Reclamation effect of freezing saline water irrigation in winter season on the heavy saline-alkali soil in Hetao Irrigation District

A three-year experiment of freezing saline water irrigation in winter season was conducted in a heavy saline-alkali area in Hetao Irrigation District. Two treatments, freezing saline water irrigation (FSWI) and no irrigation (CK), were implemented; the saline water irrigation amount was 180 mm with a salinity of 6.79-7.97 g·L^-1 in the FSWI treatment, and the planting crops were silage maize. This study aimed to analyze the effects of freezing saline water irrigation on the seasonal dynamics of soil water and salt and maize growth and to evaluate the reclamation effect of freezing saline water irrigation on the saline-alkali soil in Hetao Irrigation District. The results showed that, compared with CK, the FSWI treatment significantly changed the soil water, salt, and sodium adsorption ratio (SAR) dynamics in the spring. In the 0-20 cm soil layer of the FSWI treatment, till the seedling stage of maize, the mean soil water content (24.3%) were significantly higher than that under CK treatment (21.6%) in spring. The soil salt content and SAR level under FSWI treatment were significantly lower than those under CK treatment. Under FSWI treatment, the soil salt content was decreased from 33.86 g·kg^-1 before irrigation to < 5 g·kg^-1 during the seedling stage of maize, while under CK treatment, the soil salt content was kept at 34.2 g·kg^-1. The soil SAR level under FSWI treatment was decreased from 21.9 before irrigation to 9.86 during the seedling stage of maize, while it was 25 during the seedling stage under CK treatment. Plastic film mulching and subsequent rainfall in the summer maintained the higher soil water content (> 23.0%) and lower soil salinity (< 5 g·kg^-1) and lower SAR level (< 9) in the FSWI treatment. The trends for soil water, salt, and SAR in the 20-40 cm layer were similar to but not greater than those in the 0-20 cm layer. Under FSWI treatment, the emergence rate of maize was > 70%, and the biomass of maize was 9-12 t·hm^-2. Moreover, the soil salt content and SAR level in the same season decreased with increasing years of saline water irrigation. The lower soil water content, higher soil salt content, and SAR under CK treatment led to a lower emergence rate and maize biomass. Therefore, freezing saline water irrigation in winter season significantly changed the natural dynamics of soil water and salt; soil salinization decreased as salt leaching combined with a significant decrease in soil SAR and an increase in the soil water content by infiltration of meltwater which ensured normal planting and maize growth. This technology may support the reclamation of saline-alkali soil and forage grass plantation in the area.