Principle of soilless culture

1. Definition of soilless culture

Soilless culture refers to the use of artificial substrate instead of natural soil or substrate after planting only when raising seedlings; It is a planting technology that directly applies solid fertilizer to provide nutrition for crops by using nutrient solution containing essential elements for plant growth and development or irrigating crops only with clean water, and can make plants normally complete the whole life cycle. In short, soilless cultivation is a method of growing plants without natural soil. Solid matrix or nutrient solution replaces natural soil to provide crops with good rhizosphere environmental conditions such as water, fertilizer, gas and heat, so as to complete the whole life cycle of crops from seedling stage. Because soilless cultivation used nutrient solution earlier and longer, in the early stage, soilless cultivation was called nutrient solution cultivation, hydroponic culture, hydroponics, solution cultivation, nutrient solution cultivation and so on. Soilless cultivation is a production technology representing today's agricultural modernization. Compared with soil cultivation, the main advantages of soilless cultivation are that it can overcome the obstacles of soil continuous cropping, high yield, good quality, high commodity value of cultivated crops, save water, fertilizer and labor, less diseases and pests, and make full use of land resources. It can be used on islands, rocky mountains, Antarctica Crop production is carried out in the Arctic and in all places unsuitable for general agricultural production. However, the disadvantages of most soilless cultivation types are large investment in one-time equipment, high power consumption, high fertilizer cost, and the preparation, adjustment and management of nutrient solution require talents with some specialized knowledge, which is highly technical. In recent ten years, China has widely promoted and applied the soilless cultivation technology of organic matrix culture, using the organic matrix containing certain nutrients as the carrier, watering low concentration nutrient solution or phased nutrient solution in the cultivation process, sometimes applying organic solid fertilizer without nutrient solution and reasonable irrigation, which greatly reduces the one-time investment and production cost and simplifies the operation technology.

2. Classification of soilless culture

Soilless culture has a history of more than 160 years since the early experimental research. In the process from laboratory to large-scale commercial production and application, it has developed from the basic model of soilless cultivation by German scientists sax and Knoop in the mid-19th century to a wide variety of soilless cultivation types and methods at present. Many people have classified it from different angles, but it is difficult to classify it scientifically and in detail. Now the more common classification method is to divide it into two types: non-solid substrate cultivation and solid substrate cultivation according to whether the cultivation bed uses solid substrate materials or not The facility structure and the materials for fixing plant roots are different, and can be divided into many types.

Non solid substrate culture

Soilless cultivation with non-solid substrate means that the roots grow directly in nutrient solution or moist air containing nutrients. In the rhizosphere environment, solid substrate is generally not used except for seedling raising. Non solid substrate cultivation can be divided into two types: hydroponic culture and fog culture.

1) Hydroponic culture

Hydroponic culture refers to the soilless cultivation method in which crop roots grow directly in the nutrient liquid layer. It can also be divided into various forms according to the depth of nutrient solution layer: nutrient solution membrane technology (NFT system) for planting products with 1-2 cm shallow flowing nutrient solution; Deep water culture technology (DFT) with liquid layer depth of 6-8 cm; In a 5-6 cm deep nutrient solution liquid layer, a piece of upper layer nonwoven foam board is placed, and the root is grown on the wet non-woven fabric floated sheet capillary hydroponics (FCH). The semi substrate culture represented by the "hydroponic plant facility" developed and applied by Grick in the early stage is actually a form of hydroponic culture.

2) Fog culture

Fog culture, also known as spray culture or air culture, spray the nutrient solution directly onto the roots of crops. The roots are suspended in a container, equipped with an automatic timing spray device inside the container, spraying the nutrient solution from the spray head to the root surface of the plant every once in a while, and at the same time, it solves the root system's demand for nutrients, water and oxygen. Due to the large investment of fog culture equipment, the management is not very convenient, and the root temperature is easy to be affected by the air temperature, with a large variation range. It has high requirements for control equipment and is rarely used in production. Another type of fog culture is that some roots grow in the shallow nutrient solution layer, and the other roots grow in the fog nutrient solution space, which becomes semi fog culture. Half fog culture can also be regarded as a kind of hydroponic culture.

Solid substrate cultivation

Soilless cultivation in solid substrate is referred to as substrate culture for short. It refers to the method that crop roots grow in various natural or synthetic solid substrate environments, fix roots through solid substrate, and supply nutrition and oxygen to crops. Substrate culture can well coordinate the contradiction between water and gas in rhizosphere environment, and has less investment, which is convenient for local production.

Matrix culture can be divided into different types according to the selected substrates. For example, matrix culture with organic substrates such as peat, straw and coconut velvet as the culture substrate is called organic matrix culture, and inorganic matrix culture such as rock wool culture, sand culture and gravel culture.

Matrix culture can also be divided into trough matrix culture, bag matrix culture and three-dimensional matrix culture according to different cultivation forms. Trough substrate culture refers to the method of putting the solid substrate for cultivation into the planting trough of a certain container to cultivate crops. Generally, trough substrate culture is used for organic substrate culture and heavy substrate with large bulk density; Bag matrix culture refers to the method that the solid matrix for cultivation is put into plastic bags and arranged on the ground to plant crops; Three dimensional substrate culture refers to the method that the solid substrate is loaded into a long bag shaped or cylindrical three-dimensional container, set up and arranged in the greenhouse, and spiral holes are opened around the container to plant small plant crops. Generally, bag matrix culture and three-dimensional matrix culture can be used for light matrix with small bulk density, such as rock wool, vermiculite, coconut velvet matrix, straw matrix, etc.

