Tillage and rotation effect on corn-soybean energy balances in eastern Nebraska

Data from a field experiment conducted in eastern Nebraska over 16 years (1986-2001) were used to determine the energy balance of corn (Zea mays L.) and soybean (Glycine max L.) as affected by tillage treatments and rotation. Tillage treatments included chisel plow, tandem disk, moldboard plow, ridge-tillage, no-till and subsoil tillage. Crop sequences were continuous corn, continuous soybean, corn in a corn-soybean rotation and soybean in a soybean-corn rotation. The energy balance was assessed by comparing the parameters: energy gain (net energy output), energy intensity (energy input per unit grain equivalent, GE) and output/input ratio. Changes in plant density, crop production practices and machinery over the course of the study were taken into account in the analysis. Averaged across years, the no-till treatment required lower energy input (7.34 GJ ha-1) than tandem disk (7.65 GJ ha-1), ridge-till (7.69 GJ ha-1), chisel plow (7.83 GJ ha-1), subsoil-tillage (7.96 GJ ha-1) and moldboard plow (8.72 GJ ha-1). The energy input was lower for soybean systems than corn. Hence, the lowest energy input was required for soybean with no-tillage (5.43 GJ ha-1) and highest for corn systems with moldboard plow tillage (10.6 GJ ha-1). Within a rotation the tillage treatment had a small effect on energy output with energy efficiency being more strongly affected by crop rotation than by tillage method. Moldboard plow tillage maximized the energy gain while reduced tillage (ridge-till, no-till) minimized energy intensity and maximized output/input ratio. Within crops and crop rotations, the highest energy gain (98 GJ ha-1) and lowest energy intensity (162.4 GJ GE-1) occurred in corn production. For both corn and soybean, the energy gain was greater for crop rotations (92.8 GJ ha-1) than monocultures (78.0 GJ ha-1). The output/input ratio was greatest for rotated corn (14.0) and lowest for continuous soybean (9.9). Crop rotations that include legumes and reduced tillage improve the energy efficiency of crop production systems.