Comparison of humic fractions of Chernozemic and Luvisolic soils by elemental analyses, UV and ESR spectroscopy, A

Abstract

The Ah horizons of a Brown–Dark Brown–Black–Dark Gray–Gray Luvisolic sequence of Canadian grassland and forest soils were studied. Clay-associated humus was present in greater proportions in the grassland than in forest soils, particularly in the grassland soils of the more arid regions. Amounts of alkali-pyrophosphate-extractable humus increased in the Brown to Gray Luvisolic sequence. Alkali-pyrophosphate-extractable humic acid (HA-A) contents were greatest in the Black and Dark Gray soils. C:H ratios, extinction coefficients at 280 nm (E280), and resistance to acid hydrolysis of the HA-A and clay-associated HA-B increased in the Brown to Gray Luvisolic sequence. Free radical concentrations were least for the Brown and Dark Brown soils, moderate for the Black and greatest for the Gray Luvisolic soils. The data suggest an increase in the proportion of aromatic components in the humic acids in going from the Brown to the Gray Luvisolic soils. An objective, multivariate similarity analysis based on 22 humus characteristics showed a relationship between soil zone or soil environment and the nature of the soil's humus.