How to choose a substrate for soilless cultivation
There are many substrates for soilless cultivation, which are all excavated and selected according to the conditions of various places. The types of substrates mentioned here refer to commonly used substrates and are for reference only.
1. type
The classification of substrates is based on the morphology, composition, shape, etc. of substrates. The following is a classification system for soilless substrates, modified from Mr. Teruo Ikeda's classification system.
In this system, the inorganic matrix and the organic matrix are collectively referred to as a single matrix in order to correspond to the mixed matrix.
2. Properties of Various Soilless Culture Substrates
The properties of the substrate mainly refer to the physical and chemical properties related to the cultivated plants. Physical properties include capacity, porosity, size-to-void ratio, particle size, etc.;
Chemical properties include chemical stability, acidity and alkalinity, cation substitution capacity, buffer capacity, conductivity, etc. Sometimes it also involves some important functions of substrate, especially water, in plant life activities.
(1) water
①The role of water Water is the source of life. The important role of water in plant life activities mainly includes the following aspects:
First, water is an important component of protoplasm;
Second, water is the raw material for photosynthesis and hydrolysis of organic matter;
Third, water is the solvent and medium of biochemical reactions;
Fourth, water maintains the inherent posture of plants: this is a necessary condition for plants to perform various physiological activities such as cell division, growth and differentiation, gas exchange and utilization of light energy;
Fifth, water transpires through the stomata of the leaves, reducing the temperature inside the plant and maintaining a relatively constant body temperature in hot weather.
②The characteristics of water as the substrate of soilless cultivation Water is an invisible and tasteless transparent liquid, and it is a very good solvent for many substances. Because of this, water as a soilless culture substrate has the following characteristics:
a. Sufficient water and fertilizer but limited oxygen The various nutrients needed for plant growth can be dissolved in the water, and the plants can easily absorb them. However, the oxygen content in the water cannot meet the needs of the respiration of the plant roots. Therefore, it is necessary to artificially inflate or make the water flow in contact with the air to increase its dissolved oxygen.
b. The hydrogen ion concentration (pH) of water is easy to adjust, but the root exudates are easy to accumulate. Water can be used to increase the concentration of hydrogen ions (acid) with hydrochloric acid or acetic acid, and to increase the concentration of hydroxide ions (alkali) with sodium hydroxide or potassium hydroxide. The concentration increases.
The concentration of acid or alkali commonly used to adjust the hydrogen ion concentration of water is 0.1 mole/liter.
The root system in the hydroponic medium absorbs nutrients in the water on the one hand, and discharges some organic matter into the water on the other hand, and accumulates in the water. A considerable part of these organic matter is the habitual exudation substances formed by plants growing in the soil for a long time. The function of this kind of substances is mainly to dissolve or complex the nutrients that are not easily absorbed by the roots in the soil; Some "waste" of the root system, such as toxins, have a corresponding spatial distribution in the soil and will not affect the normal absorption function of the root system. In the water matrix, it is easy to be sucked into the body again by the root system, so repeated absorption, excretion, and a vicious cycle of reabsorption and re-excretion are not conducive to the normal growth of the root system and normal physiological functions. The solution is to frequently replace the nutrient solution or circulate the nutrient solution.
c. Nutrients are in close contact with the root system and are easily absorbed by the root system, but there are two main conditions for the root system to not anchor the plant to absorb nutrients. One is that the root system actively extends to the position of the nutrient and contacts the nutrient; Under the action of the root system, it moves around the root system and touches the root system. The root system is suspended in the nutrient solution, and nutrients can easily reach the root system during frequent physical movements. Therefore, even though the nutrient concentration in the solution is very low, if the concentration of macroelements reaches the micromolar level, it is easily absorbed by the root system, even Plants grow fastest in this nutrient solution. But the nutrient solution cannot support the huge body of the plant. As long as the weight of the plant exceeds the buoyancy of the water in the nutrient solution, the plant will inevitably sink. In order to anchor the plants, someone uses a trellis to support the plants, allowing the roots to pass through the mesh of the trellis and enter the nutrient solution. After the plant grows up, the root system is elongated, and the appropriate water-air ratio cannot be obtained in the nutrient solution. To solve this problem, some supports can be placed between the trellis supporting the plant and the trough containing the nutrient solution, and gradually increase the height. Make the tip part of the root system always in the nutrient solution, and the rest part between the liquid surface and the grid. The water vapor in this part of the space is relatively large, which can meet the ratio requirements of the root system's water and gas.
(2) fog
A major problem with water substrates is poor aeration.
The best way to solve this problem is to spray an aqueous solution of nutrients into a mist, and the root system is suspended in the space with this nutrient. Adequate water vapor and nutrients can be reached around the root system, and at the same time, the aeration conditions around the root system can be fully satisfied. It can be said that this method of nutrient mist is the best method to meet the ratio of water, nutrients and gas in the root system, and it has not been officially used in my country at present.
