Cotton acreage may be trending down in west Tennessee, but research on the crop continues at the University of Tennessee’s West Tennessee Research and Education Center at Jackson.

At a recent field day, researchers talked about their work on several projects aimed at keeping cotton competitive with corn, soybeans and wheat. New irrigation technology, for one thing, offers promise in this region, where many new center pivot irrigation rigs were installed the past couple of years.

“We’re taking a close look at subsurface drip irrigation. While that is not widely seen in Tennessee, farther west there’s more going in all the time because of limited water supply,” says Chris Main, Tennessee Extension cotton specialist. The experiment station now partners on subsurface drip irrigation work with John Deere Water and Tennessee Tractor’s irrigation division, which provides additional funding.

Farmers in this area likely will use subsurface drip differently than those in Texas, Main says. “Here, drip will be for fields where we can’t get pivots in, for whatever reason. On smaller acreage, drip works well,” he says.

This is the university’s first year of work with subsurface drip. Tape was installed in February; plots got water in early June.

“Tape was installed on every other row on 38-inch cotton. We try to feed two rows off one tape. This is thick-walled tape that should have good durability. It is 12 inches deep. We’re trying to figure out if one tape every 76 inches or 38 inches is better,” Main says.

“We see that it can be a good solution to get water on odd-shaped fields where a pivot won’t work. We can supply nutrients through the tape right at the root system. Right now, we think when farmers get started with subsurface drip, they shouldn’t be too concerned with putting nutrients through it until they figure out what they’re doing. Just doing the water is the first step. Start small. Start with 20 or 30 acres.”

In another irrigation test, moisture sensors buried at depths ranging from 4 to 40 inches below the soil surface indicate when conditions are right for watering the crop.

“I can look at what the water is doing at different places in the soil profile and see how that plant is using water. Using it, we can really see the rainfall events move in and what they did. It’s a neat tool,” Main says.

Irrigated cotton makes better use of sunlight, as well, UT’s scientists think. Their tests indicate that, with irrigation, the crop harvests 80 percent of the sunlight falling on the field. Dryland cotton, on the other hand, catches just 60 percent of the sunlight.

To truly understand how irrigation helps produce a good-yielding crop, it helps to know just how little water is required to turn one out, as well.

“We’re trying to get optimum yields without optimum water. We want to get less vegetative growth and more lint, and make better use of rainfall if there is some capacity to grab it and hold it,” says Brian Leib, UT biosystems engineer.

Cotton growing on good soil requires less water. Six of seven years, cotton in good soil actually lost yield with early irrigation. In sandy soil, though, cotton needs early irrigation to maximize yield.

“The biggest yield bumps come from applying irrigation to cotton on sandy soils,” Leib says.

This year, Leib and his co-workers began looking at how varying rates of irrigation affect crop yield.

“We’re trying to find that one irrigation decision that might optimize yield over varying soil types. On sandy soil, you probably can get close to optimum yield with one-half inch of water a week starting early, at square, and going right through cracked boll. This will probably utilize the least water and make the water most efficient,” Leib says.

“Is this going to push us to precision variable rate irrigation? That’s something to consider.”