Soil properties in relation to the sulphur and phosphorus status of some basaltic soils

Abstract

Twenty-three basaltic soils from elevated areas in northern New South Wales were examined for sulphur and phosphorus status by growing Phalaris tuberosa L. in pots in a glasshouse. Sulphur deficiency was more common and more severe than was phosphorus deficiency. To determine whether there may be some topographic control of sulphur or phosphorus status, soil colour was examined, as in general the reddest soils were found in the highest positions in the landscape. The soils were first considered as one group and then as subgroups of sedentary, colluvial, and alluvial soils. Using redness to rank the soils, there was no overall relationship to sulphur or phosphorus status. However, colour of the sedentary soils was significantly correlated with sulphur status (r = 0.92***), the reddest soils being the most deficient. The sulphur status of the brown colluvial and greyish brown alluvial soils showed no relationship to colour; they were uniformly severely deficient. Phosphorus deficiency was not associated with soil colour. Neither soil pH nor redox potential was related to the sulphur and phosphorus status of the soils. There was only a weak correlation (r = 0.60**) between the water-soluble sulphur content of all soils, but a stronger correlation (r = 0.81**) when only the sedentary soils were considered. Several soil phosphorus fractions could be satisfactorily used to distinguish between phosphorus-deficient and phosphorus-sufficient soils.