Key Technical Points for Sweet Potato Seedling Raising and Cultivation Management

1. Varieties and seedling raising: Sweet potato varieties should be selected according to the type of export product. For processing into starch noodles and vermicelli products, high-starch sweet potato varieties should be chosen, such as Jishu 98, Xushu 18, Xinnong 1, Xinyin 1, Shang SL-19, etc. For varieties used for roasting and eating, Xushu Beijing 553, Xinong 431, Sushu 8, Xinnong 4, American Black Sweet Potato, etc. can be used.
The quality of sweet potato seedlings has a great relationship with yield. Strong seedlings grow quickly after transplanting, root early, form tubers early and have strong stress resistance; while old vines and weak seedlings develop late, grow slowly in stems and leaves, and have poor stress resistance.
2. Deep plowing and fertilization: Generally, apply 4000 kg of high-quality farmyard manure, 40 kg of ammonium bicarbonate, 60 kg of superphosphate and 20 kg of potassium sulfate per 667 sq m. Plow deeper than 25 cm and form large ridges, with ridge height 30 cm, top width 40-50 cm, bottom width 90 cm and furrow bottom width 30 cm. When planting seedlings, plant double rows on the ridge surface.
In fields with medium fertility, strong seedlings increased yield by 26.5% compared with weak seedlings; in fields with higher fertility, strong seedlings increased yield by 9.6% compared with weak seedlings. Therefore, cultivating strong seedlings is one of the key techniques for obtaining high sweet potato yields. The seedbed for tuber seedling raising should be selected in a place sheltered from the wind and facing the sun, with higher terrain, good drainage and convenient management. Two seedling raising methods can be used: film mulching and open-field tuber burial. The bed width is 1.2-1.3 m, and the length depends on need. On average, about 150 kg of seed tubers are used per hectare of field. Generally, every 10 kg of seed tubers raised can provide about 5000 seedlings. In seedbed management, good work must be done in heat preservation, moisture retention, ventilation and hardening of seedlings, and cutting of seedlings.
3. Timely early planting: Sweet potato is an indeterminate-growth crop. At suitable temperatures, the longer the growth period, the higher the yield. Spring sweet potatoes with plastic film mulching can be planted 10-15 days earlier. When there is no frost, the film should be broken to release the seedlings, increasing yield by more than 30% compared with cultivation without film mulching; for open-field cultivation, spring sweet potatoes should be planted with good seedlings, using tall-cut strong seedlings about 25 cm high. When planting, plant one row on each side of the ridge surface. For spring sweet potatoes, 3500-4000 plants per 667 sq m; for summer sweet potatoes, 4000-5000 plants. Plant as shallowly as possible, leaving 5 cm above ground, and bury all the rest horizontally along the ridge direction in the soil at a depth of 5-8 cm. Water thoroughly. After the water infiltrates, cover tightly with fine soil, leaving 3-4 leaves above ground. Finally, use 80-100 g of trifluralin per 667 sq m, mixed with 60 kg of water, and spray the soil surface to prevent weed damage. About 5 days after planting, check the seedlings and fill gaps. 4. Watering and fertilization: Water thoroughly at planting. After that, if drought occurs for about 20 days, water along the furrows. During the flood season, pay attention to drainage.
Sweet potato has a high fertilizer requirement. In fertilization, four words should be achieved: sufficient, suitable, heavy and skillful. Sufficient: the sweet potato field should receive sufficient base fertilizer, accounting for 40%-50% of the total fertilization amount. Suitable: 10-15 days after transplanting, apply suitable hole fertilizer, applying 5-7 kg of urea per 667 sq m, or 1000-1200 kg of dilute livestock and poultry manure. Heavy: apply heavy side fertilizer before the stems and vines extend to the point where stems and leaves close the rows, accounting for about 40% of the total amount, mainly organic fertilizer, with an appropriate amount of chemical fertilizer. Skillful: in the late growth stage of sweet potato, when cracks appear on the bed surface, skillfully apply crack fertilizer, topdressing 1500 kg of dilute livestock and poultry manure (water) or 10 kg of urea per hectare, diluted with water and applied. Foliar spraying of 0.2% "sweet potato tuber expansion agent" or potassium dihydrogen phosphate can also be done to promote tuber expansion.
5. Intertillage and vine lifting: From transplanting until the stems and leaves close the rows, sweet potato should undergo 2-3 intertillage weedings, mainly shallow hoeing, maintaining the original ridge shape.
When rain occurs or the soil is moist, sweet potato vines produce many adventitious roots that penetrate downward. The vines should be lifted in time, and 15% paclobutrazol should be sprayed to prevent excessive vine growth. The suitable concentration is 230 g mixed with 60 kg of water.
　　
　　
Direct Sowing Cultivation of Cut Sweet Potato Pieces
　　
Direct sowing cultivation of cut sweet potato (sweet potato) pieces is planted 20-30 days earlier than traditional planting. Because its growth period is extended, it generally increases fresh tuber yield by about 1000 kg per mu. It is a comprehensive high-yield cultivation technique with low investment, large returns, and savings in labor and time.
1. Carefully select seed tubers. Choose excellent varieties suitable for local planting. Tubers should be uniform in size, each weighing about 100-150 g. Remove tubers damaged by freezing, diseases or insects. Generally, 50 kg of seed is used per mu.
2. Cutting into pieces and soaking seeds. According to the different bud eye density at the upper and lower ends of the tuber, the upper part of the tuber should be cut smaller and the lower part larger, keeping 2-3 buds per piece. Place the cut seed tubers into a 500-600 times carbendazim solution and soak for 10-20 minutes. Remove, dry, and sow immediately.
3. Land preparation and fertilization, with sufficient base fertilizer. Apply 4000-6000 kg of organic fertilizer and 50 kg of ternary compound fertilizer per mu. Plow deeply and adopt secret ridge cultivation, with ridge width not less than 80 cm and height 28-30 cm.
4. Sow in time. The time for direct sowing of cut pieces is 1 month earlier than the time for transplanting vines. After the seed tubers are taken out of the cellar, it is best to sow them in the field within two days to avoid cold damage. Before sowing, open a furrow 15 cm wide and 5-6 cm deep on the ridge back. After watering thoroughly in the furrow and allowing it to infiltrate, place the mother pieces in the furrow with the bud eye side facing south and upward, with plant spacing of 25-30 cm. After planting, immediately cover with film to help retain moisture and raise temperature.
5. Strengthen management. When seedlings are about 2 cm high, promptly make artificial holes in the film at the emergence points to avoid burning the young seedlings. At the end of May and beginning of June, when ground temperature rises, the film should be removed in time. At the same time, pay attention to weed control and insect prevention. Never turn the vines, so as to avoid reducing yield.


