Previous studies have indicated that crosses between spring and winter wheat cultivars can result in spring growth habit cultivars with cold tolerance similar to winter wheats (Larsen 2012).  Agronomic studies focusing on seeding date tend to indicate a yield advantage to early seeding of spring wheat due to a number of factors including increased leaf area at summer solstice, efficient use of spring moisture, and earlier grain fill (Lanning et al. 2012).  This project aims to combine cold tolerant spring wheat genetics with ultra-early seeding in the western Canadian prairies in order to maximize yield and identify the limits of acceptable risk for seeding into cold soils.

One of the key methods in this study was the determination of seeding date.  Most published studies report seeding date as a day on the calendar – this is subject to variation from location to location and from year to year, thus it is not an ideal standardized measure for replication.  For example, 2016 was a very early spring in western Canada while 2018 was a late spring, a grower seeding on May 1 in 2016 and 2018 would have had many more growing degree days elapse prior to seeding on May 1, 2016 than seeding on May 1, 2018.  In order to standardize seeding date, soil temperature was used as an indicator – this allowed seeding to occur relative to climate and growing degree day accumulation in each year. Soil temperatures ranging for 0^oC to 10^oC were evaluated with large variations in initial seeding date resulting from year to year.  For example, in 2016 0^oC treatments were sown as early as February 16 in Lethbridge, AB., while in 2015 the same seeding date in Lethbridge was not completed until March 6.  Despite being separated by 18 calendar days these dates are a close approximation to the same relative points within the growing seasons of 2015 and 2016. (Note: Soil temperatures were determined daily at 5cm depth during the seeding window.)

The main focus of this study was to determine the performance of cold tolerant varieties relative to conventional varieties when seeded ultra-early into cold soils in western Canada, and to determine if manipulations to agronomic management practices could mitigate risks associated with early planting.  Three cold tolerant lines and AC Stettler were seeded across the 0 – 10^oC soil temperature range, results have clearly indicated that the conventional variety (AC Stettler) performed as well as the cold tolerant varieties and that optimal grain yield was achieved when seeding occurred between soil temperatures of 2 – 8^oC.  The cold tolerant lines out-yielded AC Stettler however, this can be attributed to the lower grain quality and higher yield potential of the cold tolerant lines versus the CWRS AC Stettler.  The stability of yield under ultra-early seeding was essentially equivalent between AC Stettler and the cold tolerant lines.  A numerical yield drag was evident when seeding occurred at 0^oC and 10^oC while the 2 – 8^oC seeding dates showed greater yield and yield stability.

Seeding rate and seeding depth were also evaluated for their effect on the stability of this growing system.  Seeding depth had little effect on system stability, grain yield or grain quality.  Manipulations to seeding rate had significant effects on multiple yield and quality parameters.  Higher seeding rates (400 seeds m^-2), resulted in improved system stability and greater grain yield relative to lower seeding rates (200 seeds m^-2).

The results of this study indicate a strong potential for growers in western Canada to successfully seed spring wheat earlier than dictated by current practice.  These results have obvious impacts in terms of farm labour and resource management during the busy spring seeding season however, the greater impact may be a long term one as climate change shifts the growing season in western Canada earlier, shifts a majority of precipitation accumulation earlier, and increases heat stress later in the growing season.