Comparison of two methods of preparation of humic and fulvic acids, IHSS method and NAGOYA method

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Abstract
Two methods for preparing soil humus samples, NAGOYA (Nagoya University) method and IHSS (International Humic Substances Society) method, were compared using A-horizons of an acid brown forest soil and an ando soil. Alkali-extractable humus was recovered more effectively by the NAGOYA method, while the IHSS method recovered only 80 and 26% of the maximum yield by extraction with 0.1 N NaOH from both soils, respectively. The recoveries of fulvic acids (FAs) by the IHSS method in which XAD-8 was used as adsorbent to obtain only humic substances in the FA fraction from the brown forest soil and the ando soil were only 1/5 and 1/40, respectively, of those by the NAGOYA method in which the whole FA fraction was recovered. The FAs obtained by the NAGOYA method were further fractionated into adsorbed and non-adsorbed fractions with XAD-8 or insoluble polyvinylpyr-rolidone (PVP). The recoveries of the XAD-8-adsorbed fraction increased 3.8 and 26 times by changing the volumes of the extractant and adsorbent. Fractionation using PVP resulted in a high recovery and more distinct fractionation of FAs into humic substances and non-humic substances compared with XAD-8.