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.