Release of phosphorus, aluminium and iron in fractionation of inorganic soil phosphorus

Authors

• Raina Niskanen University of Helsinki, Department of Agricultural Chemistry, SF-00710 HELSINKI, Finland

DOI: https://doi.org/10.23986/afsci.72256

Abstract

Release of phosphorus, aluminium and iron by a modified Chang and Jackson procedure was studied in five mineral soils. Quantities of aluminium and iron released during the procedure and extracted by acid ammonium oxalate were compared. The extractability of P, Al and Fe by 1 M NH4CI and that of Al and Fe by alkaline 0.5 M NH4F was poor. Proportions of P extracted by 0.5 M NH4F (0.2—10.4 mmol/kg soil) and 0.1 M NaOH (0.1— 9.8 mmol/kg soil) were related to the molar ratio of oxalate-extractable iron and aluminium. P extracted by 0.25 M H2SO4 amounted to 2.1—12.2 mmol/kg soil. Al extracted by 0.1 M NaOH (7—174 mmol/kg soil) and 0.25 M H2SO4 (17—112 mmol/kg soil) amounted to 55—94 % and 16—245 % of oxalate-extractable Al, respectively. Fe released by 0.1 M NaOH (1—10 mmol/kg soil) and 0.25 M H2SO4 (30—196 mmol/kg soil) amounted to 1—13 % and 62—272 % of oxalate-extractable Fe, respectively. In total, 91—309 % of oxalate-extractable Al and 70—285 % of oxalate-extractable Fe were released by NaOH and H2SO4.