WHAT IS A COVER CROP
A cover crop is a plant grown for purposes other than the harvest of grain for sale. Covering the ground year round is one of the tenants of regenerative ag. On the Continuum Ag farm, we use cover crops as a tool to reduce erosion, to improve soil function and soil nutrient cycling, to build organic matter, to sequester carbon and to build overall soil health. We’ve been using cover crops for the last four years and have used mostly cereal rye and winter wheat, but we have also experimented with a large array of about 15 different cover crops. This year, we are trying interseeded cover crops as well.
PLANNING AHEAD
When planning a cover crop program, start by answering the question, “what is my overall goal?” For most people, the goal is to reduce erosion, keep the soil covered in order to feed the microbes and work towards overall soil health. But what does that really mean and how can it economically pay? We utilize soil health testing to quantify soil nutrients, carbon, and biological activity, but we will dig into that in another blog. Overall, we’ve seen really incredible increases in nutrient availability with cover crops and now have the ability to quantify that gain and help to improve fertility management based on biological function.
WHICH COVER CROPS TO USE
If you’re looking at utilizing cover crops in Southeast Iowa and you’re going to seed your covers with a drill after harvest (which is the common practice), the crop to use would be cereal rye or winter wheat. We like using cereal rye because it develops a fibrous root system, over-winters extremely well and comes back in the spring with a good amount of vegetative growth to provide coverage for the soil. It also helps to pull water out of the soil when we have extra water, to suppress weeds and to store nutrients for the next year.
What we have found is that if we don’t have a cover crop, our soil is still mineralizing nutrients at all times throughout the year, which is something that could lead to nutrient loss. We’ve seen nutrient mineralization in October and February, when our corn and soybeans are not growing. However, our data has shown that with a cover crop, we can collect nutrients that become available and store them in the vegetative body of the plant, releasing the nutrients back into the soil during the next growing season.
Winter wheat is another cover crop that we utilize a lot, very similar to cereal rye, but it does not have quite the over-wintering capabilities. It’s not going to grow as aggressively either. So on the farm, for soybeans we’ll use cereal rye and for corn we’ll utilize a less aggressive cover crop, like wheat.
Other species with great initial potential in Iowa:
- Crimson Clover: Not very aggressive growth but has the ability to fix nitrogen
- Hairy Vetch: Can get really good growth and can fix a good amount of plant available nitrogen because if its ultra low C:N ratio
- Tillage Radishes: Can develop a large tuber to break up compaction layers and hold phosphorous
- Rape Seed: Planted early, this brassica can develop nice vegetative growth
- Oats: Good tool for fibrous root systems and for stimulating fungi, however, they will die over the winter
- Annual Ryegrass: Non-aggressive growth, a great tool if you’re further south. Haven’t had a whole lot of success with over-wintering in SE Iowa, yet
- Cow Peas: Using this year for the first time in interseed mix. Has nice aggressive growth and good nitrogen fixation for next year’s crop.
- Buckwheat: Interested in how it interacts with soybeans, good pollinator habitat
- Sun Hemp: Has potential to be a diversity tool, still experimenting
Winter wheat covers