In the winter and spring seasons, the light conditions inside plastic greenhouses play a crucial role in determining the growth, yield, and quality of vegetables. Therefore, improving the lighting within these structures is essential for optimal crop performance. Here are several effective strategies to enhance light conditions:
First, optimizing the greenhouse structure can significantly improve light availability. Using galvanized iron wire (No. 8) to secure the frame not only reduces material costs but also minimizes shading. It’s recommended to use non-drip films for better light transmission and polyethylene films for general use. Additionally, painting walls and construction materials white can increase reflected light and extend the lifespan of the structure. Raising the height of the greenhouse can also improve light distribution.
The orientation and angle of the greenhouse should be adjusted based on the growing season and crop needs. For spring and autumn crops, a smaller angle (around 15 degrees) with a flat design helps distribute light more evenly. In contrast, during winter, a steeper angle (about 25 degrees) with an arched roof improves light penetration.
The width of the greenhouse and the depth of the back slope also matter. For winter production, a width of 6–6.5 meters with a 0.8–1 meter rear slope enhances both light and heat retention. During spring and autumn, a wider structure (8–9 meters) with a shorter rear slope or no slope at all is more suitable.
When planting different vegetable varieties, it's important to follow the principle of placing taller plants in the south and shorter ones in the north. Proper cultivation practices, such as tilting the front rows of cucumbers toward the south and keeping middle rows upright, can boost light utilization by approximately 10%.
Maintaining clean greenhouse films is vital. Water droplets and dust can reduce light transmittance by up to 30%. Regular cleaning of the film, removing snow promptly, and managing humidity after sunrise can help maintain higher light levels. Covering the outside with warm materials like straw, while ensuring temperature remains stable, can also improve light exposure.
Artificial lighting is essential in low-light conditions, especially during winter. Light intensity should be between 1,000 to 3,000 lux. Red and blue-violet lights are most beneficial for plant growth. Using 40W fluorescent lamps or 100W high-pressure mercury lamps placed at appropriate heights can provide adequate illumination. Lighting should be applied for 2–3 hours daily after sunrise, and extended on cloudy days.
Finally, using reflective materials like aluminum film can enhance light reflection. Hanging reflective screens made from polyester aluminum film along the sides of the greenhouse can increase ground light by 40–43%, raise shelf temperatures by 3–4°C, and improve overall crop quality. Laying silver-gray film or aluminum foil on the ground also boosts light intensity between plants, helping vegetables develop better color and preventing early leaf decay.
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