A study on a 10 ha field was conducted to investigate the performance of a hay mass flow monitoring system mounted on a large rectangular baler in estimating alfalfa hay yield. The potential of using satellite images to predict alfalfa yield was also explored. The monitoring system was used to monitor alfalfa hay yield at different baler settings (baler chamber pressure values of 5000, 6000 and 7000 kPa and forward speed values of 4, 8 and 12 km/h) that affect bale density, hence, yield monitor data accuracy. Data from the monitoring system was utilized to generate a yield map (measured yield map) that was compared, for calibration purposes, to an actual alfalfa hay yield map based on actual hay bale weight for the study field. The calibrated yield monitoring system was used to generate yield maps in a 23.5 ha alfalfa field for four harvests. These maps were compared to eighteen Landsat-8 satellite images of this field at different crop growth stages.