Soybeans are adapted to a wide range of soil types in south eastern Saskatchewan. Ideally, they are grown on loamy soils and may also perform well on clay soils if conditions are favourable for rapid seedling emergence.
- sensitive to drought, so sandy soils are not usually conducive to satisfactory performance; and
- a warm season crop requiring sufficient heat to perform well and mature in a timely fashion.
Soybean varieties in Saskatchewan need between 2325 and 2450 corn heat units. This limits production of soybean to areas receiving sufficient heat. See the Saskatchewan Corn Heat Units Map.
Recommended varieties of soybean are listed in the Varieties of Grain Crops.
These varieties are limited to either:
- Roundup Ready 1; or
- Genuity Roundup Ready 2 Yield (GENRR2Y) types.
The soybean variety trial is coordinated by Saskatchewan Pulse Growers. Mean yield of the check variety TH 33003R2Y was 46 bu/ac in 2017, 44 bu/ac in 2016 and 51 bu/ac in 2015, with an overall three-year average of 47 bu/ac.
Typical on-farm yields are 25 to 30 bu/acre. Soybean is not native to the Canadian Prairies, so must be inoculated with soybean inoculant that contains Bradyrhizobium japonicum bacteria.
Treatments - Using a registered seed treatment is recommended as soybean is susceptible to several seed and seedling pathogens and insects. See the Guide to Crop Protection, which lists commercial products appropriate for soybean.
Dates - Recommended seeding dates are from May 10 to 25, or when the average soil temperature has warmed to at least 10C. Seeding into cold soils may result in poor germination, increased incidence of diseases and poor plant stands. Soybean seedlings can generally tolerate -2C frost. Delaying the seeding date can result in lower plant height, pod counts and lower yields.
Rates/Stand Density - The target plant density for solid seeding soybean is 180,000-230,000 plants per acre or four to five plants per square foot (44 to 57 plants per square metre). This equates to a seeding rate of approximately 70 to 147 pounds per acre depending on seed size.
Exceeding these rates can lead to drought stress in dry years or lodging in wet years. Soybeans have the ability to branch out and compensate for reduced stands; however, Ontario experience indicates a loss of 24 per cent in yield if plant stands are less than half of optimum height.
Soybeans can be sown using an airseeder or row crop planter (with proper plates). If you use a row crop planter, the recommended optimum plant stand is 160,000 to 190,000 plants per acre. Row spacing should not be more than 22 inches. The following equation may be used to calculate seeding rate:
|Seeding Rate (lbs./acre) =
|Desired Plant Population/ft2 x (1,000 kernel weight)
*% Expected Seed Survival x 10
Example: Variety 23-10RY soybean = 2600 seeds/lb.
1000 seeds = approximately 174 g.
Seeding Rate (lbs. /acre) = 4 x 174 g/95% x 10
Seeding Rate (lbs. /acre) = 73
Some companies sell seed in units containing 140,00 seeds/unit.
Seeding Depth - The recommended soybean seeding depth ranges from 0.75 inches to 1.5 inches (1.9 cm to 3.81 cm). In loamy or clay soils seed in the shallow range; seed deeper in light textured soils so that the seeds remain in contact with moist soil. Deep seeding may reduce emergence and increase the risk of disease infection from soil-borne pathogens.
Fertilizer Recommendations for Soybean
Soybeans must be inoculated with Bradyrhizobium japonicum, because this type of bacteria is not indigenous to western Canadian soils. Ensure proper procedures for inoculation are followed according to manufacturer guidelines. There are liquid, peat and granular types to choose from.
Delivery of granular inoculants to the seed row requires granular attachments for air seeders and row-crop seeders.
After one or two well-nodulated soybean crops, the rhizobia population in a field may be adequate for subsequent crops; however, it is recommended that inoculation continue each time soybean is sown to ensure efficient nodulation and nitrogen fixation. Soybeans are prone to iron chlorosis, which causes interveinal yellowing of the leaves, particularly when grown on saturated soils or soils high in carbonate levels or with salinity problems.
Soil test fields and choose fields that are low in nitrogen to plant soybeans. This will allow you to take advantage of the significant nitrogen fixing capability of soybean. However, field cropping history is important, especially for possible herbicide carryover residues. Follow re-cropping intervals on the herbicide labels because soybeans are sensitive to soil residues of several herbicides. Soil testing identifies nutrient deficiencies and provides the levels of nutrients needed for optimum yield.
