That depends on where you grow the corn: In the irrigated Sacramento Valley and San Joaquin Valley of California much corn is grown with humongous quantities of highly subsidized water, obscene quantities of fertilizer, and enough pesticides to kill off a medium-size ethnic group. The yields are fantabulous.
Almost. Much of the corn grown in the central valleys of CA are fertilized courtesy of factory farming operations. Megadairies, hog farms and chicken mills need a certain amount of acreage to spread the dried animal waste on for disposal purposes. Corn is the most common crop to use for that purpose. The problem is these factory farms are still dependent on imported feed from the midwest, which of course uses fuel for transportation. It's quite remarkable to note that both Valley farming and business interests are celebrating the arrival of ethanol plants to the 99 corridor for their economic value. When I was a planner there I thought this was a bone-headed idea because the feedstock was imported (albeit at times augmented from local sources at times) from the midwest consuming fossil fuels, limited water supplies (from a depleting aquifer), electricity and natural gas. The natural gas situation needs additional comment because the valley's supply (south of fresno) has pipeline capacity limitations more constricted than the overall tight national situation. Rapid residential growth has further exasperated the situation. The wet mash was touted as a "perfect fit" for the S. Valley's factory farm operations, without any consideration to the water considerations of those facilities. Corn + Dairies + Ethanol production = considerable water and energy expenditures. This concept is not understood by government regulators and ignored by the private sector interests. More on factory farming and resource consumption: http://unplanning.blogspot.com/2006/02/plans-that-stink-to-hog-heaven.html