1. Estimate grain yield using the Thomison (2013) method (see link below) or other approach.
2. On average, in the lower Midwest, you get about 1 ton of corn silage (35% dry matter (DM)) per 7.5 to 8 bushels of corn. Therefore, if the estimated grain yield is140 bu/acre, expected silage yield would be 140/8 = 17.5 tons.
3. However, under abnormal growing conditions this may underestimate forage yield (i.e., there will be less than 8 bu of grain per ton). See methods in the corn silage pricing article (link below.)