Detailed Explanation of Key Technical Points for Broccoli Seedling Stage Management
I. Management During the Emergence Stage:
1. From sowing to the stage when the embryo emerges from the soil: the main goal is to provide sufficient moisture and suitable temperature conditions. For autumn sowing, a shade frame needs to be set up for cooling during seedling raising. After sowing, water thoroughly and cover with rice straw or a shade net to retain moisture. Because temperatures are high during autumn sowing, water should be sprayed once in the morning and once in the evening each day to keep the soil moist. Generally, sprouts begin to emerge successively 3 days after sowing; when 30% of the seeds' embryos break through the soil surface, remove the covering.
2. From the appearance of cotyledons to the stage when the first true leaf shows its heart: moisture should be properly controlled and the temperature lowered to prevent the formation of leggy seedlings.
3. From the true leaf showing its heart to the seedling transplanting stage: if sowing was too dense, thin the seedlings in time, pull out the weak and small seedlings that are too crowded or growing poorly, and appropriately increase light, ventilate to lower the temperature, and prevent seedling spindling and the occurrence of damping-off disease.
II. Seedling Transplanting (Temporary Planting):
Generally about 15 days after sowing, when the seedlings have grown to 2-3 true leaves, carry out seedling transplanting (temporary planting). One day before transplanting, first water the seedling bed thoroughly so as to reduce root damage when lifting the seedlings. After lifting the seedlings, transplant them into the transplanting bed at a spacing of 6-8 cm square. Before transplanting, first make a small hole in the middle of each soil block in the transplanting bed with a finger or a round stick as the transplanting hole, and water until the soil is moist but not soggy before planting. Plant shallowly, and seal the hole around the seedling with fine dry soil. If conditions permit, it is best to transplant directly into nutrient cups or seedling trays, with 1 seedling per cup. Planting is best done in the evening, transplanting while watering and shading at the same time; water thoroughly and sufficiently so that the roots come into close contact with the soil and seedling recovery is promoted. Seeds sown in nutrient cups do not undergo temporary planting, but thinning should be done in time to cultivate strong and uniform seedlings; generally after 2 thinnings, 1 seedling is left per cup. After transplanting, set up a shade net to protect against sun, lower temperature, and prevent rain.
III. Management After Seedling Transplanting:
Key management points: from transplanting to seedling recovery, temperature should be controlled and moisture maintained to speed up recovery; from recovery to the finished seedling stage, conditions such as light and nutrition should be improved, and before field planting, proper hardening should be carried out to prevent spindling or disease, so as to cultivate strong seedlings.
In hot weather, shade and cool the area, and sprinkle water once in the morning and once in the evening each day. After seedling recovery, to prevent spindling, change to watering once each morning. Three days after recovery or at the third true leaf stage, apply 1 application of dilute human manure and urine or a 2% urea water solution to promote seedling growth. One week before field planting, apply another application of manure water or a 2% urea water solution to meet the needs of seedling growth recovery after planting. If the seedlings spindle, reduce watering and increase ventilation and light transmission.
Common diseases and pests at the seedling stage include damping-off disease, gray mold, diamondback moth larvae, cabbage caterpillars, striped flea beetles, and others. To prevent the occurrence of diseases and pests, generally spray insecticides and fungicides 2-3 times during the seedling stage; spraying can be scheduled 3 days before transplanting (or at the second true leaf stage), 5 days after seedling recovery (or at the fourth true leaf stage), and 3 days before field planting. For fungicides, 75% chlorothalonil wettable powder at 600 times dilution or 50% carbendazim wettable powder at 600 times dilution may be used; for insecticides, 48% chlorpyrifos at 1000 times dilution or Bt emulsion at 1000 times dilution may be used. When diseases and pests are found, spray promptly for control. For damping-off disease, 75% chlorothalonil wettable powder at 600 times dilution or 50% carbendazim wettable powder at 600 times dilution may be sprayed for control. For gray mold, 50% procymidone at 2000-2200 times dilution or 5% iprodione at 1500 times dilution may be sprayed for control. For diamondback moth larvae, 5% fipronil at 3000 times dilution or 1% avermectin at 3000 times dilution may be sprayed from the peak hatching period to the second-instar larval stage for control. For cabbage caterpillars, Bt emulsion at 1000 times dilution or fenvalerate at 1500-4000 times dilution may be sprayed for control. For striped flea beetles, 90% cartap at 1000-2000 times dilution or 48% chlorpyrifos at 1000 times dilution may be sprayed for control.
IV. Preventing Seedling Spindling. Seedling spindling easily occurs at the seedling stage. Effective methods to prevent seedling spindling:
1. Do not sow too densely, so as to avoid crowding of seedlings after emergence and the appearance of leggy seedlings.
2. Remove ground coverings in time.
3. Thin, temporarily plant, and field plant in time. After emergence, thin the seedlings in time; generally thin 2-3 times. When the seedlings have two leaves and one heart, they should be transplanted (temporarily planted); the density of temporary planting should be controlled at 120-150 plants per sq m, and if conditions permit, it is best to use nutrient cups for seedling raising.
4. Strengthen ventilation and light transmission, lower temperature and humidity, and control excessive seedling growth.
5. Carry out rational fertilizer and water management. In preparing nutrient soil, attention should be paid to the amount of phosphorus and potassium fertilizer, the amount of nitrogen fertilizer should be controlled, and watering should be controlled.
6. Thin out seedlings in time. When excessive crowding occurs, the seedlings should be moved appropriately so that large and small seedlings are separated, increasing the nutritional growth area per plant.