- Nitrogen (N): Examine the plants for adequate nodulation approximately three to four weeks following emergence. Active nitrogen fixation usually occurs one to two weeks later. If insufficient nodulation is evident, the grower may apply up to 50 lbs. /acre N as broadcast.
- Phosphate (P2O5): Phosphate is best applied as a sideband application at 30 to 40 lbs, P2O5/acre or using soil test recommendations. Applications with the seed must not exceed 20 lbs./acre. These rates are recommended for narrow row spacing with good moisture conditions. In wide row crop planting, the fertilizer is best side banded.
- Potassium (K2O): Potassium deficiencies may be found on light textured soils. Potassium can be side banded with the phosphate.
- Sulphur (S): If sulphur is required, ammonium sulphate can be side banded with the phosphate. If using liquid, a blend of liquid phosphate and sulphur can be side banded based on soil test recommendations.
Early emerging weeds are very strong competitors for soybean; early season weed control is imperative to reduce yield loss from weed competition. After the soybeans form a canopy they are better able to compete with weeds. An integrated weed management system is recommended as an overall effective weed control system.
Weed management is accomplished by registered herbicide application, both pre-seed and in crop. A wide range of commercial herbicides are registered for use in soybean. In particular, glyphosate is used on Roundup Ready varieties.
The following are above ground plant feeders that feed on leaves and pods:
- Corn earworm
- Fall armyworm
Early season defoliation generally does not noticeably affect yield loss. Substantial plant defoliation may occur before flowering and losses will be minimal. Manitoba Agriculture Food and Rural Initiatives (MAFRI) report that 50 per cent defoliation before flowering results in an average yield loss of only three per cent. As the soybean plant reaches the flowering and pod-filling stage, defoliation is a greater threat to yield and controls may be needed.
Seed Corn Maggots, Wireworms, Cutworms, and Aphids
In some areas, seed corn maggots may be found feeding on the seeds, which may affect seed germination and also produce weak seedlings that do not survive. It is rarely a problem except with poor weather conditions or if seed quality delay's seedling emergence.
Wireworms may also cause some damage to seedlings in localized areas as do white grubs.
Cutworms have reportedly been a problem in Saskatchewan whereby damage they cause can reduce plant stands considerably.
Aphids have also been reported to cause damage to soybean when found in sufficient numbers. Aphids numbering more than 250 per plant in growth stages R1-R4 and found increasing beyond in growth stages R5-R6 with moisture stressed plants and few predators should be controlled.
Diseases Affecting Soybean
In wet soils, root rot may be a problem affecting soybean.
Pathogens causing root rot in soybean and considerable yield loss include:
- Pythium species
- Rhizoctonia solani
- Fusarium oxysporum
- Soybean is a non-host to Aphanomyces
Registered seed treatments are recommended. To reduce risk, use disease resistant seed varieties.
Sclerotinia sclerotiorum or white mould may infect soybean especially in wet years.
Initially, flower petals are infected and the disease continues to grow affecting the stem and pods eventually causing the top of the plant to die. Rotations with non-host crops may help reduce the incidence of this disease. Keep in mind that many crops and weeds are hosts to this disease.
Closely spaced plants that form a canopy quickly and early in the season are at increased risk.
Powdery mildew is also a potential problem in cool years. It will generally only cause yield reduction if it occurs in July.
Approximately two weeks after defoliation, harvest begins.
Things to consider:
- Leaves and leaf stems will dry down and fall off the main stem;
- Pods turn brown and seeds rattle inside when shaken indicating the soybeans are fully mature;
- Combining can begin at 20 per cent moisture content;
- Early season frosts can kill the plant and reduce quality with green moist seeds in the sample; and
- Soybean must be stored at less than 14 per cent moisture content.
Straight combining is the preferred method for soybean harvest. Swathing is also acceptable with equipment able to cut very low to the ground. Combining should follow immediately to avoid precipitation damage to the swath.
Seed damage can be high when soybean is harvested at less than 12 per cent moisture, and harvest losses can also be high under dry conditions.
Losses of only four beans per square foot equate to one bushel per acre.
A floating cutterbar is ideal to minimize harvest losses. Careful adjustment of cylinder speed and concave clearance are needed to minimize cracking and splitting of seed.
The cultivated soybean, Glycine max L., is a domesticated soybean grown in many parts of the world. It is a member of the subgenus, Soja. Soybean is thought to have been domesticated in China, then spread into Europe around the 17th century and North America in the 1800s.
Soybean has become a dominant crop in world oilseed trade.
Many foods have been developed from soybean in Asia. Soybean flour and protein fractions are being used in European and North American diets as well.