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Clay‐Fixed Labeled Ammonium as a Source of Available Nitrogen
Author(s) -
Feigenbaum Sala,
Hadas Aviva,
Sofer M.,
Molina J. A. E.
Publication year - 1994
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/sssaj1994.03615995005800030049x
Subject(s) - soil water , clay minerals , ammonium , chemistry , nitrogen , organic matter , calcareous , environmental chemistry , nuclear chemistry , mineralogy , soil science , geology , organic chemistry , paleontology
In soils low in organic matter but high in clay mineral content, the fixation and release of NH 4 by soil clay may have a significant impact on available N, in addition to the organic N. The objective of this work was to evaluate the contribution that nonexchangeable NH 4 , newly fixed by clay minerals, may have in KCl‐extractable N in soil. The source of clay‐fixed NH 4 was beidellite clay equilibrated with ( 15 NH 4 ) 2 SO 4 and then washed with either KCl or CaCl 2 solutions. Two calcareous soils were mixed with differently treated beidellite at a 2:1 ratio, mixed with sand, and incubated for 56 d at 30°C and 60% of water‐holding capacity. Periodically, NH + 4 and NO − 3 extractable in 1 M KCl and their 15 N abundance were determined. Controls for each beidellite treatment were incubated without soil. Concentrations of KCl‐extractable N were considerably higher when beidellite was saturated with Ca than when it was saturated with K throughout the experiment. They increased with time in the presence of soil and remained unchanged in the controls. The recovery of beidellite‐ 15 NH 4 as KCl‐extractable N in soil showed a continuous release of clay‐fixed NH 4 from K‐beidellite, from 4.8 and 6.5% of added NH 4 at 1 d to 10.2 and 12.5% at 56 d in the two soils. The recovery of N from Ca‐beidellite was approximately 30% of added N already at 1 d, but the change with time was inconsistent in the two soils. The difference in the release of N from Ca‐saturated beidellite compared with that of K‐saturated beidellite was attributed to incomplete collapse of the mineral lattice in the Ca‐saturated clay, which enabled renewal of exchangeable NH 4 and rendered the interlayer nonexchangeable NH 4 more accessible to exchange with K or to biological activity. In K‐saturated clay, the interlayer nonexchangeable NH 4 was trapped and, consequently, the release was slow.