Interseeding to improve winter cover crop establishment and efficiency in processed vegetable production in the Willamette Valley

Interseeding to improve winter cover crop establishment and efficiency in processed vegetable production in the Willamette Valley

Summary

Cover crop establishment following processed vegetable culture in Western Oregon is a challenge because harvest often occurs late into the fall. Soil may already be saturated from fall rains, and the combination of wet soil and crop residue on the soil surface often prevents cover crop establishment. One option to address these challenges is to interseed the cover crop mid-season into the vegetable crop. The goal of this project is to simply compare interseeding with traditional planting of cover crops. Cover crops have been interseeded with the assistance of cooperating producers on more than 40 acres of processed vegetable crops of sweet corn and processing squash over the first two years of the project in both conventional and organic systems, and performance of experimental plots compared to direct-seeded, conventionally planted, or fly-on cover crops. Field days have highlighted successes and limitations of interseeding strategies, and provided the context to develop future field tests.

Objectives/Performance Targets

1. Demonstrate the capability of interseeding with a high-clearance direct-seed planter to improve cover crop establishment and growth compared to conventional tillage or direct-seeding of cover crops after vegetable crops are harvested.
2. Determine the appropriate species and optimum time to interseed cover crops chosen by each farm cooperator so that cover crop biomass is maximized yet the cover crop does not reduce vegetable crop yield.

Accomplishments/Milestones

During the summer of 2015, a high clearance drill designed specifically for interseeding was acquired and used to interseed or relay plant cover crops into seven fields with four cooperators in Western OR. Cover crops of oat, triticale, wheat, crimson clover, red clover, and common vetch were interseeded into sweet corn (organic and conventional), silage corn, and processing squash beginning in mid-June through mid-August. Interseeded cover crops grew best in the less competitive crops such as sweet corn. Interseeding preformed best in a late-planted field of organic sweet corn that was harvested in mid-October of 2015. The plot was located near the Willamette River and went under water several times during December and January. Interseeded plots withstood the flooding very well compared to adjacent plots where cover crops were direct-seeded and that were planted following corn harvest in October.

In 2016, the high clearance drill was again used to seed cover crop on approximately 25 acres in six row crop fields with five cooperators. Interseeding of a 4 way cover crop mix was contrasted with fly-on treatments in sweet corn and squash fields; interseeding quadrupled cover crop stands. Tall fescue and crimson clover established well in sweet corn. The cover crop was planted immediately after a POST application of Laudis herbicide (without atrazine). Triticale interseeded into an organic squash field produced significant biomass in the fall, did not reduce crop yield, and helped to suppress weeds. Spring oats (Cayuse) established well in a conventional sweet corn field and survived the damage inflicted by harvest machinery in very wet soil conditions in late October. An extremely wet October (11 inches of rainfall) hampered growth of many of the cover crops and harvest of the vegetable crops at several sites. Two of the fields were bypassed by the cannery because of the wet conditions that caused more than 80 % of the corn to lodge. An entire squash field was bypassed because the harvest equipment continually became stuck. While these conditions prevented conventional planting of comparison plots of cover crops in the fall, the wet fall highlighted the utility of interseeding. Interseeded cover crops established and in several cases, are still thriving, in contrast to vegetable fields where cover crop establishment was not possible because of very wet conditions that even prevented crop harvest.

Impacts and Contributions/Outcomes

Growers and ag professionals visited on-farm field sites in March and September of 2016 to view demonstration plots and discuss the potential of interseeding to improve cover cropping outcomes. Results were presented at Oregon Processed Vegetable Commission annual grower meeting and at the North Willamette Horticulture Society meetings in January 2015  and 2016. A newsletter article highlighted the project and results from the 2015-16 cover crop season, and a poster was presented at the Within Our Reach conference in December 2016. In development are a video clip showcasing operation of the inter-seeder, and a short extension publication on cover crop interseeding strategies in summer vegetable production. The original team of producers has expanded to nine with on-farm demonstration plots again planned for 2017-18.

Collaborators: