What are the key points of formula fertilization techniques for sweet potato

According to production practice, formula fertilization for sweet potato has an obvious yield-increasing effect. The specific measures are as follows:
I. Topdressing methods
1. Base fertilizer: The application ratio of nitrogen, phosphorus and potassium is generally 1:1.5:3. For a medium-yield sweet potato field with a yield of 2500-3000 kg per mu, about 5-7.5 kg of pure nitrogen, 7.5-10 kg of phosphorus and 10-15 kg of potassium are applied per mu. Base fertilizer should account for 70-80% of the total fertilization amount. The base fertilizer is generally applied per mu as 1500-2000 kg of compost residue manure, 2.5-5 kg of urea (or 7.5-12 kg of ammonium bicarbonate), 10-15 kg of phosphate fertilizer and 50-75 kg of plant ash (or 7.5-10 kg of potassium chloride). When applying base fertilizer, a layered fertilization method should be adopted, with coarse fertilizer as the base and refined fertilizer applied shallowly. When the amount is large, it can be applied in furrows; generally it can be applied in holes. That is, after ridging and before planting seedlings, open furrows or dig holes according to row and hole spacing, apply the base fertilizer into the furrows or holes, and then harrow and mix with a hoe so that soil and fertilizer are evenly mixed. A concentrated fertilization method using box fertilizer can also be adopted, that is, when making boxes, apply fertilizer along the box, then dig the box, wrapping the fertilizer inside the box. Adopting these concentrated fertilization methods can reduce fertilizer loss and achieve the goal of economical fertilizer use.
2. Topdressing: Topdressing should be divided into 3 times. The first is seedling-promoting fertilizer, about 10 days after planting; for intercropping, apply it early through the forest 20-30 days before corn harvest. The fertilization amount accounts for 20-25% of the total topdressing amount, applying 500-750 kg of human and livestock manure urine per mu or 1.5-2.5 kg of urea, applied in holes after mixing with water. Seedling fertilizer should be applied in an appropriate amount according to the amount of base fertilizer, weather and seedling growth, to prevent excessive application from causing excessive vegetative growth of seedlings. A method of applying more to weak seedlings and less to vigorous seedlings can also be adopted to promote balanced growth in the whole field. The second time is about 60 days after planting, when stems and leaves grow vigorously and the tuberous roots gradually expand, requiring more fertilizer. For those with good growth and those that have already received seedling fertilizer, potassium fertilizer should be dominant and nitrogen fertilizer applied less; for those with poor growth, appropriately apply more nitrogen fertilizer together with potassium fertilizer. Generally, apply 1000 kg of human manure urine and 100 kg of plant ash per mu, or 10 kg of urea, 10-15 kg of superphosphate and 7.5 kg of potassium chloride, applied in holes after mixing with water, and combine with management measures such as intertillage, weeding and earthing up. The third time is carried out 80-100 days after planting, applying 2.5 kg of urea per mu. Within 30-50 days before harvest, 75-100 kg of 2% superphosphate solution or 5-10% plant ash soaking clarified liquid can also be sprayed once every 10-15 days, for a total of 2-3 sprays. For those with poor stem and leaf growth, a 1% urea solution can be sprayed. The spraying time is preferably 4-5 o'clock in the afternoon on sunny days.
II. Fertilization for autumn sweet potato
Autumn sweet potato is planted around the Beginning of Autumn, with a growth period of about 100 days. Therefore, it is necessary to grasp the characteristics of a short growth period and concentrated fertilizer demand of autumn sweet potato and adopt corresponding fertilization techniques. Fertilization for autumn sweet potato should follow the principles of applying sufficient base fertilizer, applying seedling fertilizer early, and heavily applying fertilizer for strengthening vines and forming tubers. Generally, the base fertilizer is applied per mu as 500-750 kg of barnyard manure, 2.5 kg of urea, 10 kg of phosphate fertilizer, 50 kg of plant ash or 5 kg of potassium chloride, applied in furrows or holes. About 10 days after planting, apply seedling-lifting fertilizer, applying 750 kg of clear water manure or 2.5 kg of urea per mu, applied in holes after mixing with water. About 40 days after planting, apply fertilizer for strengthening vines and forming tubers. This fertilization can use 750-1000 kg of decomposed human and livestock manure mixed with about 50 kg of plant ash for hole application, and combine with intertillage and earthing up to prevent nutrient loss.
III. Fertilization for sweet potato tips overwintering for seed production
The principles of fertilization for sweet potato tips used for seed production are: apply base fertilizer early and heavily, apply an appropriate amount of seedling-setting fertilizer, topdress wintering fertilizer according to seedling condition, and frequently apply light spring growth-promoting fertilizer. Base fertilizer is the foundation for sweet potato seedling growth. When applying it, decomposed high-quality compost and barnyard manure should be the main material, with an application amount of 100-150 kg per bed (calculated as 6.6 sq m), applied about 10 days before planting seedlings and fully mixed with the soil. After the sweet potato seedlings are planted, according to the dryness and wetness of the bed soil, apply 100-150 kg of decomposed human and livestock manure water to combine soil and seedlings and stabilize seedlings and promote rooting. During the overwintering period, sweet potato seedlings do not need much fertilizer. When sufficient base fertilizer and seedling fertilizer have been applied, topdressing may be omitted. However, if leaves are found to be thin and small, yellow in color and showing symptoms of fertilizer deficiency, some fine compost and plant ash can be applied on a sunny afternoon, which not only has fertilizer effect but can also absorb moisture, absorb heat and preserve warmth. Foliar topdressing can also be carried out by spraying 2% superphosphate or 20% plant ash extract to increase the sugar content in the seedling body and enhance cold resistance. After the beginning of spring, the young buds of sweet potato seedlings begin to sprout, so the soil should be loosened and topdressing should be carried out in time. Topdressing should be light first and then concentrated, less first and then more, first decomposed pig manure water, then decomposed human urine water and chemical fertilizer. Chemical fertilizer should be stirred evenly with water and sprinkled, and after application, the seedlings should be washed with clean water to avoid burning. For the first fertilization, 100 kg of decomposed dilute pig manure water can be applied per bed, and afterward, according to the growth of sweet potato seedlings, topdress once every 7-10 days. After cutting seedlings, topdress once for each cutting to promote rapid seedling growth.