Features Agronomy Cereals
Seeding winter wheat this fall

Aug. 18, 2010 – Spring weather conditions across much of the southern prairies were excessively wet in April, May and June, 2010. As a result, about 10 percent of land in southern Alberta was not seeded. Some fields that were seeded had excessive moisture, causing crops to drown out by mid- to late June. For farmers with fields that did not get seeded or fields that were drowned out due to excessively wet conditions, they may want to consider establishing winter wheat in these fields in early September. Seeding these fields to winter wheat would utilize soil moisture and provide a protective crop cover for soil going into winter.

Winter wheat is an excellent crop for southern and central Alberta farmers to consider growing. It is usually seeded in early September and harvested several weeks earlier than spring seeded wheat the following year. Including winter wheat in the crop rotation can spread out the workload and help with time management for farmers. In most years, winter wheat has the potential to be up to 20 percent higher yielding than spring wheat, making it an economically attractive crop.

Growing winter wheat is fairly straightforward. However, management practices are quite different with winter wheat versus spring seeded grain crops. To successfully grow winter wheat, a number of specific management practices must be followed to ensure optimum crop production. These include: seeding date, field selection for planting winter wheat, selection of the best variety for a specific area; seeding rate and depth; proper fertilizer types, amounts and times of application; and weed control.

Seeding Date
In southern Alberta, farmers ideally should seed winter wheat in the first two weeks of September. Farmers in central Alberta should seed winter cereal crops in the last week of August or first week of September, provided field and soil moisture conditions are suitable.
Seeding at the ideal time allows winter wheat to germinate, develop at least three leaves and a crown, which is the base of the shoot where secondary roots develop. Plants must develop to this stage to ensure good over-winter survival. Later seeding may result in poorly established plants, which may result in lower winter survival. Late seeding may result in delayed heading, later maturity, increased weed problems and lower yield potential. Recent research in southern Alberta has shown up to a 30 percent yield decrease with both winter wheat and winter triticale, when seeding is delayed from the second week of September to the first week of October.

Field Selection for Seeding Winter Wheat
Ideally, winter wheat should be seeded into standing stubble. Seeding into standing stubble and maintaining the standing stubble after seeding is important to trap snow in winter to provide a protective insulation layer to maintain a better over-winter soil temperature, which will help to ensure over-winter survival of winter wheat. Four inches of snow will normally provide sufficient insulation to ensure over-winter survival.
With the cold, wet spring and summer weather in 2010, most crops were two to three weeks behind compared to normal crop conditions. Delayed crop maturity and delayed harvest may mean that many fields cropped in 2010 may not be harvested in time to seed winter wheat in the fall.
Seeding into oilseed or pulse crop stubble offers crop rotation advantages such as reduced weed problems, easy-to-control volunteers and reduced potential for insect and disease problems.

However, for fields that were not seeded in spring 2010, the fall could provide an excellent opportunity to seed winter wheat. The only limitation is that these fields may not have standing stubble, which is important to ensure good winter survival. Seeding into cultivated fields will have an increased risk of winter kill; therefore, selection of a good winter hardy variety is very important.

Winter wheat should be seeded only into “clean fields,” without any green volunteer cereal growth. Volunteer grain can harbour an insect called the leaf curl mite, which can transmit a virus called wheat streak mosaic. Any actively growing green vegetation, such as volunteer grain or grass in roadside ditches and field borders can serve as a host for the mites. If winter wheat is seeded into stubble with green volunteer or adjacent to green fields, the mites will move from the host plants into the winter wheat after emergence and spread the virus. The damage from this disease can range from severe to complete crop failure. Cultural controls are the only way to control this disease. AC Radiant is the only variety with wheat curl mite resistance. If there is a concern with the wheat curl mite, AC Radiant is the only recommended variety to grow.

Variety Selection
In southern Alberta, AC Bellatrix and Radiant are the newest, best and highest-yielding varieties available for farmers to grow. Both varieties were developed at the Lethbridge Research Centre. In addition to resistance to leaf curl mite, Radiant has very good winter hardiness and lodging resistance. Bellatrix has only a fair rating for winter hardiness and good rating for lodging but has better resistance to some diseases compared to Radiant. In central Alberta, farmers should consider CDC Osprey, which is very good for both quality and winter hardiness. All three varieties are accepted by the Canadian Wheat Broad “Select” program. References for detailed information on winter wheat varieties are provided at the end of this document.

