JPH0351373B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to a method for automatically controlling the moisture status of a plant growth medium in agricultural land and plant cultivation facilities. Here, the plant growth medium refers to soil or other porous materials for growing plants, such as agricultural land soil, facility cultivation soil, microbial culture medium, porous culture medium of cultivation facilities and plant factories such as Rock Wool. . Problems to be Solved by the Prior Art and the Invention Mediums in which plants can grow generally contain a gas phase, except in the case of wet plants such as paddy rice, and the water present in the medium is sucked through the pores. It is restrained and has a negative pressure relative to atmospheric pressure. The pressure that acts on the water in the pores with this gas phase is called the water potential, and is quantified in units such as atmospheric pressure and pF. Water in drier soils has a smaller water potential than water in wetter soils, and water potential has a close relationship with water content. In agricultural land and plant cultivation facilities, water in the plant growth medium is constantly supplied and consumed by natural forces such as rainfall, evapotranspiration, and gravity drainage, and by artificial management such as irrigation and drainage construction. Conditions are constantly changing. If the moisture status of the plant growth medium, especially the moisture content and moisture potential, could be artificially controlled, it would be easy to eliminate moisture damage, control growth, and improve the quality of plants, and it would also be possible to automate cultivation facilities and reduce the cost of water. It also makes it possible to develop utilization technologies, which has great benefits. However, although the importance of moisture control in plant growth media has been recognized, automatic control methods based on physical principles remain at the research stage and have not been put to practical use. The area has not yet been reached. For example, by connecting water in a porous cup to a free water surface under atmospheric pressure via a connecting pipe with air excluded, and creating a difference in height between the porous cup and the free water surface, the water in the cup can be Negative pressure (cm
Several attempts have been made so far to adjust the negative pressure of water using the head method of applying H ₂ O) or the pressure adjustment method using a vacuum pump, and supplying negative pressure water to the soil through porous pipes. Yes. However, in these conventional static water supply methods, air enters from outside the porous tube and generates bubbles, which reduces water supply efficiency and makes it impossible to transmit negative pressure. cannot be kept constant. Further, negative pressure control is limited to a range of -0.03 atmospheres or more, and cannot secure a sufficient gas phase ratio in the culture medium and create a drier moisture condition suitable for plants. Means for Solving the Problems The method of the present invention applies a predetermined negative pressure to water in a porous pipe embedded in a plant growth medium and circulates the water, thereby applying negative pressure ( Capillary movement of water is caused between the culture medium and the porous tube so that the water potential (water potential) is equal to the negative pressure of the water in the porous tube, thereby maintaining the moisture state of the culture medium. The method of the invention consists of a pressure regulation system and a negative pressure water circulation system. FIG. 1 schematically shows an example of the entire system. The pressure regulation system provides a negative pressure of any magnitude greater than or equal to minus one atmosphere to the water in the negative pressure water circulation system. The magnitude of the negative pressure is determined based on a priori data, depending on the average diameter of the pores of the porous tube, the desired moisture state of the plant growth medium, and the like. The illustrated pressure adjustment system is a combination of a pressure reduction tank 1 and a vacuum pump 5, but in order to maintain a predetermined degree of pressure reduction, the tank is equipped with a pressure gauge 3 and a pressure switch 2. Adjust so that the pressure switch is turned on and the vacuum pump is activated. The solenoid valve 4 opens when the vacuum pump is in operation and closes after operation to prevent outside air from flowing back into the tank. The gas phase of the decompression tank is connected to the air reservoir in the upper part of the water storage tank 6 through a pressure tube, and the air pressure inside the tank is applied to the water in the circulation system. A vacuum pump is used to generate and maintain negative pressure in the pressure regulation system. In addition to the method described above, a method for adjusting the negative pressure may be a method in which a mercury manometer is used as a pressure sensor and relayed to a solenoid valve. Negative pressure water circulation system includes water tank 6 and circulation pump 7
