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Nitrogen strips may help determine fertility needs

Figuring out what do about rising nitrogen prices feels like one of those enigmas wrapped in a conundrum or two.

Farmers know that cutting back on fertility, without adequate soil reserves, may reduce costs but also will cut into yield and profit potential. They also see low commodity prices, soaring energy costs and shrinking income.

The key, say Oklahoma State University soil scientists, is applying what's needed to meet realistic yield goals, and no more. The catch is the knowing part.

Bill Raun, at a recent field day on the Oklahoma State University's Southwest Research and Extension Center in Altus,, said a combination of economic and environmental incentives should encourage farmers to be more meticulous about applying nutrients to cotton and other field crops.

“Nitrogen fertilizer prices will go higher,” Raun said. “Natural gas cost is the key.”

The first step, he said, would be to take soil tests. “But we don't have 100 percent adoption of soil tests that only cost $10. That's a good investment.”

Not taking advantage of that bargain, he said, may mean farmers are not considering excess nitrogen in their soils. He also recommended testing at two-foot depths to identify nitrogen available to root systems.

“Excess nitrogen is money in the bank,” he said.

And it's not just the economics. He said in 20 years farmers will find themselves under even more scrutiny about soil stewardship than they are today. “It may be like a CSI for the environment,” he said. “We'll be able to determine if an individual farmer is a good steward or not.”

He allows that most are, but that many can do better jobs of using that extra bit of nitrogen in the soil.

And soil tests alone may not be enough to determine how much residual remains from past crops or other sources. Raun quizzed two trailer loads of field day participants to determine how much and how they fertilized cotton for certain yield goals.

He said split applications make the most sense and he recommended zero nitrogen strips, areas where farmers apply no additional nitrogen fertilizer and then watch plant response closely.

If the strip keeps up with the rest of the field, residual nitrogen may be adequate to make the crop or at least to reduce nitrogen demand.

“It's smart business and better than a soil test,” Raun said. “Soil tests do help but these strips provide a litmus test and farmers can still apply 40 pounds of nitrogen in mid-season if it's needed. If farmers see no difference between the zero strips and the rest of the field, additional nitrogen may not be needed.”

Raun said farmers pick up nitrogen from rainfall, irrigation water and from “nitrogen mineralization of organic matter. In wet summers, we get enough nitrogen mineralization to make a difference.

“Check the strip and get an idea of how much nitrogen the environment is providing for free.”

Soil scientist Kyle Freeman discussed nitrogen-rich strips as a means of determining fertility needs. Most of his work has been in wheat but he says the concept applies to other crops.

Freeman reduces pre-plant nitrogen application on all but a strip in the field.

“That strip will tell us how much nitrogen we need,” he said.

Freeman said most farmers figure they need about 2 pounds of nitrogen for every bushel of yield goal. “The danger is to put all that nitrogen out pre-plant, regardless of environmental conditions. The risk is up front. Our goal is to reduce that front-loaded risk.

“Response to nitrogen fertilization varies from year to year and higher nitrogen rates do not always return the highest yields.”

He uses a sensor (Green Seeker) in mid-season to measure nitrogen response in representative areas of the field. “We make nitrogen recommendations based on the nitrogen-rich strip. If we recognize a need for nitrogen in mid-season, we can apply it.”


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