Seeding Rate and Depth
The ideal seeding rate for winter wheat is higher than what is used for spring wheat. Generally, winter wheat should be seeded to achieve at least 250 plants per square metre (23 plants per square foot), which is about 120 lbs per acre, depending on variety and seed size in Brown and Dark Brown soil regions. In wetter regions and under irrigation, seeding rates should be increased to achieve 300 to 350 plants per square metre. Actual seeding rate should be based on the 1000 kernel weight of the seed source to be planted. Winter wheat has considerable ability to tiller: however, best yields are obtained with higher seeding rates. Row spacing of seven to nine inches is best.

Winter wheat has a very short coleoptile, which is the extension of the seed embryo that pushes its way through the soil to the surface, from which the first leaf develops. It is very important to seed winter wheat 0.5- to 1-inch (1.5- to 2.5-centimetres) deep. Winter wheat that is seeded deeper than one inch will result in reduced emergence and poorer crop establishment. Deeper seeding will delay emergence and cause weaker, spindly plants that are more susceptible to winter kill. Seeding winter wheat too deep is a common mistake made by newer winter wheat growers that results in poor crop stand and lower-than-anticipated yield.

In our research, direct seeding comparison of a disc versus a hoe opener showed an increased spring plant density of 13 percent with a disc compared to the hoe opener; however, the opener type did not affect final grain yield.

Frequently, soil moisture is low in stubble fields in early September in southern Alberta. Farmers are faced with the decision as to whether to seed into dry soil or wait for rain. Saskatchewan research has shown that winter wheat will germinate at very low soil moisture levels. Ideally, growers should seed winter wheat in the first two weeks of September rather than wait for rain, provided that the seeding operation leaves the seed firmly covered with no more than an inch of soil.

Soil temperature can dramatically affect the time it takes winter wheat to germinate. For example, in a moist soil, winter wheat will take about seven days to germinate and emerge at a soil temperature of 20 degrees C, while it takes about 12 and 25 days to emerge at soil temperatures of 10 and five degrees C, respectively. Therefore, seeding in late September or early October will result in plants taking a longer period of time to germinate, emerge and develop a crown, a situation which increases the risk of poor winter survival.

Fertilization
It is wise to soil test to determine nitrogen (N) and phosphorus (P) soil levels, to accurately determine N and P fertilizer requirements. In fields that were not seeded this spring and left in fallow as a result of wet conditions, determination of soil N levels is critically important to determine optimum N fertilizer requirements. Soil N loss due to leaching and denitrification likely occurred during wet periods, so the only way to accurately determine N fertilizer requirements is to soil test for soil N.

Stubble fields are often low in soil nitrogen, particularly if the previous crop was high yielding. If time does not permit soil testing, or if fall soil moisture conditions are low, it is best to apply approximately 40 to 70 percent of estimated nitrogen requirements at the time of seeding, soil test in late fall, and then apply additional nitrogen in early spring based on soil moisture conditions.

Our research in southern Alberta has shown that nitrogen fertilizer banded before seeding, at times dried, out the seedbed and resulted in a rougher and lumpier seedbed, which had a negative affect on germination and emergence. Our work has also shown that seed-placed nitrogen fertilizer applied at rates of greater than 30 lbs of N per acre using urea with a seedbed utilization of 10 percent (spreading the seed and fertilizer across 0.75 inches with a row spacing of eight inches) with low soil moisture had a detrimental effect on winter wheat germination and emergence. Therefore, the maximum recommended safe seed-placed rate of nitrogen is 30 lbs of N per acre using urea. Rates higher than this must be either banded before seeding, side- or mid-row banded at the time of seeding or broadcast in late fall or early spring. However, in-crop broadcast application can be quite inefficient.

