With this year’s drought conditions there is less residue than normal in many fields. In some, the crop was harvested as a forage or cut as silage, leaving very little residue at all. Without residue to absorb the energy of raindrop impact and keep the wind off the soil surface, soil erosion will be greater and surface crusting could be a problem. Also, without the water-conserving residue mulch, soil moisture losses by evaporation will be much higher.
To reduce these problems, producers should consider planting a cover crop to help protect the soil. With the early harvest and the open fall this year, there is enough time for a cover crop to be seeded and to have adequate growth to provide some benefits. The growing cover crop will “harvest” sunlight and carbon dioxide that would be otherwise wasted as there is no cash crop growing.
Benefits of Cover Crops
Cover crops can be used for a variety of purposes including protecting the soil, improving soil structure, fixing nitrogen, feeding the soil biological life and managing soil moisture. A key soil health concept is that there should be something green and growing during as much of the year as possible. This is important to protect and feed the soil system, especially arbuscular mychorrhizae fungi.
Research has shown that while a cover crop uses some soil moisture as it is growing, it tends to use less water than what is lost to evaporation from a bare soil surface. Grasses provide the longest lasting residue cover because they have a higher carbon to nitrogen ratio in their biomass compared to non-grass species. In addition, they improve snow catch in the winter and reduce wind erosion in the spring compared to bare soil. Taller brassicas and broadleafs like rape, mustards and canola also will stand nicely to reduce wind erosion and catch snowfall, but they provide less residue.
With the drought conditions this year, there may be considerable residual nitrate in the soil following corn production. A cover crop will scavenge the residual nitrate for its growth and store it in a biological form, reducing potential losses. Some producers apply some fertilizer to encourage cover crop growth. This fertilizer and the residual nitrates are recovered later as the cover crop residue breaks down. Producers could use legume cover crops to fix some nitrogen for the next crop and to feed the soil system, but they will need the proper inoculate for the legume species.
The cover crop will add organic biomass both above and below ground and the growing roots will help build soil structure. The fibrous roots of grasses help build soil stability near the surface. The deeper tap roots of broadleafs, especially brassicas, penetrate and open up tight soils, improving infiltration. The finer roots of legumes feed the soil microbes while the taproots grow downward. Any root growing in the soil helps dewater excess soil moisture, provides some structural stability to the soil, and helps the mycorrhizae fungi recover. When using winter annual cover crops, these benefits can become very important if the next spring is a wet one. If the spring looks like it will be a dry one, the cover crops need to be killed in a timely matter so as not to use too much soil moisture.