Comparison of sequential extraction techniques and fractional composition of humic substances in chernozems and phaeozems of Poland - A review

Abstract

Studies on organic matter have always been an important part of soil environment characterization. However, an extraction of humic substances from the organo-mineral complexes is diffi cult and requires special procedures. Sodium hydroxide, sodium pyrophosphate and sulfuric acids are among the basic extractants. However, its application in various order, combinations and concentrations arises question on the comparability of the results obtained from various methods. The aim of the review was to compare the major fractionation procedures according to Tiurin, Kononowa/Belczikowa, Boratynski/Wilk, and Duchaufour/Jacquin, and the composition of soil humus as investigated by these methods, using the published data for chernozemic soils from various regions of Poland. The comparison confi rmed, that these major fractionation procedures are hardly comparable in chemical terms due to differences in extraction environment. However, taking into account the declared binding strength of extracted humus fractions to the mineral soil compounds, the methods of Tiurin and Boratynski/Wilk gave the most compatible results. In general, all applied methods indicated a predominance of the humus fractions weakly and more strongly bound to nonsilicate soil compounds (apart from the high contribution of humins/non-extractable residuum). Considering all multistage and long lasting procedures applying different reagents in various concentration, the best results can be achieved with method of Tiurin. At the same time authors suggest that more advanced studies concerning composition, structure or other properties of extracted humic substances using the non-invasive procedures need to be carried out.