Biodegradable Plastic Mulch Provided Weed Control, Yield, and Quality of Pie Pumpkin Comparable to Polyethylene Mulch

The use of polyethylene (PE) mulch in agriculture has greatly increased worldwide in the last two decades. Mulching reduces weed pressure, moderates the soil temperature, conserves soil moisture and results in higher crop yield. PE mulch in most cases is not recyclable and its disposal can be a source of pollution to the soil and environment. Hence, mulch that can biodegrade in the field after tillage incorporation with no negative impact on the soil ecosystem would be highly desirable. In 2015, an experimental field trial evaluated four potentially biodegradable plastics (Metabolix, Organix, Naturecycle and BioAgri), a cellulose mulch [WeedGuardPlus (100% biodegradable)], PE (non-biodegradable) and no-mulch treatments for effects on pumpkin (Cucurbita pepo L. cv. Cinnamon Girl) fruit yield and quality. Two U.S. trial locations were selected based on distinct climate differences: Mount Vernon, WA and Knoxville, TN. At Mount Vernon, the dry weight of weeds in the no-mulch treatment increased from transplanting to harvest (475 g^.m^-2), but there were no weeds in any of the mulch treatments except Naturecycle (0.1 g^.m^-2) at 2 weeks prior to harvest. At Knoxville, the dry weight of weeds was higher for the no-mulch treatment and Naturecyle from transplanting to harvest (71 g^.m^-2 and 25 g^.m^-2); however weeds were not of practical significance for Naturecycle. At Mount Vernon, pumpkin marketable yield with BioAgri (24.3 t^.ha^-1) and Metabolix (22.4 t^.ha^-1) were comparable with PE mulch (27.3 t^.ha^-1) while yield was significantly lower for the no-mulch treatment (11.3 t^.ha^-1) and WeedGuardPlus (16.1 t^.ha^-1); yield with Naturecycle (20.1 t^.ha^-1) and Organix (19.7 t^.ha^-1) were intermediate (P = 0.0002). These differences in yield may have been due to the difference in the soil temperature: at 10 cm depth, the temperature tended to be 2 ⁰C lower for the no-mulch treatment (20.3 ⁰C) as compared to PE, BioAgri and Metabolix (21.8 ⁰C – 23.3 ⁰C). At Knoxville, pumpkin fruit yield did not differ due to treatment (12.3-18.1 t^.ha^-1), and soil temperature was higher in general for all treatments (25.3 ⁰C – 26.9 ⁰C) as compared to Mount Vernon. Pumpkin fruit quality (total soluble solids, dry matter, length and width) at harvest did not differ due to mulch treatment at either location. These results indicate that weed control, yield and quality of pie pumpkin grown with biodegradable mulch are comparable to PE mulch.