When USDA Researcher Wilson Faircloth began his recent presentation to the annual South Carolina peanut meeting talking about cutting back on irrigation water to improve yields, he got mostly blank stares.
By the time he finished his presentation there wasn’t enough time to answer all the questions about selected water stress on peanuts, called ‘prime acclimation’ by Faircloth.
Faircloth is a Research Agronomist at the USDA National Peanut Lab in Dawson, Ga. In 10 years of research at the USDA research facility near Albany, Ga., Faircloth says irrigation does increase yield — over a 10-year average.
However, in some years irrigation has little impact on yield and in some years, at the Georgia facility, it actually decreased yields slightly. In 2005, he says, a series of tropical storms produced an excess in rainfall and irrigated fields actually produced lower yields.
When peanut plants are stressed from lack of water, especially at key times in the growing season, yields can suffer dramatically. Again, over the 10-year test period in southwest Georgia, irrigation frequently improved yield by 1,000-1,500 pounds per acre.
The bottom line, Faircloth says, is that water is the limiting factor in crop production in the Southeast. He says the irrigation application rates and timing for peanuts and most other crops grown in the Southeast are out-dated.
In the Southeast, irrigation timing and application curves go back to when Florunner was the overwhelming choice of variety. As he and colleagues set out to update irrigation timing and amount guidelines they made some interesting observations about peanuts and moisture requirements.
“When peanut growers don’t have irrigation they are at the mercy of timely rainfall to get a high yield. With 100 percent irrigation, the same is true,” Faircloth says. Running an irrigation system costs money and if it doesn’t produce increased yield, then it costs more money, he adds.
“Fully irrigating peanuts, as we have been doing, according to our best available irrigation scheduling tool, is not our best economic choice. It became clear to us, that we need more precise timing and application rates to make irrigation really pay off year in and year out for peanut growers, he notes.
Most peanut growers grow other crops, especially cotton. Faircloth says the same principle of 100 percent irrigation not paying off applies to cotton as well as peanuts.
10 years of research
“Based on 10 years of research, we knew the water curves used by many peanut growers in the Southeast were outdated. So, some colleagues and I set about to update these guidelines to help growers make more profitable use of irrigation,” Faircloth explains.
The new guidelines are quite different from the old ones. First, water amounts are depressed during most times in the growing season. The new USDA guidelines call for more water during the first couple of weeks, then an extended lower use rate during the next eight weeks of the crop.
“When the crop gets into pod development and pod fill, we step up water and stay about the same as the old guidelines at the end of the season. Overall, our water usage guide calls for less water over the course of the peanut growing season,” Faircloth says.
Some work in west Texas led to a further refinement of the irrigation scheduling guidelines that is totally new and different from the past theories about water usage for crops.
Faircloth calls the new approach prime acclimation. Basically, it is the intentional use of drought stress to improve plant water use efficiency. He says the way flu vaccines work is similar to the concept. When a person gets a flu shot, they get a small dose of the flu virus, so their body is acclimated to the flu and better able to handle a naturally occurring case of the flu, he explains.
“We started looking at production in west Texas, where they often produce 6,000-7,000 pounds of peanuts per acre. Growers frequently complain about running out of irrigation water or having restricted water usage during the season. Yet, they seem to produce these high yields with what most would consider less than optimum water usage,” the USDA researcher says.
Faircloth showed the South Carolina peanut growers an aerial infrared photograph of a 120-acre west Texas pivot with peanuts growing under the irrigation system. The grower has 24 hours a week for peanuts to be under good water conditions and for 3-4 days part of the field is okay on water.
However, in half the field, peanuts are under moderate to severe drought stress. Then the drought stressed areas get irrigation water and areas of the field that had been in a good water situation and okay water situation go to moderate to severe water stress as the pivot moves away from these areas of the field.
Still getting big yields
Even though about half the time these peanuts are under some type of drought stress, the grower consistently produces 6,000 pounds of peanuts per acre.
“During the first 10-14 days peanuts have to have adequate moisture, so cutting back during that phase of plant development isn’t an option. If you don’t get a good stand, all bets are off, so we have to give the plants 100 percent of their moisture needs,” Faircloth says.
“In the early parts of flowering, we can cut water by up to 50 percent for 30 days or so. Cutting back to half an inch will be tough, but it will pay off,” Faircloth says. “Once the plant starts to peg and pods begin to develop, the plant will again need that 100 percent of water, so go back to an inch or 1.5 inches per day.
“At the end of the season, the plant doesn’t need as much water, so the grower can cut back a little bit on water. Over the course of the growing season, cutting irrigation water in half for 35 days makes a big impact on irrigation costs.
Cutting water application in half over five weeks saves 3-4 inches of water at a cost of $10 dollars per acre inch and even more than at $4-$5 a gallon for diesel this year.
Over the course of several years and several locations, the best yields came when the plant got 25-50 percent of its water needs, compared to 100 percent of needs either by irrigation or by rainfall.
“To further test the prime acclimation theory, we drought stressed peanut plants starting at day 75 after planting for three weeks. We looked at recovery and it was clear the planned stress actually stimulated the difference in the growth of the plant and boosted yields compared to the plants that had all the water they needed,” Faircloth says.
“The luxury consumers of water, or plants with 100 percent of their water needs supplied, had all the water they needed and didn’t have to work to get it. The drought stressed plants developed better root systems and became more efficient at getting water and ultimately out-performed the plants with access to all their water needs,” he adds.
Changed entire physiology of plant
“We changed the whole physiology of the plant in terms of how it processed its nutrients, water and sunlight. These were season-long effects that clearly improved the plant’s ability to produce more peanuts versus the peanut plants that had access to all the water they needed,” he adds.
The big question, Faircloth says, is does prime acclimation work in the field, compared to in a lab or plot-sized field. The definitive answer is yes, the USDA agronomist says.
In production-sized plot research by the University of Georgia, rain-fed peanuts averaged about 3,000 pounds per acre. Using standard irrigation scheduling, which called for 12 irrigations over the growing season, yields were bumped by 300 pounds per acre — not a good impact on profitability, Faircloth notes. And, using evapotranspiration tables and 11 irrigation events, yields were bumped to 4,000 pounds per acre.
In the prime application plots, peanuts were stressed 30, 45 and 60 days and produced higher yields than rain-fed crops or peanuts irrigated 10-12 times a season.
The yield increase isn’t the most important factor, Faircloth contends, it’s the amount of water saved. Irrigation use was cut nearly in half — 6-7 times during the season — and still beat the yields of these other systems.
It works well for cotton, too. Fully irrigated on strip-tilled cotton, prime acclimation using 70 percent of water supply produced the highest yields and even 50 percent of maximum water needs produced nearly as high yields, Faircloth says.
The wave of the future for water usage on peanuts and other irrigated crops in the Southeast seems to be to cut water usage, improve yields and maximize profits.