Results of a three-year study on nitrogen sources at Jackson, Tenn., showed that ammonium nitrate produced higher winter wheat yields there than did either urea or UAN solutions. The study, which began in 1997, was conducted by Donald D. Howard at the University of Tennessee and was sponsored by Mississippi Chemical Corporation.

It compared ammonium nitrate, urea and UAN solutions as nitrogen sources for top-dressing wheat. Three-year data showed winter wheat yields were consistently higher where ammonium nitrate was used.

In the study, yield averages across the three nitrogen sources increased incrementally with nitrogen rates, up to a maximum of 67 bushels per acre with 150 pounds per acre of spring-applied nitrogen. However, when ammonium nitrate was applied, yields were increased up to 90 pounds per acre, indicating a greater efficiency of this nitrogen source, Mississippi Chemical said.

Across nitrogen rates, yield averages showed ammonium nitrate yielded the most - 48 bushels per acre - while the other nitrogen sources, urea and UAN solutions, yielded 42 and 38 bushels per acre, respectively.

The nitrogen research project was designed to determine yield differences of nitrogen sources in west Tennessee during the spring top-dressing season. Yield, disease severity, flag leaf nitrogen concentration, nitrogen uptake, grain moisture and test weight were measured in the study.

"This test site (Jackson, Tenn.) was selected because of the climate," Howard said. "Tennessee is a pivotal state for temperatures and moisture conditions for urea volatilization. These are two important factors in volatilization losses from urea-containing fertilizers. Since volatilization of urea begins as temperatures rise above 60 to 70 degrees F, we knew that if ammonium nitrate was a superior nitrogen source in Tennessee, the results should apply to the entire Mid-South region.

"We can make several recommendations to growers based on the nitrogen source study results," said Howard. "The average yields of the study showed ammonium nitrate produced higher yields at a much lower nitrogen rate than the other sources. This saves the producer money and protects the environment."

The time of nitrogen top-dressing of wheat was also studied. Dates of application in the month of March produced higher yields than did February or April applications. "It appears it is best to top-dress nitrogen in March, but early is better than late," Howard said. "In this area, the ideal application time is at five to six on the Feekes growth scale."

Working with growers in western Tennessee, Mississippi Chemical field sales representative Jim Harrelson experienced similar results in testing of nitrogen sources on wheat.

"In our two years of tests, we have found that ammonium nitrate is a more effective source of nitrogen for wheat growers in this part of the country," Harrelson said. "Even though UAN solutions are less expensive, the yield increases with ammonium nitrate have proved to be worth the extra cost and extra application." Plots fertilized with ammonium nitrate yielded 67 bushels per acre and those fertilized with UAN solution yielded 63 bushels per acre.

Bob Thompson, manager of agronomic services for Mississippi Chemical, plans to use the University of Tennessee nitrogen source study results in educational programs for fertilizer dealers, agricultural consultants and field salesmen.

"When useful information comes from a credible, thorough study such as this, we want to educate growers in the latest scientific findings and effective growing methods," Thompson said. "This study on nitrogen sources could mean the difference between profit and loss for some growers."

Diazinon, a leading insecticide in U.S. agriculture for more than 40 years, will continue to be available to U.S. farmers under an agreement reached between Makhteshim-Agan of North America, Inc., Syngenta Crop Protection USA and the U.S. Environmental Protection Agency.

Under the agreement, major agricultural uses will be retained, while indoor and homeowner uses will be eliminated or phased out over the next several years. Indoor uses will be canceled by March 2001. Lawn, garden and turf uses will no longer be allowed after December 2004.

About 40 crops will continue to be supported, including all trees and vines and some vegetables. In addition the USDA IR4 will continue to work with MANA to support additional minor uses of diazinon.

"Makhteshim-Agan is committed to the diazinon business in the United States and throughout the world," said Musa Givon, president of Makhteshim-Agan of North America. "We see many years of life left in diazinon in the agricultural markets because it is a valuable, effective and safe product. We have strong commitments to diazinon, including recent and substantial investment in production facilities. We will also continue to generate health and safety data to support diazinon and insure that it continues to meet the standards of the FQPA."