Deficiencies can be costly. McFarland said nitrogen may be the most challenging to manage since it changes and transforms after application and may be lost to soil leaching or into the atmosphere.

“We recommend a split application for wheat,” he said. “That way we make certain we have nitrogen available at peak demand and also minimize the potential for losses from heavy rainfall or other climate factors. Split applications also give us an opportunity to judge crop conditions and potential before we topdress so we can apply the most effective and most economical rate.”

Rate and timing also depend on crop use. Demand may be different for wheat intended for grain, grazing or as a dual purpose crop. Yield potential and available moisture also affect fertility rate.

McFarland said farmers should look deeper for residual nitrogen, especially if they planted and fertilized a crop last year and drought prevented typical production. “Nitrogen is very soluble and moves in the soil profile, so we recommend farmers sample deeper than the zero to six-inch depth they usually pull from.”

Nitrogen that has moved deeper into the soil profile is still available to the crop. Tests have shown substantial amounts of nitrogen as deep as 48 inches—from 78 to 210 pounds per acre, McFarland said. “At just 24-inch depths, we still find significant amounts of nitrogen available. With the current price of fertilizer, that may represent a significant savings.”

He said farmers who use residual nitrogen can decrease typical application rates by the amount identified and produce equal yields. “But farmers have to measure it to know how to adjust rates.”

Savings could range from $10 to more than $100 per acre, depending on the crop need and the amount of residual nitrogen available. “And that’s just for nitrogen; other nutrients are also found at depth. We recommend farmers consider deep sampling, especially if they put out fertilizer last year and had no crop to utilize it.”