Understanding Soybean
Soybeans are rich in phytic acid, dietary minerals, and B vitamins. Soy vegetable oil, another byproduct of processing the soybean crop, is used in both food and industrial applications. Soybeans are the most important source of protein for feed for agricultural animals, which in turn yields animal protein for human consumption.
A Brief History of Soybean
Soybeans were an important crop in East Asia long before written records existed. The origin of soybean agriculture is a topic of ongoing debate in the scientific community. The closest living relative of the soybean is the Glycine soja (formerly known as G. ussuriensis), a legume indigenous to central China. Evidence suggests that soybeans were domesticated in China between 7000 and 6600 BC, Japan between 5000 and 3000 BC, and Korea around 1000 BC. The first clearly domesticated, cultigen-sized soybean was found at the Mumun-period Daundong site. Soy was revered for its usefulness in crop rotation before it was fermented into products like fermented black soybeans (douchi), jiang (Chinese miso), soy sauce, tempeh, natto, and miso. It was also consumed alone, as bean curd and soy milk.
Around the 13th century, or possibly even earlier, soybeans were introduced to Java in the Malay Archipelago. By the 17th century, European traders (Portuguese, Spanish, and Dutch) began trading soybeans and their products in Asia through their commerce with the Far East, and by this time, they had made it to the Indian Subcontinent. By the 18th century, China had exported soybeans to the Americas and Europe. Today, African countries consume a significant amount of soy, which was first introduced to the continent from China in the late 19th century.
Soybean Climate Requirements
The ideal conditions for cultivating soybeans are between 20 and 30 °C (70 and 85 °F), with temperatures below 20 °C (70 °F) and above 40 °C (105 °F) severely hindering growth. Cultivation is successful in hot summer regions. They can thrive in a variety of soil types, although damp alluvial soils with high organic content are optimal for their growth. Like most legumes, soybeans fix nitrogen through a symbiotic interaction with the bacterium Bradyrhizobium japonicum (syn. Rhizobium japonicum). Thanks to the ability of soy to fix nitrogen, farmers can use less nitrogen fertilizer when planting other crops in rotation with soy, thereby enhancing yields. However, for optimal results, the soybean (or other legumes) seed should be combined with an inoculum of the appropriate strain of bacteria before planting. Modern crop varieties typically require 80 to 120 days from planting to harvest and grow to a height of about 1 m (3 ft).
Soybean Soil Requirements
Soybean farming is best suited to fertile, well-drained loam soils with a pH range of 6.0 to 7.5. Sodic and salinized soils inhibit seed germination. The crop is also harmed by water logging. With an ideal pH range of 5.5 to 6.5, soybeans can grow on soil that is only slightly acidic. But because the toxicity of aluminium (Al) and manganese (Mn) is likely to be an issue on such soils, they are not tolerant of strongly acidic soils (below pH 4.5). Conversely, it is not advised to grow soybean in soils with a pH higher than 8 because micronutrient shortages, such as those in zinc (Zn) and iron, can occur (Fe). Because its roots are very shallow and its structure restricts water absorption during dry periods, soybeans are not drought-tolerant.
Therefore, due mostly to drought stress, soybean performs poorly on sandy soils and soils with little water storage, such as gravelly or shallow soils. Clay soils with less rainfall have a lower likelihood of establishing new plants and germination of seeds. Between emergence and the four leaf stage, soybeans are prone to water logging. The ability of soybeans to tolerate water logging after this point makes them superior to other non-rice crops, which is another reason to grow them. Additionally, soybeans may be able to withstand flood irrigation methods better than other crops.
Soybean Farming Techniques
Land selection is very important in soybean farming as this will impact the overall production of soybean. The main land must not have been sown with soybean crop in the previous season to avoid volunteer plants that cause admixture. Land continuously cultivated with soybean may harbour wilt pathogens. So these kinds of fields must be avoided. By following the crop rotation, endemic pathogens can be reduced. A soil with high organic matter definitely helps in leading the production of vigorous seeds. In order to maximise the output of soybeans, it is crucial to choose the right land. To prevent admixture-causing volunteer plants, the main area cannot have previously been planted with soybeans. Soybean fields that are regularly farmed must be avoided because they may harbour the wilt pathogen. The prevalence of endemic pathogens can be decreased by using crop rotation. A soil with a high organic content definitely aids in the formation of a seed that is vigorous. Depending on the cultivation techniques used, the field should be divided into beds and channels of 4 feet by 6 feet or ridges and furrows measuring 1 foot wide.
