Energy output:input ratio of maize and sorghum management systems in eastern Nebraska

Abstract

Crop management systems need to be designed to help farmers maintain economic profitability, while conserving external energy resources and farming in an environmentally responsible manner. The objective of this study was to determine the energy output:input ratio of several maize ( Zea mays L.) and sorghum ( Sorghum bicolor (L.) Moench.) management systems that are typical of eastern Nebraska, USA. Management variables were, (1) nitrogen (N) fertilization, (2) previous crop (cereal or legume), (3) tillage (none or traditional), (4) herbicide (none, banded, or broadcast), and (5) water (dryland, limited irrigation, or full irrigation). Eleven management systems were delineated from different combinations of the last four variables and compared at different levels of N fertilization. The energy output:input ratio ranged from 4.1±0.5 in fully irrigated, broadcast herbicide, traditional tillage systems with cereal as previous crop and no N fertilizer to 11.6±2.5 in dryland, broadcast herbicide, traditional tillage systems with legume as previous crop and no N fertilizer. The energy output:input ratio decreased with the addition of N fertilizer in all management systems, except in fully irrigated, continuous cereal systems. Management systems with legume as previous crop had a greater energy output:input ratio than those with cereal as previous crop. Under dryland conditions with traditional tillage, the energy output:input ratio was greater with herbicide usage than without. Dryland management systems had greater energy output:input ratios than systems with irrigation. The obvious short-term advantage of greater food production from irrigated agriculture using high levels of fossil fuel derived inputs must be balanced against the long-term costs to society of depleting a scarce and non-renewable energy resource. Rotation of cereals and legumes under dryland conditions in the western Corn Belt may be more sustainable for the future based on energy use efficiency because of lower fossil fuel requirements from N fertilizer and irrigation.