CHANGES IN PHYSICOCHEMICAL PROPERTIES OF BIODEGRADABLE MULCH DUE TO WEATHERING AND AGEING AND THEIR INFLUENCE ON BIODEGRADATION

Plastic mulches are employed widely in agricultural production of vegetables and other specialty crops due to their ability to limit soil water evaporation, inhibit weed growth and increase soil temperature, promoting increased crop yield and overall good quality production. However, a lack of desirable options exists for mulches’ disposal mainly due to lack of degradability, particularly for polyethylene, the most widely used material for plastic mulches. Concerns for sustainable end-of-life has led to development of biodegradable mulch films to reduce waste accumulation. Biodegradable plastic mulches (BDMs) were designed to degrade and biodegrade after field use, yet, the inherent physicochemical properties of BDMs and the role of environmental and biotic factors on polymer degradation has not been investigated. The overall objective of this PhD dissertation study was to understand the role of both abiotic and biotic factors on agricultural weathering and biodegradation of mulch films (i.e., above-soil and in-soil degradation), including the relationship between the two. The study was conducted in two field sites in East Tennessee AgResearch and Education Center (ETREC) in Knoxville, TN and Northwestern Washington Research and Extension Center (NWREC) in Mount Vernon, WA. The research plan was partitioned into three main objectives: (i) evaluate degradation of biodegradable mulches in two locations with diverse climates during 4 cropping years; (ii) evaluate microbial utilization or biodegradation of biodegradable mulches under ambient soil and composting conditions; and (iii) determine the effect of ageing on structural integrity of biodegradable mulches.Results showed significant decrease of physical properties of BDMs due to weathering as influenced by environmental factors. Changes in chemical properties was observed; however, changes were not significantly different in two field locations, in either location (TN and WA). There was a temporal variability on physicochemical properties of BDMs throughout 4-year cropping season which were attributed to some extreme weather events experienced at both field sites. Biodegradation results showed that weathering significantly enhanced microbial utilization of biodegradable mulch films (BDMs), especially during composting. The idea of storing BDMs for possible future-use is discouraged as our study found that BDMs eventually lose their mechanical functionality even when kept in an environmentally-controlled storage.These studies will provide information on BDM biodegradation which is essential to evaluation of BDM as a potential alternative to conventional plastic films.