A discharge apparatus is disclosed for discharging materials from a container onto an open area such as a field. The apparatus includes a power discharge device which is disposed adjacent to a discharge outlet defined by the container. The arrangement is such that when the apparatus is being used to spread the materials onto the open area such as the field, the materials move from the container through the outlet towards the power discharge device for discharging the materials at a location on the field. A power source is drivingly connected to the power discharge device for rotating the power discharge device. A power sensor is provided for sensing the power supplied by the power source which is approximately the power used by the power discharge device, the power sensor generating a first signal which is correlated to the spread rate of the materials discharged.
