How to keep the fruit tree warm in the greenhouse?

How to keep the fruit tree warm in the greenhouse?

Li Hua

Fruit tree facility cultivation is mainly by improving the environmental conditions of fruit tree growth, promoting cultivation out of season, so that the fresh fruit matures early on the market, after years of development, the industry has become one of the planting industries in many areas in the north to develop green and efficient agriculture and farmers to get rich and well-off. Temperature is one of the important environmental conditions for the cultivation of fruit trees in greenhouses, and thermal insulation and warming technology is the key technology for high yield and high quality in fruit tree greenhouses. According to the actual production, the author puts forward the methods and precautions for thermal insulation and warming in fruit tree greenhouses for reference.

1 The importance of temperature

Temperature is the main environmental factor affecting the growth and development of fruit trees. In winter and spring, the northern climate is cold, and the use of solar greenhouses to "change the sky" can create suitable temperature conditions for the growth of fruit trees and realize the cultivation of fruit trees out of season. Fruit trees have specific requirements for temperature at each stage of growth and development, and the temperature has a great impact on fruit set, fruit development, and fruit quality. Therefore, under the condition of facility cultivation, thermal insulation and temperature control can be carried out to achieve the most suitable temperature for the growth and development of fruit trees, which can promote the success of off-season fruit tree cultivation.

2 Thermal insulation and warming method

2.1 Applying organic matter

Dig a deep, 60cm wide planting ditch before planting fruit trees in greenhouses, put about 10cm thick corn stalks, wheat straw, etc. at the bottom of the ditch, and then cover it with cow dung about 15cm thick, and then mix 5m 3 or 500~600kg of commercial organic fertilizer or 500~600kg of commercial organic fertilizer, 40~50kg of bio-organic fertilizer, 60~80kg of superphosphate, calcium magnesium soil conditioner and other fertilizers to the surface for backfilling, and then irrigate thoroughly and solidly. In the years after planting, the soil beneficial bacteria and microorganisms can reproduce and decompose organic matter to produce heat, and the soil temperature in the 10~40cm deep root distribution area can be increased by 2~3 °C, and the soil is loose and breathable.

2.2 Ridge formation

Before planting, take the topsoil after fertilization between the rows to raise a high ridge of 20cm and a width of 30~50cm, and the fruit trees are planted on the ridge surface, which can prevent the soil from sinking caused by the decay of organic matter in the planting ditch, and can increase the surface area, enhance the refraction of light, which is conducive to heat absorption, and can increase the ground temperature by 2~3 °C.

2.3 Construct greenhouses with good thermal insulation performance

In the construction of greenhouses, careful design and construction are carried out, the construction height and structure are reasonable, the internal support and external pressure are firm, and the wall with thermal insulation support, the thermal insulation quilt or straw curtain with good thermal insulation performance, and the greenhouse film with good light transmittance are heated quickly and have good thermal insulation performance. It should be tightly closed to prevent the wall gaps, entrance doors, wind outlets, etc. from being tightly closed, forming air convection and causing heat loss in the greenhouse.

2.4 Dig a ditch to protect against the cold

In cold areas, it is necessary to dig a cold-proof ditch with a width of about 20cm and a depth of about 60cm on the inside of the front shed film in the southernmost part of the greenhouse. The ditch is filled with organic matter such as compacted crop straw or rice husks, sawdust, and weeds. In addition to preventing the entry of cold air from the soil outside the greenhouse, the water on the greenhouse film slides into the ditch and is absorbed by organic matter, which absorbs water and decays and releases heat and carbon dioxide, which is also conducive to the growth of greenhouse fruit trees.

2.5 Mulching

After watering 1 month in advance, the surface under the canopy is covered with black mulch film or colorless mulch, which can play a role in raising the ground temperature after sealing the shed and raising the temperature. If it is covered too late, it will have little effect on raising the ground temperature.

2.6 Ground mulching

In autumn, the surface of the fruit tree greenhouse is covered with a layer of 10~20cm thick corn stalks, wheat straw and other organic matter, which can play a role in heat preservation when the ground temperature drops after winter. Note that if the ground temperature is too low when the shed is warmed, it will affect the rise of the ground temperature, therefore, the covered organic matter can be removed when the shed is warmed, which is conducive to the increase of ground temperature. The ground temperature in the greenhouse has been raised to more than 20 °C, and the ground temperature is stabilized before the ground mulching, which can prevent soil moisture evaporation, reduce soil stamping, and at the same time, the grass mulching can release heat and carbon dioxide after absorbing the moisture in the greenhouse and rotting.

