Agronomic management of winter wheat
By Ross H. McKenzie PhD P. Ag.
Winter wheat yield potential can be 15 to 40 per cent higher than spring wheat, which makes it a very economical crop to include in a crop rotation. Growing winter wheat is fairly straightforward. However, a number of specific management practices must be followed to successfully grow winter wheat.
Planning ahead is essential – the first consideration is having fields available for seeding winter wheat at the correct time in late-summer. This is often a limiting factor for farmers wanting to grow winter wheat and requires long-range planning of crop rotations.
Variety selection is important. Selection should be based on a range of agronomic factors including grain quality, winter hardiness, yield potential, disease resistance and lodging. Farmers outside of southern Alberta should select a variety with very good winter hardiness. Farmers in higher moisture regions and under irrigation should select varieties with good lodging resistance. Check your provincial seed guide to carefully review the advantages and limitations of each variety to determine which varieties have the best agronomic characteristics for your local area.
Ideally, winter wheat should be direct seeded into standing stubble. Seeding into canola or mustard stubble offers crop rotation advantages such as reduced weed problems, easy-to-control volunteers, and reduced insect and disease problems. Standing stubble is very important to trap snow, which acts as an insulator. Four inches of snow will normally provide sufficient insulation to ensure overwinter survival.
Establish a good stand early in the fall
Farmers in the Brown and Dark Brown soil zones should seed winter wheat in the first two weeks of September. Farmers in the Black and Gray soil zones should seed winter wheat in the first week of September or even in the last week of August. Seeding at the ideal time is very important to allow winter wheat to germinate, emerge, put up three leaves and then establish a crown root system. It is important that crown roots are established before winter to ensure overwinter survival. Later seeding may result in poorly established plants, which results in lower winter survival. Late seeding will result in delayed heading, later maturity, increased weed problems and lower yield potential. Alberta Agriculture research in southern Alberta has shown that up to a 30-per cent-yield decrease occurs when seeding is delayed to early October.
Generally, winter wheat should be seeded at a rate to achieve a plant stand of 25 plants per square foot. Higher seeding rates should be used in the Black soil zone and under irrigation. Thousand kernel weight (TKW) should be determined and used to calculate seeding rates so target plant populations are achieved. Winter wheat has considerable ability to tiller; however, best yields are obtained with higher seeding rates. Ideally, narrower row spacing of nine inches is best.
Winter wheat has a very short coleoptile. The coleoptile is the extension of the seed embryo that pushes its way through the soil to the surface, from which the first leaf develops. To allow for the coleoptile to emerge, winter wheat should be sown 0.5 to one inch deep. Winter wheat seeded deeper than one inch will often have reduced emergence. Deeper seeding will delay emergence and cause weaker, spindly plants that are more susceptible to winter kill.
Frequently, soil moisture is low in stubble fields in early-September. 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, it is best to seed winter wheat at the recommended time for your area rather than wait for rain, provided that the seeding operation leaves the seed firmly covered with no more than one inch of soil.
Soil temperature can dramatically affect the time it takes winter wheat to germinate. For example, with good soil moisture winter wheat will take about six days to emerge at a soil temperature of 20 C, while it takes about 12 and 30 days to emerge at soil temperatures of 10 C and 5 C, respectively. Therefore, late seeding of winter wheat into cooler soils can jeopardize good establishment of the crop.
Winter wheat should only be seeded into “clean fields” without any actively growing volunteer cereals. Volunteer grain can harbour an insect called the wheat curl mite, which can transmit a virus called wheat streak mosaic. Any actively growing green vegetation such as volunteer grain or grasses can serve as a host for the mites. If winter wheat is seeded into stubble with green volunteers or by adjacent 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 moderate to complete crop failure. The mites wrap themselves within the wheat leaves; therefore, insecticides are completely ineffective. Cultural controls are the only way to control this disease. The only winter wheat variety with resistance to the wheat curl mite is Radiant.
Look after soil fertility
Alberta research has shown that phosphorus (P) fertilizer placed with or near the seed at the time of seeding improves plant growth in the fall and results in increased winter hardiness. Approximately 20 to 30 lbs/ac of phosphate is usually adequate and is most effective when placed with the seed.
Most stubble fields are low in soil nitrogen (N). After a high production year, soil N levels are often very low. Soil testing to determine N and P are strongly encouraged to accurately determine fertilizer requirements. In the Black and Gray soil zones, potassium (K) and sulphur (S) are more commonly deficient and should also be checked. Soil sampling and testing is important to determine optimum fertilizer requirements. If soil moisture conditions are very dry at planting, it may be best to apply approximately 50 to 70 per cent of estimated N requirements at the time of seeding and apply additional N in early spring, depending on soil moisture conditions.
Previous recommendations for winter wheat suggested that N fertilizer should only be spring-applied, because fall-applied N may reduce winter hardiness. Research by Alberta Agriculture has clearly shown that fall-applied N fertilizer does not reduce overwinter hardiness when applied in balance with phosphate fertilizer. Research did show that N fertilizer banded before seeding tended to dry out the seedbed and resulted in a rougher and lumpier seedbed, which negatively affected uniform germination and emergence. Research also showed that seed-placed N fertilizer applied at rates greater than 30 lbs N/ac using urea at a seedbed utilization of 10 per cent (spreading the seed and fertilizer over 0.9 inches with a row spacing of 9 inches) with low to medium soil moisture had a detrimental effect on winter wheat germination and emergence. Therefore, side- or mid-row banded N at the time of planting is usually best when N rates are higher than 30 lbs N/ac.
In the past, ammonium nitrate (34-0-0) fertilizer was recommended for spring broadcast application, but it is no longer manufactured in Canada. One supplier near Lethbridge, Alta., imports 34-0-0 for resale to southern Alberta farmers. For most growers, very early spring-broadcast urea (46-0-0) can work reasonably well. Another option is to dribble band or use spray jet nozzles to apply 28-0-0 liquid fertilizer. For both 46-0-0 and 28-0-0, there is always concern of volatilization of urea (conversion of urea to ammonia gas). Therefore, urea or 28-0-0 should be applied as early as possible in the spring when soil and air temperatures are cool. A urease inhibitor such as Agrotain to reduce potential volatilization should be considered. For further information on fertilizing winter wheat refer to Alberta Agriculture Agdex 112/542-1 Fertilizing winter wheat in southern Alberta.
Weeds can be easily cleaned up
Due to the competitive nature of vigorously growing winter wheat, weed pressure tends to be lower than with other crops. Winter annuals are the greatest problem. However, these can easily be controlled with inexpensive products such as 2,4-D or MCPA – preferably in late-fall, but early spring application is also quite effective. Winter wheat is very competitive in spring and the need for wild oat herbicides are not always necessary.
In summary, winter wheat can be an excellent crop to include in a crop rotation. By following simple, straightforward management practices, winter wheat can be an easy and very profitable crop to grow. For more detailed information on winter wheat production, refer to provincial agricultural websites and the website http://www.growwinterwheat.ca/.
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