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Nonexchangeable Ammonium and Potassium Determination in Soils with a Modified Sodium Tetraphenylboron Method
Author(s) -
Cox A. E.,
Joern B. C.,
Roth C. B.
Publication year - 1996
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/sssaj1996.03615995006000010019x
Subject(s) - chemistry , soil water , potassium , ammonium , sodium , nuclear chemistry , inorganic chemistry , mineralogy , geology , soil science , organic chemistry
The mechanism of NH + 4 and K + fixation by clay minerals is similar, yet different analytical methods are used to estimate nonexchangeable (fixed) amounts of these nutrients in soils. Sodium tetraphenylboron (NaBPh 4 ) facilitates the release of nonexchangeable NH + 4 and K + by precipitation of these ions as NH 4 BPh 4 and KBPh 4 . A NaBPh 4 method was modified and evaluated as a common procedure for determination of nonexchangeable NH + 4 and K + in 10 midwestern soils that were either untreated or NH + 4 − or K + ‐saturated (treated with 2 M solutions of NH 4 Cl or KCl to saturate fixation sites with NH + 4 or K + ). Experiments were conducted to evaluate Cu 2+ (CuCl 2 ) as a substitute for Hg 2+ (HgCl 2 ) in the recovery of NH + 4 and K + released by NaBPh 4 in soils. A 7‐d incubation with the modified NaBPh 4 method (CuCl 2 instead of HgCl 2 ) released most of the NaBPh 4 ‐ extractable NH + 4 and K + . In untreated soils, the NaBPh 4 method extracted 71% of NH + 4 released by the conventional HF/HCl method. Nonexchangeable NH + 4 release by both methods was related in untreated ( r 2 = 0.98) and NH + 4 ‐saturated ( r 2 = 0.95) soils. Recently fixed NH + 4 in the NH + 4 ‐saturated soil was equally accessible to both methods. The NaBPh 4 method extracted up to 10 times more nonexchangeable K + than the conventional 1 M HNO 3 method in both the untreated and K + ‐saturated soils. Recently fixed K + in the K + ‐saturated soil was equally accessible to both methods, except in high‐fixing soils where K + was held too strongly to be released by HNO 3 . The results show that the modified NaBPh 4 method can be used as a common procedure to estimate nonexchangeable forms of both NH + 4 and K + .