Residual value for wheat of phosphorus from calciphos, Duchess rock phosphate and triple superphosphate on a lateritic soil in south-western Australia

Abstract

The residual values of phosphorus from triple superphosphate and from three rock phosphates were compared in a 4-year field experiment with wheat, grown on a phosphorus deficient lateritic soil in south-western Australia. The three rock phosphate fertilizers were an apatitic rock phosphate originating from the Duchess deposit in north-western Queensland, and calcined (500¦C) Christmas Island C-grade ore as a powder and as pellets. Five rates of each fertilizer were applied at the commencement of the experiment and their effectiveness was calculated from data on yield of dried plant tops, grain yield, and bicarbonate soluble phosphorus extracted from the soil. Triple superphosphate was the most effective phosphorus fertilizer initially, but its effectiveness decreased markedly with time. The effectiveness of the three rock phosphates was initially very low, and remained approximately constant for the duration of the experiment. The yield of dried plant tops depended upon their phosphorus content and this relationship was independent of the phosphorus fertilizer used.