Winter Wheat Cropping System Response to Seed Treatments, Seed Size, and Sowing Density.

Poor stand establishment resulting in lower yield is a major constraint to expanding winter wheat (Triticum aestivum L.) across western Canada.  To address this issue, we conducted a study totaling 26 site-years over three growing seasons (2011-2013) to observe crop responses to system manipulations involving seeding rate (200 and 400 seeds m^-2), seed size as a proxy for plant vigor (light/thin, moderate, heavy/plump), and a dual fungicide/insecticide seed treatment, on crop establishment, yield, and seed quality.  Fall and spring plant density was about 10 plants m^-2 greater for heavy seed vs. light seed.  Seed treatment improved fall and spring plant density slightly more than 10 plants m^-2.  The dual seed treatment improved yield and test weight for thin seed size.  Hypothesized weakest agronomic systems (low seeding rate and untreated, light seed) that often included the 200 seeds m^-2 seeding rate were the poorest performing (sub-optimal responses and highly variable) systems; however, a favorable response to seed treatments allowed for partial compensation and grain yield comparable to systems with high seeding rates.  Greater instability was generally observed in weak systems irrespective of seed treatment.  The economic advantage of the seed treatment was more apparent with thinner winter wheat stands as it resulted in greater gross (+$31 ha^-1) and net (+$22 ha^-1) returns.  This study reaffirms the importance of a strong and integrated agronomic system and indicates seed treatments can help offset weak systems comprised of poor stand establishment and lower yield performance.