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ELECTRON‐SPIN RESONANCE OF HUMIC ACIDS FROM CULTIVATED SOILS
Author(s) -
CHESHIRE M. V.,
CRANWELL P. A.
Publication year - 1972
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1972.tb01673.x
Subject(s) - soil water , humic acid , chemistry , calcium carbonate , carbonate , environmental chemistry , soil science , geology , organic chemistry , fertilizer
Summary An examination has been made of the electron‐spin resonance spectra of humic acids from (i) two groups of cultivated soils from the north‐east of Scotland, and the related natural soils from which the cultivated soils are considered to be derived, and (ii) some Rothamsted soils. With the Scottish soils the humic acids from the more acid natural soils (pH <4.6) show e.s.r. spectra with a four‐peak structure (class I), and those of the less acid soils (pH >4.6) almost structureless spectra (class II). The cultivated soils contain humic acids with the same class of spectrum as that of the soils from which they are derived, even though they are now much less acid ( P H 5.9 –6.5). Humic acids from Rothamsted soils, sampled recently, were compared with those from the same site sampled 80 years previously. Where the soil has been allowed to revert towards a natural state but still contains free calcium carbonate the pH remained high (7.8–7.9) and the spectrum of the humic acid remains class II. Where the soil contained no free calcium carbonate the pH has fallen from 7.1 to 4.5 on reversion and the spectrum class of the humic acid has changed from II to I. The results support the hypothesis that the class of spectrum of the humic acid depends on the pH at which it is formed.