What are the key techniques for raising sweet potato seedlings in cold frames
Sweet potato is rich in starch, protein, fat and various vitamins, and has become a very popular health food today. At the same time, it is also a very important chemical raw material with extremely broad development prospects. Sweet potato has the characteristics of wide adaptability, strong stress resistance, drought tolerance, barren tolerance and few pests and diseases. In particular, the soil types and climatic conditions of the Huang-Huai-Hai Plain in the central and southern parts of our province are extremely suitable for planting sweet potato. In recent years, in some places, planting sweet potato has become a good way for farmers to adjust their planting structure and achieve increased income and prosperity. Right now, the season for raising sweet potato slips has arrived again. Below is an introduction to a method commonly used by farmers in the plain areas of our province: making beds in the open field and covering them with plastic film to raise seedlings. This method has the characteristics of low cost, easy management and strong slips.
1. Site selection and bed construction. Choose a place sheltered from the wind and facing the sun, with fertile soil, high and dry terrain, good drainage, close to a water source and convenient for management to build the bed. Saline-alkali land and continuous sweet potato cropping land are not suitable for building beds. Generally, seedlings are raised in mid-to-late March. According to the number of seed potatoes and management requirements, the bed runs east-west. Dig the soil to a width of 2 m and a length of 4-6 m, with a depth of about 0.4-0.5 m. After the bed is dug, smooth the bottom and the four walls so that the seed potatoes can be arranged conveniently.
2. Carefully select seed potatoes and arrange them on the bed. At present, the high-quality sweet potato varieties widely promoted in our province include Hebei 351, Jishu 98, Jishu 99, Beijing 553, Xinong 431, Xushu 18 and other new dual-purpose or special-purpose varieties. Varieties should be flexibly selected according to market demand and production and processing goals. Seed potatoes used for raising seedlings should be harvested and stored separately. Generally, 70 kg of seed potatoes should be reserved per mu of field to be planted. Select tubers that have the characteristics of the original variety, are well shaped, bright and smooth, and have not suffered cold, freezing, waterlogging, injury or disease. A single tuber size of about 150-250 g is appropriate. In recent years, in old sweet potato growing areas, black spot disease, soft rot, dry rot and nematode disease have occurred severely. Before raising seedlings, chemical treatment of seed potatoes can achieve a very good preventive effect. Use 50% amobam diluted 300-400 times with water and soak the selected seed potatoes for 10 minutes. After soaking, the seed potatoes should be arranged on the bed immediately. When arranging, the head of the seed potato should face upward, following the principle of level on top and uneven below. The slanting placement method is mostly used, with the head of one potato pressing 1/3 of the tail of another, which produces more and faster sprouts. Generally, 25 kg of seed potatoes per sq m is appropriate.
After arranging the seed potatoes, fill the gaps between them with sandy soil, then water the bed soil thoroughly with warm well water. After the water seeps down, gently press the seed potatoes with a flat wooden board, then cover with about 3 cm of sandy soil. It should not be too thick, otherwise it is not conducive to raising soil temperature and can easily lead to thin and weak slips and easy transmission of diseases. After the seed potatoes are placed on the bed, immediately cover with plastic film and straw mats to raise the temperature.
3. Seedbed management. Strengthening seedbed management is the key to producing more seedlings and cultivating strong seedlings. Before emergence, the aim should be high-temperature sprouting promotion, with good warming and insulation measures and appropriate moisture, striving for early emergence, more seedlings and no rotting of the bed. After emergence, the temperature should be lowered appropriately for steady growth, with attention to watering and ventilation to prevent burning of sprouts. Before harvesting slips, hardening should be carried out at low temperature, and after harvesting slips, attention should be paid to topdressing fertilizer.
