Soilless culture is a new science and technology developed on the basis of plant mineral nutrition research. It uses chemical solution (nutrient solution) to cultivate plants without natural soil.
A brief history of soilless culture
Man's exploration of plant mineral nutrition can be traced back to Aristotle's era in 600 BC, but it is recognized that the earliest scientific report on plant mineral nutrition is the famous willow experiment published by Belgin Jan van Helmand in 1600. 1in the middle of the 9th century (1842), Wiegman and Polslov successfully cultivated plants with distilled water and salt for the first time, which proved that water-soluble salt is an essential substance for plant growth. But the most outstanding representative in this period should be Van Justus von Liebig (1803- 1873), who proved that carbon in plants comes from CO2 in the air, H and O come from NH3 and NO3-,and other mineral elements come from soil environment. His work completely denied the popular humus nutrition theory at that time, established the embryonic form of mineral nutrition theory, and was also the pioneer of modern "nutrition farming" theory.
1838, German scientist Slu wrangell determined that plants need 15 nutrient elements for growth and development. 1859, famous german scientists saxophone and Knoop established a method of cultivating plant mineral nutrition by solution, which is still in use today. On this basis, it has gradually evolved into a practical science and technology of soilless culture today.
The preparation of 1920 nutrient solution is standardized, but these are laboratory experiments and have not been applied to production. 1929, W.F.Gericke, a professor at the University of California in the United States, successfully cultivated a tomato with a height of 7.5 meters by using nutrient solution, and harvested the fruit 14 kg, which attracted great attention. It is considered as the beginning of soilless culture technology from experiment to practice.
From 65438 to 0935, some vegetable and flower growers carried out large-scale production practice under the guidance of Gericke. Soilless culture has developed to a commercial scale for the first time, with a maximum area of 0.8 hectares. At the same time, some techniques of sand culture and gravel cultivation were developed in the midwest of the United States, and hydroponics techniques soon spread to Europe, India and Japan. Professor Gericke also defined soilless culture as "hydroponics" (hydrar means "water" and ponics means "placement").
During the Second World War, hydroponics played a considerable role in production. Under the guidance of Professor Gericke, Pan American Airlines planted vegetables on the deserted Wake Island in the middle of the Pacific Ocean, and used soilless culture technology to solve the problem of fresh vegetables for flight passengers and soldiers. Later, the British Department of Agriculture became interested in hydroponics. 1945, the British Air Force in London began to carry out soilless culture in Habania, Iraq and Bahrain in the Persian Gulf, which solved the problem of eating vegetables by air from Palestine. Later, in Guyana, the West Indies and the barren sandy land of Central Asia, Kuwait Petroleum Company and other units used soilless culture to produce fresh vegetables for their employees.
Due to the continuous development of soilless culture in the world, the International Soilless Culture Society was established in the Netherlands in September, 1955. There was only one working group at that time, 12 members. By the time the fifth international conference on soilless culture was held in 1980, the number of members had increased to 300, distributed in 45 countries. According to incomplete statistics, there are more than 130 soilless culture research institutions in the world at present. The planting area is also expanding. In New Zealand, 50% of tomatoes are produced by soilless culture. In Italian horticultural production, soilless culture accounts for 20%. Strawberries, green peppers, cucumbers and tomatoes produced by soilless culture in Japan account for 66%, 52%, 37% and 27% of the total output respectively, with a total area of 500 hectares. The Netherlands has the largest soilless culture area, with 2500 hectares in 1986. At present, soilless culture technology has been applied and developed in more than 0/00 countries around the world.
