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Determination of Nitrate and Exchangeable Ammonium in Soil Extracts by an Ammonia Electrode
Author(s) -
Siegel R. S.
Publication year - 1980
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1980.03615995004400050013x
Subject(s) - chemistry , ammonia , reagent , ammonium , soil water , nitrate , electrode , nuclear chemistry , inorganic chemistry , soil science , environmental science , organic chemistry
A method for determination of NO 3 ‐ in waters using an NH 3 electrode was adapted for use with soils. Nitrate was determined in 1 N KCl soil extracts as the difference in NH 3 ‐N concentration between aliquots treated with NaOH and Devarda's alloy to reduce NO 3 ‐ and aliquots made alkaline without addition of Devarda's alloy. The rate of reduction of NO 3 ‐ to NH 3 was temperature dependent. The minimum recommended temperature for the procedure is 23°C. Rate of NH 3 loss from solution and NH 3 activity measured by the NH 3 electrode increased with temperature. Nitrate‐N in extracts of nine Illinois soils determined with the NH 3 electrode was highly correlated ( r 2 = 0.999***) 3 with NO 3 ‐ ‐N analyzed by the phenoldisulfonic acid method. Exchangeable NH 4 + ‐N determined with the modified electrode filling solution was highly correlated ( r 2 = 0.99***) with exchangeable NH 4 + ‐N determined by steam distillation. In addition to NO 3 ‐ , NO 2 ‐ is reduced to NH 3 by this procedure. Recovery of added NH 4 + , NO 3 ‐ , and NO 2 ‐ was 97, 97, and 91%, respectively. Precision of NO 3 ‐ and exchangeable NH 4 + determinations were 0.2 and 0.1 mg/kg, respectively. The reagents used are relatively inexpensive and safe to handle, and reduction is carried out at room temperature. Only 20 ml of soil extract is required and soils containing 1 to 250 mg NO 3 ‐ ‐N/Kg can be handled routinely. One worker can analyze 80 extracts/day.