Stevia
Introduction:
Stevia is a plant species native to South America, particularly Paraguay and Brazil. It is a member of the sunflower family and has been used for centuries by the Guarani people of Paraguay as a natural sweetener for their tea and medicinal preparations.
Stevia's sweet taste comes from a group of compounds called steviol glycosides, which are present in plant leaves. These compounds are 200-300 times sweeter than table sugar but have no calories or effect on blood sugar levels, making stevia an attractive alternative to artificial sweeteners.
In the 20th century, stevia gained popularity as a sweetener in Japan, where it was approved for use in food and beverages in the 1970s. Since then, it has been approved as a sweetener in many countries around the world, including the United States and the European Union.
Stevia is now commonly used as a sweetener in a variety of products, including soft drinks, baked goods, and other processed foods. It is also available in a granulated form for home use as a sugar substitute in cooking and baking.
Botanical Characteristics:
Stevia, scientifically known as Stevia rebaudiana, is a perennial plant that can reach a height of 60-100 cm. The leaves of the plant grow opposite to each other and are sessile, ranging in size from 2 cm to 10 cm. Each plant can have up to 40-45 leaves.
Stevia is typically grown in semi-humid subtropical regions with temperatures ranging from 20-30 degrees Celsius. It requires well-fertile soil that is rich in organic matter and has a pH level between 6.5-7.5. Sandy loam soil is preferred for cultivation, while soils with high salt or salinity are not suitable for growing stevia.
Production Technology
Land Preparation:
Before planting stevia, it is crucial to properly prepare the field. This involves plowing the land 2-3 times to bring the soil to a fine tilth. During the plowing process, trichoderma should be mixed thoroughly with the soil. In the final plowing, farmyard manure (FYM) should be incorporated into the soil to provide additional nutrients.
Soil Type and climate:
Stevia can be grown in a variety of soils, although it performs best in sandy loam to loamy soil with good drainage and high organic content. It is important to avoid cultivating stevia in saline soils, as these can be harmful to the plant's growth and yield. The ideal pH range for stevia cultivation is between 6 and 8.
Nursery Establishment:
To start stevia cultivation, it is recommended to sow the seeds indoors in containers for 6-8 weeks. After sowing, it is important to cover the beds with peat moss and provide adequate watering to retain moisture in the soil.
For bushier growth, it is recommended to pinch the tips of the plant before transplanting. This encourages the growth of lateral shoots and results in a fuller plant.
When the seedlings are ready for transplantation, typically after 6-8 weeks, they should be transplanted onto raised beds that are 60cm wide and 15cm in height. It is important to water the seedling beds 24 hours before transplanting to ensure that the seedlings can be easily uprooted and are turgid at the time of transplantation.
Sowing
Time of sowing:
The ideal time for sowing stevia is between February and March. This period provides optimal conditions for seed germination and early growth of the plant. It
Spacing:
When transplanting stevia seedlings, they should be spaced approximately 18 inches apart to provide enough room for the plants to grow and spread out. The row spacing should be 20-24 inches apart, allowing for adequate airflow and room for maintenance between the rows.
Seed Rate:
When transplanting stevia seedlings into the main fields, it is recommended to use a plant density of approximately 30,000 seedlings per acre.
Raised Bed Preparation:
Forming raised beds is considered the most effective and cost-efficient method for growing stevia. The recommended height for the raised bed is 15cm or half a foot, with a width of 15cm or half a foot as well. To ensure adequate spacing between the plants, a distance of 15cm is suggested between each plant, with a distance of 30cm or one foot between each row.
By utilizing raised beds and following the recommended spacing, it is possible to establish approximately 50,000 stevia plants within one acre of land.
Fertilizer:
To achieve optimal production of stevia, it is recommended to apply a specific amount of fertilizers to the soil. Generally, two bags of urea, one bag of DAP, and one bag of potassium sulfate should be applied per acre of land.
Irrigation:
Irrigation for stevia cultivation is typically performed using either sprinkler systems or drip irrigation. As the plant does not require excessive water, light irrigation is recommended at regular intervals. During the summer months, it is recommended to irrigate at intervals of every 8 days to prevent over-watering. It is important to avoid allowing water to stagnate in the field, as this can harm the stevia crop.
Weed control:
To control weeds in the field, hand weeding is typically performed. The first weeding is usually carried out approximately one month after planting, with subsequent weeding conducted every two weeks thereafter. Intercultural operations are also performed to remove weeds since the crop is grown on raised beds, which makes it easy for labor to access and maintain. By carefully managing weed growth, growers can help ensure that their stevia plants have the necessary resources to grow and produce a high-quality yield.
Plant Protection Measures
Pests and Their control:
Aphids are soft-bodied sucking insects that are nearly transparent. When present in large numbers, they can cause leaves to yellow and die prematurely.
Control:
To manage aphids, growers can use chrysoperla predators at a rate of 4-6 thousand per acre or use 50 grams of neem concentrate per liter. These methods are effective in reducing the population of aphids and preventing damage to stevia plants.
Disease and their control:
Stevia is vulnerable to root rot disease, which is caused by a fungus that is often present in the soil. The disease first appears as yellowing of the lower leaves, which then spreads to the upper parts of the plant and causes them to dry up. Root rot is most common in the early stages of growth and can cause the roots of affected plants to become weak and easily break.
Control:
To control root rot disease, growers can mix 400 grams of Topsin-M with 100 liters of water and spray it around the roots of the affected plants. This method is effective in managing the spread of the fungus and helping to prevent further damage to the crop.
Harvesting:
Harvesting of Stevia can be done when the plant attains a height of 40-60 cm. Flowering is induced by shorter days, which can impact the quality and quantity of the stevioside content.
Yield:
Typically, three to four harvests are conducted annually, resulting in an average yield of 3-3.5 tons of dry green leaves per hectare. Stevia plants can be grown for up to five years after the initial planting, providing a sustainable source of leaves for production.
Drying and Threshing
The drying time for Stevia depends on factors such as weather conditions and loading density, typically ranging from 24 to 48 hours at a temperature of 40°C to 50°C. Once the leaves are dried, a specialized thresher/separator is required to remove the dry leaves from the stems.:
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