Nitrogen transformations in plastic-film mulched soils

Plastic film mulching (PFM) induces strong soil warming and alters the water balance, thereby influencing microbial activities, particularly those associated with nitrogen (N) transformations, including mineralization from soil organic matter. The impact of PFM on interactions between N fate and soil N transformations remains unclear. We investigated the complex interplay of soil N transformation processes through 15N labeling and tracing, analyzing N availability and N fate in the PFM-covered soil compared with a non-mulched flat soil (control). PFM reduced gross N mineralization and nitrification rates by 20–28% and increased microbial gross N immobilization rates. In the PFM-covered soil, maize N uptake and N accumulation (up to 80 cm depth) increased by 19% and 127%, respectively, compared with the control soil. PFM effectively mitigated N leaching and reduced N2O and NH3 gaseous emissions (by 32 kg N ha−1). During the early stages of maize growth, the PFM increased N availability in soil owing to accelerated rates of gross N mineralization from soil organic matter and nitrification, which in turn increased N uptake by maize plants and microorganisms. PFM effectively mitigated gaseous N emissions and N leaching, increasing N retention in soil and raising N use efficiency. Despite gross N mineralization and nitrification rates were reduced in the late stages of maize growth, PFM-covered soil maintained high N availability by reducing N leaching and microbial N immobilization. This contributed to raised N uptake and increased maize yields. PFM altered soil N transformation processes, including gross N mineralization from soil organic matter, nitrification, and immobilization by microorganisms, leading to increased N availability, maize N uptake, soil N retention, and reduced N losses. Concept of N transformation and fate in soil with and without plastic film mulch (PFM) planting system describing the mechanisms of N supply and N retention. The units are in kg N ha−1 per maize growth period. Control, soil without film mulching; PFM, soil under plastic film mulch