Decomposition of biodegradable packing materials jute, Biopol, BAK and their composites in soil

Abstract.

We investigated the effects of the biodegradable polymers jute, Biopol and BAK 2195 and their composites on the mineralisation activity and biomass of microorganisms in soil and on the fungal component of the microbial community. Two different pre-treatments of jute were used to produce the composites, treatment of the fibres with sodium hydroxide (SH-jute) and co-polymerisation with acrylonitrile (AN-jute). All products tested were highly degradable, as indicated by the increase in CO₂ evolution after amendment. The additional amount of CO₂-C evolved after polymer incorporation into the soil corresponded to between 21% and 34% of the added C after 85 days incubation at 25°C. The extra CO₂-C evolved decreased in the order BAK > jute > Biopol. Composites of AN-jute were less mineralisable than those of SH-jute. Degradation of jute is characterised by a rapid increase, then a slow decline of microbial respiratory activity. In contrast, in the Biopol treatments, and especially in the BAK treatments, maximum CO₂ evolution rates occurred considerably later, indicating that the soil microorganisms needed some time to colonise the polymer particles. All polymers and composites tested increased the soil microbial biomass in the order jute ≤ Biopol < BAK. The net increase in microbial biomass C was 3% of the added polymer C in the jute treatment, an average of 4% in the three Biopol treatments, and 7% in the three BAK treatments. The content of ergosterol, an indicator for fungal biomass, was also increased by all amendments, but the effect on ergosterol content was much more pronounced than on microbial biomass C.