2. Function and application of soilless culture

The main advantage of soilless cultivation is that it can avoid soil borne diseases and pests and continuous cropping obstacles, which is one of the main problems in greenhouse crop production. Crops have strong growth, high yield, good quality, high fertilizer utilization efficiency, water conservation and less diseases and pests. It can produce crops in places that are not suitable for general agricultural production, reduce labor intensity, and enable women and the elderly to engage in such production activities. It is also a good way to carry out agricultural education for urban students.

The disadvantages of soilless cultivation are large investment in one-time equipment, large power consumption, high fertilizer cost, and the preparation, adjustment and management of nutrient solution require people with some expertise. Therefore, it is difficult to popularize it in economically underdeveloped areas. Although the organic ecological soilless cultivation eliminates the links that are not easy for farmers to master, such as the preparation and adjustment of nutrient solution, the organic fertilizer used needs to be treated strictly, and the water management also needs some planting experience.

As a new modern agricultural technology, soilless cultivation has many incomparable advantages and broad development prospects, but there are also some defects and deficiencies. Only by correctly evaluating soilless culture technology and fully understanding its characteristics, can we give full play to the role of soilless culture, develop strengths and avoid weaknesses, and properly and truly apply this new technology. Soilless cultivation is mainly used in the following areas

1. Protected land production with serious soil continuous cropping obstacles

With the adjustment of rural industrial structure, vegetable cultivation in protected areas has developed rapidly. Frequent continuous cropping of the same vegetable can easily lead to soil continuous cropping obstacles, such as salinization, acidification, serious soil borne diseases and so on. The traditional treatment methods, such as soil replacement, soil disinfection, irrigation and salt washing, have great limitations. For the resulting decline in vegetable yield, quality and efficiency, vegetable farmers generally adopt the measures of increasing the amount of chemical fertilizer and uncontrolled use of pesticides, resulting in rising production costs and increasingly serious environmental pollution, which directly affect the production efficiency and sustainable development of protected horticulture. Soilless cultivation technology, as an effective way to solve the obstacles of soil continuous cropping in greenhouse and other horticultural protection facilities, has been widely used all over the world. Today, with the rapid development of protected horticulture in China, it is of great significance. Various soilless cultivation forms suitable for China's national conditions provide a technical guarantee for the sustainable development of protected horticulture.

2. Local production of land unsuitable for traditional agronomic cultivation

Soilless cultivation has no special requirements for land. Non cultivated land can be used. Soilless cultivation can be carried out in barren mountains, wasteland, beaches, islands, even deserts, Gobi and other places where traditional agricultural cultivation is difficult and easy. It breaks the dependence of plants on soil. Vegetables can be produced by soilless cultivation in remote areas such as desert, wasteland and reef island to meet the needs of garrison officers and soldiers, oil field or mining workers.

3. High grade vegetable production

Soilless cultivation can better meet the requirements of plant growth and development on environmental conditions, and can supply nutrients according to the law of plant growth and development. Therefore, compared with soil cultivation, soilless cultivation vegetables have higher commodity quality, flavor quality and nutritional quality. Soilless cultivation is mostly carried out in protective facilities relatively isolated from the external environment, and does not contact with the soil, so there are slight diseases and pests, and less or no pesticides can be applied in the planting process. No weeds, no herbicides. High fertilizer utilization rate. After China's entry into WTO, the vegetable industry, like other industries, is under great competitive pressure. If Chinese vegetables want to occupy a place in the international market, they must improve the commodity quality of vegetables. At the same time, with the improvement of people's living standards and the enhancement of health awareness, the demand for high-grade vegetables is also increasing. Soilless cultivation is recognized as one of the ways to produce high-quality vegetables and improve the grade of vegetables.

4. Application in economically developed areas

Economically developed areas have the ability to spend more money on soilless cultivation, form economies of scale, and produce high-quality high-grade vegetable products through soilless cultivation. Due to the high level of local consumption, these vegetables can be supplied to shopping malls, supermarkets or hotels at high prices, so as to obtain higher profits and achieve high input and high output.

5. Application in home gardening

Ordinary urban residents can use small soilless cultivation devices to plant flowers and vegetables in their own courtyards, balconies and roofs. It is not only entertaining, but also has certain ornamental and edible value, which is convenient for operation, clean and sanitary, and can beautify the environment. Cultivation in office, hall and other indoor spaces can beautify the environment and relieve people's mental pressure. This is a very interesting form of "urban agriculture" and "indoor gardening".

6. Application in agricultural sightseeing park and high-tech demonstration park

Sightseeing agriculture is a new industry and a new tourism project rising in recent years. The high-tech demonstration park is a window to show people the future agriculture. At present, the most widely used cultivation methods in these parks are soilless cultivation with high scientific and technological content, especially some beautiful and unique three-dimensional cultivation methods, which are more favored by people. Soilless Cultivated Plants are novel, intuitive, vivid and persuasive. They can help primary and secondary school students understand the knowledge of plant growth and development, root absorption and mineral nutrition, and cultivate young people to learn science and love science. Many existing modern agricultural science and technology parks have been listed as science and education bases of Education departments, It has played a positive role in students' understanding of modern agricultural science and technology and contacting the reality of agricultural production.

7. Application in space agriculture

With the development of space industry and the need of human living in space, soilless cultivation and planting green plants in space can be said to be the most effective way to produce food. Soilless cultivation technology plays an important role in the research and application of aerospace agriculture. For example, Kennedy Space Center has done a lot of research and application work on the production of food needed by astronauts in space. The cultivation of some food crops and vegetable crops has been successful and achieved good results.