Time to Think About Planting Fall Cover Crops
Why plant cover crops? Cover crops have several important benefits: they improve soil structure and fertility by adding organic matter, nitrogen (legumes), taking up, storing, and then releasing plant nutrients, thereby keeping them from leaching or washing away, and by covering the soil and preventing erosion. Growing fall cover crops that overwinter and produce a lot of plant material is a method of growing your mulch in place, saving the grower from needing to import and apply as much during the following growing season. In addition to producing weed suppressing mulch, cover crops can serve other purposes as well, such as providing food and habitat for beneficial insects, and enhancing soil microbial activity. To achieve maximum benefits from cover cropping, it is often recommended that at any one point in time, at least 1/3 to ½ of the grower’s field should be planted to cover crops and they should be incorporated into the crop rotation scheme. Some good resources on how to incorporate cover crops into your crop rotations include: Crop Rotation on Organic Farms: A Planning Manual. (http://www.southernsare.org/Educational-Resources/Books/Crop-Rotation-on-Organic-Farms), and A Truly Regenerative Agriculture (http://newfarm.rodaleinstitute.org/features/1204/nordell/index.shtml).
When to Plant Fall Cover Crops: Fall cover crops should generally be planted from mid-September through mid-November in AL. In mid-September there will be more competition from any grass or weeds currently growing in the field. Tillage may be needed in order to give the cover crop a good start. Later in this planting window, toward mid-November, there is less competition from weeds and grass and the grower may be able to establish a good cover crop stand by broadcasting the cover crop seed onto the soil surface and then mowing the standing vegetation to cover the seed. Another consideration is rainfall. October is generally a dry month in AL, but in November we generally get more rain. So, a cover crop planted before the end of October may suffer from drought. If the cover crop seed is broadcast, it may require more than one seeding to get a good stand established, depending on the rainfall. A good practice is to broadcast your seed before rain is forecast, especially if there is more than one rain forecast for the next few days. Once the plants have sprouted and established roots, they are hardier. As in most aspects of farming there is a delicate balance to be achieved and some seasons are more conducive to success than others. Though it may be good to wait until the rains come in November, this must be balanced with the fact that the sooner the cover crop is seeded before cold weather arrives, the more growth there will be.
How to Choose Your Fall Cover Crop: What cover crop should you grow? The best choice depends upon what the grower’s plans are for the following season. For summer row crops, rye is a very good choice. It will produce a lot of residue for weed suppression if left on the soil surface the following season. One drawback, however, is that grass cover crops can tie up nutrients that the next crop needs. A solution is to mulch the plant rows with compost when planting the cash crop in the spring if practicing no-till, otherwise, till in the cover crop at least 2 weeks before planting the next crop and much of it will have decomposed by planting time.
If you plan to plant early spring crops, such as salad greens, brassicas (kale, turnips, broccoli, collards) or potatoes, then a legume cover crop such as Austrian winter peas may be a good choice. Rye needs to complete its life cycle so that regrowth will not occur. If it is cut or rolled down before flowering, it will probably grow right back to interfere with the early spring crop. Clover, canola, and hairy vetch will also regrow if cut too early, if these cover crops are tilled in, this is not a problem. Austrian winter pea can be terminated early without re-growth. The disadvantage to Austrian winter pea is that the nitrogen rich residue will decompose rapidly and leave the next crop without any mulch to suppress weeds. Again, if you are tilling in the residue, then early release of nitrogen and nutrients will make them available to the next crop when it most needs it. The disadvantage to tilling in the cover crop is that the cover crop residue breaks down so quickly that by the end of the growing season most gains to soil organic matter content will have burned up in CO2. This is another example where a delicate balance is needed: the need to conserve soil organic matter must be balanced with the need to control weeds and provide nutrients to subsequent crops. For more information on choosing a good cover crop visit the SARE website and read: Managing Cover Crops Profitably (http://www.southernsare.org/Educational-Resources/Books/Managing-Cover-Crops-Profitably-3rd-Edition).
Attracting Beneficial Insects: For attracting beneficial insects, all of these cover crops are very good. Rye attracts lady beetles and other types of beneficials, clover attracts bees, butterflies, and pollinators, as do the other legumes. For more information on attracting beneficial insects read: Farmscaping to Enhance Biological Control, (https://attra.ncat.org/attra-pub/summaries/summary.php?pub=145).
