Best Management Practices for Soybean Planted as Cover Crops
July 5, 2019
Written By William J. Wiebold
Cover crops have many benefits including protecting soil surfaces from wind and water erosion, weed suppression, and improving soil health. This year many Missouri acres intended to be planted to corn and soybean were either flooded or too wet to be planted in a timely manner. Leaving these fields fallow without beneficial plants can lead to increased soil erosion, heavy weed growth that adds to the weed seed-bank, and detrimental effects on the soil microbiome. These effects may influence the field well after this season.
Planting a cover crop after flood waters recede and/or as deadlines are met for prevented planting is an appropriate consideration. Please read the latest Risk Management Agency (RMA) Fact Sheet (available at https://www.rma.usda.gov) addressing prevented-planting insurance provisions. It is critical that producers contemplating planting any species of cover crop obtain permission from their crop insurance agent and follow RMA guidelines. Do not put prevented-planting insurance benefits at risk by performing an unapproved action. In a year like 2019, with highly unusual weather affecting crop management, it is important to check with regulating agencies often because revised provisions are possible.
Cover crop management and crop choice for summer differ from choices for fall-planted cover crops. The heat in summer dictates that warm season crops be used. Cool season crops that are typically used for cover crops planted in fall will not grow successfully during hot and humid months. A warm season crop not usually considered for cover crop use is soybean. Soybean is an excellent choice. It is a warm season crop that grows quickly. Seed and planting equipment are available. And, soybean is a legume and fixes nitrogen. Again, please check with your insurance agent and RMA for appropriate cover crop selection.
Farmers are familiar with soybean management, but management as a cover crop may differ somewhat. For best results as a cover crop, consider these soybean management practices.
- Broadcast seeding, including by airplane, is an acceptable practice for cover crops and can be successfully accomplished with summer annuals such as soybean. But the soil surface must remain wet during the entire germination process. At a minimum, germination will require five days. Seeding rates may need to be increased if broadcast planting is used. Planting with a row unit or drill will increase chances for successful establishment, but broadcast planting is usually faster.
- Plant varieties that are available with acceptable cost. Do not worry about maturity group or biotech trait. Remember that most patented seed agreements prevent the use of grain for planting purposes. Check with your seed dealer.
- For a cover crop to be successful, it must develop full canopy closure quickly. Row width should be as narrow as possible with available planters. Rows 15 inches apart are preferred over 30-inch rows. Using a drill with row spacing less than 10 inches for soybean will increase canopy closure by a few days. However, if the only equipment available is a planter with 30-inch row spacing, it is an acceptable management practice.
- Seeding rate should be selected to best balance seed expense with successful soil coverage. Choose a seeding rate between 60,000 and 100,000 seeds per acre. More seeds may seem advantageous for canopy closure, but the difference is too small to balance increased cost.
- Pesticides such as fungicides or insecticides either as seed treatments or foliar applied are not required for soybean use as cover crops. There is minimal risk of seedling diseases with untreated soybean seeds.
- Planting into a clean field and scouting for weeds after emergence are critical. One reason to plant cover crops on flooded and prevented-planting acres is weed suppression. Apply a post-emergence herbicide if weed growth becomes excessive.