Interactions of Humic Acids and Minerals in Presence of Calcium Carbonate and Iron during Composting

Composting of humus substance with kaolinite, bentonite, sand, calcium or iron over six months did not form any insoluble or gano-mineral complex like natural ones. Greater proportion of humic acids (HA) was soluble in 0.1M NNaOH (fraction I) and that of fulvic acids (FA) in water and 0.05 M N₂SO₄ (fraction I). Addition of CaCO₃ and Fe did influence binding humus material only after six months composting. HA-mineral mixture increased the well combined form of HA content resulting information of fractionn (binding with Ca). Fe addition did not influence combination withHA. In case of FA-mineral mixtures, composting increased FA fractions II and III after six months. Addition of CaCO₃ augmented FA binding. Fe addition decreased FA solubility in H₂O and 0.05M N₂SO₄. In HA-mineral mixtures, large proportion (12–29%) of NA transformed to FA. A sequential grouping of both HA and FA was observed as a result of interaction of humus and minerals. The pH of the mediumd eviated slightly from neutrality except HA in H⁺ form with kaolinite, bentonite and sand where it sharply dropped.