Soil phosphorus tests and grain yield responsiveness of maize (Zea mays) on Ferrosols

The grain yield response of maize (Zea mays) to various rates of applied phosphorus (P) was measured at each of 17 sites in the South Burnett region of south-eastern Queensland. The soils at all sites were Ferrosols. Relative grain yield of the nil applied P treatment [100x (yield at nil applied P/maximum yield)] was related to Colwell (0.5 M NaHCO3) extractable P (P-B), CaCl2-extractable P, and equilibrium P concentration and P buffer capacity calculated from P sorption curves. Of these P measurements, P-B was most highly correlated with relative grain yield (R-2 = 0.94 for a linear response and plateau fit, R-2 = 0.92 for a Mitscherlich fit), and the P-B values at 90% maximum grain yield were 20 mg/kg for the linear response and plateau model and 32 mg/kg for the Mitscherlich equation.