How to Plant Sweet Potatoes in Early Spring? A Detailed Explanation of the Key Cultivation Techniques
Sweet potato has the characteristics of high and stable yield, wide adaptability, strong stress resistance, rich nutrition and wide range of uses. So, are you clear about the cultivation techniques for early spring sweet potatoes?
1. Early Spring Sweet Potato Cultivation Techniques
1. Balanced fertilization, ridging for planting
According to experiments, producing 1000kg of tuberous roots 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 the seedlings sprout early; steady 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 age prematurely. High-yield fields generally should 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 forming ridges.
The characteristics of high-yield sweet potato soil are loose structure, high porosity, good aeration, sufficient oxygen supply, and the ability to drain water and discharge waterlogging. Combined with deep plowing and ridging 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 helps the decomposition of organic matter, and can absorb heat quickly during the day, raising the ground temperature, and dissipate heat quickly at night, creating a large diurnal temperature difference, which is beneficial to sweet potato growth and root nutrient accumulation. When forming ridges, the ridge shape should be plump, the ridge 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, selecting strong seedlings
Sweet potato tuberous roots are vegetative bodies of asexual reproduction and have no obvious maturity period. Generally, growth stops when the temperature is below 15°C, and tuberous roots stop expanding when the ground temperature drops to 16°C--18°C. Timely early planting can extend the growth period, and tuberous roots form early, which can both use the temperature conditions before the rainy season arrives to make the tuberous roots expand rapidly, and in the hot and rainy season store the photosynthetic products formed by stems and leaves in the expanded tuberous roots, 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 tuberous root expansion period by 7d compared with planting on May 10, increases yield by about 10% per mu, and the tubers are neat and the fresh sweet potato quality is high.
In order to improve the survival rate of seedlings and promote early sprouting and rapid growth, the seedlings should be selected from the first batch of strong seedlings harvested from the seedbed. The first batch of seedlings has thick stems, vigorous leaves, and well-developed roots. The harvested seedlings must undergo full hardening. Generally, before planting, the seedlings are 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 out from the cut surface. Planting this kind of seedling 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 buds.
3. Timely vine lifting, topping and pinching
When the rainy season arrives, sweet potato stems and leaves grow luxuriantly, and nodal roots are prone to develop, dispersing nutrients and hindering the transport of photosynthetic products to the tuberous roots. 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, vine turning in sweet potatoes is both labor-intensive and reduces yield. The main reason is that after vine turning, the stems and leaves are seriously damaged, breaking the optimal distribution of leaves receiving light energy, reducing photosynthetic intensity by 30%, increasing respiration intensity by 19%, and reducing yield by about 10%. In production, vine turning should be changed to vine lifting, which avoids damage to stems and leaves and does not destroy the distribution of leaves, 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 completed 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 branch development. When the branches grow to 12 nodes, remove the growing points of the branches. This can favorably coordinate the contradiction between the aboveground and underground parts and is conducive to tuberous root expansion.
4. Chemical control to suppress excessive growth, skillful supplementary fertilizer and water
Excessive fertilizer and water in sweet potato fields, especially too much N, often causes excessive stem and leaf growth, affecting tuberous root expansion and reducing 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, then once every 10-15d thereafter, for 3-4 consecutive sprayings. Each time, use 50-100g of paclobutrazol or 7-15g of mepiquat chloride per mu, mixed with 50-75kg of water and sprayed evenly. When spraying, flexibly adopt the pesticide dosage according to stem and leaf growth, rainfall amount, variety characteristics, soil fertility, etc.
On the basis of applying sufficient base fertilizer to sweet potato, supplementary fertilization is mainly crack fertilizer and foliar spraying. For crack fertilizer, use 4-5kg of urea per mu, 10kg of superphosphate extract, and 3kg of potassium sulfate, mixed with 150-200kg of water to make a nutrient solution. When cracks generally begin to appear in the field, pour it along the cracks plant by plant on a cloudy day or in the afternoon of a sunny day, and apply it evenly. Foliar spraying depends on plant growth. For those with weak growth showing signs of premature aging, mainly spray N, together with P and K fertilizers, using 100kg of water plus 0.5kg of urea and 0.2kg of potassium dihydrogen phosphate, stirred evenly and sprayed. For those with excessive growth, mainly spray P and K fertilizers, and a 0.2% potassium dihydrogen phosphate aqueous solution can be sprayed. In late August, use one packet of sweet potato tuber swelling agent per mu, add 20kg of water to dissolve and filter, then evenly spray on the plant leaves, for two consecutive sprayings, with an interval of about 10d each time. In case of autumn drought, timely irrigation can prevent premature aging, extend the functional period of leaves, and increase the speed of tuberous root expansion. Generally, irrigate once in early September; the leaf area index is 0.6 higher than without irrigation, and yield increases by 24.2% per mu. Sweet potato likes abundant soil moisture, and the irrigation amount should not be too large, about 40m3 per mu. Also note that after irrigation, do not tread on the sweet potato ridges, so as not to affect soil permeability.