Effect of lime and organic matter on distribution of zinc, copper, iron, and manganese in acid soils

Liming is essential in highly leached acid soils for increasing soil fertility as it promotes congenial chemical and biological environment. Application of organic matter along with lime has also been found beneficial for crop productivity in such soils. As external addition of organic matter provides easy source of organic carbon (C), it proliferates heterotrophic microorganisms. Addition of such amendments is expected to have profound effect on the availability of cationic micronutrients which are present in low amount. An experiment was undertaken at B.C.K.V., West Bengal, India to study the effect of lime and cellulose (as organic C source) additions on the transformation of zinc (Zn), copper (Cu), iron (Fe), and manganese (Mn) in two soils with different cropping history. Results indicated that in tea garden soil, metals were mobilized into organically complexed (in case of Zn a Mn) and amorphous Fe oxides bound (in case of Zn, Cu, and Fe); whereas in field cropped soil these were mobilized into 'gel' hydrous oxides and amorphous oxides fractions (except Cu) due to lime application. Lime decreased readily available water-soluble plus exchangeable forms of metals in both the soils. Providing external organic C source to tea garden soil did not result any significant changes in the micronutrient fractions. In field cropped soil, external organic C addition resulted mobilization of metals mainly into organically complexed and amorphous oxides bound fractions from water-soluble plus exchangeable and crystalline Fe oxides bound fractions. Significant interaction was observed between lime and organic C treatments on the transformation of Cu-fractions in field cropped soil. In presence of added lime, added organic C mobilized Cu into potentially plant available organically complexed and amorphous Fe oxides fraction from relatively inert fractions. Whereas, organic matter, in absence of added lime immobilized Cu from these active fractions into inert residual fraction.