Chemical fractions and bioavailability of nickel in alluvial soils

The present study was undertaken to sequentially fractionate nickel (Ni) in soils of divergent physicochemical characteristics and evaluate the contribution of different fractions towards plant uptake. For this, fifteen bulk surface (0-15 cm) soil samples were collected from the cultivated fields of northwestern Indo-Gangetic alluvial plains. A pot experiment was conducted with these soils to assess the contribution of soil Ni fractions to plant uptake using soybean as test crop. Results showed that residual Ni was the most dominant fraction in soil constituting 3.19-63.6% of total Ni. The water soluble plus exchangeable Ni accounted for only 0.70-4.04% of total soil Ni. Organically bound Ni varied from 1.60-6.85% of total Ni; these values are relatively lower as compared to those reported for temperate soils. Correlation studies showed that the free iron oxide (Fe2O3) and soil organic carbon correlated with various fractions of Ni in soil. Water soluble plus exchangeable and organically bound are the dominant fractions which contributed positively and manganese oxide (MnO2) bound and residual fractions contributed negatively towards the phytoavailability of Ni in soil.