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Soybeans

The common cultivated soybean is botanically classified as Glycine max L. and is a member of the subgenus soja, genus Glycine and the family Fabaceae. Soybean is not a true pulse crop. This subgenus contains only one other species, Glycine soja L., which is the wild ancestor of Glycine max

Soybeans are grown and marketed for both human and animal consumption as a source of protein and oil. Soybeans are used for both fermented and unfermented products; as an ingredient for many meat and dairy substitutes; and a fat-free (defatted) soybean meal is a significant source of protein for animal feeds.

Figure: 1 Soybean Field

Seeding

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Diseases

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Weed Control

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Insects

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Harvesting

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Where do soybeans grow?

While the cultivated form, Glycine max, has never been found in the wild, Glycine soja is found throughout China and the adjacent areas of the Russia, Korea, Japan and Taiwan. Soybeans have been cultivated in Asian civilizations for thousands of years, and are one of the most important food crops globally today. 

As of 2019, the top five producing countries of soybean are the United States (108 Million metric tonnes (MMT), Brazil (86.8), Argentina (53.4), China (12.2), and India (10.5). Canada is #7 with 6 Million metric tonnes.  Source: World Atlas, https://www.worldatlas.com/articles/world-leaders-in-soya-soybean-production-by-country.html

Main importers are the European Economic Community, Japan, Spain and Eastern Europe.

In 2019, Alberta’s pulse growers grew 4,900 metric tonnes of soybeans on 6,500 acres. Statistics were not available for farm cash receipts or export values.

(Source: Alberta Agriculture and Forestry, Economics and Competitiveness Branch)

Figure 2: Soybean Plants

Consider growing soybeans if…

  • You live in Southern Alberta under irrigation, and get the needed crop heat units (CHU).
  • You’re looking for a warm weather crop that likes lots of moisture.
  • You’re growing in the brown and dark brown soil zones of Alberta.
  • You want to spread out your workload with early seeding and harvest.
  • You’re interested in marketing flexibility that includes markets for both human consumption (including fractionation) and animal feed.
  • You are looking for a pulse option that is resistant to several root diseases.
  • You want to reduce your input costs (as pulses are nitrogen fixing); break disease cycles in your field; obtain a second-year yield boost in other crops following a pulse crop; improve your soil health; promote soil conversation and sustainable farming practices; and improve farm profitability.
    Figure 3: Soybeans

Description

Soybeans are an annual legume plant with a branched tap root. Soybeans are a dicot crop and exhibit epigeal germination – during the vegetative stage, the cotyledons and the growing point push up above ground and are the first above-ground structures. The size of the cotyledons on the soybean are quite large, so crusted hard soils can impede emergence. Germination occurs within three to four days at an air temperature of 25˚ to 30˚C. 

Soybeans are sensitive to day length in their growth and reproduction. Soybeans have two common growth habits, determinate and indeterminate. There is a preference for determinate soybean varieties in Alberta and virtually all soybean grown south of 36˚N plus most tropical soybeans are determinate.

Leaf Structures

The first true leaves of the soybean plant are unifoliate, and opposite of the stem on short petioles. All other true leaves following are trifoliate on long petioles and alternate from side to side up the steam. The number of trifoliate leaves that a soybean will have will fluctuate with variety and environmental conditions. New vegetative stages appear about every five days from VC (Vegetative Stage Cotyledon) when the plant unrolls its unifoliate leaves, through to VC5 (Vegetative Stage 5), where the first five nodes (growing points) on the main stem with fully developed leaves beginning with the unifoliolate nodes. Then every three days from V5 to shortly after R5 (Reproductive 5), where the seeds are 1/8 inch in the pod at one of the four uppermost nodes on the main stem with a fully developed leaf. This is the maximum number of nodes, however the seed begins to rapidly fill, and the root growth slows. It will take the plant approximately four to five weeks to form all nodes. See “Soybean Growth Staging Guide” and other links in resource section below. 

Figure 4: Soybean Leaves

Reproductive nodes (flower)

Soybean is almost completely self-pollinated. As the days begin to shorten, flowering is initiated in the crop. Growth stages are heavily influenced by heat, and increased mean temperatures will hasten flowering. Reduced mean temperatures will delay flowering, in relation to photoperiod length – which is the period of time each day during which the plant receives illumination (day length). Flowering will begin within 25 to 50 days of planting, or even later (depending on cultivars and environmental conditions).

Determinate types produce flowers at all nodes over a short period, and each terminal bud forms a distinct raceme. Raceme are an inflorescence in which the main stock bears the flowers on stalks (pedicels), appearing as a dense cluster of lateral flowers growing from any node on the main stem, to flowers at one of the two uppermost nodes on the main stem with a fully developed leaf.

Determinate cultivars are usually shorter and more branched than the indeterminate ones.  Indeterminate types begin to flower at lower nodes while terminal buds continue to grow vegetatively. Flowering normally begins at the fourth or fifth node above the soil surface and proceeds at successive nodes above and below this node. Terminal buds eventually turn reproductive and flower, with fruits first forming close to the base of the plants.

