Integrating green manure and grazing systems: A review

Abstract

Thiessen Martens, J. R. and Entz, M. H. 2011. Integrating green manure and grazing systems: A review. Can. J. Plant Sci. 91: 811–824. Green manuring, also referred to as cover cropping, is an ancient practice that is gaining popularity, especially in ecologically integrated farming systems. Much green manure research in Canada has focused on legumes, where green manure plant material is incorporated into soil. This review focuses on the role of livestock in utilizing traditional and novel green manure crops adapted to the Canadian prairies. Legume and non-legume green manure plant species are discussed in terms of suitability to grazing management by different livestock species. Integrating grazing livestock into green manure systems affects nutrient cycling and potential nitrogen (N) loss pathways. However, losses may not be substantially different from other production systems, especially when loss mitigation practices are employed. Grazing green manures may also affect soil biological and physical properties. We conclude that grazing green manures may provide economic as well as biological advantages over the traditional approach of soil incorporation. For example, a green manure biomass yield of 5000 kg ha−1 is sufficient to produce 175 kg ha−1 of animal live weight gain, providing a gross revenue of $385 to $770 ha−1 at April 2011 prices, while returning at least 75% of N and other nutrients to the field. Barriers to farmer adoption of grazed green manure systems include a lack of livestock management knowledge and infrastructure.