(3) sand
Sand is a commonly used substrate in soilless culture. Especially the desert area is the only substrate that has no choice.
Sand as a soilless cultivation substrate has the following characteristics:
①Constant water content No matter how much water you pour into the sand, as long as the surrounding drainage is good, it will allow the excess water to seep out quickly and maintain its corresponding water content; no matter whether you water or not, as long as there is enough water in the bottom of the sand , it can make water reach a relatively high part through siphon action, and maintain an appropriate water content.
The water content of sand depends on its particle size, and the particle diameter of sand is 0.06-2 mm. The finer the particles, the higher the water content, but in general, sand drains easily.
②No water and fertilizer retention, good air permeability Sand is mineral, compact texture, almost no pores, water is kept on the surface of sand grains, so the fluidity of water is large, and the nutrients dissolved in water are easily lost with the loss of water . After the water and nutrients in the sand are lost, the pores between the particles are filled with air. Compared with clay minerals, sand has good air permeability.
③Provide a certain amount of potassium fertilizer, and the concentration of hydrogen ions is affected by sand quality. Commonly used sand contains some potassium-containing inorganic substances, which can slowly dissolve and provide a small amount of potassium fertilizer. Even the roots of some plants can secrete some organic matter, which dissolves or chelates potassium in the sand so that it can be absorbed by the roots. Plants that can grow in sand are usually not deficient in potassium.
Some sand is composed of calcareous minerals. The hydrogen ion concentration of this sand is less than 100 nmol/liter (pH greater than 7). If it is not modified, it is not suitable for general plants. The modified method can be solved by adjusting the hydrogen ion concentration of the nutrient solution. It is best to use the sand of the river bank alluvial land or the sand of the aeolian land.
④ Heavy sand is not suitable for soilless cultivation on high-rise buildings. However, it is still an ideal soilless culture substrate because of its abundant sources, low cost, and economic benefits for grassroots planting.
⑤Safe and hygienic Sand seldom spreads diseases and insect pests, especially river sand, which does not need to be disinfected when it is used for the first time.
(4) Gravel
Gravel is the same as sand, but the particle diameter is thicker than sand, larger than 2 mm. The substrate surface is more or less rounded.
Its ability to retain water and fertilizer is not as good as that of sand, but its air permeability is stronger than that of sand. Some gravels contain calcareous matter, and such gravels cannot be used as soilless culture substrates.
(5) Ceramsite
Ceramsite is a shale material that is fired at about 800°C and has a relatively uniform aggregate size, pink or red. The internal structure of ceramsite is loose, with many pores, similar to honeycomb, with a bulk density of 500 kg/m3, light texture, and can float on the water surface in water. It is a good soilless cultivation substrate.
As a soilless cultivation substrate, ceramsite has the following characteristics.
① Good water retention, drainage and air permeability. The internal pores of ceramsite are filled with air when there is no water. When there is sufficient water, part of the water is absorbed and part of the gas space is still maintained. When the water around the root system is insufficient, the water in the pores diffuses through the surface of the ceramsite into the pores between the ceramsite for the root system to absorb and maintain the air humidity around the root system.
The size of ceramsite aggregates is related to its water absorption and air permeability, and also related to the physiological requirements of the root system. Generally, when ceramsite with larger aggregates is used as the soilless cultivation substrate, the pores between the aggregates are large. Compared with the ceramsite with small aggregates, the air humidity and moisture content are smaller. By choosing the size of the ceramsite, you can get the good water conditions and aeration conditions required by the plants.
② Moderate fertilizer retention capacity Many nutrients can not only adhere to the surface of ceramsite, but also enter the pores inside the ceramsite for temporary storage. When the nutrient concentration on the surface of ceramsite decreases, the nutrients in the pores move outward to meet the needs of the root system to absorb nutrients demand. Just like the water retention performance of ceramsite, the fertilizer retention capacity of ceramsite is in a moderate range compared with other substrates.
③Hydrogen ion concentration of chemically stable ceramsite
It is 1~12590 nanomole/liter (pH9~4.9), and has a certain amount of cationic substitution (60~210 mmol/kg). Different sources of ceramsite have differences in their chemical composition and physical properties (Table 4-1, Table 4-2), but they are all suitable as soilless culture substrates.
④ Safe and hygienic Ceramsite rarely breeds insect eggs and pathogens. It has no peculiar smell and does not release harmful substances. It is suitable for soilless cultivation of flowers decorated in buildings such as homes and restaurants.
