Analytical and physical characteristics of humic substances in relation to vegetation on three alfisols in Greece

Abstract Humic and fulvic acids were extracted from the surface horizons of three Alfisols under oak, erica and grass, respectively. These profiles are in the thermomediterranean climatic zone. The extracted humic substances were characterized by elementary and functional group analyses, IR-spectroscopy and differential thermal analysis (DTA). Some differences in the humic substances are associated with the types of vegetation. Humic acids (HA's) have higher contents of carbon, greater thermal stability and lower total acidity in the Al horizon under grass than in those under oak and erica. The fulvic acid (FA) of the Ao horizon under erica has the highest carbon content. The FA in the Al horizon under grass has more phenolic than carboxylic groups, whereas the reverse is true under erica and oak. The FA's have resolved exothermic peaks at higher temperature in the horizons under erica than under oak and grass. The IR-spectra of the HA's and the FA's, under all three types of vegetation, are generally similar. Such differences as noted correspond to those between spectra of HA's and FA's high and low in ash content. The slope between 2500–1800 cm −1 in the spectrum of the purified HA of the Al horizon under grass was greater and more continuous than in the spectra under oak and erica.