Cultivation techniques of stevia rebaudiana

Stevia is the dried leaf of stevia (SteviarebanianumBertoni), a plant of Compositae. Alias stevia, sugar herb, sweet grass. Stevia has a sweet taste in the whole plant, and the leaf is the sweetest. Stevia can increase blood sugar, lower blood pressure and promote metabolism, and can be made into health bars or food additives, which can treat diabetes, obesity, regulate gastric acid, restore nerve fatigue, prevent dental caries in children, etc. Stevia originated in subtropical South America, was successfully introduced in China in 1977 and has been cultivated in more than 20 provinces and cities.

(1) morphological characteristics

Stevia is a perennial herb with a height of 1.3 meters. The roots and shoots are enlarged, with 60 branches of 50ml, up to 25 cm in length. The stem is erect, the basal tip is woody, the upper part is tender, densely short pilose. The leaves are opposite or the upper part of the stem is alternate, draped in shape, the margin is shallowly serrate, both sides are short pilose, and the leaf veins are Ternate. Inflorescences small, involucral bracts tubular, involucral bracts 5-layered, margins equal; receptacle flat, bald; Corolla basally purplish red or white, distally white. Achenes linear, slightly flat, brown, with crown hairs. Flowering from July to September and fruiting from September to November.

(2) growth habits

Stevia likes to grow in a warm and humid environment, but it can also withstand a low temperature of-5 ℃. The temperature of 20 ℃ is the most suitable for stem and leaf growth. Stevia stevia is a short-day plant with strong sensitivity to light, and the critical day length is 12 hours, so it blossoms early in low latitudes. The ovule of flowering and fertilization takes 25 mi 30 days to develop into a mature seed. When the seed is mature, the crown hair flutters and spreads everywhere in the wind.

The seed is small, and the weight of a thousand seeds is only 0.25Mel 0.32g. During the non-dormant period, the germination temperature of mature seeds was 20 ℃ and 25 min, and light could promote seed germination. The life span of seeds is less than 1 year.

(3) cultivation techniques

1. Stevia stevia is not strict on soil, but the loose and fertile land with more humus grows well. The previous crop is suitable for soybean, peanut, mung bean and so on, but not for continuous cropping. The soil pH is neutral, and it is not suitable to be less than 5.5or more than 7.9.

The land where stevia is planted should be ploughed in autumn. the depth of ploughing has a certain effect on the yield, and the depth is better. At the same time, 25 kg of calcium superphosphate is used as base fertilizer per mu.

2. Seed propagation is the main way of propagation, and it can also be propagated by cutting and striping.

The main results are as follows: (1) the method of sowing and raising seedlings and then transplanting is often used in seed reproduction and production. Flat bed sowing is usually used to raise seedlings in the southern provinces of China, while hotbeds are used to raise seedlings in the north. On the south bank of the Yangtze River, the suitable sowing time is 10Mel month. The seedlings overwinter in the seedling border and can be transplanted to the field for cultivation in the middle and late March of the following year. The north generally uses greenhouse or hotbed to sow seeds and raise seedlings for 24 months. In order to spread the seeds evenly, the seeds can be mixed with fine sand before sowing, then soaked in lukewarm water for 10 minutes, and then mixed with a small amount of vegetation. After sowing, gently press the seed with the plank to make it come into contact with the soil, and then spray water to the bed once to keep the bed moist and improve the seedling emergence rate. The temperature and humidity are suitable, and it can be germinated and unearthed 10 days after sowing. Sowing rate: 500g per 100m2 nursery bed, the actual number of strong seedlings is 20-250000, which is enough to plant 1215 mu of land. Generally, 8000,000 seedlings are planted per mu, and the dense planting can reach 12000 seedlings.

(2) Cuttage propagation can be done from late March to late August, and the survival rate of cuttings cut before budding is higher. When cutting, select the robust branches and lateral stems that meet the requirements, cut off a 20 cm long section, insert the 1/3-l/2 of the cuttings into the bed soil, and the row spacing is 2 cm × 5 cm. Watering in time after insertion, covering the top with grass curtains or plastic film, keeping warm at night, avoiding direct sunlight at noon, properly ventilating and transparent when new buds grow, gradually exercise the adaptability of seedlings to the outside world, and form strong seedlings with developed roots, strong stems and leaves, and normal color.

