Energy Input and Output Analysis of four Field Crops in California¹

TLDR

Four crops—corn, sweet sorghum, fodder beet, and sugarbeet—were grown in irrigated plots at UC Davis in 1980–1981. The study aimed to identify the most energy‑efficient nitrogen input for each crop by evaluating six fertilizer levels (0–280 kg ha⁻¹). Energy input and output were analyzed by measuring cultural energy costs and potential ethanol yields for each crop. Energy input costs per hectare were 30.9 GJ for corn, 30.4 GJ for sweet sorghum, 49.4 GJ for fodder beet, and 41.0 GJ for sugarbeet, with liquid fuel operations accounting for 35 % of inputs, irrigation 23 %, and nitrogen fertilizer 19 %; fodder beet yielded the highest fermentable carbohydrate at 13.05 Mg ha⁻¹, followed by sugarbeet (11.5 Mg ha⁻¹), sweet sorghum (9.71 Mg ha⁻¹), and corn (8.09 Mg ha⁻¹), translating to energy inputs per liter of potential ethanol of 6.42 MJ L⁻¹ for corn, 5.25 MJ L⁻¹ for sweet sorghum, 6.35 MJ L⁻¹ for fodder beet, and 5.95 MJ L⁻¹ for sugarbeet.

Abstract

Abstract Four crops, corn ( Zea mays L.), sweet sorghum ( Sorghum bicolor L.), fodder beet ( Beta vulgaris L.) and sugarbeet ( Beta vulgaris L.) were grown in irrigated plots at the experimental farm of the University of California, Davis, in 1980 and 1981. Six fertilizer N levels ranging from 0 to 280 kg ha −1 were used to estimate the most efficient N input for each of the tested crop in terms of energy input and output analysis. Calculations of cultural energy input costs in relation to potential ethanol yield showed production requirements of: corn 30.9 GJ ha −1 , sweet sorghum 30.4 GJ ha −1 , fodder beet 49.4 GJ ha −1 and sugarbeet 41.0 GJ ha −1 . Highest average energy inputs were for liquid fuels for operations 35%, irrigation 23% and fertilizer nitrogen 19%. Fodder beet had the highest fermentable carbohydrate yield at 13.05 Mg ha −1 followed by sugarbeet at 11.5 Mg ha −1 . Sweet sorghum and corn yields were lower at 9.71 and 8.09 Mg ha −1 , respectively. Crop production inputs of energy per liter of potential ethanol were: corn 6.42 MJL −1 sweet sorghum 5.25 MJL −1 , fodder beet 6.35 MJL −1 and sugarbeet 5.95 MJL −1 .