Environmental protection facilities and construction requirements of soilless cultivation

Environmental protection facilities and construction requirements of soilless cultivation

Soilless cultivation is an efficient technique in protected cultivation. The reason why it is more high-yield, high-quality and efficient than soil cultivation is not only because the soilless cultivation facility itself has the function of regulating the crop rhizosphere environment, but also needs the matching greenhouse and other environmental protection facilities. so that the aboveground growth conditions of crops are in the best condition as underground. Soilless cultivation, as a commercial production, is carried out under the condition of comprehensive environmental control in protective facilities.

The soilless cultivation facility itself does not have the function of anti-seasonal and annual production of vegetables, flowers and other crops, but only under the condition of greenhouse and other protection facilities, can anti-seasonal cultivation or annual supply be realized, thus improving the utilization rate of facilities. Therefore, soilless cultivation facilities and greenhouse facilities are not only closely related, but also two different facilities. [Jishan Huayao]

Modern agriculture, that is, factory agriculture, can create temperature, humidity, carbon dioxide concentration, light and other conditions suitable for crop growth in fixed facilities. Most of the production facilities of soilless cultivation in developed countries are large-scale multi-span glass greenhouse with large operation scale and high production efficiency.

I. types and classification of environmental protection facilities

At present, the environmental protection facilities commonly used for soilless cultivation in China are solar greenhouse, plastic greenhouse, modern greenhouse, rain shelter, sunshade net and so on. Plastic greenhouses are widely used all over the country, especially in the south, and are developing in the direction of connecting pillars, high size and large scale in recent years. The solar greenhouse is mainly located in the north of 330,460 north latitude.

It has been popularized and applied in Fang area. In the alpine area of-15 years, 20 ℃, basically no heating has realized the production of temperature-loving fruits and vegetables in winter, which has written a brilliant chapter in the history of facility horticulture in China. After entering the 1990s, large modern greenhouses were introduced from abroad, and through study, digestion and absorption, domestic modern greenhouse facilities were studied and developed, which promoted the scientific and technological progress of greenhouse horticulture and the modernization of agriculture in our country. it provides a huge space for the development of soilless cultivation technology. Summer protective facilities such as rain shelter and sunshade net play an important role in overcoming the disastrous climate and adverse environmental stresses such as high temperature and torrential rain in summer, typhoons and frequent occurrence of diseases and insect pests in summer, especially in the southern region. it provides a simple and effective new way to alleviate the supply of horticultural products in the off-season of summer and autumn in southern China, and extends the season of soilless cultivation from winter and spring to summer and autumn. Due to the differences in nature, climate, economy, technology, labor and other conditions, the types, structural materials and sizes of facilities are different, so they should be selected and located in accordance with local conditions.

Environmental protection facility is a kind of cultivation facility which can be operated by people in order to regulate temperature, light, water, air and other environmental factors, and its cultivation space is covered with transparent covering material. According to the different covering materials, plastic greenhouses are usually divided into two categories: glass greenhouse and plastic greenhouse. According to the different covering materials, plastic greenhouse is divided into hard (PC board, FRA board, FRP board, composite board, etc.) plastic greenhouse and soft plastic greenhouse (PVC, PE, EVA film, etc.); according to shape, it is divided into single-span and multi-span types; according to the form of roof, it is divided into double roofs, single roofs, inequality double roofs, arched roofs, etc.

(1) Solar greenhouse

Solar greenhouse is a horticultural protection facility with three walls with a ridge height of more than 2m and a span of 6m to 8m. The source of heat (including at night) mainly depends on solar radiation energy. Most of them use plastic film as lighting covering material and solar radiation as heat source, and rely on a series of daylighting and thermal insulation equipment such as maximum daylighting, thickened wall and back slope, cold ditch, paper quilt, grass clover and so on, so as to achieve the effect of increasing temperature and heat preservation, so as to make full use of light and heat resources and reduce the influence of adverse meteorological factors. Generally, there is no heating, or only a small amount of auxiliary warming. The main forms of solar greenhouse are low rear wall long back slope solar greenhouse, high rear wall short back slope solar greenhouse, string solar greenhouse, steel bamboo mixed structure solar greenhouse and all steel frame non-pillar solar greenhouse (Fig. 4). I am the energy-saving solar greenhouse covered with plastic film.

