A cover crop used in conjunction with a conservation tillage system may help conserve soil and improve soil health, fertility, water quality, weed/disease/pest control, biodiversity, and wildlife habitat.
But it requires “educated management decisions,” says Paul DeLaune, Texas AgriLife Research agronomist at Vernon, Texas. He discussed ongoing cover crop research on the Texas Rolling Plains during the Red River Crops Conference.
“Cover crop production is not a new concept,” he says, “but we have seen renewed interest in recent years.” Part of that interest could be associated with cost share programs available through the USDA’s Natural Resource Conservation Service (NRCS), which supplements cost of cover crop seed in eligible counties.
“A cover crop is grown for the protection and enrichment of the soil,” he explains. It is not managed as a typical cash crop. “We are not trying to produce an award-winning cover crop. We’re not trying to match what you see in a farm magazine. We do not seed at full seeding rates We do not fertilize cover crops, and with the exception of one year under a pivot during exceptional drought, we have not irrigated cover crops.”
He also does not apply in-season herbicides to cover crops — only burndown prior to planting and to terminate. “We have applied insecticide to summer cover crops, but we hope to keep management as low as possible.”
DeLaune has studied cover crops planted ahead of wheat and irrigated and dryland cotton, compared to crops with no cover and under several tillage systems.
Systems for wheat production include conventional till with no cover; no-till with no cover; and no-till with mixed covers and various monospecies. Cover crop and double-crop options included cowpeas, guar, mungbeans, buckwheat, turnips, pearl millet, foxtail millet, and forage sorghum.
In 2016, the conventional tillage trial produced the highest yield; in 2015, conventional till was the lowest yielding treatment. “However, we took a 10 bushel to 15 bushel hit in 2016 following a cover crop. We’re not sure of the exact cause of yield loss in 2016, but the preceding cover crop had very high calcium-to-nitrogen, conducive to nitrogen immobilization, which could have been a significant factor.”
In another study, allowing the cover crop or double-crop to mature resulted in better yields in all but one treatment, compared to termination at reproduction stage. The exception was a cover crop 60/40 seed population mix. Differences among the treatments were less than 3 bushels per acre.
“Initial data show wheat yields did not lag in a double-cropping system, compared to a terminated cover crop system,” DeLaune says.
In cotton trials, results from 2008 through 2010 show no-till accounted for the highest net return. Dryland cotton treatments included no-till without a cover; conventional till without a cover (bedded); and no-till with cover.
An additional study evaluated monospecies cover crops and mixed species cover. Species evaluated under dryland systems included Austrian winter field peas, hairy vetch, crimson clover, and wheat. The mixed species and wheat cover crop were also evaluated under irrigated systems.
“Within dryland and irrigated cotton systems, net returns were not significantly different among treatments when averaged over three years,” DeLaune says. “We expect greater risks in dryland/rainfed systems.”
Stored moisture and the amount of moisture removed by the cover crop are concerns for many producers. His studies evaluated how much soil moisture is removed and how well the soil recharges, compared to conventional tillage systems.
“By the time of termination, stored soil moisture can be significantly lower due to cover crops,” he says. “However, stored soil moisture is restored by planting time for the cash crop if adequate rainfall is received.”
The potential exists for cover crops to improve soils, possibly improve net returns, and improve water infiltration and reduce potential for erosion, DeLaune says. Selecting the proper cover crop, or blend of crops, as well as determining the best tillage system and termination date for the cover, are important.
“Certain cover crop species have consistently performed over time, even under drought conditions, and later than ideal planting dates. We wonder if cover crops may be more appropriate for degraded or low residue systems. Cover crops have potential with educated management decisions.”