P.C. KERRIDGE1 and D. RATCLIFF2
1CSIRO, Division of Tropical Crops and Pastures, and
2CSIRO, Division of Mathematics and Statistics, Cunningham Laboratory, St. Lucia, Queensland.
A pot culture study was made of the comparative response of Centrosema pubescens (centro), Desmodium heterophyllum (hetero), Pueraria phaseoloides (puero), Stylosanthes guinanensis (stylo) and Panicum maximum (guinea grass) to superphosphate and Christmas Island "A" grade and calcined "C" grade rock phosphate dusts on a highly acid soil.
Hetero, puero, stylo and guinea grass had the same requirements for phosphorus and their utilisation of rockphosphate, relative to superphosphate, was similar. Centro had a higher phosphorus requirement and utilised rockphosphate less effectively. Guinea grass utilized the "C" grade as effectively as the "A" grade rockphosphate but legume yields were poorer, initially, with the "C" grade rockphosphate. Plant analyses for phosphorus and nitrogen confirmed the differences in response between sources were due to the supply of phosphorus. Higher nitrogen yields were obtained with centro and hetero than puero or stylo, with hetero giving higher increments of nitrogen yield at the lower levels of P application.