The practice of double cropping is increasing in dairy farming in parts of the 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 use efficiency. Field data were collected in Landisville, Lancaster County, Penn. Double cropping lowered main crop yields, probably due to later planting of the main crop (corn). Corn silage yields (16 t DM/ha) were closely predicted by the model (14 t/ha). Double cropping produced higher total annual dry matter (23 t/ha) than single cropping systems (20 t/ha), including main crop and winter small grain. The experiment suggested positive effects of double cropping on total forage yield. Yield differences might be more significant after several years of double-copping practices. Total silage yields increased with double cropping, resulting in improved water-use efficiency. Forage quality was improved by small-grain double cropping, with an increase in neutral detergent fiber (31 %) and in crude protein (27%). Total forage yields were predicted reasonably well by the model, considering the scaling between experimental plots and large farm fields.