Effect of soil properties on zinc retention in agricultural calcareous soils

The distribution of Zn in several agricultural calcareous soils with different physico-chemical and mineralogical properties was investigated using a five-step chemical fractionation procedure, Zn was mostly concentrated in the residual fraction (FV) (36% to 56%, mean values). Clay and carbonate contents were significantly correlated (r = 0.590, P = 0.003 and r = 0.495, P = 0.016, respectively) with the percentage of Zn in the residual fraction. Among the non-residual fractions, the third fraction of sequential procedure, corresponding to the Fe-Mn oxide fraction, as well as the fractions of carbonate remaining from the dissolution of the carbonate fraction (F11), contained the greatest amount of Zn (29% to 35%, mean values). A very small portion of Zn was in the readily exchangeable forms. Zn adsorption was studied in suspensions of seven selected soils. Zn adsorption was conformed to the Langmuir isotherm and two linear portions of the curves were found. Illite in the clay fraction and secondary organic matter and clay content were related to the maximum adsorptive capacity of these soils. Clay sites present the higher bonding energy. Carbonate did not appear to be related with the Lagmuir adsorption coefficients.