Mid-stage Management Methods for Sweet Potato

The mid growth stage of sweet potato is the tuber expansion stage. This stage goes from the closing of stems and leaves over the rows to the peak of stem and leaf growth, while tubers correspondingly thicken and expand. Spring sweet potatoes generally take 60-90 days after planting, and summer sweet potatoes 40-70 days after planting. The growth center at this stage is stems and leaves, and by mid-to-late August stem and leaf growth reaches its peak. This stage coincides with the high-temperature and rainy season. Fertilizer decomposes quickly and water supply is sufficient, making excessive growth likely. Upper leaves are dark black, leaf nodes and petioles are longer, the leaf layer is thick, leaves shade each other, and ventilation and light penetration are poor. There are many yellow leaves, fallen leaves, dead stems and rotten leaves in the lower layer, tubers expand slowly, and it is easy to cause large vines and small tubers, reducing yield. Therefore, management during this period is the key to high sweet potato yield.
1. Prevent drought and drain waterlogging. During this period, most areas in the north are hot and rainy. The aboveground stems and leaves of sweet potato grow rapidly, and nutrients move upward rather than downward. At this time, attention should be paid to drainage, that is, promptly remove surface water after rain, and control excessive aboveground growth. In dry years, watering is needed to prevent drought, so that tubers can expand rapidly in soil that is neither wet nor dry.
2. Lift vines and cut roots; do not turn vines. In the hot and rainy season, soil humidity is too high, some varieties root too much, or high-yield fields with heavy fertilizer and water have many deep white roots. Lifting vines can reduce water and nutrients supplied to leaves, control excessive stem and leaf growth, and at the same time air-dry the ridge soil and improve soil permeability. During this period, vines must not be turned, because turning vines damages stems and leaves, disrupts the uniform distribution of leaves, affects leaf photosynthetic efficiency, and causes yield reduction.
3. Spray paclobutrazol multiple times. For excessively growing fields, use 50-70 g of 15% paclobutrazol per mu mixed with 50 kg of water and spray, generally 2-3 times, with good results.
4. Apply tuber-promoting fertilizer. Pay attention to topdressing in the mid growth stage, mainly potassium fertilizer such as potassium sulfate and plant ash. This is because potassium fertilizer can prolong leaf age, improve photosynthetic efficiency, promote the transport of photosynthetic substances, increase the potassium-to-nitrogen ratio, and promote rapid tuber expansion. Apply potassium sulfate at 10 kg per mu, and plant ash at 100-150 kg per mu.
5. Control leaf-eating pests. In recent years, sweet potato hornworm has occurred seriously in some fields. Observation should be strengthened, and control should be carried out promptly after discovery. Before the third instar of larvae, promptly spray 2.5% trichlorfon powder at 1.5-2 kg per mu, or use 90% crystalline trichlorfon 1500 times solution, or 50% phoxim 1000 times solution, sprayed at 4 p.m.


