A lot is hard to define, but there is probably some risk in grazing cows on a soybean field with that amount of beans left in the field. Soybeans are high in protein and fat. Cows will likely select the beans and pods and therefore the majority of their diet will be very high in protein and fat. Cows will have loose stools and experience acidosis. Even if you fill them up with hay before going out to the bean field, there is still a lot of risk in grazing this field of beans.