Our recent work with ESN (Environmentally Smart Nitrogen) nitrogen fertilizer, a polymer-coated urea, shows that it can be safely seed-placed with winter wheat up to a rate of 80 lbs of N per acre, with a 10 percent seedbed utilization. This is an excellent option for producers who have single shoot openers, to allow them to place all their N and P fertilizer requirements with the seed, in a one-pass seeding operation.
When subsoil moisture conditions are poor at the time of seeding, another option is to use a split application of nitrogen fertilizer, applying a safe rate of N fertilizer with the seed at the time of seeding and then apply additional N fertilizer in early spring, based on soil moisture conditions and crop yield potential. For spring broadcast N, producers can either broadcast urea very early in the spring or dribble band liquid N fertilizer, to minimize potential volatilization losses. Urea or liquid N can also be treated with a urease inhibitor such as Agrotain to reduce potential volatilization of nitrogen.

The optimum N fertilizer rate is a function of soil N, stored soil moisture (SSM) in spring and expected growing season precipitation (GSP). Therefore, soil testing for nitrate N to 24 inches (60 centimetres) and determining the amount of stored soil moisture before seeding are critical to aid in determining optimum fertilizer N rates.

In the Brown Soil zone, if there are two inches (50 millimetres) of stored soil moisture, and assuming that six inches (150 millimetres) of average growing season precipitation is received, the total amount of N needed by winter wheat would be approximately 60 lbs of N per acre. Subtracting the amount of soil N from this will provide the approximate rate of N fertilizer to apply.

Determining N requirement in the Brown Soil Zone
With 2” of SSM + 6” of GSP then soil N + fertilizer N needed is approximately 60 lbs/ac
With 4” of SSM + 6” of GSP then soil N + fertilizer N needed is approximately 75 lbs/ac
With 6” of SSM + 6” of GSP then soil N + fertilizer N needed is approximately 90 lbs/ac

Determining N requirement in the Dark Brown Soil Zone
With 2” of SSM + 8” of GSP then soil N + fertilizer N needed is approximately 70 lbs/ac
With 4” of SSM + 8” of GSP then soil N + fertilizer N needed is approximately 85 lbs/ac
With 6” of SSM + 8” of GSP then soil N + fertilizer N needed is approximately 100 lbs/ac

Determining N requirement in the Thin Black and Black Soil Zone
The total amount of N (Soil N + Fertilizer N) required to achieve optimum yield is approximately 140 to 160 lbs of N per acre.

Determining N requirement under irrigation
The total amount of N (Soil N + Fertilizer N) required to achieve optimum yield is approximately 180 to 200 lbs of N per acre.

Our research has shown that phosphate fertilizer placed with or near the seed at the time of seeding improves plant growth in the fall, resulting in better winter hardiness. Approximately 20 to 25 lbs of P per acre are usually adequate and are most effective when placed with the seed.

Most soils in southern Alberta have adequate amounts of soil potassium (K) and sulphate sulphur (S). However, soil S levels may be low in surface soil (0-6 inch depth) this fall due to leaching during wet periods in spring and early summer. Therefore, soil testing for K and S is also important for all fields to be seeding to winter wheat this fall.

Weed control
Due to the competitive nature of vigorously growing winter wheat, weed pressure tends to be lower than with other crops. Winter annuals, such as stinkweed and flixweed are the greatest problem. However, these can often be controlled with inexpensive products such as 2,4-D or MCPA.

Summary
Winter wheat can be an excellent crop to include in a crop rotation. By following basic, straightforward management practices, winter wheat can be an easy and very profitable crop to grow.

For more detailed information refer to Alberta Agriculture publications on the website Ropin’ the web including:

Agronomic management of winter wheat in Alberta
www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex11601

Fertilizing winter wheat in Alberta
www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex96

Winter wheat in the parkland area of Alberta
www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex94

Winter wheat variety descriptions
www.agric.gov.ab.ca/app95/loadCrop?action=display&id=59

Further information on winter wheat varieties and a list of seed growers is at:
Alberta Seed Guide
Click here to download the PDF document.

*Dr. Ross McKenzie is a research scientist in agronomy, with Alberta Agriculture and Rural Development in Lethbridge. Top Crop Manager gratefully acknowledges and welcomes his contribution.