Preceding crops and nitrogen effects on crop energy use efficiency in canola and barley

Energy use efficiency (EUE) is a key concept which may be used to benchmark best practices in cropping systems through comparison of the impacts of both preceding crops (PCs) and agricultural inputs on crop yield. The EUE is a metric to measure how cultural practices, such as N application and rotational crop use, can influence sustainability in a canola (Brassica napus L.) (C)–barley (Hordeum vulgare L.) (B) rotation. In a 2009 to 2011 PC–C–B rotation study, six PCs (fi eld pea [Pisum sativum L.], lentil [Lens culinaris Medik.], faba bean [Vicia faba L.], canola, wheat [Triticum aestivum L.], and green manure [GRM] legume faba bean) were grown in factorial combination with five N rates (0, 30, 60, 90, and 120 kg ha−1), on field experiments at seven sites across western Canada. When the PC was GRM, the energy output of C or C–B was highest, but insufficient to compensate for lost output during the GRM phase (2009). For all cropping systems, the quadratic response of energy output to optimal N indicated that N applied could be reduced below 120 kg ha−1 without diminishing energy output at some locations. Over the entire 3-yr crop sequence, legume PCs (lentil or field pea) grown for seed provided the greatest EUE. The GRM improved the yield, and therefore energy output and EUE, of the following crops considerably, but the increased canola and barley energy outputs were not able to alleviate the lost energy output during the preceding crop phase.