Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: March 29, 2006
Publication Date: August 10, 2007
Citation: Olk, D.C. 2007. Organic Forms of Nitrogen. In: Carter, M.R., Gregorich, E.G., editors. Soil Sampling and Methods of Analysis. 2nd Edition. Boca Raton, FL: Taylor & Francis Group, CRC Press. p. 667-674.
Interpretive Summary: Nitrogen (N) is essential to crop growth. Most nitrogen in the soil is bound in stable organic molecules. Some of this organic nitrogen is slowly released from the organic molecules as inorganic forms that are immediately available to the crop. This inorganic pool is a vital supply of nitrogen to a growing crop. Identification of the chemical structures of the organic nitrogen molecules would allow better understanding of the gradual release of organic N and contribute to improved management of this large nutrient pool. However, current laboratory analyses allow identification of only half of all organic nitrogen molecules in soil. A newly developed laboratory analysis identifies more than 80 percent of all organic nitrogen molecules in soil. This report explains the steps and analytical instruments that are involved in the new procedure. Use of this procedure will enable scientists to better understand the factors of nitrogen cycling in the soil, possibly leading to more precise fertilizer rates and less environmental contamination by excess nitrogen.
The classical procedure for identifying the chemical forms of soil nitrogen (N) involves extraction of soil N with 6 M HCl. This procedure identifies only about half of total soil N, a shortcoming that has limited our management of soil N. A newly developed procedure identifies more than 80 percent of total soil N as 17 amino acids, two amino sugars and ammonium. Soil is extracted by methanesulfonic acid and for shorter times than in the HCl procedure. Forms of organic N in the extract are separated by ion chromatography and identified by pulsed amperometry. This report explains the procedure for extracting soil samples and preparing extracts for analysis.