Ammonium is extracted by shaking 3 g of moist soil with 30 mL of 2 M KCl for 30 min. After filtering, the extract is analyzed on a Lachat QuikChem 8500 Flow Injection Analyzer. In this method, the ammonium reacts with salicylate in the presence of nitroprusside (catalyst) to form an emerald green complex, which is measured colorimetrically at 660 nm. [Nitrate and nitrite can also be determined from the 2 M KCl extract.]
NOTE: Extraction of moist and frozen samples by manual crushing and sieving is done to prevents changes in levels of ammonium and sometimes nitrate that occur upon drying. The higher the clay content, the more difficult it is to crush and sieve wet, frozen samples. It is recommended that such samples be broken up and mixed as much as possible before freezing. Moisture content also needs to be determined on these samples in order to express the results on a dry weight basis.
(Extraction: Ref. No. 6, Analysis: Ref. No. 7 - Method References)
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