To establish zinc phosphate relations on black earths of the Darling Downs.

• Two pot experiments were conducted to evaluate the response of wheat to 3 rates of zinc sulphate on 3 contrasting black earths.
• On all 3 soils zinc concentration plant tops increased with application of zinc but declined as the application of phosphorus increased due to dilution from increased plant growth.
• The results of these experiments suggest that response to zinc fertiliser only occurred on the alkaline soils where the available zinc was less than 1 ppm.
• No evidence was obtained that phosphorus supply had any effect on the availability of zinc for plant uptake but other experiments indicated that zinc absorption was reduced by increasing phosphate concentrations in solution.