Department of Plant, Soil and Microbial Sciences Cropping Systems Agronomy

Optimal planting time and seeding rate are important factors in winter wheat (Triticum aestivum L.) stand establishment and can lead to significant improvements in yield potential. However, data on the responses of recently released cultivars to seeding rates is lacking and is needed to update recommendations, as well as to determine the current yield penalty from delayed planting. Therefore, research was conducted to evaluate the impacts of planting date and seeding rate on stand establishment and grain yield in winter wheat. A replicated field experiment was conducted over two growing seasons (2019–2020 and 2020–2021) in Mason, Michigan in a split-plot design. Whole plots consisted of five planting dates (starting mid-September and planting every 12–18 days until mid-November). Subplots consisted of five seeding rates (2.0, 3.0, 4.0, 4.9, and 5.9 million seeds ha^-1). Data collection included stand counts at Feekes 1–2, phenology (emergence, anthesis, physiological maturity), and final yield. No interaction between planting date and seeding rate was observed in either year. Both years showed a decrease in yield from planting after late September, but the rate of decrease varied significantly between years, likely due to differences in winter weather. The agronomically optimal seeding rate based on ANOVA was 4.9 million seeds ha^-1 in 2019–2020 and 3.0 million seeds ha^-1 in 2020–2021, but the differences between seeding rates >3.0 million ha^-1 were minor and associated with a high degree of variability. Overall, results indicated that planting after late September reduces yields, but the rate of decrease depends on weather conditions after planting. Furthermore, it may be possible to reduce seeding rates for late planting below the current recommendation of 4.0 million seeds ha^-1 or more for late planting without suffering a yield penalty.