How to Choose a Cover Crop
How do I choose a cover crop?
When someone asks that, there are two response questions that should immediately come to mind: “What is your resource concern?” and “What is your window for seeding?” It is hard to say which is more important or which should come first (kind of like the chicken and the egg...)
The timing of cover crops in a rotation takes some planning ahead. As you consider the goals of your cover crop, you have to know when a realistic seeding window is for your operation. We have given an overview of the following different cover crop seeding windows: Pre-Plant Cool Season, Early Interseeding, Interseeding into Wide Rows, After Small Grains, and After Fall Harvest. Take a look at those posts to see where your cover crop will land in the year.
Identifying your resource concern is something that should be happening at the same time as deciding your cover crop window. Here are some common goals of cover crops and how to achieve them:
Fixing Nitrogen – Utilizing cover crops that will fix nitrogen and then release it to the following crop is an amazing way to eventually lower input costs. A rule of thumb is that at flowering before setting seed is when legumes produce their peak amount of nitrogen. This means legumes have to have an adequate amount of time to produce enough growth to give you that nitrogen credit. This goal can generally be met for cover crops planted early spring, throughout the summer, and early fall with enough time before a frost. After fall harvest of corn or soybeans, nitrogen fixing options become limited. Keep in mind other nutrients that can be made available by cover crop such as phosphorus, potassium, sulfur, etc. when considering what to use in a blend. Nitrogen fixing cover crops are beneficial, but not as much when another nutrient is your limiting factor. Diversity in a blend to make as many nutrients available as possible is key.
Soil Structure Correcting – Compaction is an extremely common resource concern that producers want to address with cover crops. While brassicas like Pick-Axe radish are often the first to be desired, annuals such as annual ryegrass can be a great compliment to those deep taproots with their own fibrous, branching system. A mix of the two can do wonders for compacted soil by creating various channels throughout the soil for air, water and soil biology. To improve overall soil structure, almost any variation of a cover crop blend that has diverse species and root systems will do the job. That being said, the blend you choose is completely dependent on that previously mentioned seeding window you are able to use.
Forage – While it can be argued that a crop planted for a grazing or harvesting is simply a forage crop, many fit the role of a cover crop simultaneously. Need grazing in the spring before pastures are ready? A fall planted winter annual (like cereal rye) will provide that while also serving as a cover crop over the winter. You will have a living root in the ground all winter and the topsoil will be stabilized during spring rains. Need summer forage when pastures slow down? Use a soil building blend of summer annuals (like Summer Blend) to provide high quality forage and varying root systems to keep your underground livestock happy. For fall grazing, use a combination of annual grasses, brassicas, and legumes planted late summer to extend your grazing season into the fall while also providing cover on what may otherwise be bare ground.
Show that cover crop to your cows and your soil biology and they will both be interested!