The main form of vegetable protected land facilities in the north of China, with low investment and high benefit, is suitable for the current technical and economic conditions in rural areas of our country, and it has obvious advantages in lighting, warmth, low energy consumption and practicality. it is a facility cultivation mode that farmers in the north are happy to apply and the area continues to grow year after year.

(2) plastic greenhouse

Usually, the large-scale protection and cultivation facilities which only use bamboo, wood, cement or steel as the skeleton and cover the surface with plastic film are called plastic film greenhouse, referred to as plastic greenhouse. According to the shape of the roof, it can be divided into two types: arch and ridge, and most of them are arch-round roof. According to the skeleton material, it can be divided into bamboo-wood structure, steel frame (pipe) structure, steel-bamboo mixed structure, concrete steel frame structure, inflatable type and so on; according to the connection mode, it can be divided into single-span greenhouse, double-span greenhouse and multi-span greenhouse. The plastic greenhouse has simple facilities, generally has no environmental control equipment, relies on natural light for production, and develops rapidly in the southern region with a warm climate.

At present, the plastic greenhouse is mainly in the form of bamboo-wood structure greenhouse, suspended beam hanging column bamboo-wood arch greenhouse, reinforcement hanging column greenhouse, non-column steel frame greenhouse and assembly galvanized thin-walled steel pipe greenhouse (Fig. 4melan5). Among them, the assembled galvanized thin-walled steel pipe greenhouse has large space, no columns, convenient operation, belongs to national stereotyped products, unified specifications, convenient assembly and disassembly, convenient film covering, and is widely used in production.

Fig. 4 main forms of solar greenhouse (unit: M)

1. String solar greenhouse 2. Steel-bamboo hybrid structure solar greenhouse

3. Liao-Shen Ⅰ solar greenhouse 4. Improved Jiyou Ⅱ energy-saving solar greenhouse

Fig. 4 main forms of plastic greenhouse (unit: M)

1. The suspension beam is hoisted to the bamboo-wood arch shed 2. The ribs are hoisted to the greenhouse.

3. Non-column steel frame greenhouse 4. Fabricated galvanized thin-walled steel pipe greenhouse

(3) Modern greenhouse

Modern greenhouse is an advanced type of facility horticulture. The environment in the facility is automatically controlled by computer, which is basically not affected by disastrous weather and adverse environmental conditions under natural climatic conditions, and is a large greenhouse that can produce horticultural crops around the clock. At present, the modern greenhouses introduced into China mainly include the Venlo type glass greenhouse with multi-ridged multi-span roofs developed by the Netherlands and then popular all over the world (figure 4: 6), and a popular plastic film Richel greenhouse developed by Ritchie greenhouse Company of France. The top side roof can be covered with film from bottom to top, an arched multi-span coiled film fully open plastic greenhouse (Full open tyPe) and a fully open glass greenhouse (Future greenhouse) developed by the Italian company Serre Italia. Typical modern self-control greenhouses designed and manufactured in China are: double-layer inflatable multi-span plastic greenhouse, double-slope glass greenhouse, North China type large-scale multi-span plastic greenhouse, South China type large-scale multi-span plastic greenhouse, Golden Top type multi-span greenhouse, LGP- 732 type multi-span greenhouse, XA and GK series greenhouse, FRP (lightweight fiberglass fiber reinforced plastic) multi-span greenhouse, etc.

Fig. 4 Mueller 6 Holland Fenlo glass greenhouse (unit: mm)

Fig. 4 several configurations of Mel 7 multi-span greenhouse

1. Arch plastic multi-span greenhouse 2. Double-layer inflatable plastic multi-span greenhouse 3.FRP multi-span greenhouse

(4) Plant factories

Plant factory refers to the production mode of high efficiency, labor-saving and stable planting of plants by using artificial light source to realize automatic control of environment in factory-like fully enclosed building facilities. According to the different light sources, plant factories are divided into three types: artificial light, natural light and the combination of artificial light and natural light. It belongs to "controllable agriculture", which is the highest level of horticultural protection facilities, and its management is completely mechanized and automated. Crops are cultivated in soilless and stereoscopic planting in large facilities, and the changes of environmental elements are transmitted to the computer through the sensor. all aspects of the operation and production of various environmental control equipment can be accurately controlled by calculation. the temperature, humidity, light, water, fertilizer and gas needed are optimally configured according to the requirements of plant growth, not only by computer monitoring and control. In addition, robots and manipulators are used to carry out closed production management to realize the assembly line operation from sowing to harvesting, which completely gets rid of the shackles of natural conditions. To achieve the rational use of space and facilities, to achieve economic and efficient production, to achieve all-weather, no season, pollution-free production. It has the characteristics of high integration, efficient production, high commodity and high investment.

