Plastic film mulching increases maize yields and mitigates NH₃ emissions under climate change and N deposition

Plastic film mulching (PFM) increases crop yields in semi-arid regions by reducing water losses and increasing soil temperatures, while crop production in these areas also serves as a significant source of ammonia (NH₃) emissions. The effects of PFM on NH₃ emissions are mostly unknown because of interactions between greater N mineralization at higher temperatures and the film cover preventing NH₃ diffusion. Therefore, our objectives were to (1) evaluate the effects of PFM on NH₃ emissions under field conditions, and (2) identify the maize yield and NH₃ emissions under climate change and atmospheric N deposition conditions using the DeNitrification-DeComposition (DNDC) model. The experiment included four treatments: (1) no plastic film mulching without N fertilization (control), (2) plastic film mulching without N fertilization (PFM), (3) N fertilization without plastic film mulching (N), and (4) plastic film mulching with N fertilization (PFM+N). The PFM increased maize yields by 211% and yield stability across the years when combined with N fertilization. PFM reduced NH₃ emissions by 35% through three mechanisms: ⅰ) the high water content under PFM saturates soil pores, hindering NH₃ gas movement to the atmosphere; ⅱ) the hot and wet conditions under PFM accelerate the nitrification rate, thus increasing pH buffering capacity during urea hydrolysis; and ⅲ) the physical barrier created by PFM reduces NH₃ exchange between soil and air. Daily NH₃ emissions increased with soil temperature, NH₄⁺ content, and pH, but declined with soil moisture under N fertilization. The NH₃ emissions under PFM+N increased with NH₄⁺ content. The parameterized DNDC model simulated the yield and daily NH₃ emissions very well. PFM+N increased yield and reduced NH₃ emissions under the shared socioeconomic pathway (SSP) scenario and with N deposition. Yield under PFM+N increased with increasing N deposition, whereas NH₃ emissions under PFM+N increased only under the high N deposition (N4) scenario compared with the no-deposition scenario, with no apparent increase under the N2 and N3 scenarios. In conclusion, PFM increases yields and mitigates NH₃ emissions, and it can also potentially achieve similar benefits under future conditions.