With the increase of the greenhouses growing in greenhouses, the planting area is growing all over the country. In recent years, drought and short rain have led to high summer temperature and long photoperiod, resulting in an increase in the number of malformed fruit (twins or even multiple births), affecting the yield of fruit trees, and the increase of labor costs due to fruits and vegetables. It was found that the incidence of malformed fruit increased significantly when the illumination intensity reached more than 100 000 LUX and the ambient temperature reached 35 degrees for more than 5 hours. High intensity of solar radiation could increase the ambient temperature of buds and promote the formation of double pistils. Therefore, in the temperature sensitive period of flower bud differentiation, if extreme high temperature is encountered, short-term shading with shading net above the tree body to reduce temperature and solar radiation intensity can effectively reduce the occurrence of double pistil flower buds, thereby reducing the occurrence of malformed fruit in the next year. The use of shading net to shade cherries in the facility has become a necessary operation every summer. In summer, in order to prevent high temperature obstacles, friends of fruit and vegetable farmers often use shading to reduce the temperature in the shed. In actual production, the sun shading methods used are varied, some of which are covered with black, silver gray shade nets, and some are splashed mud onto the greenhouse film and ink is cooled down. These different shading methods certainly have different shading effects.
Scientific and Rational Selection of Shading Net
The main function of shading net is to shade the light and temperature of greenhouse. Covering shading net is an important measure for greenhouse vegetable production in high temperature season. However, if improper shading net is selected, not only will the plant grow longer, but also is not conducive to flowering and fruit setting. Therefore, we must scientifically and rationally select the screen.
1. Don't judge the advantages and disadvantages of the shading net by its color: at present, the shading net sold in the market is mainly black and silver-grey. Black shading net has high shading rate and fast cooling, so it is suitable for short-term covering in fields requiring fine management in summer. Silver-gray shading net has low shading rate and is suitable for long-term covering of sunny vegetables.
The quality of shading nets is not has the final say of color, the shade of shade nets is added in the process of raw material manufacturing. Therefore, different vegetables should choose different shading nets with different colors and shading rates. For example, tomatoes are photophilic crops. As long as 11 to 13 hours of sunshine are satisfied, the plants will grow strong and blossom earlier. Although the influence of illumination time on tomato is not so important, the intensity of illumination is directly related to yield and quality. Insufficient light can easily cause malnutrition, elongation and flowering reduction. The light saturation point of tomato is 70,000 lux, the light compensation point is 30,000-35,000 lux, and the light intensity is 90,000-100,000 lux at noon in summer.
The shading rate of black shading net is high, up to 70%. Using black shading net, the light intensity can not meet the normal growth needs of tomatoes. It is easy to cause the growth of tomatoes and the accumulation of Photosynthate is insufficient. The shading rate of most silver-gray shading net is 40%-45%, and the light transmittance is 40,000-50,000 lux, which can meet the normal growth needs of tomatoes. So tomatoes are best covered with a silver-gray shade net.
2. It is necessary to distinguish what kind of material shading net is made of: there are two kinds of materials for shading net sold on the market at present, one is high density polyethylene 5000S produced by petrochemical enterprises with color masterbatch and anti-aging masterbatch weaved by drawing; the market price of pure new material polyethylene is about 12,000 yuan a ton, with Color Masterbatch added and anti-aging material 3% to 5% and other production costs; the cost should be in the production of high density polyethylene 5000S. 16,000 tons; bright black color, soft feel; anti-aging, durable, its service life can reach 6 years.
So the other one on the market is made from recycled old sunshade nets or plastic products; about 12,000 yuan a ton. The sunshade net produced with recycled materials not only has low brightness, hard handle, pungent odor, but also has short service life, most of which can only be used for one year.
3. In order to achieve different shading rates, each shading net has different weaving densities. Generally there are three kinds: two needles shading rate 45%; three needles 70%; four needles 90%. So when choosing the shading net, we should choose the density of the shading net according to the crops planted.
According to the growth characteristics of cherry, its light intensity is the same as that of ginger planting, so it is recommended to choose two pins of shading net.
4. There are two ways to sell sunshade nets on the market: one is by area (per square price) and the other is by weight (per kilogram price).
The Following Misunderstandings Should be Avoided When Choosing Sun Shade Net
1. Fruit growers who use shading nets are very easy to buy nets with higher shading rates when they buy shading nets. He will think that shading rates are higher and cooler. But the high shading rate causes the problems of weak light in the shed, reduced photosynthesis, weak stalks and elongation, which reduce crop yield. So we must choose the shading net according to the light intensity of the plant.
2. The heat shrinkage characteristic of shading net is easy to be neglected. It shrinks most in the first year, about 5%, and then gradually becomes very small. As it shrinks, the shading rate increases. Therefore, the heat shrinkage characteristics should be taken into account when fixing the chute.
The future development of shading net is mainly based on color, and different colors have different functions. White shading net, reflecting and scattering light, increase light flux, prevent crop growth.