This paper introduces a medium-sized double-span glass greenhouse provided by M-type hydroponics Research Institute in Japan (figure 4Mel 8). It is 60m long, 50m wide and 4m high, and each unit area is 3000m2. In terms of environmental control, it is monitored by indoor and outdoor sensors, including sunshine sensors (measuring sunshine time), outdoor temperature sensors and indoor temperature sensors, together with wind speed, wind direction sensors and rainfall sensors to control the opening and closing of skylights, side windows, canopy and the operation of heating and cooling units. The humidity sensor controls the operation of the mist finer and dehumidifier. The supply of nutrient solution needs the help of nutrition tank group (4) and water pump. Conductivity meter, acidity meter, liquid temperature sensor, water level meter and so on control nutrient solution components, liquid temperature, PH value and balanced timing. The carbon dioxide sensor is used to measure the concentration of carbon dioxide in the greenhouse and send a signal to the carbon dioxide generator to maintain the concentration of carbon dioxide in the greenhouse. The above data are inputted into an electronic computer, and the parameters are set according to the types of cultivated crops, and the full automatic control is realized. A similar greenhouse introduced in China is the soilless cultivation greenhouse of Nanjing vegetable Research Institute.

Fig. 4 Mel 8m hydroponic research institute soilless cultivation tomato double-building automatic computer-controlled greenhouse

1. Sunshine sensor 2. Temperature sensor 3. Skylights and opening devices 4. Spray heating device 5. Side window and opening device 6. Outdoor temperature sensor 7. Rainfall sensor 8. Wind direction and speed sensor 9.C02 sensor 10. Humidification unit 11. Computer control cabinet 12. Nutrient pump 13. Four kinds of fertilizer tank 14 nutrient tank 15. Cold and warm wind control 16. Room temperature sensor 17. CO2 generator 18. Nutrient solution heating device

(5) Rain shelter and sunshade net devices

There are many Rain Water in summer, and they are vulnerable to strong light and high temperature stress, diseases and insect pests occur frequently, so that the growth of vegetables and other crops is inhibited, and the production is not guaranteed. Using the greenhouse skeleton, only cover the top curtain (sky curtain) and remove the edge film (apron curtain), so that the summer can be rain-proof, and the surrounding ventilation, this is one of the easiest rain-proof greenhouse cultivation. If the top curtain is covered with silver gray or black shading net, the strong light can be reduced, and the substrate temperature in the greenhouse can be reduced by 8: 12 ℃ at noon in summer, which can effectively reduce the harm of high temperature, and can carry out out-of-season cultivation of leaf vegetables and root vegetables in summer. With the existence of sunshade net and rain shelter, which are other protective facilities in summer, greenhouse and solar greenhouse can also carry out soilless cultivation in summer. The over-summer rain protection cultivation of some tomatoes, cucumbers, melons, lettuce and spinach which are difficult to cultivate in summer has become a reality.

II. Structure and performance of major environmental protection facilities

(1) Solar greenhouse

1. The structure of solar greenhouse Solar greenhouse is a single-roof greenhouse, commonly known as "winter greenhouse", which is the largest protective production facility in the north of Huaihe River in China. The skeleton of solar greenhouse is composed of back wall, back slope, front roof and two gables. The length, width, size, thickness and materials of each part determine its lighting and thermal insulation performance. Low cost, easy to operate and high efficiency. Table 4 MUE 7 is the structural parameters of common solar greenhouses in China.

