Production, economic, and energy life cycle analysis can produce contrary results for corn used in ethanol production

To prepare for a carbon (C) constrained economy, crop production energy audits or life cycle analysis (LCA) must be conducted. However, energy audits may not maximize profitability. This study conducted simultaneous production, economic, and energy audits to evaluate differences among these assessments. The 2005 and 2006 South Dakota field experiment contained two nitrogen (N; 0 and 224 kg N ha⁻¹) rates, two corn population levels (76,500 and 149,000 plants ha⁻¹), and two simulated landscape positions (upper backslope and lower backslope). The energy inputs, outputs, and net energy gain for corn grain used in ethanol production were calculated using the Nebraska Biofuel Energy Simulator (BESS) version 2008.3.1. For LC analysis, corn grain was used in ethanol production and dry distiller's grain was used as a livestock feed. Manure was not applied to the field. A partial economic analysis to examine profitability was conducted where seed, N fertilizer, and corn values were $312 (100,000 seeds)⁻¹, $1.25 (kg N)⁻¹, and $158 (Mg grain at 15.5% moisture)⁻¹, respectively. Results showed that: 1) to maximize profitability and energy gains, inputs must closely match crop needs for a site; 2) increasing the population level from 74,500 to 149,000 plants ha⁻¹ increased energy input and output, increased yield and energy gain by 11%, but did not influence profitability; 3) increasing N from 0 to 224 kg N ha⁻¹ increased yield 7%, reduced profit by $145/ha, increased energy input and output values, but did not impact energy gain; and 4) corn grown in high yielding areas of landscapes may have higher yields (P = 0.08), profitability (P = 0.08), and energy gains (P = 0.08) than other areas. These calculations demonstrate that yield, profitability, and energy audits may have divergent results.