Phosphorus (P) fertilizer prices are high, no question, but wheat producers should not overreact to the lofty price tags by cutting back on phosphate fertilizer if it´s needed for the wheat crop, said Kansas State University agronomist Barney Gordon.

"Where soil phosphorous levels are low (10-20 parts per million Mehlich III or Bray-1 P) or very low (less than 10 ppm), the likelihood of a wheat yield response to phosphorous is greater than 50 percent," said Gordon, who is the agronomist-in-charge at the K-State Research and Extension North Central Experiment Field near Belleville. "Often, the yield response is great enough to more than pay for the phosphorous fertilizer, even at today´s prices."

In mid-August, prices in Kansas for dry and liquid forms of phosphorus ranged from $1 to $1.30 per pound-approximately 180 to 210 percent higher than a year ago.

Wheat tends to be highly responsive to P input if the soil test category is low or very low, he said. Phosphorus is generally the second-most limiting nutrient in wheat production behind nitrogen, but in some areas of the Great Plains, phosphorous is even more limiting than nitrogen.

"Early-season phosphorous deficiency can limit wheat yield potential. The first five to six weeks after emergence is the critical period. Wheat absorbs about 18 percent of its total seasonal phosphorus uptake in just the first two weeks of growth," Gordon said.

Phosphorus has major impacts on tillering and rooting of wheat, and an early-season P deficiency can reduce those important aspects of growth and development, he explained. In turn, a poorly developed plant is more susceptible to stresses in winter and spring.

"It doesn´t take much added phosphorous fertilizer, with the proper timing and placement, to have a big effect on early-season development and yields," the agronomist said.

Later-season phosphorous deficiency has a much lower impact on wheat production than early-season phosphorous deficiency.

Gordon said the biggest response to phosphorous will come from placing the fertilizer with the seed -- either as a dry product, such as 11-52-0, or a liquid, such as 10-34-0.

Broadcasting P can also improve early-season wheat growth in some cases (especially on soils testing medium for Mehlich III or Bray-1 P). But, broadcasting is less efficient and requires a higher rate to obtain a similar response, making it more expensive.

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