Assessment of Degradable Alternatives for Plastic Mulch for Organic Tomato (Solanum lycopersicum) Production in the Southeast

Since the 1950s, plastic has been used as soil mulch in agriculture to increase yield, quality, and earliness of harvest, while reducing weed growth, irrigation requirements, soilborne plant diseases, and nutrient leaching. However, once removed from the field, plastic disposal and recycling can be expensive. Degradable mulches were introduced into agricultural production nearly 30 years ago as an alternative to plastic or polyethylene mulch, with the intention to reduce agricultural plastics in the waste stream. Degradable mulches have the potential to reduce removal costs and lessen environmental impacts, while providing similar benefits as plastic during the growing season.  Four degradable mulch products, BioAgri Ag-Film, BioTelo Agri, WeedGuardPlus, and an experimental spunbond nonwoven fabric (SB-PLA-10/11/12), were evaluated during 2010, 2011, and 2012 in Knoxville, TN.  These four products were compared with black plastic mulch and a bare ground (no mulch) control with respect to tomato (Solanum lycopersicum) yield, weed control, and degradability in high tunnel (HT) and open field (OF) production systems.  Marketable yields in degradable mulch plots were comparable to those from the black plastic plots across all three years. Weed growth was minimal in both production systems in all three years except under SB-PLA-10 in 2010.  The SB-PLA was reformulated in subsequent years and effectively suppressed weed growth, though showed very little visual degradation during the production season.  While SB-PLA did not breakdown in the field, it may be useful for other agricultural purposes, such as mulching applications for multiple cropping seasons, row cover, or ground cover between rows.  The commercially available products, BioAgri, BioTelo Agri, and WeedGuardPlus, achieved > 50% degradation in the OF system by the end of the season in two out of three years of the study. WeedGuardPlus breakdown in the HT system was < 10% in all three years, likely due to protection from wind, rain and solar radiation; however, WeedGuardPlus can be tilled into the soil at the end of the season and will fully degrade.  Both BioAgri and BioTelo were more variable in breakdown (10% to 40%) in the HT system, but must be removed from the field in certified organic systems, due to their formulation, which includes non-organically approved additive(s).  However, by the end of season, the consistency of BioAgri and BioTelo was so brittle that physical removal was time consuming and difficult, reducing their practical application in the field.