Estimation of charcoal (Char) in soils
1999
Skjemstad, J.O. | Taylor, J.A. | Smernik, R.J.
A method for the semiquantitative estimation of charcoal (char) in soils is reported. The technique, performed on the <53 micrometer fraction of soils, utilizes the highly aromatic nature of char and its relative stability to two hours of high energy ultraviolet photo-oxidation compared to other soil carbon fractions. The proportion of char in the <53 micrometer fraction is estimated as the aromatic carbon (C) content measured by solid-state nuclear magnetic resonance spectroscopy using cross polarization and magic angle spinning. Corrections are made for the underestimate of aryl C by the cross polarization method in highly condensed aromatic char structures and for the small lignin content that occurs in some samples. Evidence is also provided for the occurrence of >90% of soil char in the <53 micrometer fraction. Because of the assumptions used, estimates of char by this approach must be considered to be semiquantitative, but are conservative and provide estimates of the minimum char content of a soil.
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