Planting Date Matters

map depicting the optimum planting dates for winter wheat across Ontario

By: Joanna Follings and Emma Dieleman

Ontario’s winter wheat planting recommendations were established in the 1990s using research trials conducted across the province. This research led to the development of the Ontario winter wheat planting date map (Figure 1). This research found that by every day planting is delayed beyond the optimum planting date for a region, 1.1 bu/ac of yield potential is lost. However, with newer genetics and a changing climate, many wondered about the yield potential of later planted wheat and what really leads to increased yields in earlier planting dates. These questions have been answered thanks to new research conducted by Emma Dieleman at the University of Guelph, Ridgetown Campus, under the supervision of Dr. Dave Hooker and Dr. Joshua Nasielski, which provides greater insights into why early planting is so important to maximize winter wheat yield potential.

map depicting the optimum planting dates for winter wheat across Ontario
Figure 1: Optimum planting dates for winter wheat in Ontario.  Winter barley should be seeded 7-10 days prior to the optimum date outlined here for your region.

Four planting dates and two management regimes were assessed and crop biomass accumulation, radiation interception, grain filling rate and duration to compare crop growth and yield formation were measured. The research found that early winter wheat planting increased yields by 10.4 – 50.7 bu/ac (Figure 2). Much of the yield increases could be attributed to an increase in the number of productive heads with early planted wheat having an average of 284-383 heads/ m2 more than the late planted wheat across all locations, regardless of management strategy (Figure 3). Kernels per head and test weight were strongly influenced by environmental conditions during the grain fill period.

Figure 2: Winter wheat yields were maximized with earlier planting dates regardless of management strategy. Seeding rates were the same across all planting dates.

Figure 3: Early planted winter wheat had an average of 284-383 heads/m2 more than late planted wheat across all locations.

Emma’s research also found that by planting wheat early or within the optimum planting window for a particular region, there was earlier canopy closure (Figure 4) and higher biomass accumulation at every single growth stage throughout the season enabling the plants to intercept more solar radiation which ultimately led to an increase in yields.

Figure 4: Winter wheat at mid-early and late planting dates. Earlier planting dates had earlier canopy closure, an increase in biomass accumulation and increase in solar radiation capture compared to later planting dates.

This research re-emphasizes the need to plant winter wheat within the optimum planting date window for a region for maximum yield potential and that current recommendations are still optimal. Implementing strategies such as selecting shorter season soybean varieties in those fields intended for winter wheat, planting after edible beans or canola and early equipment preparation will help ensure winter wheat is planted timely in the fall, maximizing its yield potential.