To develop sustainable cropping systems we need to predict both short-term and long-term effects of management practices on soil fertility. For this purpose agro-ecosystem simulation models are valuable tools. We used the Daisy model to simulate a three-year crop rotation (beetroot, onion, white clover, potato) over a period of 40 years. With this rotation, three rates of farmyard manure were tested (0, 15, 28 t ha-1 year-1). After 40 years without manure soil organic matter carbon (SOM-C) decreased by approximately 40%, and increased by 27% with the highest application rate. SOM turnover did not reach equilibrium at the end of the experiment. Nitrogen mineralization from SOM followed in the long-term (40 years) the slowly changing time courses of SOM. However, manure applications affected mineralization and hence crop yield and nitrogen losses much more in the short-term (1 to 2 years) than in the long-term
