Overview of technique
This method describes the extraction of nitrogen as ammonium from soil by potassium chloride (KCl) extraction using Soil Science Society of America Methods of Soil Analysis section 33-3 and colorimetric analysis using APHA 4500-NH3 G.
A 4-g aliquot of homogenized moist material is shaken for 1 hour with 20 mL of 2 molar KCl at room temperature in plastic centrifuge tubes. The tubes are centrifuged for 10 minutes at 3000 rpm and the supernatant is pipetted into scintillation vials. Each nitrogen form (NH4-N and NO3-N) is analyzed by continuous-flow colorimetry. Concentration is calculated by multiplying the colorimetrically-measured N-value by the volume of added KCl extract and divided by the wet weight of the sample. Nitrogen content per dry mass requires additional processing available for a fee upon request.
Keeney, D. R. and D. W. Nelson. 1987. Nitrogen–Inorganic Forms, sec. 33-3, extraction of exchangeable ammonium, nitrate, and nitrite. pp.648-9. In A. L. Page et al., eds., Methods of Soil Analysis: Part 2, Chemical and Microbiological Properties. Agronomy, A Series of Monographs, no.9 pt.2, Soil Science Society of America, Madison, Wisconsin USA.