Can't wait for the analysis on Orc numbers. Given that their home turf is a barren wasteland, riddled with fire, ash and dust I don't see them fielding the numbers they do. Not much arable land in Mordor, is there?
It actually comes up in LOTR, The Gorgoroth Plateau isn't representative of all of Mordor, the fertile lands (because of the volcanic soil) around lake Nurnen in southern Mordor is mentioned as the source of Mordor's food.