Suitability of Biodegradable Plastic Mulches for Organic and Sustainable Agricultural Production Systems

Biodegradable plastic mulch has the potential to be a sustainable technology in agricultural production systems if the mulch performs equally to polyethylene (PE) mulch and biodegrades completely into constituents that do not harm the soil ecology or environment. Reduced labor costs for removal and disposal, and reduced landfill waste add further appeal to the sustainability of biodegradable plastic mulch. Biodegradable paper mulch has been allowed in certified organic production systems in the United States for many years, while the National Organic Program (NOP) added biodegradable biobased plastic mulch to the list of allowed synthetic substances for organic crop production in Oct. 2014. Although biodegradable plastic mulch may meet the NOP biodegradability requirements (90% biodegradation within 2 years), currently no products have been approved for use in certified organic production because, so far, none meet the requirement of being completely biobased. Additionally, while the synthetic manufacturing processes that are used to make biodegradable plastic mulch are allowed by the NOP, the use of genetically modified organisms (GMOs) in the feedstocks, including their fermentation, is not allowed. Organic growers are advised always to check with their certifier before applying a product as some biodegradable mulch manufacturers and marketers erroneously advertise their product as organic. Looking forward, if biodegradable plastic mulch meets the NOP requirement of 90% biodegradation after 2 years, there is a possibility that 10% of plastic mulch residuals will persist (if the mulch contains nonbiodegradable ingredients); in this case, after 8 years of annual biodegradable mulch application, plastic residuals in the soil would exceed twice the amount of mulch applied per year. The current methods used by the NOP to test mulch biodegradation are laboratory based and it is uncertain if the results accurately represent field conditions. Reliable field sampling methods to measure residual mulch fragments in the soil need to be developed; however, it is unlikely such field tests will measure CO2 evolution, and thus will not be a true measure of biodegradation. Additional testing is needed under diverse field conditions to accurately quantify the rate and extent of biodegradation of mulch products that are marketed as biodegradable.