Detailed explanation of sweet potato cultivation techniques: master the key points to grow sweet potatoes well
Sweet potato is rich in protein, starch, pectin, cellulose, amino acids, vitamins and various minerals, and has the reputation of being a “longevity food”. Its sugar content reaches 15%-20%. It has effects such as anti-cancer, protecting the heart, preventing emphysema, diabetes, and weight loss. In the Ming Dynasty, Li Shizhen's Bencao Gangmu recorded that “sweet potato tonifies deficiency, strengthens the spleen and opens the appetite, and strengthens kidney yin”, and said that people by the sea who eat it live long. Traditional Chinese medicine regards sweet potato as a good medicine.
Seedling raising methods
Sweet potatoes need to be raised as seedlings 2 months before transplanting, that is, spring sweet potatoes begin seedling raising in late January, autumn sweet potatoes in mid-to-late June, and early winter sweet potatoes in early-to-mid August. One-time seedling raising can be used, or they can be propagated in batches.
Seed selection and seedling raising for purification and rejuvenation are carried out every year. Select seeds in fields free of viral disease and scab disease and with consistent varieties, and choose medium-sized seed potatoes with long, uniform, ridge-free, straight shapes, smooth skin, and no disease or insect spots or wounds as seeds. Before planting, soak them in 1.0% copper sulfate solution or 2% sodium hydroxide solution for 5-10 min, or soak the seed potatoes for 2h in biological agents permitted for organic production such as Bt and Beauveria bassiana. It is best to use insect-free conditions in gauze greenhouses to propagate virus-free seedlings.
The seedling bed base fertilizer should be applied sufficiently. Generally, 500-1000kg of self-composted organic fertilizer and 50kg of mineral potassium-magnesium fertilizer are applied per 667 sq m. Before sowing, disinfect the seedling bed with lime sulfur or lime, or disinfect by sealing the shed.
Seedling stage management
During sweet potato seedling raising, topdressing should be applied in a timely manner according to seedling conditions. The fertilizer used should be bio-organic fertilizer certified as organic or permitted for use by an organic certification body (total NPK nutrient content ≥6%, organic matter content ≥40%). The total amount of topdressing during the seedling raising period is generally 250kg per 667 sq m. At the first “red bud” stage, generally apply thin fertilizer water; when the seedlings are 10-13cm high, the second topdressing can be carried out. After each fertilization, splash water to wash the seedlings to prevent fertilizer from sticking to the seedlings and causing seedling burn.
Earthing up can be carried out in 2-3 sessions. When the seedlings are about 10cm high, the first earthing up can be carried out, and the second earthing up is carried out after 7d, with a total of 3-5cm of soil. For earthing up, it is best to use fertile, loose, fine soil mixed with burnt mud ash or decomposed compost, and evenly scatter it into the seedling bed. Earthing up can be combined with applying liquid fertilizer, doing earthing up first and then fertilizing, so that the soil and the base of the seedlings are closely combined to facilitate early and abundant new root growth.
After sowing, spray biological agents permitted for organic production such as Bt and 300-fold tea seed cake water once every 15d, spread wood ash once; and place sex pheromone traps around the seedling bed or outside the seedling raising shed.
Seedling bed management should also focus on measures such as heat preservation, moisture retention, and ventilation, with temperature as the main factor. Before emergence, cover with straw curtains at night and keep the bed temperature at 25-35°C. After emergence, control the temperature at 20-25°C, and prevent high-temperature scorching of seedlings. If the temperature inside the film exceeds 30°C, ventilate and dissipate heat in time to prevent seedling burn. When a cold wave comes, do a good job of heat preservation.
Generally do not water before the seed potatoes emerge, so as to facilitate high-temperature sprouting, disease prevention, and emergence. If the seedling bed is too dry, spray clean water on the seedling bed with a sprayer. After emergence, pay attention to the humidity of the seedling bed. When the seedling bed turns white, water in time, moisten the bed soil and sprinkle thin fertilizer water to promote sweet potato seedling growth; when the seedling bed is too wet, uncover the film and ventilate in time.
Fertilizer and water management
Sweet potato's demand for the three elements nitrogen, phosphorus, and potassium varies with the growth period. Nitrogen fertilizer is absorbed more during the stem and leaf growth period and less during the tuberous root enlargement period; phosphorus fertilizer is absorbed less in the middle stage of stem and leaf growth and more during the tuberous root enlargement period; while potassium fertilizer absorption from planting to harvest is greater than that of nitrogen and phosphorus, and is even more significant during the tuberous root enlargement period. Therefore, sweet potato fertilization should be carried out around this characteristic, N:P:K=5:6:20. It is best to use soil testing and formula fertilization technology.
Organic sweet potato cultivation prohibits the application of any chemical fertilizer, and mainly uses base fertilizer, with the general base fertilizer amount accounting for 60%-80% of the total fertilization amount. The base fertilizer is applied in combination with land preparation and ridging.
After the transplanted seedlings survive, apply 1 topdressing of biogas slurry or fully decomposed thin manure water in combination with replanting missing seedlings, as a seedling-promoting fertilizer. The second time is during the sweet potato tuber formation period, that is, about 60d after planting in spring and autumn, and about 70d after planting in winter, apply 1 topdressing of tuber-promoting fertilizer. The tuber-promoting fertilizer is mainly potassium fertilizer. Generally, 500kg of homemade organic fertilizer (or organically certified organic fertilizer), 250kg of wood ash, or 25kg of mineral potassium-magnesium fertilizer are applied per 667 sq m. The application method is generally to use a plow to break open both sides of the ridge, or use a small hoe to open small ditches at the waist of the ridge, then mix the fertilizer with probiotics and apply it in bands. After application, water once to promote the fertilizer effect as quickly as possible. At the same time, after fertilization, earthing up can be carried out in combination with manual weeding.
After sweet potatoes are watered at planting to settle the seedlings, 30-40d after planting, they begin to branch and trail vines, and the water requirement increases. If drought occurs at this time, water in time. Furrow irrigation can be used, but the irrigation amount cannot exceed 1/2 of the ridge height. Overall, water management should keep the soil basically moist. If there is rainy weather, drain waterlogging in time to prevent water accumulation from causing excessive growth of sweet potato seedlings and the phenomenon of only growing fibrous roots without forming tubers.