Chapter 9
Regional Adaptation

REGIONAL WINTER HARDINESS REQUIREMENTS

The Crop Development Centre (CDC) winter cereal program has conducted a large number of agronomy and physiology studies that have established the relationship between winter survival of wheat and weather conditions in western Canada. The relationship established in these studies has been used to create the computer program that estimates winterkill in wheat in the CERES crop growth simulation model that was developed as part of the United States Department of Agriculture's ARS - Wheat Yield Project and the multi-agency Resources Surveys Through Aerospace Remote Sensing (AGRISTARS) program. In cooperation with the CDC winter cereal program, Environment Canada researchers have analyzed 29 years of climatic data for 53 weather stations in western Canada utilizing the CERES model to determine the winterkill risk for properly managed stubbled-in Norstar winter wheat. These simulations indicated that when snow is maintained uniformly on winter wheat fields by snow trapping in standing stubble, a large area in western Canada has a winterkill risk level as good or better than the traditional production area in southwestern Alberta ( Figure 1 and Figure 2).

The CERES model predicted a low incidence of winterkill for the Wynyard east region and the southeastern tip of Saskatchewan, southern Manitoba and the Banff-Edmonton corridor in Alberta (Figure 1). Eighteen consecutive years of commercial winter wheat production without significant winterkill at the CDC off-station site at Clair (north of the Quill Lakes) verified the reliability of the CERES winterkill risk estimation for the Wynyard east region. In recent years, a significant acreage of stubbled-in winter wheat has been produced both in southwestern and southeastern Saskatchewan. A good potential for stubbled-in winter wheat has been identified in southern Manitoba, but the limitations imposed by the rust hazard in this region have yet to be effectively dealt with. Factors such as the overlap of harvest with the optimum dates for seeding winter wheat have hindered the growth of stubbled-in winter wheat acreage in more northerly regions.

The combined effects of drier air, which crosses the Rockies, and cold arctic invasions were evident in the higher winterkill risk predicted for the area that includes a large part of the Dark Brown soil zone in Alberta and Saskatchewan (Figure 2). However, even in this region, the risk of significant winterkill was low. The consequences of winter damage are further reduced when one considers that most stubbled-in winter wheat fields would be summerfallow in the normal spring crop - summerfallow rotation practised in this region and the option to summerfallow or reseed a winter damaged winter wheat field to a spring crop is always available.

Figure 1. Frequency (%) that more than 10% of the stubbled-in Norstar winter wheat crop is expected to winterkill as estimated by the CERES model (from Savdie, Whitewood, Raddatz and Fowler,1990).



Figure 2 . Frequency (%) that more than 50% of the stubbled-in Norstar winter wheat crop is expected to winterkill as estimated by the CERES model (from Savdie, Whitewood, Raddatz and Fowler,1990).


REGIONAL GRAIN YIELD POTENTIAL

The influence of weather on stubbled-in winter wheat grain yield have been studied in detail in Saskatchewan. Evaporation during the two week period immediately prior to heading, root zone extractable soil water at heading and evaporation during the last two weeks in July have been found to be the primary weather factors determining grain yield in these studies.

Most of the highly drought sensitive stem elongation to heading period for winter wheat occurs in June, which is usually the wettest month of the year (Figure 3). In spring wheat, this critical period occurs later in the growing season when precipitation is normally lower and evaporative demand is higher (Figure 4). A development pattern that is more favorable for western Canadian conditions has been associated with a 32 percent higher grain yield for properly managed stubbled-in winter wheat compared to re-cropped spring wheat in comparative yield trials conducted in Saskatchewan from 1975 to 1979 and 1986 to 1988.

Evaporation rates during the average growing season in western Canada gradually increase from May to July and then drop off quickly in August (Figure 4). Evaporation rates are highest in the southwest and lowest in the north and east of the agriculture region. Consequently, maximum potential grain yield often increases as we move from the Brown soil zone to the Black and Grey soil zones. These environmental differences were reflected in field trial grain yields observed for the ten crop years between 1982 and 1991 in Saskatchewan. In these trials, Norstar grain yields in the Grey/Black were twice as high as those in the Brown soil zone (Figure 5). As with winter hardiness, a greater grain yield potential was found to exist in the Wynyard/Yorkton/Kamsack region of the Grey/Black soil zone of Saskatchewan (Figure 5).


Figure 3. Mean monthly precipitation (25 mm = 1 inch) at the selected stations in Saskatchewan 1951-80 (from Guide to Farm Practice in Saskatchewan, 1984).



Figure 4. Calculated monthly lake evaporation (25 mm = 1 inch) for Swift Current, Wynyard, and Nipawin, Saskatchewan (from Canada Climate Normals, Vol. 9, Environment Canada, Atmospheric Environment Service).


As a re-crop, stubbled-in winter wheat is highly dependent upon precipitation that occurs between harvest of the previous crop (August) and heading (June). Field studies have demonstrated that soil water reserves only contribute approximately 20 percent of the total winter wheat annual water use, while 80 percent is derived from rainfall. These studies also established that stubbled-in winter wheat often exhausts most of its available soil water reserves by heading making later season growth even more dependent upon growing season rainfall. Since growing season precipitation can vary greatly, grain yield of stubbled-in winter wheat can also be expected to vary considerable from year to year (Figure 6).

Large variation in average maximum grain yield was observed among years in the 1982 to 1991 period (Figure 6). In many regions, an extremely dry fall in 1990 resulted in 1991 spring stands that were the least vigorous of the entire ten year period. However, in spite of a poor start, these stands produced excellent grain yields. In contrast, extremely vigorous early spring stands in 1988 produced the lowest grain yields of this ten year period. The yield reduction caused by extreme June drought stress in 1988 and the high yields resulting from a cool, wet June in 1991 once again emphasized the large influence that weather conditions during the stem elongation to heading period have on stubbled-in winter wheat productivity.


Figure 5. Average grain yield trials grown between 1982 and 1991 in Saskatchewan. Total number of trials = 84. Values shown are the average of 10 yearly means for each soil zone. 1000 kg/ha = approx. 15 bu/acre.



Figure 6. Average (brown+dark brown+grey black soil zone)/3 grain yield of NOrstar winter wheat in trials grown in Saskatchewan. Total number of trials = 84. 1000 kg/ha = approx. 15 bu/acre.


The crop years 1984/85, 1985/86, and 1990/91 produced the highest average grain yields in research trials throughout Saskatchewan (Figure 6). Unfortunately, management errors prevented many producers from capturing the grain yield potential offered in 1984/85 and 1985/86. For example, in the severe winter of 1984-85, a difference in seeding depth of 1 inch (2.5 cm) compared to 2 inches (5 cm) often meant the difference between a crop and no crop in the spring. In the winter of 1985-86, seeding at the optimum date and the use of starter phosphate fertilizer was critical to survival in many areas. Late planting and phosphate deficiencies also both resulted in delayed crop maturity that increased yield losses from a severe rust problem in 1986. Seeding date, seeding depth, and fertilizer use are all under the direct control of the farmer once again emphasizing the important role that management skills play in the production of winter wheat in western Canada.