Abstract: A harvesting machine including a chopper mechanism for cutting harvested crop into short lengths, a crop feed arrangement for feeding the harvested crop to the chopper means and a drive arrangement for driving the crop feed arrangement and the chopper means. The drive arrangement including at least one adjustable component for driving one of the crop feed arrangement or chopper means at a variable speed thereby changing the length into which the harvested crop is cut. A control device is connected to the adjustable component and to a crop parameter sensor to measure at least one parameter of the crop being harvested. The control device automatically controls the adjustable component such that the length into which crop is cut by the chopper mechanism is a function of the sensed crop parameter.