Modeling and assessing feasibility of long-term brackish water irrigation in vertically homogeneous and heterogeneous cultivated lowland in the North China Plain

In the North China Plain (NCP), increased water shortages and food yield increase present serious threats to thesustainability of cultivated lands. Irrigation by brackish or saline water is a possible solution to alleviatefreshwater shortages. It is critical to understand the soil salt variations and the characteristics of salt accumulationand leaching under long-term brackish water irrigation in cultivated croplands. In this study, theHYDRUS-1D model was calibrated and validated, and then applied to evaluate that how 20 years of irrigatingwith brackish water affects soil salinity and soil salt transport in wheat-maize cultivated lands with differenttexture layers in the lowland of NCP. The results showed that the simulations of soil matric potential and soil saltconcentrations fitted well with the measured values. Soil salt dynamics were dominated by seasonal precipitationand hydrological years. Seasonal rainfall distribution determined seasonal characteristics of saltchanges in shallow layers (0–100 cm). Soil salt accumulated during the growth period of winter wheat corresponding to the dry season, and was greatest at the harvest. Soil salt leached down to deeper soil layers underabundant rainfall during growth period of maize. The annual soil salt in 300 cm profiles were driven by hydrologicalyears, and soil salt could be accumulated in dry and normal years and leached in wet years, especiallyin the extremely wet year. Soil salt accumulation was higher under two brackish water irrigations compared toone irrigation for winter wheat, and soil salinity in homogeneous soils was less than in the heterogeneous soilwith clay loam interlining. The results showed the effect of irrigation times of brackish water was greater thanthat of soil texture on soil salt accumulation. Our results demonstrated that wheat and maize could be grownwell under one irrigation with brackish water a year. Salt accumulation increased with the number of irrigationevents that used brackish water for winter wheat. The brackish water irrigation was evaluated and the resultsdemonstrated that partial substitution of fresh water by brackish water for irrigation is feasible in the lowlandarea of the NCP. It is more suitable for long-term brackish water irrigation in relatively homogeneous soil than inheterogeneous soil. These simulated results are helpful to provide appropriate management measures for