Das Projekt "Humusmanagement in Wasserschutzgebieten des Köln-Bonner Raumes: Auswirkungen der landwirtschaftlichen Bewirtschaftung auf den Humushaushalt und den Nitrataustrag" wird vom Umweltbundesamt gefördert und von Rheinische Friedrich-Wilhelms-Universität Bonn, Institut für Nutzpflanzenwissenschaften und Ressourcenschutz (INRES), Bereich Bodenwissenschaften, Allgemeine Bodenkunde und Bodenökologie durchgeführt. Recent legislation (Cross Compliance, Soil Protection Act of Germany) has forced farmers to keep the level of soil organic carbon (SOC) in their arable soils within certain limits. In the region Cologne/Bonn, an unfavourable constellation of factors (low cattle density, intensive soil tillage etc.) resulted in low contents and stocks of soil organic carbon (SOC). Thus, the farmers are challenged to increase the humus content of their soils. However, the rapid achievement of this objective may conflict (i) specifically with the interests of the local waterworks, and (ii) generally with the environmental targets of the European Community Nitrate Directive: Within Nitrate Vulnerable Zones, application rates of organic manures are restricted to avoid diffuse water pollution from nitrate. Against this background, our project aims at optimizing a system of soil use and management, that (i) assures an adequate humus support and sustainable soil fertility, and that (ii) minimizes the pollution of groundwater. The experiments include (i) quantifying the spatial heterogeneity of various soil parameters (Corg, Ntotal, Nmin, texture, nutrients) within arable fields in order to assess the possibility of a site-specific management; (ii) repeated sampling at selected sites in order to quantify C and N dynamics (incl. nitrate leaching) under different management options; (iii) spiking of soils with 15N in order to detect the fate of fertilizer N; (iv) modelling C and N dynamics for selected fields on the basis of long-term management data.