Biodegradable Mulches and Soil Quality

Biodegradable mulch films could be desirable alternatives to black plastic in agriculture, however, little is known about their degradability in soil across contrasting environments. The objectives of our study were to:  1) measure % area reduction of four potentially biodegradable mulches for up to 2-year burial in soil following use in tomato crop production; and, 2) assess soil biological properties (enzyme assays, microbial biomass, and nitrogen mineralization potential) as soil quality indicators. Four replications of both high-tunnel and open-field sites were established in three distinct eco-regions of the United States (Southeastern TN; Northwestern WA; Southern High Plains TX). Mulch plots at each site included: experimental spunbond poly-lactic acid (SB-PLA-10), BioBag and BioTelo (two commercially-available starch-based films), and WeedGuardPlus (cellulose-based commercial mulch). No mulch was the control. Following 2010 tomato harvest, used mulches were removed and cut into pieces, soil was tilled, and 161 cm² nylon mesh bags each containing 103 cm² of a mulch and ~400 g of resident soil were reburied into each mulch’s corresponding plot. To date, mesh bags have been extracted at two 6-month intervals. At 12-month field incubation, 0% reduction was observed for spunbond at all plot locations. Reduction of BioBag and BioTelo was greatest in TX (84 and 75%, respectively) with no differences between high-tunnel and open-field. In WA, no obvious reduction was observed among BioBag and BioTelo, with one exception (88% in open-fields); in TN there was also minimal reduction with one exception (87% in high-tunnels). BioBag and BioTelo showed an average of 15% and 57% reduced area, respectively, in open fields in TN. WeedGuard showed 100% area reduction at all sites across all three regions with one exception (81% in TN). WeedGuard also showed enhanced enzymatic potential relative to no-mulch control (11% higher averaged across all plots). Soil biological responses were variable among plot locations, treatments and sampling dates. No specific trends were observed for nitrogen mineralization potential among mulch treatments, but WeedGuard samples generally had higher enzymatic potential than no-mulch with variable responses from the other BDM treatments. The lack of consistent responses among mulches, sites, regions, and post soil incorporation, indicates that other factors (temperature, moisture, soil pH) may play a more important role in soil quality than actual degradation of these materials over time.