All routine physicochemical analyses were carried out following the conventional laboratory methods on air-dried soil samples ground to pass a 2-mm sieve. Oxalate-extractable Fe was determined according to Schwertmann (1964). Phosphorus sorption was carried out following Blakemore et al. (1987). A simplified four-step sequential extraction procedure adapted from Hedley et al. (1982) was used to evaluate the soil P inorganic status before and after the pot experiment. About 1 g of soil was weighed in a 50-mL centrifuge tube and 30 mL of successive extractants were added. The tubes were shaken overnight for 16 hours with the successive extracting solutions: 0.5 mol L−1 NaHCO3 at pH 8.5 (Olsen et al., 1954), 0.1 mol L−1 NaOH, 0.5 mol L−1 HCl, and finally 2 mol L−1 H2SO4 after ignition at 550 ◦C. At each step of the sequential extraction procedure, centrifugation was carried out at 3 000 r min−1 for 15 min. All P analyses were done using the molybdenum blue method (Murphy and Riley, 1962). The P and N concentrations in the shoot maize samples were determined following Novozamsky et al. (1983).