INFLUENCE OF SOIL PROPERTIES ON THE RELEA SE OF DISSOLVED ORGANIC-MATTER (DOM) FROM THE TOPSOIL

A percolation experiment over a period of three month with small monol iths from forest and grassland:soils varying in their anthropogenic ch anges wa carried gut to identify, to weigh and to quantify important s oil properties for DOM release from the topsoil. Quality of soil organ ic matter determines the amount of DOM released from the topsoil if th e soils have a low ability to adsorb and to precipitate DOM. Favorable conditions for high DOC concentrations in the soil solution are wide C/N ratios in the soil and in the hot water soluble fraction, a high s oil content of hot water soluble organic carbon and a high portion of hot water soluble organic carbon in the total organic carbon content. Anthropogenic changes of the Soils are effective to DOM release via ch anging quality of soil organic matter. Long dry periods : and large wa ter fluxes can further increase DOM release. The effects of soil organ ic matter can be disguised in soils with a high DOM retention capacity (high CEC, high content of exchangeable bases, Fe-ox and Fe-d). Then adsorption and precipitation determine DOM release from the topsoil an d contribute;to a decrease of DOM release.