Published on 08/05/98

Irrigation Lapses Proving Costly to Georgia Farmers.

It's not just the drought hurting Georgia farmers this year. A University of Georgia expert said the way many water their crops could cut $100 million from cotton yields alone.

Struggling to keep their crops healthy, Georgia farmers often declare that even in irrigated fields, they need rain to get good yields.

But that's not necessarily true, said Tony Tyson, an Extension Service engineer with the UGA College of Agricultural and Environmental Sciences.

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Kerry Harrison -- UGA CAES

PUMPING WATER AS FAST AS THEY CAN, many Georgia irrigation systems can't keep up with plants' water needs. Underdesigned systems or hesitant farmers supplement rain, instead of replace it, as irrigation systems are engineered to do. But using it to supplement rain means lost yields, said a University of Georgia engineer. "You have to be committed to supplying the moisture needs of the crop," said Tony Tyson. "Sometimes that means irrigating 24 hours a day. But you have to do it." (Photo courtesy the UGA College of Agricultural and Environmental Sciences.)

"For the most part, people have drawn that conclusion from past experience," said Tyson, an irrigation specialist. "But either their system was underdesigned or the farmer was hesitant to run it long enough to supply the peak water demand."

Usually, the problem isn't the system. "Most systems less than 10 years old are adequately designed," he said.

The problem, he said, is that many Georgia farmers use supplemental irrigation. They just fill in between rains. When their crop shows signs of moisture stress, they crank up the irrigation.

That approach is costly, he said, in years like this, when dry spells are long and temperatures high.

"If you wait until you see signs of stress, you've already hurt the yield potential," he said. "That's especially true in the critical pollinating and fruiting period."

Losing any yield is costly. Georgia growers get up to 1,400 pounds of cotton from irrigated fields. A loss of 230 pounds per acre would mean about $100 million over Georgia's 600,000 acres of irrigated cotton.

The Georgia Agricultural Statistics Service rates 73 percent of Georgia's 1.4 million acres of cotton as only "fair" or worse. About 40 percent is irrigated.

Tyson figures most yield losses on irrigated acres could be avoided if the systems were designed and used right.

"We recommend designs that will meet peak demand," he said. "That means that with no rainfall at all, the system will supply the highest demand of a given crop."

With most row crops, he said, the system must provide up to one and one-quarter inches of water every three days.

Some systems can't meet that demand. "In the late 1970s and early '80s, irresponsible or inexperienced irrigation contractors sometimes cut the system capacity to come up with a competitive price," he said. "Some of those systems can't put out enough water in conditions like this."

Some farmers irrigate out of ponds they have already pumped dry. But Tyson said that shouldn't happen.

"That's one of the things we look at in the design," he said. "It's hard to justify making the kind of investment you have to make on irrigation if you don't have adequate water."

Some strategies, though, avoid problems even with underdesigned systems. "We recommend splitting the system," he said, "and planting different crops under them that don't require peak irrigation at the same time."

Most crops have a water-use curve, he said, that ranges from less than one-tenth to about one-third of an inch per day. The peak water demand for corn and tobacco is in May and June. For cotton and peanuts, it's July and August.

Most farmers, though, have systems that can put out plenty of water. But for various reasons, they hesitate until they've already lost valuable yields.

"Some of our farmers do a good job with irrigation management," Tyson said. "I can just about guarantee you somebody will make 1,400 pounds of cotton per acre even this year."

The ones who manage their irrigation well, he said, are committed to supplying water whenever their crops need it.

"You're not going to make peak yields with supplemental irrigation in stressful conditions," Tyson said. "You have to be committed to supplying the moisture needs of the crop. Sometimes that means irrigating 24 hours a day. But you have to do it."

Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.