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 [100
× (yield at nil applied P/maximum yield)] was related to
Colwell (0·5 M NaHCO3) extractable P
(PB), CaCl2-extractable P, and
equilibrium P concentration and P buffer capacity calculated from P sorption
curves. Of these P measurements, PB was most highly
correlated with relative grain yield
(R2 = 0·94 for a
linear response and plateau fit,
R2 = 0·92 for a
Mitscherlich fit), and the PB 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.