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Nitrite Transformations during Soil Extraction with Potassium Chloride
Author(s) -
Stevens R. J.,
Laughlin R. J.
Publication year - 1995
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/sssaj1995.03615995005900030044x
Subject(s) - chemistry , soil water , nitrite , extraction (chemistry) , dilution , potassium , decomposition , environmental chemistry , chloride , chromatography , nitrate , soil science , environmental science , physics , organic chemistry , thermodynamics
Nitrite is a key intermediate in both NH + 4 oxidation and NO − 3 reduction. There is increasing concern over its origin and significance in food and water. Measuring NO − 2 concentrations in soils requires extraction procedures, KCl (2 M ) being the most commonly used extractant. We investigated the effect of soil/extractant ratio, extraction procedure, shaking time, and pH on the transformations of 15 NO − 2 from a range of grassland soils. We measured the recovery of NO − 2 and 15 N as 15 NO − 2 or 15 NO − 3 . Nitrite destruction and pool dilution occurred at 1:10 and 1:1 soil/extractant ratios. Using a 1:1 soil/extractant ratio, average 15 NO − 2 recovery for six soils was 86% with a blending procedure (10 min), and 32% with a shaking procedure (70 min). About two‐thirds of the 15 NO − 2 lost during extraction appeared as 15 NO − 3 . When the pH of the soil suspension was adjusted with KOH to 7.8, recovery of NO − 2 was not significantly less than 100% for reaction times up to 40 min. Pool dilution and decomposition of NO − 2 appeared to be due to chemical rather than microbial reactions. When 20 soils were tested using the blending procedure and extractant pH of 8.0, 14 gave recoveries >97% and an additional six gave recoveries >90%. One of the mineral soils giving >97% recovery was extracted at two pH values, and NO − 2 stability measured in filtered extracts during 28 d of storage at 4°C. Nitrite was more stable in extracts at pH 5.6 than 8.0. To ensure at least 95% recovery of 15 NO − 2 , extracts at pH 8.0 had to be filtered through a 0.7‐µm filter and analyzed within 2 d of extraction.