GB1558581A

GB1558581A - Method of growing plants without soil

Info

Publication number: GB1558581A
Application number: GB38485/76A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1975-09-17
Filing date: 1976-09-16
Publication date: 1980-01-03
Also published as: NO139245B; DE2641945A1; DE2641945C2; DK417976A; NO763170L; FI762657A; DK148374C; FI60485C; CA1048270A; SE7510385L; DK148374B; NL7610395A; SE398436C; FI60485B; SE398436B

Description

(54) A METHOD OF GROWING PLANTS WITHOUT SOIL (71) We, ERNST HORST SEVERIN SJÖSTEDT of Bolestad Handelsträdgård, S-260 73 Ostra Ljungby, Sweden a citizen of Sweden and JIM ARTHUR NISSMO of Repslagarevagen 8, S-245 00 Staffanstorp, Sweden, a citizen of Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a method of growing plants without soil by means of a plant nutrient solution circulating in a closed system.

It is known that there can be obtained, in growing plants without soil in this way, a good growth and a high yield by continuously maintaining an accurately adjusted nutrition condition in the circulating nutrient solution, raw water and plant nourishment being supplied as they are consumed, while a predetermined balance between the nutrient substances included in the plant nutrient solution is maintained. However, an incorrect balance will rapidly manifest itself as a reduced yield or as plant death and, therefore, there are great demands as far as the control of the nutrition condition of the plant nutrient solution is concerned. This control is performed by adding concentrated main solutions of different compositions in dependence of measured values of the pH concentration and the conductivity of the nutrient solution.

Method and means for growing plants without soil is described in United States Patent Specification No. 3578431. This method has been used in practice for growing tomatoes in greenhouses; a nutrient solution is disclosed having the following relative composition of the macro nutrient substances therein: N 100 P 15 K 95 Mg 15 S 10 Ca 30 Moreover, the nutrient solution contained necessary micro nutrient substances (trace elements) such as iron, manganese, zink, boron, copper, molybdenium and cobalt.

80 % of the nitrogen was in the form of nitrate nitrogen, and 20 % thereof in the form of ammonium nitrogen. In the practice of this previously proposed method, we noted that after some time the plants presented evident indication of lack of potassium - yellow leaf edges, poor quality of the fruits - and therefore the relative potassium content was raised from 95 to 123, i.e. to a value which considerably deviated from the value prescribed according to the aforesaid U.S. Specification. Then, the pH value decreased after some time and continued to decrease although the supply of potassium was increased. After three months a pH value of 3.6 had been reached according to laboratory analysis (continuous pH control was not performed at this practical test) while the ideal pH value is about 5.5; the pH value should in any case be above 4.Now the plants were characterized by relative lack of water, death being a consequence thereof (pistil putrefaction was observed).

According to the present invention we provide a method of growing plants without soil by means of plant nutrient solution circulating in a closed system, wherein plant nourishment consumed is replaced by the supply of one or the other of two concentrated stock solutions in dependence on a measured pH value and conductivity of the plant nutrient solution, the stock solution being supplied in dependence on the decrease of the conductivity below a predetermined value, and the supply of stock solution thus controlled by the conductivity being made from one stock solution providing nitrogen as metal nitrate when the pH value of the solution is below a predetermined value, to increase the pH value by the plants taking up metal nitrate, and from the other stock solution providing nitrogen as ammonium salt, when the pH value of the nutrition solution is above said predetermined value to decrease the pH value by the plants taking up ammonium salt.

Preferably the plant nutrition solution contains potassium ions, the number of potassium ions in the nutrition solution being maintained at 100 to 150 % of the number of nitrogen ions in the nutrition solution.

Embodiments of the invention will now be described with reference to the accompanying drawings in which: Figure 1 discloses diagrammatically equipment for growing plants without soil; and Figure 2 discloses schematically another form of equipment for growing plants without soil.

