Optimizing Biodegradable Films with Varying Induction Periods to Enhance Rice Growth and Soil Carbon and Nitrogen Dynamics

Polyethylene film (PE) mulching produces substantial "white pollution," prompting the use of biodegradable film (BF) alternatives, yet their performance in rice systems on Northeast black soils is still uncertain. We compared three BFs with different induction periods (45 d, BF45; 60 d, BF60; 80 d, BF80), PE and a no-film control (CK) to quantify their effects on soil hydrothermal conditions, rice growth, yield, grain quality, irrigation water use efficiency (IWUE) and soil C, N. Results showed that mulching increased soil temperature and soil moisture. Across the growing season, the mean soil temperature at the 0-5 cm depth under PE was 5.5% and 2.2-5.5% higher than that under CK and BFs, respectively. Specifically, compared with CK, PE increased grain yield by 31-77% and IWUE by 75-123%, while BFs improved yield by 25-73% and IWUE by 48-101%. PE only slightly outperformed BF80 in yield (by 2.3% in 2023 and 2.1% in 2024) but achieved higher IWUE (11.0-11.7%). Grain chalkiness and sensory scores under BFs were comparable to PE and better than CK. At 0-20 cm, PE increased SOC (2.3-6.8%) and the C/N ratio (0-0.8%) but reduced total nitrogen (TN) (2.7-3.9%) and total carbon (TC) (2.5-3.1%), whereas BFs increased Org-N by 0.4-4.2%, SOC by 2.9-7.1%, and TN by 0.2-0.7%, with BF80 showing the greatest stimulatory effect. Overall, BFs-particularly BF80-are promising substitutes for PE in black soil rice systems, supporting sustainable rice production with strong application potential.