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In summer, as the light becomes stronger and the temperature rises, the temperature in the shed is too high and the light is too strong, which becomes the main factor affecting the growth of vegetables. In production, vegetable farmers often use the method of covering shade nets to reduce the temperature in the shed.
However, there are also many vegetable farmers who reported that although the temperature has decreased after using the shade net, the cucumbers have problems of weak growth and low yield. From this point of view, the use of shading nets is not as simple as imagined, and unreasonable selection may lead to excessive shading rates and affect the growth of vegetable crops.
How to choose the sunshade net scientifically and reasonably?
1. Select the color of the shade net according to the type of vegetables
The color of the shade net is added during the raw material manufacturing process. The shade nets currently on the market are mainly black and silver-gray. The black shade net has high shading rate and rapid cooling, but has a greater impact on photosynthesis, and is more suitable for use on leafy vegetables. If it is used on some light-loving vegetables, the coverage time should be reduced; It has little effect on photosynthesis and is suitable for light-loving vegetables such as nightshade.
2, clear shading rate
When vegetable farmers buy sunshade nets, they must first determine how high the sunshade rate they need for their sheds. Under direct sunlight in summer, the light intensity can reach 60,000-100,000 lux. For vegetables, the light saturation point of most vegetables is 30,000-60,000 lux. For example, the light saturation point of pepper is 30,000 lux and eggplant is 40,000 lux. Lux, cucumber is 55,000 lux, and the light saturation point of tomato is 70,000 lux. Excessive light will affect the photosynthesis of vegetables, resulting in blocked carbon dioxide absorption, excessive breathing intensity, etc. This is the phenomenon of photosynthetic “noon break” that occurs under natural conditions. Therefore, the use of shade net covering with suitable shading rate can not only reduce the temperature in the shed before and after noon, but also improve the photosynthetic efficiency of vegetables, killing two birds with one stone.
The black shading net has a high shading rate of up to 70%. If the black shading net is used, the light intensity cannot meet the normal growth requirements of tomato, which is easy to cause leggy growth of tomato and insufficient accumulation of photosynthetic products. Most of the silver-gray shade nets have a shading rate of 40% to 45%, and a light transmittance of 40,000 to 50,000 lux, which can meet the normal growth needs of tomato. So tomatoes are best covered with silver-gray shade nets. For those with a low light saturation point such as peppers, you can choose a shading net with a high shading rate, such as a shading rate of 50%-70%, to ensure that the light intensity in the shed is about 30,000 lux; for cucumbers and other high light saturation points For vegetable species, you should choose a shading net with a low shading rate, such as a shading rate of 35%-50%, to ensure that the light intensity in the shed is 50,000 lux.
3. Look at the material
There are two kinds of production materials for sunshade nets currently on the market. One is high-density polyethylene 5000S produced by petrochemical enterprises with addition of color masterbatch and anti-aging masterbatch. , Light weight, moderate flexibility, smooth mesh surface, glossy, large shading rate adjustment range, 30%-95% can be achieved, the service life can reach 4 years.​​
The other is made from recycled old sunshade nets or plastic products. The finish is low, the hand is hard, the silk is thick, the mesh is hard, the mesh is dense, the weight is heavy, the shading rate is generally high, and it has a pungent odor, and the service life is short, most of which can only be used for one year. Generally more than 70%, no clear packaging.
4. Be more careful when buying sunshade nets by weight
Now there are two ways to sell sunshade nets on the market: one is by area, and the other is by weight. The nets sold by weight are generally recycled nets, and the nets sold by area are generally new nets.
Vegetable farmers should avoid the following mistakes when choosing:
1. Vegetable farmers who use shading nets are very easy to buy nets with higher shading rates when purchasing shading nets. They will think that the higher shading rates are cooler. However, if the shading rate is too high, the light in the shed is weak, the photosynthesis of crops is reduced, and the stems are thin and leggy, which reduces the yield of crops. Therefore, when choosing a shading net, try to choose a shade with a lower shading rate.
2. When purchasing shading nets, try to choose products from large manufacturers and brands with guaranteed brands, and make sure that products with a warranty of more than 5 years are used in the greenhouse.
3. The heat shrinkage characteristics of the sunshade net are easily overlooked by everyone. In the first year, the shrinkage is the most, about 5%, and then gradually becomes smaller. As it shrinks, the shading rate also increases. Therefore, the thermal shrinkage characteristics should be considered when fixing with the card slot.
The above picture is the tearing of the sunshade net caused by heat shrinkage. When the user uses the card slot to fix it, he ignores the characteristic of heat shrinkage and does not reserve the shrinkage space, resulting in the sunshade net being fixed too tightly.
There are two types of shading net covering methods: full coverage and pavilion-type coverage. In practical applications, pavilion-type coverage is used more because of its better cooling effect due to smooth air circulation. The specific method is: use the skeleton of the arch shed to cover the sunshade net on the top, and leave a ventilation belt of 60-80 cm on it. If covered with a film, the sunshade net cannot be directly covered on the film, and a gap of more than 20 cm should be left to use the wind to cool down.
Covering the shade net should be carried out between 10:00 am and 4:00 pm, according to the temperature. When the temperature drops to 30 ℃, the shade net can be removed, and it should not be covered on cloudy days to minimize the adverse effects on vegetables. .