Suitability of Biodegradable Plastic Mulches In Certified Organic Production

Biodegradable plastic mulches are currently not likely to be allowed for use in certified organic production at the national level. Presently there are no biodegradable plastic mulch products allowable for use in organic production in the state of Washington or many other states.  Petroleum-derived polymers which are included in most existing biodegradable mulch formulations currently render many mulch products unacceptable in certified organic crop production. To be acceptable,  plastic mulches designed for biodegradability need to be derived from plant-based polymers like polylactic acid (PLA) and/or polyhydroxyalkanoates (PHA). Feedstock for plant-derived polymers also must be free of genetically modified organisms (GMO). Further, methodologies for creating the polymers, including resins or any additives, must be acceptable according to the National Organic Program (NOP) standards. The organic crop production industry needs to become familiar with the issues surrounding the definition of biodegradability and why many existing available products may not be eligible for such assignment.  According to the American Society for Testing and Materials (ASTM), biodegradability must be defined by the system (composting, anaerobic digestor, soil, marine, etc.), the timeframe (180-365 days is considered optimal), and the complete utilization of the substrate carbon by microorganism naturally present in the system (as measured by the evolved CO₂). The relative ability of existing and emerging plastic mulch products to completely biodegrade in the soil environment needs to be researched and studies should include information on the presence or absence of residues and/or toxic by-products as well as physical and temporal impacts on soil ecology and plant health.  It is essential for organic producers to conform to the current standards of their organic certifying agency regarding the use of biodegradable mulches, however, comprehensive studies on the long term impacts of biodegradation of plastic mulch products will help to promote new information and product development.