Description of the phosphorus sorption and desorption processes in lowland peaty clay soils

To determine phosphorus (P) losses from agricultural land to surface water, information is needed about the behavior of P in soils. In this study, the sorption and desorption characteristics of lowland peaty clay soils are described based on experimental laboratory studies. The maximum P sorption capacity is comparable to that of acid sandy soils if based on the amount of oxalate-extractable aluminum and iron. A fraction of the maximum amount of sorbed P is bound reversibly (Q), which can be measured with an iron-impregnated paper. The fraction of the maximum reversibly sorbed P depends on the amount of oxalate-extractable aluminum and iron. In the topsoil, the maximum of the fraction of reversibly bound P (Qm) is about one third of maximum P sorption capacity; and in the subsoil, about two thirds. All sorption and desorption parameters are related to soil characteristics of peat samples