DISTRIBUTION OF SOIL Zn FRACTIONS IN BRITISH COLUMBIA INTERIOR ORCHARD SOILS

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Abstract
The distribution of Zn in soil fractions was determined for 20 representative orchard soils from the British Columbia Interior. This was part of a larger study to examine Zn availability to fruit trees. Medium to high levels of total soil Zn were measured (51.5–226.3 mg kg−1) with an average of 89.7 mg kg−1. A sequential fractionation showed that 0.3–23.2% of total soil Zn was exchangeable, 0.5–29.7% was associated with organic matter, 1.3–15% was associated with Fe + Al oxides and 45.6–92% was residual. A separate determination indicated that 6.4–24% soil Zn was associated with Mn oxides. Except for the Fe + Al oxide fraction for which no correlations were made, amounts of Zn in the fractions were significantly positively correlated with total Zn, and also, with Bray P1 extractable P and organic matter content. Zinc in the exchangeable and organic fractions was negatively correlated with both pH and residual Zn. This suggested a redistribution of soil Zn from the residual fraction into the exchangeable and organic fractions with acidification. For exchangeable Zn this was further evidenced in the much smaller amounts of Zn extracted by M NH4OAc (pH 7.0) than by M MgCl2 from acid soils. The observed range of total Zn and exchangeable Zn suggests that a wide range of Zn availability could exist in B.C. Interior orchard soils. Key words: Soil Zn, Zn fractionation, orchard soils, pH × exchangeable Zn interaction

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