Revised diagnostic leaf nutrient standards for macadamia growing in Australia

Abstract

Leaf nutrient analyses are widely used to determine the nutritional status of macadamia orchards. A commercial database was developed from 2186 observations collected from 186 farms across 56 geographical areas spanning New South Wales and Queensland. The data were collected over 10 years, with 1 to 9 sequential annual observations on each farm. An experimental database was also developed where several of the most popular commercial cultivars growing in the Lismore area of New South Wales and the Bundaberg area of Queensland were sampled at monthly intervals over a 2–3 year period. Two canopy sampling heights were used to confirm the effect of shading (irradiance) on leaf nutrient composition. This latter study confirmed that spring was an appropriate time to sample and that irradiated leaves, usually located in an upper canopy position, should be sampled. The most important change to the recommended leaf nutrient standards was the increase in the leaf nitrogen range from 1.3–1.4% to 1.4–1.7% for all cultivars except 344, where we recommend 1.6–2.0%. The study also confirmed that the adequate concentration range for zinc should be much lower than originally recommended. We recommend concentrations of 6–15 mg/kg. Minor changes were made to most other macro- and micronutrients. We also advise caution when interpreting the analyses of some nutrients because concentrations can change over the spring period. The revised leaf nutrient standards were developed from two large and comprehensive databases and reliably represent adequate leaf nutrient concentrations in productive, well-managed macadamia orchards in Australia. A single leaf analysis will not reliably indicate the nutritional status of a macadamia orchard. Additional information is required on trends in leaf and soil analyses over time as well as fertiliser, yield and management history.