CONTROL THE GROWING TEMPERATURE

Generally speaking, 30℃ is the upper temperature limit for the most suitable growth of most solanaceous vegetables and melon vegetables. On this basis, increase it by 2-3℃ to make the greenhouse temperature reach 32-33℃, which is what I want to tell you. The topic of greenhouse temperature control discussed
So, why do we need to regulate the temperature in this way? Judging from the actual production operations of vegetable farmers, by controlling the temperature in this way, the greenhouse temperature can be adjusted to the most suitable range for vegetable growth.

First of all, the thermometers in the greenhouse are mostly hung on the upper part of the plants. The air temperature in different parts during the day is basically positively correlated with the height. Especially when the plants are lush and tall, due to the shading effect of the branches and leaves, the temperature is measured from the growing point to the ground. The temperature drop gradient is very obvious. Generally, the ground temperature can be 3-7°C lower than the temperature at the growing point. If the temperature at the growing point of the crop is around 34°C, then the temperature at the main branches and leaves of the crop will be between 27-30°C, which is the most suitable temperature for photosynthesis. within the range.

Secondly, greenhouse cultivation is covered with mulch and the soil water supply is sufficient, thus accelerating the transpiration of crop leaves and reducing leaf temperature. The leaf temperature is generally 3-5°C lower than the air temperature, even if the air temperature is significantly higher than the light optimum temperature 2 At -4°C, the leaf temperature is still within the optimum temperature range for photosynthesis.

Thirdly, increasing the temperature inside the shed will help increase the ground temperature. If the ground temperature is too low, it will not only be detrimental to the growth and development of crop roots, resulting in less rooting, poor root absorptive capacity, and low physiological activity, but will also cause the occurrence of a variety of physiological diseases, even root rot and dead roots, causing crop death.

Generally speaking, the temperature at a depth of 5 cm in the soil during the day can be 5-7°C lower than the air temperature in the shed, and at night the temperature at a depth of 5 cm in the soil is 3-5°C higher than the air temperature. It can be seen from this that the ground temperature in the greenhouse is below 20°C most of the day, which is 3-5°C lower than the 23-25°C soil temperature suitable for the root growth and development of melons, fruits and vegetables.

Increasing the temperature in the shed can significantly increase the ground temperature. Higher ground temperature can promote root development, increase the amount of roots, increase root activity, and promote the absorption, transformation and utilization of water and nutrients by the roots. In order to achieve the purpose of promoting the growth and development of above-ground parts of crops and improving crop yield and quality,

Greenhouses must take corresponding control measures. In order to prevent vegetables from being harmed by low temperatures, sufficient lighting must be provided during the day to increase the temperature in the shed, and strict cold protection and heat preservation must be carried out at night. When the temperature of the shed is low, additional coverings must be added to the shed. When the cold wave comes and the temperature drops below 0°C, a small shed is placed inside the greenhouse and covered with straw curtains. The lowest temperature at night is 2-4°C higher than that without covering it. If the greenhouse is well sealed, it can be 4-6°C higher. Ground covering can increase the soil temperature and reduce the humidity in the shed. The method of spreading mulch on the border and spreading straw in the furrow is cost-effective and effective.

According to the principles of greenhouses, the growth of greenhouse crops is related to light intensity and duration, light distribution, and light quality. Usually, plastic greenhouses encounter continuous cloudy days and poor indoor lighting conditions. Low light has become a limiting factor for greenhouse production in winter and spring. Therefore, increasing the amount of indoor lighting and extending the lighting time are the main purposes of adjustment technology. First, there must be a reasonable greenhouse structure, and then there must be covering materials with good light transmittance. These are two necessary conditions. Generally, the light transmittance loss of a clean film is 20%, and if there is dirt, it will lose 20%. Therefore, choosing a drip-free, long-lasting, and multi-functional film is an effective measure to increase the light transmittance. Long-life non-drip film is an ideal material for covering solar greenhouses. First of all, it has a good non-drip effect and its light transmittance is about 7% higher than that of ordinary films. Secondly, it has good thermal insulation performance, strong resistance, high mechanical strength, and its service life is more than 1 times longer than ordinary polyethylene film.

Currently, the commonly used cooling methods in production are ventilation and appropriate shading.
Let's first talk about humidity conditions and conditioning techniques. There is a large difference in humidity between the greenhouse and the open field. The main reason is that air exchange is inhibited. The water supply of the greenhouse mainly relies on irrigation. Traditional furrow irrigation causes high soil humidity and increased evapotranspiration, forming a high-humidity environment for both the air and the soil. Once encountering low temperature conditions, the water vapor turns into water droplets and sticks to the crops, causing frost in the greenhouse. Mildew, late blight, early blight, etc. are serious and often cause devastating disasters.
The second is that according to the high humidity environment of the greenhouse, corresponding measures should be taken to adjust. The cause of high humidity indoors is airtightness. In order to prevent the room temperature from being too high or the humidity being too high, ventilation methods should be used. As mentioned earlier, natural ventilation is generally used to reduce indoor humidity by adjusting the size, time and location of the vents. Mechanical forced ventilation is more effective if conditions permit. In addition, covering the greenhouse with mulch can greatly reduce the evaporation of soil water and effectively reduce air humidity. Micro-irrigation technology is used to control the amount of irrigation water to save water and reduce humidity.