Detailed Explanation of the Technical Regulations for Pollution-Free Production of Purple Sweet Potato
On July 28, 2016, the Hengshui Municipal Bureau of Quality and Technical Supervision issued the "Technical Regulations for Pollution-Free Production of Purple Sweet Potato" as a Hengshui municipal local standard. The specific techniques are as follows:
I. Scope
This standard specifies the terms and definitions, production area environment, soil disinfection, cultivation techniques, weed control, chemical regulation, pest and disease control, harvesting, seed potato storage and other cultivation techniques for the technical regulations for pollution-free production of purple sweet potato.
This standard applies to open-field pollution-free cultivation of purple sweet potato within the territory of Hengshui Municipality.
II. Soil Disinfection
The selection of soil disinfectants shall comply with the relevant requirements of GB/T8321.(1-9) and NY/T2798.2. Apply 500-1000 grams of high-efficiency soil disinfectant per mu, mix with 15 kg of soil and spread evenly on the ground surface, then plow the soil to control soil-borne diseases such as stem nematode disease and root rot.
III. Cultivation Techniques
1. Variety selection. It is advisable to select varieties with high yield, good quality, disease resistance and suitability for local cultivation, such as Chaozishu, Zishuwang, Shanchuanzi, Heizishu, Ziluolan, etc.
The selection of seed potatoes shall comply with the relevant requirements of GB4406. Use first-generation and second-generation purple sweet potato varieties bred at the improved seed propagation base of sweet potato breeding units as seed potatoes; the potato skin should be bright and smooth, free from disease and damage, and the tubers should not have suffered freezing injury or waterlogging damage; remove mixed tubers. A seed potato size of 150-250 grams is more suitable.
Seed potato treatment: Soak seed potatoes or seed plants in a 500-fold dilution of 50% carbendazim wettable powder or a 400-fold dilution of 50% thiophanate-methyl wettable powder for 10-12 minutes; use warm water at 20°C-30°C when preparing the solution.
2. Sowing and seedling raising.
(1) Seedbed site selection. Choose a field that is sheltered from the wind and facing the sun, with fertile soil, high terrain, good drainage and convenient management, and where sweet potatoes have not been planted within 2 years.
(2) Seedling raising methods. ① Fermentation hotbed seedling raising method: The length of the seedbed can be determined according to the terrain and needs, generally 1.2-1.3 m wide and about 40 cm deep. The bottom of the bed should be higher in the middle and lower around the edges, deeper on the south side and shallower on the north side, so as to make the bed temperature as uniform as possible and the seedlings emerge uniformly. Fully decomposed livestock manure and crop straw, etc. can be used as fermentation materials. The thickness of the fermentation material should preferably be 25-30 cm, on top of which 4-5 cm of fine soil is spread, then the seed potatoes can be placed, followed by 2-3 cm of fine soil, plastic film mulching, and the building of a small arched shed covered with film to increase temperature, with straw curtains covered at night. Seed potato arrangement: (a) Arrangement time. March each year, preferably when the temperature is relatively low; (b) Arrangement method. Use vertical arrangement or slanting arrangement; (c) Arrangement density: 20-25 kg/sq m. ② Electric heating wire temperature-controlled seedling raising method. The seedbed is 1.2-1.3 m wide and about 15 cm deep. Lay electric heating wires at the bottom of the bed at intervals of about 10 cm, slightly sparser in the middle and slightly denser on both sides, so as to make the bed temperature as uniform as possible; spread 2-3 cm of fine soil on top, then the seed potatoes can be placed, with the temperature controlled at about 30°C; spread 2-3 cm of fine soil on top, cover with film to increase temperature; when a small number of seedlings emerge, build a small arched shed, cover with film, and cover with straw curtains at night. Seed potato arrangement: (a) Arrangement time, determined according to transplanting needs; (b) Arrangement method, use vertical arrangement or slanting arrangement; (c) Arrangement density, 20-25 kg/sq m. ③ Film seedling raising method. The seedbed specifications are similar to those of the fermentation hotbed, with a depth of about 15 cm. Seed potato arrangement: (a) Arrangement time, around early April; (b) Arrangement method, either slanting arrangement or flat arrangement; (c) Arrangement density, 15-20 kg/sq m.
(3) Seedbed management. Before seedling emergence, maintain a seedbed temperature of 30°C-35°C and a relative humidity of 80%. After seedling emergence, promptly remove coverings such as plastic film on the bed surface, maintain a bed temperature of 25°C-30°C, strengthen light, water frequently with a small amount of water, keep the soil moist, and combine watering with ventilation. Harden the seedlings 4-5 days before collecting seedlings for transplanting.
(4) Standards for strong seedlings. The weight of 100 seedlings is 500-700 grams, seedling height is 20-25 cm, with 5-7 nodes, thick stems, short internodes, thick leaves, the top three leaves level, thick sap at the cut, and no pests or diseases. After cutting seedlings, promptly apply fertilizer and water to cultivate the second batch of seedlings.
3. Transplanting.
(1) Land preparation and fertilization. Fertilization should mainly use harmlessly treated organic fertilizer, combined with the application of inorganic fertilizer. The selection of fertilizers shall comply with the relevant requirements of NY/T2798.2. Nutrients throughout the whole growth period should be mainly based on base fertilizer; about 15 days before planting, apply 2000-3000 kg of high-quality organic fertilizer, 10 kg of potassium sulfate, 5 kg of urea and 10 kg of diammonium phosphate per mu as base fertilizer, and apply 2.5-5 kg of microecological microbial agent per mu. All organic fertilizer should be spread before plowing, and inorganic fertilizer should be band-applied when ridging. Before ridging, the plowing depth should preferably be 25-30 cm, fully break up the soil clods, crush and rake level, and make ridges 35-40 cm wide and high with a spacing of 80-100 cm.
(2) Planting. Seedling preparation: 3-5 days before collecting seedlings, appropriately lower the temperature to harden the seedlings and cultivate strong seedlings; 2 days before lifting the seedlings, spray a protective broad-spectrum sterilant and insecticide once. Planting and precautions: (a) Planting density. 3000-3500 plants/mu for spring-planted fields, and 4000-4500 plants/mu for summer-planted fields; (b) Planting date. Spring potatoes are preferably from late April to late May, and summer potatoes can be delayed to late June; (c) Planting method. Insert slantingly into the soil with 2-3 nodes buried and about 3-4 nodes exposed above the soil surface; insert flatly into the soil with 3-5 nodes buried and about 3 nodes exposed; (d) Precautions. Do not damage the seedling leaves during planting; after planting, water thoroughly to settle the roots, cover with soil within 3 days to preserve moisture, and irrigation water shall comply with the relevant requirements of GB5084.