Referring to Figure 1 the equipment disclosed comprises a tank 10 for nutrient solution which is provided with an output conduit 11 having a liquid pump 12 by means of which the nutrient solution is pumped from the tank to channels 11' or flat tubes or hoses made of plastic foil in a greenhouse the plants being "planted" in these channels, tubes or hoses by locating their root systems more or less in the plant nutrient solution circulating therethrough. There is no soil in the channels, tubes or hoses, but there can be provided therein a suitable material wherein the nutrient solution is sucked up. If channels are used, these are preferably covered with plastic foil 13' or the like in order to reduce the direct evaporation from the channels.The rbot systems of the plants thus extend in the channels, tubes or hoses, and the plants take their nourishment through the root systems directly from the nutrient solution. From the channels the nutrient solution which has not been taken up by the plants - the nutrient solution is of course supplied in a large excess - returns to the tank through a return conduit 13. To the tank there is connected a tube conduit 14 for the supply of raw water and this supply is controlled by means of a solenoid valve 15. For the supply of concentrated nutrient solution, stock solution, there is a conduit 16 having a solenoid valve 17 which has two inputs namely through a conduit 18 provided with a solenoid valve 19, from a vessel 20 and through a conduit 21 provided a solenoid valve 22, from a vessel 23.The solenoid valves 19 and 22 are controlled by a pH meter 24 the test probe 25 of which is immersed into the nutrient solution in the tank 10, while the solenoid valves 15 and 17 are controlled by means of a conductivity meter 26 the test probes 27 of which are also immersed into the nutrient solution in the tank 10, as well as by a float controlled level guard 28 for maintaining a predetermined liquid level in the tank. Finally, the tank is provided with a spillway 29 and with one or more perforated tube or hose conduits 30 which extend along the bottom of the tank and are connected to a compressor for blowing air into the nutrient solution from below and upwardly for oxygenating the nutrient solution and for providing turbulence and stirring of the nutrient solution such that this solution will have a uniform concentration and composition. Instead of air, carbon dioxide can be blown into the solution so that the plants will take up this carbon dioxide through the root system; for the rest carbon dioxide is taken up through the leaves. It is also conceivable to blow into the solution air as well as carbon dioxide or a mixture thereof.

The plant is operated with two concentrated stock nutrient solutions which are received in the vessel 20 and the vessel 23, respectively. These stock solutions preferably both have a pH value of approximately 5.8 and thus both are acid. Below is given the relative proportions of components of the two stock solutions: Vessel 20 Vessel 23 N 100 100 P 15 15 K 123 123 Ca 32 74 Mg 20 20 As far as the stock solution in the vessel 20 is concerned 80 % of the nitrogen can be provided by Ca(NO3)2 and 20 % of the nitrogen by NH4NO3, while the nitrogen of the stock solution in the vessel 23 can be provided solely by Ca(NO3)2. This explains the difference in the content of calcium in the two solutions. A calcium content which is higher than that which can be taken up by the plant can be accepted without disadvantage because the plant does not take up more calcium than it is in need of.Tests have indicated that the excess is harmless to the plants. As will be seen the potassium content is high and is considerably higher than the content prescribed according to the aforesaid U.S.

Specification wherein the potassium content is limited to 40 - 100 % of the nitrogen content.

