Plant material for ensilage is harvested using at least one harvesting vehicle in the field, is hauled to a silo and is compressed using a compression device. The compression output of the compression device is compared to the harvesting output of the at least one harvesting vehicle, and a command to increase the harvesting output or to decrease the harvesting output of the harvesting vehicle (1) to a non-vanishing value is generated when the harvesting output deviates significantly from the compression output.
