In this article we will discuss about:- 1. Introduction to Soybean 2. Origin and History of Soybean 3. Geographic Distribution 4. Botany 5. Classification 6. Growth and Development.
Contents:
- Introduction to Soybean
- Origin and History of Soybean
- Geographic Distribution of Soybean
- Botany of Soybean Plant
- Classification of Soybean
- Growth and Development of the Soybean Plant
1. Introduction to Soybean:
Soybean is the most important grain legume crop in the world and among the top five of all food crops grown. Soybean is one of the important and cheapest sources of vegetable proteins and oils. It is cheapest, richest and easiest source of best quality protein and fat.
Owing to its multiplicity of uses as food and industrial products, it is called as a ‘wonder crop’. On an average, soybean grains contain about 20.5% carbohydrates, 43.2% protein, 20.0% oils, 4.5% minerals, 3.7% fibre and 8.1% water. It is the number one oilseed crop of the world.
The oil contains linolenic, linoleic, and oleic fatty acids. The protein is complete and contains all the essential amino acids. In diets, it provides the amino acids lysine and tryptophan that are deficient in foods from the grass family such as corn and wheat.
In addition, it contains a good amount of minerals, salts and vitamins (thiamine and riboflavin). The carbohydrates in the seed are mostly sucrose and sachyrose (a compound of sucrose and galactose). Seed also contains the insoluble carbohydrates cellulose, hemicellulose, and pectin that have value as dietary fiber.
A large number of Indian and western dishes such as bread, kachori, pastries, biscuits, sweets, khoa, paner, rabdi, powdered food material, chocolate, ice cream, protisnacks, soybari (nutrilla), green pods as vegetable, canned seed vegetable, dry seed-roasted, etc. can be prepared from its seed/flour.
Soybean is a food that is as nearly perfect as cow’s milk and at the same time rich in iron and vitamin C, when sprouted. Its fortification (5%) with wheat flour is done for alleviating protein malnutrition in the country.
The yield of protein from soybeans, weight for weight, is approximately twice that of meat, four times that of eggs, wheat and other cereals, five or six times that of bread, twice of navy beans, walnuts and other nuts and twelve times of milk.
Soybeans are extensively used in human foods as a source of many essential nutrients. Products include soymilk, infant formula, and flour. Soy protein can be processed into textured vegetable protein for production of vegetable burgers. Soybeans are fermented to produce soy sauce. Tofu is produced from the separation of the solids from soybean milk. Sprouted soybean seeds are consumed in salads.
It is able to leave residual N effect for succeeding crop equivalent to 35-40 kg N/ha. Soybean can tolerate mild drought as well as floods and survives better than maize. It provides a good protective cover to intercept rain and wind and thus minimize soil wind erosion.
It is widely used for manufacturing of edible oil, and vanaspati ghee. Soybean oil is used for frying, and as a component of margarine and salad dressing. The oil is also used for production of inks, paints, cosmetics, and biodiesel. Biodiesel is a renewable fuel for combustion engines.
Soybean meal is extensively used to supply protein as an ingredient for poultry, swine, and cattle feed. It can be used as forage, hay, silage etc. Its forage and cake are excellent nutritive foods for livestock and poultry. Soybean builds up the soil fertility by fixing atmospheric nitrogen through the root nodules, and also through leaf fall on the ground on maturity.
2. Origin and History of Soybean:
Soybean is a native to China. It is one of the oldest cultivated crops and is likely related to Glycine ussuriensis, a small seeded wild relative still found in the region, originated in China around 2800 B.C. The wild form, a slender twinning vine, Glycine soya is considered to be the predecessor of Glycine max (cultivated form) occurring in China, Manchuria and Korea. The Chinese domesticated it nearly 3000 years ago, and it was regarded as a sacred grain essential for survival of their culture.
It was introduced into North America in the early 1800s and were first used an annual hay crop and for plow down as a green manure. George Washington Carver experimented with soybean as a food source in the early 1900s. An early promoter of soybean was Henry Ford, founder of the Ford Motor Company.
It is introduced into northern India in 1000 AD from Central China through silk route and is an important source of food in Kumaon hills and Naga Hills. Black seeded soybean was also grown in Kumaon and Garhwal hills region and some places of Madhya Pradesh.
