Physico-chemical Studies on Formation of Humic Acids (Part 7) : Comparison of Humic Acids Obtained by Different Extracting Methods

Abstract

SrL humic acids, humic acids obtained by treating L or Si humic acids with 5% HCL at 70℃ and the acids treated by 0.5% NaOH at 100℃ for 30 minutes were compared each other in their absorption spectra and elementary composition. Above mentioned acid or alkali treatment seemed to cause no fundamental change in the nature of the humic acids, although there occured a slight decrease of light absorbability of these humic acids. The intensity of light absorption of humic acids was more or less greater than that of the original humic acids, their carbon contents becoming higher and their nitrogen contents lower. These changes took place remarkably on the humic acids of low humification degree. It may be presumed that humic acid extracted from soil, no matter what extraction method may be applied, contains not only humified organic matter, in its true sense, i.e. organic matter which shows characteristic absorption spectrum , but also non-humic, that is, fresh or somewhat decomposed and transformed organic matter. The more the method of extraction, pretreatment of the samples and its after-treatment are drastic, or the more the humification is promoted, the more the non-humic matter contained in the humic acid may be decreased.