By Jenny Rees, Roger Elmore, Chris Proctor, Steve Melvin, and Michael Sindelar
An increasing number of growers are integrating cover crops into their cropping systems with goals of reducing erosion, increasing soil health properties, adding/capturing nitrogen, grazing livestock, or aiding in weed suppression. Cover crop establishment after corn and soybean harvest can be challenging with mixed results. Thus, an increasing number of growers have asked about the potential for interseeding cover crops (Figure 1) into an established crop.
Interseeding is primarily done prior to crop canopy closure or prior to harvest when the crop canopy begins to re-open. After the crop harvest, the hope is the cover produces greater biomass since it’s already established compared to if it was seeded post-harvest. This article shares the research on interseeding, considerations for interseeding, and an on-farm research protocol for obtaining more cover crop interseeding data in Nebraska.
Figure 1. University of Wisconsin researchers studied drilling cover crops into V5 corn.
Key Points
- Most studies show minimal corn yield impact with interseeding cover crops during the V5-V7 growth stages. Few studies exist with interseeding into soybean.
- Research consistently shows that rimsulfuron (Resolve, Basis) and safluenacil (Sharpen) tend to result in little to no herbicide injury on interseeded grasses, legumes, brassicas, or mixes. Penn State University lists additional herbicide injury ratings.
- Most successful legume options include clovers such as red, crimson, berseem, and balansa. Cereal rye and annual ryegrass are the most common grasses interseeded. Buckwheat and phacelia were used in organic studies to attract beneficial insects.
- Many types of equipment have been retrofitted/purchased to interseed cover crops (Figure 2).
- Have your plans together a few growth stages before you actually interseed. From grower conversations, once the crop takes off, it is hard to catch up if interseeding plans aren’t already in place. If you hope to interseed by V5-V8, have your seed and interseeder ready by V3 so you can actually get the cover crop interseeded at V5-V8 when the weather allows. The window is narrow and closes quickly.
- Regarding crop insurance, the USDA Risk Management Agency (RMA) addresses interseeding in its cover crop guidelines. In a Q&A with the guidelines, it noted that coverage of an insured grain crop would not be affected by “seeding a cover crop into an existing crop (e.g., corn or soybeans) at a time that will not impact the yield or harvest of the insured crop. These examples do not affect the insurability of the insured crop, but if not done properly, may impact the indemnity received in the event of a loss on the insured crop.” Please contact your crop insurance agent with any questions.
Figure 2. Interseeder being used to sow cover crops into V5 corn in Wisconsin
Nebraska Research
Angela Bastidas investigated interseeding in her Ph.D. work at UNL, broadcasting cover crops into corn- simulating aerial seeding (
Bastidas, 2017). She interseeded several cover crop species [60 lb/ac rye; 20 lb/ac hairy vetch; 40 lb/ac soybean MG VIII; 10 lb/ac radish; and a 38 lb/ac mixture of rye , hairy vetch, and radish (30, 5, and 3 lbs, respectively.)] at the time of corn planting as well as at the V8 stage. The later seeding date had no effect on corn yields but produced very little cover crop biomass. However, the interseeding at planting reduced yields by up to 160 bushels per acre. As summer cover crop and weed biomass increased with the interseeding at corn planting, corn yields decreased.
In a
2018 on-farm research and NRCS demonstration study, farmers in Merrick County compared a fall dormant seeding versus fall dormant seeding + spring interseeding versus a check. In the fall of 2017, both the dormant-seeded treatment strips and the dormant + interseeded treatment strips had a cover crop mix. The cover crop mix in both treatments was terminated with glyphosate on May 10, 2018. Corn was planted on May 17 followed by a post application of 32 oz glyphosate + 5 oz Status per acre on June 1. They used a Hiniker interseeder to plant the cover crop mix on June 26 which included 6 lb/ac cowpea, 6 lb/ac soybean, 0.5 lb/ac crimson clover, 5 lb/ac sunhemp, 2 lb/ac hairy vetch, 3 lb/ac buckwheat, 0.5 lb/ac chicory, 0.5 lb/ac flax, 0.5 lb/ac rapeseed/canola, 6 lb/ac Elbon cereal rye, 6 lb/ac spring oats. There were no differences in corn yield with any treatments; no biomass measurements were reported in the study.
Research from Other States
Researchers at Penn State have conducted numerous studies on interseeding cover crops and have even commercialized an
interseeder. This
FactSheet provides a summary of their research and their recommendations on the timing of interseeding into V5 corn, herbicide use, and cover crop species to use.
Figure 3. Established cover crop interseeded into corn.
Researchers at the University of Wisconsin seeded radish, red clover, and winter rye into V5 corn (Figure 3). The covers had good growth up to grain harvest. Biomass of the cover crop species varied after harvest due to being covered by the corn residue. The rye was the only crop that needed to be terminated the following spring. There was no corn yield reduction and no visible stress to the corn in the two years of their study. This
FactSheet summarizes findings from the University of Wisconsin trials.
Thirteen lb/ac annual ryegrass, 30 lb/ac cereal rye, and 27 lb/ac oats were interseeded at soybean development stages R3, R5, and R7 in twin-row soybean in a
2017 on-farm research study conducted in Ohio. The soybean interseeded with the oats at R5, and soybean interseeded with cereal rye and annual ryegrass at R7 yielded significantly less than the check (no interseeded cover crops).
Testing via On-Farm Research
Our hope is to obtain more research data from Nebraska. If you are interested in testing interseeding via on-farm research, the following two-treatment and three-treatment protocols can be found at:
https://go.unl.edu/kvjf. The two-treatment protocol compares interseeding versus a check.
The three-treatment protocol can be altered a number of ways including:
- Interseeded species/mix 1 versus interseeded species/mix 2 versus check
- Broadcast interseeded versus drilled interseeded versus check
- Timing 1 versus timing 2 versus check
Source:unl.edu