Four years of continuous use of soil-biodegradable plastic mulch: impact on soil and groundwater quality

There is an increased interest in the use of soil-biodegradable plastic mulch due to limited disposal options for conventional polyethylene mulch. However, information about the impact of continuous use of soil-biodegradable plastic mulch on the environment is limited. Here, we show the effects on soil and groundwater quality from the use of soil-biodegradable plastic mulches for crop production for four consecutive seasons. Two soil-biodegradable plastic mulch products were assessed at two locations (Knoxville, TN and Mount Vernon, WA) having different climates (humid subtropical and cool Mediterranean), with cellulosic-paper mulch, poly-ethylene mulch, and no-mulch included as control treatments. Soil physical, chemical, and biological properties were first assessed in the spring of 2015 (prior to any field operations), and then a few days after harvest in the fall of 2015, 2016, 2017, and 2018. Water samples were collected in the fall of 2018 from lysimeters installed at 55-cm depth and analyzed for nutrient composition. Compared to the no-mulch treatment, the soil-biodegradable plastic mulches and polyethylene mulch increased the soil aggregate stability (by 6-16%) and water infiltration rate (by 10-12%) by protecting the soil surface from disturbance. Residual nitrate and nitrite under the plastic mulch after harvest were lower than under no-mulch (by 4.1 kg ha(-1) to 7.3 kg ha(-1)) due to increased yield and associated enhanced nutrient uptake. However, plastic mulching, especially the polyethylene mulch, reduced soil microbial activity, measured as burst CO2-C by 6 g kg(-1 )day(-1) to 54 kg(-1) day(-1), but had no effect on extractable organic carbon concentrations nor specific extracellular enzyme activity rates. Within the fouryear period, the soil-biodegradable plastic mulches had overall positive effects on soil and groundwater quality, except for reduced burst microbial respiration, which was more pronounced in Mount Vernon.

Automated summary

The study found that soil-biodegradable plastic mulches protect soil from disturbance, increase soil aggregate stability, and water infiltration rate, leading to higher yields and enhanced nutrient uptake, thus having a positive impact on soil and groundwater quality.