Nutrient Film Technique
NFT (Nutrient Film Technique) is a hydroponics method in which plants are planted in a shallow-flow nutrient solution. It was invented in 1973 by A.J. Cooper of the Institute for Greenhouse Crops. After 1979, the technology rapidly in the world to promote the application. According to 1980 data records, 68 countries have been studying and application of the technology for soilless culture production, China in 1984 began to carry out this soilless cultivation technology research and application work, the effect is good.
First, the facility structure
The NFT facility consists of planting tanks, storage tanks, and nutrient recycling units (Figure 6-7). In addition, according to the actual production and financial possibilities, choose to configure some other auxiliary facilities, such as concentrated nutrient storage tank and automatic delivery device, nutrient heating, cooling devices.
Figure 6-7 NFT facilities composition diagram
A: system-wide diagram; B: planting slot section view
1. Return pipe. Storage tank. Pump 4. Planting slot 5. Main supply pipe. Liquid supply branch pipe. Miao 8. Nursery bowl 9. Clip 10; Polyethylene film
(A) planting tank
The NFT can be divided into two types according to the type of crop planted: one for cultivating large plant type crops (Figure 6-7) and the other for cultivating small plant type crops (Figures 6-8).
Figure 6-8 NFT planting slots for small plant type crops
A. Cross-section B. Side overlooking
1. Bracket 2. Plastic corrugated tile 3. Planting plate cover 4. For the liquid 5. Reflow
1. Planting slot for cultivating large plant type This groove is an isosceles triangle groove which is temporarily enclosed by a polyethylene film having a thickness of 0.1 to 0.2 mm and having a surface of black and white. The groove length is 20 to 25 m and the bottom width is 25 to 30 cm. Groove height 20cm. That is to take a width of 75 ~ 80cm, length 21 ~ 26m of the film, shop in the pre-smooth compaction, and a certain slope (1:75 or so) on the ground, the long side and parallel to the direction of the slope. The seedling with the seedling bowl was placed in the center of the film width line, and then the two sides of the film were pulled up, so that the width of the film width of 20 ~ 30cm close to the ground, pull up the two sides together with a clip Clamped, as a high 20cm isosceles triangle slot. The stems and leaves of the plant protrude from the groove in the groove top, and the root is placed in the bottom of the light-tight groove.
Nutrient solution from the high-end flow to the low end, so the bottom of the groove can not have potholes, so as to avoid tank water. With a hard board (wood or plastic) pad groove, adjustable slope, slope not too small, not too much to nutrient solution flow in the tank smooth as well. Nutrient solution in the tank to shallow flow, the depth of the liquid should not exceed 1 ~ 2cm. In the groove bottom width of 20 ~ 30cm, slot length of not more than 25m tank, every minute into the 2 ~ 4L nutrient solution is appropriate.
In order to improve the water absorption and ventilation conditions of the crop, a non-woven fabric can be laid at the bottom of the tank, which can absorb water and diffuse the water without passing through it, and then plant the plant on the non-woven fabric. Its role is mainly: ① shallow nutrient solution directly on the flow of plastic film will produce turbulence, in the young plants, the nutrient solution will flow to the root to go, resulting in water shortages. Non-woven fabric can spread to the bottom of the nutrient solution to ensure that the plant absorbs moisture; ② roots directly to the plastic film growth, the plant grows large enough, the root volume, weight, form a thick root pad and Plastic film sticks very tight, nutrient solution in the root of the bottom of the poor flow, resulting in root pad under hypoxia, prone to necrosis. There is a layer of roots to wear, but non-woven, the root can only grow in the non-woven above the root and the plastic film of a layer of non-woven fabric, nutrient solution can flow in between the root to solve the problem of hypoxia; Cloth can absorb a lot of water, when the power outages, can alleviate crop water shortages and the risk of rapid wilting.
