The University of Arizona and the USDA’s Natural Resources Conservation Service are conducting research trials to improve the cotton production system through improved soil quality with cover crops. Trials are under way in three Arizona locations in commercial cotton fields: Thatcher in Graham County’s Gila Valley, Marana in Pima County, and Elfrida in Cochise County.

“We are looking at cover crops to add organic matter to the soil to improve soil quality in cotton production,” said Randy Norton, UA regional Cooperative Extension cotton specialist based in Safford.

Cover crops under field evaluation include the grains triticale and oats; the legumes hairy vetch and Austrian winter (snow) pea, and the Brassica crops turnip and kale. The crops are planted after the fall cotton harvest with spring termination with glyphosate and then shredded.

Norton and Eddie Foster, NRCS district conservationist in the Safford Field Office, checked the status of the first year of a three-year acre trial in Thatcher in late May. The farm is located near the base of majestic Mt. Graham which reaches skyward 10,700 feet.

The Thatcher trial field includes subsurface drip irrigation fed by surface water and groundwater. The Marana trial features surface water level basin irrigation. Groundwater-fed center pivot irrigation waters the Elfrida trial.

“A successful cotton production system boils down to soil quality in the end,” Norton said gazing across the field. “We’re looking at cover crop benefits including improved nutrient levels, the potential suppression of root knot nematodes, plus the issue of seedling disease associated with and without cover crops. Good evidence suggests that leguminous plants can reduce the need for nitrogen applications the following year.”

Norton says organic matter built up in the soil creates nitrogen released over time through mineralization which increases soil health.

“We have issues in the Gila Valley with high sodium and pH soils,” Foster explained. “Anytime you add organic matter to the soil it decreases the pH while improving tilth, pore space, water holding capacity, and the ability to release nutrients into the soil.”

The Gila Valley has a steep history in cotton production. The valley includes about 25,000 irrigated acres in agricultural production; about 90 percent of that cotton. 

“This is a good cotton growing area,” Norton said.

Planting kickoffs off in late April with harvest wrapped up around Thanksgiving.

Pima cotton was king in the 1980s and early 1990s, but production shifted to upland due to the pink bollworm (PBW) and Bt technology. Double cropping is impossible in the valley due to the area’s colder climate and shorter growing season at the 2,900-foot field elevation.

Valley cotton farmers are extremely efficient in land preparation, planting and harvesting, Norton says. Growers are willing to consider new technology and farming systems to increase efficiency, including cover crops.

The first auto steer GPS system in the valley was purchased in 2003. Within several years every major grower owned at least one unit. Last fall, five module-building cotton pickers harvested cotton in the valley.

Drip irrigation

One of the reasons for cover crop interest is subsurface drip irrigation which is gaining traction due in part to water availability concerns. About 1,100 acres have drip. Drip eliminates deep tillage practices so farmers shift to minimum till or no till. Cover crops become a viable production option.

As with other cotton-growing areas, it is difficult for farmers to budge from a century-plus history of deep tilling meticulously clean fields each spring.

“Trying to get these guys to be ‘trash farmers’ with cover crop residue has been a chore,” Foster chuckled. “They are used to clean tilled fields but understand change can increase productivity and efficiency.”

Drip irrigation and reduced tillage allow farmers to maximize soil health, Norton says. “It’s amazing to walk on the spongy, porous soil created by the cover crops.”

On the Thatcher farm last year, a barley cover crop generated about 4,100 pounds of residue per acre on the field surface. By the cotton harvest window, the majority of the residue was in the soil. This is a strong indicator of soil health, Foster says. Microbial action helps release nutrients from the organic matter for uptake by the cotton plant.

The owners of the Thatcher trial field, Denny and Lance Layton of Layton Farms and Ranches, are enthusiastic about cover crops. This spring, they installed a row cleaner on the cotton planter to remove residue from the top of the seed bed.

Foster says generating natural nutrient value from cover crops reduces the need for commercial fertilizers while still achieving maximum cotton yield.

“Maximum yield does not always mean max profit,” Foster said. “Through the trials we are illustrating that you can maximize your profits by minimizing your inputs with cover crops and in fact make more money.”

Foster and Norton plan to conduct the trials for three years.

What cover crop lessons have been learned so far? Weeds have been substantially reduced with cover crops which save spray and cultivation costs. A nearby farmer saves $14 per acre from cover crop-controlled weeding in combination with reduced till allowed by drip irrigation.

Some cover crops may not prosper in the Gila Valley’s colder temperatures. The thermometer dropped into the single digits in early February for several days.

“The freeze burned the oats back a little,” Foster said. “The triticale kept growing. The snow peas tolerated the cold fairly well. The vetch took longer to germinate but took off once the temperatures warmed up.”

Norton and Foster are closely following the oats, focusing on the crop’s natural ability to reduce pathogens and nematodes. Legumes are new to the valley and could serve as a good cover crop because of their ability to “fix” atmospheric nitrogen and increase the soil concentration of that nutrient.

Seedling disease has been a major issue in the Gila Valley for the last two years; likely tied to cool temperatures and wind.  Cover crops can also cause seedling disease due to reduced soil temperatures caused by the crops. Norton is experimenting with the fungicide Quadras applied in the drip to target the high residue-caused problem.

Farmers should be aware that cover crops must be managed and require time and money.

“You can’t just plant it and walk away,” Norton said. “Cover crops need to be watered. However, cover crop benefits, particularly in a drip situation, are well worth the costs associated with them.”

The trials are funded by the UA, NRCS, and the farmer cooperators. NRCS can offer first year matching funding for cover crops in cotton.

Other contributors to the project, all from Arizona, include: Sam Wang, UA Maricopa Agricultural Center, Maricopa; Art Meen, NRCS Field Office, Douglas; and Bruce Munda, NRCS Plant Materials Center, Tucson.