Eucalyptus seedling cultivation is a critical process that requires careful planning and execution to ensure healthy growth and successful afforestation. The following guide outlines the key steps involved in seedbed preparation, sowing, germination management, and large seedling care.
1. Seedling Cultivation
1.1 Seedbed Preparation
(1) Seedbed size: The seedbed should be 1.2 meters wide and no longer than 5 meters. A 5 cm wide path should be left between beds for easy access.
(2) Soil preparation: After removing weeds and topsoil, apply 50-100 g of 25% trichlorfon oil (active ingredient) per square meter or mix it with rice to spread over the bed. This helps control underground pests such as grubs and earthworms. Then, add a 5 cm layer of yellow mud soil followed by a 10 cm layer of well-sieved nursery substrate. The substrate consists of 4 parts yellow mud soil and 6 parts fired soil, with 11 kg of compound fertilizer added per cubic meter. River sand can also be included in small amounts to improve drainage.
(3) Disinfection: Use a sprayer to apply 40% formalin or 1500 ppm thiophanate solution to the seedbed. Then, mix 300-400 ml of 20% methylisothiazolinone per 20-30 kg of poisoned sand and spread evenly. Cover the bed with plastic film for at least 24 hours to sterilize the soil and eliminate pests.
(4) Final bed preparation: After drying for 1-2 days, level the bed, water it thoroughly, and spread a thin layer of fired soil. Flatten and press the surface with a wooden board. Before sowing, spray the wet bed with a sprayer and sow the seeds after re-leveling.
1.2 Sowing
(1) Sowing time: Sow in mid to late October when temperatures are still warm, which promotes seed germination and seedling growth. Seedlings will be ready for planting after 3.5-4.5 months, aligning with the next year's afforestation schedule. For large areas, stagger sowing to better manage labor.
(2) Seeding rate: Calculate based on the formula: Sowing amount = (2-3) × afforestation area (ha) × planting density (trees/ha) × number of seeds per gram. Typically, 2000-3000 seeds per square meter are used.
(3) Seed treatment: Treat each gram of seeds with 0.1-0.2 g of carbendazim or thiophanate-methyl. Mix with 20-30 times sifted fired soil and spread evenly. Cover with a thin layer of soil, then water and cover with plastic film. Maintain a 45 cm height for the film to allow ventilation. Spray a methylisoflunomide solution around the nursery to disinfect the surrounding soil.
1.3 Germination Management
The ideal temperature for eucalyptus seed germination is 25-35°C with 85-95% humidity. If temperatures exceed 35°C, open the film for ventilation or apply cooling water. On sunny days, use 50% shade nets if necessary. Most seeds will germinate within 15 days. Keep the bed moist by watering twice daily. Once 50% of the seedlings have developed true leaves, increase watering frequency.
1.4 Seedling Care
During the early seedling stage, focus on root development and maintain proper soil moisture. Water once in the morning and evening, adjusting based on weather. Avoid overwatering to prevent root diseases. Fertilization is minimal—apply 1-2 doses of diluted nitrogen fertilizer like urea, ensuring it’s not concentrated to avoid leaf burn.
2. Large Seedling Management
After transplanting into bags, seedlings typically develop new roots within a week. Remove the film if there's no frost; otherwise, extend coverage. Check for dead seedlings and replace them promptly.
(1) Water and Fertilizer: Water daily in the morning or evening to keep the substrate moist. Apply liquid nitrogen fertilizer (2-5%) weekly, aiming for 15-50 days post-transplanting. When seedlings reach 25 cm, they are ready for planting. Adjust fertilization based on growth.
(2) Seedling Classification: After one month in bags, sort seedlings by height and thickness to ensure uniformity for planting.
(3) Height Control: If seedlings exceed 30 cm before planting, control growth using PP333 or pruning. At 20-25 cm, remove the rootstock to encourage fibrous root development. Avoid disturbing the soil during removal. Water the seedlings before transplanting, and do so in the early morning or late afternoon. Avoid planting on rainy days. If planting conditions are unfavorable, repeat this process every 10 days until suitable.
When seedlings reach 30 cm, apply 15% PP333 (50-100 ppm) to control leggy growth. While manual pruning is an option, it should be done carefully in timber plantations to avoid compromising tree quality.
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