The research and application of soilless culture technology in China started late, but the relatively primitive soilless culture technology has a long history. Raw bean sprouts and daffodils have been recorded for a long time (at the latest in the Song Dynasty), but more formal scientific research and production experiments have been carried out for nearly ten years. Shandong Agricultural University began to cultivate watermelons, cucumbers and tomatoes with vermiculite on 1975, all of which were successful. 1987, the extended area of Shengli Oilfield reached 6000m2. Soilless seedling raising technology has been widely used in China. In Chaoyang District, Beijing, the number of soilless seedlings has accounted for 33.5% of the total number of seedlings. 1985 A national conference was held in the Vegetable Research Institute of Hebei Academy of Agricultural Sciences, and the China Soilless Culture Research Group was established. 1986 and 1987 held national academic seminars with as many as 100 participants. 1988 in may, China attended the 7th annual meeting of the international soilless culture society held in the Netherlands for the first time, and delivered a paper at the meeting, which attracted the attention of many countries.
Second, the advantages of soilless culture
Soilless culture can develop rapidly in the world because this new cultivation technology has many advantages compared with conventional soil.
(1) High yield and good quality.
Soilless culture can give full play to the production potential of crops, and compared with soil culture, the yield can be increased by several times or dozens of times, as shown in 4-4- 1.
As can be seen from the above table, soil culture not only has low yield, but also consumes a lot of water.
The Department of Horticulture of Beijing Agricultural University conducted a soilless culture experiment of cucumber in greenhouse in autumn in Beijing. From July 30th to September 14, it took 46 days to water (nutrient solution) ***2 1.7 cubic meters. If soil culture is carried out, water it at least 5-6 times in 46 days, which requires 50-60 cubic meters of water. According to statistics, the water saving rate is 50-66.7%. The water-saving effect is very obvious, which is one of the effective measures to develop water-saving agriculture.
Soilless culture saves water and fertilizer. According to general statistics, the loss rate of soil culture is about 50%. In China's rural areas, due to the low water content of scientific fertilization technology, the fertilizer utilization rate is even lower, only 30-40%, and the nutrient loss is more than half. The process of fertilizer dissolving in soil and being absorbed by plants is very complicated, which not only loses a lot, but also loses different nutrients, so it is difficult to keep the balance between elements in soil solution. In soilless culture, all kinds of nutrient elements needed by crops are artificially prepared into nutrient solution, which not only will not be lost, but also can maintain balance. According to crop types and different growth stages of the same crop, scientific supply of nutrients can make crops grow healthily, have strong growth potential and give full play to their yield-increasing potential.
(3) Cleanliness and hygiene
Soilless culture uses inorganic fertilizer, which has no odor and does not need composting site. The application of organic fertilizer in soil cultivation, chemical fertilizer decomposition and fermentation, produces odor, pollutes the environment, and also causes the eggs of many pests to breed and endanger crops. Soilless culture does not have these problems. Especially indoor flower planting requires cleanliness and hygiene. In some high-end hotels or guesthouses, it is difficult to solve the problem of using organic flower fertilizer to pollute the environment in the past, and soilless flower cultivation will be solved.
(4) labor-saving and easy to manage
Soilless culture does not need intertillage, digging, weeding and other operations, which saves labor and effort. Watering and topdressing are solved at the same time, and the liquid supply system is regularly and quantitatively supplied, which is very convenient for management. When watering soil culture, it is a labor-intensive operation to open and block the border one by one, while soilless culture only needs to open and close the valve of the liquid supply system, which greatly reduces the labor intensity. Some developed countries have entered the era of microcomputer control, and the control of liquid supply and nutrient solution components is completely controlled by computer, which is almost similar to the way of industrial production.
(5) Avoid the obstacles of continuous cropping in soil.
