Agricultural contractors often face the complex planning problem of having to optimize the utilization of their heterogeneous vehicle fleet. In this paper, we present a mathematical model that optimizes of the logistics processes of silo corn harvest and slurry application. The model simulates the use of primary vehicles (forage harvesters or slurry spreaders) in the field, whereby their utilization rate depends on the support vehicles assigned to them (crop or slurry transport vehicles) and the distance between the field and the silo. Using real data of the corn harvest of an agricultural cooperative in Brandenburg, we show that practical problems can be solved with a software-based approach using mixed-integer programming.