Double cropping is increasing in dairy farming in parts of northeastern United States. The effect of double cropping on forage yields and quality are yet unknown, and there is particular concern with respect to the field water balance. This study compares experimental results of double cropping (corn/rye, corn/barley) and single cropping (corn, corn/soybean) rotations with model (Integrated Farm Systems Model) predictions for silage yields, quality and water balance components. Field data was collected between 2003 and 2005 in Landisville, Lancaster County, PA. Corn silage yields (26 t/ha) were nearly twice as high as predicted corn yields (14 t/ha). Double cropping produced higher total annual dry matter (25 t/ha) than single cropping systems (20 t/ha), including main crop and winter small grain. Similarly, water use efficiency (total annual DM/precipitation) of double cropping rotations was higher than that of single cropping rotations, both for predicted and experimental data. Predicted and measured runoff show that double cropping with winter small grains reduced runoff. Field data show up to 30% of rainfall lost to runoff, compared to a maximum predicted of 17%. Field and model results both produce drainage (deep percolation) below the root zone up to 45% of precipitation. Simulations suggest that double cropping increases drainage compared to single cropping rotations. However, field results do not confirm this finding.