In protected cultivation, the soil is rarely leached by natural rain, and the movement direction of water and nutrients is from bottom to top. Soil moisture evaporation and crop transpiration make the mineral elements in the soil move from the lower layer to the surface layer. Over the years, a large amount of salt has accumulated on the surface of soil, which is harmful to crops. Especially greenhouse cultivation, once built, it is not easy to move. Soil salt accumulation, after planting the same crop for many years, has always been a difficult problem to solve, resulting in soil nutrient balance and continuous cropping obstacles. As a last resort, we can only use the labor-intensive "foreign land" method to solve it. The application of soilless culture, especially hydroponics, has fundamentally solved this problem. Soil-borne diseases are also the difficulty of protected cultivation. Soil disinfection is not only difficult, but also consumes a lot of energy and costs considerable, and it is also difficult to disinfect thoroughly. If disinfectants are used, there is a lack of efficient drugs, and the residues of harmful components in disinfectants are harmful to health and pollute the environment. Soilless culture is an effective method to avoid or fundamentally eliminate soil-borne diseases.
(6) Make full use of space without geographical restrictions.
Soilless culture makes crops completely out of the soil environment, thus getting rid of the bondage of land. Cultivated land is considered as a limited, most precious and non-renewable natural resource, especially for some areas and countries lacking cultivated land, soilless culture has special significance. After soilless culture enters the field of biology, many deserts, wasteland or areas difficult to cultivate on the earth can be used by soilless culture. For example, in the Middle East and Mexico, people have built many plastic greenhouses on the beach, combined with seawater desalination system, and used soilless culture technology to produce fresh vegetables, which has become an oasis in the desert, bringing good news to solve the living difficulties of people in many poor areas on earth.
In addition, soilless culture is not limited by space, and vegetables and flowers can be planted on the flat roofs of urban buildings, which invisibly expands the cultivation area. According to the satellite survey of 1986, there are more than 6000 mu of flat roofs in Beijing, which will bring great economic and social benefits if fully utilized.
(seven) is conducive to the realization of agricultural modernization.
Soilless culture makes agricultural production get rid of the restriction of natural environment and can be produced according to people's will, so it is a controlled agricultural production mode. Farming according to quantitative indicators is conducive to mechanization and automation to a greater extent, thus gradually moving towards industrialized production methods. At present, Austria, the Netherlands, the Soviet Union, the United States and Japan all have hydroponic "factories", which are the symbols of modern agriculture. China Aviation Industry Import & Export Corporation introduced Japanese soilless culture equipment in 1986, and set up a small water-increasing factory, which showed people's interest in this new technology.
Third, the types and methods of soilless culture
There are many ways and means of soilless culture. Different countries and regions have different types and methods of soilless culture due to different levels of scientific and technological development, different local resource conditions and different natural environments.
At present, the commonly used classification method is based on the fixation method of crop roots. Generally, it can be divided into two categories: substrate-free cultivation and substrate cultivation (Table 4-4-3).
(1) hydroponic method
Hydroponics refers to the cultivation method in which plant roots directly contact nutrient solution without substrate. The earliest hydroponics is to soak plant roots in nutrient solution to grow, which will lead to hypoxia, affect root respiration and even lead to root death. In order to solve the problem of O2 supply, British Cooper put forward a hydroponic method called "nutrient membrane technology" in 1973. Its principle is to make a thin layer of nutrient solution (0.5- 1cm) continuously circulate in the roots of crops, which not only ensures the continuous supply of water and nutrients to crops, but also provides fresh O2 for the roots. NFT method can greatly simplify irrigation technology, and it is not necessary to calculate crop water demand every day, so that nutrient elements can be supplied in a balanced way. Root system is isolated from soil, which can avoid all kinds of soil-borne diseases without soil disinfection.
(2) Fog (gas) culture
Also known as aeration or fog culture. It compresses nutrient solution into aerosol, which is directly sprayed on the roots of crops, and the roots are suspended in the space of the container. Usually, polypropylene foam plastic plates are used to drill holes at a certain distance and plant crops in the holes. Two foam boards are obliquely built into a triangle to form a space, and the liquid supply pipeline passes through the triangle space and is sprayed on the hanging roots. Generally, spray it for a few seconds every 2-3 minutes, so that the nutrient solution can be recycled, and at the same time, ensure that the roots of crops have enough oxygen. However, the equipment cost of this method is too high, it needs to consume a lot of electricity, and there is no room for buffering. At present, it is limited to scientific research and application, and there is no mass production.
