Study of the effect of biodegradable plastics on soil fertility

Biodegradable materials for agriculture represent a tool which can reduce the dispersion of plastic waste in the environment.The use of biodegradabe mulch film (BDM) in agronomical practices has grown over time, but still some doubts on their environmental suitability are perceived and represent a barrier for their further adoption. This work aims to study what could be the impact of BDMs on soil, examining relevant aspects related to soil functionality, and in particular the effects on soil microbial biomass and activity, on the biogeochemical cycles, on soil aggregates and N cycle and enzymatic activities. Together with the laboratory experiments, the study analyzed the presence of microplastics derived from long-term use of BDMs and the effects on soil functionality in real field conditions in soils exposed and not exposed to bioplastics. The outputs of showed that the effects induced by bioplastic loads corresponding to realistic bioplastic doses (from 0.01 to 0.1% w/w) were comparable to those of the control (soil with no bioplastic) in terms of C and N cycles, and physiochemical properties. On the contrary, higher bioplastic loads (1% w/w) strongly affected the C and N cycles, increased the mineralization and the immobilization of available N (priming effect), as a result of a strong imbalance in C/N. In real field conditions no effects were induced by the continuous use of biodegradable plastic mulch either on soil functionality parameters or in terms of accumulation of permanent particles (microplastics) derived from BDMs. This study represents one of the first analysis performed in real field conditions with a long-term perspective. Overall, the results obtained demonstrated that the use of overloading quantities of bioplastics greatly exceeding the real usage dose, do not help in the understanding the potential impacts of these materials, but on the contrary create artefacts leading to incorrect conclusions.