To address the issue of residual pollution caused by polyethylene mulch, this study explored the effects of different mulching methods on the soil environment of the yam field, as well as on yam yield and quality. The experiment comprised six treatments in total: one non-mulched treatment served as the control (CK), along with five different film-mulched treatments, namely PE, FZS12, FZS15, FC12, and FC15. The degradation of these films and their effects on soil physicochemical properties, microbial community, yam yield and quality were compared. The results showed that the FZS12 treatment achieved grade 5 degradation by the end of the planting period. Compared with PE treatment, the total soluble sugar content and yield of yam treated with FZS12 were significantly increased by 35.78% and 74.97%, respectively (p < 0.05). Compared with CK and PE treatments, FZS12 significantly increased soil available nitrogen by 31.62% and 6.20%, respectively (p < 0.05), and significantly increased soil available phosphorus by 8.58% and 4.45%, respectively (p < 0.05). Soil pH, available nitrogen, and available phosphorus were the main environmental factors affecting the soil bacterial community. The FZS12 treatment significantly increased the relative abundances of soil bacteria phylum including Acidobacteriota, Myxococcota, Patescibacteria, and Proteobacteria compared with the CK and PE treatments. Functional prediction using Picrust2 revealed that the FZS12 treatment had significantly higher levels of signal transduction and amino acid metabolism than the CK and PE treatments. In conclusion, covering with 12 μm PBAT/PLA humic acid biodegradable film enhances yam yield and total soluble sugar content by shaping beneficial soil microbial communities, activating soil nutrients.

Biodegradable plastic film provides a new way to solve “white pollution”. However, there is an urgent need to solve the problems of residual plastic film and tail vegetable pollution after planting. Currently, the continuous degradation of polyethylene plastic film and biodegradable plastic film after returning to the field and their impact on soil environment and vegetable crop growth need further research. This study is expected to provide some theoretical support through residual membrane addition experiments. We uniformly buried PBAT/PLA humic acid biodegradable film (BIO1), PBAT/PLA-lignin biodegradable film (BIO2), and polyethylene film (PE) at 200 kg film residue per ha in potted soil. After burial 120 d, the crystallinity of BIO1 and BIO2 residue decreased by 7.37% and 3.91% respectively, compared to that of PE. Additionally, the water contact angle of BIO1 and BIO2 film was lower, and the weight loss rate significantly increased. Microplastics (polyethylene) abundance in the PE treatment substrate was (166.67 ± 169.96) n ·kg⁻¹ after 150 days of burial, and microplastics (PBAT/PLA) were not found in BIO1 and BIO2 treatments in this study. Residual film reduced the percentage of 2-1 mm and >2 mm water-stable agglomerates and increased the percentage of < 0.25 mm water-stable agglomerates, ledto soil compaction and water upward migration; reduced urease and sucrase activities in substrate, further reduced root vigor and increased leaf proline content, eventually reduced tomato yield. However, compared with PE, BIO1 have lower substrate volumetric weight, higher aeration porosity, alleviated soil compaction, stronger substrate enzyme activity and root activity, residues significantly increased soil Ascomycota relative abundance and decreased Zoopagomycota relative abundance; reduced leaf proline content, significantly increased tomato yield, and improved tomato quality by significantly increasing lycopene content by 12.80%. Overall, 200 kg · ha⁻¹ of residual humic acid biodegradable plastic film can improve tomato quality, reduce “white pollution”, and reduce microplastic residues caused by residual film in a solar greenhouse.