(3) substrate cultivation
Substrate culture is one of the most commonly used methods in soilless culture. It fixes the roots of crops in organic or inorganic substrates and provides nutrient solution to crops through drip irrigation or drip irrigation. The cultivation substrate can be packed in plastic bags or scattered in cultivation ditches or grooves. The nutrient solution of substrate culture is not circulated, which is called open-circuit system. The spread of diseases can be avoided through the circulation of nutrient solution.
Substrate culture has strong buffering capacity, no contradiction in water, nutrients and O2 supply, simpler equipment than hydroponics and fog culture, and even no need of power, with less investment and low cost, which is widely used in production. From the current situation in China, substrate cultivation is the most practical method.
Rock wool, which is widely used in many European countries, is composed of 60% diabase, 20% limestone and 20% coke, which are calcined and melted at a high temperature of 1600℃, then sprayed into fibers with a diameter of 0.005 mm, and then cooled and pressed into plates or various shapes. The advantage of rock wool is that it can form a series of products (rock wool plugs, blocks, plates, etc. ), easy to use and carry, and can be used many times after disinfection. However, it can not be reused after several years of use, and the waste rock wool is difficult to treat, which has become a public hazard in the Netherlands, which has the largest planting area of rock wool. Therefore, some people in Japan now advocate the development and utilization of organic substrates, which can be turned into soil as fertilizer without polluting the environment.
Four, the key points of soilless culture technology
No matter what type of soilless culture is adopted, several basic links must be mastered. In soilless culture, nutrient solution must be dissolved in water and then supplied to plant roots. In substrate culture, nutrient solution is poured into the substrate and then absorbed by crop roots. Therefore, it is necessary to know the physical and chemical properties of water quality, nutrient solution and substrate used.
(1) water quality
Water quality is closely related to the preparation of nutrient solution. The main indicators of water quality standards are electrical conductivity (EC), pH value and content of harmful substances.
Electrical conductivity (EC) is an index of salt concentration in solution, usually expressed in millisiemens (mS). The salt tolerance of various crops is different, and the ones with strong salt tolerance (EC= 10mS) are beet, spinach and cabbage. Moderate salt tolerance (EC=4mS), such as cucumber, kidney bean and sweet pepper. Soilless culture requires strict water quality, especially hydroponics. Because it is not as buffering as soil culture, many elements are lower than the allowable concentration standard of soil culture, otherwise it will be poisoned. Some farmland water may not be suitable for soilless culture. Collecting rainwater for soilless culture is a good method. The pH value of soilless culture water should not be too high or too low, because the requirements of general crops for the pH value of nutrient solution should be neutral. If the pH value of water itself is low, it should be adjusted with acid or alkali, which is both a waste of medicine and time.
(2) nutrient solution
Nutrient solution is the key to soilless culture, and different crops need different nutrient solution formulas. At present, there are many formulas published in the world, but all of them are similar, because the original formula originated from the analysis of the chemical composition of soil extract. In the formula of nutrient solution, the biggest difference is the ratio of nitrogen and potassium. Table 4-4-4 introduces the formulas adopted by different scientists from 1950s to 1980s for reference.
The purity and cost of chemical reagents should be considered in the preparation of nutrient solution, and chemical fertilizers can be used to reduce the cost in production. The preparation method is to prepare the mother liquor (original source) first, and then dilute it, which can save containers and facilitate storage. Calcium-containing substances need to be placed in a separate container. When in use, the mother liquor is diluted and mixed with the diluent of calcium-containing substances to avoid precipitation as much as possible. After determination, the PH value of nutrient solution must be adjusted to the range suitable for crop growth, and special attention should be paid to the adjustment of pH value when adding water to avoid poisoning.
