Biodegradable Mulches: Short-Term Degradability and Impacts On Soil Health.

A 3-year SCRI research project (Award 2009-02484) is evaluating experimental and commercial biodegradable mulches in high tunnel (HT) and open-field (OF) tomato production systems in three eco-regions of the U.S. (Southeast TN; Pacific Northwest WA; High Plains TX). Treatments include: an experimental spunbond poly-lactic acid (SB-PLA-10), two currently-available starch-based films [BioBag (BB) and BioTelo (BT)], a cellulose-based product [WeedGuardPlus (WG)] and a no-mulch control (NMC). Following 2010 tomato harvest, mulch was removed and plots were tilled. A set of five nylon mesh bags (161cm²) containing one piece (103cm²) of each mulch and resident soil was buried (8-10cm depth) in corresponding plots (four replications) at each site for in situ incubation; one set extracted every 6 months. The first set of mesh bags were extracted in Spring 2011 and the impacts on mulch integrity, soil pH, EC, total C and N, N mineralization potential (Nmin), beta-glucosidase (bGluc) and N-acetyl-beta-glucosaminidase (NAG) activities, microbial biomass carbon (MBC), and community composition (fatty acid methyl ester profiles) then assessed. In TX and WA (HT and OF), no visible remaining mulch pieces were found from WG (i.e., ~100% area reduction) whereas reductions in WG for TN samples were more variable (5-98% reductions). Only TX (HT and OF) showed marginal reductions (0-29%) for BT and BB mulches. WG had significantly greater MBC than BB at all sites except TN-OF. In WA samples, Nmin was significantly greater in WG than BB, SB-PLA-10, and BT in both HT and OF. Although not statistically significant, Nmin and bGluc were lower in TN-HT SB-PLA-10, BB and BT (average 16.7mg NH₄⁺g^-1soil7d^-1 and 50.5 ug PNPg^-1 soil, respectively) compared to WG and NM (average 22.1mg NH₄⁺g^-1soil7d^-1 and 66.4 ug PNPg^-1 soil, respectively).  None of the SB-PLA-10 pieces showed visible structural changes and the experimental SB was redesigned for 2011 field tests.