Three Key Points for Late-stage Field Management of Sweet Potato

1. Apply expansion fertilizer well: apply 15 kg of superphosphate and 10 kg of ammonium sulfate per mu, and also spray 0.3% potassium dihydrogen phosphate and 1% urea solution.
2. Clear ditches to reduce waterlogging damage: During the tuber expansion stage of sweet potato, there is more rainfall, so field drainage ditches should be cleared in time to reduce waterlogging damage.
3. Control leaf roller moth: When the population density of sweet potato leaf roller moth is high, it can eat all the leaves of plants in the whole field. Before the third instar larvae have rolled leaves, spray 32% shamibi emulsifiable concentrate 3200 times solution for control. Spraying is best done after 5 p.m. on sunny days. For fields with high insect density and severe damage, spray again after 3-5 days.
　　
Fertilization Techniques for Late Growth Stage of Sweet Potato
　　
In the late growth stage of sweet potato, reasonable fertilization can prevent premature aging of plants, maintain leaf assimilation capacity, promote nutrient transport to tubers, and thereby increase yield.
Foliar fertilization: After sweet potato enters the late growth stage, root absorption capacity weakens, so foliar fertilization can be carried out. For hilly sloping land, plain sandy land, or fields with a trend of premature aging and weak growth, spray 0.5% urea solution. For fields with relatively vigorous growth and higher fertility levels, spray 0.2% potassium dihydrogen phosphate solution or 2%-3% superphosphate extract. For general fields, spray a mixed solution of 0.4%-0.5% urea and potassium dihydrogen phosphate, once every 7-10 days, for a total of 2-3 sprays, applying 70-100 kg of fertilizer solution per mu each time. The best spraying time is evening on sunny days.
Fertilizer-water crack application: Use 3%-5% potassium sulfate solution or 10%-20% plant ash extract and apply it along the ridges into cracks, using 100-150 kg of fertilizer solution per mu. For fields with a trend of premature aging, 2% ternary compound fertilizer solution can be used for topdressing.


Key Points for High-yield Management of Summer Sweet Potato

1. Prevent excessive stem and leaf growth. The growing season of summer sweet potato is in a season of high temperature and abundant rain, and stems and leaves grow quickly. If not controlled in time, excessive growth is easy to cause. Generally, when sweet potato vines grow to 50-60 cm, spray 10 mL of mepiquat chloride per 667 sq m, or 20-25 mL of daminozide. For seedlings lacking fertilizer, topdress 10 kg of urea or 20 kg of diammonium phosphate per 667 sq m, and apply 1000 kg of decomposed human manure and urine. The method is to open holes beside the ridge back. Water after fertilization, and cover with soil immediately after the water infiltrates.
2. Protect stems and leaves; do not turn vines. Because turning sweet potato vines damages stems and leaves, reduces photosynthesis, produces less nutrients, and causes yield reduction. At the same time, turning vines also causes leaves to turn over, overlap and become dense, damages vine tips, promotes axillary buds to produce new branches and small leaves, and causes yield reduction, with a range of up to 20%-30%.
3. Timely control of diseases and insect pests. In recent years, sweet potato hornworm has occurred relatively seriously. Once found, promptly spray 4.5% beta-cypermethrin emulsifiable concentrate 3000 times solution, or 20% fenvalerate 2000 times solution for control, to ensure that sweet potato has sufficient leaf area. At the same time, during the growth period, aphids should be controlled in time to prevent the introduction of viruses.


