HYDRUS-1D model simulation of soil water and salt movement under various brackish water use schemes in the North China Lowplain

Freshwater resource in the North China Lowplain is nearly been depleted due to continuous overexploitation of deep groundwater resources. This has led to a series of ecological and environmental problems, including land subsidence and soil salinization. The use of brackish water in agriculture to alleviate water crisis in the region has become the new focus of research. In order to determine the sustainability of various irrigation modes of saline water, this study used the Hydrus-1D model to simulate eight different brackish water irrigation schemes in Nanpi County. The model simulated water and salt fluxes in the 0–2 m soil layer in the winter wheat-summer maize crop rotation system for the period of 2008–2013. The simulation results of soil salinity profile distribution showed that the 100–200 cm subsoil layer was the main salt accumulation zone. The upper 0–100 cm soil layer was lower in salt solution concentration with 2 g.L^-1 salt solution in most time, which generally ensured normal growth of crops. Soil profile salinity concentration peaked at late winter wheat grain-filling stage. Peak salinity increased with increasing salt concentration of irrigation water. Leaching soil salt in the study area depended mainly on rainfall intensity, especially in July when precipitation was heaviest. Proper leaching of salt after sowing corn in wet years significantly enhanced soil desalination. Based on comprehensive analysis of the effects of three tested factors (hydrological year type, dynamic distribution of soil profile salinity and soil salt migration/leaching), the paper proposed two suitable brackish water irrigation schemes in the North China Lowplain. 1) Pre-winter irrigation of brackish water with less than 2 g.L^-1 salt concentration combined irrigation at jointing stage with 2–4 g.L^-1 brackish water. 2) Without pre-winter irrigation, wheat was irrigated at jointing and grain-filling stage with 2 g.L^-1 brackish water. The amount of freshwater used to leach soil salt at summer seedling stage and the total water consumption of the winter wheat-summer maize system under the above two irrigation schemes were 60–70 mm and 250–260 mm, respectively. This research provided the theoretical basis of water-saving potential through the use of brackish water for sustainable use of the limited water resources in the North China Lowplain.