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Soybeans are adapted to a wide range of soil types in south-central Manitoba. Loamy soils are ideal. While heavy clay soils can lead to planting and emergence problems, once established, soybeans perform reasonably well. Soybean performance can be poor on sandy soils prone to drought stress.
Temperature is a main limiting factor - soybean is a heat-loving crop. Current varieties are rated at 2375 - 2675 corn heat units (Ontario data), limiting suitability mainly to the south-central area of the province.
Soybean is susceptible to seed and seedling rots. Use a recommended fungicide seed treatment.
May 15 to 25, or when the average soil temperature has warmed up to at least 10° C, 18 - 22° C is ideal. Seedlings can tolerate a light spring frost (-2.8° C for a short period), but cannot recover if damaged. Later seeding results in decreased plant height, lower pods and reduced yields.
The ideal plant density is estimated at 180,000 to 210,000 plants/acre or 4 plants/ft2 (40 plants/m2).
Depending on seed size, this stand density will require a seeding rate of 70-120 lb/acre. By branching, soybean can compensate for reduced stands. Experience from Ontario suggests that at a stand of 50% less than optimum, expected yield will be 24%, and replanting should be considered.
Sew 0.75 to 1.5 inches deep. Within this range, seed shallow in loamy or heavy soils, or with early seeding dates; sow slightly deeper in lighter soils to ensure that the seed remains in contact with moist soil. Soybeans are sensitive to deep seeding, which results in poor emergence and increased risk of soil-borne diseases.
Delivery of granular inoculants to the seed row may require granular attachments for grain drills or air seeders.
Peat-based and liquid inoculants are also available. After one or two well-nodulated soybean crops, the rhizobia population in a field may be adequate for subsequent crops. Soybean crops grown on poorly-drained soils with high carbonate and salinity levels may be prone to iron chlorosis, which causes yellowing of plants.
|Nitrogen (N):||Not recommended. If nodulation does not occur and the soybeans are yellowing at early flowering consider a broadcast application of nitrogen. Apply 50 lb/acre N as broadcast ammonium nitrate.|
|Phosphate (P2O5):||Phosphorus is recommended at 30 to 40 lb/acre. Apply as a sideband application or as an application one inch directly below the seed. If applied with the seed, the maximum rate recommended is 20 lb/acre. This seed placed rate is for soybeans seeded in narrow rows, where seed bed utilization is high. Applying these rates to soybeans in wide rows may cause stand reductions.|
|Potassium (K2O):||Sands, sandy loam and organic soils are frequently low in available potassium. On these soils, apply 30 to 60 lb/acre potash. Potassium should be placed away from the seed.|
|Sulphur (S):||Sulphate sulphur at a rate of 20 lb/acre is recommended on well- drained soils and grey luvisol (grey wooded) soils. Sulphur deficiency may occur in many other soils and in any area of the province. Because of this, a soil test is recommended to determine the available sulphur status of your fields.|
Soybean seedlings are non-competitive. Weed management is primarily by herbicide. Cultivation is possible if soybeans are grown as a row crop. In this case, herbicides can be applied in a band over the row.
Insects that feed on the leaves and pods include grasshoppers, the corn earworm, and the fall armyworm. Under most conditions, moderate defoliation early in the season has no appreciable effect on soybean yield. Fifty 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.
Some soil-inhabiting insects may also feed on soybeans. Seed corn maggots feed on the seeds, which may result in seeds not germinating. Less-severely damaged seeds that germinate may produce weak seedlings that die. This insect is seldom a problem, except when weather conditions or seed quality delay seedling emergence. Risk can be reduced by applying seed treatments containing insecticides. Wireworms feed on seeds and seedlings, and damage is most likely in low-lying and poorly drained portions of the field. White grubs are root feeders, and damage symptoms may vary from dead to stunted, yellow plants.
Root rot disease may occur under moist soil conditions. Use treated seed and/or resistant varieties to minimize risk. Soybean is susceptible to sclerotinia (white mould), so avoid other sclerotinia-susceptible crops in rotations, and ensure that rotation is of adequate length. Soybeans are also susceptible to powdery mildew, but this will cause yield reduction only if it occurs in July.
Direct-combine when the pods are dry and the seeds are hard. Combining can take place when seed moisture is below 20%, but soybean must be stored at less than 14%. Seed damage is high when soybean is harvested at less than 12% moisture, and harvest losses can also be high under dry conditions (four beans per square foot represents a harvest loss of 60 lb/acre, so caution is advised). 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.