INTRODUCTION - PLAN AHEAD
No-till seeding into standing stubble of a previous crop (stubbling-in) is required to provide a trap for snow that protects overwintering wheat from low temperature extremes experienced in most of western Canada. Plant establishment is the critical step in the stubbling-in production system. Surveys have shown that western Canadian farmers have had great difficulty with this step and it has become the factor most limiting the growth of winter wheat acreage. Successful plant establishment requires the acquisition of special management skills and the placement of a high priority on stubble management and the seeding operation.
The production of stubbled-in winter wheat is straightforward and simple, but it does require the use of management practices different from those commonly employed by farmers. Therefore, it is important that winter wheat producers start their planning by obtaining reliable information.
No-till seeding of winter wheat provides most farmers with new challenges, and many of the initial problems encountered are due to inexperience. Farmers geared for spring crop production do not easily make the adjustments required to put their drills in the field in the fall. However, if the production of winter wheat is a priority, a little preparation before the start of seeding can eliminate many frustrations. The first steps are to make sure that the drill is in good repair and that fertilizer and clean seed are available well before the day seeding should start. Most successful no-till winter wheat producers in regions with a short growing season go even further in their planning. They will plan their rotations to include early maturing crops, thereby ensuring that standing stubble is available at an early date. They also make extensive use of aeration grain drying to permit prompt removal of the previous crop from the field allowing for winter wheat seeding during the optimum period. They will aid their seeding operation by spreading chaff and straw uniformly during the harvest operation. Experienced no-till producers have winter wheat on their mind the year round. Novices start to think about it a day or so before they pull into the field to start seeding.
Date and Depth of Seeding
Seed Rate and Row Spacing
Broadcast (Aerial) Seeding
Importance of Management
DATE AND DEPTH OF SEEDING
Note: See Chapter 7 for a detailed discussion of the importance of optimizing seeding date and depth for successful winter wheat production.
Optimum winter wheat seeding dates differ among production areas in western Canada (Table 1). The main factor dictating seeding date is soil temperature. Therefore, optimum seeding dates become progressively earlier as one moves north and east in the prairie provinces.
|1. Lethbridge, AB
2. Maple Creek/Estevan, SK
3. Kindersley/Swift Current, SK
4. North Battleford/Saskatoon/Wynyard/Yorkton, SK
5. Meadow Lake/Prince Albert/Nipawin, SK
Winter wheat survives the winter in the seedling stage. To attain maximum cold tolerance and to provide optimum energy reserves for the following spring, healthy vigorous plants must be established before freezeup. For this reason, seeding date has a large influence on the degree of success that can be achieved in the production of stubbled-in winter wheat. Plants that enter the winter with well developed crowns (area at the base of the shoot from which secondary roots develop) are most desirable. However, plants with 2 to 3 leaves by freezeup are not usually disadvantaged.
Winter wheat undergoes two important physiological changes in the fall. The processes that bring about these changes are known as vernalization and cold acclimation. Vernalization is required before heading will take place the next summer. If seeding takes place after the optimum date, vernalization will be affected and maturity delayed. Cold acclimation is necessary before plants can survive the low temperatures of winter. Vernalization and cold acclimation require growth at morning and afternoon soil temperatures below 7o and 10o C, respectively. In western Canada, soil temperatures below these values are reached between 4 to 5 weeks after the optimum seeding date (Fig. 1). However, the 4 to 5 weeks of growth at higher temperatures is required before complete vernalization and cold acclimation will occur (Fig. 2). This period of growth also insures that the plant develops sufficient energy reserves for a quick start in the spring. Seeding when afternoon soil temperature is approximately 18o C (Fig. 1) usually allows sufficient time for this growth and development to take place before freezeup.
The minimum soil moisture required for germination of wheat is quite low. In fact, germination has been observed in soils where the moisture level has been less than the permanent wilting point (soil moisture so low that established plants will wilt and will not recover under humid conditions at night). The moisture content of the soil influences the amount of water present in the seed at germination and as the soil moisture deceases the amount of water present in the seed at germination also decreases. Consequently, speed of germination is not affected significantly by level of soil moisture ranging from field capacity to permanent wilting point. The effect of soil moisture on speed of plant emergence is also small (Fig. 3).
