Key Technologies for Tobacco Seedling Cultivation

1. Seedbed Site Selection and Bed Preparation Standards

1.1 Seedbed Site Requirements

Prohibited areas: Avoid using vegetable fields, old seedbeds, tobacco fields with heavy cropping, areas in front or behind houses, and under tree shades (prone to diseases).
Ideal conditions:
- Sheltered from wind, sunny, and elevated (to prevent waterlogging)
- Flat ground with deep soil (≥30cm)
- Close to large fields, convenient for transportation and management
- Surrounded by drainage ditches (to prevent waterlogging)

1.2 Seedbed Preparation Specifications

Bed size: 10m long × 1m wide, with a 0.5m path between beds (for walkways), ideally oriented east-west.
Soil treatment:
- Deep tillage to 20cm, disinfection (formalin or methyl bromide steam treatment)
- Shallow plowing and leveling to maintain soil moisture, ensuring “three-drainage coordination” (bed drainage, waist drainage, and edge drainage)
Floating seedling pools: Use black plastic film at the bottom of the pool to prevent algae, maintain water depth at 8-10cm.

2. Nutrient Soil Preparation and Tray Filling

2.1 Nutrient Soil Formulation (for every 10㎡ standard bed)

Formula	Ingredients	Amount	Treatment Requirements
Formula 1	Fertilized soil + decomposed farm manure + decomposed chicken manure	600kg + 250kg + 10kg	Sift and mix evenly
Formula 2	Fertilized soil + compound fertilizer + sifted slag	800kg + 2.5kg + 50kg	Slag particle size ≤3mm
Formula 3	Fertilized soil + farm manure + compound fertilizer	600kg + 250kg + 2.0kg	Do not use undecomposed fertilizer

Key points: All fertilizers must be crushed and sifted; chicken manure/cake fertilizer must be fully fermented (to prevent seedling burn).

2.2 Tray Filling Operation

Substrate requirements: Uniform particle size, good water retention (when squeezed into a half-ball, it should scatter upon release).
Filling standards:
- Fill the seed tray (288 holes) to 5mm below the hole’s top, ensuring moderate firmness (light finger pressure should not cause sinking).
- Sow immediately after filling to prevent substrate loss, which could lead to “empty holes.”

3. Sowing Technical Key Points

3.1 Seed Treatment

Disinfection: Soak in 0.1% silver nitrate or 1% copper sulfate solution for 10-15 minutes, then rinse with clean water.
Germination: Soak seeds in warm water at 25-28℃ for 8-12 hours, then germinate at 25℃ until the root is as long as the seed (about 5 days).

3.2 Sowing Operation

Coated seed sowing in clear water:
- Wet the bottom soil with 2-3mm water, sow when the water reaches the bed surface → Wait for the coating to crack → Cover with 2mm soil (to cover the seed).
- If the coating doesn’t crack, use a sprayer to water the seeds to encourage cracking.
Precision sowing:
- 2-3 seeds per hole, hole spacing 4-5cm (to avoid overcrowding and difficulty in thinning)
- Use 1 bag per bed (standard packaging), manual spreading for uniform distribution.

3.3 Covering Film for Heat Preservation

Arch frame setup: Bamboo rods placed at 40-45cm height, spaced 50cm apart, fixed with rope netting.
Film management: Cover immediately after sowing to prevent rain and snow; ventilate at both ends when 70% of seedlings have emerged.

4. Detailed Management During Seedling Stage

4.1 Temperature and Humidity Control

Growth Stage	Temperature Range	Humidity Range	Ventilation Requirements
Sowing to seedling emergence	25-28℃ (night ≥12℃)	85%-90%	Sealed for heat preservation
Small cross-leaf stage (2 true leaves)	≤35℃ (to prevent heat damage)	70%-80%	Ventilate from 9 AM to 4 PM at both ends
Large cross-leaf stage (4 true leaves)	25-28℃	60%-70%	Extended ventilation, uncover one side at noon
Vertical-leaf stage (7 true leaves)	Daytime 25℃/Night 15℃	55%-65%	Ventilate all day for hardening

Response to extreme weather:

High temperature: Cover with shade nets (from 10:00 AM to 4:00 PM), spray for cooling on the roof.

Low temperature: Use double-layer film for insulation (+4℃), and assist heating with coal blocks or warm air fans.

4.2 Water and Fertilizer Management

Watering:
- Seedling emergence: Water daily to maintain moisture (no film covering)
- Vertical-leaf stage: Bed irrigation with “dry top, wet bottom” principle
- Strong seedling stage: Control water for hardening (do not water unless extremely dry)
Fertilization:
- Base fertilizer as the main source (to meet needs up to the 3 true leaf stage), follow-up fertilization with compound fertilizer (5-10g/㎡).
- For floating seedlings, apply fertilizer in stages:
  - Small cross-leaf stage: 50ppm nitrogen
  - Large cross-leaf stage: 100ppm nitrogen
  - 15 days before strong seedling stage: stop fertilizing to harden seedlings

4.3 Thinning and Topping

Thinning: Thinning should be done in three stages at the 3rd/4th/5th true leaf stage, leaving a spacing of 6-8cm.
Topping: Remove the lower yellow leaves and some upper functional leaves (to prevent leggy growth and promote root development).

5. Integrated Pest and Disease Control

5.1 Disease Control

Disease	Symptoms	Control Measures
Anthracnose	Brown spots on leaves	Bordeaux mixture (1:1:150) or 50% Mancozeb 500x solution (spray at 4-5 true leaves)
Damping-off disease	Water-soaked rot at stem base	Disinfect the seedbed + control humidity, use Metalaxyl for root soaking at early stages
Green algae	Green film on substrate surface	0.015%-0.02% copper sulfate solution spray (do not exceed 0.03%)

5.2 Pest Control

Wireworms/Grubs: Poison baiting (90% Dicofol 0.5kg + 20kg water + 40kg roasted wheat bran).
Slugs: Sprinkle lime powder in the evening or spray 1:100 rapeseed cake solution.

6. Strong Seedling Standards and Pre-Transplant Treatment

Strong seedling criteria:
- Stem height 7±0.5cm, stem diameter 0.7cm
- 8-10 true leaves, deep green leaves
- Well-developed roots (no spiral roots)
- Seedling age 50-60 days
Hardening operation:
- 7 days before transplanting: Uncover and sun-dry seedlings, control water and fertilizer
- 3 days before transplanting: Spray 0.1% potassium dihydrogen phosphate to enhance stress resistance

7. Solutions to Floating Seedling Specific Problems

Problem	Cause	Corrective Measures
Uneven germination	Coating cracking unevenly / low temperatures	Add covering material for heat preservation, adjust sowing time to avoid low temperatures
Salinity damage	White surface on substrate (salt crystallization)	Ventilate and moisten, spray clean water to dissolve
Spiral roots	Shallow sowing / tight substrate	Sowing depth 0.5cm, ensure proper substrate firmness
Dripping damage	Condensation on film	Use non-drip film, cover with woven bags before germination