Continuous years of biodegradable film mulching enhances the soil environment and maize yield sustainability in the dryland of northwest China

Due to the limited disposal options for traditional polyethylene film (PF) mulch, interest is increasing in the use of biodegradable film (BF) mulching. However, little information is available regarding the impact of the continued use of BF on the soil environment and crop productivity. Therefore, we compared the effects of BF and PF on the soil total nitrogen (TN), soil organic carbon (SOC), soil carbon:nitrogen ratio (C:N), soil moisture, soil temperature (ST), leaf area index, accumulated aboveground biomass, grain yield, and water use efficiency (WUE) in the dryland of northwest China for four consecutive seasons. The results showed that BF and PF had similar effects on ST and soil moisture conservation in the early growth stage (0–60 days after sowing), but when the BF degraded, the ST and soil water content were significantly lower under BF than PF. After 60 days after sowing, the ST values were similar under BF and the control with no mulching (CK), which effectively alleviated the damage caused by high temperatures to a certain extent. The grain yield and WUE did not differ significantly under PF and BF, except in 2018. Compared with CK, the average grain yield and WUE increased by 12.8% and 6.8% under PF, respectively, and by 16.2% and 10.4% under BF. Both mulching methods reduced the SOC and TN contents in the 0–40 cm soil layer compared with the uncovered plots. However, they had different effects on the soil C:N where PF significantly reduced the C:N ratio whereas BF slightly increased it, thereby indicating that BF played an important role in maintaining the SOC and TN balance. Therefore, BF is recommended as a viable alternative to traditional PF for maize production in the dryland of northwest China. This study provides new evidence that BF can replace PF to address the problems of food security and residual film pollution in areas with similar conditions.