Table 4 structural parameters of main types of solar greenhouse in China (unit: M)

Table 4-8 horizontal distribution of light intensity in different types of solar greenhouses

The basic structure of solar greenhouse generally adopts the direction of sitting in the north, south and east-west extension, has a larger light surface and light angle, and uses solar energy as the main energy source of the greenhouse. In order to improve the thermal insulation, the north side of the solar greenhouse and the east-west gable can adopt the hollow wall structure, and the rear roof can also be built with multi-layer composite materials. The first generation solar greenhouse is mostly made of bamboo and earth walls. the waiting price is low, and there are pillars inside (front column, middle column and back column). Generally every 3m row, called one. The second generation solar greenhouse is mostly made of steel and brick walls, with no internal pillars, expanded space, better operation, firm structure, higher wind and snow resistance, longer service life, higher cost, but lower depreciation cost. There are also many forms, such as steel-bamboo mixed structure, GRC skeleton structure and so on.

two。 The performance of solar greenhouse the characteristics of solar greenhouse are mainly reflected in thermal insulation, from the structural point of view, there is less light entering than plastic greenhouse, especially less scattered light into the room, indoor light distribution is uneven, the south side is stronger, the north side is lower (Table 4: 8); at the same time, the covering of thermal insulation grass curtain will affect the light time, which can reduce the light time to more than 2~3h/d in winter. Generally, when the temperature of the straw curtain dropped to about 18 ℃ (around 16:00 in the afternoon), until it was opened around 8:30 the next morning, the lowest temperature could be maintained at 8: 13 ℃, with an average cooling rate of 0.4 ℃ / h, which was much lower than that of the plastic greenhouse (1 ℃ / h), so that the diurnal range of temperature in the solar greenhouse was significantly lower than that in the greenhouse, and the lowest temperature increased significantly (5 ℃). Compared with plastic greenhouse, the crop growing period can be earlier (spring) or delayed (autumn) for 35-45 days respectively. The humidity in the solar greenhouse is similar to that in the plastic greenhouse. Because of its small volume, the air temperature and humidity are greatly affected by the changes in radiation. During the rapid warming stage in the morning, the humidity decreases rapidly, even to about 15%. In the afternoon rapid cooling stage, the relative humidity increases rapidly, and the humidity will exceed 80% around 16:00 in the afternoon. In the evening when the temperature drops rapidly, fog is often produced indoors, condensation on the plants, causing diseases. This is also one of the important reasons why the diseases in solar greenhouse and plastic greenhouse are serious and it is difficult to achieve pollution-free production. At the same time, due to the uneven indoor temperature distribution, there is a certain local humidity difference, and the morning and evening humidity is higher in the south where the heat dissipation is faster.

There are more vegetables in soilless culture, but in the low solar greenhouse, the growth space of crops is limited, which will affect the growth of large-plant crops.

(2) plastic greenhouse

1. The structure of plastic greenhouse is relatively simple, the skeleton mainly includes arch frame, longitudinal beam, column, gable column, skeleton connection fixture and door, etc., due to different construction materials, the structure of skeleton members is also different. The arch is the main component of the plastic greenhouse to bear wind, snow load and load. According to the structure, the arch mainly has two forms: single bar type and truss type. Longitudinal beam is a member that ensures the longitudinal stability of arch frame and connects each arch into a whole. Longitudinal beams also have two forms: single bar type and lattice type. When the arch frame material section is small enough to bear the wind or snow load, or the span of the arch frame is large, and the strength of the ownership structure is not enough, it is necessary to set up columns in the shed to directly support the arch frame and longitudinal beam in order to improve the overall bearing capacity of the plastic greenhouse; the gable column is the shed head column, which is commonly vertical, and the circular arch type and oblique support type are suitable for strong wind areas. The connection between the skeletons of the plastic greenhouse, such as the connection between the arch frame and the gable column, between the arch frame and the arch frame, between the longitudinal beam and the shed head arch frame, except for the bamboo-wood structure plastic greenhouse using wire rope and iron wire, the fabricated galvanized steel pipe structure plastic greenhouse and the steel-glass fiber reinforced cement structure plastic greenhouse are connected by specially prefabricated fixtures. The door of the plastic greenhouse is not only an entrance for management and transportation, but also a ventilation outlet. The door of a single greenhouse is generally located in the center of the shed head. In order to keep warm, the door can be opened at the south end of the shed. After the temperature rises, in order to enhance ventilation, another door can be opened at the north end. The shed door is in the form of hinge door, hanging rail sliding door and so on. As a plastic greenhouse for soilless cultivation, it should have a firm structure, strong resistance to wind and snow, a certain growth space and a large area, and at the same time, it is easy to ventilate and control the environment. Generally, the plastic greenhouse with steel structure with no or no pillars is suitable, with a span of 812m, a length of 40m and a ridge height of 2.4m and 3.0m. At present, the assembled galvanized thin-walled steel pipe greenhouse is the most.

