Soil Health and Weed Suppression
By Jessica Kelton, Soil Health Educator, Soil Health Institute
Soil health management practices such as minimized disturbance and maximized soil cover provide numerous benefits such as reduced erosion, increased water infiltration, and increased soil productivity. Implementation of cover crops can provide an additional benefit of weed suppression, which is particularly important for cotton, a slow-growing crop that suffers from early-season weed competition. Moreover, cotton is inherently a very low- residue crop, and cover crops integrated into cotton-based systems offer tremendous soil health benefits.
Although many benefits are attributed to cover crop use, and cover crop adoption has increased across the U.S. in recent years, the adoption of cover crops is still less than 10% of row crop acres in the country. In cotton producing states, the adoption of cover crops can vary from as low as 1% to as high as 29%.
Weed Suppression from Cover Crops
Cover crops are a key tool for integrated weed control and may reduce the need for herbicides. Cover crops can slow weed emergence and growth. Using cover crops rather than cultivation to control weeds enhances soil structure and minimizes the amount of light that reaches weed seedlings. Cover crops can also reduce the risk of herbicide resistance by minimizing the number of weeds that need to be controlled using herbicides, delaying weed seed emergence, and weakening seedling growth vigor.
Cover Crop Management
Although the benefits of cover crops for improved soil health and weed suppression are well known, using cover crops does require planning and managing to be successful. For successful cover crop establishment and growth, species selection, time of seeding, seeding rate, and termination are all important factors to consider. Choice of cover crop species and seeding rates can be highly variable from region to region in the Cotton Belt, but Table 1 provides an overview of many of the most used and studied cover crop options.
Cover Crop Planting for Weed Suppression
Proper planning is essential for growing a successful cover crop that has the ability to control weeds. Growers need to purchase seeds in a timely manner because some cover crop species sell out early. Planting the cover crop early can improve the likelihood of good cover crop establishment. If planting after cash crop harvest, the sooner the cover crop is planted, the better. Planting cover crops early provides good establishment for winter survival and spring growth. Well-established plants enhance the weed suppression effects of cover crops in the fall and spring.
Cover Crop Termination
There are several different methods for terminating cover crops, including chemical, frost, mowing, crimping, and tillage. Termination methods like tillage and mowing can speed up the release of nutrients to the soil and help the soil dry out prior to planting cash crops, but these methods weaken the weed suppression effects of cover crops. Chemical termination and crimping keep the residue intact, allowing for better weed suppression.
Figure 1. Zeb Winslow’s row crop farm in eastern North Carolina uses cover crop mixes to feed the soil biology, keep his soil in place, and provide a level of residue for weed suppression. Photo Credit: Zeb Winslow
Choosing when to terminate cover crops involves tradeoffs. Later termination allows more time for biomass production, which makes weed suppression more efficient. At the same time, providing enough time to ensure complete termination before cotton planting is important to avoid any negative effects on cotton establishment.
Grower Experiences
Experience with cover crops can be highly variable based on species, years of using cover crops, and region of the farm. However, growers can learn quite a bit from other farmers that have been successful with cover crops in rotation with cotton. Two such farmers, Zeb Winslow of North Carolina and Myron Johnson of Alabama, routinely share their knowledge and insights with cover cropping with other growers interested in implementing cover crops.
Zeb Winslow’s row crop farm in eastern North Carolina is in its tenth year of using cover crop mixes. If not planting into a single species (Figure 1), his go-to six-way mix of rye, triticale, oats, clover, vetch, and radish allows him to feed the soil biology, keep his soil in place, and provide a level of residue for weed suppression. By using this mix, Winslow can hedge his bets and make sure he gets a cover crop stand should one species not perform well that season.
When using cover crops for the first time or changing up cover crop selection, starting small and learning from that experience has been the key to Winslow’s success.
Myron Johnson, a row crop producer in southeast Alabama, says of cover crops, “You’ve got to have a lot of biomass for weed suppression. Don’t be afraid of the biomass, but make sure you have the right equipment to work with it. Make sure to spray your cover crops at least two weeks ahead of planting. You also need to have a roller on the strip-till and a sweeper on the planter.”
Summary
Cover crops have the potential to assist with long-term sustainability through soil health improvement as well as increased weed suppression. With a wide variety of cover crop choices and management systems, reaping the multiple benefits of cover crops takes practice and active management. Therefore, it is wise to start with small acreage that is easily managed and seek advice from local practitioners or advisors who have been successful at using cover crops enough to get the benefit of adequate biomass production.
