Summary and Sharing of Experience in Double-Season Sweet Potato Cultivation

I. Variety Selection  Choose virus-free early-maturing varieties, which can be harvested just over 3 months after planting, allowing off-season marketing and yielding considerable economic benefits. Early-maturing varieties can include Japanese Yellow Sweet Potato, Yushu 10, Sushu 8, etc. These early-maturing varieties have vines 50-70 cm long and are suitable for close planting. Plant in mid-to-late April, harvest in mid-to-late July, and another crop of sweet potato can still be planted. 

II. Fertilization and Ridging  Sweet potato is drought-tolerant and afraid of waterlogging. For early-maturing cultivation, sandy soil with good drainage and relatively high terrain should be chosen. Sweet potato requires nitrogen, phosphorus, and potassium in a ratio of 1:0.7:2, and also needs a certain amount of trace elements such as zinc, iron, manganese, and boron. Sweet potato is sensitive to chlorine; the chloride ions in potassium chloride are difficult for sweet potato to absorb and affect sweet potato quality, so potassium sulfate is better to use in production. Per mu, apply 2-3 cubic meters of fully decomposed high-quality farmyard manure, 20-30 kg of ammonium bicarbonate, 100 kg of superphosphate, and 30-40 kg of potassium sulfate. Combine fertilization with deep plowing and ridging. The ridges should be about 30 cm high and 50-60 cm wide, with small row spacing of 50-60 cm and large row spacing of 70-80 cm. Plastic film mulching cultivation can be used, and double mulching with small arched sheds can also be added.

III. Timely Planting  Planting can be done when the average daily temperature is stable at 15°C and the soil temperature at 5-10 cm depth is stable at 17°C. Strong seedlings and weak seedlings should be planted separately to prevent large seedlings from suppressing small ones. Before covering with plastic film, phorate or 9% trichlorfon crystal mixed with roasted bran or grain can be spread in the soil. In old sweet potato-producing areas, 5% sweet potato stem nematode granules can be applied at 1-1.5 kg per mu at the same time. The planting depth should be 5-6 cm, and it is best to leave 3-4 leaves above the soil surface. For excessively vigorous seedlings, a section can be cut off from the root end, leaving about 20 cm for planting. Because early-maturing cultivation should use high-density planting to achieve early harvest and high yield, generally 4000-5000 plants per mu.

IV. Scientific Management  Check seedlings and replant missing ones promptly 3 days after planting, and timely carry out intertillage, weeding, and hilling. In the middle growth stage, sweet potato must be protected from waterlogging. Timely control leaf-rolling worms, sweet potato hornworms, etc. When the rainy season arrives, it is easy for sweet potato vines to take root and grow excessively. At this time, while pulling weeds, lift the rooted sweet potato vines to break the roots, then put them back in place. Turning the vines is strictly prohibited. For plots where severe excessive growth has occurred, pinch the tips and use chemical control. For plots with average soil fertility and premature senescence, apply about 15 kg of potassium sulfate compound fertilizer per mu together with watering, and at the same time spray potassium dihydrogen phosphate and sweet potato swelling agent 2-3 times.