3. Geographic Distribution of Soybean:
Soybean is globally cultivated over an area of 91.2 million ha with a production of 206.5 million tonnes (2004). The important soybean growing counties are USA, China, Brazil, Mexico and Russia.
In India, Madhya Pradesh and Maharashtra states are major producers of soybean accounting for 87% of acreage and 82% of the production.
4. Botany of Soybean Plant:
Soybean belongs to sub-family papilionaceae of family fabaceae. The soybean is an erect, bushy annual plant of great morphological diversity.
Soybean consists of tap root formed by the radical. Numerous secondary roots, arranged in four rows along the tap root, and several highly branched adventitious roots arising from lower portion of the hypocotyls are found in soybean plants, however, tap root has somewhat larger diameter.
The root consists of nodules on their surface which are visible about 10 days after sowing and the root system becomes extensively nodulated at maturity. The depth of root system becomes extensively nodulated at maturity. The depth of root system depends upon soil type and cultural practices viz. in open soil types the tap roots may go as deep as 2 meters and the laterals up to 2.5 meters.
Root Nodulation:
Nodulation begins when rhizobia attach themselves to the root epidermal cells in a narrow region just behind root cap. Maximum soybean yield depends to a large extent upon a well nodulated, extensive root system.
The characteristic pink colour of healthy nodules is due to leghaemoglobin which increases during first weeks after nodulation. Nodule initiation takes place after root hairs are formed and is initiated by Bradyrhizobium japonicum. Roots secrete substances which promote rapid growth of soil microbes including Rhizobium.
Regardless of mechanism of entry, Rhizobia enter roots via root hair epidermal cell. First sign of infection is elongation and curling of root hair tip. After entry the bacteria form thread and enter inside the host cytoplasm. The host cells concomitantly rapidly divide causing breakage and disappearance of infection thread. After two weeks of cell division, further growth of cell is due to cell enlargement in acropetal direction.
Diameter and growth ceases by the end of 4th week after nodule initiation, resulting in a mature nodule 3-6 mm in diameter. Bacteria also divide rapidly so that cells in the central region of nodule become filled with bacteria known at this stage as bacteroid.
Bacteroid in groups of 4-6 become enclosed in membrane envelopes. Leghaemoglobin increases during first two weeks of nodule initiation. Nitrogen fixation begins with appearance of leghaemoglobin and cessation of bacterial division. N-fixation continues till 6th to 7th week of nodule age when nodule senescence begins.
Stem:
Stems are formed as a result of hypocotyls elongation of the seed axis which forms the lower portion of the stem. The height of stem and its branching habit depends upon variety. The forage types are very profusely branched with long prostate or horizontal creeping branches whereas they are short and erect in grain types. The stems are hairy or purbescent due to which they look whitish in colour and the hairs remain throughout life cycle of the plant.
Leaves:
Soybean has four different types of leaves viz. cotyledons or seed leaves which emerge with seedlings, two simple primary leaves, trifoliate leaves and the prophyllus. Primary leaves are essentially oval in shape having petiole of about 1-2 cm length. All the leaves have pinnate venation.
Simple primary leaves and seed leaves are arranged opposite while trifoliates are alternatively arranged on the stem. Each of the leaves has a pair of stipules at its base. The leaflets of trifoliate leave have glabrous and pubescent, though the extent of pubescence varies according to varieties. The fourth types of leaves are very tiny paired prophylls that are present at the base of each lateral branch.
Flowering:
Flower initiation is controlled by photoperiod, temperature and genotype. Soybean stem growth and flowering habit are of two types; indeterminate and determinate. In case of indeterminate stems, the terminal bud (apical meristem) continues to grow and produce axillary raceme type of inflorescence and the pods are evenly produced on the stems/branches with a diminishing frequency towards the tops of the stems. Examples are Ankur, Kalitur, T- 49, etc.
The determinate type is characterized by vegetative development which ceases when the apical meristem becomes an inflorescence. This type of stems has both axillary and terminal racemes and pods are found in dense clusters along the stems. Examples are Alankar, Bragg, PK 472, PK 416, etc. The flowering period and the time of overlap of vegetative and reproductive growth is greater for the indeterminate than determinate type. The genes Dt1 and Dt2 are responsible for determinate and indeterminate growth habit, respectively.
