Water-use efficiency becoming priority for peanut producers who irrigate Water-use efficiency becoming priority for peanut producers who irrigate
• As Southeastern states begin to take a closer look at regulating agricultural water use, it might be some small comfort for farmers to know that peanuts have been proven to be more drought-tolerant than other commonly grown row crops.
June 26, 2013
The 2012 peanut production season was literally one for the record books, with growers throughout the U.S. making record-high yields and production. Having accomplished such a feat, many in the industry are asking, “What’s next?” For the answer to this question, it’s important to take a look at what is in the peanut research pipeline – those problems, issues and initiatives currently being addressed that will lead to even more efficient and profitable peanut production. For the next several dys, “Pipelines to Peanut Profitability” will take an in-depth look at these areas of research, what they could mean to growers, and when producers can expect to see practical, on-farm applications of this research.
As Southeastern states begin to take a closer look at regulating agricultural water use, it might be some small comfort for farmers to know that peanuts have been proven to be more drought-tolerant than other commonly grown row crops.
Still, it’s important for growers to know the physiological needs of the crop so they can improve their water-use efficiency.
“Peanuts are more tolerant to dry conditions, and there are more physiological tools that we can use to help the crop respond better to drought,” says Diane Rowland, University of Florida crop physiologist.
Some crops naturally respond to irrigation better than others, she says, and that is linked directly to their physiological responses.
Crop comparisons have shown that irrigation can increase corn yields by 40 percent with, soybeans by 32 percent, cotton by nearly 98 percent, and peanuts by about 25 percent.
“But more isn’t always better – there’s a point of diminishing returns with excess water,” says Rowland. “When you reach the point beyond which a crop can use water physiologically, then it just can’t use anymore.
“At this point, any yield benefit starts to flatten out, and then you’ll start to see detrimental effects from irrigating a crop. When you add in the cost of pumping water, you can really see those diminishing returns.”
The keys to efficiency for growers include maximizing irrigation, applying water just when the crop needs it, and applying it as efficiently and as timely as possible, she says.
Low early-season requirements
“We know that crops use water based on their growth stage, so we see that water requirements start off low at early season, increase at mid-season, and then drop off later in late-season.
“Crop water-use changes with the developmental stage of the crop. In the initial stage, we must support increased vegetative growth, including the canopy and the root system. Then when we move into reproduction, the plant requires a lot more energy than when growing a leaf. Also, environmental conditions normally change during the growing season, with more heat and drought and less rainfall as it progresses.”
The peanut water-use curve currently being used was developed in the 1970s, says Rowland.
“We’ve been working to update these water-use curves, and we’re finding that they’re different based on the peanut cultivars being grown today. We can increase our efficiency by understanding how different our water-use requirements are for the various cultivars.”
The University of Georgia has translated this water-use curve into weekly water use by peanuts, considering each week after planting, with a peak at about .30 inches per day at about mid-season.
Looking at the water required by the most commonly grown row crops in the Southeast, peanuts need from 20 to 27 inches per growing season, cotton 27 to 51 inches, corn 20 to 31 inches, and soybeans 18 to 27 inches.
“It seems kind of simple — we can approximate how much water is needed at different points in the season, and we can apply it at that time. But we have to remember that water use differs by peanut cultivar, and it also differs by the maturity of the cultivar.
“So if you’ve got a 150-day peanut versus a 125-day peanut, the longer maturity cultivar will require more water just by the fact that it has a different maturity date.
“We also add soil conditions and weather conditions, and this is where it can become complicated. The primary factor is stress. Whenever stress is added into the equation, we’ve got a whole new ballgame.”
From a physiological standpoint, drought causes stress at the cell level, leaf level and plant level, explains Rowland.
“One of the first things that happens is that we lose the turgor or the rigidity of that cell. It automatically stops growing with decreased cell division, and the metabolism is slowed.
“That leads to growth stopping at the leaf and plant levels. That’s why we see leaves drop off — that’s how a plant reacts to the stress. As water use drops, photosynthesis decreases.
“Then we begin to see that the crop changes the allocation of its energy. As it comes under stress, it won’t put resources into reproduction.”
Some crops more sensitive to drought
Some crops are physiologically more sensitive to drought stress, she says. Peanuts have a low to medium sensitivity to drought, while corn has a medium to high sensitivity.
“Overall, we know crops are more sensitive to drought during the reproductive stage. And when we look at that, it’s directly related to the water-use curve. The most sensitive stages to yield loss will be during the reproductive stages.”
Peanuts is an indeterminate crop, which means it’ll continue flowering and putting on pods, says Rowland.
“When drought occurs, the peanut will do a couple of different things. In the early stages, up to about 45 days after planting into early bloom, it has strategies to respond to drought stress, and it actually becomes stronger and more tolerant to drought stress during mid-season, when it could be more susceptible.
“During reproductive stages, 45 to 100 days after planting, when it begins to mature and fill the seed, it is highly susceptible to drought stress. It has the ability to actually stop filling pods rather than shedding them. It has the ability to survive, but you could end up with a split crop with differing maturity levels, and that’s not optimal.”
There are several ways for farmers to conserve water and make a crop more tolerant to drought, says Rowland.
“We know there are certain stages — especially early season in the vegetative stage — when we can prepare the crop to be stronger and more tolerant to drought later on in the season. We call that primed acclimation. Also, through Regulated Deficit Irrigation (RDI), we can make the crop stronger. You expose the crop to a temperature stress, and through its development, it will be more tolerant to the temperature to which it was exposed.”
Irrigation scheduling tools also are available that will help growers improve their water-use efficiency significantly, she says.
“These scheduling tools also can provide a means of record-keeping for growers who irrigate. And as we get closer and closer to water restrictions, growers will be required to have very detailed records.”
One of these programs is PeanutFARM from the University of Florida. This is actually two tools, says Rowland, one being a harvest recommendation two and the other being an irrigation scheduling tool.
PeanutFARM is a group of tools aimed at helping growers manage peanut development and maturity by tracking adjusted growing degree days (aGDD). aGDD’s use upper and lower daily air temperatures, plus the amount of water the crop receives from rainfall and irrigation, to predict the development of the crop.
In addition to tracking peanut maturity, aGDD’s are used by PeanutFARM to help schedule irrigation through estimating crop canopy cover and daily water use.
Modified using weather data
This daily water use is then modified using weather data — which can be automatically drawn from state networks or input for individual fields, depending on grower preference.
As the grower develops their own profile, each field can be managed separately and processed by PeanutFARM to accurately predict the need for irrigation and optimum harvest time.
The purpose of PeanutFARM is to provide the producer with tools to ease both in-season and harvest management decisions.
Another irrigation scheduling tool is Irrigator Pro for Peanuts, developed at the National Peanut Research Laboratory in Dawson, Ga. This computerized expert system is designed to manage peanut irrigation and pest management decisions.
The objective is to improve economic returns for irrigated peanut production and reduce risk associated with aflatoxin, foreign material, immaturity, off-flavor, chemical residues and negative environmental impact.
Irrigation recommendations for Irrigator Pro are based on more than 25 years of scientific research data and information. Generally, irrigation recommendations are made to maintain soil temperatures and water in the optimum ranges.
Graphs can be viewed to show the maximum and minimum soil temperatures in relation to the optimum zones, and the cumulative water use in a field.
These graphs are useful in determining how Irrigator Pro is performing in a particular situation and can help in diagnosing any problems that may be occurring.
Yield increases of over 300 pounds per acre and 2 percentage point increases in Sound Mature Kernels and Sound Splits have been demonstrated from the use of the program.
Irrigator Pro models are also available for cotton and corn production.
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