Modeling approaches for centrifugal fertilizer spreaders have so far been based on analytical expressions for single particle trajectories derived in the early 60's. However elegant this approach was, it suffers from several disadvantages, the most important of which is failing to incorporate the interaction between the particles in the flow. This paper is the first in a series aiming at simulating the complete spreading process based on the laws of physics and a physically meaningful model for the interactions between the particles, c.q. the contact forces. The result is a model that allows the development of a deeper understanding of the physics underlying the spreading process and provides better predictions. In this paper the model is presented in detail and a series of simple computer experiments are analysed and compared to theoretical predictions. Also, single particle trajectories from DEM simulations are compared to experimental results. Further, some effects of the model parameters are analysed. This paper demonstrates that the model is not only capable of producing realistic simulations, but also provides detailed insight in the physics of the spreading process. (c) 2006 Elsevier B.V. All rights reserved.