Nickel transformations in soil as influenced by amendments and soil moisture regimes with reference to ageing effect

The effect of ageing and addition of lime, farm yard manure (FYM) and zinc (Zn) as amendments on different fractions of nickel (Ni), in soil after spiking with Ni was estimated over a 60-day incubation period. The soil was spiked with ni @25 mg kg⁻¹ soil through its nitrate solution. Lime, FYM and Zn were added @ 5%, 20 t ha⁻¹ and 25 mg kg⁻¹, respectively. The treated soil samples were incubated for 1, 45 and 90 days at field capacity and under submerged soil moisture regime. Significant decrease in the water soluble and exchangeable fractions of Ni with ageing was observed and it was in the order of 1day > 45 days > 90 days. the magnitude of this decrease was higher with the addition of amendments and it was in the order of lime > FYM > Zn > unamended soil. On the other hand, a temporal increase in organically bound, oxide bound and carbonate fractions of ni with addition of amendments was observed, but the per cent distribution among these fractions varied. Residual fraction of Ni was not significantly affected by ageing, amendments and moisture regimes. Overall, soil moisture regime did not change the direction and pathways of transformations of ni, but it increased the transformation rate. Submerged conditions showed higher metal reactivity compared with field capacity resulting in the pronounced transformation of ni towards stable fractions. the results enable us to understand natural attenuation of ni contamination and also to assess the effect of different amendments and moisture regimes on Ni transformations o work out the capacity of soil to serve as a source of supply of ni.