inoculating legumes

Several farmers have asked me why they need to spend an “extra” 4-6 cents per pound to inoculate the legume seed they are planting for producing nitrogen with their cover crops.  I get asked this especially about Austrian Winter Peas and Cowpea. However, if you are planting Crimson Clover, Berseem Clover, Kura Clover, Alsike, Hairy