In 2002, when Professor Carol Miles certified the first organic ground in the Washington State University Vancouver Research Extension Unit (REU), she used plastic mulch to keep the pernicious, abundant weeds at bay. Plastic mulch (made of polyethylene) reduces weed pressure, moderates soil temperature, conserves moisture, and results in higher crop yield. Disposing of used plastic mulch, however, crowds landfills, and causes pollution when it is burned or stockpiled. Fragments that remain in the field threaten soil health and the environment, endangering microorganisms, insects, fish, and mammals.

Carol Miles and Shuresh Ghimire
Ph.D. student Shuresh Ghimire and Dr. Carol Miles in a field plot at WSU’s Mount Vernon Northwest Washington Research and Extension Center.

Early in her career at WSU Vancouver REU, Professor Miles started looking for biodegradable alternatives to plastic mulch and was the first scientist at WSU to do so. Biodegradable mulch is a good alternative to plastic because it provides similar benefits, and if it is 100 percent biodegradable it should not form any toxic residues in the field, soil or compost. Fully biodegradable mulch can also be tilled directly into the soil at the end of the season, eliminating removal costs. In 2007, Professor Miles moved to the WSU Mount Vernon Northwestern Research and Extension Center and brought the idea with her.
Professor Miles collaborated with Professor and Extension Plant Pathologist, Debra Inglis. Together they tested polyethylene and biodegradable plastic mulch in research plots so they could give growers information regarding just how long it took to remove the mulch and how much soil adhered to it. Miles and Inglis are now on their third U.S. Department of Agriculture Specialty Crop Research Initiative (SCRI) grant on biodegradable mulches. In addition, Professor Miles recently visited with other scientists in Spain, Italy, Germany, and France to share ideas and research findings, and to help organize an international symposium on biodegradable mulch.

Currently, Professor Miles and her Ph.D. student Shuresh Ghimire, and Professor Inglis, are part of a five-year study that evaluates four potentially biodegradable plastic mulches on pumpkin and sweet corn yield and quality, and mulch deterioration before and after soil incorporation. Preliminary results show that the pumpkin fruit yield using a couple of the biodegradable mulches were comparable to the use of plastic mulch.

Shuresh Ghimire was born and raised in a rural farming family in Rupandehi, Nepal, where the majority of the population works in agriculture. From an early age, Shuresh was involved in crop farming. That experience influenced his desire to help farmers improve their livelihoods through sustainable production systems. Before coming to WSU, Shuresh worked as a Horticulture Development Officer for the Nepalese Department of Agriculture, where he was dismayed to see the frequent use of unsustainable approaches in agriculture, including the “haphazard application of chemical pesticides for vegetable production.”

He combined his two passions, agriculture and education, to help solve the problem. Shuresh conducted training sessions for the growers in which he explained the potential hazards of pesticides, how to reduce those hazards, and the importance of integrated pest management for sustainable production. The work he conducts with Professor Miles is the focus of his Ph.D. project: The Effect and Efficacy of Biodegradable Plastic Mulches on Pumpkin Production and Quality, including investigating mulch degradation in the field over time.

Part of the study involves measuring mulch biodegradation on the soil during crop production and in the soil after the mulch has been tilled-down at season’s end. These measurements are unique in that they will be taken for several consecutive years. Professor Miles and Shuresh are also measuring the impact of biodegradable mulch on crop yield and quality in both a pumpkin and sweet corn test crop. Other scientists and graduate students on the project are measuring the impact on soil and water quality in the test field (Markus Flury), and the costs for producing biodegradable mulch from different feedstock (Suzette Galinato). They will also assess bridges and barriers for grower adoption of biodegradable mulch (Jessica Goldberger).

Results from Professor Miles and Shuresh’s project will encourage manufacturers to create new bio-based formulas. Mulch products on the market currently contain less than 20 percent bio-based content, and not all biodegradable mulches reach manufacturers’ goals of 90 percent biodegradation within two years of tillage into the soil. Because of these and other findings, biodegradable mulch films are unable to be certified organic in the US. On a positive note, growers are gaining a better understanding of the management practices needed to attain maximum biodegradation. And as the demand for biodegradable mulch increases, the costs of mulch production will compete more successfully with polyethylene mulch.

Ph.D. student Shuresh Ghimire (fourth from right) teaches soil sampling methodology to estimate the amount of mulch remaining in the soil to undergraduate students from Edmonds Community College, Mount Vernon, Washington.
Ph.D. student Shuresh Ghimire (fourth from right) teaches soil sampling methodology to estimate the amount of mulch remaining in the soil to undergraduate students from Edmonds Community College, Mount Vernon, Washington.

Shuresh earned his B.S. in agriculture and his M.S. in horticulture from Tribhuvan University, Nepal. Since he was interested in sustainable and organic agriculture, the horticultural research opportunities available at WSU attracted him. “My main interest,” Shuresh said, “is to contribute meaningfully in the reduction of agricultural plastic waste.” Shuresh looked forward to furthering his studies at WSU with Professor Miles, his major advisor, who offered him this opportunity. He took leave from his job at the Nepal Department of Agriculture because he saw the opportunity to learn and grow as a graduate student and member of a multi-disciplinary research project.

Professor Miles and Shuresh in collaboration with Assistant Professor Lisa DeVetter have received funding from the Washington Red Raspberry Commission and Washington Commission of Pesticide Registration to investigate the application of biodegradable plastic mulches (BDMs) for weed control and improved establishment of tissue culture (TC) red raspberry. “I look forward to our investigations of the potential sustainability of biodegradable plastic mulch in conventional and organic agriculture,” he said. “I see the likelihood of biodegradable plastic mulch replacing plastic mulch, which would greatly reduce agricultural plastic waste around the globe.”

Part of the project focuses on how to evaluate biodegradable plastic mulches for the yield and quality of vegetables, as well as mulch biodegradation and accumulation over time after repeated mulch applications. Currently there is no standard protocol to measure the rate of mulch biodegradation under field conditions, and Shuresh’s research will contribute to filling this information gap. The research project is funded by a NIFA USDA SCRI grant (award number 2014-51181-22382). The project is multi-institutional, interdisciplinary, and includes 19 scientists and several other graduate students, each in a different discipline. In addition to his Research Assistantship from this grant, Shuresh received a scholarship grant from Annie’s Sustainable Agriculture fund ($10,000).

Professor Miles and Shuresh agree that more studies involving mulch degradation in different locations and climates, and its impact on crop yield and quality, need to be conducted. New field experiments have been initiated this year—led by Professor Inglis—to expand this research into how biodegradable mulches affect plant disease management.

“I have greatly appreciated getting to learn and grow as part of a multi-state, multi-institutional team,” Shuresh said. “Traveling nationwide to present my research plans and results to a variety of audiences is one of my favorite parts of my job.” Shuresh’s career goal is to continue to serve as a leader in biodegradable plastic mulch research and education, and contribute to sustainable agriculture by reducing the plastic waste from crop production systems in the US and worldwide.