A square baler has a baling chamber, a plunger reciprocable at one end of the baling chamber, a pre-compression chamber within which charges of crop are amassed and pre-compressed by a rotor prior to transfer into the baling chamber, and a pickup roller having radially projecting tines for picking up crop from the ground and advancing the crop to the rotor. A torque sensor is connected to at least one tine of the pickup roller to produce an electrical output signal indicative of the torque experienced by the pickup roller, and a processing circuit is operative to estimate the rate of crop flow into the chute by analysing the electrical output of the torque sensor only at times when the position of the tine lies within a predetermined angular position of the pickup roller.
