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 (BlackNotBioM), 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