Attention to peanut nutrition needs critical with higher fertilizer prices

West Texas peanut farmer Andy Timmons said he’ll keep his options open as long as possible as he decides on peanut and cotton acreage for 2008.

“If cotton prices go up I may plant more cotton,” he said during a recent production meeting in Littlefield. “The decision will be based on crop prices, but either way we go, production costs are up. I want to be flexible. Fortunately, cotton and peanuts work well together and I can switch from one to the other.

“With costs, I don’t know how do things cheaper than I do. We’ve cut as much as we can and I don’t know where else to cut.”

Fertility may be one option, but not necessarily a good one, said Extension Agronomist Todd Baughman.

“We can look at budgets and show how much we can trim by reducing fertility,” he said. “But we can also look at budgets and show how much we lose by reducing yields.”

He said fertilizer costs have doubled since last planting season and understands the temptation to cut back. “But maintaining yield is the best way to produce an economical crop. You don’t want to dig out of a hole in the middle of the season.”

Knowing what’s available in the soil and understanding the best sources and application options for fertilizer will improve efficiency, said Extension Agronomist Calvin Trostle.

Trostle put numbers to the nitrogen fertilizer cost increases: Urea is running $550 a ton; anhydrous ammonia (NH3) is at $725 a ton and 32-0-0 liquid is at $420 a ton.

“But remember that peanuts respond better to residual fertilizer. Fertilization of the crop preceding peanuts is important. Also, develop a uniformly high level of fertility through the root zone.”

He said fertility research suggests requirements for peanuts, per 1,000 pounds of yield are: nitrogen, 70 pounds per acre; phosphorus, 8 (18 pounds of P205 per acre); potassium, 24 (29 pounds of K20 per acre); calcium, 21; magnesium 9; and sulfur 5 to 6.

He discussed nutrient recommendations for West Texas production.

“Calcium must be taken directly from the soil and adequate calcium must be in the moist pod production zone.”

IF soil test calcium levels are less than 600 ppm, then calcium recommendations call for application of gypsum at 600 pounds per acre in a 12-inch to 14-inch band over the row or 1500 pounds per acre broadcast. Liquid calcium applications would best be timed at peak pegging at 10 to 15 gallons per acre with subsequent applications if needed.

But Trostle said Texas A&M tests in West Texas have never shown a measurable yield or grade difference, even on Virginia peanuts.

He said the same holds for foliar fertilizers. Evaluation of nine different products at nine different locations showed no influence on peanut yield though field test methods may have difficulty noting small differences in yield. “We’ve also seen no comprehensive studies to show petiole testing is reliable in peanuts.”

Inoculants are a different story.

“Prior peanut fields in West Texas have minimal carryover of Bradyrhizobium nodulation, and 1999 through 2001 field observations then suggested up to 25 percent of South Plains fields were undernodulated. That’s none to 10 to 20 nodules per plant.”

Tests showed both granular and liquid inoculants increased nodulation and yield. Liquid inoculants proved better than granular. Trostle said adapting an 8-row planter to apply liquid inoculants in-furrow should be worth the expense. He also said tests indicate that adding nitrogen may reduce peanut nodulation. “Peanut plants are lazy. If a nitrogen source is available they’ll pick it up and produce fewer nodules.”

He said double rates of granular inoculants improved nodulation and yield but double liquid rates showed no advantage.

Trostle said application and planting process within an inoculant type may be more important than the particular product choice. Planting deeper, for instance, improves performance. He said planting peanuts at 2 inches instead of 1 or 1 ½ inch is better because it minimized the chance the inoculant may not survive in hotter or dryer conditions near the soil surface.

“Evaluate nodulation five to six weeks after planting and consider adjusting mid-season nitrogen application based on the nodulation counts.”

For the Texas South Plains counts from zero to 5 nodules per plant six weeks after planting is not good. Fair is 6 to 10; 11 to 15 is good; 16 to 20 is very good; and anything above 20 is excellent. At the upper end, Trostle said growers might consider dropping mid-season nitrogen rates from 75 pounds per acre to about 50. “Assess the situation in mid-June to determine need.”

Growers should apply phosphorus prior to a winter cover crop or before planting peanuts. “Reduce broadcast rates by 20 percent if banding the material.”

Micronutrient availability of iron, manganese, zinc, copper and boron usually decline as soil pH increases. “Late season foliar treatments seldom result in economic returns,” Trostle said.

He said West Texas fields might occasionally be zinc deficient. (“The deficiency is hard to see as visual symptoms would be rare, but we might have an indication of low test zinc based on a soil test.”) With low potassium, Texas A&M recommendations call for zinc only if below 0.20 parts per million. With high phosphorus levels, zinc may be recommended.

Iron deficiency, with pale green, yellowing symptoms, may show up with pH higher than 7. Trostle said in this case foliar iron applications may be needed, though it is often difficult to be sure foliar iron actually helps.

Boron deficiencies are rare, Trostle said. “But we have a narrow range between deficiency and toxicity. Though some soil tests often recommend boron, check irrigation water before applying.” He said farmers should consider boron levels approaching 0.75 parts per million a red flag.

Trostle said farmers should rely on soil tests to evaluate fertility needs and to control costs. Checking for deep nitrogen also may reduce expenses.

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