The porous tube 8 and the plant growth medium surrounding it are connected by piping. The circulation pump maintains the transmission of negative pressure to the capillary water in the porous tube wall by eliminating air bubbles generated in the system into the air reservoir of the water tank, increasing the efficiency of water exchange with the plant growth medium. Circulate negative pressure water in the system with the purpose of increasing it. It is preferable that the water tank is provided with a scale so that the amount of water supplied can be measured. The porous tube may be a tubular body made of a material that allows capillary movement of water; for example, an unglazed tube is a preferable example. Other porous materials made of synthetic resin can be used. No matter what material is used, it goes without saying that the porous tube must not corrode easily in the plant growth medium and must be able to withstand negative pressure, the weight of the plant growth medium, etc. be. A so-called circulation pump is used as a means for circulating the negative pressure water. What should be noted about the negative pressure water circulation system of the present invention is that the water pressure distribution within the circulation system changes somewhat due to the operation of the circulation pump. That is, in the schematic illustration of FIG. 2, the water pressure in the water circulation system is determined by the suction pressure (negative pressure) applied by the pressure reduction control system, the height difference between the water level in the water tank and the porous pipe position, It is determined by the combination of the pressure difference due to water supply and suction by the circulation pump and the drop in water pressure due to friction within the piping. However, in the practical stage, water pressure changes due to circulation means and friction loss in the piping are proportional to the square of the flow velocity, so by not increasing the water flow velocity too high, and by adjusting the pressure of the decompression tank, it is possible to By controlling the water pressure in the system, the water pressure in the system can be leveled to a level that does not cause any practical problems. Furthermore, by arranging the porous tubes in parallel rather than in series, the moisture state of the culture medium can be made more uniform. Effect By applying a predetermined negative pressure to the circulating water, a negative pressure of approximately the same magnitude is transmitted to the water in the porous tube, and the pressure of the water in the porous tube and the pressure of the water in the medium (moisture potential) are If there is a difference between maintained. Example 1 Test of water supply ability to corn seedling growth pot <Size of device> Pressure adjustment system Small vacuum pump decompression tank (made of hard PVC, 4
Pressure switch (use range 1-40cm)
Hg sensitivity ±10mmHg) Negative pressure water circulation system Circulation pump (0.5/min.) Water tank (acrylic resin, 0.2
capacity, with scale) Porous tube (alumina biscuit tube, 92
% Al ₂ O ₃ +0.5% SiO ₂ , average pore diameter 2.1 μm, outer diameter 0.8 mm, inner diameter
6.7 mm, length 70 mm) Root water absorption system A hard PVC pipe container with an inner diameter of 75 mm and a height of 50 mm is filled with soil (2 stages of coarse and dense), and a porous pipe is buried in the middle. As a result of preliminary tests using the above system without cultivation and under natural evaporation, the results showed that pF3.5 (minus
dry soil at pF2.4 (minus 0.25 atm)
It takes less than 3 days to reach the soil moisture condition (field condition moisture) of pF2.4 (atmospheric pressure) and pF2.0.
It took less than two days to reach the temperature (minus 0.10 atmospheres). These are the times required for complete equilibrium, and the approximate times required for equilibrium were all within one day. The above system increases soil water potential.
Corn was grown under controlled conditions at pF2.4 (minus 0.25 atm). Active water absorption occurred with maximum daily transpiration of 3.5 to 5.2 mm, and corn grew normally. The amount of water absorbed per day was measured by the amount of water lost in the water tank. It was observed that the amount of decrease in soil moisture during the experiment period was extremely small, and the medium was maintained at an almost constant moisture state. The test results are shown in Table 1.