2. Planting troughs for cultivating small plant type The trough is made of corrugated tiles made of fiberglass or cement. The valley depth of corrugated tile 2.5 ~ 5.0cm, peak distance as the size of plant strain and width of 100 ~ 120cm, can be kinds of 6 to 8 lines, according to this calculation of the size of the peak distance. Full slot length of about 20m, slope down 1:75. Corrugated tiles connected, overlapping mouth must have sufficient depth and anastomosis, to prevent leakage of nutrient solution. The general slot are erected in the wooden frame or metal frame, the height to facilitate the operation for the degree. Corrugated tile above to add a cover to cover it, make it opaque. Board cover made of rigid foam board, drilling holes above the planting. Pitch spacing planted by the spacing to be set, the length and width of the board cover and corrugated tile bottom to match the thickness of about 2cm.
(B) storage tank
Construction materials and construction methods are described in Chapter 4.
(C) of the nutrient solution circulating flow device
Mainly by the pumps, pipes and flow control valve and other components.
1. Pump pump selection see the fourth chapter.
2. Pipes shall be made of plastic pipes to prevent corrosion. Pipe installation should be strictly sealed, the best use of tooth without sockets. At the same time as far as possible buried in the ground below the pipeline, on the one hand to facilitate the work, on the other hand to avoid sunlight and accelerated aging. Pipes are divided into two types: one for the liquid pipe, from the pump out of charge, in charge of the branch. One of the branches back to the storage tank, so that part of pumping up the nutrient solution back into the storage tank, on the one hand from the role of nutrient agitation to make it more uniform and increase the dissolved oxygen in the liquid; the other hand, through its The valve regulates the flow. And then connected to many branches of the capillary tube to the top of each planting slot, the capillary tube of each tank set flow control valve, and then connected to the capillary tube into the small infusion tube planting slot. Large plant-type planting slot each set a few ø2 ~ 3mm small infusion tube, the number of tubes to control the flow to each slot 2 ~ 4L / min for the degree. Set up a number of small infusion tube is designed to have 1 to 2 of them blocked, there are 1 to 2 smooth, to ensure that no shortage of water. Small plant-type planting trough each valley are located two small infusion tube to ensure that each trough has a flow, flow per valley 2L / min. The second is the return pipe. The lower end of the planting tank is provided with a discharge port, and the pipe is connected to the liquid return main pipe, and then is led back to the storage tank. The director of the liquid return to have a large enough caliber to avoid sluggish overflow.
(4) Other auxiliary facilities
NFT nutrient solution for less use, resulting in rapid changes in nutrient solution, must always be adjusted. In order to reduce labor intensity and make adjustment timely, can use some automatic control of auxiliary facilities for automatic adjustment. But even without these auxiliary facilities, with artificial adjustment can also be normal production, but more trouble nothing more. Auxiliary facilities include timers, conductivity (EC) automatic control, pH-controlled devices, nutrient fluid temperature regulators and safety alarms (Figure 6-9).
Figure 6-9 NFT nutrient solution automatic control device schematic diagram
A, B: concentrated nutrient solution storage tank; C: concentrated acid (alkali) storage tank
1. Pump 2. Timer 3. Feeder tube 4. pH controller 5. EC controller 6. Injection pump 7. Nutrient return tube 8. EC and pH sensor 9. Heating or cooling tube 10. Heating ( Cold water) back and forth tube 11. Heating (cold water) control valve 12. Pump screen 13. Storage tank 14. Water and float
1. Timer intermittent liquid supply is NFT Hydroponics specific management measures. An accurate control of intermittent liquid feed is achieved by installing a timer on the pump. But set the intermittent time to meet the actual crop growth.
2. Conductivity (EC) automatic control device consists of conductivity (EC) sensors and control instruments and concentrated nutrient solution tank (sub-A, B two) into the pump composition. When the EC sensor senses the concentration of nutrient solution is reduced to the set limit, it will be directed by the control instrument into the pump will be concentrated nutrient solution into the reservoir, so that the concentration of nutrient solution back to the original concentration. On the contrary, if the concentration of nutrient solution is too high, it will instruct the water source valve to open, add water dilute the nutrient solution to achieve the required concentration.
