FRACTIONATION OF ZINC IN SOME NEW-ZEALAND SOILS

The amounts and forms of zinc in twenty surface soils from Canterbury and Southland, New Zealand were determined using a sequential fraction ation scheme. Total soil zinc concentrations ranged from 38.1 mg . kg( -1) to 113.8 mg . kg(-1). Although the proportions of zinc found in in dividual fractions varied between soils, on average approximately 3% o ccurred as exchangeable zinc, 5% as organic-bound zinc, 9%, 18%, 24% w as associated with manganese, amorphous iron and crystalline iron oxid es, respectively, and 40% was in the residual fraction. In a group of soils formed in greywacke alluvium or loess, exchangeable zinc was inv ersely related to soil pH. Within the same group of soils, those of si milar age with greater concentrations of total and organic-bound zinc were present in imperfectly- and poorly-drained soils compared with we ll-drained soils. Zinc extracted from the soils with a range of reagen ts used to assess 'plant available' zinc was correlated strongly with the concentrations of zinc present in the exchangeable and organic-bou nd zinc fractions.