In many places, a variety of sweet potatoes are planted in arid, thin soil and low fertility barren land. In some places, sweet potatoes are planted year after year, so the soil can not be rotated and fallow, and the soil's water and fertilizer conservation ability is reduced. Soil water and fertilizer conditions can not meet the growth requirements of high-yield sweet potato, which is one of the main reasons for low yield and poor quality of sweet potato. Sweet potato has well-developed root system, creeping growth of stems and vines, and the stem nodes can take root in the soil, which has strong fertilizer absorption ability. Sweet potato mainly absorbs nitrogen, phosphorus and potassium fertilizer, and the demand for potassium is the most, followed by nitrogen and phosphorus. Nitrogen can promote the growth of sweet potato stems and leaves, expand the photosynthetic area, thereby increasing the photosynthetic capacity and directly increasing the yield of stems and leaves. Early application of nitrogen fertilizer can promote the early growth and development of sweet potato, with multiple branches, fast growth of stems and leaves and early closure of ridges, which lays a good foundation for high yield. Insufficient supply of nitrogen fertilizer, slow growth of stems and leaves, small leaf area, pale color, poor plant growth, and ultimately affect the yield. However, too much or too late application of nitrogen fertilizer will easily lead to excessive growth of stems and leaves and poor potato yield, which will affect the yield.

Phosphorus can accelerate the synthesis and operation of nutrients in sweet potato and improve the quality of sweet potato chips. Phosphorus-deficient stems have small thin leaves, which are dark green and dull. Old leaves appear yellow spots and fall off after turning purple.

Potassium can promote the cambium activity of sweet potato roots and make the tuberous roots expand continuously. In the middle and late growth stage, potassium fertilizer can improve the synthesis and transportation ability of sweet potato carbohydrates, and promote the root swelling, weight gain and quality improvement. Potassium deficiency in the early growth stage, short internodes, small leaves and no leaf extension; Potassium deficiency in the middle and late growth stage, slow growth of stems and leaves and serious yellowing of leaves.

According to research, sweet potato has a long growth period and needs more nutrition. The target yield per mu is 3 tons of fresh potatoes, and pure nitrogen (N) is about 15 kg, phosphorus pentoxide (P2O5) is about 12 kg, and potassium oxide (K2O) is about 24 kg. The general principle of fertilization is to balance fertilization, pay equal attention to promotion and control, promote seedling prosperity in the early stage of fertilization, control seedling length in the middle stage, and protect tail to prevent premature aging in the later stage. The specific fertilization principles are organic fertilizer, chemical fertilizer, base fertilizer, topdressing and early and late stages. Generally speaking, due to the variety of sweet potato in sandy loam or thin land, it is necessary to pay attention to early and heavy application, more organic fertilizer and plant ash, and adequate base fertilizer, early seedling fertilizer and reasonable close planting, closing ridges in advance to enhance coverage, reduce water evaporation and increase soil water content, thus improving sweet potato yield.

Recommended fertilization method

Seedling fertilizer: when ploughing or ridging, apply organic fertilizer such as 1~3 tons of burning soil per mu, and apply 20~30 kilograms of phosphate fertilizer per mu. Before transplanting potato seedlings, urea and compound fertilizer can be applied to the ridge center, and then the soil is covered. Potato seedlings can be inserted or put, and then the soil is covered, which is labor-saving. Potato seedlings can not contact fertilizer to prevent seedling injury, and can absorb fertilizer nutrition as soon as possible at seedling stage, and grow early and quickly. If no fertilizer is applied during ploughing and seedling transplanting, seedling fertilizer can also be applied as early as 7~ 15 days after sowing, when seedlings and leaves turn green and erect. Generally, human excrement and urine can be sprayed appropriately, or urea and compound fertilizer can be applied. Generally, urea10kg per mu and compound fertilizer 20kg (15: 15: 65438).

1. 1 month, then apply Zhuang potato fertilizer. Generally, urea15 ~ 20kg and potassium chloride 20 ~ 30kg are applied per mu, and furrowing and fertilizing can be done. If conditions permit, plant ash or burning soil on the ridge surface can be properly removed.

Three months after planting, applying strong tail fertilizer according to the growth situation, considering late-maturing varieties or sweet potatoes with poor growth in the later period, generally not applying.

Irrigation, weeding, loosening soil, raising soil and turning vines.

The advantages of irrigation, weeding, loosening soil and ridging soil are: sufficient water and ventilation are beneficial to high yield and high quality of sweet potato, and can prevent and control pests and diseases. When the weather is dry and the evaporation is large, irrigation is mainly judged according to the dry cracking of the ridge surface, and water is usually poured once every half month. Irrigation should run through the whole ridge. Generally, when the water is over half of the ridge, it is necessary to observe whether the water can gradually wet to the top of the ridge, and to observe whether the ridge is soaked when spraying water.

After irrigation, the border is slightly dry, which means weeding, loosening soil and ridging. The cracks on the ridge surface should be covered with loosening soil to prevent underground pests, such as weevils and stem borers, from getting into the border and eating root tubers and vine heads, which will affect the yield and quality. No matter after irrigation or during the whole growth period of sweet potato without drought irrigation, you can cover the border seam with border mud at any time to prevent and control pests and diseases.

Before and after planting, water properly to keep alive and promote growth. Before closing the ridge at seedling stage, combine with fertilization, loosen the soil 1~2 times, cut off the surface capillaries, and reduce the surface evaporation. When the stems and leaves of sweet potato basically cover the ridge surface, don't pull the vines, so as not to disturb the normal distribution of the stems and leaves and damage the roots, affecting photosynthesis and nutrient absorption. The adventitious roots of sweet potato vines can be used to absorb water and fight drought.

