Dissolution and Fractionatoon of Calcium-Bound and Iron-and Aluminum-Bound Humus in Soils

This paper deals with the development of a sequential extraction method to separate the Ca-bound and Fe-and Al-bound humus from soils. First, comparative analyses were carried out on dissolution of synthetic organo-mineral complexes by different extractants, i. e. 0.1M Na4P2O7, 0.1M NaOH + 0.1M Na4P2O7 mixture, 0.1M NaOH, 0.5M (NaPO3)6 and 0.5M neutral Na2SO4. Among the five extractants, 0.1M NaOH +0.1M Na4P2O7 mixture was the most efficient in extracting humus from various complexes. 0.5M Na2SO4 had a better specificity to Ca than 0.5M (NaPO3)6, by only extracting Ca-bound humus without destorying Fe- and Al-bound organo-mineral complexes. Then sequential extractions first with 0.5M Na2SO4 and then with 0.1M NaOH + 0.1M Na4P2O7 mixture were applied to a series of soil samples with different degrees of base saturation. The cations were dominated by Ca in the 0.5M Na2SO4 extract and by Al in the 0.1M NaOH +0.1M Na4P2O7 mixture. The sequential extraction method can efficiently separate or isolate Ca-bound and Fe- and Al-bound humus from each other.