Effects of plastic film mulch biodegradability on nitrogen in the plant-soil system

The application of biodegradable film mulching (BFM) instead of non-biodegradable film mulching (NBFM) is a promising way to mitigate the negative impacts of residual film in agricultural mulching systems. But the effects of BFM on soil mineral nitrogen (N) are not known. To investigate the effects of BFM on N mineralization, nitrate (NO₃^-) accumulation and leaching, and plant N uptake, we conducted two-year field experiment with five treatments: no-mulching (No-M), white non-biodegradable film mulching (White-NotBioM), black non-biodegradable film mulching (Black-NotBioM), white biodegradable film mulching (White-BioM), and black biodegradable film mulching (Black-BioM). The net N mineralization in NBFM was greater than that in BFM due to the disintegration of biodegradable films in the middle and late stages of maize growth, resulting in a decrease in soil water content under BFM. Higher net N mineralization caused a higher NO₃^- accumulation in the topsoil (0-20 cm) under NBFM. The NO₃^- accumulation in the topsoil in Black-NotBioM was 23-88% higher than that in Black-BioM; while in White-NotBioM it was 16-63% higher than that in White-BioM. After two years of cropping, the NO₃^- accumulation in 100-180 cm (defined as N leaching in deep layers, NLD) in NBFM was 52-63% higher than that in BFM, implying that the higher NO₃^- accumulation in the topsoil in NBFM caused more N leaching. The yields and plant N uptake were similar between NBFM and BFM, but BFM had higher N harvest index values. Compared with NBFM, BFM showed less NO₃^- accumulation in the topsoil and less NLD, whereas yield, plant N uptake and net economic benefits were not reduced. Therefore, BFM, especially Black-BioM, could be an alternative to NBFM in maize production on the Loess Plateau. However, the higher N accumulation in root soil layer (0-100 cm) under Black-BioM should be accounted for in N fertilizer management.