Irrigation Pond Saves Groundwater

Researchers at the LSU AgCenter’s Macon Ridge branch station at Winnsboro have found a way to irrigate their fields during the summer without resorting to pumping water from wells.

They’ve created a 16-acre pond they fill with surface water during the winter and use for irrigation in the summer.

The pond grew out of necessity. The irrigation water from wells on the station had become relatively high in salt content. And while cotton is tolerant of this salinity, other crops, such as corn, soybeans and rice, are more sensitive to the salts, explains Dr. Bob Hutchinson, the LSU AgCenter regional director for the area.

"We’re blessed to have a lot of water that’s not too deep," Hutchinson says of the irrigation wells in the Macon Ridge area, which consists of parts of northeastern Louisiana and southeastern Arkansas. In Louisiana, it lies in Catahoula, Franklin, Richland and West Carroll parishes and portions of other parishes between the Ouachita River floodplain and the Mississippi River floodplain.

Although water from underground wells is available, some wells produce salty water because of salt domes. For farmers there, "The choices are don’t farm or develop other sources of water," Hutchinson says.

An alternate source of water is a pond.

The pond at the LSU AgCenter’s Macon Ridge station was constructed in conjunction with a wetland that couldn’t be farmed.

Based on a permit from the U.S. Army Corps of Engineers that allowed the wetland to be included, researchers dug a "trough" around the wetland and used the soil to build a levee for the pond.

Then lift pumps are used to capture water from a nearby canal, which drains several thousand acres, during the rainy season when water flows heavily through it. That water is used to fill the pond.

"Research has shown the benefits of supplemental irrigation to crop production on the Macon Ridge," Hutchinson says. That’s despite an average annual rainfall of around 53 inches. "We get periods of excess rain and periods of inadequate rain."

The LSU AgCenter administrator, who also has been a researcher in the area for years, explains that the Macon Ridge has droughty soils over a fragipan – a natural ground layer that’s very low in organic matter and is extremely hard when dry. It’s root-restricting, too, so Hutchinson stresses that farming in these conditions is difficult.

"It’s a lot like growing plants in a flower pot," he says. "The plants need regular rain to thrive."

Irrigation replaces rain during the hot, dry summer months. Farmers generally apply 6-7 inches of water for cotton during the course of a growing season. "It’s not a tremendous amount, but it’s water that’s critical," Hutchinson says.

Hutchinson says early research showed the value of irrigation on the Macon Ridge. "You most always get a statistically significant increase in yield with irrigation," he says. "We can’t afford to have low yields any more."

Hutchinson says when land values and production costs were lower, a farmer could sustain a bad year now and then. But not any more. "We have to even out production and eliminate the low-yield years," he says.

Northeast Louisiana farmers typically use furrow irrigation, where water is piped across one end of a field and allowed to flow between rows. As it moves down the furrows, some water is absorbed by the soil, and the remaining water drains out the other end of the field.

"Our local silt loam soils have an infiltration rate that’s not too fast and not too slow," Hutchinson says. "And the soils don’t waterlog."

Although the quantity of irrigation water is rather low, farmers could capture the runoff from the fields and pump it back into the pond for later use. This could be most advantageous for rice farmers, who use larger quantities of water for flooding.

"This allows us to be more efficient with what Mother Nature gives us," Hutchinson says.

The environmental advantages of irrigating out of a pond during the dry periods of the year include putting some water back into the canal to support wildlife, Hutchinson says. In addition, the captured water often is full of suspended soil particles that settle out in the pond and don’t end up clogging waterways downstream.

Hutchinson also points out the advantages of diverting possible floodwater from downstream areas where it could be a problem.

The researchers expect the construction cost of the pond will be offset by enhanced crop production from the use of fresh water, says Wink Alison, an LSU AgCenter agronomist at the Macon Ridge station.

Alison points out that the pond site at Macon Ridge included land not really suited for cultivation anyway, because of the natural wetland that ended up being enclosed by the levee.

In order to get water from the pond to fields, researchers at Macon Ridge use two techniques – pumps and gravity.

One side of the pond features a pump that lifts water out of the pond and sends it into a pipe that lies alongside a field. A field on another side of the pond is fitted for gravity flow feed from the pond. Risers in both fields distribute water for furrow irrigation.

So Allison points out it’s imperative for the water level inside the levee to be high enough to allow adequate flow in the gravity-flow system throughout the irrigation season.

Using ponds for storing irrigation water can have both crop production and environmental benefits, Allison says. It can provide leisure benefits for operators as well as the potential for a recreational business enterprise.

10/4/2004 4:25:53 AM
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