3. PH control device from the pH sensor and control instruments and injection pump with a strong acid (alkali) storage tank, and its working principle and EC-controlled device similar (usually nitric acid or phosphoric acid) or concentrated alkali (usually with sodium hydroxide, and sometimes Using potassium hydroxide).
4. Heating and Cooling of the Nutrient Solution The liquid temperature is too high or too low to suppress the growth of the crop. It is much more economical to adjust the liquid temperature to improve the growth conditions of the crop than to heat or cool the greenhouse or greenhouse.
Nutrient fluid temperature control device mainly by the heating device or cooling device and temperature control device composed of two parts. Heating or cooling method see the second chapter.
5. Safety device NFT determines the characteristics of the planting tank is very thin, once the power failure or pump failure can not be timely circulation of liquid, it is easy because of lack of water Erzhi crop wilting. A non-woven fabrics do absorbent bottom of the tomato liner, in the summer conditions, 2h will stop wilting. No non-woven liners planting tank planting leaves, stop the liquid more than 30min will be dead dry. The NFT system must be equipped with a backup motor and a water pump. But also in the circulatory system equipped with alarm devices, water pump failure occurs in time for timely warning in order to remedy.
Conductivity, pH, temperature and other automatic adjustment device to the quality of sensitive and stable, every day to regularly monitor their failure to ensure that no disorder and harm crops.
Second, cultivation and management of technical points
(A) planting tank treatment
For the new tank is mainly to check whether the components meet the requirements, especially the bottom of the groove is smooth, whether the plastic film damage leakage. Replace the trough after the re-use, pay attention to check for leaks before use and to thoroughly clean and disinfect.
(B) nursery and planting
1. Seedling cultivation and planting of large plant type Because NFT nutrient solution layer is very shallow, when planting the root of the crop are placed in the bottom of the tank, so the seedlings are planted with solid matrix or porous plastic bowl to anchor the plant. Seedling when the application of solid matrix block (usually rock wool block) or use of porous plastic bowl nursery, colonization should not be solid matrix block or plastic bowl off, even the seedlings with a bowl (block) together at the bottom of the tank.
Large plant-type planting tank of the triangular tank closed higher, so the breeding of seedlings should have enough height to colonize, so that placed in the slot when the seedlings can protrude out of the triangular slot above the slot.
2. Seedling cultivation and planting small plant can be rock block or sponge block seedlings. Rock wool block size can be rotated into the planting hole, not lying on the bottom of the groove can be. Can also be rolled into non-woven or Yanmian cut into pieces of block seedlings. Seedling in the upper cut a small slit, the germination of seeds placed in them, intensive breeding 2 to 3 leaves of seedlings. And then into the planting hole in the plate cover. After planting seedlings to touch the bottom of the bar and the young leaves out of the board above.
(C) the preparation and management of nutrient solution
1. Nutrient solution selection NFT system nutrient solution concentration and composition changes quickly, so to select some of the better stability of the nutrient solution formula.
2. Liquid supply method NFT for the liquid method is more particular about. Because it is characterized by a very shallow liquid layer, not more than 1.0 ~ 2.0cm. Such a shallow liquid layer, which contains nutrients and oxygen can easily be consumed to a very low level. When the nutrient solution is fed from one end of the tank to a length of 25m, many plants absorb their nutrients and oxygen, so that one of them is sucked from the tank to the end of the tank. , The nutrient solution in the oxygen and nutrients have been left much, resulting in slotted and slot tail plant growth vary greatly. When the amount of liquid for a certain limit will cause the impact on production. Which indicated that the fluid volume of NFT was related to multiple factors.
NFT is more than 30m in the tank length, and the plant is dense, the use of intermittent liquid supply method to solve the problem of root aerobic. In this way, the NFT liquid supply method is derived for the two, namely continuous liquid supply and intermittent liquid supply method.
