It’s been an Extension mantra for decades but “get a soil test,” remains one of the most important activities farmers can perform to manage a fertilization program. “Soil testing gives us the ability to develop a prescription system field-by-field,” McFarland says.

With the likelihood that many growers have nutrients carried over from failed or poorly yielding crops last year, a soil test is a good bargain for 2012 management. “Farmers need to identify carryover and naturally-occurring nutrients. Also, available organic matter breaks down and releases nutrients back into the soil.”

He says some crop fertility programs may require up to $200 per acre. “Residual fertilizer may be worth more now than when growers applied it because of the higher price,” he says. But it’s not going to reduce fertilizer expense if they don’t know it’s there. “It’s important to identify what’s already there and determine what else is needed for balanced nutrition. Growers need to avoid deficiencies, too.”

By the time producers identify nutrient deficiencies the crop has already suffered potential yield loss.

Typical soil test recommendation is to collect samples from zero to 6 inches deep. “That gives us a prescription for each field,” McFarland says. “It should be routine and it’s not complicated.”

But that may not be enough this year. Nitrogen is the nutrient growers are most likely to spend the most money for. “It’s soluble and very mobile. With rain, it moves below that zero to 6-inch area. And we know that crop roots will explore down to 24 inches to find nutrients.”

The question is: How deep do nutrients go into the soil and how deep can the crop reach it? McFarland and other Extension specialists set up trials to answer those questions and tested soil as deep as 4 feet.

“The results showed us that we have a lot of available nitrogen at depth. In some areas we found as much as 400 pounds per acre, and residual nitrogen at depth was consistent all across the state.

“So, can the crop use it?”

They set up a study and found that in most locations in soils that had sufficient nitrogen at depth cotton needed “little to no additional fertilizer to make yield goals. Out of 55 locations across the state, 33 had more than 100 pounds of nitrogen available at depth. Only 13 of those 55 locations responded to extra fertilizer.”

He says most growers will not sample to 4 feet. “But if they can get to 1 foot or 24 inches, they can take advantage of residual nitrogen. A good amount of nitrogen is available at that level.”

He said trials in grain showed similar results. Trials from 2010 showed residual nitrogen at 1 foot to 24 inches, resulted in the same corn yield response as if the grower applied the full rate of fertilizer, based on his yield goals.

“If we find 80 to 120 pounds of nitrogen in the soil, we cold back off by that amount and lose no yield and still save the money we would have spent for the extra fertilizer.”