I. Fernandez et al., Thermal resistance to high temperatures of different organic fractions from soils under pine forests, GEODERMA, 104(3-4), 2001, pp. 281-298
Thermal resistance of the organic matter from two Humic Cambisols from the
NW of Spain, developed over granite and under pine forest, was determined b
y heating samples of the upper 5 cm of soils at 220 and 350 degreesC for 30
min, Unheated samples of the same soils were used as control. Lignin, holo
cellulose, lipids and water-soluble compounds as well as humic substances w
ere determined by different chemical fractionation methods. At 220 degreesC
, the losses of holocellulose exceeded 75%, this being the most vulnerable
organic fraction. At this temperature, the lipidic fraction exhibited diffe
rent thermal resistance in both soils, showing losses of 73% in one case an
d only 11% in the other. Lignin exhibited the lowest losses. increasing pro
portionally, Fulvic and humic acids decreased at 220 degreesC but humin exh
ibited a net increase. At 350 degreesC, holocellulose practically disappear
ed and lignin losses were significant, whereas lipid loss slightly increase
d compared with the loss observed at 220 degreesC All humic substances decr
eased at 350 degreesC, but humin was the most resistant humic fraction. Hea
ting the soils at 220 and 350 degreesC increased the Fe and Al extracted wi
th Na4P2O7 and NaOH and the percentage of humification of the remaining soi
l organic matter. (C) 2001 Elsevier Science B.V. All rights reserved.