Soybean Physiology
The taproot of the soybean plant has tiny, spherical, occasionally lobed nodules. The stems have branches, and the cotyledon axils have buds. Unless the tip is destroyed, the major leaves do not often form. The majority of cultivars shed their leaves as the maturation of the pods progresses. The leaves are alternate, trifoliate, and infrequently five-flowered; the petiole is long, narrow, and cylindrical; the stipules are small and minute; the leaflets are ovate to lanceolate, typically pale green in colour, with rounded bases and acute or obtuse apexes. Short clustered axillary racemes with terminal inflorescences are the type. Flowers are tiny, bracteoles two, oblong, sharp. The norm is self-pollination. Early in the morning, flowers open, and pollen is released shortly before or at the moment of opening, landing squarely on the stigma. Flowers are visited by bees and other insects so that cross-pollination can occur, however, this is typically less than 1%.
Soybean Crop Development
Understanding growth stages can help farmers carry out more timely production practices, which in turn leads to higher yields. There is always field variation in maturity so a field is considered to be at a particular growth stage, only when more than 50% of plants in the field are at that stage.
- Germination Stage: The radical, or primary root, leaves the seed first. Soon after, the cotyledons (seed leaves) are pulled along by the hypocotyl (stem) as it starts to grow toward the soil’s surface. As the cotyledons open up and the hypocotyl emerges, it straightens up. Depending on the cultivar, planting depth, moisture levels, and temperature, emergence typically takes five to 10 days. At this time, the primary root is also beginning to send out lateral roots.
- Cotyledon Stage: Unifoliate leaves are fully extended at this stage. The young plant’s nutritional requirements are met by the cotyledons (for about seven to 10 days). Approximately 70% of the cotyledons’ dry weight will be lost as a result of the nutrition reallocation.
- First trifoliolate: The first trifoliolate has opened and fully emerged.
- Second node: The 6 to 8-inch-tall plants have three nodes and two leaflets that are fully extended. Just now, the bacteria are beginning to actively fix nitrogen. The majority of these root nodules contain millions of bacteria and are located less than 10 inches below the soil’s surface. The nitrogen fixation process is active in nodules that are pink or crimson within. Nodules that are white, brown, or green are presumably parasitic on the plant since they are ineffective at fixing nitrogen.
- Third to Fifth nodes: Soybean plants are about 7-9 inches tall with four nodes (three unfolded leaflets). The number of branches seen on the plant may increase at this point.
- At this stage the plant normally has axillary buds in the top stem that will develop into flower clusters (racemes).
- Sixth node: At this stage, plants are typically 12 to 14 inches tall with seven nodes that have unfurled leaflets. The plant’s cotyledons and unifoliolate may have died. Each two to three days, new phases are rapidly developing. In any rows 30 inches or fewer, lateral roots have underground crossed the row.
- Flower Initiation: Every node along the main stem of the plant has at least one flower. The plants are now 15 to 18 inches tall. Depending on the vegetative stage, soybean flowering always starts at the third to the sixth node on the main stem. The plant will go through several stages of this blossom initiation. Eventually, branches will also bloom. Basal pods are always more developed because flowering occurs from the base to the tip of each raceme.
- Full Bloom: Beans are roughly 17 to 22 inches long. One of the two top nodes of the main stem has an open blossom on it. These two top nodes each have a leaf that is fully formed. At this point, the soybean has acquired roughly 50% of its mature height and around 25% of its entire dry weight and nutrient content.
- Pod Initiation: Plants can grow to a height of 23 to 32 inches. Each of the top four nodes has a 3/16 inch-long pod. At this period, yield can be impacted by temperature or moisture stress through total pod count, beans per pod count, or seed size.
- Full Pod: At the start of the full pod stage, this stage displays quick pod growth as well as the emergence of the seed. The most significant time for seed output is at this stage.
- Seed Initiation: At this stage, the plant needs a lot of water and nutrients to finish filling the seeds. The soybean provides almost half of the necessary N, P, and K from the plant’s vegetative portions and approximately half from N fixation and nutrient uptake by the roots, resulting in nutritional redistribution in the plant.
