Methods of Analysis for Nitrate in Forages

Recently, much of the U.S. has been under drought conditions. Lack of water has limited the availability and quality of normal forages. In addition, livestock producers have often been forced to utilize alternative roughage sources. During normal years, nitrate-nitrogen (NO3-N) is taken up by plants and quickly converted to protein. When forages grow under drought stress, however, they tend to accumulate nitrate. Alternative forages may accumulate even higher levels of nitrate than normal forage crops. Nitrate-nitrogen in excess of 1400 ppm is generally considered potentially toxic to livestock. A recent survey of samples sent in to the Servi-Tech Laboratories indicated an average of 2200 ppm and a range of <100 to> 13,000-ppm NO3-N in forages. Accurate determination of NO3-N is crucial for management of such forages. Numerous methods of analysis for nitrate in forages are available to the forage-testing laboratory. Several of the most common methods will be discussed, addressing both the accuracy and precision of methods. Interpretation information will be presented to allow laboratories to consult with their clients on the management of nitrate-containing forages. Finally, recommendations for a standard reporting format will be made.