Plastic greenhouse has stereotyped products since 1980s, mainly including GP series developed by China Agricultural Engineering Design Institute and PGP developed by Shijiazhuang Agricultural Modernization Research Institute of Chinese Academy of Sciences. The main product specifications are shown in Table 4.

2 the performance of plastic greenhouse plastic greenhouse is characterized by covering plastic film, which has the characteristics of good daylighting, uniform light distribution, easy entry of short wave radiation, but difficult penetration of long wave radiation and good tightness.

The main results are as follows: (1) the vertical light intensity in the greenhouse decreases gradually from high to low, and it is the lowest near the ground. The horizontal light intensity in the greenhouse is relatively uniform in the north-south extended greenhouse, and the east-west extended greenhouse in the south side is higher than that in the middle and north side. The greenhouse with single steel and hard plastic structure receives light better, while the greenhouse with single-family bamboo and wood structure receives poor light. In addition, the larger the span of the greenhouse is, the higher the scaffolding is, and the weaker the light in the shed is.

(2) when the temperature is fine, the temperature rises rapidly in the daytime and has a certain heat preservation effect at night. However, due to the lack of night heating measures, there are obvious diurnal and seasonal changes of temperature, and the lack of necessary environmental control equipment, most of them only adjust temperature and humidity through ventilation windows, and indoor environmental factors change greatly. On a sunny day, the sun will enter a rapid warming period when the sun comes out for 1 h, and a linear temperature rise period will enter at 8 h, with a heating rate of 5 ℃ per hour, and the heating rate slows down from 11 to 13:00. And reached the highest temperature, which could be more than 20 ℃ higher than the open field, and then began to decrease, and entered a rapid cooling stage after 15-17:00, with an average cooling rate of 5: 6 ℃ per hour. With the reduction of the internal and external temperature difference, the night cooling range will rapidly decrease, about 1 ℃ / h, and the room temperature is only 3-5 ℃ higher than that in the open field. Sometimes the indoor temperature is lower than the external temperature, which is called the "temperature inversion phenomenon". The temperature inversion phenomenon often occurs in the early spring or late autumn and the early morning breeze on a sunny day.

(3) humidity due to the good tightness of the film, the humidity in the shed is significantly higher than that in the open field, with an average daily increase of 3540% (Table 4Mel 10). In the northern region with obvious four seasons, due to the long low temperature period in winter and limited utilization time (only one month earlier or later than the open field), the development of plastic greenhouse is relatively slow, while it is widely used in warm areas or mild climate areas in the south. In soilless culture, the substrate culture is mainly composed of fruits and vegetables with longer growth period, and more leafy vegetables with fast growth speed and short cycle are produced by hydroponic culture.

Table 4 Specification table for plastic large skeletons of GP and PGP series

Table 4 diurnal variation of air humidity inside and outside the greenhouse

(3) Modern greenhouse

Modern greenhouse can achieve comprehensive control of various environmental factors to meet the requirements of crop growth and development. Plastic greenhouse and solar greenhouse can be said to be the form of protection facilities of "making use of nature", while modern greenhouse is the form of protection facilities of "creating nature". In addition to the large scale of the main structure, there are all kinds of environmental control equipment, including heating system. Heat preservation system, cooling system, humidification or dehumidification system, CO2 application system, forced ventilation system and natural ventilation system, light or shading system, fertilizer supply and water supply system, drainage rain collection system, protection system (insect prevention net, snow removal equipment), weather station, power system, control system, etc. Because the composition of the system is different and the equipment selection is different, the cost is quite different. expanding the greenhouse scale is the main way to reduce the equipment cost per unit area, and connecting the single-family greenhouse is an effective way to expand the greenhouse scale. large-scale is the trend of greenhouse.

