Little is said about the soil erosion associated with the corn crop that feeds ethanol. Based on a OTA document (”Gasohol, Technical Memorandum, Office of Technology Assessment, US Congress, 1978) which cited 7.3 tons of topsoil loss per acre per year in the Corn Belt.  Assuming 100 btu/acre corn yield and 2.6 gal/btu ethanol yield we get seven pounds of top soil for one pound of fuel ethanol.

Now add in amounts non-renewable phosphate and potash fertilizer used.  Include nitrogen fertilizer, and petroleum fuel, which the farmers choose to use instead of ethanol, since ethanol is much too expensive for them to use.

Corn is especially harmful because:

• Row crops such as corn and soy cause 50 times more soil erosion than sod crops [e.g., hay] (Sullivan 2004) or more (Al-Kaisi 2000), because the soil between the rows can wash or blow away. If corn is planted with last year’s corn stalks left on the ground (no-till), erosion is less of a problem, but only about 20% of corn is grown no-till. Soy is usually grown no-till, but [leaves] insignificant residues to harvest for fuel.
• Corn uses more water, insecticide, and fertilizer than most crops (Pimentel 2003). Due to high corn prices, continuous corn (corn crop after corn crop) is increasing, rather than rotation of nitrogen fixing (fertilizer) and erosion control sod crops with corn.
• The government has studied the effect of growing continuous corn, and found it increases eutrophication by 189%, global warming by 71%, and acidification by 6% (Powers 2005).
• Farmers want to plant corn on highly-erodible, water protecting, or wildlife sustaining Conservation Reserve Program land. Farmers are paid not to grow crops on this land. But with high corn prices, farmers are now asking the Agricultural Department to release them from these contracts so they can plant corn on these low-producing, environmentally sensitive lands (Tomson 2007).
• Crop residues are essential for soil nutrition, water retention, and soil carbon. Making cellulosic ethanol from corn residues — the parts of the plant we don’t eat (stalk, roots, and leaves) – removes water, carbon, and nutrients (Nelson, 2002, McAloon 2000, Sheehan, 2003).

Biofuels are an economic failure; it is not sustainable without large subsidies. The ideal biomass fuel program needs to be environmentally sustainable, replicable, flexible, and economically efficient when all the externalities are considered (Hall 1991). These externalities must include the costs of environmental degradation to systems other than the atmosphere.

Current practices will lead to lower crop production and ultimately deserts. Growing plants for fuel will accelerate the already unacceptable levels of topsoil erosion, soil carbon and nutrient depletion, soil compaction, water retention, water depletion, water pollution, air pollution, eutrophication, destruction of fisheries, siltation of dams and waterways, salination, loss of biodiversity, and damage to human health (Tegtmeier 2004).

A more detailed treatment of this subject may be found here:

Peak Soil: Why cellulosic ethanol, biofuels are unsustainable and a threat to America