Soybean flower is small and purple or white in colour. It is a self-pollinated crop. Soybean pods are straight or slightly curved and vary in length from less than 2 cm up to 7cm or more in some varieties.
The pod colour at maturity varies from light yellow to yellow-grey, brown or black depending upon extent of carotene and xanthophyll pigments present on them. The number of pods varies from two to more than 20 on a single inflorescence and up to 400 on a single plant.
Seeds:
The fully developed seeds are formed after 35 to 45 days of blooming. Seeds are small, hard, round to oval with a smooth, shiny testa and small distinct hilum. Seed may be yellow, green, red, black, slightly mottled or occasionally bicoloured depending upon the variety.
Germination of soybean is epigeal where cotyledons come out of the soil. Growth of radicle (downward growth) is rapid and when it is 2-3 cm in length the first branch root appears. The cotyledons are elevated above the soil by rapid growth of hypocotyl.
5. Classification of Soybean:
Soybean belongs to family leguminosae, subfamily papilionaceae belongs to genus Glycine with chromosome number 2n=40. Based on form, colour of pods, size, shape of grain, soybean may be classified as follows.
Manchurian Classification:
As per this classification based on colour of seed, soybean has been classified into 3 groups:
(i) Yellow group – They fetch higher price. Yellow seeds with light hilum. Yellow seeds with golden hilum. Yellow seeds with brown hilum.
(ii) Black group – Seeds are of black colour with small, large and flat seed. Market value is low.
(iii) Green group – Epidermis of seed is green with yellow and green embryo.
Martin’s Classification:
Based on shape of soybean seed, Martin’s classified soybean in to three groups, namely soya eliptica (egg type seed), soya spherical (round seed) and soya compress (pressed seed).
6. Growth and Development of the Soybean Plant:
It is important to understand how soybeans grow and develop. Since their vegetative and reproductive growth stages occur for several weeks, many environmental conditions can affect final yield. Too much or too little moisture at specific stages of growth can affect performance. Even the type of soybeans, i.e., determinate or indeterminate, influences when a plant starts the flowering or pod-filling stage.
Growth Stages of Soybean:
A descriptive system has been worked out for soybean growth and development. The pictures and descriptions given below are representative of a group II indeterminate soybean variety. Typical soybean plants follow the same general pattern of development. The specific time between stages, the number of leaves, and plant height, however, may vary among varieties, environments, locations, planting dates, and planting patterns.
VE -Emergence:
Depending on soil moisture, soil temperature, and planting depth, VE or emergence occurs one to two weeks after planting. At this stage, cotyledons are above the soil surface. Loss of the cotyledons prior to the VI growth stage may cause a yield reduction of 8 to 9 percent. Nodule formation typically begins at this growth stage.
VC -Cotyledon:
At this growth stage the cotyledons have fully expanded and the unifoliate leaves have unfolded. The unifoliate leaves are located at the first true node on the plant. Numbered V-stages begin at the first node above the unifoliate leaves (V1 is actually at the second true node on the plant).
V1 – First Trifoliolate (Second Node):
Although it is the second true node, this stage marks the first node at which the first trifoliolate is produced. The trifoliate is considered to be fully developed when the leaflets at the third true node are unfolded (leaflet edges are no longer touching)
V2 – Second Trifoliolate (Third Node):
Soybean plants at the V2 stage have two fully developed trifoliolates. Nodules formed at the VE growth stage begin actively fixing nitrogen for the plant. Lateral roots are growing rapidly in the top 6 inches of the soil between soybean rows.
V3 – Third Trifoliolate (Fourth Node):
Three trifoliolates are now fully developed above the unifoliate leaves.
V4 – Fourth Trifoliolate (Fifth Node):
Four trifoliolates above the unifoliate.
V5 – Fifth Trifoliolate (Sixth Node):
Five fully developed trifoliolates above the unifoliate leaves. The axillary buds in the top stem axils appear bushy and are beginning to develop into flower clusters. The total number of nodes the plant will develop is set at this growth stage.
