Soil samples were extracted with Mehlich 3-extracting solution(0.2 M CH3COOH + 0.25 M NH4NO3 + 0.015 M NH4F + 0.13 M HNO3 + 0.001 M EDTA) by shaking for 5 min at a 1:10 soil to solution ratio to determine P (M3-P), Fe (M3-Fe), and Al (M3-Al) (Mehlich,1984). Water-soluble P (WSP) was determined by extracting each soil sample with deionized water at 1:10 soil-to-water ratio, and analyzing P on the filtrate collected after passing through a 0.45 μm filter. Watersoluble P concentrations were determined on an autoanalyzer followingthe Murphy and Riley (1962) procedure.