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

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 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).

• 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.