As July comes to a close, it is time to make plans to seed fall cover crops. Cover crop species, seeding method, seeding rate, and timing will all depend on the goals for that cover crop. In broad terms there are three methods: 1) overseeding, 2) drill seeding, and 3) broadcast seeding with incorporation. Each of these methods has pros and cons, which will be discussed in this article.
Overseeding. Overseeding can be done into a standing corn or soybean crop either by broadcasting with an airplane or using high clearance equipment. Overseeding allows the cover crop to be planted earlier, which can lead to greater biomass growth in the fall. However, overseeding does have some drawbacks. For one, distribution of seed can be more variable with aerial seeding. The best distribution comes from uniform seed lots and heavier cereal grain such as cereal rye and winter wheat. Additionally, stand establishment can be lower than with other seeding options due to rodents and birds scavenging seed as well as if dry conditions exist following seeding. To ensure adequate establishment, overseeding should be done late August to early September, assuming adequate soil moisture. Some of the most successful overseedings are done shortly before a rainfall. The seeding rate for over seeding should be 15-25% higher than drill seeding.
Drilling. Drill seeding provides the most uniform seed distribution and excellent seed to soil contact for establishment, which results in a more consistent stand. One of the biggest drawbacks of drill seeding is that corn and soybean harvest can delay cover crop planting beyond ideal planting dates. Delayed planting can result in reduced biomass growth and less nitrogen uptake. Drill seeding should be completed by mid- to late October.
Broadcasting with incorporation. Broadcast seeding with incorporation after corn and soybean harvest is also a viable option to plant cover crops. It can be accomplished as a 1-pass or 2-pass process. One-pass systems typically have an air seeder attached to the combine or broadcast cover crop seed with fertilizer application. Incorporation can be accomplished with vertical tillage or other tillage implements, but care must be taken to ensure that incorporation is not too deep for plant emergence. Broadcast seeding with incorporation can improve overall stand establishment compared to broadcast seeding without incorporation. Like drill seeding, broadcast seeding with incorporation should be completed by mid- to late October.
For more information on cover crop species and cover crop management visit:
Cover Crop Decision Tool - Midwest Cover Crops Council (MCCC)
Herbicide Grazing Restrictions – ISU Extension and Outreach (ISUEO)
Post Corn, Going to Soybean: Use Cereal Rye – ISUEO and MCCC
Post Soybean, Going to Corn: Use Oats – ISUEO and MCCC
Cover Crop Resources – Iowa Learning Farms
Cover Crop Resources – Practical Farmers of Iowa
Conservation Choices: Cover Crops – USDA NRCS