When the plants take up metal nitrate Ca(NO3)2 from the nutrient solution the roots of the plants will give off OH- and HCO3- which are both basic, and therefore this emission from the plants increases the pH value of the nutrient solution. On the other hand, when the plants take up ammonium salt e.g. NH4NO3 the roots of the plants give off an II ion which provides a decrease of the pH value of the nutrient solution.By sensing the pH value by means of the meter 24 the two solenoid valves 19 and 22 are controlled in such a way that the valve 19 is open for connection of the vessel 20 through the conduit 18 to the solenoid valve 17 when the pH value is above a predetermined value which is the nominal value of the pH concentration of the nutrient solution in the tank 10, while on the contrary the solenoid valve 21 is open when the pH value of the nutrient solution in the tank 10 is below the said predetermined value, so as to maintain a connection between the vessel 23 and the solenoid valve 17.Thus, either connection from the vessel 20 or from the vessel 23 is always open to the solenoid valve 17 but the supply of concentrated nutrient solution from one or the other of these two vessels through valve 17 is controlled not by the pH value of the nutrient solution but by the conductivity of the solution in tank 10, thus the pH value determines the vessel from which the supply of stock solution, initiated in dependence on the conductivity value, shall take place. When the solution in the tank 10 is impoverished of the nutrient salts contained therein, the conductivity decreases which is sensed by means of the conductivity meter 25 which opens solenoid valve 17 at a predetermined value for the supply of nutrient solution to the tank.If on the other side the concentration of nutrient substances in the nutrient solution should be too high, which is not inconceivable as a result e.g. of high rates of evaporation from the channels or the plants, the conductivity meter will cause solenoid valve 15 to open at a predetermined value of measured conductivity, resulting in the supply of raw water to the tank and thus dilution of the nutrient solution therein. Excess, if any, will escape through the spillway 29. The necessary amount of sulfur can be supplied with the raw water. Supply of raw water also takes place in dependence on the float controlled level guard 28 when the liquid level in the tank 10 decreases below a predetermined value, so that there is always maintained in the tank a predetermined liquid level.If the concentration of nutrient substances in the solution is disturbed at the refill in dependence of the level guard, appropriate concentration will be reset in dependence of the conductivity meter, the existing pH value as sensed by means of the pH meter determines if the stock solution in the vessel 20 or that in the vessel 23 shall be used for the supply.

If the liquid level in the tank 10 sinks so far that the test probes 27 of the conductivity meter are free this would mean that the conductivity meter measures a resistance of indefinite value which would result in a signal to valve 17 to open and supply of nutrient solution from the vessel 20 or 23. This could happen if leakage arises in the circulation system or if the supply of raw water fails. If a concentrated nutrient solution is circulated to the plants this could be catastrophic and could involve total destruction of the plants. In order to eliminate this risk the level guard 28 is arranged such that it will close the solenoid valve 17 at a still lower level than that at which the supply of raw water starts, although the conductivity meter orders opening of said soleniod valve.The control signal from the level guard to the solenoid valve 17 thus overrides the control signal from the conductivity meter 26 and closes the valve 17 so that no further concentrated nutrient solution will be supplied to the tank.

When the plants take up Ca(NO3)2 from the nutrient solution the pH value of the solution will increase as mentioned above, the supply of concentrated nutrient solution taking place from the vessel 20 when the concentration of the solution has decreased sufficiently for the supply to be made. In case the pH value should decrease following a decrease of the nitrogen content due to the plants taking up NH4NO3, the supply will take place instead from the vessel 23 at a refill order from the conductivity meter. Excess of calcium, if any, is of no harm to the plants as mentioned above.

In the nutrient solutions used there should also be tracer elements. Iron is one such trace element but it cannot, as in known nutrient solutions for growing plants without soil, comprise a nitrate because the iron in that case would deposit in the nutrient solution and thus the plants would lack iron. The iron is therefore, usually supplied as iron chelate. The same is true for manganese which is usually supplied as manganese chelate.

The conductivity of the nutrient solution in the tank 10 should range from 1400 to 4000 ,uS/cm and preferably between 1600 and 1800 FS/cm. The pH value should range from 5.7 to 6.5 and preferably should be 5.8 with a variation of + 0.1.

In the practice of preferred embodiments of the invention our method has turned out to give good plant growth and rich crops, in many cases up to more than three times the crop obtained when growing in the conventional manner by using soil. The control involving use of the two stock solutions in the vessels 20 and 23 has turned out to be less sensitive than a control in which there is used a basic and an acid as well as a third, acid or neutral solution as proposed before according to the aforesaid U.S. Specification. The equipment furnishes the plants with plant nutriment as required for their growth and fruit setting without serious risk of such deviations in the balance of the plant nutrient solution would result in a lack of nutriment in one aspect or other whereby the plants are damaged occasionally or permanently.The system can be completely automatic and, as will be seen from the embodiment described, can include a security system to prevent dangerous concentration in the nutrient solution in the event of raw water supply failure.

