Interaction of different humic acid fractions from clayey soddy-podzolic soils with calcium

Interactions of the first and second humic acid (HA) fractions isolated from clayey soddy-podzolic soils of the Novgorod Experimental Agricultural Station with calcium were studied. It was found that the formation of calcium humates with different HA fractions followed common regularities, but significant differences in the parameters characterizing the course of the reaction and the properties of the resulting products (including the capacity of precipitates to be peptized in water and to prevent calcium from leaching) were observed between the HA-1 and HA-2 fractions. For many of the parameters studied, the difference between the HA-1 and HA-2 fractions was comparable to that between black and brown HAs. The persistence of positive changes related to liming in the soil largely depended on the functional properties of the HAs and their capacity to actively interact with calcium and prevent it from leaching.