- Full Seed: The overall pod weight will peak at this stage, which is also referred to as the “green bean” stage or the beginning of the complete seed stage. The growth of the beans is quick.
- Initial Maturity: On the main stem, this stage starts with one regular pod that develops the mature colour (brown or tan). Individual seeds reach their apex in terms of dry matter. This can be noticed visibly when the seeds and pods lose all of their green hues (they appear yellow). When seeds reach physiological maturity, they have roughly 60% moisture.
- Full Maturity: It will only take five to ten days of suitable drying weather beyond this point for the soybeans to be at less than 15% moisture, or harvest moisture, on the soybean plant, when 95% of the pods have reached their maturity colour.
Soybean Crop Diseases
- Bacterial Pustule: The Bacterial Pustule disease is caused by Xanthomonas campestris pv. glycines bacteria. This disease thrives in warm and rainy conditions and spreads rapidly in wet weather. It is seed borne and causes early yellowing and defoliation of the soybean crop resulting in losses of up to 18 percent. On the upper side of the leaves, small yellowish-green pods with reddish brown centres appear. The centre of each individual spot appears to be slightly raised. On the underside of the leaves are tiny pustules. Similar pustules can be seen on pods. The pods could combine to create huge, irregular dead patches. Sometimes, the dead tissue may tear and separate. Heavy infestation causes the leaves to turn yellow, fall off, and in sensitive plants, complete defoliation. The bacterium survives in crops.
- Myrothecium Leaf Spot: This disease is caused by Myrothecium roridum Tode ex Fries. Previously, it was known as a minor disease. It has recently gained significant proportion. The disease spreads rapidly during rainy weather and is made worse by warm, humid conditions. The disease can potentially cause yield losses for the soybean crop of 20 to 40%. On the leaves of the diseased plants, small round or oval brown spots appear with a dark brown or purple border. Around these spots, which appear as concentric rings, translucent areas develop. These spots later develop dark green sporodochia. Other aerial parts, such as the stem, petiole, pods, etc., may also show the symptoms. The leaves may dry out as a result of the spots merging to form irregular shapes. The disease survives in crop debris and seeds.
- Rust: The Rust disease is caused by Fafopsora Pachairaisi. This can be found in India’s north-eastern regions. The leaves initially have brown spots on them. They then covered the entire leaf. On leaves, there is a brown powder that over time makes the entire leaf brown.
- Yellow Mosaic: The Yellow Mosaic disease is caused by the Mung bean yellow mosaic virus (MBYMV). This virus is extremely harmful and can result in significant yield losses. Conspicuous systemic bright yellow mottling of leaves is a defining symptom. The yellow areas are sporadic or appear in random bands along the main veins. This virus can infect a variety of hosts and cannot be transmitted through sap or seeds. Whiteflies are the MBYMV insect vector. Bemelia tabaci Infection within 75 days of planting causes a significant yield drop; infection after 75 days causes non-significant production losses.
- Soybean Mosaic: The Soybean Mosaic disease is caused by the Soybean Mosaic virus. The virus can be transmitted through sap, aphids, and seed. Plants that are diseased are typically stunted and have distorted leaves (puckered, crinkled, ruffled, stunted, narrow). Often, the parts are stunted. fewer and smaller seeds, and are flattened or curled. Infected seeds either do not germinate or produce diseased seedlings. The disease is transmitted when virus-infected seeds are sown and the disease overwinters in living plants.
Soybean Harvesting and Storage
When weather conditions are not ideal, harvesting can be done when the grain moisture content is between 14 and 15 percent. This can help farmers to reduce harvest-related losses. The choice of the cultivars impacts the amount of soy lost. Early maturing varieties typically experience greater loss during harvest. If it rains during the harvest, harvesting should be completed immediately. Harvesting can be resumed promptly following a rainstorm and all available drying techniques should be used to minimise rain damage. The impact of weathering and seed deterioration can be minimised by harvesting at the most opportune time. Harvested crops should be stored in a high, clean area separate from other seeds and materials to maintain the good quality of the seed. Careful handling can prevent mechanical damage to soybean seeds and reduce germination during harvesting and threshing processes.
