 mm during the growth period, when the sand layer was similar to the S1WI and S2WI treatment. The recommendation can be attributed to avoiding the leakage loss of irrigation water in the deep soil water of the farmland with the sand layer. The findings can also provide important theoretical guidance for the formulation of a farmland irrigation system with the sand layer in the Hetao Irrigation District.