Premium
The Use of Nitroso‐R‐Salt in the Determination of Exchangeable Potassium in Soils
Author(s) -
Reed J. Fielding,
Mehlich A.,
Piland J. R.
Publication year - 1945
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/sssaj1945.036159950009000c0008x
Subject(s) - citation , chemist , salt (chemistry) , soil water , library science , chemistry , mathematics , environmental science , computer science , soil science , organic chemistry
M ANY methods are to be found in the literature for the determination of exchangeable potassium in soils. Yet when determination of exchangeable potassium is desirable, the choice of methods is usually a difficult one. Even after the choice of an extracting solution has been made, the method of determination to be applied to the extract must be decided. Since its introduction by Schollenberger (4) , ammonium acetate is rather widely used as an extracting solution and in this country has become almost a standard extractant for exchangeable potassium. On the other hand, there are some workers who prefer to use a dilute acid. Hydrochloric, nitric, and acetic acids are commonly used. Where it is desired to effect replacement by a bivalent cation, barium is often proposed and solutions of its salts are used as extractants. After extraction, most methods for determining the content of potassium involve precipitation as sodium potassium cobaltinitrite, although precipitation as the chloroplatinate is still preferred by some. After pre-; cipitation, the potassium, may be determined by gravimetric, turbidimetric, volumetric, or colorimetric methods. The gravimetric method is seldom used. Turbidimetric estimation is usually considered inaccurate. A volumetric method proposed by Volk (7), involving titration with permanganate, is in rather wide use. Among the most common colorimetric methods is one employing Nitroso-R-salt (disodium salt of i-nitroso2-hydroxy-3, 6-naphthalene disulfonic acid). This method has been described by Peech'(3). It was felt desirable to obtain some fundamental information on comparison of extractants and methods for the determination of exchangeable potassium in these extracting solutions. In this investigation three extracting solutions were studied, vis., ammonium acetate (i.o'N at pH 7.0) ; hydrochloric acid (.05 N) ; and barium chloride (0.2 N buffered with triethanolamine at pH 8.1) ( i ) . Methods for determining potassium in these ex, tractants were (a) precipitation as the chloroplatinate and colorimetric determination with potassium iodide; (b) precipitation with sodium cobaltinitrite •and determination by turbidimetric estimation.; (c) precpitation wth sodium cobaltinitrite and determi.nation by titration with permanganate; and (d) precipitation with sodium cobaltinitrite and determination colorimetrically by means of the Nitroso-Rsalt. For some undetermined reason the chloroplatinate method did not prove at all satisfactory. Results are therefore included only for the last three methods.