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Wiley, Soil Science Society of America Journal, 4(79), p. 1237-1242, 2015

DOI: 10.2136/sssaj2015.02.0061n

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Improving Nitrite Analysis in Soils: Drawbacks of the Conventional 2 M KCl Extraction

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This paper is available in a repository.

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Abstract

Soil nitrite (NO 2-) is an important source of nitrous acid to the atmosphere as well an intermediate in nitrification and denitrification. Few studies, however, have directly linked NO 2-pools with N emissions because NO 2-is reactive and seldom detectable in soils. Here, we test whether the elusiveness of soil NO 2-is due to its reactivity or to problems associated with conventional 2 M KCl extractions. We extracted acidic, neutral, and alkaline soils (pH 5.4– 8.2) in 2 M KCl, pH-8-adjusted 2 M KCl, and deionized water (DIW). Unbuffered KCl consistently underestimated soil NO 2-compared with DIW; soils with lower pH had lower NO 2-in unbuffered KCl than in DIW water. In acidic soils, unbuffered KCl favored the transformation of NO 2-to nitric oxide. Because KCl lowers the pH of extracts by ~1 unit, this increase in acidity likely favored the transformation of NO 2-to gaseous N products. Although buffered KCl minimizes NO 2-destruction , it can cause colorimetric interferences when done on small soil samples (4 g). Deionized water extractions offer an alternative for measuring NO 2-in small samples, but filtering beyond the traditionally used 2.5-mm filter paper is necessary to remove suspended solids. Despite its widespread use, unbuffered 2 M KCl should not be used for the analysis of soil NO 2-. Abbreviations: DIW, deionized water; DTPA, diethylenetriaminepentaacetic acid; EDTA, ethylenediaminetetraacetic acid; NED, N-(1-naphthyl)-ethylenediamine dihydrochloride; SOM, soil organic matter.