Comparison of Weathering at Two Diverse Geographic Locations and Simulated Weathering on the Physicochemical Properties of Biodegradable Plastic Mulches

Plastic mulches are an integral component of specialty crop production. Yet, conventional plastic mulches, prepared typically from polyethylene, are problematic due to their poor sustainability. Firstly plastic mulches require labor-intensive retrieval after harvest, and secondly because they are so resilient they have long-term accumulation in the environment. Biodegradable plastic mulches (BDMs) address many of the concerns with using conventional mulches; but, their widespread use by growers is limited by unpredictable and variable performance both during their use and following their incorporation into the soil. This study focuses upon the changes in physicochemical properties of three commercially available plastic mulches marketed as biodegradable: BioAgri, a film prepared from polyesters sometimes blended with starch (BioBag Americas, Inc. Dunedin, FL, USA); Organix, prepared from Ecovio®, a polyester film developed by BASF (Organix Solutions, Maple Grove, MN, USA); and Naturecycle, a proprietary starch-polyester blend (Custom Bioplastics, Burlington, WA, USA). In addition, the study included one experimental mulch prepared from biobased polymers (prepared by Metabolix Inc., Cambridge, MA), and two control mulches [black polyethylene mulch (non-biodegradable control), and WeedGuardPlus, (fully biodegradable control) Sunshine Paper Co., Aurora, CO]. The study was carried out at two diverse geographic sites: Knoxville in eastern Tennessee and Mount Vernon in northwestern Washington. Our findings demonstrate that mechanical properties (tensile strength and % elongation at break) the mulches underwent the greatest extent of change in Knoxville. All three commercially available plastic BDMs underwent a major decrease of tensile strength and elongation, reflecting embrittlement, due to the stronger sunlight and higher temperatures in Knoxville as compared to Mount Vernon. In contrast, conventional PE mulch did not undergo deterioration at either site. Results from simulated weathering demonstrated that tensile strength decreased exponentially with time. The overall results of this study demonstrate that weathering has a major impact on the structural integrity of BDMs during their use in the field. The extent of weathering also impacts the inherent biodegradability of BDM. Therefore the environmental factors of the location where the BDM is used will influence the biodegradation of the product both during its use and after.