Biodegradable Plastics as Alternative to Polyethylene Mulch for Watermelon Production Systems

Polyethylene mulch is widely used for vegetable production in the U.S as a tool to conserve water, control weeds and produce earlier and cleaner products.  However, the increasing labor costs for mulch removal and disposal after harvest, and air and soil environmental pollution are major concerns. The objectives of this study were to assess yield, fruit quality, mulch degradation, soil microbial activity and nutrient changes in watermelons grown with biodegradable plastic mulches. Watermelon (Citrullus lanatus L.) cv. Stargazer was grown at the Texas A&M AgriLife Research Center at Uvalde, Texas, during the spring of 2014 using three biodegradable experimental mulch formulations (4030, 4031, and 4032; EcoPoly Solutions Inc., Ontario, Canada) and two polyethylene (control and experimental 4035) plastic mulches. Yield, fruit sugar content (Brix), and mulch degradation percentage were evaluated. At the end of experiment, soil nutrient and microbial activity of control and 4032 biodegradable plastic mulch were also determined.  Our result showed that total yield and sugar content of watermelon grown with biodegradable and polyethylene mulches did not differ significantly.  However, the degradation percentage of biodegradable mulches was 10-20%, 40-60%, and 90-100% at 4, 8, and 12 months after field transplanting, respectively.  Additionally, the degradation speed of 4032 and 4030 mulch was about 20% faster than 4031.  There were no statistical differences in soil total and active bacteria and total and active fungi, although nitrate content increased (P=0.08) in soils with the 4032 biodegradable as compared to polyethylene mulch.   Detailed chemical and biological soil analyses are required to evaluate the long-term impact of biodegradable mulches on soil nutrients and microbial activity.  The future implementation of biodegradable mulches into commercial vegetable farming practices appears promising.