The leaching of nutrients from arable land through drainage pipes causes non point source pollution of water bodies. For a fundamental reduction, the conversion to organic farming has been politically encouraged. Rerouting of two drainage lines through measuring stations allowed auto gauging of discharge and analyses on the following parameters: pH-value, E.C., NO3, SO4, Cl, Ca, K, Mg, Na. Field monitoring of the groundwater level enabled a rough definition of the drainage area. On both field plots, nitrate concentrations in drainage water showed close connection to crop growing, cultivation scheme and nutrient supply: • Grass-clover-ley established in autumn and recurrently cut effected small nitrate concentrations of averagely 29,1 mg NO3/l. • NO3 concentrations rised after mulching on averagely 71,5 mg NO3/l. • Ploughing of grass-clover-leys in autumn results in a strong increase of nitrate concentration as well (62,6 mg NO3/l). The quantity of leachate as second factor which is responsible for the amount of nitrate loads is influenced by cultivation: Perennial plants and undersown crops, which are important component of organic farming can have a reducing effect. Leachate rate amounted 28,1% of rainfall under grass-clover leys and rose up to 40,1% in crop rotations without undersowing. The collected data are going to be used to calibrate CoupModel and thus optimize the representation of specifics of organic farming. Period and amount of N-fixation and incidence of leachate must be calculated for every soil layer to be able to quantify the plant-available and easily movable N-pool.