Improved weed control, improved soil health, better nutrient and moisture retention, and reduced potential for water and wind erosion are among the many benefits cotton farmers may see from cover crops.
But managing a cover crop to take advantage of those benefits presents a few challenges, say soil scientists from across the Cotton Belt.
Primary challenges vary across regions but include planting, moisture management, and termination.
In Texas, Texas A&M AgriLife researchers recently addressed some of the challenges cotton producers see in managing a cover crop.
In a recent report from that research project, Paul DeLaune, AgriLife Research environmental soil scientist in Vernon, said cover crops come with added expenses, including cost of seed and use of soil moisture. “The benefits can outweigh the costs over time,” he said.
“In pivot or subsurface irrigated systems, we have noted a 9% to 12% increase in net returns over a six-year average for a wheat cover crop compared to no-till or conventional tillage without a cover crop,” he added. “In dryland, no statistical differences have been observed among cover crop and non-cover crop treatments.”
His team uses neutron probes in all cover crop research plots to document water use.
“We observe a decrease in stored soil water at cover crop termination in mid-to-late April,” DeLaune said. “However, a much higher infiltration rate has been noted if we record precipitation between cover crop termination and cotton planting. By planting season, we are back to status quo.”
Termination timing is a key, DeLaune said. He prefers to let small grains surpass boot stage before terminating. He concedes that waiting that long may use a little more water, but the additional residue is important to protect the soil and seedling cotton. The residue also builds root biomass and improves infiltration.
“Rye matures earlier than wheat and may be terminated sooner than wheat to meet this goal,” he said.
Planting time is also critical. “The ultimate goal with cover crops is to build soil structure and make it more functional,” he said. “When planting cover crops after cotton harvest, the biomass produced occurs over a four-to-six-week period March through April.”
“We’ve done very well with just a wheat cover crop. That’s a $6 or $8 treatment per acre compared to the $20 to $25 per acre with some species mixes.”
Katie Lewis, AgriLife Research soil fertility scientist, Lubbock, worked with Wayne Keeling, AgriLife Research cropping systems and weed specialist, on optimizing cover crop use while reducing moisture risks.
Reducing seeding rate, she said, is one option. Research shows that reducing wheat and rye seeding rates from 60 pounds per acre to 30 pounds per acre and terminating at least six weeks prior to planting does not affect cotton yields negatively.
She cautions that lint yield reductions have been observed in long-term continuous cotton, no-till cover crop systems.
“Also, decreasing above-ground biomass with earlier termination has a positive impact on yield but doesn’t result in increased potential for erosion.”
Cotton farmers might want to consider changing fertilization timing. “We’ve determined that when following a cover crop, applying a larger percentage of total nitrogen closer to planting or shortly after emergence can overcome early season nitrogen limitations created by the cover crop and result in a greater return on fertilizer investment,” Lewis said.
Jourdan Bell, AgriLife Extension agronomist, Amarillo, looked at corn-cotton rotations with conservation tillage and considered if corn residue provides similar benefits to the live cover crop.
“Some of the questions we are trying to answer include: Are we achieving the benefits from the cover crop in this short period, and are we replenishing water use with timely precipitation? Should we use limited groundwater to replenish stored soil water if we do not receive late spring rains? Many producers no longer have the well capacity to do that.”
Her research included large, replicated plots comparing fallow, wheat cover crop, and mixed species cover crop. The first cover crop was planted in the fall of 2018 behind corn; cotton was evaluated in the first cropping year, 2019.
Her 2019 data showed, after four months of cover crop growth, improved infiltration with the cover crop, but above-average rainfall in May planting provided a benefit. Bell also recorded “a significant difference in plant emergence between treatments. Although emergence was delayed, plants developed more quickly in the cover crop treatments, once established.
“We saw a benefit from the wheat cover protecting the young cotton seedlings from severe winds in June 2019,” she said.
“Ultimately, multi-year yields tell the story for a farmer,” Bell said. “We have seen completely different results the last two years. Neither the 2020 corn grain nor the 2021 cotton lint yields were significantly different between treatments.”
Across the Belt
Challenges are different in other parts of the Cotton Belt.
Tyson Raper, University of Tennessee Institute of Agriculture Extension cotton specialist, says cover crops are beneficial to cotton soils but do pose challenges.
“Adding cover crops to cotton production isn’t always easy,” Raper said. “The biggest challenges stem from cotton establishment, especially along the northern edge of the Cotton Belt. While my colleagues in more arid regions must consider cover crop water use and potential lack of water for the cash crop, the Mid-South often fights excessive moisture planting into cover crops.”
He added that soils under cover crops warm up more slowly in the spring. “Even when the cover crop is terminated in a timely and proper manner, planters can struggle to achieve adequate seed-to-soil contact through the cover crop biomass. These challenges can delay planting in a system where delays of only a few days can equate to hundreds of pounds.”
He recommends several practices to overcome the challenges.
“First and foremost, it is best to start small. Planting a five-way mix across 1,500 acres in year one almost always spells disaster. Instead, start with a few farms where you believe a cover crop has the most to offer.
“Terminate the cover crop early with a herbicide mixture recommended specifically for your mix. That will limit challenges associated with very large levels of biomass and ease the planting operation.
“Scout for altered insect populations and be prepared to add insecticides.
“Finally, be prepared to slow down and adapt. The best system for one farm likely will not be the best one for the next.”
Ask a neighbor
Cristine Morgan, Soil Health Institute, Raleigh, N.C., recommends that farmers considering adding cover crops to their operation do some homework first.
“Find someone who is already doing it,” Morgan said. Deciding when to plant the cover can be a chore. Again, she recommends talking to a neighbor who has been successful. “We see a lot of success from producers planting from mid-summer through the time crops are harvested and mowed down.
“We see a lot of variability, but the best outcome is to plant the cover as soon as you can. Local conditions matter. See what others do.”
She agrees with Raper that conditions across the Cotton Belt will determined best planting dates. “What works in South Carolina may not work in Texas.”
Termination is another important concern. “The biggest concern is timing,” she said. “Some producers terminate too early, just when the cover crop is making the important biomass. Failure with a cover crop often comes from terminating too early.”
Planting the cash crop into the cover also poses some challenges. Morgan said the least expensive option is to plant into the green. “Some farmers plant straight into green cover crop; others burn it down and plant.”
She said the art of learning cover crop and soil health management is to talk to others in the area with similar systems.
“We have a lot of ways to do this; every farmer does something a little different. A cover crop is a biological system. The options are unlimited.”
To hear from Texas Plains producers about the benefits and challenges of planting cover crops, watch the following videos:
*The Texas A&M AgriLife Research videos were supported by the Soil Health Institute.