Chapter 17

Soil Management for Field Crops

Interseeding with Cover Crops

In traditional corn rotations, overwintering with a cover crop is an attractive option for producers wanting to make strategic improvements to field conditions or take advantage of forage potential for livestock. While it is common practice for cover crops to be established post-cash crop harvest, this can become a challenge for several reasons. Regions with a shorter growing season can pose a challenge for establishing many cover crops after fall harvest due to the colder climate which limits early growth potential before plants go dormant. This can often lead to poor soil coverage, leaving the field susceptible to erosion by winter snow melt and spring rains. But even in good conditions, a lot of regions are limited on what species can be successful when seeded after corn harvest.

Interseeding Time

The best time for interseeding with a cover crop depends on the growth stage of the cash crop. Since corn is such a competitive plant, interseeding at the right time is important to ensure the incoming cover crop still has access to light before the canopy of the already established corn. For corn this is done during the V3 to V7 growth stages in conjunction with side dressing, allowing the cover crop to establish and grow before light access is closed off with the canopy.

Cover Crops for Interseeding

The best species are cool season annuals or perennials, somewhat drought and shade tolerant, and easy to establish. Grasses include oats, barley, cereal rye, wheat, triticale, buckwheat, annual ryegrass, Italian ryegrass, millet, and sorghum-sudangrass. They tend to germinate quickly and can produce adequate biomass under different growing conditions. This allows them to be great for erosion control, adding organic matter, scavenging nitrogen, and suppressing weeds. They can be used as a forage crop as well. Annual ryegrasses don't head out and often have superior winter hardiness.

Interseeding Corn with Cover Crops

Interseeding cover crops into standing corn is becoming a common conservation practice in the Midwestern Corn Belt. The ideal species for interseeding are those that are cool season, somewhat drought and shade tolerant and relatively easy to establish. These have mostly included annual ryegrass, and red and crimson clovers. Annual ryegrasses are available as true annuals or Italian ryegrasses. The annual ryegrass is less expensive, and sometimes produce a bit more biomass, but they can head out in the fall and are more subject to winter-kill.

Interseeding Winter Wheat with Red Clover

Red clover overseeded into winter wheat is one of the most common types of interseeding in growing field crops. Frost seeding red clover is the practice of broadcasting red clover into winter wheat prior to green-up. Timely frost seeding usually allows this method to achieve sufficient seed-soil contact for successful seedling establishment while also avoiding rutting and soil compaction. Seasonal freeze-thaw cycles cause the soil to repeatedly develop small cracks on the surface, allowing the clover seed to achieve adequate soil contact and to germinate. To be effective, avoid saturated soils, keep fertility up, and make sure pH is at least neutral.

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