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Iron Oxide Sink Method for Extracting Soil Phosphorus: Paper Preparation and Use
Author(s) -
Myers R. G.,
Pierzynski G. M.,
Thien S. J.
Publication year - 1997
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/sssaj1997.03615995006100050017x
Subject(s) - soil water , filter paper , desorption , sink (geography) , chemistry , analytical chemistry (journal) , mineralogy , adsorption , chromatography , geology , soil science , organic chemistry , cartography , geography
Since the FeO‐sink method to estimate plant‐available P in soils was first introduced in 1983, modifications have continued to improve the procedure. Recently FeO‐coated paper circles (5.5‐cm diam.) were used in place of the traditional 2 by 10 cm strips. The objective of this study was to more clearly describe the preparation and use of the FeO‐coated circles. We used Whatman no. 50 hardened filter paper (2.7‐µm pore openings). Standard methods for FeCl 3 treatment of the papers were used. After the papers had been air dried, one paper was secured between two 10 by 10 cm fiberglass screens. By simultaneously immersing stacks of 25 of these paper‐screen units in 2.7 M NH 4 OH for a 30‐s immersion time, 100 papers could be uniformly coated with FeO in about 10 min. Immersion times of 30, 60, and 180 s in NH 4 OH solution showed that papers immersed for 30 s in NH 4 OH solution extracted P as effectively as those immersed for longer times. One 5.5‐cm FeO circle was as effective as three circles in extracting P from most soils. A desorption model for soil P was used that can relate soil‐test P to desorption kinetics. In soils with maximum reversible P ranging from 25.1 to 106.5 mg kg −1 , desorption constants ranged from 0.141 to 0.232 h −1 with a mean of 0.191 h −1 . Low‐P soils released P slower than did high‐P soils. Such information may be of interest in assessing P availability in soils.