Abstract
Phosphorus speciation provides useful information about the dominant P fractions in soils and their availability for plant nutrition and environmental sustainability. Chemical P fractions (H2O, 0.5 M NaHCO3, 0.1 M NaOH, 1.0 M HCl and H2SO4-P) in soils of contrasting lithologies in Imo State, Southeastern, Nigeria were determined using sequential extraction technique. Also, P fractions were correlated with selected soil properties using correlation analysis. Mean water, NaHC03, NaOH, HCl and H2S04-P in soils of various lithologies varied as 0.11, 0.15, 0.36, 0.07 and 0.14 mg kg-1 respectively in decreasing order of NaOH > NaHCO3 = H2SO4 > H2O > HCl for the top soil. Also, mean concentrations were 0.12, 0.14, 0.36, 08 and 0.17 mg kg-1 for water, NaHCO3, NaOH, HCl and H2SO4-P respectively P in a decreasing order of NaOH > H2SO4 > NaHCO3 > H2O > HCl for the subsoil. Averaged over lithologies, NaOH-P was higher while averaged over chemical fractions, concentrations in Coastal Plain Sands were better than other lithologies at both soil depths. Chemical P fractions correlated with selected soil properties especially sand, silt, clay, pH, ECEC, clay, OM and exchangeable Al, Ca and Mg. In general, amorphous and crystalline Fe and Al oxides/hydroxides, in addition to clay minerals and organic P compounds associated with NaOH-P dominated P chemistry of the soils.
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