Soil salinity and the growth of macadamia seedlings1

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Abstract
Several salt levels were imposed on a silica sand and a soil to determine the tolerance of macadamia (Macadamia integrifolia) seedlings to salinity. Visual symptoms, plant height increases and plant nutrient composition were used to measure plant response. Subsequently, five soils with different mineralogical and chemical properties were subjected to salinization then desalinization to study changes in soil and plant chemical composition. Results suggest that macadamia seedlings are moderately sensitive to soil salinity. A 50% growth reduction occurred at an EC of 5 dS/m in the saturation paste extract. Salinization not only increased the Na concentrations in soil and plant, but also reduced the relative proportion of other nutrients (e.g., Ca and K). When plant K/Na ratios were ≤ 2.5, adverse effects of salinity could be expected. A K/Na ratio of 1.5 corresponded to a 50% growth reduction. Other nutritional problems seemingly unrelated to soil salinity, such as Al and Mn phytotoxicities, were brought about by salinization in two acid soils used in the experiment. Desalinization restored ionic balances in the plants within 4 weeks when adequate tapwater was used to leach the soils.