V6 – Sixth Trifoliolate (Seventh Node):
Six trifoliolates above the unifoliate leaves. However, by this growth stage the cotyledons and the unifoliate leaves have dropped off leaving scar tissue at the nodes, but still need to be recognized for proper staging.
R1 – Beginning Bloom:
A plant is at the R1 growth stage when one open flower is at any node on the main stem. Typically, plants at the R1 stage are 15 to 18 inches tall and are in the V7 to V10 growth stage. Flowering tends to begin on the third to sixth node, and progresses upward and downward. Axillary branches initiate flowering a few days after the main stem.
The appearance of new flowers is almost complete by R5 with the peak of flowering occurring between R2.5 and R3. Vertical root growth sharply increases at this growth stage and growth rate of the roots remains high until th R4 to R5 reproductive stage.
R2 – Full Bloom:
A plant is at the R2 stage of reproduction when there is an open flower at one of the two uppermost nodes on the main stem with a fully developed leaf. Plants tend to be in the V8 to V12 growth stage and are approximately 17 to 22 inches tall. At this stage, the plant has attained about 50% of its mature height and total mature node number.
At this stage the plant is rapidly accumulating dry matter and nutrients initially in the vegetative tissues, but nutrient accumulation will shift to the pods as seeds begin to develop. Nitrogen fixation in the nodules increases rapidly. Roots continue to grow deeper into the soil profile and lateral roots have grown across the inter-row space at this stage. Yield will be reduced by approximately 6% if plants are defoliated by 50%.
R3- Beginning Pod:
When pods are 5 mm (3/16 inch) long at one of the four uppermost nodes on the main stem with fully developed leaf the plant is at the R3 stage. Typical plants at the R3 stage are in the V11 to V17 growth stage and are approximately 23 to 32 inches tall. It is common to find developing pods, withering flowers, open flowers, and flower buds on the same plant.
R5- Beginning Seed:
The seed in the pod at one of the four uppermost nodes with fully developed leaves on the main stem is 3 mm (1/8 inch) long at this stage. Plants at the R5 stage are normally V15 to V23 and are approximately 30 to 43 inches tall. This stage is characterized by rapid seed growth, with nutrient accumulation and dry matter distribution shifting from vegetative development toward the growing seed.
At about R5.5, plants have attained their maximum height, node number, and total leaf area. Nitrogen fixation in the nodules has peaked at this stage and will decline rapidly. Seeds have begun to rapidly accumulate dry matter and nutrients.
Shortly after R5.5, nutrient redistribution begins to occur from the vegetative tissues to the developing seeds. Rapid seed dry weight accumulation continues until approximately R6.5, with 80% of the total seed dry weight acquired.
Demand for water and nutrients is large at this time of seed development. A 75% yield reduction may occur is plant are completely defoliated between the R5 to R5.5. Yield reductions between R5.5 ad R6 are usually due to aborted pods and seeds per pod.
R6 – Full Seed:
A plant is at the R6 stage when a pod containing a green seed that fills the pod cavity is present at one of the four uppermost nodes on the main stem with a fully developed leaf. Plants at R6 are typically in the V16 to V25 vegetative stage and are approximately 31 to 47 inches tall.
The growth rate of the whole plant at R6 is very rapid, with a decline in the growth rate beginning around R6.5. Rapid leaf yellowing begins shortly after R6 and continues to about R8. Leaf senescence begins on the older (lower) nodes first, with the possibility of 3 to 6 trifoliate leaves falling off before leaf yellowing begins.
R7 – Beginning Maturity:
One normal pod on the main stem has reached its mature pod color. Physiological maturity of a soybean seed occurs when dry weight accumulation has stopped, and occurs when the seed as well as the pod turn yellow.
At this stage the plant is basically at physiological maturity because very little additional dry weight will be accumulated. Soybean seeds at physiological maturity are approximately 60% moisture and contain all necessary plant components for the next generation of soybean.
R8 – Full Maturity:
At this stage 95% of the pods have reached maturity, but 5 to 10 days of drying weather are needed after R8 before soybeans have less than 15% moisture. Ideal moisture for harvest and storage is 13%, with moisture below 13% causing increased pre-harvest shatter loss, increased number of split beans, and loss of weight to sell.