Cover crops, residue management

Crop production in the semi-arid drylands of the Southwest demands that farmers follow rigorous conservation practices. “They have to conserve every drop of rainfall possible and control water erosion,” said Louis Baumhardt, a soil scientist with USDA-ARS at Bushland, Texas.

Baumhardt said farmers in much of the Southern Great Plains, including chunks of Texas, Oklahoma and New Mexico, face serious production challenges, including low precipitation, high evaporation rates, and periods of extreme heat.

“Pan evaporation throughout much of the region can be 4.5 times as much as the amount of precipitation,” he said during a conservation seminar, part of the 24th annual Southern Soil Conservation Conference, held recently in Oklahoma City.

Baumhardt said conserving enough water to produce crops is difficult. He and other researchers are looking for ways to increase water infiltration and improve crop yields and profitability. He's looking at a wheat, grain sorghum and fallow rotation.

“We may add cotton to the mix further south,” he said. “But we get two crops, wheat and grain sorghum, from a field in three years.”

Rotation starts with a wheat crop, harvested in June or July. The land lies fallow “to preserve water for 11 months,” Baumhardt said. “We plant grain sorghum in June — 24,000 plants per acre — and harvest in October. We fallow the field until the following September and plant wheat again.”

Baumhardt said residue management also plays an important role. “Retaining residue at the soil surface is crucial to water availability to dryland crops by reducing evaporation and reducing raindrop impact,” he said. “We've tested both a stubble-mulch tillage system and no-till.”

He said systems that retain residue limit raindrop impact, reduce crusting and improve moisture infiltration.

Baumhardt said no-till methods are more effective than stubble-mulch at retaining moisture at the soil surface.

With cotton in the mix, however, residue is inadequate to prevent crusting. Planting a wheat cover crop just after cotton harvest, taking advantage of fall rains to establish the cover, may improve infiltration and will help protect soil from wind erosion the following spring. Researchers terminated the cover crop chemically in the spring.

“It is risky,” Baumhardt said, “because farmers may use moisture to grow the cover crop instead of preserving it for the cotton.”

He said conditions in the semi-arid region of the Great Plains may result in inadequate crop growth and corresponding residue production. “Consequently, the degree of protection provided against raindrop impact is inadequate, and soil crusting reduces infiltration.”

He said soil crusting and surface compaction reduce infiltration with no-till systems, compared to conventional stubble-mulch. “This may be more prevalent in fine-textured soils,” he said.

He noted that infiltration improved when tillage practices disturbed the soil surface.

“When residues are limited, as is the case in semi-arid crop production, stubble-mulch systems that disturb the soil surface and fractures the crust improve infiltration rates.”

“Compared to conventional stubble-mulch tillage, no-till residue management increases the amount of water stored in the soil. The greater soil water conservation with no-till is likely attributable to reduced evaporation.”

He said no-till sorghum also may not provide as good infiltration as stubble-mulch, which “improves soil porosity and infiltration rates. Even with a paratill operation, infiltration rates were not as good as with stubble-mulch. The amount of residue in the system is the key,” he said.

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