⑤ Not suitable for soilless cultivation of plants with slender roots
The diameter of matrix ceramsite aggregates is larger than that of sand, perlite, etc. For plants with thick root systems, the water and air environment around the root system is very suitable, but for plants with slender root systems such as rhododendrons, the large pores between ceramsites are easy for roots to grow. Air-dry, therefore, should not be used to grow this type of plant.
(6) Vermiculite
Vermiculite is hydrated magnesium aluminum silicate, which is formed when mica-like inorganic substances are heated to 800-1000 °C. Mica-like inorganic substances contain water molecules, and when heated, the water molecules expand into water vapor, which bursts the hard inorganic substance layer and forms small, porous, spongy nuclei. The volume of vermiculite expanded by high temperature treatment is 18-25 times of the original, the volume density is very small, 80 kg/m3, and the porosity is large. Vermiculite used as a soilless culture substrate has the following characteristics:
① Strong water absorption, strong ability to retain water and fertilizer Vermiculite can absorb 100-650 liters of water per cubic meter, which is 1.25-8 times more than its own weight. Among the soilless cultivation substrates introduced in this book, vermiculite has the largest water absorption capacity, cation replacement capacity of 10 mmol/kg, and strong water and fertilizer retention capacity.
② The porosity is large (95%), and the breathable vermiculite absorbs water to reduce the gas space, and the vermiculite that reaches the saturated water content has poor air permeability. Because vermiculite has a large gas space and strong water absorption capacity, the water content of vermiculite can be artificially adjusted to achieve the best water-air ratio suitable for certain flowers and plants. Vermiculite is a good soilless substrate for most flowering plants.
③The hydrogen ion concentration is 1-100 nanomole/liter (pH9-7), which can provide a certain amount of potassium, a small amount of calcium, magnesium and other nutrients. These properties are determined by the chemical composition of vermiculite.
The chemical composition of vermiculite is (Mg2+, Fe2+, Fe3+)3[(Si, Al)4O10](OH)2·4H2O. Although vermiculite contains hydroxide ions, so that the concentration of hydrogen ions is less than 100 nmol/L (greater than pH7), due to the strong permeability of the matrix, the roots of most flower plants can be adjusted by the concentration of hydrogen ions in the nutrient solution. Get a good living environment.
④Safe and hygienic Vermiculite is formed at high temperature and has been sterilized. When new vermiculite is used, it will not be sterilized and will not infect pathogenic bacteria and insect eggs. The used vermiculite can be sterilized by high temperature, or sterilized with 1.5 g/L potassium permanganate or formalin (available in chemical reagent stores) and can be used continuously.
Vermiculite itself has no peculiar smell and does not emit harmful gases.
⑤ It is not suitable to use vermiculite for a long time, its structure will be broken, the porosity will be reduced, and the drainage and air permeability will be reduced. Therefore, it cannot be under heavy pressure during transportation and use. Generally speaking, if the vermiculite is used 1-2 times, it can no longer be used to plant the same kind of flowers, but flower plants with slender root systems should be replanted.
(7) perlite
Perlite is a mineral formed from siliceous volcanic rocks, named for its pearl-shaped spherical cracks. The water content of siliceous volcanic rock is about 2% to 5%. When crushed and heated to about 1000°C, it expands to form expanded perlite for soilless cultivation, and its bulk density is small, 80 to 180 kg/m3. This mineral has a closed cellular structure.
①Characteristics of perlite
a. Good air permeability and moderate water content The porosity of perlite is about 93%, of which the air volume is about 53%, and the water holding capacity is 40%. When watered, most of the water stays on the surface and flows easily due to the small water tension. Therefore, perlite is easy to drain and easy to aerate.
Although the water absorption of perlite (4 times its own weight) is not as good as that of vermiculite, when there is water in the lower layer (such as in an anti-seepage flowerpot), perlite can transfer the water in the lower layer through the water conduction between the particles. Draws in the perlite throughout the pot and maintains proper permeability. Its water content has fully met the needs of plant root life. Therefore, it is better to choose perlite than vermiculite when cultivating some flowers that have strict requirements on the ratio of water and air. Especially when cultivating some acid-loving southern flowers, perlite can better reflect its advantages.
b. The hydrogen ion concentration of chemically stable perlite is 31.63-100 nmol/liter (pH7.5-7.0).
The cation substitution amount of perlite is less than 1.5 mmol/kg, and it has almost no nutrient absorption capacity. Most of the nutrients in perlite cannot be absorbed and utilized by plants. Its hydrogen ion concentration is higher than that of vermiculite, which is one of the reasons why it is more suitable for planting acid-loving flowers in the south.
c. It can be used alone as a soilless cultivation substrate, or it can be mixed with peat, vermiculite, etc. The related mixed substrates will be introduced in the following chapters.
