Some producers may be thinking of harvesting soybeans for forage rather than a grain crop. While we seldom think about using beans as forage, certain circumstances may make it more advantageous for us to harvest soybeans as a forage. Soybeans may make an excellent forage if harvested properly. As with most legumes, they will be high in protein and low in fiber.
The optimum time to harvest soybeans for silage is when seeds completely fill the pods and the lower leaves of the plant are just beginning to yellow. A mower-conditioner is recommended, so that leaves and stems dry at a similar rate and leaf loss is reduced. Ideal moisture is 65-70% for tube or bunker silos, and 60-65% for upright silos.
One of the biggest cautions that need to be exercised when considering harvesting soybeans for forage is the herbicide program used. Few herbicides are cleared for use on soybeans harvested for use as forage. Remember that it is illegal to harvest soybeans for forage if it is not listed on the herbicide label.
Source:psu.edu