Introduction

Canada was the sixth largest global producer (32.3 MT) and third largest exporter (22.8 MT) of wheat (Triticum aestivum L.) in 2019 (FAOSTAT 2021). The average wheat grain yield in Canada has more than doubled from 1.5 Mg·ha⁻¹ (1961–1970) to 3.2 Mg·ha⁻¹ (2010–2019) as a result of improved genetics, agronomic management, synthetic fertilizer use, adoption of new technology and mechanization, and increased growing system efficiency (Beres et al. 2020; FAOSTAT 2021). Ultra-early seeding systems have been proposed as a new management approach to increase current grain yield; and enhance the resiliency of Canadian spring wheat growing systems against impending negative yield impacts of climate change (Collier et al. 2020; Collier et al. 2021). Wheat grain yield reduction on the northern Great Plains has been predicted in multiple studies, primarily as a result of reduced in-season precipitation and increased daily temperatures during the critical grain fill period (Kouadio et al. 2015; He et al. 2018; Qian et al. 2019; Collier et al. 2020). An early seeding strategy to avoid environmental stress during grain filling periods has been evaluated in the Australian grain belt and the United States Pacific Northwest (Kirkegaard et al. 2015; Hunt et al. 2018). Ultra-early wheat seeding systems for the northern Great Plains growing region are based on the use of soil temperatures to trigger planting, combined with optimized agronomic management, and are characterized by planting into soils at 2 °C–6 °C and maintaining optimal seeding rates of 400 seeds m⁻². Previously, we evaluated ultra-early wheat seeding systems using experimental cold tolerant spring wheat lines and one Canada Western Red Spring (CWRS) cultivar as a standard check (Collier et al. 2020). Wheat cultivar did not impact grain yield stability in this study; however, a broad evaluation of multiple Canadian spring wheat market classes and hexaploid spring wheat cultivars for adaptation to ultra-early spring wheat growing systems has not been completed to date. The purpose of the present study is to investigate grain yield and grain yield stability of multiple western Canadian spring wheat market classes and registered western Canadian hexaploid spring wheat cultivars planted in an ultra-early wheat seeding system on the northern Great Plains.

Materials and Methods

We conducted the present study at three sites in western Canada in 2017 and 2018, and one site in 2019 resulting in seven total site-years (Table 1). The experiment was seeded as a factorial randomized complete block design with four blocks. Treatment combinations consisted of two seeding dates and twelve wheat cultivars (Table 2). Wheat cultivars were selected based on a combination of the significance of the seeded area of the cultivar within its wheat class in 2016, and the widest genetic variation available within commercial Canadian cultivars for vernalization, photoperiod and height genes (Kamran et al. 2013; Canadian Grain Commission 2021; Statistics Canada 2021). Soil temperatures were determined, and seeding was triggered as previously reported (Collier et al. 2021, 2020). To identify spring wheat lines and classes with increased sensitivity to ultra-early seeding, a sowing density of 200 viable seeds m⁻², known to be sub-optimal in ultra-early wheat seeding systems, was used (Collier et al. 2021). Seeding equipment and operations, nutrient and pest management and data collection was completed as reported by Collier et al. (2021).

Table 1.

Post-seeding air temperature extremes and cumulative freezing events recorded at each location × year.

Table 2.

Least square means for grain yield, grain quality parameters, and plant counts for multiple western Canada wheat cultivars/classes planted ultra-early.

Statistical analyses were completed using the MIXED procedure of SAS (Version 9.4, Cary, NC, USA) and followed the procedure of Collier et al. (2021), with the exception that the combined ANOVA was completed with site-year, replication, soil temperature trigger and cultivar as variables in the CLASS statement (SAS Institute 2018).

An LSMESTIMATE statement for grain yield with soil temperature trigger × cultivar as a fixed effect was used to compare the grain yield of each cultivar when seeded at either 2 °C or 8 °C soil temperature.

A biplot grouping methodology using mean grain yield on the vertical axis and adjusted coefficient of variation (aCV) on the horizontal axis, as originally described by Francis and Kannenberg (1978) and modified by Doring and Reckling (2018), was used to explore system stability and variability of grain yield with multiple wheat cultivars and wheat classes. We categorized data on the biplots into four groups/quadrants divided by the mean aCV and the mean grain yield of the growing system: (Group I) high mean grain yield and low variability, (Group II) high mean grain yield and high variability, (Group III) low mean grain yield and high variability, and (Group IV) low mean grain yield and low variability.

Results

Wheat class and grain yield stability

To visualize the effect of planting date, wheat cultivar and wheat class on grain yield and growing system stability, a modified biplot grouping methodology was employed. The original methodology of Francis and Kannenberg (1978) was modified to include an adjusted coefficient of variation (aCV) in the place of a traditional coefficient of variation as described by Doring and Reckling (2018). The use of an aCV negates the dependence of system stability on the magnitude of the realized grain yield. Biplot A in Fig. 1 illustrates the stability of each cultivar when planted ultra-early into 2 °C soil and when planted into soil at 8 °C. All points related to the 8 °C soil temperature planting trigger are located right of the mean aCV value and are located in Groups II and III of the biplot; which are defined by lower grain yield stability than the data points in Groups I and IV. All of the cultivars planted ultra-early are represented on the left side of the mean aCV value, in Groups I and IV. This indicates the greatest grain yield stability occurred when the cultivars in this study were planted at an ultra-early timing triggered by 2 °C soil temperatures despite the harsh environmental conditions experienced after planting. Biplot B presents the same data points grouped by Canadian wheat market class rather than by specific cultivar. The CWSWS and CWSP cultivars had the greatest grain yield, while CPSR and CWRS cultivars had relatively lower grain yield. Relative grain yield between wheat classes was consistent regardless of planting time. All wheat classes performed similarly in response to ultra-early planting, with similar grain yields relative to planting at 8 °C, but exhibited improved grain yield stability and thus, improved growing system stability when planted in 2 °C soil.