In contrast to the effect of soil moisture on plant establishment, temperature has a large influence on rate of seed water uptake, speed of germination, and rate of plant emergence. As temperature increases, both the rate of water uptake and speed of germination increase and time to emergence decreases for winter wheat (Fig. 4). For these reasons it is usually advisable to seed at the optimum date as indicated by soil temperature regardless of soil moisture conditions.
Increases in seeding depth result in delays in emergence that are magnified by reduced soil temperatures associated with late seeding. Seeding depth can also have a large influence on plant establishment under conditions of poor soil moisture. Rainfall simulation studies have demonstrated that winter wheat seeded into a dry soil on the optimum seeding date will successfully establish with as little as 1/3 inch of rain. When seeding depth is increased to 1 1/2 inches at least 1/2 inch of rain is required to successfully establish winter wheat when soil temperatures are above 15o C.
The Field Survival Index (FSI) was developed to provide an objective measure of the relative winter hardiness of wheat cultivars (see Chapter 12). For example, the FSI of Norstar, Sundance, and Winalta winter wheat cultivars are 514, 494, and 463 respectively. Differences in cultivar FSI reflect the average percent differences expected in winter survival. Consequently, Norstar is expected to have a 51 percent
The highest level of winter hardiness is usually found in plants from stands that are sown on or near the optimum seeding date (Fig. 2). Seeding too early can result in excessive growth in the fall and plants that are less resistant to winter injury and diseases such as root rot. Early seeding is usually not a problem with stubbled-in winter wheat since removal of the previous crop rarely occurs before the optimum period for seeding. Late dates of seeding often result in plants that are less tolerant to cold (Fig. 2). As an example of the magnitude of the effect of late seeding on winter hardiness, seeding Sundance (FSI = 494) on 1 October in the Saskatoon area would, on average, reduce its FSI
There are significant yield increases and advances in maturity of stubbled-in winter wheat when phosphorus deficiencies are corrected with seed-placed phosphate fertilizer. Phosphorus deficiencies or excesses will also reduce the winter hardiness of winter wheat (Fig. 5). Where deficiencies exist, fertilizer P may act through promotion of spring recovery and not cold hardiness directly. As an example of the magnitude of the effect of phosphorous on winter hardiness, a 15 lb/acre P2O5 deficiency for the cultivar Norstar (FSI = 514) reduces its FSI
The improved plant establishment with shallow seeding often results in better winter survival and higher yield for stubbled-in winter wheat grown in western Canada. Seed placement at a depth of one inch compared to two inches can mean the difference between an undamaged crop and complete winterkill during high stress winters. This represents a cultivar winter hardiness reduction of greater than 100 FSI units due to one inch deeper seeding.
The risk of winter damage is increased when nitrogen (N) is seed placed. Urea (46-0-0) and ammonium nitrate (34-0-0) are the two most common N forms that are seed placed and both can reduce seedling number and size, especially when the soil is dry at seeding. The effect of seed-placed urea is more insidious and damage is usually less of a problem with ammonium nitrate.
It is difficult to establish risk levels for seed-placed N because drill row spacing and opener type determine the concentration of fertilizer in the row and immediately adjacent to the seed. For one of the more common row spacing (8 inch)-opener size (3/4 inch wide) combinations, the reduction in winter survival potential with 30 lb N/acre seed-placed ammonium nitrate (Fig. 6) is similar to the difference in winter hardiness potential between Norstar (FSI = 514-15 = 499) and Sundance (FSI = 494) winter wheat cultivars. This suggests that, even under conditions of good soil moisture, 30 lb N/acre seed-placed ammonium nitrate should be avoided when cultivars with marginal winter hardiness are utilized. The use of high rates of phosphate fertilizer will not counteract the effect that seed-row banded N has in reducing winter hardiness. Placement a minimum of one inch from the seed will minimize seedling damage from high rates of both urea and ammonium nitrate.
