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Intermittent flooding for rice crops

Delta agricultural researchers are testing rice-growing practices common in the Far East to avoid future water resource problems already prevalent out West.

Mississippi State University's Department of Plant and Soil Sciences is heading a three-year project that monitors the progress of rice fields less dependent on continuous flood control and more dependent on rainfall.

The study was prompted by evidence of a slow, but steady natural aquifer decline in the Delta.

Joe Massey, MSU assistant professor, presented the study during the Delta Ag Expo last month in Cleveland, Miss.

He said results, thus far, show promise.

“The potential agronomic benefit here is reducing water use in our rice production by capturing rain. By doing that we have to pump less and consume less fuel,” he said.

Relying more on rainfall for irrigation was begun by Chinese rice farmers during the 1980s, in response to that country's population explosion and needs for industrial modernization.

“They made a decision in the '80s that they had to do something more efficient with their water so they could have water for power plants and things such as that,” Massey said.

An intermittent irrigation program begins with flooding a field, then permitting it to naturally subside to the point where half of the upper field is revealed and remaining as mud.

At that point, water pumps are turned on and the flood is re-established.

“We are trying to increase use of rainfall,” Massey said. “By keeping those levees not all the way full, we can gain some benefits from the natural rain, if it does fall.”

In 2003, the group of researchers created a side-by-side comparison study (part of the field continuously flooded, an equal portion flooded intermittently) on five 40-average acre rice fields, three in Mississippi and two in Arkansas.

The study's finding revealed about a 30-percent water savings using an intermittent irrigation program as opposed to a continuous flood program.

That discrepancy could translate into an economic savings for Mississippi rice growers estimated between $15 and $30 per acre.

Massey said that although more studies are necessary to verify initial results, the comparison study found no dramatic differences in yield, nitrogen fertility or rice quality. Neither was there a substantial difference in weed control effectiveness, he added.

“On average, Mississippi receives about 10 inches of rainfall from mid-May to mid-August and typically we are applying 28 to 32 inches of water per acre of rice,” he said.

“Research has shown it really only needs between 12 and 25 inches. If we could capture the average 10 inches of rain water per year, we'd have about half of the water the rice needs. That is what we are targeting.”

He insisted that research models have intentionally not factored in the predictable seasonal periods of heavy rain or those with little or none at all.

“There will be times when rice fields, because the pumps have just been turned on and the levees are full, that there is no more rainfall holding capacity than in the continuously flooded side,” he said. “But 60 to 70 percent of the time there is more rainfall-holding capacity than normal.

“So we are not trying to time the rainfall, we are just trying to gain it, on average. There is a greater ability to capture that rain than with the continuously flooded field.”

But water conservation is not the singular benefit farmers might find appealing in the potential new model; advantages could include a reduction in agrochemical runoff, a reduction in hazardous emissions into the atmosphere and one more distinct gain.

“The more producers can do to show voluntary use reduction, the more likely it is that regulators will not come in and tell you how to use water to irrigate your crops,” Massey said.

Terry Dulaney, co-owner of Dulaney Seed, Inc., in Coahoma County, Miss., said results of the comparative study conducted on that company's fields surprised him.

“We were a little concerned about lowering the water levels in the beginning, but it's been a very positive program,” Dulaney said. “We see a definite decrease in water pumping and labor costs and basically no change in rice yield or in weed pressures.”

While a new model — if proven reliable — could provide economic savings for rice farmers in the short term, a wide-scale adoption by Delta farmers could help avert a potential long-term problem Mid-South scientists are keeping a close eye on.

Research shows there has been an annual 0.9-foot average aquifer decline in the Mississippi Delta over the past decade, centered on Sunflower and Bolivar counties — two large rice production areas.

Meanwhile, in Grand Prairie, Ark., the problem is more severe, as aquifer levels are dropping as much as 3 feet annually.

“There is a real concern about this,” Massey said.

World rice demand is projected to increase 30 percent by 2020, but many regions that grow rice are already experiencing difficulties linked to water decreases, particularly in California.

“As population continues to grow, the number of current rice growers out West will likely decline because the small amount of water they are able to use now to grow rice would be diverted for other uses,” he said. “Already near Houston, Texas, rice producers are selling their water to the city. It's much more valuable to sell it than to grow rice.

“We have good water resources here (in the Delta). If we can find ways to conserve the use, we might have a good, sustainable future for rice production.”

Based on the test results at Dulaney Seed, Dulaney is optimistic the company will switch to the intermittent program after the test models are completed. He foresees the model one day becoming commonplace.

“I think this is a program we will see a lot more of in the future because the water issue is going to get bigger and bigger,” he said.


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