In the system schematically represented in Figure 2 the conductivity meter 26 which receives signals from the test probes 27 thereof comprising for example oxidizing platinum electrodes, (and preferably including a thermistor means for temperature compensation), is connected to an amplifier 31 wherein the nominal value of the conductivity of the nutrient solution in the tank 10 can be adjusted. It is also connected to an amplifier 32 which in turn is connected to an alarm apparatus 33 for emitting an alarm signal at a predetermined maximum value of the conductivity, and to an amplifier 34 also connected to the alarm apparatus 33 for emitting an alarm signal at a predetermined minimum value of the conductivity.The amplifier 31 is arranged to supply start and stop signals, respectively, in dependence of a discrepancy between the actual value of the conductivity and the nominal value thereof, to a timer 35 which is connected to the pH meter 24. This meter receives a signal from the test probe 25.

Solenoid valves 17, 19 and 22 in Figure 1 are replaced in this case by two pumps 36 and 37 arranged to pump stock nutrient solution from the vessel 20 and the vessel 23, respectively, to the tank 10, and one of these pumps is started to be operated for a predetermined time interval in dependence on the conductivity measured, over the period set or determined by timer 35. The pump which is started is dependent on the measured pH value and is selected by the pH meter 24.

Two level guards 28a and 28b are provided, level guard 28a being connected to the solenoid valve 15 to close this valve at a predetermined maximum level in the tank 10. The amplifier 32 is also connected to the solenoid valve 15 in order to open said valve when the conductivity has reached a predetermined maximum value. Level guard 28b is connected to the soleniod valve 15 to open this valve at a predetermined lowermost liquid level in the tank 10 and is also connected to the timer 35 simultaneously to stop the pump, 36 or 37, which is operating.

Thus it will be seen that the function is principally the same as has been described above with reference to Figure 1.

The timer 35 is arranged to control the operation of the pump 36 or 37 in such a manner that this pump is operated for intervals of 5 to 20 seconds and is allowed to be de-energized between these intervals for 1 to 10 minutes. The timer comprises means for manual presetting of these intervals which have to be adjusted to the total liquid volume of the system.

WHAT WE CLAIM IS: 1. A method of growing plants without soil by means of a plant nutrition solution circulating in a closed system, wherein plant nourishment consumed is replaced by the supply of alternatively one or the other of two concentrated stock nutrition solutions in dependence on measured pH value and conductivity of the plant nutrition solution, the stock solution being supplied in dependence on the decrease of the conductivity below a predetermined value, and the supply of stock solution thus controlled by the conductivity being made from one stock solution providing nitrogen as metal nitrate when the pH value of the nutrition solution is below a predetermined value, to increase the pH value by the plants taking up metal nitrate, and from the other stock solution providing nitrogen as ammonium salt, when the pH value of the nutrition solution is above said predetermined value, to decrease the pH value by the plants taking up ammonium salt.

2. A method according to Claim 1, wherein the number of potassium ions in the nutrition solution is maintained at 100 to 150 per cent of the number of nitrogen ions in the nutrition solution.

3. A method according to Claim 2, wherein the number of potassium ions is kept at substantially 125 per cent of the number of nitrogen ions.

4. A method according to any of Claims 1 to 3, wherein both said stock solutions are

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

The conductivity of the nutrient solution in the tank 10 should range from 1400 to 4000 ,uS/cm and preferably between 1600 and 1800 FS/cm. The pH value should range from 5.7 to 6.5 and preferably should be 5.8 with a variation of + 0.1.

In the practice of preferred embodiments of the invention our method has turned out to give good plant growth and rich crops, in many cases up to more than three times the crop obtained when growing in the conventional manner by using soil. The control involving use of the two stock solutions in the vessels 20 and 23 has turned out to be less sensitive than a control in which there is used a basic and an acid as well as a third, acid or neutral solution as proposed before according to the aforesaid U.S. Specification. The equipment furnishes the plants with plant nutriment as required for their growth and fruit setting without serious risk of such deviations in the balance of the plant nutrient solution would result in a lack of nutriment in one aspect or other whereby the plants are damaged occasionally or permanently.The system can be completely automatic and, as will be seen from the embodiment described, can include a security system to prevent dangerous concentration in the nutrient solution in the event of raw water supply failure.