Number of heads per square foot is the main factor that determines grain yield of stubbled-in winter wheat. Properly managed winter wheat has a tremendous ability to tiller and thereby compensate for thin stands. However, in spite of a large capacity for tillering, highest grain yields are consistently achieved with narrow row spacing at seeding rates that are higher than most producers currently use for spring wheat. In general, the higher the crop yield potential the higher the seeding rate required to achieve maximum grain yield (Figure 7). Therefore, producers in regions with favorable growing season weather conditions should use higher seeding rates than producers in areas with a high risk of drought. In all cases, row spacings should be as narrow as possible (Figure 8) while still allowing for effective trash clearance by the drill.
The practice of spring seeding winter wheat with a spring crop, such as barley, received considerable attention in the mid-1980's. With this winter wheat production system the spring crop is harvested in the fall, leaving the stubble for snow trapping, and the underseeded winter wheat remains to produce the next crop. The main attraction for underseeding was that it avoided potential conflicts between fall seeding of winter wheat and spring crop harvest.
Underseeding winter wheat was not a new idea in 1980. However, it had never been adequately researched and several disadvantages of this system for establishing winter wheat soon became apparent. The underseeded winter wheat competes with the spring sown crop for moisture and nutrients during the first growing season thereby reducing the production potential of the spring crop. Also, early sown winter wheat is more subject to winter damage and is not as productive as that sown at the optimum date. In addition, the risk of a build-up of diseases, such as Wheat Streak Mosaic virus, is a genuine concern with this system.
BROADCAST (AERIAL) SEEDING
Research studies have shown that seed placement in the soil creates the most favorable environment for successful winter wheat establishment. However, in most of western Canada, the need to no-till seed into standing stubble from a previous crop often produces a conflict between fall seeding and spring crop harvest. This conflict can delay the winter wheat seeding operation until after the optimum date (Table 1). Broadcast seeding of winter wheat on the soil surface in an established immature spring crop in July or August provides an option that would avoid the problems associated with late harvest. The winter wheat begins to grow in the standing spring crop. After the spring crop is harvested in the fall, the winter wheat seedlings are already established and will continue to develop.
Winter wheat seed can be broadcast from ground operated equipment, such as a fertilizer spreader, or an airplane. When compared to ground operated equipment for broadcast seeding into a standing crop, the airplane offers the advantages of less crop damage, speed, and the ability to seed onto wet soils.
Rainfall, dense crop canopy cover, and low evaporation rates are all factors that should favour winter wheat plant establishment with broadcast seeding. However, research trials conducted in east-central Saskatchewan have shown that type of spring crop canopy, or even the presence of an unharvested crop canopy, is not a critical factor in determining the level of broadcast winter wheat germination, seedling establishment, and crop performance. In these studies, optimum broadcast seeding date was approximately two weeks earlier than for conventional no-till drill seeding (Table 1) of winter wheat and, unlike conventional drill seeding, pre-seeding soil moisture was not an important factor in broadcast seed germination.
When seeded on the optimum dates and at the same seeding rate, broadcast winter wheat stand establishment has only been 25 percent of that achieved with conventional no-till drill seeding methods in Saskatchewan. Consequently, yield potential is sacrificed unless broadcast seeding rates are increased to compensate for poor stand establishment (Figure 9). Extrapolation of the grain yield response curve has indicated that maximum grain yield would not be achieved until broadcast seeding rates approach 265 lb/acre (300 kg/ha). In addition to increased seed costs, weight and volume limitations make these high broadcast seeding rates impractical, especially if seeding is done by airplane.
In summary, poor plant establishment has been identified as the main factor limiting success of broadcast seeding of no-till winter wheat in Saskatchewan. A heavy reliance on post-seeding rainfall, high seeding rates, difficulties in seed placement of phosphorus, and a higher risk of failure more than offset the advantages of speed, better opportunity for timely seeding, and improved labour distribution with broadcast compared to drill seeding methods.
IMPORTANCE OF MANAGEMENT
The management practices considered above all have a direct influence on plant establishment and the ability of a cultivar to realize its full winter hardiness potential. These variables are all under the direct control of the producer emphasizing the important role that management skills play in the successful production of stubbled-in winter wheat.