DEPTHWISE DISTRIBUTION OF COPPER FRACTIONS IN SOME ULTISOLS

Abstract

We studied the depthwise distribution of different forms of Cu, namely water soluble + exchangeable (WSEX), organically complexed (OC), MnO2 (MnOX), amorphous Fe-oxides (AMOX), and crystalline Fe-oxides (CRYOX) bound in 12 Ultisols of West Bengal, India. On an average, the OC, AMOX and CRYOX forms accounted for 20, 19, and 13%, respectively, of the total Cu in the surface soils (0–15 cm), while the WSEX and MnOX forms constituted only negligible fractions, accounting for 2.0 and 0.4% of the total amount. With depth, the content in the OC, AMOX, and WSEX forms recorded a decrease, while that in the MnOX and CRYOX forms recorded an increase. Such increase/decrease has been explained by the variations in the content of organic C, Mn-oxide, and amorphous and crystalline Fe oxide content in the different layers of soils. Significant correlations were obtained between WSEX-Cu versus pH (r = −0.47**), OC-Cu versus organic C (r = 0.78**) and amorphous Fe oxide (r = 0.44**), and AMOX-Cu versus organic C (r = 0.46**) and amorphous Fe oxide (r = 0.48**). The different Cu forms also showed significant correlation amongst themselves, suggesting the existence of a dynamic equilibrium. Simple correlation, multiple regression, and pathcoefficient analyses indicated that the WSEX-, OC-, and AMOX-Cu played the most important role in maintaining the available Cu pool in these soils.