Quick field test for lime rates of pyritic drain-spoil in NSW canelands

Knowledge of soil texture class and soil pH folIowing peroxide oxidation. both from a survey of low-lying soils from northern NSW cane farms. was integrated with laboratory data on peroxide-oxidised pH and lime requirements to extend the value of an existing field test used to indicate the presence of acid sulfate soils (ASS). The rapid field test now enables prediction of the quantity of agricultural limestone required to neutralise drain spoil containing actual and potential pyritic acidity. The paper describes the data-gathering process and the statistical approach used to develop the lime rate calibration curves. There are supporting data on field and laboratory derived soil pH values before and following oxidation with hydrogen peroxide. The data cover three mill regions and five depths to 1.5 m. A 'look-up' Table to simplify use of the quick field test for lime requirements for three soil texture classes (fine, medium, coarse) is provided, although the great majority of soils to 0.8 m were fine textured. The new application, supported by validation data from 68 samples, is now routinely used in northern NSW as one tool to assi"t the management of drain spoil in acid sulfate affected areas, both within the sugar industry and externally.