Optimizing the nitrogen supply of prairie organic agriculture with green manures and grazing

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2014, 2014
Cicek, Harun
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Agricultural Institute of Canada
Grazing and no-till management in organic systems have been recently proposed tools to improve nutrient cycling and sustainability. From 2008 to 2012 a series of field experiments were established to identify green manure species and green manure management options to maximize N benefit to following cash crops and explore the opportunities to reduce tillage during the green manure phase of an organic rotation. A total of four green manure systems (double-cropped green manures, relay-cropped green manures, full season green manures, and catch crops after grazed full season green manures), three green manure management options (soil incorporation, grazing and no-till), and 10 green manure species, as well as, three green manure mixtures were tested. Double-cropped pea (Pisum sativum cv. 40-10) and relay-cropped red clover (Trifolium pratense) produced around 900 kg ha-1 and 2000 kg ha-1 of biomass respectively. The greatest biomass producing full season green manures were hairy vetch (Vicia villosa L.), pea/oat (Avena sativa cv. Leggett/Pisum sativum cv. 40-10) and sweet clover (Mellilotus officinalis cv. Norgold). Pea/oat and hairy vetch were the most weed competitive species and on average contained less than 15% weed biomass. Among all the systems and managements tested, nitrogen availability was greatest when full season green manures were grazed. On average grazing increased soil NO3-N by 25% compared to soil incorporation using tillage. Among grazed species, pea/oat mix and hairy vetch green manures resulted in the greatest amount of soil available NO3-N. Catch crops after grazing green manures, regardless of the species, significantly reduced N leaching risk compared to no catch crop treatment, but also reduced wheat productivity the following year. Catch crop biomass productivity and N uptake, soil NO3-N, and wheat productivity were similar in direct seeded and conventionally seeded plots. Grazing may be an effective tool in reducing tillage in organic agriculture because of its ability to accelerate the N mineralization from catch crop biomass. This study was the first study to use grazing as a management tool for green manures in organic systems. Results provide strong evidence that green manures, especially when grazed, can be effective nitrogen suppliers in organic grain based rotations.
Organic agriculture, Grazing green manures, Cover crops
Cicek, H., Thiessen-Martens J.R., Bamford K., Entz, M.H. (2014). Effects of grazing two green manure crop types in organic farming systems: N supply and productivity of following grain crops. Agriculture, Ecosystems and Environment. 190, 27-36.
Cicek, H., Entz, M.H., Thiessen-Martens J.R., Bullock (2014). Productivity and nitrogen benefits of late season legume cover crops in organic wheat production. Canadian Journal of Plant Science. 94(4): 10.4141/cjps2013-130.