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

Final report for OW15-007

Project Type: Professional + Producer
Funds awarded in 2015: $49,464.00
Projected End Date: 03/31/2019
Grant Recipient: Oregon State University
Region: Western
State: Oregon
Principal Investigator:
Dr. Ed Peachey
Oregon State University
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Project Information


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 80 acres of processed vegetable crops of sweet corn and processing squash over the three 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.

Project Objectives:
  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.


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Materials and methods:

Eight cooperators participated in this project. In discussion with growers, we developed research objectives relevant to their farming system. OSU provided the interseeding planter, planted the cover crops, and then monitored cover crop growth and development and estimated crop yield with small plot harvests and by processor weights, depending on acreage. Producers provided the seed and managed the plots agronomically in line with standard practices. Cover crops of oat, triticale, wheat, tall fescue, crimson clover, red clover, and common vetch were interseeded into sweet corn (organic and conventional), processing squash, and a winter market garden (organic) from mid-June through mid-October.

Interseeding common vetch into organic sweet corn.








Triticale cover crop interseeded into fall Brassica crops.



Research results and discussion:

Interseeded cover crops (planted with the high clearance drill) grew best in the less competitive crops such as squash and organic 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 that were direct-seeded (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 compared to fly-on.

    Tall fescue in late spring when interseeded into sweet corn in mid-July of the previous year.
  • Tall fescue and crimson clover established well enough in sweet corn that the grower wished that the entire 22 A field had been planted, rather than only half (see photo to right). The fescue was planted immediately after a POST application of Laudis (tembotrione) herbicide (without atrazine). A comparison of yields from the interseeded 11 A fescue field and unseeded 11 A comparison field indicated no yield penalty caused by the cover crop.
  • Triticale interseeded into squash fields 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.
  • An extremely wet October in 2016 (13 inches of rainfall, 7 inches above normal) hampered growth of the cover crops at some sites and harvest of the vegetable crops. Two of the fields were bypassed by the cannery because of the wet conditions that caused more than 80% of the corn to lodge at one site. An entire squash field was bypassed because the harvest equipment continually became stuck. While these conditions prevented planting of comparison plots in the fall, the wet fall highlighted the utility of interseeding. Interseeded cover crops established and thrived through winter, in contrast to vegetable fields where cover crop establishment was not possible because of very wet conditions that even prevented crop harvest.

In 2017, cover crops were interseeded on 7 farms in 9 demonstration trials on approximately 43 acres.

  • Common vetch was seeded into organic sweet corn after the last cultivation and by mid-April had produced 106 lb N/A compared to 78 lb N/A for the portion of the field that was fall tilled and planted to vetch (see table below).
Cover crop Cover crop drymatter Total nitrogen
C. vetch Weed Total C. vetch Weeds
-------------t/A-------------- --------------lb/A------------
Interseeded common vetch 1.1 0.4 1.6 106 23
Fall-tilled common vetch 1.0 0.5 1.5 78 32
Fallow 0.0 0.5 0.5 0 29









  • Tall fescue was planted into 33 acres of sweet corn following the success in 2016, but establishment was erratic and the grower chose to remove the fescue cover crop in the fall before harvest.
  • Winter wheat was planted into conventional sweet corn at V7 (interseeded) and after corn harvest (conventional and direct-seeded cover crops), and runoff collectors were placed in the field to measure sediment losses from inter-seeded plots compared to conventional and direct-seeded cover crop plots. During the first 3 runoff events in the fall of 2017, soil loss in the the interseeded plots was 1/3 of the soil loss in conventional and direct-seeded cover crop plots (see chart to right).
  • Triticale, common vetch, and mixes of the two were seeded into fresh market winter vegetables so successfully that the producer may buy the high clearance interseeding planter when this project concludes.

The final year of the project in 2018 commenced with follow-up on-farm plots in systems that had the best success previously. Fescue was interseeded into sweet corn (11 ac), common vetch interseeded in organic sweet corn (11 acres), and triticale and common vetch mixes interseeded into a winter market garden of cauliflower, kale, fennel, and other crops. The tall fescue crop failed to establish consistently and the field was tilled under in the fall. This strategy has only worked in 1 of the 3 years tested.

In summary, the high clearance drill from InterSeeder Technologies efficiently planted large-seeded cover crops such as small grains and common vetch. We have had less success planting red and crimson clover. Cover crops grew and survived sweet corn harvest even in very competitive sweet corn crops with fresh weight ear yields of up to 14 t/A. Triticale was the most consistent performer when interseeded, but spring oats also survived well.

Drilling was very effective where moisture was short, but sometimes buried clover seed too deep causing very poor stands. Interseeding tall fescue (for seed production) into V6 or V7 sweet corn garnered the most attention from producers, but we have only been successful in one of three years, and for unknown reasons. This system has the potential of not only providing soil coverage during the fall, but also shortening the tall fescue establishment cycle by one season, which would greatly improve profitability in a processed vegetable/sweet corn system that is suffering economically. We will continue to develop the sweet corn-tall fescue system in 2019.

On-farm trials reinforced one of the main challenges to successful interseeding: weed control. In conventional systems, preemergence herbicides and rates had to be adjusted to allow cover crops to establish, while in organic systems growers often had to delay planting until the last minute so that essential cultivation could be completed, thus reducing cover crop growth. The best time to interseed in sweet corn was the V6 growth stage; at this stage cover crops produced sufficient biomass to survive harvest equipment, yet did not compete with the crop. In a couple cases, interseeding at V8 or more was successful but this was usually in compromised plant stands in organic fields.

Participation Summary
9 Producers participating in research

Research Outcomes

2 Grants received that built upon this project
2 New working collaborations

Education and Outreach

31 Consultations
1 Curricula, factsheets or educational tools
28 On-farm demonstrations
1 Online trainings
3 Tours
7 Webinars / talks / presentations
3 Workshop field days

Participation Summary:

190 Farmers participated
68 Ag professionals participated
Education and outreach methods and analyses:

Growers and ag professionals visited on-farm field sites in March and September of 2016 to view demonstration plots and discuss the potential of inter-seeding 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 through 2019, and a poster was presented at the WithinOur Reach conference in December 2016. The project was presented at the ASHS meetings in September 2017. A field tour of successful sites was held in March of 2018. In development is a short extension publication on cover crop interseeding strategies in summer vegetable production. A webinar summarizing the entire project with reference to organic production was presented nationally on April 2, 2019 in cooperation with NRCS and Penn State University Extension

3 Farmers intend/plan to change their practice(s)

Education and Outreach Outcomes

3 Producers reported gaining knowledge, attitude, skills and/or awareness as a result of the project
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.