A square baler is disclosed which comprises a baling chamber, a plunger reciprocable at one end of the baling chamber, and a pre-compression chamber within which charges of crop are amassed and pre-compressed by a rotor prior to transfer into the baling chamber. The baler also includes a pickup roller having radially projecting tines for picking up crop from the ground and advancing the crop to the rotor. A transducer is provided for producing an electrical output signal indicative of the load on the rotor and a processor is operative to estimate the rate of crop flow into the pre-compression chamber by analysing the output signal of the transducer over a complete filling and emptying cycle of the pre-compression chamber. The estimated crop flow rate into the pre-compression chamber may be used to ensure that the crop density attains a desired level at the time that it is transferred into the baling chamber.