(3) Physical and chemical properties of the matrix
There are many substrates for soilless culture, which are listed in Table 4-4-3 for reference. According to the local source of the substrate, we can choose materials with abundant and easily available raw materials, low price and good physical and chemical properties as the substrate for soilless culture. The requirements of soilless culture for substrates are:
1. A solid substance with a certain size. This will affect whether the matrix has good physical properties. The size of matrix particles will affect the capacity. Porosity, air and water content. According to the particle size, it can be divided into five grades, namely:1mm; 1-5mm; 5 5- 10/0mm; 10-20mm； 20-50 mm, which can be selected according to the species of cultivated crops, root growth characteristics and local resources.
2. It has good physical properties. The substrate must be loose, water-retaining and fertilizer-retaining, and breathable. Wu Zhixing of Nanjing Agricultural University and other researchers believe that the ideal substrate for vegetable crops is 0.5- 10 mm, with total porosity >: 55% and bulk density of 0. 1-0.8g? Cm-3, the air volume is 25-30%, and the water-gas ratio of the substrate is 1: 4.
3. Stable chemical properties, no harmful components and no change in nutrient solution. The chemical properties of the matrix mainly refer to the following aspects:
PH value: The pH value of the reaction substrate is very important. It will affect the pH value and composition changes of nutrient solution. PH = 6-7 is considered as an ideal substrate.
Electrical conductivity (EC): It reflects the concentration of ionized salt solution, which directly affects the composition of nutrient solution and the absorption of various elements by crop roots.
Buffering capacity: it reflects the buffering capacity of the substrate to quickly change the pH value of fertilizer, and the stronger the buffering capacity, the better.
Base substitution: refers to the content of replaceable cations measured at pH = 7. Generally speaking, there are many substitutes, such as bark, sawdust and peat. Vermiculite has many substitutable substances in inorganic matrix, but there are almost no substitutable substances in other inert matrices.
4. The matrix needs to be easily available, widely available and low in price. The Horticultural Research Institute of Zhejiang Academy of Agricultural Sciences chose rice bran ash (fuel residue used for family dinner in rural areas) widely existing in southern rural areas as soilless culture substrate to cultivate tomatoes, with good results and greatly reduced costs.
In soilless culture, the role of substrate is to fix and support crops; Adsorption nutrient solution; Enhance the permeability of root system. Substrate is a very important material, which is directly related to the success or failure of cultivation. Substrate cultivation must be strictly selected according to the above aspects. The Department of Horticulture of Beijing Agricultural University conducted an experimental study of 1986- 1987. In the process of cucumber substrate cultivation, there is a significant interaction between nutrient solution and substrate, which affects each other and complements each other. Therefore, the formula of hydroponic nutrient solution, especially when using organic substrate, will be affected by the element content and substitution degree of the substrate itself, thus changing the cultivation effect of the formula. This is a problem that should be considered, and it cannot be copied mechanically.
(4) liquid supply system
There are many ways to supply liquid for soilless culture, including NFT irrigation, flood irrigation, double-wall pipe irrigation system, drip irrigation system, siphon method, spray method, artificial irrigation and so on. To sum up, it can be divided into two categories: circulating water (close system) and non-circulating water (open system). At present, nutrient solution film and drip irrigation are widely used in production.
1. nutrient solution membrane method (net)
(1) Prepare three mother liquor storage tanks (tanks). One contains calcium nitrate mother liquor, the other contains other nutrients, and the other contains phosphoric acid or nitric acid to adjust the pH value of the nutrient solution.
(2) Liquid storage tank. Store the diluted nutrient solution, pump the solution from the high end of the culture bed and reflux it from the low end. The size of the liquid tank is related to the cultivation area. General 1000 square meters requires that the capacity of the liquid storage tank is 4-5 tons. Another function of the liquid storage tank is to recover the nutrient solution returned from the return pipeline.
(3) filtering device. Filters are required to be installed at the water inlet and outlet of nutrient solution to ensure that the nutrient solution is clean and will not block the liquid supply system.
