Detailed Explanation of Key Management Techniques for Picea koraiensis Seedlings

(1) Shading: Picea koraiensis seedlings prefer shade and humidity. After the seedlings emerge, appropriate shading yields a survival rate 30%-40% higher than full-light seedling cultivation, with a 32% increase in seedling height and tender leaves that are bright green. Generally, when 50% of the seedlings have emerged, begin erecting daily shade curtains for shading, until they are removed in early to mid-July. If covering materials are difficult to obtain, tall-stem crops (such as corn) can be planted along the bed edges to replace reed curtains. In some areas with sufficient water sources and convenient irrigation, watering 2 to 4 times daily in small amounts but frequently, with timely and appropriate watering, can also make full-light seedling cultivation successful.

(2) Topdressing and irrigation: Topdressing can be carried out in mid to late June, using 4.5 kg of urea per mu, applied in 2 split applications. After topdressing, rinse promptly to avoid burning the stems and leaves. Before early June, under dry weather conditions, water 2-4 times daily, preferably in small amounts but frequently. After mid to late June, the rainy season begins, and depending on weather changes, the frequency of irrigation can be gradually reduced while the amount of water per irrigation is appropriately increased, watering every other day with timely irrigation to keep the surface soil of the bed moist. By late July or early August, fertilizer and water should generally be controlled to promote full lignification of the seedlings.

(3) Frost prevention: In Baiyinaobao of Inner Mongolia and the forest regions of Northeast China, located in high-cold areas, the late frost period ends around late May, and late frost has a relatively large impact on seedlings. According to observations at the Tieli Nursery in Heilongjiang Province, when the air temperature at 5-10 cm above the bed surface drops to 0-2°C, newly sown seedlings suffer 10%-13% damage; when the temperature drops to -2°C, the new growth tips of 2-3 year old seedlings suffer 3%-10% damage. Frost-damaged seedlings grow poorly, and the seedling formation rate is very low. Therefore, frost forecasting and prediction should be done well, promptly using the smoke method or covering with grass.

(4) Pest and disease control: The main hazards during the seedling stage are damping-off disease and underground pests such as mole crickets. Prevention should be the priority, with integrated control (see the relevant content on seedling pest and disease control for details).

(5) Winter cold protection: Cold protection for Picea koraiensis seedlings is an important measure to ensure safe overwintering of seedlings and reduce losses. Soil covering for cold protection is mostly adopted. The specific method is: turn up and break apart the soil from the paths between seedling beds, lay the seedlings toward one side, and evenly cover with soil, with a thickness that should exceed the seedlings by 4-5 cm. The timing of soil covering for cold protection should not be too early, otherwise the seedlings are prone to heating and molding. It is generally carried out in late October or early November before the soil freezes. The timing of removing the covering soil should not be too early or too late; generally, the cold protection soil is removed in two stages before Grain Rain. To prevent physiological drought of seedlings caused by dry spring winds, irrigate promptly after removing the soil.

(6) Bed changing: Seedlings over 1 year old are transplanted for cultivation. Bed changing and transplanting should be done in mid to late April, preferably before the sap begins to flow. The transplanting density is 200 plants per sq m, with a plant spacing of 5 cm and row spacing of 10 cm, producing about 80,000 seedlings per mu. To avoid root balling during transplanting, the main root of the seedlings should be properly trimmed, maintaining 8-10 cm.

According to the experience of Tieli Nursery, bed-changed seedlings have well-developed root systems and short, thick, sturdy stems, with a survival rate after afforestation 6% higher than that of seedlings left in the bed and a 3% increase in annual growth. Therefore, in current production, seedlings over 2 years old are mostly cultivated through bed changing and transplanting.