Determination of Winter Irrigation Quotas for Corn and Oil Sunflower Considering Crop Salt Tolerance Threshold under Subsurface Pipe Drainage Technology

Abstract

Subsurface pipe drainage (SPD) is an important technique for the improvement of saline–alkali lands in China. Winter irrigation after crop harvest is a key measure used in the Yellow River irrigation area in northwest China to reduce soil salinity in the root zone of crops. To optimize winter irrigation under SPD, the calibrated HYDRUS-2D model was utilized in this study to investigate the effects of soil texture (clay loam, silt loam, loam, and sandy loam), initial soil salinity (1, 3, 5 g/kg), and the winter irrigation quotas (80, 100, 120, 150, 180 mm) on the rate of soil desalination. In this study, soil salinity levels during the stable production of common crops such as sunflower and corn in the Yinbei Irrigation District in Ningxia, China, were taken as the thresholds, efficient utilization of irrigation water was considered, and suitable crops and appropriate winter irrigation quotas for different soil textures and levels of soil salinity were proposed. Soil with a salt content of 1~3 g/kg is suitable for the planting of corn with 80 mm of irrigation water. Sandy loam soil with a salt content of 3~5 g/kg is suitable for sunflower–corn intercropping with 120 mm of irrigation water. Sandy loam soil with a salt content exceeding 5 g/kg is suitable for the planting of sunflower with 80 mm of irrigation water. Other types of soils need to be improved by reducing the spacing between subsurface pipes, using desulfurized gypsum, biochar, and other additives. People engaged in agriculture can utilize this research to determine the appropriate volumes of irrigation water, crop types, planting systems, and subsurface pipe parameters based on local conditions.