2. Irrigation methods of drip irrigation system
(1) Prepare two concentrated nutrient solution tanks to store mother liquor. One jar contains calcium, and the other jar contains other elements that do not contain calcium.
(2) concentrated acid tank. Adjust the PH value of nutrient solution by industry.
(3) Liquid storage tank. Used to preserve nutrient solution diluted as required. The general area is 300-400 square meters, and the volume of the liquid storage tank is 1- 1.5 tons. The height of the liquid storage tank is related to the liquid supply distance. As long as it is higher than 1 meter, it can provide a distance of 30-40 meters. If pumping is used, the height of the liquid storage tank is not limited. It can even be set underground.
(4) Pipeline system. Use black plastic pipes with various diameters instead of white to avoid algae breeding.
(5) dripper. Liquid supply devices fixed near the crop rhizosphere are usually used with orifice emitters and linear capillary tubes. The flow rate of orifice dripper in low-pressure liquid supply system is uneven, but the capillary is relatively uniform. But the same problem is that it is easy to be blocked, so a filter must be installed at the entrance and exit of the liquid storage tank to filter out impurities.
The prospect of verb (verb's abbreviation) soilless culture
Historically, the symbol of agricultural civilization is the degree of human intervention and control on crop growth and development. Practice has proved that it is easy to control the environmental conditions of the aboveground part of crops under the condition of conventional soil culture, but it is difficult to control the underground part (root control). The emergence of soilless culture technology has enabled human beings to accurately control all environmental conditions for crop growth, including inorganic nutrition conditions, thus making it possible for agricultural production to completely get rid of the constraints of natural conditions and develop into automation, mechanization and factory production in full accordance with human wishes. This will increase the output of crops by several times, dozens or even hundreds of times.
From the perspective of resources, cultivated land is extremely valuable non-renewable resources. Because soilless culture can develop and utilize many uncultivated land, the non-renewable cultivated land resources have been expanded and supplemented, which has far-reaching significance for alleviating and solving the increasingly serious cultivated land problem on the earth. Soilless culture can not only turn many deserts on the earth into oases, but in the near future, oceans and space will also become new areas for development and utilization. The United States listed soilless culture as one of the top ten high-tech exchange meetings to be developed by the country in this century. It is a research report on space plant cultivation, which can only be cultivated without soil. Therefore, soilless culture technology has been used by many scientists as a powerful means to study Japan's "cosmic farm", and what people call space-age agriculture is no longer an incredible problem.
The problem of water resources is also a big problem that threatens the survival and development of human beings in the world. Not only in arid areas, but also in developed and densely populated cities, the problem of water shortage is becoming more and more prominent. With the continuous growth of population, all kinds of water resources are overexploited, and some areas are almost exhausted. Therefore, controlling agricultural water use is one of the water-saving measures. Soilless culture avoids the leakage and loss of a large amount of water, making it difficult to compensate the reclaimed water resources. It will surely become the only way for water-saving agriculture and agriculture in dry areas.
Admittedly, there are also many problems in the process of soilless culture technology moving towards practicality. The outstanding problems are high cost and large one-time investment; At the same time, it also requires high management level, and managers must have certain scientific knowledge, which can not be done everywhere.
Theoretically speaking, it is also an urgent problem to further study the physiological indexes of mineral nutrition status and reduce the blindness in management. In addition, the prevention and control of pests and diseases in soilless culture, the disinfection of matrix and nutrient solution, the treatment of waste matrix, etc. Further research and solution are needed.
Soilless culture has just started in China, and it has not been widely used in production, especially in facilities and liquid supply system engineering itself, and has not yet formed a special production industry. Due to the influence of various factors, cultivation technology and agricultural engineering technology can not be coordinated and synchronized, which leads to the development of soilless culture technology in China is not as fast as that in developed countries. However, with the development and perfection of science and technology, more importantly, the inherent advantages of this new technology show people an infinitely broad development prospect.