Managing cover crops ahead of the 2023 corn crop

If you’re like many Ontario farmers, you are not only watching as your crops head toward the finish line, but also keeping an eye on the progress of the cover crops you seeded after cereal harvest. With recent rainfall in many parts of the province, cover crop growth is taking off.

Cover crops provide benefits by capturing sunlight and building soil carbon, competing with weeds, fixing atmospheric nitrogen, and protecting soil from erosion. They benefit crop yields over time. Cover crops require extra management, however, and can affect many aspects of your soil, from fertility to residue cover and soil drying and warming in spring. It’s important to consider how to manage for these conditions, especially prior to planting corn. In this week’s crop report, we will share some information on common cover crop species and how best to set up for success ahead of the 2023 corn crop.

Cover crop species

Winterkilled species die consistently following freezing temperatures in Ontario and present simplified management. Oats, field/forage peas, tillage radish and sunflower are the most used winterkilled cover crops (image at top). While common advice used to be to seed cover crops as early as possible following cereal harvest, some Ontario growers have moved toward slightly delayed seeding. This provides an opportunity to manage volunteer wheat and can result in a more manageable amount of residue, especially where manure is applied.

Overwintering species survive winter and, in some cases, put on their most vigorous growth in the spring. Common examples include winter cereals such as cereal rye and legumes like red clover and hairy vetch. These species remain alive for a longer period, which can assist in capturing excess nutrients in fall and competing with weeds in spring. When left to grow into spring, they require additional management and are not well suited to cover crop beginners. Cereal rye grows rapidly in May, as does hairy vetch. Timely termination or the use of a planter equipped for high residue are key. Fall termination of red clover – ideally done in late October – provides a full nitrogen credit (70-80 kg/ha) and simplifies spring management. Also consider your problem weeds and whether the benefits of an overwintering cover crop outweigh a fall herbicide application.

Certain species are unreliable in their winter survival. Examples include crimson clover, Austrian winter pea and some brassicas. Don’t assume these species will die and be prepared to control them in the spring if no fall herbicide is applied.

Finally, there has been a trend away from complex mixtures to simple blends of 2-5 species. Often, a small number of species dominate a mixture. Seeding fewer helps ensure a balance of growth amongst species, keeps seed cost lower and reduces the risk of some species setting seed.

Tips for managing cover crops ahead of corn

Cover crops protect soil best when they are left on the soil surface over winter. For those not comfortable leaving soil undisturbed, ensure your tillage will leave at least 30% cover on the soil surface up until after planting to significantly reduce erosion.

For those who prefer to leave soil untouched over winter, consider the impact of cover crop residue in spring. Winterkilled or fall terminated cover crops will keep soil cooler and wetter. You may be surprised, however, at how much residue breaks down by spring. Lighter stands of cover crop provide more flexibility in this regard. In minimum tillage systems, residue should be moved away from the corn row to ensure a uniform seeding environment. Overwintering species such as cereal rye may keep soil cool and wet initially but assist with drying once growth accelerates in May. Best practice for managing cereal rye ahead of corn is to terminate it at least two weeks prior to planting or when 6-12 inches tall, whichever comes first. This reduces risk of disease transfer and nitrogen tie-up. Under dry spring conditions, winter cereal cover crops can deplete soil moisture quickly and their termination should not be delayed beyond corn planting. Including nitrogen at planting is important as well. For more detailed information on corn following cereal rye, visit the Field Crop News website.

For growers who plant corn “green” into cover crops, common keys to success include adequate nitrogen applied at planting, sharp, well-maintained opening discs, and achieving sufficient planting depth and slot closure.

Key take-aways

Cover crops provide their greatest benefits through consistent use over time. To ensure long-term success, consider the following strategies ahead of planting corn:

• Seed a modest number of cover crop species and consider slightly delayed summer establishment if soil fertility is high
• Be prepared to manage species that may survive winter, e.g. crimson clover
• Adapt to the impact of residue, dead or alive, on spring soil conditions.

– Click here to read the Sept. 7 field crop report at the Field Crop News website.