The effects of legume green manures, perennial forages, and cover crops on non-renewable energy use in western Canadian cropping systems
Hoeppner, Jeffrey Wayne
Inputs such as machinery, fuel, pesticides and fertilizers contribute to energy expended in cropping systems. Reducing non-renewable energy use (EU) and increasing energy use efficiency (EUE) can make cropping systems more sustainable. Nitrogen benefits of legumes to succeeding non-leguminous crops are well documented. This study examined the effect of green manure and perennial forage legumes on energy efficiency of crop production for four western Canadian crop rotation studies: Lethbridge, AB; Swift Current, SK; Indian Head, SK; Glenlea, MB. Relative to continuous grain rotations, rotations containing 50% perennial forage legumes decreased EU by up to 85% and increased EUE by up to 438%. Relative to cereal, pulse and oilseed rotations, they reduced EU by up to 28% and increased EUE by up to 294%. Rotations containing green manure legumes decreased EU by up to 65%, and increased EUE by up to 196%. The primary contribution of legumes to lower energy use was nitrogen addition to the soil. Depending on site and rotation, economic performance of legume rotations varied compared to annual grain rotations. The rotational benefits of relay intercropped and double cropped legumes in cont nuous grain systems in Manitoba were also investigated. When examining relay intercropped alfalfa and red clover and double cropped chickling fetch and lentil, it was found that considerable nitrogen benefits were provided to a succeeding oat crop by all legumes at Winnipeg, and by some legumes at Carmen. Reduced legume growth at Carmen, due to drought conditions, resulted in few yield benefits from the relay intercropped and double cropped legumes. Including relay intercropped and double cropped legumes in continuous grain rotations reduced energy use by up to 39%, and increased energy use efficiency by up to 28%. Increasing the frequency of legumes in cropping systems shows promise to enhance agricultural sustainability.