2.7 Set up water storage pipes

On the cold-proof ditch in the southernmost part of the fruit tree greenhouse, place a hard plastic bucket pipe with a diameter of 15~20cm and greater than the length of the shed body of 3~4m, and lift it along the gable on both sides, the nozzle is higher than about 1.5m, fixed and stable, and filled with water when sealing the shed to raise temperature. 1kg of water can absorb or release 4 200JB of heat per liter of 1°C higher or lower. Due to the good light in front of the greenhouse, the water in the plastic barrel tube can absorb a lot of heat during the day, when the temperature in the greenhouse decreases at night, the water temperature in the plastic bucket tube will gradually decrease, so as to emit a lot of heat, play the role of "radiator", because the water temperature is equivalent to the temperature in the shed, it will not reduce the ground temperature. The water in the hard plastic bucket can be replaced once every half a month, which is used for watering fruit trees or spraying pesticides, foliar fertilizer, etc.

2.8 Enhance thermal insulation measures

2.8.1 Maintain the light transmittance, integrity and heat preservation of the shed film

The main source of temperature in fruit tree greenhouses is sunlight radiation, so drip-free greenhouse films with high light transmittance can be used. Attention should be paid to the observation of the canopy film in the usual management, and if there is a cover, wipe it with a mop or rinse it with water in time to remove the dust, snow and other things outside the canopy film to ensure good light transmission. The shed film should be kept intact and tight, and the film pressing line should be tight to prevent the shed film from fanning and being damaged due to wind. If there is a broken mouth, it should be repaired in time to ensure the integrity and heat preservation of the shed film.

2.8.2 Use good mulch for insulation

The use of mulch covering and thermal insulation is the main way to block heat conduction and dissipation in greenhouses, so that the heat accumulated in the greenhouse during the day is stored in the greenhouse as much as possible, so that the temperature at night will not drop too low, therefore, it is necessary to use the cover with good thermal insulation effect. Generally, you can use a tight straw curtain or a thicker insulation quilt, the thicker the insulation material, the better the insulation effect. In order to prevent rain and snow from getting wet and aggravating the covering, you should pay attention to the weather forecast at any time, and when rain and snow are forecast, cover it with a layer of old plastic film to waterproof.

2.8.3 Enhance the thermal insulation of the back slope and gable of the back wall

The greenhouse wall material has the properties of heat absorption, heat storage and heat dissipation. The back wall, gable and back slope of the greenhouse can be covered with a layer of 10~20cm thick corn stalks, which can be wrapped and pressed with old greenhouse film, just like putting on a "down jacket" for the back wall, reducing the heat dissipation of the back wall and improving the thermal insulation effect of the fruit tree greenhouse.

2.9 Fast-sealing shelves

Seal the film early in late autumn, increase the windbreak, set up a shade net, so that the temperature in the greenhouse is not too high, if necessary, put down the insulation cover early during the day, and remove the insulation quilt at night to reduce the air temperature in the greenhouse, so that the fruit trees can enter the dormant period as soon as possible, and complete the dormancy as soon as possible. During the cold northern winters, permafrost forms when the topsoil temperature reaches below -5 °C. Use canopy film and insulation quilt or straw curtain to cover it appropriately so that the minimum temperature is not too low. Under the combined action of ground mulching and mulching, the soil around the root system of fruit trees can be kept at a relatively high ground temperature.

2.10 Implement moderate high temperature management

Affected by the rise of hot air, the air temperature in different parts of the greenhouse is basically positively correlated with the height of the greenhouse, especially when the branches and leaves of fruit trees are dense or high, due to the shade of the branches and leaves of the tree, the temperature drop gradient from top to bottom is obvious. Generally, the ground temperature is 4~7°C lower than the air temperature at the highest part of the tree. Therefore, in the temperature control, moderate high temperature management, especially after fruit set, the temperature at the highest point of the treetop of the fruit tree in the greenhouse can be set to the upper limit of the most suitable temperature requirements in different growth and development periods, and even 1~2 °C higher, so that the temperature of the lower part of the treetop is the most suitable temperature for the fruit tree in different periods, which is conducive to the growth and development of the fruit tree. At the same time, because the temperature in the greenhouse is high most of the time, the wall and soil and the water storage pipe water will absorb a lot of heat, and its temperature is also high, and when the temperature in the greenhouse decreases at night, a large amount of heat can be released, which can keep warm and not be too low at night. In the evening, as long as the temperature in the greenhouse is not lower than 8 °C, the insulation quilt should be covered as late as possible to delay the light time and promote the growth of fruit trees.