[Table] By providing an appropriate scale on the water storage tank, it was possible to read the amount of water consumed with high accuracy, and it was also possible to measure changes in water absorption rate over time (see Figure 3). Example 2 Using the same system as in Example 1, the results of a cultivation test under humid water conditions with a set pressure of minus 0.1 atm (pF2.0) also confirmed that the method of the present invention was effective. It was done. The results are shown in Table 2.

[Table] Example of water supply amount from porous pipe 3 Soil moisture adjustment test for large pot (scale of equipment) Pressure adjustment system Same as Example 1 Water circulation system Circulation pump (water supply rate 0.5/min.) Water storage tank (capacity 1.2 ) Porous pipes (alumina biscuit pipes, outer diameter 14 mm, inner diameter 10 mm, length of soil contact part 100 mm, 3 pipes connected in series and buried at 7 cm intervals in a pot) Soil capacity 7.0 In this device, the set pressure is -9cmHg and-
Table 3 shows the change in soil water potential over time at 4 cmHg.

[Table] Looking at the relationship between the number of meters after the start of water supply to the porous pipe and the soil moisture potential (measured by a tensiometer), it can be seen that under the conditions of this example, the soil moisture reaches equilibrium in approximately 3 days. This shows that even if the soil volume per unit surface area of the porous tube is more than five times as large as that in Example 1, there is sufficient supply capacity. Table 4 shows the distribution of soil moisture in the pot by depth after almost equilibrium in the case of -9 cmHg pressure setting. As a result, it can be seen that according to the method of the present invention, a substantially uniform moisture distribution can be obtained even if the depth of the plant growth medium changes. Table 5 shows the difference in equilibrium soil water potential when two pots are connected in series or in parallel and placed a certain distance away from the pump in the water circulation system. In the case of a series connection, the water potential appears small in the pot connected far away from the circulation pump, and as already shown in the explanation of water pressure distribution in the circulation system, the difference in water pressure caused by the circulation pump and the flow in the piping occur. This shows that the influence of pressure loss due to friction appears. In the parallel case, the soil moisture in the two pots is approximately equal regardless of the difference in distance from the pump.

【table】

[Table] The above Examples 1, 2, and 3 demonstrated that the negative pressure water circulation system of the present invention is valid in principle and effective in practice. In practice, it is recommended to use a highly sensitive pressure switch, increase the density of porous pipes for culture media with high water consumption rates, and adjust the cross-sectional area of the water tank appropriately depending on the purpose. This selection enables highly accurate control over a wide range of moisture potentials. Effect Water can be removed by installing a new negative pressure water circulation system and circulating negative pressure water inside the porous pipe.
By forcibly removing air bubbles generated in the system, the efficiency of supplying and removing plant medium water is further increased, and the medium moisture state can be maintained constant over a long period of time. The negative pressure control range can be expanded to a moisture potential of minus 0.5 atmospheres, which is the limit value for capillary movement of water. By institutionalizing the present invention, for example, as shown in FIG. 4, the following effects can be obtained. (1) The moisture state of the plant medium is automatically adjusted according to weather and growth conditions, and water can be continuously supplied to the culture medium for a long time while keeping the moisture level of the medium almost constant. (2) At the same time, the plant medium is drained efficiently.
That is, by applying negative pressure to the water in the porous pipe, water can be drained to a moisture state that was impossible with conventional engineering drainage methods. Previous drainage methods such as underdrains utilize gravity and can only remove water that flows out due to gravity, but this method can also remove water held in capillaries. (3) By providing the necessary and sufficient air phase to the medium and keeping plant roots healthy, it helps improve the quality of plants and crop harvests. (4) It is possible to suppress the occurrence of diseases because it does not increase the humidity in the air and prevents the movement of pathogenic bacteria in the medium (many pathogenic bacteria can only move in the medium when there is gravity water). (5) Water is supplied only to the necessary parts of the culture medium in a manner that matches the plant's water absorption, and water loss due to downward movement due to gravity is prevented, making it possible to maximize water-saving cultivation. (6) Since water movement due to gravity water can be eliminated, it is possible to prevent groundwater contamination due to substances added to or generated from the culture medium such as agricultural chemicals and fertilizers, and discharge into open systems caused by cleaning of the culture medium is undesirable. It is also possible to recover contaminated water. (7) In addition to the plant culture medium, moisture can be controlled in porous sediments where water is consumed and supplied.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of the system of the present invention, Figure 2 is a diagram showing the water pressure distribution in the system of the present invention, Figure 3 is a graph showing the daily change in water absorption rate by the system of the present invention, and Figure 4 is FIG. 2 is a schematic diagram of an example of actual institutionalization of the system of the present invention. 1...Reduction tank, 2...Pressure switch, 3...Pressure gauge, 4...Solenoid valve, 5...Vacuum pump, 6...Water tank,
7...Circulation pump, 8...Porous pipe.

Claims (1)

[Claims] 1. Circulating water with a negative pressure of any magnitude in the range of -1 atm to 0 atm relative to atmospheric pressure, which is pre-adjusted by a vacuum pump, through a porous pipe buried in a plant growth medium. , wherein the water content or water potential of the plant growth medium is controlled by supplying water into the plant growth medium or excluding water from the plant growth medium through the porous tube. Moisture control method.