1) Temperature management. Before emergence, in order to achieve high-temperature sprouting promotion and disease prevention, warming and insulation work must be done well. Within 3 days after the seed potatoes are placed on the bed, keep the tuber layer temperature at about 35°C, which helps promote sprouting and wound healing and can produce a disease-resistant substance, ipomeamarone, thereby inhibiting black spot disease. Under normal circumstances, on sunny days uncover the straw mats in the morning to sun the film and raise the temperature, and cover the straw mats at three or four o'clock in the afternoon to keep warm. Before emergence, the bed temperature should be kept at 30-32°C. After emergence, as the seedlings grow, gradually lower it to about 25°C. Before harvesting slips, carry out low-temperature hardening, lowering the bed temperature to 20-22°C. Within one or two days after harvesting slips, increase temperature and keep warm to facilitate the sprouting of new buds and promote rapid growth of small slips. Then carry out low-temperature hardening, generally harvesting slips once every five or six days.
2) Water management. Watering the seedbed is one of the important measures for cultivating strong seedlings. The amount and frequency of watering should be determined according to the dryness and wetness of the bed soil, the growth of the slips and the bed temperature, and should coordinate water, temperature and air to promote vigorous growth of the slips. On the basis of watering thoroughly when the seed potatoes are placed on the bed, generally do not water before the seed potatoes emerge, so as to facilitate high-temperature sprouting promotion, disease prevention and emergence. If the seedbed is too dry, use a sprayer to spray clean water on the seedbed. After the seedlings emerge completely, water heavily once before hardening and once on the second day after harvesting slips. Between these two heavy waterings, according to slip growth and the moisture condition of the bed soil, water lightly and evenly in small amounts. The watering time follows the principle of "before noon in the early stage, after noon in the later stage." In early spring, when the temperature is low, water in the morning, cover the film at noon to raise the temperature, and the temperature can recover in the afternoon, preventing the bed temperature from being too low at night. In the later stage, when the temperature is higher, watering in the afternoon is appropriate to prevent the nighttime temperature from being too high and the slips from growing quickly but tender and weak.
3) Hardening. Hardening is an important measure for cultivating strong seedlings. In order to make the slips grow robustly and increase the survival rate, before planting, the seedbed must be hardened by measures such as ventilation and cooling and uncovering the film for airing. After the slips emerge completely, choose clear weather and begin gradual ventilation so that the bed temperature gradually decreases, which is beneficial for steady growth of the young seedlings and prevents the appearance of spindly seedlings. When the seedlings grow to 12-15 cm and the temperature is stable, ventilation can be carried out day and night. Two or three days before harvesting seedlings, the straw mats and film can be completely removed so that they are hardened day and night to adapt to the external field environment. In this way, after planting, the seedlings recover quickly and the survival rate is high.
4) Topdressing. In order to increase the number of seedlings and meet the nutrient needs of the slips, topdress with watering after each slip harvest. Topdressing should mainly use quick-acting nitrogen fertilizer, such as urea (avoid ammonium bicarbonate to prevent burning the young slips), and combining it with phosphate and potassium fertilizer gives better results. Generally, for 10 sq m, use 0.5 kg of urea with 50 g of potassium dihydrogen phosphate. Mix the two fertilizers evenly and spread them evenly on the seedbed. Immediately after spreading, gently knock the fertilizer off the seedling leaves, then water to wash it clean.
4. Harvesting slips. When the seedlings grow to 20 cm, harvest them in time. If slips are harvested too late, the slips become crowded and can smother the small seedlings below, affecting the number of seedlings in the next crop. There are two methods of harvesting slips: cutting and pulling. The cutting method is generally often used. Its advantages are that it is less likely to transmit diseases and move the seed potatoes, and it allows the small slips of the next crop to grow quickly and produce more seedlings. Especially in places where sweet potato black spot disease occurs severely, high cutting of slips is advocated, leaving stubble more than 3 cm to help prevent disease. The best time to harvest slips is generally early morning. The cut slips are best planted the same day to help survival. If they cannot be planted in time, they can be placed in a cool, ventilated place (do not sprinkle water), and strive to plant them early in the following days. After cutting the slips, cover with film during the day to raise the temperature, add straw mats at night, and water and topdress the next day.