Cover crop integration after corn and soybeans
Establishing cover crops after corn and soybeans offers a unique opportunity for soil improvement. For the many Ontario acres that don’t receive the benefits of a third crop in rotation, it is one way to help maintain soil productivity. Winter cereals, such as winter cereal rye, are the main species option at this time of the season. This report will explore a range of techniques available to seed cover crops into or after late-harvested crops, each with their own strengths and weaknesses. It will finish with tips for managing cereal rye residue ahead of the next crop.
Biomass and uniformity are key
According to global research summarized by Washington State University’s Andrew McGuire, biomass is directly correlated to cover crop benefits. A minimum of 900-1,800 lbs per acre (1-2 tonnes/hectare) of aboveground (dry) biomass is recommended to provide significant erosion reduction and measurable soil and nutrient benefits. Figure 1 gives an idea what this looks like.
A uniform stand is important, too. While it doesn’t need to be perfect, a patchy cover crop stand does not provide benefits equally across the field and can contribute to variable seedbed conditions for the following crop. Figure 2 shows an example of an uneven stand.
Establishment strategies
There is no single perfect way to establish a cover crop; the chosen strategy depends on the farmer’s goals, available labour, equipment, and environmental conditions.
- Drilling provides the most consistency but is also the most costly and time-consuming.
- Broadcasting alone is fast and inexpensive, but often gives variable results, especially without favourable weather. Tillage after broadcasting enhances stands by improving seed-to-soil contact. It should be balanced against increased erosion risk, especially in soybean stubble.
- Application using drones offers flexibility, enables in-crop seeding possibilities, and can provide enhanced growth through earlier establishment. Be aware, however, that drone seeding can result in spottier stands than with post-harvest seeding. Seeding at the correct crop stage, e.g., majority yellow leaves in soybeans and dent stage in corn, and receiving rainfall after seeding is key. Learn more about on-farm drone seeding research (ontariosoilcrop.org/livinglab/).
Table 1 profiles various strategies for establishing cover crops in or after corn and soybeans. An optimal seeding method provides strong growth potential, reasonable uniformity, and perhaps most importantly, is doable year in, year out.
Table 1. Cover crop establishment strategies in or after corn and soybeans
| Strategy | Pros | Cons |
| Early season interseeding (e.g., V4-V6 stage; corn only) | Broader range of species options (e.g., clovers, annual ryegrass), assuming compatibility with herbicide programIncreased biomass potential | Specialized equipment required for best results Poor stand establishment and uniformity possible due to dry conditions, crop competition, or herbicide sensitivities |
| Late season interseeding (e.g., by drone, high clearance equipment) | Earlier establishment and potentially greater biomass Intermediate cost Flexibility in application timing (drone)No compaction potential (drone) | Dependent on rainfall for germinationConsistency yet to be determined |
| Drilling | Results in strong, uniform stands | Equipment wear and tearTime consumingCompeting demands for drillRequires crop harvest |
| Surface application, post-harvest (e.g., spinner spreader, airflow) | FastInexpensive | Poor seed-to-soil contact Requires crop harvest |
| Surface application, post-harvest with incorporation (e.g., vertical tillage) | Improved seed-to-soil contact enhances uniformityPotential for earlier establishment and greater biomass (vs. broadcast only) | Added costs and labour relative to broadcast onlyPossible increase in soil erosion |
Combining cover crop seeding with existing operations offers an appealing approach. Figure 3 shows an innovative technique implemented by an Ontario farmer that enables three actions in a single pass: cover crop seeding, fertilizer application, and vertical tillage. The grower has found this provides improved consistency for cereal rye in corn stalks relative to broadcasting alone.
Minimizing risk to the following crop
Cover crop benefits can quickly be outweighed by negative impacts on the following crop if appropriate management practices aren’t followed. Have a plan in place well in advance for spring control, and a backup plan in case conditions are difficult. Use the following tips as a guide for spring management:
- Terminate on time. Aim to terminate cereal rye at least two weeks prior to corn planting, when rye is less than 12 inches tall. For soybeans, do the same, or delay termination just prior to planting if soil conditions are not excessively dry and appropriate seeding equipment is available.
- Use the right tillage tool. Avoid equipment that can’t handle large root balls, such as a cultivator. Spring strip-till is a good option ahead of corn, as is disking – assuming there is modest cereal rye growth (e.g., less than 12 inches height). For soybeans, no-till seeding is effective into cereal rye.
- Adapt nutrient management. For corn, consider shifting a greater balance of nitrogen up front and band a higher-than-normal (but crop-safe) rate if possible. Soybeans typically do not require fertility adjustments for a cereal rye cover crop.
Bottom line
Late-season cover crops into corn and soybeans that don’t rotate to wheat represent an added opportunity to protect and improve soil. Talk to other farmers and test out different approaches. Move ahead with the one that gives the greatest growth potential and uniformity, weighed against cost and on-farm labour and equipment realities.
