Experience and Key Techniques for High-Yield Spring Sweet Potato Cultivation

Sweet potato is a root tuber crop with the characteristics of high yield, stable yield, wide adaptability, strong stress resistance, rich nutrition, and wide use. In the adjustment of planting structure, it has become a hot crop. How can sweet potato achieve a high yield? 

1) Balanced fertilization and ridge planting. According to experiments, producing 1000kg of tubers requires the absorption of 4-5kg of N, 3-4kg of P2O5, and 7-8kg of K2O, so applying sufficient and complete fertilizer is an important condition for high sweet potato yields. Fertilization should achieve fast fertilizer effect in the early stage, so that seedlings sprout early; stable fertilizer effect in the middle stage, so plants are strong but not excessive; and long-lasting fertilizer effect in the late stage, so plants do not decline prematurely. For high-yield fields, generally apply more than 4000kg of organic fertilizer per mu, 10kg of urea, 20kg of diammonium phosphate, and 25kg of potassium sulfate. The fertilization method should preferably be band application when making ridges. 

The characteristics of high-yield sweet potato soil are loose structure, large porosity, good air permeability, sufficient oxygen supply, and the ability to drain water and relieve waterlogging. Combined with deep plowing and ridge cultivation, it can improve the physical and chemical properties of the soil. The ridge protruding above the ground is not only conducive to drainage in the rainy season, but also to the decomposition of organic matter, and can absorb heat quickly during the day, raising the ground temperature, and dissipate heat quickly at night, making the day-night temperature difference large, which is beneficial to sweet potato growth and root nutrient accumulation. When making ridges, the ridge shape should be plump, the furrow narrow and deep, the ridge surface flat, and the ridge soil firm, with no large clods or hard cores. The ridge spacing is generally about 70cm. 

2) Timely early planting and selection of strong seedlings. Sweet potato root tubers are asexually propagated vegetative bodies and have no obvious maturity period. Generally, growth stops when the temperature is below 15°C, and root tuber enlargement stops when the ground temperature drops to 16°C--18°C. Timely early planting can extend the growth period, and root tubers form early. This can not only use the temperature conditions before the rainy season to make root tubers expand rapidly, but also, in the hot and rainy season, store the photosynthetic products formed by stems and leaves in the expanded root tubers, promoting coordinated growth of the underground and aboveground parts. According to many years of meteorological data, the time for planting spring sweet potatoes in our city is around May 1. Experiments show that planting on April 28 extends the root tuber enlargement period by 7d compared with planting on May 10, increases yield by about 10% per mu, and produces neat tubers and high fresh tuber quality. 

To improve seedling survival rate and early rapid growth, seedlings should be selected from the first batch of strong seedlings cut from the seedbed. The first batch of seedlings has thick stems, vigorous leaves, and well-developed roots. The seedlings should undergo full hardening. Generally, before planting, seedlings should be exposed to sunlight in the seedbed for 3-5d, so that the leaves become dark green and thicker. If a section of the seedling is pinched off, white milky sap flows from the cut surface. Planting such seedlings gives a high survival rate, fast growth, and high yield. Do not select seedlings that have not been hardened, seedlings with black roots, or seedlings with burned sprouts. 

3) Timely vine lifting and topping/pinching. Entering the rainy season, sweet potato stems and leaves grow luxuriantly, and nodal roots are likely to develop, dispersing nutrients and hindering the transport of photosynthetic products to the root tubers. To prevent this phenomenon, vine turning was mostly used in the past to reduce soil moisture, raise ground temperature, and prevent nodal root formation. According to experiments, turning sweet potato vines is both labor-intensive and reduces yield. This is mainly because after vine turning, stems and leaves are seriously damaged, breaking the optimal distribution of leaves for receiving light energy, reducing photosynthetic intensity by 30%, increasing respiration intensity by 19%, and reducing yield by about 10%. In production, vine turning has been changed to vine lifting, which avoids stem and leaf damage, does not destroy leaf distribution, and is conducive to high yield. However, vine lifting should not be done too many times; generally 1-2 times is sufficient, and it should be finished before the end of August. 

Topping and pinching sweet potato can control the length and growth vigor of the main stem, promote the development of lateral buds, and make branches grow quickly. The specific method is: after sweet potato planting, when the main stem length reaches 12 nodes, remove the growing point at the top of the main stem to promote branching. When the branches grow to 12 nodes, remove the branch growing points. This can effectively coordinate the contradiction between the aboveground and underground parts and is conducive to root tuber enlargement. 

4) Chemical control to suppress excessive growth and skillful supplemental fertilizer and water. Excessive fertilizer and water in sweet potato fields, especially excessive N, often causes excessive stem and leaf growth, affects root tuber enlargement, and reduces yield. Practice has proved that spraying plant growth inhibitors such as paclobutrazol or mepiquat chloride in sweet potato fields can control the aboveground and promote the underground. Generally, the first spraying is before the rainy season arrives in early July, and afterward spray once every 10-15d for 3-4 consecutive times. Each time, use 50-100g of paclobutrazol or 7-15g of mepiquat chloride per mu, and spray evenly with 50-75kg of water. When spraying, flexibly adopt the pesticide dosage according to stem and leaf growth, rainfall amount, variety characteristics, soil fertility, and so on. 

On the basis of applying sufficient base fertilizer, sweet potato topdressing is mainly crack fertilizer and foliar fertilizer. For crack fertilizer, use 4-5kg of urea per mu, 10kg of superphosphate extract, and 3kg of potassium sulfate, mix with 150-200kg of water to make a nutrient solution, and when cracks generally begin to appear in the field, irrigate plant by plant along the cracks on cloudy days or in the afternoon of sunny days, requiring uniform application. Foliar fertilizer spraying depends on plant growth. For those with weak growth and signs of premature decline, mainly spray N, combined with P and K fertilizers, using 100kg of water plus 0.5kg of urea and 0.2kg of potassium dihydrogen phosphate, stir evenly and spray. For those with excessive growth, mainly spray P and K fertilizers, and spray a 0.2% potassium dihydrogen phosphate aqueous solution. In late August, use one packet of sweet potato swelling hormone per mu, add 20kg of water to dissolve and filter, then evenly spray on plant leaves, for two consecutive sprays, with an interval of about 10d each time. In case of autumn drought, timely irrigation can prevent premature decline, extend the leaf functional period, and increase root tuber enlargement speed. Generally, irrigate once in early September; the leaf area coefficient is 0.6 higher than that without irrigation, and yield increases by 24.2% per mu. Sweet potato likes moist soil, and the irrigation amount should not be too large, about 40m3 per mu. Also note that after irrigation, do not step on the sweet potato ridges, so as not to affect soil permeability.