Planting a Cover Crop this Fall Ensures Good Soil Conditions Next Spring
Dr. John F. Bradley Conservation Tillage Specialist Monsanto Company
Dr. John Bradley is widely recognized by farmers across the Cotton Belt as one of the top experts in the science of conservation tillage. For 14 years, Dr. Bradley was the leader of the University of Tennessee's Milan Experiment Station, where he conducted research on conservation- and no-till cropping systems. He also directed the Milan No-Till Field Day, which became-under his leadership-the preeminent reduced tillage field event for farmers in the United States. Currently, Dr. Bradley is working with farmers across the Cotton Belt to encourage and ease the switch to crop production systems that utilize conservation tillage practices.
At this time of the year, many farmers are finishing harvest and are already planning for next year. If you're planning to use a no-till or con-till system in 2001, it's worthwhile to spend a few more days in the field this fall to plant a cover crop. Managed properly, a cover crop can reduce erosion, aerate the soil and maintain higher moisture levels, all of which help to ensure good soil for planting next spring. The effectiveness of no-till or any other conservation tillage system as a method of erosion control is dependent on the amount of residue cover present at critical times such as winter months. A residue cover level of 30 percent immediately after planting is considered to be the minimum amount for effective erosion control.
There are several reasons why it is a good idea to plant a cover crop this fall. The added residue and coverage provided by cover crops is vital to low-residue crops such as cotton and soybeans. Cover crops also provide food and cover in winter months for earthworms, soil microbes and wildlife. They also add organic matter and tilth to the soil and keep the surface particles from running together and/or "baking out" in late spring. The residue from a cover crop also helps to keep the soil cooler in early summer, which reduces moisture loss and provides a more suitable environment for root growth. When the cover crop is terminated in early spring, the decaying roots leave macropores in the soil which improve water infiltration and aeration of the soil. The residue left from winter cover crops will also help protect seedlings from wind and sand-blasting in early summer.
When deciding which cover crop to plant, choose one that will meet your main objective, whether it's preventing erosion, providing organic matter or conserving moisture. Depending on your situation, some cover crops to consider are wheat, rye, oats, and legumes. If you're growing continuous cotton, I recommend growing wheat during the winter. It doesn't get too tall to manage, has good winter hardiness, is relatively inexpensive and has rapid growth. Rye is also a widely adopted cover crop in the South. It is cold-tolerant, suppresses nematodes and certain weeds and grows rapidly. However, rye seed costs more than wheat seed, and rye can produce too much biomass. Grasses such as wheat or rye can be planted later in the fall and provide a quicker plant canopy than legumes. Oats aren't as cold-tolerant as wheat or rye. Legumes such as hairy vetch and crimson clover add nitrogen to the soil. However, the extra nitrogen may delay maturity of cotton in the fall. Legumes are also more expensive than grasses and can be tougher to manage.
It is also important to select a cover crop that can be killed easily and at a reasonable cost. Make sure you research what herbicide or combination of herbicides is required to terminate the crop in the spring. Crops such as Austrian winter pea and vetch are generally more difficult to eliminate than wheat or rye.
Timing is critical to the effectiveness of a cover crop. Cover crops must be planted early enough in the fall to enable establishment before the onset of winter. Early planting is directly associated with canopy and biomass development, protection against erosion and nitrogen accumulation by legumes. Cover crops planted too late will lose their effectiveness since their growth time is so short, the plant will not mature enough. If you plan to use a no-till drill, plant your cover crop immediately after harvest. In cotton, cover crops can be seeded when defoliating by airplane or with a cyclone seeder on a tractor or high-boy. Wheat, rye and oats can be seeded by air. For those of you intent on tillage in the fall, you can also seed cover crops when you disk. If you do any tillage in the fall, I strongly suggest the use of cover crops.
Proper seeding rates are also key in the production of an effective cover crop. Wheat and oats should be planted at a seeding rate of 60 to 90 pounds per acre, while rye only needs to be planted at 45 to 60 pounds per acre. If you decide to grow Crimson Clover or hairy vetch, these should be drilled at 15 to 20 pounds per acre. I would recommend trying to avoid high seeding rates. However, if it is done just prior to leaf drop in soybeans and cotton, it can work if soil moisture is adequate. Be sure to use a grain drill or no-till drill in this type of situation to obtain a good stand. Be aware that high seeding rates may cause the cover crop to hold too much moisture, which can result in delayed planting in the spring. It's important to use quality, clean seed to ensure an even stand and reduce weed contamination.
Proper management practices are key to growing an effective cover crop. It is especially important to successfully manage inputs necessary for fertilization and control of weeds and diseases. If there are a lot of green weeds in the field at seeding, a good burndown herbicide such as Roundup Ultra(r) should be applied. Fall is also a good time of the year to control perennial weeds such as johnsongrass, vines and bermudagrass. One quart of Roundup Ultra per acre applied prior to heavy frost aids greatly in the control of perennial weeds for the next season. Diseases can be controlled by following fertility recommendations, observing suggested planting dates, and using resistant varieties and recommended fungicides properly. It is also a good idea to lime and fertilize by soil test recommendations. If lime is needed, it should be applied into the soil before seeding. Phosphate and potash can be applied immediately before or at planting time.
The best way to kill cover crops in the spring in a no-till or con-till situation is to spray with a burndown herbicide such as Roundup Ultra Max(tm). In cotton, this should be done about two to three weeks prior to the intended planting date of the summer crop. Burndown of the cover crop will help warm and dry the soil, and if done in a timely manner, will minimize the damage from insects present in the crop. Retention of the cover crop residue as a mulch in no-till helps to suppress early-season weeds and to reduce erosion and water losses into the summer. Cover crops ahead of soybeans can be terminated at planting because the insects contained in the cover crop generally do not harm the soybeans. Leave the cover crop standing in the spring. Although it may not look "pretty", standing cover crops are much easier to plant into.
If you are planning to use a con-till system next year, consider planting a cover crop this fall. Besides enhancing the quality of the soil, cover crops make it much easier to set the planter and obtain a good stand in next year's crop. By reducing erosion and improving the soil, cover crops also benefit the environment. Planting a cover crop means a little more work in the fall, but you'll be glad you did it in the spring.