The data below applies to corn grain in Iowa (e.g., the yields are harvestable g

Question

The data below applies to corn grain in Iowa (e.g., the yields are harvestable grain, not total biomass), and comes from a spreadsheet developed by Drs. Raj Raman and Katrina Christiansen. The spreadsheet uses literature values of critical biological, engineering, and economic values to make predictions about the yield and energy returns of various crops - in this case the predicted yield of corn grain is 19.8 Mg/ha/yr. (Which is a very optimistic value, near the highest yields reported in the state.) Assume that the crop transpiration ratio (on a grain basis) is 410 kg/kg. Based on the data above, and using clearly stated assumptions where necessary, compute the following in a spreadsheet: Gross energy yield of system (GJ/ha/yr, gge/ac/yr) Total energy inputs for system (GJ/ha/yr, gge/ac/yr) Net energy yield of system (GJ/ha/yr, gge/ac/yr) Energy return on investment (dimensionless - gross output/gross input) Total water use of system (m^3/ha/yr, cm/yr, gal/ac/yr, in/yr) Water intensity of system (m^3/GJ_net, gal/gge) Total cost ($/ha/yr, $/ac/yr) Energy cost - gross basis (S/GJ, $/gge) Discuss your findings, making reference to each of the eight line items above.

Explanation / Answer

1) Gross energy yield = 400 * 0.12

                                = 48 GJ/ha/yr

2) total energy input = 250 * 0.15

                                = 37.5 GJ/ha/yr

3) net energy = 300 * 0.18

                        = 54 GJ/ha/yr

4) energy return   =   5000/1.5

                            = 3333.33

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