EDAFOLOGIA, Vol. 11 (3), pp. 275-278, 2004
PYROLYTIC AND SPECTROSCOPIC APPROACHES TO THE STUDY OF REFRACTORY FORMS OF ORGANIC CARBON. SOILS AFFECTED BY FIRES.
1F.J. GONZÁLEZ-VILA, 1J.A. GONZÁLEZ; 1O. POLVILLO, 2G. ALMENDROS, 3H. KNICKER
1Instituto de Recursos Naturales y Agrobiología, CSIC, P.O. Box 1052, 41080 Sevilla, 2Centro de Ciencias Medioambientales, CSIC, Serrano 115 bis, 28006 Madrid, Spain 3Lehrsthul für Bodenkunde, TU München, 85350 Freising-Weihestephan, Germany
Vegetation fires and fuel-wood combustion transfer carbon from the relatively fast biolo- gical-atmosphere carbon turnover to the long-term geological one, the processes in which biomass burning is involved, may represents a significant sink for carbon dioxide. The so-called “black coal”, is composed mainly of polyaromatic and relatively inert carbon forms. In this work, the composition of the potential re- fractory carbon forms present in the different soil particle fractions of a pine forest soils from Sierra de Az- nalcollar, Seville, Spain affected and unaffected by a wildfire is described using pyrolytic (Py-CG/MS) and spectroscopic solid state 13C NMR techniques. An enrichment in total carbon was found for all particle size fractions in the fire affected soil, with the lowest enrichment factor in the sand-size fraction (1.4) and the highest in the coarse silt-size (2.8) and clay-size fractions (2.7). When analysing the pyrograms of the fo- rest soils affected by fire, most pyrolysis products present in undisturbed natural soils disappears and the do- minance of charred “non pyrolyzable” refractory carbonous material is clear. The formation of condensed refractory materials after the wildfire is again apparent in the solid-state 13C NMR spectra, showing a neat increase in the intensity of the aromatic C region (160 to 110 ppm), which occurs at the expenses of the O- and N-alkyl C region (110 to 60 ppm). This together with other evidences, indicates that the increase in C observed in all size fractions of the fire affected soil is mainly due to the formation of refractory, polyaro- matic and relatively inert carbonaceous (Black coal) material, rather than to the input of fresh litter after the fire event.
Key words: soil size fractions, carbon sequestration, refractory carbon, Py-GC/MS, NMR