Soil chemical properties affecting NH 4 + sorption in forest soils

Fourteen European forest soils from the boreal to the mediterranean climate on different parent materials were investigated with respect to their ability to store NH 4 + in exchangeable form, using sorption isotherms. Distribution coefficients for NH 4 + sorption per unit weight of soil were in the range of 0.02 to 0.77. NH 4 + sorption coefficients were usually highest in the forest floor of a given soil. NH 4 + sorption behaviour of mineral soil horizons was correlated to soil parameters that are determined during routine soil analysis. A combination of CEC and base saturation explained up to 95% of the variability Of NH 4 + sorption. In the forest floors, variability in NH 4 + sorption could not be explained quantitatively from independent soil parameters. The affinity of the sorption sites for NH 4 + was the most important factor for explanation of the variability in NH 4 + sorption in the forest floors but was of low importance in mineral soil horizons. As NH 4 + exchanges predominantly base cations, susceptibility of NH 4 + to transport through the soil profile increases with Iowbase saturation of a soil as well as with low CEC values.