Investigation of Salt and Nitrogen Distribution under Belt Plastic Film Mulching in Surface- and Drip-Irrigated Maize Field in Hetao Irrigation District

Hetao Irrigation District (HID) is one of the main regions for maize and sunflower production in North China. However, water resource shortages and soil salinization greatly limit maize and sunflower production. The surface irrigation method is the main irrigation method in HID; however, now, the plastic mulching and drip irrigation area is increasing to reduce irrigation water and enhance crop yield. In this study, the soil water, salt, and nitrogen contents at the 0–100 cm soil layer under plastic mulching and non-mulching conditions with the surface irrigation—fertilizer broadcast practice and drip fertigation method were investigated at the maize elongation and maturation stages in the 2021 and 2022 seasons. The results show that the mulching practice and irrigation methods greatly influenced the soil salt and ionic nitrogen (NO3− and NH4+) distributions and, ultimately, the maize yield. Mulching reduced the soil salt content in the 0–20 cm soil layer by a mean of 35.7% under surface irrigation and by 18.6% under the drip irrigation condition. The NO3− content in the 0–20 cm soil layer with the drip fertigation system was approximately 8 times higher in mulching soil than that out of mulching. However under the surface irrigation condition, the NO3− content was 8–10 times lower under mulching than that out of mulching. The soil salt and NO3− contents were distributed uniformly at each soil layer deeper than a 40 cm depth, indicating minor effects of mulching. The soil NH4+ content decreased as the soil depth increased and distributed uniformly at each soil layer, indicating the insignificant influence of the mulching practice. As a result, the maize yield under the drip-mulching condition was approximately 11% (10.6~11.4%) higher than that under the surface-mulching condition in the two maize seasons. Given that surface irrigation is currently the primary irrigation method in the Hetao Irrigation District (HID), we have proposed three approaches aimed at enhancing maize production through the improvement of nitrogen levels in surface-mulching practices.