By Mark Glady

Planting a cover crop to obtain nutrient benefits and mitigate erosion could make a lot of sense for you and your operation.

Nutrient management can be tricky, however. Here are some situations where growing a cover crop may be beneficial.

* You have some acres in sugarbeets or small grains. If you have harvested your sugarbeets, wheat, barley, durum or another small-grain crop and have open land in September and October, a cover crop can keep soil from blowing around and soak up residual soil nutrients. That cover crop can also sequester nitrate from nitrogen that’s left in the soil, using the nitrate to increase the cover crop’s biomass and keep it from leaching into tile lines, drainage ditches, lakes, streams and rivers. When the cover crop disintegrates the following growing season, it releases nutrients for the current year’s crop, providing an ongoing benefit.

* You want to seed your cash crop and cover crop in the same field — but don’t seed them at the same time. In one of our test plots last year, we planted corn and then seeded a cover crop over the top the same day the corn was planted. In the plot next to that, we planted corn without a cover crop. The corn grown along with a cover crop was extremely deficient in nitrogen when we sampled soil the first week of August (about 25 pounds of nitrogen in the soil), compared to the plot without the cover crop (about 90 pounds of nitrogen in the soil). The cover crop was obviously competing with the cash crop grown for grain.

It’s important to realize that cover crops do not magically take nitrogen out of the air and give it to the cash crop. It’s not until that cover crop disintegrates and decomposes — what we call mineralization — that it releases nutrients to the crop that follows it. So, you won’t get a fertilizer credit from a cover crop until the following year. If you want to plant corn and a cover crop on the same acreage, a better plan is to wait until later in the season to plant the cover crop.

* You want to minimize soil erosion. If you grow sugarbeets in Minnesota, you know the ground is bare and black following harvest — as opposed to a corn harvest, which leaves residue on the soil. Planting a grass species with a fibrous root system — such as ryegrass — instead of a broadleaf with a taproot — such as tillage radish — as a cover crop is a better management decision for reducing erosion.

Fibrous root systems are much better at holding soil in place. Particularly on highly erodible ground on steep slopes, or on flat stretches where wind erosion is likely, planting a grass species as a cover crop can be a good environmental, as well as economic, decision.

Cover crop root systems provide many additional benefits. They penetrate compacted soils, creating root channels that make soil more porous. This results in improved infiltration of air, water and subsequent crop root systems. Live root systems also foster soil microbial growth and produce organic compounds that bind soil particles together to create better soil structure, which also helps decrease erosion.

Put your fields to work after harvest, promote the health of your soil and potentially earn some extra cash by planting a cover crop. Talk with your adviser to see if exploring this option would be a good agronomic and economic choice for you this fall.

Glady is an agronomist with WinField United in southwestern Minnesota. Contact him at [email protected].