Research Uncovers Benefits of Cover Crops on Cotton Yield and Nitrogen Use
Uncover the Value of Cover Crops
Robbie Faust considers his southwest Georgia farm's use of conservation practices not only good for the land but also the bottom line. An added benefit: It's also good for securing future business.
"I have very happy landlords because we use cover crops," says Faust, the third generation of his family to farm near Dawson. "The cover crops don't generate new leases in and of themselves, but if you do certain practices, people notice that.
"The first irrigated farm I took on in 2006, minimum tillage was in the contract by the owner," he continues. In 2021, Faust was named Conservationist of the Year by the Georgia Association of Conservation Districts as well as Friend of Conservation by the National Association of Conservation Districts that same year.
The awards noted Bellflower Farms' use of strip-till, no-till cover crops, terraces, grassed waterways and low-pressure drip nozzles for irrigation. The farm grows corn, cotton, soybeans, wheat and peanuts.
RESEARCH PLOTS
In 2020, the Fausts (Robbie's father, Mike, also still farms) began participating in a research project with several entities that included the University of Georgia (UGA) Extension. The idea was to promote cover crop outreach and education using demonstration plots. Primarily, the Fausts created a 65-acre test plot using various cover and cash crops over a two-year period.
The 65-acre pivot-irrigated field was broken into four sections. Each was planted the first week of November with a different cover crop or a combination of cover crops in the fall and then burned down the last week of March prior to planting cotton in the spring.
Cover crops in the four sections were:
-- rye only
-- crimson clover only
-- hairy vetch and rye
-- hairy vetch, rye, oats and clover.
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Further, the four sections were halved, with one half receiving the usual prescribed amount of nitrogen fertilizer, while the other half received reduced amounts of applied nitrogen based on calculations showing how much nitrogen the soil should have because of the biomass from cover crops.
RESEARCH RESULTS
In the test field where the cover crop was a mix of rye and hairy vetch, the half that received considerably less applied synthetic nitrogen (reduced by 50%) had a better yield than the half that received a full rate of nitrogen -- 1,320 pounds per acre cotton lint compared to 1,255 pounds.
A second plot with a full rate of applied nitrogen and a cover crop of rye alone yielded 1,395 pounds per acre. This plot, a kind of control, didn't reduce the nitrogen application.
A third plot that used crimson clover alone yielded 1,255 pounds when applied nitrogen was reduced by 50%. The other half of this plot with a full rate of nitrogen applied yielded 1,325 pounds.
On the fourth plot, which used a cover crop combination of rye, hairy vetch, oats and clover, the yield was 1,407 pounds per acre with a full rate of applied nitrogen. The other half of the plot using 50% less applied nitrogen yielded 1,395 pounds.
An economic analysis by UGA Extension found that the average adjusted revenue per acre for the rye-vetch cover combination and full rates of applied nitrogen varied from $1,077 per acre when nitrogen was less expensive to $1,000 per acre, depending on the cost of nitrogen.
As for the other half of that plot using reduced amounts of applied nitrogen, the average adjusted revenue varied from $1,146 to $1,170 per acre.
Even when cotton yields were less with halved rates of applied nitrogen, there was still a financial benefit, explains Seth McAllister, UGA Cooperative Extension Agent, Terrell County, who worked with Faust on the test plot. In the plot that used the combination of four cover crops, Faust spent $28.75 per acre to establish the blend but saved $59 per acre in reduced nitrogen costs.
"So, it paid [Faust] $30.25 per acre to plant the four-way and cut nitrogen if you look at it like that," McAllister says. Overall, he says the cost per acre demonstrates "you would basically break even planting the cover crop or putting out the standard rate of nitrogen." Considering the additional benefits, such as reduced erosion, increased organic matter and higher water-holding capacity, "cover crops are gravy on top of the fertility."
NITROGEN AVAILABILITY CHALLENGES
On a head-to-head basis, "It was amazing to me that the rye and vetch blend outyielded the half with full synthetic nitrogen," McAllister says. "The most frustrating part is that the nitrogen from the cover crops was more readily available to the cotton than to corn and other grains."
In real practice, that's one of the biggest challenges Faust has had with this research project, the inability of some crops to fully utilize nitrogen in the soil as a result of cover crops.
"The nitrogen is there, but the crop can't get it," Faust explains. "We do seem to get the nitrogen boost in the fall when we plant the next cover crop. But, the cash crop doesn't want to pick it up."
"Ironically, the lignin in a grass cover crop can tie up the nitrogen," McAllister adds. And, their research didn't account for changing soil types within a field, and stands of cover crops may not be uniform across a field.
Most definitely, the cover crops ahead of cotton planting appear to be a better option given this research, he believes. "Corn planting is too early in the spring to get the full biomass needed out of a cover crop to generate that extra fertility."
Interestingly, in 2024, two years after the experiment was ended, Faust noticed pretty good yields from his corn in fields that had cotton after cover crops. "Maybe it takes a couple of years for most of the nitrogen to be available," he says. "It's a bit of a mystery."
A key difficulty doing cover crops, McAllister says, is that farmers are already finishing the hardest part of their year as harvest of corn, soybeans, peanuts and cotton winds down. "They are ready to be done, and the daylight is getting shorter," he adds.
But, cover crops need to be planted as soon as possible in November in South Georgia, not December and January. "A lot of cover crop species are very cold tolerant but are subject to freezing during germination," McAllister explains.
Separate from the test plot, Faust has also used the blue lupine legume as a cover crop. "It looks like a soybean but produces a bunch of nitrogen," he says. They planted some in 2023. "We found the deer love it, and they grazed a field of blue lupine down to nothing." The blue lupine use ended as a result.
WATER MANAGEMENT
Faust points out one of his main jobs on the farm is managing water -- the irrigation -- especially when you can get a 3-inch rain in an hour. "That's when you have problems trying to deal with water -- where it goes and where it needs to go. That's where your grass waterways come into play. The strip-till and cover crops help, but that's still not 100%," he says.
The Fausts put some of their first low-pressure drop nozzles -- a system that is better at metering out water at a rate that fits the plants without applying what can't be used -- in around 2008. They've been able to use some local and federal cost-sharing for this work.
"If I was giving advice to someone starting off like I did, I'd say don't necessarily fall in a rut of doing what your family's been doing for ages and ages," Faust says. "Look at other options and the time involved, and the savings you can get."
Certainly, the move to more cover crops has been beneficial in conjunction with irrigation. "We have seen, especially with cotton planted after heavier cover crops, that we are not having to irrigate as much," he continues. The covers help with erosion, moisture control and a reduction in irrigation needed. "You put all that stuff together, and it has some value."
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