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Release of NH 4 + in Soils by Oven Drying
Author(s) -
Frye W. W.,
Hutcheson T. B.
Publication year - 1981
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/sssaj1981.03615995004500050014x
Subject(s) - soil water , chemistry , significant difference , environmental chemistry , mineralogy , soil science , geology , mathematics , statistics
There is often a pronounced increase in exchangeable NH 4 + content when soils are dried, particularly when oven‐dried. The origin of the NH 4 + is unknown. The objectives of this study were ( i ) to determine the effects of oven drying on the release of NH 4 + in soils with different properties, and ( ii ) to evaluate possible sources that may account for the release. Samples form the Congaree, Davidson, Huntington, and Maury soils were oven‐dried at 110°C for 24 hours and analyzed for 2 N KCl‐extractable NH 4 + (exchangeable NH 4 + ) and NO ‐ 3 . Values for moist samples of soils were subtracted from values for oven‐dried soils to determine the amounts of NH 4 + released by drying. The amounts ranged from 5 to 20 ppm N, with the greatest amounts released from the top 30 or 45 cm of the Davidson and Maury soils. Generally, the amount of NH 4 + released by oven drying decreased with depth in the soils. Monochloracetic acid (CH 2 ClCOOH) extracted more NH 4 + than did KCl from oven‐dried surface samples of the Congaree and Davidson soils, but there was little or no difference in the amounts of NH 4 + extracted by the two solutions from moist samples of Ap horizons or from samples below the Ap horizons, whether moist or oven‐dry. These results suggest an organic source of NH 4 + in the Ap horizons. The relatively large amount released from deep in subsoils suggests the presence of an inorganic source also. We conclude that NH 4 + is released from both organic and inorganic compounds during oven drying. Nonexchangeable NH 4 + in interlayers of clay minerals usually increased with oven drying. We therefore conclude that nonexchangeable NH 4 + is not a source of released NH 4 + . In fact, some of the NH 4 + released by oven drying appears to be simultaneously fixed as nonexchangeable NH 4 + in certain cases. The organic source of NH 4 + is probably several constituents of rather highly decomposed soil organic matter. The inorganic source is thought to be NH 4 + ‐phosphate complexes, perhaps taranakite‐like compounds. Further research is needed to identify specific sources.