Soil Microclimate and Degradation of Biodegradable Plastic Mulches.

There has been increased interest in biodegradable plastic mulches, but their successful application will depend on how well they maintain microclimate and biodegrade in soil. This study is examining the effects of four biodegradable plastic mulches on soil heat dynamics and light penetration under pie pumpkin (Cucurbita pepo) production at two locations (Mount Vernon, WA and Knoxville, TN), which have distinct climatic conditions. We are also evaluating mulch degradation by incorporating the mulches in soil and retrieving at 6-month intervals for four years. Bare ground and polyethylene mulch were included to serve as control treatments. Soil temperature was assessed within each field at 10-cm and 20-cm depths. Soil surface temperature and light penetration through the mulches were also monitored with sensors placed directly underneath the mulches. Preliminary results showed minimal degradation (less than 10%) in all the biodegradable plastic mulches after 6-month soil incorporation. Compared to bare ground, the mulch treatments reduced light penetration by two orders of magnitude. The reduced light penetration resulted in effective weed control. At Mount Vernon, the average daily soil temperature at 10-cm depth under biodegradable plastic mulches (21.5 °C) was higher than under bare ground (20.3°C), but lower than under polyethylene mulch (23.3 °C). Similar trend was observed at the 20-cm depth, but the temperatures were comparatively lower. At Knoxville, the average soil temperature at 10-cm depth under biodegradable plastic mulches (26.1 °C) was higher than the bare ground (25.2 °C), but same as the polyethylene mulch. Lower temperatures were observed at the 20-cm depth, but the results followed a similar trend as the 10-cm soil depth.  Overall, yield benefit corresponded to higher temperatures in colder climate conditions in Mount Vernon, but not in the warmer climate conditions in Knoxville.