At present, the breeding target of new sweet potato varieties is mostly improved varieties with short vines and few roots, and it is generally not recommended to turn over vines. However, after continuous heavy rain or rainy days, the stems and vines of sweet potatoes will grow white and grow new roots, which will increase the loss of nutrients. It is difficult for new roots in the middle and late stages to bear potatoes. Even if they grow into potatoes, they should be properly controlled to prevent the stems and vines from rooting. Turning over vines should be lifting vines and cutting roots, and gently putting them back in place. The original normal distribution of stems and leaves should not be disturbed, especially when the stems and leaves are inverted, it takes a long time to recover, which seriously affects photosynthesis and yield.

Fertilizer requirement law of sweet potato

The amount of three elements absorbed by sweet potato: Sweet potato is a potassium-loving crop. According to research, for every 1 1,000 kg of fresh potato, 3.5 kg of available nitrogen,10.8 kg of phosphorus pentoxide and 5 kg of potassium oxide need to be absorbed from the soil. 2. Absorption characteristics of sweet potato in different growth stages: sweet potato absorbs more potassium than nitrogen and more nitrogen than phosphorus in the whole growth stage. The absorption of three elements by sweet potato is mainly from the peak of stem and leaf growth to the late stage of potato expansion, in which the absorption of potassium is more from the peak of stem and leaf growth to the turning green period, and the absorption of nitrogen is more from the peak of stem and leaf growth. The absorption of phosphorus was relatively balanced during the whole growth process, but it increased slightly before the green turning period. 3. Yield-increasing effect of ternary fertilizer: According to research, potassium has the greatest influence on sweet potato yield, followed by nitrogen and phosphorus. Therefore, in order to achieve high quality and high yield of sweet potato, more potassium fertilizer, nitrogen fertilizer and phosphorus fertilizer must be applied. The main diseases of sweet potato include sweet potato black spot, sweet potato stem nematode, sweet potato soft rot, sweet potato blast, sweet potato scab, sweet potato tendril blight, sweet potato root knot nematode, sweet potato root rot, sweet potato virus disease and sweet potato purple feather disease. The main pests of sweet potato are weevil, mole cricket, chafer, cutworm, sweet potato moth and so on. The prevention of sweet potato diseases and insect pests should focus on prevention. At present, weevil is the most harmful.

Weed weevil-sweet potato pest

Weed weevil, also known as sweet potato ant scale or sweet potato weevil, belongs to COLEOPTERA, ant weevil family, and is a destructive pest in sweet potato production in tropical and subtropical regions, which usually reduces the yield of sweet potato by 20-50% or even causes serious losses, and is one of the main limiting factors in sweet potato production. It is distributed in the provinces south of the Yangtze River and has 6-8 generations throughout the year. Adults live longer and generations overlap. From seedling to harvest, weevil larvae and adults can harm sweet potatoes. The larvae mainly eat potato vines and potato pieces, which makes the stems and leaves grow slowly. At the same time, a large number of larvae eat potato pieces, which make them black and smelly and inedible for people and animals. Gene, so far, has not cultivated a variety with high resistance to weevil.

Because weevils mostly damage underground tubers and their generations overlap, it brings great difficulties to artificial and drug control. At present, there is no ideal control method for this pest. The main methods to control underground pests of sweet potato are ecological control and chemical control. General chemical pesticides are expensive to control, and they are rarely used because of problems such as residual poison. In addition, weevils also have recommended sex pheromones, and the control effects vary from place to place. Sex pheromone of weevil is a volatile and non-toxic chemical substance secreted by female weevil, and there is no residual toxicity and drug resistance. They are used to trap and kill males, so that females can't find males to mate and can't reproduce, thus greatly reducing the density of weevils in the field. However, it has also been reported that it is difficult to kill all males, even if a few males are left, it may trigger a new round of weevil harm.

It is suggested to take comprehensive measures to control weevil:

(1) paddy-upland rotation;

(2) Irrigate the fields with many sweet potato diseases and insect pests, kill the insect source, fully plough and harrow the soil, and treat it with soil treatment agents such as "Haoniandong" and "Insecticidal Pill";

(3) In order to kill the insect source of the seedlings, pesticides such as dimethoate can be sprayed on the sweet potato fields to be harvested. Before planting, soak the base of sweet potato vine with 500 times dimethoate solution for 1~2 minutes, and after planting 1 week, spray dimethoate or trichlorfon (normal dosage) on potato seedlings and vines, or use 500 times solution of 80% trichlorfon. All the above control measures need not be used, but should be selected flexibly according to the specific situation, and pesticides such as dimethoate should be used according to the normal drug use instructions.

Other main pests of sweet potato are leaf roller moth, sweet potato moth, Spodoptera litura and so on. Insecticides such as dimethoate, dichlorvos and chlorpyrifos can be used according to the normal medication instructions and sprayed in the afternoon.

Main measures to control sweet potato diseases;

(1) Select disease-resistant varieties and pay attention to disease quarantine of seed potatoes and seedlings;

(2) cultivating disease-free seedlings, selecting and retaining disease-free potatoes and seedlings from disease-free areas, or selecting virus-free seedlings;

(3) soaking the sweet potato vine with 500 times of 50% carbendazim or 50% thiophanate methyl for more than 2 minutes, drying and planting;

(4) The diseased plants found in the field should be immediately pulled out and burned, and sprayed with 1000 times of 50% carbendazim. According to the situation, it can be sprayed continuously 1 time every 7 days until eradication;

(5) Thoroughly clean up the sick and disabled plants during harvesting, pay attention to the rotation of paddy and upland, strengthen the management of water and fertilizer, pay attention to drainage, ventilation and air exchange, and properly apply more plant ash and lime to make the plants grow healthily and enhance the disease resistance.