<p>A square baler is described comprising a control system having a closed loop mode of operation in which at least one of the volume of the feeder duct 16 and the threshold pressure of the pressure sensor 32 is varied automatically to maintain the capacity parameter within one of a plurality of desired capacity ranges. The desired capacity range is selected by the control system in such a manner as to maintain the width of each slice in the finished bale within predetermined limits.</p>
