Evaluation of Christmans Island C-grade phosphate as a fertilizer on some soils in southern NSW

Finely-ground calcinated C-grade phosphate from Christmas Island was compared with other forms of phosphate as a source of phosphorus for plants. In the glasshouse there was little P uptake from Christmas Island phosphate at first harvests of subterranean clover and ryegrass, but uptake by both species increased at later harvests, both in absolute amount and relative to that from soluble phosphate. The availability of the calcined phosphate varied from soil to soil. In the field, pasture plants made appreciable use of the phosphate only in second or subsequent years ; mixtures of calcined C-grade phosphate with ,superphosphate (1:1) were more effective in the first year on pasture than the C-grade phosphate alone, and produced similar responses to equivalent amounts of superphosphate. Wheat made little use of C-grade phosphate in the field.