DESORPTION OF NATIVE AND ADDED ZINC FROM A RANGE OF NEW-ZEALAND SOILSIN RELATION TO SOIL PROPERTIES

Compared with zinc (Zn) sorption, there is very little information on the effect of soil properties on Zn desorption from soils. In this stu dy, desorption of native and added Zn from 7 Canterbury (NZ) soils was determined using a technique involving repeated equilibration of soil in 0.01 M Ca(NO3)(2). The concentrations and patterns of desorption o f both native and added Zn varied between the different soils. Greater concentrations of native Zn were desorbed from surface soils than fro m subsoils, and greater concentrations of added Zn were desorbed from subsoils than from their corresponding surface horizons. Correlation a nalysis showed that cation exchange capacity (CEC) and organic carbon (C) were the dominant soil variables contributing towards sorption or desorption of Zn. However, simple linear regressions involving CEC or organic C explained only 48-62% of the total variation in Zn sorption or desorption from the different soils. Multiple regression analysis i ndicated that cumulative native Zn desorption (expressed as percentage of DTPA-extractable Zn) was strongly related to CEC and the content o f Mn oxides, which in combination explained 80% of the variability bet ween soils. Regression analysis also showed that CEC plus Mn oxides an d pH explained 91% of the variability in Zn sorption between the soils ; whereas for added Zn desorbed (%), CEC plus pH and crystalline Al ox ides explained 93% of variability in added Zn desorption.