Two common misunderstandings about greenhouse ventilation

Misconception 1: No ventilation during low temperatures

When encountering continuous cloudy days or continuous low temperatures outside, many growers will continue to keep the air out for heat preservation.

In an unventilated greenhouse, crops cannot get carbon dioxide for photosynthesis, which is equivalent to not getting enough food during crop growth, which will not only affect the growth rate of crops but also the quality of fruits.

If there is no ventilation for a long time, the water evaporated from the soil and leaves into the space cannot be removed, which will increase the probability of crop disease outbreaks, thereby increasing management and drug costs, and posing a threat to product safety and quality.

Solution：

For greenhouses with heating conditions, the temperature in the greenhouse can be increased before and after ventilation. When the temperature is not lower than the temperature range suitable for crop photosynthesis, ventilation should be carried out for more than one hour every day. For cold greenhouses without heating conditions, ventilation should be carried out for about half an hour at no less than 10 degrees Celsius around noon when the temperature is most suitable in the day.

Misconception 2: Ground film is attached to the ground

Nowadays, the use of ground film has been widely popularized in greenhouse production, and its role in preventing weeds, raising ground temperature, retaining moisture, and reducing greenhouse air humidity has also been widely recognized. However, a common misunderstanding when covering with ground film is that the ground film is attached to the ground. The disadvantage of this is that it will cause the soil aeration to deteriorate, and because of the existence of the ground film, the soil structure cannot be loosened by inter-cultivation.

Solution：

Soil is the growth environment of the root system, and its permeability directly affects the root function, which in turn affects the growth and development of crops. Under the premise of not affecting the function of ground film covering, more practical methods can be adopted, such as the following two:

● Ditching in the ridge This method is mainly aimed at the cultivation mode of one ridge and two rows. The specific method is to open a ditch about 10cm deep in the middle after the cultivation ridge is completed. When planting, the seedlings are planted at higher places on both sides of the ditch. When covering with film, the middle of the ridge is in a hollow state, which can be more effectively ventilated, and the speed of gas exchange will be significantly higher than the method of directly using the ground film to stick to the ridge surface.

● The method of pulling the rope on the top is also mainly aimed at the cultivation mode of one furrow and two rows. The specific method is to make a flat furrow, and then pull a nylon rope about 10cm high in the middle of the furrow surface. To prevent the nylon rope from falling in the middle, several support points can be set on the furrow. When covering the film, the ground film is suspended on the rope, and a larger space is formed between the ground film and the furrow surface, so as to achieve more efficient ventilation.

Choose a suitable ventilation method according to the greenhouse conditions, manpower conditions, and crop growth needs

Top ventilation

Ventilation through the vents on the top of the greenhouse is a ventilation form that is particularly suitable for off-season production in winter and early spring or delayed cultivation in autumn. The most feared thing about ventilation in winter is that the cold air from the outside will quickly and directly impact the seedlings, causing seedling flashing. Improper operation can often make the leaves, faucets, and even the entire seedlings flash into the appearance of being scalded by boiling water in a few minutes. Once this happens, it means that the cell membrane has been broken, the cell fluid has flowed out, and the cell function is completely lost.

When the top is vented, the hotter air in the greenhouse will evaporate from the vents, while the cold air from the outside sinks into the greenhouse. In the process of cold air diffusing into the greenhouse, the path it travels is relatively long, and the relatively hot air in the greenhouse has a better preheating effect on the cold air, so that when this part of fresh air reaches the seedlings, the temperature is close to the temperature around the seedlings, which can minimize the occurrence of cold air damage to the seedlings.

Waist ventilation

Waist ventilation is suitable for the late stage of early spring cultivation or the early stage of autumn delayed cultivation. When venting, the temperature can be stabilized at 8-10 degrees Celsius. The specific form is to set a vent at a height of about one meter from the edge of the shed to the ground when covering the shed film (usually the overlapping area of ​​the upper shed film and the bottom shed film). During this period, due to the small temperature difference between the inside and outside of the shed, the outside air will not cause damage to the seedlings when the wind speed is not particularly high. However, this method is generally not suitable for off-season cultivation.

Bottom windproof

That is, the greenhouse film is directly rolled up from a position close to the ground for ventilation. Bottom ventilation is suitable for early summer and autumn crops, late spring and summer crops, and greenhouse cultivation in summer. In this cultivation season, due to the high outside temperature, it can generally be stabilized above 12 degrees Celsius, and the air flow outside the greenhouse will not have a negative impact on the growth of crops due to low temperature. The advantage of this ventilation method is that the ventilation is fast, the air exchange volume between the inside and outside of the greenhouse is large, which can reduce the temperature inside the greenhouse, make the air in the soil circulate more efficiently, and promptly meet the increase in carbon dioxide demand for crops at higher temperatures and stronger photosynthesis.