Effect of nitrogen rate and weed density on spring wheat yield at two landscape positions
Ross, Delaney Meredith
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Site-specific fertilizer applications may have implications for weed population dynamics that have been largely ignored. The purpose of this study was to determine the effect of landscape specific nitrogen application on wild buckwheat ('Polygonum convolvulus' L.) or wild oat ('Avena fatua' L.) competitiveness in spring wheat (' Triticum aestivum' L.). This experiment was separated by weed species. The layout was a split-split plot design wherein the main plot was landscape position (knoll/foot), the subplot was nitrogen rate (not applied/applied), and the sub-subplot was target weed density (0, 25, 50 or 100 plants m -2). The experiment was conducted at sites near Birtle and Carman, Manitoba. Measurements of weed competitiveness included wheat grain yield (as percentage of weed-free treatment), and plant dry biomass (g m -2) for both weed and crop. For analysis, these measurements of weed competitiveness were converted to wheat yield loss, weed biomass, and weed relative biomass. In order to provide a description of the landscape encountered at each site, measurements of soil fertility, gravimetric soil moisture, soil profile characterization, and site topography were taken. Results for the wild buckwheat treatments from three site-years suggest that applied nitrogen increased in the rate of wheat yield loss at the Carman site, and no significant effect of any factors at the Birtle site were observed. In some instances yield of wheat was increased in the presence of wild buckwheat. For the wild oat treatments, results from three site-years indicated that with applied nitrogen, wild oat competitiveness increased significantly, as did wild oat biomass and relative biomass measurements. Landscape position had no consistent effect on wild buckwheat or wild oat competitiveness in spite of significant differences in soil moisture levels between landscape positions.