Biodegradable Plastic Mulch: Impacts on Soil Quality and Degradation in Soil and Compost.

Sustainable application of biodegradable plastic mulches in agricultural systems will largely depend on their complete degradation, and minimal impacts on agroecosystems. We evaluated the degradation of four biodegradable plastic mulches in soil at two locations (Mount Vernon, WA and Knoxville, TN), as well as in compost, with paper-based and polyethylene mulches included as control. Field-weathered mulches were harvested and placed into 250µm nylon-meshbags and buried at 10cm depth in soil and 60cm depth in aerated static pile compost. The meshbags were retrieved at 6-month intervals from soil and 2-week intervals from compost, and mulch degradation were assessed based on reduction in surface area using image analysis. In addition, the effects of continuous mulch application on soil health were evaluated. Except for small differences in nitrate and electrical conductivity, there were no significant differences in other soil quality parameters. Also, the overall estimated soil quality index was not different among treatments. The biodegradable plastic mulches underwent minimal degradation in soil, where the maximum and minimum percent degradation after 12-month were 56.4% and 6.4%, respectively in Knoxville, and 17.7% and 1.6%, respectively in Mount Vernon. As expected, the paper-based mulch underwent the greatest extent of degradation (98.3%) in soil, whereas the polyethylene mulch did not degrade. After 18-week composting, the maximum and minimum percent degradation of the biodegradable plastic mulches were 99% and 97.3%, respectively. However, the paper-based mulch underwent lower degradation in compost (87.6%), and the polyethylene mulch did not degrade. While it appears that polymers of the biodegradable plastic mulches degrade in compost, micro- and nanoparticles were also released, which were conglomerate of carbon-rich materials containing carbon black. The lack of effects of biodegradable plastic mulch on the overall soil health enhances the potential to adopt biodegradable plastic mulch, but the release of micro and nanoparticles may pose environmental concerns.