② Problems that should be paid attention to when using perlite
First, after the perlite is poured into the nutrient solution, it is easy to grow green algae on the surface exposed to light. In order to control the growth of green algae, you can replace the perlite on the surface, or turn it over frequently, or avoid light.
Second, perlite dust is highly irritating to the throat (throat), so care must be taken. It is best to spray it with water before use to prevent dust from flying.
Third, the specific gravity of perlite is lighter than that of water, and it will float on the water surface when there is a lot of rain. As a result, the contact between perlite and the root system is not reliable, it is easy to damage the roots, and the plants are prone to lodging. Plans for flood control and waterlogging should be arranged in advance.
All plant roots are suitable for growing in perlite, especially acid-loving slender fibrous root flowers,
It is not easy to grow in other substrates but grows robustly in perlite.
(8) rock wool
Rock wool is a fibrous mineral made of a mixture of 60% diabase, 20% limestone and 20% coke. into filaments with a diameter of 0.005mm, and then press it into a sheet with a bulk density of 80-100kg/m3, and then add a phenolic resin to reduce the surface tension when cooling to about 200°C. Make it water-retaining.
Rock wool was first used in soilless cultivation by Hornum in Denmark in 1969. It soon attracted the attention of the Netherlands, and now 80% of the soilless cultivation of vegetables in the Netherlands uses rock wool as the substrate. In the world's soilless cultivation, the area occupied by rock wool ranks first.
①The characteristics of rock wool as a wood-free cultivation substrate
a. Low price, easy to use, safe and hygienic
The main reason for flowers. The cost of the facilities used in rock wool cultivation is also low.The rock wool has been treated at high temperature. It is not necessary to sterilize when using new rock wool. When changing the pot, you only need to put the original small rock wool block in the big rock wool block, which is very convenient.
b. Wide range of uses The rock wool substrate can be used for soilless cultivation of various vegetables and flowers. in nutrient film technique
Rock wool can be used as a substrate in technologies such as deep liquid flow technology, drip irrigation, and multi-layer three-dimensional cultivation; whether it is a thick root system or a slender root system, it can grow well in rock wool. Especially for flowers that do not need to change the substrate frequently, it is very suitable.
c. The water-air ratio is right for many plants
Cotton has large pores, up to 96%, and strong water absorption. In a thick enough rock wool layer, the water content of rock wool gradually increases from top to bottom. The gas gradually decreases from top to bottom, so the water-gas ratio in the rock wool block forms a gradient change from top to bottom. The root growth of plants planted in rock wool blocks tends to be in the most suitable root environment (that is, the ratio of water and air is suitable). See Table 4-3 for the vertical distribution of moisture and air in the rock wool block.
② Problems that should be paid attention to when using rock wool
First, the hydrogen ion concentration of new unused rock wool is relatively low. Generally, the hydrogen ion concentration is below 100 nmol/liter (greater than pH 7). If a small amount of acid is added to irrigation before use, the hydrogen ion concentration will increase after 1 to 2 days.
Second, rock wool is non-decomposable, and the treatment after use has not yet been resolved. The usual method is to use the used rock wool as a soil conditioner, and some are recycled as raw materials for rock wool production. But these methods are still being explored.
In soilless cultivation, rock wool is still very suitable as a substrate for roof gardens, especially for planting evergreen perennial tree species, such as five-needle pine, podocarpus, and cypress. In the landscaping design with drip irrigation system, rock wool can be used for a long time, but it is not suitable for planting fast-growing or biennial grass flowers, because the old rock wool after replacement is difficult to dispose of.
(9) Silicone
There are two types of silica gel used as substrates for soilless cultivation, one is silica gel G and the other is silica gel B. Silica gel G is a color-changing silica gel, which is blue-green when dry and turns pink or colorless after absorbing water. Its water absorption and nutrient adsorption are not as good as silica gel B. Silica gel B is expanded during the firing process, and has more pores in the structure, and its ability to absorb water and store nutrients is more than twice that of silica gel G.
Its properties are better than sand.
Since silica gel is a crystalline particle, the spatial distribution of plant roots can be seen clearly, which adds to the fun of soilless cultivation.
Except for plants with slender roots such as rhododendrons, which are not suitable for silica gel soilless cultivation, most of the thicker, visible root systems such as some aerial or fleshy root flower plants are suitable.
(10) Ion exchange resin
Ion exchange resin is also called ion soil. It is a kind of soilless cultivation substrate obtained by mixing the nutrients required by plants with cationic or anionic adsorbents such as epoxy resin in different proportions. This substrate is the same as other substrates, safe and hygienic, non-toxic and tasteless, and the ions adsorbed on the resin are released slowly for plants to absorb, even if the concentration of ions adsorbed on the resin is high, it will not harm the plants.
The disadvantage of ion exchange resin is that it is expensive and needs to be regenerated when it is reused.