In addition, although pressing can also reproduce, it is only used in seed selection to retain a good single plant, so it is not suitable for large-scale cultivation and production.

3. Field management Stevia stevia is resistant to wet and afraid of dry, high temperature and little rain in summer, and the lower leaves are easy to fall off when there is insufficient moisture. The demand for fertilizer is also high, so the cultivation of stevia needs to supply enough complete fertilizer of nitrogen, phosphorus and potassium. Ammonium sulfate is usually applied in the first year 7.5Mu 10kg per mu, and in the second year around the Yangtze River, 15MUR 20kg ferric sulfate is applied. The use of potash fertilizer should be applied frequently and thinly, generally 8 Mu 10 kg per mu, 2 MUE 3 times per year as well. Topdressing and irrigation can be combined with weeding to loosen the soil twice to keep the field clean and the soil loose. In order to promote luxuriant stems and leaves and increase yield, topping and coring can be carried out when the seedling height is 20-25 cm, and the new branches of each plant can reach 17 branches after topping, which is the period of fertilizer and water demand. Phosphorus and potassium fertilizer should be applied to the roots, or potassium dihydrogen phosphate should be sprayed to the leaves to achieve the goal of high quality and high yield.

Stevia consumes a lot of nutrients at the stage of flowering and pollination, so it is necessary to strengthen management in time. The stems and branches cross too closely, the lower leaves are easy to fall off, and the whole plant is easy to lodge in case of strong wind and torrential rain. Therefore, in addition to topdressing and watering, we should also combine with mid-tillage to cultivate soil beside the roots, pay attention to field drainage, maintain light and ventilation between the borders, and pick the lower leaves properly.

4. Pest control

The main results are as follows: (1) Seedling blight is a disease at seedling stage. Prevention and control methods:

① can choose land with good drainage and loose soil to raise seedlings.

Before sowing ②, soil was treated with 50% carbendazim per mu and 2kg / mu.

The initial stage of ③ was irrigated with carbendazim spray or 500x solution borrowed from 1000Mel 1500.

The diseased plants were pulled out in time by ④, and the diseased points were treated with 3 ∶-1 plant ash and quicklime powder.

(2) Leaf spot disease is easy to occur from July to October, which is harmful to stems and leaves. Prevention and control methods:

From May to June, ① paid attention to drainage to reduce soil moisture, and applied more potassium fertilizer to improve plant disease resistance.

Prevention and treatment of ② by spraying 50% carbendazim 1000 times solution in the early stage of the disease

After harvest, ③ cleared the garden, treated the residual plants and burned them centrally.

(3) White silk disease has more rainfall from April to May, and the soil moisture is too large, which is easy to occur and damage the roots. Prevention and control methods:

Reasonable close planting of ①, pay attention to ventilation and light in the field

② increases the application of phosphorus and potassium fertilizer to avoid excessive growth of seedlings.

As soon as the diseased plant is found in ③, it is immediately removed and disinfected with lime around the diseased point.

In the early stage of ④, 50% carbendazim 1000 times liquid can be used to irrigate the disease area to control the spread of the disease.

(4) Control methods of inchworm (measuring inchworm, bridge worm): cocoon wasp, the natural enemy of inchworm, can be protected, or sprayed with 40% omethoate 1000 times diluent, which is prohibited 20 days before harvest.

(4) harvesting and processing

The content of glycosides in the leaves of stevia increased with the growth of the plant, and the amount of synglycosides was usually the highest in the bud stage, which was the best harvest time. The crops cultivated to the south of the Yangtze River can be harvested three times a year, two times along the Yellow River, and only once a year in the northern part of North China, Northeast China and Inner Mongolia. When harvesting, be sure to choose a sunny day to cut the branches, the branches harvested on the same day should be picked leaves that night, and then spread out to dry, can not be accumulated, otherwise the leaves will turn black and affect the quality. Large area planting is suitable for dryer processing and drying, and after drying, it is packed in bundles and packaged. In order to prevent mildew and deterioration, it can be packed in human plastic bags and sealed after drying.