USDA SCRI Biodegradable Mulch Project
WSU Mount Vernon faculty, staff and students have been working on a large, multi-state USDA Specialty Crop Research Initiative (SCRI) project evaluating the use of Biodegradable Plastic Mulch in vegetable cropping systems.
Plastic mulch is used to suppress weeds and conserve water when growing specialty crops, like pumpkins, tomatoes, and strawberries. Biodegradable plastic mulches (BDMs) have been developed as a substitute for conventional plastic mulch to reduce removal, storage, and disposal issues and costs. The widespread use of BDMs is limited by lack of knowledge and by concerns about their unpredictable breakdown and potential residues.
Our research team of 19 scientists from three universities is taking the lead to investigate these issues in a field experiment at Washington State University Northwestern Washington Research and Extension Center (NWREC) in Mount Vernon and the University of Tennessee in Knoxville (UTK). In our on-going five-year field study (we are currently in year 4), we tested six BDMs in years 1–2, and seven BDMs in years 3–5 (Table 1). In all years, the field experiment included two treatments for comparison with BDMs: polyethylene (PE) mulch and no-mulch.
In the first two years, ‘Cinnamon Girl’ pie pumpkin was grown as the test crop at both locations (discussion of pumpkin as a test crop (pdf)). BDMs remained intact throughout the growing season both years and suppressed weeds similarly to the PE mulch. An important finding was that paper BDM, which is one of the treatments, was the only mulch to suppress nutsedge. Overall average pumpkin yield was 8 tons per acre at both WSU NWREC and UTK, but at WSU NWREC yield was 40% greater with mulches than for bare ground whereas at UTK there was no difference in pumpkin yield due to mulch treatment. Yield differences at WSU NWREC was likely because the soil temperature (5 inch depth) was 2 °F higher with mulch (70 °F), which was more favorable for pumpkin growth, but at UTK soil temperature was 77-82 °F for all treatments.
Mulch adhesion is an important consideration with BDM, and was defined in our experiment as fragments of mulch measuring 1 cm2 or greater adhered to the fruit such that pieces would not wipe off easily. Marketability of fruit can be reduced due to mulch adhesion. At WSU NWREC, with BDMs approximately 50% of the pumpkin fruit had mulch adhesion whereas at UTK only 8% of the fruit had mulch adhesion. This difference was because at WSU NWREC fruit set was on the mulch whereas at UTK fruit set was in the alleyways due to longer vine length (even though the same cultivar was grown at both locations).
In years 3 and 4, sweet corn is being grown at WSU NWREC while bell peppers are being grown at UTK. Results from year 3 indicate sweet corn yield is following the same trend as pumpkins at NWREC such that yield is 52% greater with mulch than for bare ground. Of additional interest is that first harvest of sweet corn grown with mulch was 1 week earlier compared to bare ground. At UTK, there was a difference in mulch product impact on yield of bell pepper as four mulch products had yield similar to bare ground and three mulch products had yield less than bare ground. Similar to sweet corn, harvest was up to 2 weeks earlier with mulch compared to bare ground.
Additional research at WSU NWREC includes the development of a soil sampling protocol to assess how much mulch remains in the field after soil incorporation each year. Further research at both sites includes assessing soil quality, soil moisture, plant pathogens, mulch physiochemical properties due to weathering, economics, and on-farm utilization. Our project website includes fact sheets and journal articles that we have published based on our results.
The project Performance and Adoptability of Biodegradable Plastic Mulch for Sustainable Specialty Crop Production is funded by the United State Department of Agriculture (USDA) National Institute for Food and Agriculture, through its Specialty Crop Research Initiative, under award 2014-51181-22382. Any opinions, findings, conclusions, or recommendations expressed on the website “Biodegradable Mulch” are those of the site authors and do not necessarily reflect the view of the U.S. Department of Agriculture.