Growth and chemical composition of Townsville lucerne (Stylosanthes humilis). 2. Chemical composition, with special reference to cations, as affected by the principal constituent elements of molybdenized superphosphate

Abstract

The chemical composition of Stylosanthes humilis H.B.K. in response to a factorial combination of phosphorus, sulphur, molybdenum, and calcium carbonate treatments was studied with special reference to cation composition and protein synthesis. The aim was to assess the potential of S. humilis to adapt to a wide range of nutrient treatments. Protein synthesis was enhanced by high phosphorus-high sulphur treatments, and was accompanied by a low soluble : residual nitrogen ratio. This occurred despite the development of an apparent potassium shortage at this treatment combination. High phosphorus-high sulphur plants had low potassium : sodium ratios, and, although large, their potassium content was below critical levels (9-14 m.-equiv. per 100g). Potassium was partially substituted for by sodium and to a lesser degree by magnesium under these conditions. Although high protein levels were achieved, the full potential for protein synthesis did not seem to be attained by reason of the potassium shortage which developed. S. humilis was able to grow and fix significant quantities of nitrogen that bore a close relation at all levels to the wide range in chemical composition and yield response that developed with treatment.