Karol B. Osborne, Blanchard, Tobie M., Gould, Frances I.
Increased consumer demand for cover crops has led LSU AgCenter researchers to study ways to improve soil health, reduce fertilizer rates, increase yield and manage moisture and remove weed pressure.
AgCenter soil microbiologist Lisa Fultz is coordinating five cover crop projects in four locations and beginning to see ecological benefits that are also economically feasible for producers.
Going into the fourth year of her cover crop trial, Fultz is comparing four nitrogen rates behind seven winter cover crop treatments at the Macon Ridge Research Station near Winnsboro to learn how producers can reduce the amount of nitrogen applications from commercial sources.
Fultz saw increases from 40 to 50 pounds per acre of ammonia nitrogen in the soil from cover crops before planting corn this spring. By increasing the difference between high and low nitrogen-rate applications this year, she hopes to get a clearer picture of how much nitrogen may be plant-available.
“If I have 40 pounds of nitrogen already from the cover crop and put out another 160 pounds, can I get 200 pounds of nitrogen out of that system? That’s what we’re looking at,” she said.
Fultz said it takes from three to five years to start seeing additional benefits, such as potential improvements in yield, come into play.
“That’s where we are now,” she said. “So it will be exciting to see the results with this corn harvest.”
Also at the Macon Ridge station, AgCenter research coordinator Donnie Miller has completed the second year of trials looking at four different chemistries and two application timings to determine how far in advance cover crops need to be terminated before planting.
“Tillage radish seems to take the brunt of whatever we apply,” Fultz said, “so if planted in combination with another cover and without competition from the radish, the second cover may have a delayed reaction or come back, requiring a second application.”
Comparing February and March termination applications, the latter showed better results from all four chemistries, hitting the covers just before flowering achieved the greatest benefit, Fultz said.
One of the big drivers for putting in cover crops is surface protection, Fultz said.
“Every time it rains, little bombs go off when raindrops hit bare ground, leading to potential issues with crusting, runoff and reduced infiltration,” she said.
A study at the Red River Research Station near Bossier City is in the second year of data collection looking at soil moisture over concern that cover crops may reduce water availability for the cash crop.
Fultz said first-year data showed no significant difference on soybeans.
“We saw a lot of heavy rainfall last year so it will be interesting to see the results for this year,” she said.
Another study conducted at the Dean Lee Research Station near Alexandria is looking at how cover crops impact soybean production in central Louisiana by comparing crimson clover, cereal rye and tillage radish for changes in soybean yields.
“We didn’t expect to see an increase in yield the first year, but were encouraged that yields didn’t decrease either,” Fultz said. “It will take a few years before we can start making any recommendations.”
In the southern part of the state, a study at the H. Rouse Caffey Rice Research Station near Crowley is evaluating treatments comparing five cover crops with both sprayed and unsprayed fallow plots focusing on weed control over the winter season.
First-year data showed slightly higher — but not significantly higher — soybean yields in all cover crops compared to sprayed fallow and unsprayed fallow plots with only winter weeds present, Fultz said.
A three-year study at the Northeast Research Station near St. Joseph and at Dean Lee will evaluate fall residual herbicides for controlling weeds that affect cover crops, such as glyphosate-resistant Italian ryegrass, marestail, henbit, and annual bluegrass, said AgCenter agronomist Josh Copes. The project includes two studies.
“Our main purpose is to determine if we can use herbicides in cover crops and maintain cover,” Copes said. “And if we do, how much injury will we see with each herbicide?”
Looking at four common winter herbicides applied to four different cover crops, the first study will evaluate the effectiveness of the herbicides when applied two weeks after emergence.
“We want the benefits of the cover crop,” Copes said. “But we are concerned with weed control first.”
The first study evaluated 20 treatments using Zidua, Valor SX, Boundary and Leadoff on cereal rye, tillage radish, crimson clover and Austrian winter pea.
While first-year data are still being analyzed, Copes said he has been able to make some observations.
“Zidua two weeks after emergence looks to be fairly easy on injury and would maintain cover,” Copes said.
The second part of the study looked at cereal rye and crimson clover with both Zidua and Valor SX.
Two planting dates with two herbicide application timings were scheduled to better understand how both might influence cover crop injury and weed control.
By looking at different planting and herbicide timings, Copes can observe how much injury will occur. He can also learn how much biomass will be available for improved erosion control and nutrient cycling and increased organic matter and water-holding capacity of the soil.
In fall 2016, the AgCenter received a $992,000 Conservation Innovation Grant from the USDA Natural Resource Conservation Service, largely based on the data from AgCenter cover crop research supported by the Soybean and Feed Grain Research and Promotion Board, Fultz said.
The main driver of the three-year grant is to work with producers across the state, Fultz said. The study is already underway with sugarcane and is moving forward with soybeans, cotton and corn this fall.