The retention of nutrients by 10-m-wide grass buffers and buffers under natural vegetation has been studied over 10 years in Jokioinen in southern Finland. The results have been compared with those from 70-m-long plots without buffers Grass was sown on the adjacent field and plots without buffers in 2002, and the field plots and these were grazed for 24 and 48 days in summer 2003 and 2004, respectively. The COUP model was applied both to the field and to vegetative filter strips to model water balance and nitrogen dynamics. Modelling was based on measured surface runoff, soil moisture, and physical, chemical and microbiological properties of soil. Annual precipitation was 584 mm in 2003 and 726 mm in 2004. Simulated cumulative evaporation from grass buffer was 130 mm higher than from field during this period due to dense vegetation with well-developed roots. Simulated nitrogen leaching from the fertilized pasture was 22-23, and from the unfertilized grass buffer 7 and from the unfertilized buffer under natural vegetation 5 kg ha-1 a-1. Grazing with short duration did not seem to increase leaching of inorganic nitrogen.