Nitrogen Rate and Harvest Corn Stover Impacts the Profitability and Energy Gains of Corn Grown in South Dakota.

Abstract

To maximize energy gains and profitability, research that addresses differential responses of corn (Zea mays) to N and water stress is needed.  The objective of this study was to assess the impact of N rate, corn harvesting approach and simulated landscape positions on the energy and economic efficiency of corn (Zea mays) used in ethanol production.  The field experiment was conducted in 2002, 2003 and 2004.  The experiment contained 4 nitrogen (0, 56, 112 and 168 kg N ha^-1) rates, two soil water regimes (moderate and high) and two harvesting methods (grain with 100% stover returned and grain + 40% corn stover returned). No till was used at the site. Energy gains and efficiency for corn grain used in ethanol production were calculated using the Nebraska Biofuel Energy Simulator (Bess) Model version 2008.3.1.  Profitability was estimated where seed, nitrogen (N) fertilizer, corn grain, and stover values were $312 (100,000 seeds)^-1, $1.25 (kg N)^-1, $158 (Mg grain at 15.5% moisture)^-1, and $66.3 (Mg)^-1 of dry stover, respectively.  Non seed and N production costs were estimated at $741 ha^-1.  The highest energy gains and financial returns were observed in the 112 kg N ha^-1 (46.61 GJ ha^-1 and $427 ha^-1) treatment and the lowest values were observed in the 0 kg N per ha^-1 (37.49 GJ ha^-1 and $192 ha^-1) treatment. Applying additional N beyond the 112 kg N/ha rate did not further increase energy gains. Profits were increased by 60% when corn stover was harvested for ethanol production. These results were attributed to all costs being attributed to grain production. Unfertilized corn had a higher (2.06) energy efficiency than corn fertilized with 112 kg N ha^-1 (1.91).  The moderate water regime had a lower energy gain (40.2 GJ ha^-1 and $453.29 ha^-1) and financial return than the high water regime area (46.0 GJ ha^-1 and $644.26 ha^-1).  These results showed that N, harvest corn stover and water regime can impact energy gains, energy efficiency, and financial returns.  At this study site, corn used in ethanol production had a positive energy balance.  

Keywords: Energy ratio, landscape position, Life cycle assessment (LCA), Ethanol