Determining optimal plant population density for annual green manure crops under weedy and weed-free conditions

Yvonne E. Lawley and Steven J. Shirtliffe

Green manure crops are critical to maintaining soil fertility in organic cropping systems. However, little research has been conducted to address their contribution to weed control. Indian Head lentil (Lens culinaris), AC Green Fix chickling vetch (Lathyrus sativus), and Trapper field pea (Pisum sativum) are legumes developed for use as annual green manure crops in the Northern Great Plains. Currently, the recommended plant population density for these crops are based on those developed for seed production of similar genotypes under weed-free conditions. Thus, our objective was to determine to optimal plant population density for these three annual green manures crops under weedy and weed free conditions. The competitive ability of the green manure crops was assessed based on their ability to maintain crop biomass and reduce weed biomass. Each green manure crop was grown at five plant populations (10, 24, 64, 160, and 400 plants m-2) with weedy and weed free treatments. Wild oat
(Avena fatua) and wild mustard (Brassica kaber) were planted in the weedy treatment to supplement the natural weed community. Biomass samples were taken at early and late flowering to simulate when these crops would be terminated. Significant differences in green manure biomass and weed biomass have been found between the three green manure species. Trapper field pea was the most competitive crop while Indian Head lentil appeared to be the least over all plant population densities.

Recommendations for plant populations developed from this experiment will help organic producers take advantage of the weed control offered by a competitive annual green manure while still achieving their objectives of improved soil nutrient status and soil quality.


Source
2nd OACC Organic Research Workshop, Presented in association with the Organic Connections: Prairie Wide Organic Conference and Trade Show, November 14-16th, 2004


Author Locations and Affiliations
University of Saskatchewan, Saskatoon SK, Canada


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