In situ degradation of three contrasting plastic mulch films under maize cultivation in tropical conditions

The widespread use and release of plastics, including conventional and biodegradable mulch films, has become a major environmental concern due to their impact on soil quality and ecosystem functioning. Herein, we examined degradation patterns of three plastic mulch films (i) low-density polyethylene (LDPE) mulch (PEM), (ii) reflective LDPE mulch (RPEM), and (iii) biodegradable PLA-PBAT mulch (BDM), over two maize growing seasons in Sri Lanka. Mulch films were sampled monthly, with changes in mass, chemical composition, and physical integrity assessed using FTIR-ATR, TGA, GC, and GC-MS. FTIR spectra confirmed progressive compositional changes in all films with BDM showing significant peak compositional changes. Visual observations of physical breakdown showed that > 30% of soil surface coverage provided by BDM was lost while LDPE films showed minimal signs of surface breakage. BDM lost 50% of its mass over first growing season while RPEM and PEM films demonstrated only 1% and 6% mass loss, respectively. In conclusion, the study provides evidence of the rapid degradation and compositional changes of BDM mulches compared to LDPE mulches, likely due to prevailing tropical climate. Future research should focus on improving physical integrity of BDMs and analysing the effects of plastic additives and leachates on soil and microbes.