Irrigation Journal

February 26, 2010 05:21 AM

More Water Needed

In the next four decades, Georgia farmers will need 20% more water to produce their crops, says a recent University of Georgia report put together by a team of crop and weather experts. It will be used by the state to help develop a long-term water plan.

Georgia's rainwater recharge is not predictable, says Jim Hook, University of Georgia professor of agricultural and environmental sciences. He says it is easier for Western states to anticipate how much water they'll have since their system is based on reservoir storage and snowpack.

The report says if 2011 is a dry year from spring through fall, Georgia farmers will need 800 million gallons of groundwater per day and 300 million gallons of surface water per day. In 2050, it predicts, they will need 1 billion gallons of groundwater per day and 400 million gallons of surface water per day.
"Georgia's agriculture sector will continue to be a major water user in the state,” Hook says.

USDA economic models were used to predict farmers' cropping choices. University of Georgia models were used to outline crop water needs and climate data.

About 23,000 fields in Georgia currently have irrigation systems, and 15,000 are center-pivot systems. The state's farmers have invested about $3 billion in irrigation equipment and infrastructure. The report says future irrigation growth will occur mostly in southwest Georgia, where most irrigation systems are located. The Floridan Aquifer supplies water to those systems.

"The Floridan is a massive water supply,” Hook says.

The Floridan Aquifer recharges in south Georgia and is not connected to water use in more-populated north Georgia, which depends on surface water supplies.


Moisture Monitoring

Plenty of methods exist for monitoring soil moisture. The equipment you use might not be as important as making sure it gets done.

"I highly recommend soil moisture monitoring using gypsum blocks, watermark sensors, tensiometers, the ‘feel' method or other devices for measuring the current water status in the root zone,” suggests Guy Fipps, an agricultural engineer with the Texas AgriLife Extension Service. "This provides an excellent check to ensure that irrigations are keeping up with crop water demand.”


What About Sprinkler Placement?

Locating irrigation sprinklers above the mature corn canopy is a good idea, according to University of Nebraska research. Do that and you can still use low-pressure devices but operate them without interference from the canopy. Drop sprinklers into the canopy and the crop changes the water's distribution pattern, creating runoff problems.

In Nebraska, low-angle impact sprinklers lost 8% of water due to the canopy. Spray heads lost 3% of water. Low-angle impact sprinklers wet the canopy longer, allowing more evaporation. Convert the low-angle impact sprinklers to a low-energy precision application (LEPA) system and efficiency can increase 10% to 12%.

LEPA applies water through drop tubes and socks near the soil surface. Some production practices have to change, however. The crop must be planted in a circular pattern with center pivots so the drop tubes run in the row middles. LEPA systems can also apply more water than the soil can immediately take up, meaning the LEPA system is only about 98% efficient.

With above-canopy sprinklers, you still need to work hard on efficiency to reduce evaporation losses. "For sprinkler irrigation systems, we can lose anywhere from 10% to 40% of the water in the air before the water reaches the ground, depending on wind and other weather conditions,” says Guy Fipps, Texas AgriLife Extension Service agricultural engineer.


Know When to Stop

Watch corn carefully to know when to stop irrigating the crop. It's tempting to cut water off too soon, reducing yield potential, say Mississippi State University researchers.

Stopping too soon accelerates maturity, keeping kernels from reaching full potential size and weight. Kernels may look mature at the dent stage, but kernel weight is only about 75% complete then. In hot dry conditions, that can reduce yield 15% to 20%. Corn reaches physiological maturity about 20 days after dent stage or 60 days after silking. To coax full yield from the crop, it should be irrigated until then.

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