Exchangeable and non-exchangeable phosphate sorption in Portuguese soils

Total amounts of phosphate (P) sorbed were measured for 6 Portuguese soils of widely varying properties.32P was used to assess the isotopically exchangeable and non-exchangeable sorbed P. Total sorbed and exchangeable P were described by modified Freundlich equations and non-exchangeable P by a Temkin equation. The Langmuir equation also proved to fit the data for non-exchangeable P well. The amount of total sorbed P required to attain 0.2 mg P 1−1 in solution ranged from 5.3 to 819 mg P kg−1. At this concentration exchangeable and non-exchangeable P values varied from 62.4 to 536.6 and from 0.4 to 322.1 mg P kg−1 respectively.