In the system schematically represented in Figure 2 the conductivity meter 26 which receives signals from the test probes 27 thereof comprising for example oxidizing platinum electrodes, (and preferably including a thermistor means for temperature compensation), is connected to an amplifier 31 wherein the nominal value of the conductivity of the nutrient solution in the tank 10 can be adjusted. It is also connected to an amplifier 32 which in turn is connected to an alarm apparatus 33 for emitting an alarm signal at a predetermined maximum value of the conductivity, and to an amplifier 34 also connected to the alarm apparatus 33 for emitting an alarm signal at a predetermined minimum value of the conductivity.The amplifier 31 is arranged to supply start and stop signals, respectively, in dependence of a discrepancy between the actual value of the conductivity and the nominal value thereof, to a timer 35 which is connected to the pH meter 24. This meter receives a signal from the test probe 25.

Solenoid valves 17, 19 and 22 in Figure 1 are replaced in this case by two pumps 36 and 37 arranged to pump stock nutrient solution from the vessel 20 and the vessel 23, respectively, to the tank 10, and one of these pumps is started to be operated for a predetermined time interval in dependence on the conductivity measured, over the period set or determined by timer 35. The pump which is started is dependent on the measured pH value and is selected by the pH meter 24.

Two level guards 28a and 28b are provided, level guard 28a being connected to the solenoid valve 15 to close this valve at a predetermined maximum level in the tank 10. The amplifier 32 is also connected to the solenoid valve 15 in order to open said valve when the conductivity has reached a predetermined maximum value. Level guard 28b is connected to the soleniod valve 15 to open this valve at a predetermined lowermost liquid level in the tank 10 and is also connected to the timer 35 simultaneously to stop the pump, 36 or 37, which is operating.

Thus it will be seen that the function is principally the same as has been described above with reference to Figure 1.

The timer 35 is arranged to control the operation of the pump 36 or 37 in such a manner that this pump is operated for intervals of 5 to 20 seconds and is allowed to be de-energized between these intervals for 1 to 10 minutes. The timer comprises means for manual presetting of these intervals which have to be adjusted to the total liquid volume of the system.

WHAT WE CLAIM IS: 1. A method of growing plants without soil by means of a plant nutrition solution circulating in a closed system, wherein plant nourishment consumed is replaced by the supply of alternatively one or the other of two concentrated stock nutrition solutions in dependence on measured pH value and conductivity of the plant nutrition solution, the stock solution being supplied in dependence on the decrease of the conductivity below a predetermined value, and the supply of stock solution thus controlled by the conductivity being made from one stock solution providing nitrogen as metal nitrate when the pH value of the nutrition solution is below a predetermined value, to increase the pH value by the plants taking up metal nitrate, and from the other stock solution providing nitrogen as ammonium salt, when the pH value of the nutrition solution is above said predetermined value, to decrease the pH value by the plants taking up ammonium salt.
2. A method according to Claim 1, wherein the number of potassium ions in the nutrition solution is maintained at 100 to 150 per cent of the number of nitrogen ions in the nutrition solution.
3. A method according to Claim 2, wherein the number of potassium ions is kept at substantially 125 per cent of the number of nitrogen ions.
4. A method according to any of Claims 1 to 3, wherein both said stock solutions are

acidic.
5. A method according to any one of Claims 1 to 4, wherein the nitrogen is supplied through said other stock solution as a mixture of metal nitrate and ammonium salt.
6. A method according to Claim 5, wherein the mixture contains metal nitrate providing substantially 80 per cent of the nitrogen content while the rest comprises ammonium salt.
7. A method according to any one of Claims 1 to 6, wherein the metal nitrate consists substantially of calcium nitrate.
8. A method according to any one of Claims 1 to 7, wherein air is blown into the nutrition solution.
9. A method according to any one of Claims 1 to 8, wherein carbon dioxide is blown into the nutrition solution.
10. A method of growing plants without soil, substantially as described herein with reference to Figure 1 or Figure 2 of the accompanying drawings.