Effect of crop rotations and fertilization on energy balance in typical production systems on the Canadian Prairies

Abstract

Non-renewable energy inputs (both direct and indirect), metabolizable energy output and the energy efficiency of 10 spring wheat ( Triticum aestivum L.) rotations were examined over an 18-year period on a loam soil in the Brown soil zone of the Canadian Prairies. The rotations, which were managed using conventional tillage methods, included a range of crops, cropping intensities, crop sequences and fertilizer practices. The results showed that the total energy input per unit of land was lowest for the traditional fallow-wheat (F-W) rotation (3482 MJ ha −1), intermediate (4470 MJ ha −1) for N- and P-fertilized fallow-wheat-wheat (F-W-W) and highest for N- and P-fertilized continuous wheat (7100 MJ Ha −1). Substituting flax ( Linum usitatissimum L.) or rye ( Secale cereale L.) for wheat in the rotations reduced total energy input by 3 to 8%, while withholding the application of either N or P fertilizer reduced total energy input by 16–37%. Liquid fuel for field operations and local product transport, and fertilizer (primarily N) were the major energy inputs; both increased with cropping intensity. Fuel accounted for 30–50% of the total energy input of the rotations. Fertilizer represented 15–49% of the total energy input and was of greater importance than fuel for the continuous crop rotations. Despite the high energy content in pesticides, they accounted for only 4–11% of the total energy input of the rotations. Metabolizable energy output displayed similar response patterns as total energy input reflecting the higher total annual grain yields as cropping intensity increased. For example, energy output averaged 12639 MJ ha −1 for F-W, 14641 MJ ha −1 for F-W-W and 17764 MJ ha −1 for continuous wheat. In contrast, the energy output to input ratios and the quantity of wheat produced unit −1 of energy input decreased with cropping intensity. The average energy output to input ratio for F-W was 3.6, or 262 kg of wheat GJ −1 of energy input, while those for F-W-W and continuous wheat were 3.3 and 2.6, or 240 and 191 kg of wheat GJ −1 of energy input, respectively. Rotations that included flax or cereal forage crops had the lowest energy efficiencies.