Maize seedling management is crucial for cultivating strong, healthy seedlings suitable for mechanical transplanting, which directly affects the success of rice mechanization. "Good seedlings produce good rice," and the quality of seedlings significantly influences panicle number, grain count, and grain weight during the later stages of rice growth. For mechanized transplanting, seedlings must be well-balanced and individually robust, with uniform height and thickness—no tall or thin seedlings should be present.
High temperatures and humidity are beneficial for seedling development. After germination, a period of high temperature and humidity is essential to ensure uniform emergence. To maintain this, it's important to manage temperature and moisture effectively, using techniques like raising the bed and controlling water levels. At the same time, proper drainage should be maintained to avoid waterlogging, which can lead to root rot.
Covering seedlings with grass or plastic film is common in high-temperature conditions. This includes double-membrane seedlings, floppy disk sowing, and direct machine seeding. When managing these, two key points should be considered: first, ensuring the cover is even and not too thick to prevent heat damage during midday sun; second, removing excess water from the film after rain to avoid wet straw sticking to the seedlings, which can cause poor growth and weak shoots.
Arch sheds are ideal for early spring planting in colder regions. Once the seedlings are established, the temperature inside the shed should be kept below 35°C at midday to prevent heat stress. During the seedling stage, the bed is usually covered with plastic, mainly for insulation and moisture retention. Ventilation is needed when the temperature inside exceeds 35°C, and it should be closed promptly afterward. If the bed appears dry and the leaves are rolled, it's time to apply "Happy Valley Water" to rehydrate the seedlings.
Timely hardening off is essential for acclimating seedlings to outdoor conditions. The timing for removing the cover depends on the temperature. Generally, the film should be removed when the seedlings have emerged about 2 cm and the first leaf has unfolded (around 3–5 days after transplanting). Prolonged covering can lead to heat damage. The principle for removal is: expose on sunny evenings, cloudy mornings, before light rain, and after heavy rain. In cold weather, it’s better to delay removal and cover at night if necessary.
After the seedlings turn green, the arch shed can be removed once the minimum temperature stabilizes above 15°C. Otherwise, keep the soil moist and expose the seedlings to sunlight at night.
Water management is critical for healthy seedlings. A wet-dry irrigation method is recommended, alternating between wet and dry periods to regulate water, temperature, and protect the seedlings. When the film is removed, drain the water and let the bed dry naturally before refilling. If the leaves curl in the afternoon, spray a thin layer of water to protect them. During cold snaps, block the water to prevent damage. Once the temperature stabilizes, change the water and improve air circulation to boost root health. Three to five days before transplanting, control the water supply to prepare the seedlings.
Water management should mimic traditional practices, such as dry feeding. After removing the film, fill the bed with enough water and allow it to drain through the soil. Keep the ditches clear to prevent water stagnation. If the leaves curl in the afternoon, spray water in the evening or early morning. Avoid watering if the leaves don’t curl. Use clean water to prevent seedling death.
Applying weaning fertilizer is important, depending on soil fertility, seedling age, and temperature. It is typically applied around the one-leaf-one-heart stage (7–8 days after sowing). For each mu of land, use 500 kg of compost tea or 1000 kg of urea solution. Apply it in the evening to the seedlings. If the bed soil is already fertile, reduce the amount to prevent overgrowth.
In case of cold stress, deep water can help protect the seedlings. Adjust the water level to regulate temperature and gas exchange. If a cold wave hits, fill the field with deep water but avoid submerging the growing point. After the weather clears, don’t immediately drain the water, as sudden temperature changes can harm the plants. Deep water helps stabilize the temperature in the seedbed.
Before a cold snap or after a frost, apply 100–150 grams of fungicide per 1000 liters of water to prevent disease. After prolonged rainy weather, spray Zhuang Bao to prevent blight.
If the weather remains cold for a long time, combine the above measures with building an arch shelter to provide additional protection.
Avoid applying fertilizer too soon after a cold spell. Seedlings may be weakened, and premature fertilization could worsen their condition. Wait 3–4 days after the cold snap before topdressing.
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