I've wondered about this since so much alfalfa and corn are specifically grown on arable land to feed cattle. What fraction of beef calories is derived from non

I've wondered about this since so much alfalfa and corn are specifically grown on arable land to feed cattle. What fraction of beef calories is derived from non-arable grazing lands? There is also the extensive use of water to irrigate pasture in arid areas just to feed cattle. That water could be used more efficiently. to grow food directly.