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Peanut physiology: Improve yields by knowing plants

Craig Kvien, University of Georgia research plant physiologist, spends much of his time learning what makes a peanut plant tick. He's convinced that the more a farmer knows about a peanut the better he can manipulate growing conditions to coax it into producing better yields.

Kvien shared some of his research findings during the recent Southern Peanut Growers Conference in Panama City, Fla.

Kvien said it's no secret that peanut yield and moisture availability are closely tied. But he explained that the peanut plant can overcome a lot of stresses, including drought, if those stresses don't hit when the plant is most vulnerable.

“A peanut can overcome an early drought or a late one,” he said. “It's the mid-season drought stress that hurts the most.”

Kvien said tests show that moisture stress from 30 to 65 days after planting will lower yields by some 500 pounds per acre (3960 pounds versus 4540 with no drought stress) with profit losses dropping from around $1480 to $1310 per acre.

Moisture stress from 65 to 100 days after planting knocks yields to 2900 pounds per acre and profit to $910.

Outlook improves with drought stress hitting at 100 to 135 days. Yields may be close to those with no drought stress, 4120 pounds per acre, and profit climbs back to $1380.

“The crop can survive early and late drought,” Kvien said. “It's the mid-season stress that splits crop maturity and hurts yields. Peanuts have an amazing recovery potential and will come back from early drought, if they get a good season and don't get frosted out.”

Humidity also matters. Kvien said during prolonged drought peanut plants will not send down pegs.

“From 10 to 12 days after flowering, peanut plants begin pegging. But it's to the plant's advantage not to send down pegs on dry soil where they will be scalded. When the drought ends, a flush of pegs will come down. It's an amazing way to handle drought.”

Kvien said soil temperature in the pod zone also affects yield. “Drought will affect soil temperatures,” he said. “Canopies get lighter and soils heat up. We've learned to mitigate the problem with twin-row peanuts. With twins, we fill in the gaps quicker and keep soil temperatures lower.”

The calcium to potassium ratio also affects peanut pod production. Kvien said calcium is essential for pod development. “But high potassium or magnesium levels can interfere with calcium intake.”

High potassium may be particularly troublesome in peanuts following cotton.

“Cotton farmers need potassium to make decent yields,” said John Beasley, University of Georgia Extension peanut specialist.

But calcium to potassium ratio needs to be 3:1 for peanuts.

“In the Southeast, we need at least 500 pounds of calcium per acre,” Beasley said, “and farmers should pull samples from the top three inches of soil, where the peanuts will need it.”

He says if cotton has been in a field for several years, the ratio may be skewed toward potassium. “The trick is to continue to apply adequate potassium to cotton without getting calcium out of balance for peanuts.”

He says farmers must sample and add calcium as necessary to balance the nutrients.

Kvien says the most important factor in peanut production is rotation.

It's the basis, he said, for avoiding many peanut production challenges.

“Rotation is the key to how the plant uses soil and water,” he said. “Grass crops are best because they send down deep root systems that open pathways into the subsoil. These openings stay for several years after the crop is gone and that helps peanuts.”

Kvien said many peanut farmers continue to grow field corn, even though the economics are not particularly favorable. “But they risk lower peanut yields when they do not have corn. Grain sorghum also works well in rotation with peanuts. Cotton is not as good as grasses, he said, “especially bahia, bermuda, corn and millets.”

Kvien said manufacturers have asked how to select for peanuts for the highest quality. “Tests show they need to go to the best producers,” he said. “If manufacturers pick good growers, they get the best flavor from peanuts.”

New technology will help farmers improve water efficiency “and keep the production engine going,” Kvien said.

Precision irrigation, using Global Positioning System (GPS) technology, promises to help farmers save water and maintain or improve yields.

“We can use GPS technology to turn irrigation units on or off.” Kvien said farmers do not have to apply the same amount of water across a field. Sandy soils may get more water than heavier clays.

“We can apply water where we need it with variable-rate irrigation. We also can use different nozzles, depending on soil types and crop needs.”

Kvien said pulsating nozzles, for instance, get more water into the foliage.

“I hope this system will be cost effective,” Kvien said. “To retrofit a center pivot system covering 100 acres costs from $8,000 to $10,000.”

He said the GPS also tracks the pivot and farmers can dial up from a cell phone to determine position of the system. The system offers growers an opportunity to maximize water efficiency and profit in each area of a field. “We may want to increase inputs in the most productive areas and decrease inputs or leave less productive areas out of production.

“We want to enhance rather than reduce field variability.”

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