A bale composition determination system comprising a baler configured to pick up crop material cut and lying on the ground in the form of a windrow and to form bales of the crop material. The system additionally includes one or more sensors configured to obtain electromagnetic reflectance information for the crop material. The system further includes a control system configured to receive the electromagnetic reflectance information for the crop material and to generate vegetation index values for the bales of crop material based on the electromagnetic reflectance information.