If done correctly, interseeding cover crops into corn can uplift grain yields
To get a head start on establishing winter covers, interseeding has started to become a popular practice by producers in the northern region of the Corn Belt. Quite a bit of experimentation has been done over the last few years by farmers and researchers trying to dial in which species work best, when to plant, how to plant and which herbicides to avoid.
Along with early establishment, the benefits of a diverse plant population can be cashed in on by producers throughout the country. If done correctly, and with the right cover crop varieties, interseeding can significantly increase grain yields and reduce synthetic fertilizer requirements while improving soil health.
In a 2015-2016 trial conducted at The Ohio State University (OSU) by researcher Dr Ryan Haden, interseeding cover crops into corn improved grain yield up to 12 bushels per acre compared to a corn monoculture.
Radish, annual ryegrass, FIXatioN Balansa Clover and red clover were included in the trial, all contributing to notable grain yield and biomass increases.
How To Interseed Cover Crops Into Corn?
Seeding should be done with a drill between the corn rows for best establishment. Broadcasting can work, but you’re depending on rain to get the seed worked into the soil. Depending on the species, seed rates may need to be set back by as much as 50 percent.
The earlier a cover crop can be drilled, the better chance it has for a successful establishment before the corn canopy begins to limit sunlight and moisture access. While the OSU trial interseeded into corn at the V6 stage, many have success when planting at the V3-V5 stage or even at the same time the corn is seeded.
On the GO Seed Research Farm, we used a high clearance drill to interseed cover crops into corn at the V6 growth stage in three rows spaced 7.5 inches between 30-inch corn rows. We did this for several reasons:
- Improved seed-soil contact
- Less dependent on weather
- More consistent establishment
- Can be seeded up to V6 in corn (maybe up to V7)
- Large menu of cover crop species can be used
The corn was a glyphosate resistant variety planted at a population of 32,000 plants per acre on March 21. Glyphosate was sprayed to control weeds one day prior to interseeding cover crops into corn.
Grain yields at harvest were measured based on a 15.5% moisture content for corn grain. Cover crop biomass (reported on a dry weight basis) was measured in late November prior to the first killing frost, and in mid-April just prior to termination with herbicide.
Challenges And Risks To Interseeding
As with anything there are risks and it seems that drought is one of the biggest when it comes to successfully establishing an inter-seeded crop into corn.
When we first heard of inter-seeding we thought we would try it on our SE Iowa research farm. The first year it worked well. I was nervous our annual clovers or annual ryegrass would quickly go to seed. However, it appears the shade from corn is enough to defeat the photoperiod maturity aspect of these species. The only spots where we saw any flowering was along the edge of the field, something that is easily adjusted for.
Our second year we planted later than I would have liked and it got too dry before we could get much size on the cover crops. As a result, most did not make it and we didn’t have much of a stand when the corn crop started to dry down. The one variety that did perform the best was our Frosty Berseem clover, which has better drought tolerance than the other species.
Later we tried to duplicate our trial on a nearby farm but pre-emergent herbicide residual kept anything from establishing. If you are going to try inter-seeding you will want to limit your use of pre-emergent herbicide or test germinate some quick germinating seed in an area where you can watch and water it regularly. If it doesn’t live where you baby it, don’t bother seeding across the rest of the field
Weeds & Herbicides
Fields without a lot of weed issues are best for interseeding cover crops into corn to avoid problems caused by herbicide residuals. After a spring burndown with glyphosate and 2,4-D, residuals will have to be avoided in order to get the cover crop established. If weeds will be a problem without a residual, then the chance of success is low.
Best Cover Crops For Interseeding Into Corn
Depending on your soil type, climate and goals, there are multiple species of cover crops that can be successfully established into standing corn.
Legumes like red clover, cowpeas, crimson clover, berseem clover and balansa clover can fix atmospheric nitrogen to help feed the corn plants. Flowering plants like buckwheat and phacelia bring in beneficial insects to help keep harmful ones in check. Grasses with deep fibrous roots add carbon to the soil and help with water infiltration and retention.
However, because plants will go dormant in July and August when the corn canopy is closed, species must grow quickly, possess shade tolerance, and have an extensive root system to sustain themselves until the canopy opens at harvest. It is essential to choose cover crops based on variety traits, rather than buying variety not stated (VNS) seed. Traits like maturity and cold tolerance are important and will allow you to reach your goals.
Benefit Of Interseeding Cover Crops Into Corn
Perhaps the biggest benefit cover crops can bring to a corn field is soil rejuvenation. Extensive root systems required to survive summer dormancy will loosen compaction while burrowing deep into soil. A diverse mix of plants will also work together to form an underground network of fungal pathways and microorganisms that transfer and share vital plant nutrients like nitrogen, phosphorous, manganese and sulphur.
While there are multiple species and multiple ways to interseed cover crops into corn, they all require careful and early planning for successful establishment. What works on one farm may not always work on yours so small-scale experimental trials are the best way to get started. If you have questions about how to incorporate interseeding into your crop system, feel free to give Grassland Oregon a call at 503-566 9900.
OSU Study: Interseeding Cover Crops Into Corn at V6
We felt that we had learned enough that when we were approached by Dr. Ryan Haden of Ohio State to help fund his inter-seeded cover crop trial, we were happy to do so.
See Dr. Ryan Haden’s presentation below.
In the OSU interseeding trial, FIXatioN Balansa Clover contributed to the greatest grain yield increase by an additional 12 bushels per acre and was second in biomass measurements. Because it has been bred specifically to fix significant amounts of nitrogen from the environment into soil, the companion and subsequent crops can cash in on 100’s of pounds of free nitrogen.
The variety has also been bred for cold tolerance, surviving in sub-freezing temperatures at minus 20 degrees Fahrenheit with zero snow cover. However, if VNS balansa clover seed was used instead, yield, nitrogen fixation, biomass and persistence could be inconsistent field to field, and may not respond well to the environment.
Cover Crop Corner is a new educational column from forage application company Grassland Oregon and free for print or digital distribution by media outlets. To be added to the distribution list, please email email@example.com
Click HERE for a printable PDF version of this article.