To arrive at our estimation of the embedded carbon emissions associated with producing an acre of corn, we started with Patzek's 2004 meta analysis. Based on the this paper, we made the assumption that corn farming used roughly 23 GJ/HA worth of fossil fuels. This includes fuel, fertilizer, herbicides, electricity and transportation. That's equal to ~175 gallons of diesel fuel per acre. That much diesel fuel would generate 1,741.25 pounds of CO2 per Acre.
In calculating the emissions savings from using corn we estimated the energy content in the corn and the CO2 emissions from a comparable amount of oil or propane, with the assumption that the grower would have used the same amount of energy to heat their greenhouse. In many cases this assumption is not entirely accurate, as in some cases the growers kept the greenhouse warmer with the corn furnace than they would have with a more expensive fuel.
Please note that these are very rough estimates, and will vary wildly with production methods, weather, soil type, and furnace efficiency. These numbers are not meant to reflect scientific precision, but rather to provide a working comparison between fossil fuels and corn.