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Water for agriculture may be more restricted by future water legislation
<p> Water for agriculture may be more restricted by future water legislation</p>

Efficient water management becoming critical

The combination of rotation and minimum tillage provides a means to stretch water resources. The kind of irrigation system in use makes a difference in moisture management. Wireless sensors improve remote sensing capabilities by monitoring crop status and soil moisture over a large area.

Even before last year’s devastating drought no one who makes a living trying to farm the arid soils of West Texas needed to be reminded of the urgency of improving water use efficiency.

But 2011 served as a stark reminder that irrigation can go only so far in providing adequate moisture to make a crop. So farmers are anxious to learn better ways to manage soil, crops and water and to stretch water resources as far as possible.

Several researchers at the recent “Wheat and Water Issues” field day at the USDA-ARS/Texas AgriLife Research Station at Bushland offered some insight into opportunities to make the most of available water.

“Residue is your friend,” said Louis Baumhardt, USDA-ARS research soil scientist. “Use it.”

Baumhardt said the combination of rotation and minimum tillage provides a means to stretch water resources. “Rotation for moisture management will be more important as water districts begin to limit water use to 12 or 15 inches a year,” he said.

He suggested that a system that produces two crops in three years may improve moisture management. That system could include a high water-use crop, such as corn, along with a less water-demanding crop, such as winter wheat, followed by fallow.

“Growers can redistribute water to irrigate high water use crops,” he said.

The wheat crop also provides residue that affects two important water management factors—infiltration and evaporation. He’s experimenting with a rainfall simulator that can apply 3 inches of water per hour. “That’s a lot of water,” he said. “The average storm lasts 15 minutes or less.”

He uses the rain simulator to compare infiltration rates of soils with residue and bare soils. At 15 minutes, he said, little difference shows up between the residue and the bare soil. At longer intervals of rain, however, the residue shows a significant advantage.

At longer intervals on bare soil less than half of the water infiltrates. “The rest runs off.”

Baumhardt said soil stores from 6 inches to 8 inches of storm water that falls on fallowed, no-tilled wheat straw. If the soil is tilled, storage drops to 4 inches to 6 inches.

He said residue also reduces evaporation loss. During peak growth period on bare soil he measures 6 inches of loss from soil and 6 inches lost through the crop.  With residue, 8 inches goes through the crop and 4 inches is lost from the soil. “Cotton yield increased from 560 pounds per acre for bare soil to 760 pounds per acre in the wheat residue.”

System differences

Paul Colaizzi, USDA-ARS research agricultural engineer, says irrigation systems also make a difference in moisture management. He’s studied LESA (Low Elevation Spray Application), MESA (Mid Elevation Spray Application), LEPA (Low Energy Precision Application) and SDI (Subsurface Drip Irrigation) systems in cotton and compared those with spray irrigation.

“LEPA resulted in a 15 percent increase in lint yield compared with MESA and LESA. With drip irrigation (SDI) lint yield increased 30 percent compared with MESA and LESA. We’ve tested a range of irrigation rates, from dryland to near full irrigation,” he said.

“Cover (residue) results in greater water penetration. That means less soil loss and more water for the plant.”

He said 2012 will be the first year of irrigation system comparison data on winter wheat.

 Susan O’Shaughnessy, USDA-ARS research agricultural engineer, said wireless sensors improve remote sensing capabilities by monitoring crop status and soil moisture over a large area. “Infrared technology is not new,” she said, “but wireless is somewhat new and the combination of wireless sensor networks for monitoring crop status over an entire field and controlling variable rate irrigation equipment to deliver irrigation where it is needed is new.”

Steve Evett, a USDA-ARS research soil scientist, said soil water sensors are useful tools to help schedule irrigation. “It is common for producers to over-irrigate,” he said. “With the right sensors, we can determine plant moisture needs.”

Evett and his cooperators have compared most existing soil water sensors and can recommend ones accurate enough to save water when scheduling irrigations. “And,” he said “we are developing new even more accurate sensors for irrigation management.”

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