This method involves the extraction of nitrate (NO3-N) and ammonium (NH4-N) from soils using an equilibrium extraction with 2.0 N KCl solution. Nitrate is determined by reduction to nitrite via a copperized cadmium column. The nitrite is then determined by diazotizing with sulfanilamide followed by coupling with N-(1-naphthyl) ethylenediamine dihydrochloride. The absorbance of the product is measured at 520 nm. Ammonia is determined by heating with salicylate and hypochlorite in an alkaline phosphate buffer. The presence of EDTA prevents precipitation of calcium and magnesium. Sodium nitroprusside is added to enhance sensitivity. The absorbance of the reaction product is measured at 660 nm and is directly proportional to the original ammonia concentration. Extracts can be stored for up to three weeks at low temperature (<4°C) or frozen. The method has a detection limit of approximately 0.10 ppm (on a soil basis). The results of analysis of un-dried soil are reported on a dry soil basis.
Sample amount requested: 20 g for nitrate and/or ammonium. Please contact the Analytical Laboratory with questions concerning limited sample.
Hofer, S. 2003. Determination of Ammonia (Salicylate) in 2M KCl soil extracts by Flow Injection Analysis. QuikChem Method 12-107-06-2-A. Lachat Instruments, Loveland, CO.
Keeney, D. R. and Nelson, D. W. 1982. Nitrogen-inorganic forms. pp. 643-698. In: A. L. Page (ed.) Methods of soil analysis: Part 2. Chemical and microbiological properties. ASA Monograph Number 9.
Knepel, K. 2003. Determination of Nitrate in 2M KCl soil extracts by Flow Injection Analysis.QuikChem Method 12-107-04-1-B. Lachat Instruments, Loveland, CO.