Impacts of biodegradable plastic mulches on soil health

Plastic pollution in agricultural soils, caused by the incomplete removal of polyethylene mulch after usage, is a growing environmental concern. There has therefore been increased interest in biodegradable plastic mulches as alternative to polyethylene mulch; however, little is known about their impact on soil health. We evaluated the effects of four biodegradable plastic mulches on soil health at two sites (Knoxville, TN and Mount Vernon, WA) under pie pumpkin (Cucurbita pepo) production. Cellulosic paper, polyethylene, and no-mulch served as controls. Soil health was first assessed in May 2015, and then every six months until May 2017, by measuring 19 soil properties (physical, chemical, and biological). Soil properties were converted to index scores and aggregated into six soil health indicators and five soil functions. The results showed poor correlations and high spatial variations for most of the soil properties. We performed repeated measure analyses using raw values and change scores to account for the initial variations. The soil properties, soil health indicators, and soil functions were affected more by site and time than by the mulch treatments. Nonetheless, we did observe significant effects of some of the mulch treatments on six soil properties (aggregate stability, infiltration, soil pH, electrical conductivity, nitrate-N, and exchangeable potassium), four soil health indicators (hydraulic, biological, fertility, and salinity & sodicity), and one soil function (nutrient cycling). However, these effects were not consistent among all the biodegradable plastic mulches, across the two sites, and the sampling times. Overall, biodegradable plastic mulches may be a viable alternative to polyethylene. However, evaluation under long-term studies is needed to better establish their effects on soil health.