Embodied energy and energy return on investment analyses in maize production for grain and ethanol under center pivot, subsurface drip, and surface (furrow) irrigation with disk tillage and no-till practices

Abstract

Various inputs and outputs, including irrigation systems and tillage practices, play important roles in irrigated maize production in terms of the embodied energy used for producing grain. The energy used for yield production can also be a strong function of the irrigation method. Comprehensive studies that analyze these dynamics in the context of the energy requirement of each input in crop production are rare. Using the system material flow approach as a basis for energy input and output calculation, the energy return on investment (EROI), and embodied energy concepts, this study analyzed multiple scenarios to determine the energy use of different irrigation methods for maize grain and ethanol production under center pivot, subsurface drip, and surface (furrow) irrigation and under no-till and conventional (disk) tillage in Nebraska. No differences in EROI were found for the same irrigation system between the two tillage practices. However, subsurface drip irrigation had greater EROI than furrow and center pivot irrigation under both tillage practices. Subsurface drip irrigation had 43% and 29% greater EROI than center pivot and furrow irrigation, respectively, under both no-till and conventional tillage. Direct energy used to pump, elevate, and/or pressurize the irrigation water ranged from 25% (for subsurface drip irrigation) to 29% (for center pivot irrigation) of the total embodied energy used for maize production. Among various irrigation amounts and grain yields analyzed, the best value of EROI was 0.24 MJ MJ-1 with subsurface drip irrigation when applying 100 mm of water with a yield of 14 Mg ha-1. The lowest value of EROI was -0.07 MJ MJ-1 with center pivot irrigation when applying 500 mm of irrigation water with a yield of 9.5 Mg ha-1. When the co-product credit is considered, the resulting EROI values were 0.08, 0.14, and 0.10 MJ MJ-1 for center pivot, subsurface drip, and furrow irrigation, respectively, under conventional tillage. The embodied energy for machinery and diesel fuel consumption in the field operations ranged from 5% to 7% of the total energy. The energy associated with chemicals and seed ranged from 45% to 50% of the total energy and was always highest in no-till for the same irrigation method. The energy used for grain drying ranged from 13% to 14% of the total embodied energy. The total labor for maize production, including labor for irrigation, was only 1% of the total embodied energy with furrow irrigation and was less than 1% with the other irrigation methods. The total embodied energy for irrigation exhibited a non-linear correlation with the amount of water applied for all irrigation systems, emphasizing the importance of using individual analysis to incorporate irrigation‘s substantial role in studies involving energy use versus crop production.