Fig. 1.

Biplots summarizing grain yield means versus adjusted coefficient of variation (aCV) for each wheat cultivar planted at each soil temperature (A), and for each Canadian wheat market class planted at each soil temperature (B). Abbreviations are as follows: (I) The first word represents the soil temperature at planting (early = 2 °C soil temperature, late = 8 °C soil temperature). (II) The second word denotes the wheat cultivar in Biplot A (See Table 2 for full wheat cultivar names), or the functional class of the wheat cultivar in Biplot B (CWRS, Canada Western Red Spring; CPSR, Canada Prairie Spring Red; CWSWS, Canada Western Soft White Spring; CWSP, Canada Western Special Purpose; CT, cold tolerant). The use of colour serves to group data points by soil temperature at planting (Biplot A), and by wheat functional class (Biplot B). Biplot group definitions: (Group I) high mean grain yield and low variability; (Group II) high mean grain yield and high variability; (Group III) low mean grain yield and high variability; (Group IV) low mean grain yield and low variability.

Discussion

We have reported that planting wheat ultra-early based on soil temperature on the northern Great Plains of western Canada not only maintained grain yield, but can also lead to increased grain yield over delayed planting (Collier et al. 2021, 2020). These previous studies reported that specially developed cold tolerant spring wheat lines were not required to successfully plant wheat ultra-early; however, these studies only evaluated one cultivar from the CWRS wheat class. Here, we evaluated nine wheat cultivars from four Canadian wheat market classes, as well as three cold tolerant lines. In all cases, when wheat cultivars were planted earlier (2 °C soil temperatures in the top 5 cm of soil) the growing system stability was superior to the same cultivars planted later at 8 °C soil temperatures. Collier et al. (2021) evaluated manipulations to agronomic management of ultra-early wheat seeding systems to increase grain yield and growing system stability, and reported that using optimal seeding rates (400 seeds m⁻²) was a critical agronomic management strategy to maintain or increase grain yield and growing system stability in an ultra-early wheat seeding system. In the present study, a sub-optimal seeding rate (200 seeds m⁻²) was used to identify wheat cultivars or classes susceptible to decreases in grain yield or growing system stability as a result of ultra-early seeding. The lack of a negative response in grain yield and growing system stability when planted ultra-early at sub-optimal seeding rates indicates that broad adaptation to ultra-early seeding systems exists within a majority of Canadian wheat germplasm and commercially available cultivars representing dominant market classes in western Canada.

This work corroborates the results of previous studies and supports the expansion of current ultra-early wheat growing system recommendations to include additional wheat classes in western Canada. Spring wheat from Canadian wheat market classes including, but not limited to, CWRS, CWSWS, CPSR, CWSP and Canada Northern Hard Red (CNHR) can successfully be planted in ultra-early wheat growing systems. The impacts of a changing climate including fewer precipitation events and increased daily temperatures may disproportionately affect higher-yielding, lower protein wheat cultivars such as CWSWS and CWSP class cultivars that require longer grain-filling periods and longer growing seasons. Shifting planting to earlier in the season and optimizing agronomic management within an ultra-early wheat growing system acts as an avoidance mechanism to negate, or reduce, future grain yield losses resulting from climate change. In such a scenario, a shift to ultra-early seeding may serve as a mitigation strategy to maintain current grain yield potential and achieve further yield gap closure on the northern Great Plains.

Conclusions

Canadian hexaploid spring wheat cultivars exhibited broad suitability for use in ultra-early wheat growing systems. The most successful ultra-early wheat growing systems will incorporate commercial Canadian hexaploid spring wheat cultivars, planted at optimal seeding densities of not less than 400 seeds m⁻², when soil temperatures of 2 °C–6 °C in the top 5 cm of the soil surface are first observed. Ultra-early growing systems incorporating these management tactics will lead to increased grain yield and grain yield stability relative to current conventional wheat growing practices and increase the resiliency of wheat growing systems on the northern great plains.

Competing Interests

The authors declare there are no competing interests.

Author Contributions

Mr. Collier, Senior Corresponding Author — co-developed and conceptualized the hypotheses and field experiments. Used project for partial fulfilment of PhD thesis requirements at the University of Alberta. Analyzed data and prepared manuscript. Participated in meetings and presented findings at conferences, field days and grower meetings.

Dr. Beres, Co-Investigator/Corresponding Author — co-developed and conceptualized the hypotheses and field experiments. Identified and recruited Collaborators, PhD student, and led workshops to finalize proposal. Participated in meetings and presented findings at conferences, field days and grower meetings. Co-supervises Mr. Graham Collier.

Dr. Graf, Co-Investigator — developed cold-tolerant lines used for field experiments. Reviewed and edited manuscript.

Ms. Gampe, Co-Investigator — site collaborator at Scott, SK Research Farm. Reviewed and edited manuscript.

Dr. Spaner, Principal Investigator — responsible for the field experimentation at the Edmonton sites. Co-Supervisor of Mr. Graham Collier. Reviewed and edited manuscript and mentored manuscript preparation and statistical analyses.