Figure 5:  Close-up of Soybean Flower

Figure 6: Soybean Plant – Flowering

Soybean Pods

The fruit is a hairy pod that grows in clusters of three to five, and each pod is 3 – 8 cm (1.2 – 3.1 in) long. Pods contain from one to five ovules, but most cultivars have three ovules per pod.

Figure 7: Soybean at Full Seed

Figure 8: Soybean – Ready to Harvest

Seed Shape & Size

Soybean seeds come in a wide variety of sizes and hull colours such as black, brown, yellow, and green. Bicoloured seeds and variegated (seeds that are edged or patterned in a second colour) and are also common. The hull of the mature bean is hard, water-resistant, and protects the cotyledon and hypocotyl (or “germ”) from damage. If the seed coat is cracked, the seed will not germinate. The scar, visible on the seed coat, is called the hilum (colours include black, brown, buff (a light brownish yellow color), grey and yellow) and at one end of the hilum is the micropyle, or small opening in the seed coat which can allow the absorption of water for sprouting.

Adaptation Characteristics

Optimal Temperature

  • Soybean is a summer-growing annual legume well adapted to moderately high temperatures. This crop is generally limited to production only in the southern regions, usually grown under irrigation as it requires 16 – 20 inches of water for maximum yield potential.
  • Air temperature above 20˚C is required for optimum flowering and seed formation.
  • Even at ripening stage, temperatures should ideally be above 18˚C.
  • Highest yields are obtained when the full growth cycle is completed under high temperatures.

Frost & Drought Tolerance

  • Seedling stages are frost susceptible.
  • 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.
  • Limitations in crop heat units may push harvest well into the fall and at risk of killing frost.
  • Aim to plant during the second to third weeks of May for high yield potential and reduced frost risk. Two weeks after the last spring frost or when the average soil temperature has warmed up to at least 10°C, 18 – 22°C is ideal. 

Type

  • Indeterminate and determinate types.

Varieties

  • Soybean in Alberta requires earlier-maturing varieties.
  • Rate of development is controlled primarily by photoperiod and temperature. Most are short day plants, but some early maturing cultivars (adapted to extreme latitudes) and a few later maturing and tropical cultivars are day length neutral during the period from planting to flowering.
  • Herbicide tolerant (RR) soybean varieties have been developed primarily for the crush (oil/meal) market whereas conventionally type of soybeans that are used for human consumption (tofu, for example).
  • Breeding efforts have resulted in the development of soybean varieties that are adapted to more northern climates.
  • Yield, characteristics, and standability data are found at Pulse RVT .
  • For more information on the varieties of pulse crops in Alberta, please see Alberta Agriculture’s Varieties of Pulse Crops for Alberta.

Maturity/Dates

  • Early flowering varieties result in crop maturity between 116 to 120 days.
  • Flowering should begin within 25 to 50 days of planting, or even later (depending on cultivars and environmental conditions). In an Alberta Agriculture study, flowering varied from 53 days for the highest performing varieties to 61 days for the lowest performing. 

Soil

  • Soybean is adapted to a wide range of soil types.
  • While neutral pH is preferred, the crop has been grown in soils ranging from pH 4.0 to 8.5.
  • Since high moisture availability is an important requirement for optimum yield, soil types with low moisture holding capacity can limit yield.
  • In more arid areas, irrigation is essential for successful soybean production. Soil types with poor water infiltration (which prevents successful irrigation) can be a limiting factor.

Stages of Development

The life cycle of the soybean plant has four principal stages:

  • germination and emergence
  • vegetative stage
  • reproductive stage
  • senescence (mature stage)

Resources

History

The domestication of soybean took place in the eastern half of China as early as the 11th Century BC where they were cultivated into a food crop. From China, it was introduced into Korea and Japan, probably after 200 BC, and has since spread widely throughout Asia. From about the 15th to 16th Century, soybeans were introduced into several countries such as Japan, Indonesia, the Philippines, Vietnam, Thailand, Malaysia, Burma, Nepal and India. The spread of the soybean was due to the establishment of sea and land trade routes. The earliest Japanese reference to the soybean is in the classic Kojiki (Records of Ancient Matters) which was completed in 712 AD. (History of Soybeans)

Europeans became aware of soybean around the late 17th Century, and movement of the crop into the United States took place in 1765 by Samuel Bowen, who sent seeds from Georgia to the American Philosophical Society in Philadelphia for Testing. (T. Hymowitz and W.R. Shurleff) . During the 20th Century, soybean was subject to major development in the U.S., resulting in the crop becoming dominant in world oilseed trade. Other countries, including Australia, Brazil and Argentina, have adopted soybean varieties directly from the United States.

 

Special thanks to Saskatchewan Pulse Growers and Manitoba Pulse & Soybean Growers.