2017 Technical Guidance on Production of Sweetpotato for Fresh Consumption and Processing

Sweetpotato is an important food and industrial raw material crop in China. In recent years, the consumption structure of sweetpotato has undergone marked changes, with the proportion used for feed decreasing and the proportion used for fresh consumption and processing gradually increasing. The National Planting Structure Adjustment Plan (2016-2020) proposes that the adjustment focus for root and tuber crops is to expand the area, optimize the structure, transform through processing, and improve quality and efficiency. In order to effectively utilize the light and heat resources of various regions and give full play to the advantages of sweetpotato for fresh consumption and processing in structural adjustment, stabilizing grain production and increasing income, and transforming and adding value, this 2017 Technical Guidance on Production of Sweetpotato for Fresh Consumption and Processing is hereby formulated.

(1) Select improved varieties and cultivate healthy seedlings. Select excellent varieties according to resource endowments, climatic conditions and planting purposes. When virus diseases are found, promptly remove the affected plants, strictly enforce quarantine for seedling transport, and in southern sweetpotato regions avoid continuous annual use of field-grown sweetpotato vines for planting, so as to prevent the spread and damage of sweetpotato virus disease (SPVD) and leaf curl virus disease. Strengthen seedbed management, cultivate healthy seedlings, and select clean fields free of virus contamination for producing seed potatoes.

(2) Rational close planting and optimized cropping systems. Determine a reasonable planting density according to local conditions; for sweetpotato for fresh consumption, attention should be paid to increasing the rate of marketable tubers. In northern sweetpotato regions, spring sweetpotato for fresh consumption can be planted slightly later and more densely, at a density of 3500-4000 plants per mu; summer sweetpotato for fresh consumption can be planted slightly earlier, in early to mid-June, at a density of 4000-4500 plants per mu. In southern sweetpotato regions, summer sweetpotato predominates in the north, while in the south it can be planted throughout the year, with a planting density of about 3000 plants per mu. Strengthen crop rotation and succession, either paddy-upland rotation, or rotation with crops such as peanut, corn, wheat and foxtail millet, to reduce pests and diseases and continuous cropping obstacles, and to increase yield and efficiency. For starch sweetpotato, large-scale planting is advocated, and planting density can be appropriately reduced.

(3) Strengthen field management and optimize the population structure. In the early stage after planting, focus on promoting growth, early seedling emergence and early row closure; in the middle stage, control excessive vine growth, with the focus on establishing a reasonable population structure, and when necessary carry out chemical growth control according to the aboveground vine growth; in the middle and late stages, focus on promoting tuber expansion, and according to actual conditions, in combination with growth control, apply an additional 100 grams of potassium dihydrogen phosphate per mu; in the late growth stage, pay attention to waterlogging prevention and drain standing water from the field. Technical measures such as plastic film mulching can be used; in northern and middle-lower Yangtze sweetpotato regions, the key points are to mulch when wet rather than dry and to mulch good fields rather than poor ones, so as to promote increases in yield and benefits. For arid and infertile hilly and mountainous land, film mulching is generally not recommended.

(4) Scientific fertilization to promote high and stable yields. Fertilize rationally, adhering to the principles of mainly basal fertilizer with supplementary topdressing, mainly organic fertilizer with supplementary chemical fertilizer, and mainly increased potassium fertilizer with supplementary phosphorus fertilizer. Before ridging, apply sufficient basal fertilizer according to soil conditions. When total soil nitrogen content is below 0.08% and available nitrogen is below 20-30 mg/kg, apply 5 kg-20 kg of pure nitrogen per mu as basal fertilizer; when available nitrogen is above 80 mg/kg, nitrogen fertilizer may be omitted. When available phosphorus content is below 20 mg/kg, apply 5 kg of pure phosphorus per mu as basal fertilizer; when above 50 mg, phosphorus fertilizer may be omitted. When available potassium content is below 30 mg/kg, apply 20 kg of pure potassium per mu; when available potassium content is 30-100 mg/kg, apply 10-20 kg of pure potassium per mu; when it exceeds 150 mg/kg, potassium fertilizer may be omitted.

(5) Prevention first, integrated control of pests and diseases. For diseases such as root rot and sweetpotato bacterial wilt for which no effective chemical control is available, select disease-resistant varieties and plant in disease-free land, and strengthen planting control to inhibit pathogen infection. For black spot disease, select strong seedlings 25-30 cm high, and before planting soak the basal portion of the seedlings, about 10 cm, in a 500-800 times dilution of 50% carbendazim wettable powder or a 300-500 times dilution of 50% thiophanate-methyl wettable powder for 8-10 minutes for control. For soil-dwelling pests, adopt a combination of physical and chemical control measures for targeted prevention and control to increase the rate of marketable tubers. For example, set up black light traps in the field to kill adults, and select highly effective and low-toxicity chemical pesticides and other measures to control white grubs and wireworms. In southern sweetpotato regions, comprehensive measures should be taken to prevent damage by ants.