2.11 Cultivating high-light trees

Nectarines, apricots, large cherries, etc., are made in the shape of a trunk, a stick, and a happy tree, and grapes are made of a fence or a "T" frame. Through bud wiping, topping, twisting, thinning, shrinking and pruning, timely, multiple and meticulous reasonable shaping and pruning, adjust the density of branches in the canopy, and improve the light conditions between the trees and rows, so as to increase the ground temperature.

3 Pay attention to the problem

3.1 Optimize temperature

As with the cultivation of fruit trees in the open field, the temperature requirements of various fruit trees in the greenhouse in different growth and development periods are also different, and only the most suitable temperature to meet the growth period of fruit trees can maintain good ecological environment conditions, promote the growth and development of fruit trees, and achieve the purpose of increasing yield, improving quality, early maturity and achieving efficient cultivation. Therefore, at the same time of heat preservation and warming, it is necessary to optimize the temperature regulation to ensure the temperature requirements of fruit tree growth and fruiting, especially in the germination period and flowering period before fruit set, the temperature can not be too high, and the temperature can not be too fast.

3.2 Ways to regulate temperature

There are two main ways to regulate the temperature: artificial and intelligent, to prevent the temperature in the fruit tree greenhouse from being too high or too low.

3.2.1 Manual observation and control

Generally, when the growers seal the greenhouse of fruit trees, they hang thermometers in the middle of the greenhouse, the top of the canopy at 3~4m away from the north wall, the underground of the entrance to the greenhouse, and the underground near the east and west walls of the greenhouse, set up multiple temperature observation points, and often manually observe the temperature changes in the greenhouse regularly, and manually regulate the temperature requirements of the cultivated fruit trees in different growth periods.

3.2.2 Intelligent control

Qualified greenhouse scale growers implement standardized production, adopt Internet of Things technology, install modern intelligent control system, install intelligent sensors and automatic temperature control equipment, conduct real-time monitoring of cultivation elements such as light, temperature, water, fertilizer and gas, and carry out early warning and forecasting according to the limit value, which can be carried out through the smartphone APP Grasp the environmental changes of greenhouse fruit trees, and automatically regulate and control the key nodes of each growth period, especially the flowering stage, according to the temperature change target, so as to prevent the harm of high and low temperatures, or the drastic temperature changes of high and low and damage to the fruit tree body.

3.3 Methods of temperature control

3.3.1 Cooling method

Opening the air outlet is the main way to reduce the temperature in the greenhouse, the method is simple, the cooling effect is obvious, and it can be carried out according to the season, weather conditions, the appropriate temperature and humidity reduction of the fruit tree species and the growth period in the greenhouse, and it can be flexibly mastered. Generally, it should be carried out when the indoor temperature is high, and the size and time of the air outlet should be strictly controlled to prevent the temperature from dropping sharply. Generally, there are two upper and lower vents, do not be too hasty, generally open the upper vent first, put a small gap, and gradually increase the vent as the temperature rises. When the temperature is too high, open the lower air vent. In the afternoon, as time goes by, the light intensity weakens, and the temperature in the greenhouse gradually decreases.

3.3.2 Heating

In the cold areas of the north, emergency warming measures are taken in the event of rain, snow, strong cold air and other undesirable extreme cold and cold weather. When the temperature in the greenhouse is lower than 6°C, warming measures must be used to prevent frost damage to the fruit trees in the greenhouse. The commonly used methods of warming are mainly as follows.

1) Solar water heater. Place the solar water heater on the roof of the greenhouse management room, and after 11 p.m. in cold weather, flow the hot water in the water heater through the water pipe into a container such as a large plastic bucket or iron drum placed in the greenhouse, and let the hot water slowly release some heat.

2) Burner. According to the actual local situation and economic conditions permitting, coal, natural gas, biogas, alcohol, firewood and other different types of temporary or permanent burners can be set up, using furnace fire to burn fuel, and at the same time using container water heating, fuel heat dissipation and heated water slow heat dissipation, heating and heat preservation for the greenhouse. Use 2 old buckets, knock off the bottom of the bucket, match the stove, use a small open flame in the barrel, burn dry firewood with sufficient oxygen, manually carry the stove, and burn about 20min on the aisle on the north side of the greenhouse to avoid the harm of harmful gases such as carbon monoxide, and slow down the drop in temperature in the greenhouse.

3) Electric heating appliances. Electric heating appliances such as electric heaters, hot air conditioners, and electric water heaters are used to generate some heat.