(1) continuous supply method NFT root absorption oxygen situation can be divided into two stages, namely from planting to the root pad began to form, root immersed in nutrient solution, mainly from the nutrient solution to absorb dissolved oxygen, which is the first One stage. With the increase in the amount of root, the root pad after the formation of a part of the root exposed to the air, so from the nutrient solution and air to absorb oxygen in two aspects, this is the second stage. The second phase of the emergence of speed, and for the amount of fluid on the number. For the amount of liquid, the root pad to reach a thicker extent to be exposed in the air, which entered the second stage later; for the liquid less, then quickly enter the second stage. The second stage is the root to obtain more adequate oxygen source stage, should promote its early.
Continuous liquid supply for the amount of liquid, in the 2 ~ 4L / min range, with the crop growth and change. In principle, day and night are required for liquid. Cessation of liquid supply at night, for example, inhibits nutrient and water uptake by crops (by 15 to 30% less), leading to crop losses.
(2) intermittent liquid supply method is to solve the NFT system due to the slot is too long, too many strains of root causes anoxic effective way. In the case of the normal tank length and the normal number of plants, the intermittent liquid supply was also higher in intermittent liquid supply than in the continuous liquid supply. Intermittent liquid in the liquid supply stops, the root pad of the large pores in the nutrient solution with the outflow of air, so that the root pad until the bottom of the roots are sucked into the air of oxygen, thus increasing the oxygen in the entire root system the amount.
Intermittent supply of the beginning of the period, the root pad to form the initial stage is appropriate. The intermittent liquid supply has no effect when the root pad is not formed (ie, the root system is small and there is no backlog to form a thick layer).
Intermittent for the degree of liquid, such as non-woven mat in the bottom of the tank under the conditions of planting tomatoes, the summer for every 1h for 15min, stop for 45min; winter 2h for 15min, stop for 105min, so repeated day and night for the liquid. These parameters should be adjusted in relation to crop specific growth and climate conditions. Stop the supply of time can not be too short, such as less than 35min, then reach the role of supplemental oxygen; but can not stop too long, too long will make crops dry and wilting.
3. Liquid temperature management NFT cultivation slot (especially plastic film triangular groove) poor performance, coupled with the use of liquid less, so the stability of liquid temperature is also poor, prone to the same slot in the head And the tail of the liquid temperature is significantly different. In particular, the temperature difference between the liquid inlet and the liquid outlet of the tank in the winter and spring season can reach 6 ° C, so that the liquid temperature, which has been adjusted to the crop requirement, becomes significantly lower than the crop requirement at the end of the tank. Visible, NFT to pay special attention to the management of liquid temperature.
A variety of crops on the liquid temperature requirements are different, in summer not more than 28 ~ 30 ℃, winter is not less than 12 ~ 15 ℃ is appropriate.
Third, the evaluation of the NFT
1. Facilities investment, construction is easy and convenient. NFT planting slot is made of lightweight plastic film or corrugated tile splicing made of light, simple structure, easy to install, easy to disassemble, low investment costs.
2. The liquid layer is shallow and flowing. The nutrient solution layer was shallow, the root part of the crop was immersed in the shallow nutrient solution, partly exposed to the moisture in the planting tank, and the shallow nutrient solution circulated flow, which could better solve the oxygen demand of root respiration.
3 easy to automate the production process management.
1.NFT facilities, although less investment, construction is easy, but because of its poor durability, follow-up investment and maintenance work frequently.
2.NFT liquid layer shallow and intermittent liquid supply, better solve the problem of root aerobic, but the rhizosphere environmental stability is poor, the management of the technical level and equipment performance requirements are higher.
3. To make the management of both fine and not heavy, it is bound to use automatic control devices, which need to increase the equipment and investment, promotional surface is limited.
4.NFT is a closed circulatory system, in the event of root diseases, easier to spread throughout the system. Therefore, the use of facilities before the cleaning and disinfection of the higher requirements.