Evaluation of the biodegradation rate of mulch films

In Brazil in 2010 about 2,500 t of mulch films was used in horticulture. After the crop cycle, polyethylene mulches are often buried or burned with crop residues, as mulch films recycling is time-consuming and expensive due to high removal labour cost. Biodegradable mulch films appear as an alternative to polyethylene use, once they are incorporated in soil with crop residues at the end of the crop cycle. This study was performed in order to evaluate the biodegradation of different types of mulches in both real and laboratorial conditions, in tropical soils. The experimental design used was randomized blocks with five repetitions and four treatments: bare soil (BS), rice husk mulch (RHM), polyethylene mulch (PM), and biodegradable mulch (BM). In the laboratory a respirometric test was performed with the soil, at 70% of water holding capacity and 28°C. Carbon dioxide production was measured every 2 days, during a 20-days period. Microbial carbon was also determined by fumigation method, at the end of respirometric test. The results showed that the BM modality produced more carbon dioxide, 82.01 mg C-CO₂ g soil^‑1, than other modalities. Microbial carbon was higher on RHM modality with 21.56 µg C_mic g soil^‑1, followed by BM with 19.60 µg C_mic g soil^‑1 and lower values were found on BS and PM, with 12.18 and 13.57 µg C_mic g soil^‑1, respectively. From the results obtained, RHM and BM higher CO₂ verified were probably due to a synergetic effect between mulches carbon content and microorganism growth rate.