Detailed Explanation of Key Points of Korean Pine Seed Treatment Technology
Korean pine (Pinus koraiensis Sieb. et Zucc.), also known as fruit pine, belongs to the Pinaceae family, genus Pinus. It grows well in the Kuandian area of Liaoning, China. Its wood is soft and durable, the seeds are edible and can be pressed for oil, and it is a natural green food. In recent years, as the export volume of Korean pine kernel products has increased, the commercial value of Korean pine has become higher and higher, and the demand for Korean pine afforestation seedlings has also greatly increased, thereby mobilizing the enthusiasm of the vast number of seedling cultivation workers to grow Korean pine seedlings.
In the process of Korean pine seedling cultivation, seed treatment is the key step. The emergence rate, seedling yield, and the quality of the seedlings are all related to the quality of seed treatment. Combining the climatic conditions of the Kuandian area and many years of seedling cultivation experience, several treatment methods for Korean pine seeds, as well as seed selection and sowing, are introduced below for everyone's reference in seedling production work.
I. Seed Selection
For seedling cultivation projects in the Kuandian area, superior seeds with Caohokou as the central area should be selected. Seeds from the Huangyishan Seed Orchard in Kuandian can also be used. Seeds can be selected from Korean pine mother tree forests over 30 years old, Korean pine clonal seed orchards, and seeds produced by superior trees in Korean pine timber-and-seed dual-purpose forests. The seed collection time should be after September 20.
II. Seed Treatment
1. Overwintering Mixed Sand Burial Method
Choose a shady place with higher terrain and good drainage to dig a storage pit. The upper opening of the pit is 1.0 m wide, the bottom is 0.8 m wide, and the depth is 1.3 m (the pit bottom should be a sand and gravel bottom). The length depends on the amount of seeds stored. From October 20 to November 10, choose clean fine river sand, and mix the seeds and sand at a volume ratio of 1:3. If the seeds were collected before September 20, they need to be soaked for 3 days before mixing, and the immature seeds floating on the water surface should be removed so that the seeds absorb enough water. When storing, the moisture content of the sand should be such that it forms a ball when held in the hand but does not drip, and disperses when the hand is opened. Place a 20 cm thick layer of fine sand at the bottom of the pit, pile the seed-sand mixture on top of the fine sand, and when the pile reaches 25 cm from the ground surface, fill in river sand, then pile fine soil above the pit into a mound shape, with the mound 80-100 cm high. Use de-leaved corn stalks tied into ventilation bundles with a diameter of 15 cm, and place one bundle every 2-4 m in the storage pit for ventilation. In mid-March of spring, cover above the seed cellar with a shade net or corn stalks to prevent the seeds in the cellar from thawing too early. After the seedbed is prepared, take out the seeds 2 days before sowing, sift out the fine sand, and place them in a shady place for sowing. If the seed cracking rate is below 40%, turn and mix them in the sunlight until the cracking rate meets the standard, and then sowing can be carried out.
This method saves labor, is convenient, and is simple to operate, so it is widely adopted.
2. Rapid Germination Method
About 40 days before sowing, soak the seeds in cold water for 2 days, remove the immature seeds floating on the water surface, and take out the remaining seeds; then disinfect with 2% copper sulfate or 3% quicklime emulsion, soak for 3 hours and take them out, then pour the seeds into a vat and soak them in warm water at 45 degrees Celsius, stirring while pouring the water, and stop stirring when the water temperature drops to 20 degrees Celsius. Do not discard the seeds floating on the surface; they will sink after soaking for a few days. After soaking for a week, when the kernel is pressed close to the inner wall of the outer seed coat, it indicates that the soaking is appropriate. If this standard is not reached, continue soaking, and change the water once every 2-3 days during the soaking period.
After the seeds are soaked appropriately, choose an outdoor place on the south side of a building, sheltered from the wind and facing the sun. Take out the seeds and mix them with fine wet sand at a volume ratio of 1:3. Pile the seed-sand mixture in a manner higher in the north and lower in the south, with the north side 60 cm above the ground and the south side 20 cm above the ground. The length depends on the number of seeds. Surround the seed-sand mixture with wooden boards to form a frame on all four sides. After leveling, cover with plastic sheeting, and in the evening add straw curtains or corn stalks to help keep warm. In the first half of the treatment, turn and mix once every 2-3 days, and in the second half, once a day, to ensure that the temperature and moisture of the seeds in the upper and lower layers remain consistent. If water is lacking during turning, water can be added, and it is appropriate to keep the sand moisture at 60%. Remove the plastic sheeting 5-6 days before sowing. After the bed is prepared, take out the seeds 1-2 days before sowing, sift out the sand, and place them in a shady place for sowing. If the seed cracking rate is below 40%, turning and mixing in the sunlight or soaking with gibberellin can both be used.
This method can be applied when the seeds are transferred in relatively late, the ground has already frozen, and there is no permanent seed cellar. Practice has proved that seeds treated by this method emerge early, uniformly, and evenly, but it is labor-intensive.
3. Seed-Ice-Sand Mixed Burial Treatment Method
Before treatment, prepare wet river sand, small ice blocks of 6-10 cm, and large ice blocks. Mix the seeds, small ice blocks, and wet river sand at a volume ratio of 1:2:2 into a seed-ice-sand mixture and place it into the seed cellar. When it reaches 30 cm above the ground, place a layer of large ice blocks on top, and then place a 10 cm thick layer of wet river sand on top of the ice blocks. Under weather conditions below -15 degrees Celsius, leave it for 8 days to freeze the seed-ice-sand mixture, then cover with a 20 cm thick layer of wet sand, and cover the sand tightly with corn stalks to prolong the freezing time. Take out the mixture 15 days before sowing, germinate it indoors or in an outdoor warm shed, keep it moist, turn and mix once a day, and sow when 40% have cracked open.
In terms of time and labor, this method falls between the winter storage method and the rapid germination method. It can be carried out around the fifteenth day of the first lunar month, provided a ready-made seed cellar is available.
III. Sowing
After the seedbed is prepared, sowing can be carried out. To ensure uniform seedling emergence, the seeds should be evenly divided before sowing, and the broadcast sowing method should be adopted. The sowing rate is 150-165 kg/mu. After sowing, press immediately, cover with sand, and press again, with a sand-covering thickness of 2.0 cm.