This work presents the evaluation of resources and quality of organic matter in arable luvisols of the Siedlce Upland. This was performed based on determination of organic carbon content and fraction composition of organic matter as well as of quantitative analyses of humic acids in humus horizons of twelve soil profiles. In the studied humus horizons a number of features were found indicating the lack of ability to accumulate considerable amount of humus. Organic matter resources amounted to 4.67-9.90 kg·m^-2 and correlated with the value of pHKCl and content of clay fraction. Even fraction composition of organic matter was found. Humic substances (extracted with 0.1M NaOH) constituted about the half of organic matter resources and were characterized by predominance of humic acids over fulvic acids. Proportion of humic acids, amounting to about 1/3 organic matter resources, significantly positively correlated with the value pHKCl and the clay fraction content. Based on the elemental composition and spectrophotometric properties, similar properties of humic acids were found, rather low degree of their aromatization and a high degree of internal oxidation of particles.

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