Skillful Topdressing of Expansion Fertilizer for Sweet Potato

From late August to early October is the tuber expansion stage of spring and summer sweet potato. This period is the key period for yield formation and also the period with the greatest fertilizer demand. The following three methods can be used for topdressing.
1. Hole-eye topdressing method: Use a wooden peg to make a hole about 30 cm deep 20-30 cm away from the main root, put in an appropriate amount of ternary compound fertilizer, and seal it with wet soil. If one hole is made on each side of the ridge, the effect is even better. This method increases yield by about 20% per mu.
2. Crack topdressing method: When cracks appear on the ground during sweet potato expansion, use 500 g of potassium dihydrogen phosphate per mu, add 400 kg of water, or 2.5 kg of urea and 10 kg of superphosphate, add 500 kg of water, prepare a fertilizer solution and pour it into the cracks, 0.7-1 kg per plant. Half a month later, use 100 kg of plant ash per mu, add 500 kg of water (soak for 4 hours), pour the filtered clear liquid into the cracks, and seal them tightly. This method increases yield by more than 300 kg per mu.
3. Foliar topdressing method: Spray 0.3% potassium dihydrogen phosphate (or 2.5% potassium sulfate, 10% plant ash, 2% ammonium sulfate, 0.3% superphosphate, 0.3% urea) aqueous solution on the leaves, once a week. This method increases yield by 18%-20% per mu.


Five Points to Grasp in the Late Stage for Increasing Sweet Potato Yield

After late August, summer sweet potato enters the key stage of expansion. At this time, management should be strengthened. On one hand, the nutrients needed for tuber expansion should be met to the greatest extent; on the other hand, premature aging of stems and leaves should be prevented, photosynthesis should be enhanced, and nutrient accumulation should be increased. Specific yield-increasing technical suggestions are as follows:
1. Remove the top bud: Removing the top bud can regulate nutrient movement and promote nutrient transport to tubers. Remove the top bud twice in total. The first time, when the sweet potato vine grows to 30-40 cm long, remove the 1-2 cm tender tip. The second time, when branches grow to about 30 cm again, remove the tender tips of the branches.
2. Pruning: For sweet potato fields with many branches and vigorous growth, use scissors to cut off 2-3 branches. This can allow nutrients to flow back, let tubers obtain more nutrients, and at the same time improve light penetration among sweet potato branches and accelerate photosynthesis, etc. However, on poor soil, topping should not be done.
3. Increase potassium fertilizer application: After sweet potato vines close the rows in August, spray potassium dihydrogen phosphate solution, that is, prepare potassium dihydrogen phosphate with water into a 1%-2% solution, and spray 50-70 kg per mu, once every 5-7 days, for 2-3 consecutive sprays. For fields with insufficient base fertilizer, thin stems and leaves, or late-stage fertilizer deficiency, use a mixed solution of 0.3% potassium dihydrogen phosphate solution plus 0.5% urea fertilizer solution, and spray 50-70 kg per mu, once every 5-7 days, for 2-3 consecutive sprays.
4. Lift vines: For excessively growing sweet potato fields, the method of lifting vines can be used to prevent too many roots from running. After sweet potato closes the rows, if growth is excessive, gently lift the sweet potato vines and then put them back in place. The time for lifting vines should be before the end of August, lifting vines 2-3 times in total.
5. Topdress crack fertilizer: The time for topdressing crack fertilizer is generally 70-80 days after planting, when tubers enter the peak expansion period and cracks appear on the bed surface. Specifically, it should be determined according to the growth of summer sweet potato and soil conditions. For fields with insufficient early fertilizer, shallow and poor soil, and relatively poor plant growth, apply earlier and more appropriately; the topdressing amount can be 800-1000 kg of decomposed human and livestock manure water per mu, or 6-7 kg of urea mixed with 600 kg of water, applied along the cracks. If early fertilizer is sufficient and plants grow vigorously, apply less or only apply farmyard manure and potassium fertilizer, without nitrogen fertilizer.