Fertilizer for peanuts is a little better bargain this year than a year ago, but paying attention to soil test recommendations and application techniques still makes sound economic sense.
“Prices are fluctuating,” says Oklahoma State University soil fertility specialist Brian Arnall, “so soil samples are worth every dime a farmer spends, even if he just gets nitrogen, phosphorus, potassium and pH levels.”
Arnall, speaking at the Oklahoma Peanut Expo at Lone Wolf, Okla., said since peanuts are a legume farmers get little yield benefit from adding nitrogen, but “studies show a little yield boost. Adding 10 to 20 pounds per acre is not a bad idea. For early planted peanuts, a starter is a good idea.”
He said with nitrogen prices at 30 cents to 40 cents a pound, farmers are only out about $4 per acre by adding 10 pounds to get early growth.”
Phosphorus may be more important and Arnall recommends farmers apply by soil test if results show less than 65 pounds per acre. “A 10 percent phosphorus deficit may result in a 10 percent yield reduction,” he said. “At 90 percent phosphorus sufficient, a farmer loses $90 per acre. At 20 percent deficient, he loses $180. With today’s prices, adding phosphorus if soil is 90 percent sufficient is money in the bank,” he said.
He recommends banding over broadcast applications.
Potassium at less than 250 pounds per acre is deficient but Arnall cautions growers not to apply potassium unless it’s needed. “Too much potassium can cause calcium deficiency,” he said. Again, band applications are more efficient than broadcast.
“Also, potassium is more expensive than phosphorus so look at the economics at 90 percent sufficient. At 70 percent sufficient, it pays to add 40 pounds of K2O.”
Boron, at less than 0.5 pound per acre, is deficient and peanuts may display hollow heart. “But do not apply more than 1 pound of boron per acre. It can be toxic, is highly mobile and leachable.”
Iron deficiency shows as yellowing in the top of the plant and Arnall says deficiencies are common in high pH soils, above 7.5. “Broadcast applications are less efficient and may bind up. Banded or foliar applications are better options.”
Manganese deficiencies result in interveinal chlorosis and may be related to high pH, high calcium or high magnesium. “Foliar applied manganese can correct deficiencies, or growers may apply to the soil along with fungicide.”
Zinc, at less than 0.8 pound per acre, based on soil tests, is deficient. High pH, high calcium and high phosphorus levels can be factors.
Calcium can be a critical nutrient for peanuts, especially Virginia types, to manage soil pH. Arnall says optimum pH for peanuts is 6.5. “Calcium deficiency results in a high incidence of pod rot and unfilled pods, or ‘pops.’ Peanuts need calcium for maturation and need more in sandy soils than in clay.”
Arnall said runner type peanuts may need as much as 750 pounds of lime per acre and Virginias may need as much as 1,500 pounds per acre. “Lime takes time to solubilize, as long as 100 days,” he said. “Sandy soils and irrigated fields may respond a little faster. Lime applied at emergence in sandy, irrigated soils has been effective.”
He said dolomitic lime contains magnesium, but calcitic is better in low pH, high magnesium soils.
“Gypsum is very water soluble. Apply at early bloom; if applied earlier it may leach out. High levels of magnesium and potassium can cause deficiencies.”
Arnall said foliar calcium applications, according to “many reports, do not correct deficiencies.”
He also said surface-applied gypsum in no-till or reduced-till situations may build up a layer near the soil surface.