Determining the water use efficiency of commonly grown peanut varieties is the focus of research being conducted at the National Peanut Research Laboratory in Dawson, Ga.
The research, funded by the National Peanut Board, is a repeat of studies conducted in 1976. The original study looked at water-use curves for the popular varieties of the time, including Florunner.
“The water-use curve basically tells you how much water a peanut is using throughout a season,” says Diane Rowland, USDA-ARS researcher with the National Peanut Laboratory. “The curve can help determine how much water certain varieties need.”
Water-use curves are important, she adds, because they are the basis for much of the irrigation scheduling done on peanuts. They help growers decide when and how much water to apply to a crop.
“We thought we could repeat the 1976 study to create a curve for currently grown varieties so we can increase the efficiency of these irrigation scheduling methods,” says Rowland.
Varieties used in the most recent study include Georgia Green, Andru II and NC-V11. The research requires that the amount of precipitation reaching the plant is controlled. This is accomplished through the use of rain-out shelters, she explains.
“We have sensors that close these shelters when it rains to prevent water from falling on the plant. This allowed us to quantify exactly how much water we were putting on those peanuts,” says Rowland.
It also was important to the research, she says, to prevent evaporation. This was accomplished through using drip irrigation tape in the plots.
Three soil sensors were used to help determine when and how much water to apply, she says. “We looked at the water going in and out based on these three sensors. The first one was just under the surface, down to about a foot. A sensor at the top monitored the soil moisture for pegging and pod formation.
“Then, we had a sensor from about a foot down to about 2 feet. In addition to measuring the water being taken up at that depth, it also helped to prevent water from flowing out the bottom.”
By combining all three sensors into a formula, researchers were able to determine how much water to replace, or how much water the plant is taking up, says Rowland.
“We found that the total amount of water taken up over the season really didn't vary that much among the three varieties. Although there isn't much difference, Georgia Green was using a little more water than the other two varieties.”
The water-use pattern observed during the season was interesting, says Rowland, because it differed from those in the original 1976 study.
“The water-use curves for our three varieties probably are lower than in the previous study. This is important because it can help us increase the efficiency of our irrigation decisions.”
The most recent study showed a dip in the curve in the same location as the previous study showed maximum water use, notes Rowland.
“The reason for this is the very mild summer we saw this past year., with low temperatures, high humidity and lots of rainfall.”
To insure that what is happening in the plots also is occurring in a typical field, researchers attached sensors to the stem of a peanut plant in a field situation. “We measured the actual water that is flowing to the stem. When comparing the two, we saw the same pattern, and we see the effect of environment on the peanut plant.”
It's important, says Rowland, to have environmental data when scheduling irrigation. Scheduling methods such as IrrigatorPro and the University of Georgia pan evaporation method have an environmental component, she says.
“We also can go back and look at that relationship between the environment and water use and make predictions. The curve we created this past season was for a mild, wet year. We can go back and predict what it would be for a drought season.”
Researchers also wanted to look at water-use efficiency in the study, says Rowland. “You can have a plant that uses a lot of water during the season, but the yield is high. That may not matter if you have plenty of water to apply to the crop. As long as you have a high yield, that's fine.
“However, you can have a variety that uses a lot of water and is not high yielding. That represents a low water-use efficiency. In this case, water-use efficiency is the amount of yield we get from the amount of water we're using.”
In looking at the water-use efficiency of Georgia Green, Andru II and NC-V11, Georgia Green tended to use more water, she says, but its yields were not much higher.
“So Georgia Green's water-use efficiency was lower than Andru II. This wasn't too surprising. In surveys conducted throughout the Peanut Belt, Georgia Green has a lower water-use efficiency than most other varieties. The reason for that may be its rooting pattern.”
Researchers went back to the plots, she says, and applied a tracer in the water so they could follow the water's path.
“This allowed us to look at the water as it traveled through the soil, into the roots, and up to the stem. We found that Georgia Green and Andru II have many different water uptake habits. Georgia Green is taking up a lot more water from the surface than Andru II because it has more roots near the top. So the rooting system may be causing Georgia Green to have a lower water-use efficiency.”
Researchers will repeat the test this year.