Divergent aging behaviors of mulch films in biochar-amended soil under dark conditions: Enhanced fragmentation yet suppressed surface oxidation

The integration of biochar with mulch films holds promise for sustainable crop production, yet the influence of biochar on mulch films aging in soil remains poorly understood. To address this knowledge gap, we conducted a 12-week soil incubation experiment simulating the coexistence of biochar (pyrochar and hydrochar) with three types of mulch films—polyethylene, poly(butylene adipate-co-terephthalate) (PBAT), and polylactic acid (PLA)—under dark conditions. Our results demonstrated that both pyrochar and hydrochar accelerated the physical fragmentation of biodegradable PBAT and PLA films, as evidenced by visible pores, cracks, and a substantial increase in surface roughness. In contrast, Fourier-transform infrared spectroscopy, contact angle measurements, and X-ray photoelectron spectroscopy analysis indicated that biochar suppressed surface oxygen enrichment, suggesting a mitigating effect on chemical oxidation. Biochar also substantially altered the composition of soil dissolved organic matter (DOM); co-incubation with biodegradable mulch films led to a marked reduction in dissolved organic carbon content, accompanied by enhanced DOM humification. These divergent aging behaviors—enhanced physical fragmentation alongside suppressed chemical oxidation—suggest that biochar may promote microbial-driven physical breakdown while mitigating chemical oxidation or hydrolysis, possibly through surface coverage or DOM-mediated quenching of reactive oxygen species. Our findings provide a nuanced understanding of mulch films aging in biochar-amended soils and offer critical insights for managing the co-application of these materials in agricultural systems.