LUBBOCK - Cotton farmers will want to be penny-wise with their nitrogen fertilizer this year, says a Texas Agricultural Experiment Station soil scientist.

"Gasoline prices at the pump are well over $2 per gallon, and diesel prices are going higher, too. The price of nitrogen fertilizer is following the same trend B going higher," said Dr. Kevin Bronson, Experiment station associate professor of soil fertility and nutrient management. "All fertilizer is more costly nowadays, but nitrogen prices are closely linked to the cost of natural gas B a key component in its manufacture."

Bronson is based at the Texas A&M University System Agricultural Research and Extension Center at Lubbock. He holds a joint appointment with the Experiment Station and Texas Tech University.

Urea ammonium nitrate currently costs 37 cents per pound of nitrogen, or about $235 per ton. That is almost 50 percent higher than the 21 cents per pound of nitrogen farmers paid in 1999 and 2002, he said.

"Given the price increase, farmers are asking if they should reduce their nitrogen application rates. The answer is no," Bronson said. "The optimum economic nitrogen rate is not sensitive to wide fluctuations in nitrogen prices. In other words, net returns per acre will decrease with higher nitrogen prices, but the most profitable nitrogen application rate remains the same.

"Based on research we have conducted here on the High Plains, the optimum target nitrogen supply for irrigated cotton is 120 pounds per acre for a two-bale-per-acre yield goal. For a 2.5-bale-per-acre yield goal it is 150 pounds of nitrogen per acre, and for three-bales-per acre it is 180 pounds. These targets are a combination of nitrogen fertilizer and existing soil nitrate."

So what's the best way to maximize returns from every dollar spent on nitrogen? Soil test, soil test, soil test. "Know what is out there to begin with, buy and apply what you need to make your yield goal, and put it where the plants can use it," said Jay Yates, Texas Cooperative Extension economist based at the Lubbock center. "The cost of a soil test is money well spent when fertilizer prices are rising."

Bronson recommends an annual winter or spring soil test for irrigated cotton fields. "Take multiple samples from each field with a shovel or probe, down to a depth of 24 inches. Then combine soil from all the samples into one composite sample," Bronson said. "Try to include equal amounts of soil from the upper and lower profile of each individual sample. Send the composite sample to a soil testing lab and ask for a nitrate nitrogen analysis.

"It's also a good idea to pull a composite sample from the top 6 inches of soil once every two or three years and have it analyzed for all other nutrients B such as phosphorus and potassium. A composite sample from about 6 inches deep is enough to accurately gauge these nutrients."

A soil test from the Texas A&M University Soil, Water, and Forage Testing Lab in College Station costs about $10. It includes basic nutrients, nitrate-nitrogen and fertilizer recommendations.

The lab is online at http://soiltesting.tamu.edu . Prices at commercial soil testing labs may be higher.

Bronson and Randy Boman, Extension cotton agronomist based at Lubbock, put together an on-line High Plains cotton nitrogen fertilizer calculator in 2003. The calculator resides on the Lubbock center's Web site: http://lubbock.tamu.edu under the "What's New" heading.

The online calculator combines the accuracy of a soil test with the utility of a desktop calculator. It is a basic spreadsheet that allows growers to enter up to seven production variables to generate a total recommended nitrogen fertilizer application rate, Boman said.

The 2004 High Plains cotton crop achieved high yields under higher-than-normal rainfall conditions B two factors which can deplete soil nitrate.

"Despite higher prices, nitrogen fertilizer requirements will probably increase this year on the High Plains," Bronson said.

Bronson, Boman and Eduardo Segarra, Experiment Station economist, recently posted a cotton fertilizer guide on the Lubbock center's Web site B also under the "What's New" heading. Segarra also holds a joint appointment with Texas Tech University.