Harvest is approaching and this will bring much discussion about cover crops.
I feel that all too often cover crop promotion is just like promoting the sizzle of a steak, rather than its flavor and all the side dishes. Just as a little research can help one select the best steak for his or her personal tastes, the same needs to be done before simply following the sizzle of cover crops.
Begin by determining what you wish to accomplish with the cover crop. Soil erosion control, nutrient immobilization, livestock feed and soil improvement are some reasons for planting a cover crop. The most popular, and perhaps the most wrong, reason to plant a cover crop is simply because there is a cost-share program to do so. Not understanding why a cover crop is being established is a sure way to create a poor first experience.
Species selection is often determined by the intended use of the cover crop. Grasses such as cereal rye, winter wheat, triticale, and spring oats are all excellent considerations for erosion control, nutrient immobilization and livestock feed. Turnips and radishes make for good fall grazing. If immobilizing excess nitrate-nitrogen is your intended purpose, it is advisable to first collect a 12-inch soil sample and have it analyzed to determine if you have excess nitrate.
Although cover crops may increase the amount of organic material or humus in the soil, it takes approximately 60 years to increase soil organic matter one percent. Most soil laboratory procedures for determining soil organic matter do not distinguish between organic material and true soil organic matter, and it is probable that any cropping system that includes high residue will create greater reported soil organic matter.
The next critical step when making a cover crop decision is to check if there are any herbicide rotation restrictions preventing seeding. Many of the commonly used row crop herbicides have a four to 26 month restriction following application and planting certain species of cover crop. The successful establishment of a cover crop when planted prior to the expiration of the restricted rotation period does not mean that all is well. Abiding by the restricted period may be necessary for avoiding potential herbicide residues in the cover crop. The label is the law.
Keep in mind that these are cover crops. Successful establishment requires good seed-to-soil contact for germination and four to six weeks of favorable growing conditions.
Grandin serves the FS System as GROWMARK’s senior field sales agronomist. He can be reached at email@example.com.