ABILENE – There are several tools small grain producers can use to gauge the nitrogen use efficiency of their crop and achieve a savings in production costs, said a Texas Cooperative Extension small grains specialist.

"When we look at production inputs, we need to put them in two categories," said Dr. Gaylon Morgan, Extension agronomist based at College Station. Morgan spoke at the recent Big Country Wheat Conference in Abilene. "There are yield-building inputs and yield-preserving inputs.

"Nitrogen fertilizer could fall into both categories, but we chiefly use and manage it as a yield-builder. More important is nitrogen use efficiency."

Wheat has an average nitrogen use efficiency of 33 percent, he said. In other words, about 33 percent of applied nitrogen is used by the plant to produce grain. The U.S. consumes about 7.3 million pounds of nitrogen fertilizer annually.

"So if we can improve our nitrogen use efficiency, we could achieve a potentially significant savings in nitrogen costs," Morgan said. "But how do we do that ... what tools do we need?"

Producers who grow wheat, for example, should rely on soil tests to gauge actual available nitrogen for a crop and consider their crop's realistic yield potential before applying nitrogen, he said. Soil test results matched to yield potential and the producer's yield goal can help ensure that nitrogen is applied according to crop need and not prevailing tradition.

"Our current thinking and our current recommendation for nitrogen fertilizer is 2 pounds per acre for each bushel in your yield goal," Morgan said. "Breeders are working to produce new varieties with higher nitrogen-use efficiency. Even so, we can do a better job with the genetics available today.

"We can better assess the crop's true nitrogen need and time the application of fertilizer to coincide with critical growth times."

Winter wheat, for example, needs little nitrogen in the fall. Producers who want to guarantee nitrogen availability for wheat roots should assess their crop's nitrogen need in late winter or early spring ... possibly in February, he said.

"If you time nitrogen application to coincide with wheat's late winter and early spring growth, you can determine the needs of the wheat crop and probably use a lower fertilizer rate while achieving the same or higher yields that a higher fertilizer rate will provide," Morgan said. "This spring top-dress application allows you to assess the crop's yield potential and match the nitrogen fertilizer rate to the yield potential."

One good way to gauge nitrogen need in early spring is to visually assess crop/plant growth in nitrogen test strips – strips in the wheat field where producers can experiment with different fertilizer rates and combinations. This provides the producer a visual reference of the crop's needs and how much nitrogen fertilizer should be applied for the top-dress application.

"You can readily see how the crop is doing and how it responds to different application rates," Morgan said.

Producers seeking a higher-tech approach to gauging nitrogen needs can use sensors to help them develop "prescription" fertilizer rates and applications, he said.

"Dr. Jeff Edwards, Oklahoma State University Extension small grains specialist at Stillwater, Oklahoma, has done a lot of good work on precision and variable rate nitrogen application," Morgan said. "Their variable-rate nitrogen tests use optical sensors to measure plant biomass, which tells them how much crop is out there and what condition it is in.

"They use sensors in conjunction with nitrogen-rich test strips and visual assessments. They even have a sensor-based nitrogen calculator available online."

The Oklahoma State University Extension wheat fertility Web site is at: http://www.wheat.okstate.edu/fert/index.htm .

Hand-held optical sensors are available commercially for about $3,500, while those suitable for use on fertilizer application machinery are more expensive, Morgan said. Edwards' work indicates that the cost of optical sensors can be recovered in a year or so through savings achieved in nitrogen costs and application costs, he added.

"OSU Extension has logged a nitrogen cost savings of $12.11 per acre using nitrogen test strips and optical sensors," Morgan said. "But it may be higher. The indirect savings, or value, of a correct nitrogen rate probably varies from $18 to $30 per acre.

"It's certainly not a silver bullet, but these tools can help us achieve a higher nitrogen use efficiency by tailoring fertilizer applications to actual plant needs. That could save input dollars and allow us to be more specific and efficient with our nitrogen fertilizer. We can adjust rates by field or crop condition."

Producers who grow wheat for grain and grazing can also use optical sensors as part of their fertility strategy but may have to make slight adjustments in when crop assessments are made, he added.

"Grazing removes biomass ... the cows/calves eat the plant material that's out there," Morgan said. "Because the sensors measure available biomass, you fence off an area in late winter and wait about two weeks after you terminate grazing to assess crop condition with optical sensors or nitrogen strips."