Poly-γ-glutamic acid enhances corn nitrogen use efficiency and yield by decreasing gaseous nitrogen loss and increasing mineral nitrogen accumulation

In arid and barren northwest of China, excessive application of nitrogen fertilizer not only did not increase nitrogen use efficiency (NUE)and yield of crops, but also caused serious ecological environment pollution. Poly-γ-glutamic acid (γ-PGA) is a non-toxic and harmless polymer with good water and fertilizer retention ability. However, there is still a lack of relevant research on how γ-PGA affects crop productivity and nitrogen footprint in farmland ecosystems under film mulching conditions. Therefore, this study conducted the field experiment in oasis on the desert edge from 2021 to 2022 to explore effects of different γ-PGA applied rates (0,20,60 and 80 kg ha⁻¹) on soil nitrogen content, NH₃ volatilization, yield and NUE under mulched drip irrigation, and to determine the optimal γ-PGA application strategy. The results showed that with increase of γ-PGA application rates, soil mineral nitrogen accumulation increased, cumulative NH₃ volatilization loss decreased first and then increased, maize yield increased first and then decreased, and NUE increased first and then decreased. Compared with P0 (without adding γ-PGA),γ-PGA maintained the content of NO^-₃-N and NH⁺₄-N in 0–100 cm depth, and increased mineral nitrogen accumulation. In addition,γ-PGA treatments decreased cumulative NH₃ volatilization loss by 8.38 %-19.39 %, promoted nitrogen uptake of each organ, increased leaf area index (LAI)and aboveground dry matter. Therefore, γ-PGA increased corn yield by 4.94 %-21.60 %, increased NUE by 4.94 %-21.60 %, and decreased nitrogen loss. Moreover, through the Gaussian optimization model and combined with the local actual situation, the optimal γ-PGA application strategy in the region was determined to be 70 kg ha⁻¹. The result will provide a further information for improving fertilizer efficiency and reducing agricultural ecological environment pollution in corn under mulched drip irrigation, ensuring sustainable agricultural development and the health of the ecological environment.