The service life of modern greenhouse is mostly in 20-50 years, using hot-dip galvanized steel or aluminum profile as structural material, concrete as basic material and truss structure. Generally, the north-south direction extends to the east-west direction, the visible light area is large, and there is more light in winter, while the east-west direction extends to the north-south direction, resulting in uniform indoor temperature and light. Due to the different climatic characteristics of different countries and regions, especially the different disastrous weather conditions such as wind, snow and hail, there are great differences in greenhouse design. The greenhouse structures produced by different countries and some domestic manufacturers are as shown in Table 4mur11.

Modern greenhouse generally has a large building area and strong ability of environmental control, but the ability of indoor ventilation and summer cooling is low. The research shows that when the total span of the greenhouse is more than 40m, a high temperature "closed" area will appear in the middle of the greenhouse, which will affect the transport of CO2 and plant growth. therefore, it is necessary to add forced ventilation equipment or micro-spray system and cooling system (sunshade or spray). In addition, large multi-span greenhouse is difficult to implement external thermal insulation, rapid cooling at night, heating in winter consumes a lot of energy, in order to save energy, internal thermal insulation system is often used. In order to adjust the flowering period in the cultivation of flowers and some fruits and vegetables, it is necessary to adjust the light. Therefore, light supplement equipment should be added in the greenhouse. In order to control the occurrence of the disease, the ground needs film mulching to reduce the air humidity, and the ground is often hardened in soilless cultivation, which leads to the lack of source of CO2, which must be supplied by CO2 generator to meet the needs of light synthesis. In order to prevent the invasion of insect pests, an anti-insect net (about 30 mesh nylon net) should be set up at the vents and entrances of the greenhouse. In order to maintain a long-term and stable environment, it is also necessary to set up a power-matched ventilation, humidity control and heating system. Comprehensive environmental control is a complex system engineering, manual control and mechanical control are difficult to meet the requirements of economic production, and computer control system is the main form of modern greenhouse.

Table 4 Mui 11 greenhouse structure specifications produced by some domestic and foreign manufacturers

The equipment of modern greenhouse is relatively perfect, and the environmental factors of greenhouse can be controlled according to the requirements of crop growth and development, so as to achieve annual production and maintain stable yield, high yield and high quality of greenhouse crop production. However, the construction cost of greenhouse is high, and the combination with soilless cultivation technology can give better play to the production efficiency of greenhouse facilities, which is the main place for the development of soilless cultivation.

General requirements for the construction of solar greenhouses for soilless cultivation

1. When choosing the location of greenhouse buildings, in addition to paying attention to comprehensive conditions, the convenience of irrigation and drainage should be taken into account, especially the flow direction and treatment of disinfectant solution to avoid public hazards.

two。 In the greenhouse building, in addition to paying attention to daylighting and thermal insulation, there should also be good ventilation conditions, preferably with cooling facilities.

3. When determining the height, span and direction of the greenhouse, it should be determined according to the way of nutrient solution cultivation. The greenhouse with nutrient solution can adopt the greenhouse with east-west extension and light transmission facing south. In order to facilitate multi-layer frame seedling raising, the greenhouse height can be appropriately increased or semi-underground (below ground level 60~80cm). It is better to extend the nutrient solution in the north and south of the plastic greenhouse, and the span should be comprehensively considered according to the design requirements of the cultivation bed and building materials.

4. In the design of facilities, attention must be paid to strengthening Greenhouse Effect and optimizing the shed structure to absorb, accumulate and utilize solar radiation energy as much as possible. In the area of 35 °~ 40 °north latitude, the solar greenhouse should face due south, and the lighting angle should not be less than 25 °. In order to reduce the loss rate of light reflection, the front roof had better build a sphere with a ratio of sagittal height to span greater than or equal to 0.4663, and the three walls had better be insulated by heat insulation material or thick soil layer. The plastic greenhouse should be extended from north to south, the ratio of sagittal height to span should be about 0.3, and use thermal insulation film and cover thermal insulation paper quilt, grass quilt, quilt and so on. In addition, the facilities for nutrient solution cultivation are generally fixed, so the greenhouse or greenhouse should also be fixed. Because continuous cropping obstacles such as soil salt accumulation and soil infectious diseases generally do not appear in nutrient solution cultivation, which is beneficial to the use of fixed facilities.