In-field degradation of polybutylene adipate-co-terephthalate (PBAT) films, microplastic formation, and impacts on soil health

Polybutylene adipate-co-terephthalate (PBAT) mulch films are potential alternatives to traditional polyethylene (PE) mulch films in agriculture. Here, we investigated the degradation rate and microplastic formation of PBAT films in an agricultural field and the impacts on soil health as well as maize yields. We compared two biodegradable films (PBAT clear film: BCF and PBAT black film: BBF) with two conventional films (PE clear film: PCF and PE black film: PBF) in a field experiment over three growing seasons. Biodegradable films consisted of >90% PBAT and 5% polylactic acid. After three years of mulching, more microplastics were detected for the BCF (1820 particles kg^-1) and BBF (1560 particles kg^-1) treatments than for PCF (840 particles kg^-1) and PBF (747 particles kg^-1). The majority (about 70%) of microplastics in BCF and BBF were <0.25 mm, while in PCF and PBF the fraction of microplastics <0.25 mm made up only 24-41%. Biodegradable films increased soil organic carbon, microbial biomass carbon, and nitrate nitrogen by 0.16-0.48 g kg^-1, 5.5-33.8 mg kg^-1, and 32.6-109.6 mg kg^-1, respectively, compared to PE films. Yield was highest for BBF, exceeding that of non-film, PCF, PBF and BCF by 2550, 566, 960 and 367 kg ha^-1, respectively. Overall, the biodegradable films had a positive impact on soil health and maize yields.