Farming systems strongly affect soil humus. In this study some humus characteristics were used to compare the humus quantity and quality under two different farming systems. The field experiment was established in 1990 on an Orthic Luvisols in Slovakia. A higher content of organic carbon (C_T) in topsoil (13.1 g·kg^-1) was recorded in soil under ecological farming where only organic manures were applied rather than in topsoil from integrated farming (12.5 g·kg^-1) where both organic and inorganic fertilisers were applied. The quality of humus (HA : FA ratio) was similar in soils under both farming systems. Humic acids (HA) were isolated and analyzed for elemental composition, UV–VIS spectra and thermal properties. HA extracted from soil under ecological farming, as compared with HA from soil under integrated system, were characterised by a lower value of the H : C ratio and by a higher degree of internal oxidation. It shows that HA from ecological farming have higher aromaticity, humification degree and therefore are of a higher quality than HA from integrated farming. A higher aromaticity of humic acids from soil under ecological farming was confirmed by lower values of absorbance ratios (A_2/6, A_2/4 and A_4/6) compared with the other HAs analyzed. The degree of aliphaticity determined thermogravimetrically was lower in HA from ecological farming, as compared with the integrated one, and it confirmed the results of spectral and elemental analyses referring to a higher humic acids quality in ecological farming.

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