Meat farming replaces artificial fertilizer, by providing a source of manure, so doesn't that relationship run the other way? But having 1/4 of the land under

Meat farming replaces artificial fertilizer, by providing a source of manure, so doesn't that relationship run the other way? But having 1/4 of the land under soy beans or other locally appropriate nitrogen-fixing plants doesn't seem like it would hurt yields too much.