Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
48;Z~
The invention re.Lates to ~ method and apparatus for
growing plants withou-t soil by means of a plant nu-trient
medium circulating in a closeci system.
It is known that in growing plants without soil, good
grow~h and a high yield can be obtained by maintaining
accurately adjusted nutritional conditions in the circulating
nutrient medium, water and plant nutrients being supplied .
as they are consumed, while a predetermined balance is
maintained between the nutrient substances. However, an
10. incorrect balance will rapidly show in reduced yield or in
direct symptoms of killing of the plants. Control of the
nutrient conditions is carried out by adding concentrated
solutions of different compositions to the nutrient solution ~ :
depending on measured values of pH and conductivity of the
nutrient solution.
A method and means for growing plants without soil
are described in Swedish patent 323,255 of Astra Home
Product AB granted 6 August 1970, and patent of addition :
` thereto, 331j610 of Astra Home Product AB granted 15 April 1971.
20. This method has been used for some time for growing tomatoes
in greenhouses; the nutrient medium used had the following
relative composition of the macro nutrient substances therein: .
N 100
p 15
K 95 :
Mg 15
S 10 ' ~ ~
Ca 30 : -~.
The nutrient medium also contained the necessary micro nutrient
30 substances (tracers) such as iron, manganese., zink, boron, .
. copper, molybdenum and cobalt. .... :
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80~ of the nitxoqen was in the form of nitrate nitro-
gen, and 20~ thereof in the form oE ammonium nitrogen.
After some time the plants showed evident indication of lack
of potassium (yellow leaf edges, bad quality of fruit)and
therefore the potassium content was raised from 95 to 123,
i.e. to a value which deviated considerably from the value
specified according to the patent. The pEI value then
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 (continuous pH control
was~ not performed for this test3 whereas the ideal pH value
is about 5.5; the pH value should in any case be above 4.
The plants were now characterized by relative lack of water,
-~ symptoms of death of the plant being a consequence thereof
('pIS'ti:l putrefaction), ..
~ Because of the aEore~entioned disadvantages of the ;~
-- prior art method, an Improved method and apparatus have
been developed. Thus, the present inVention provides a method
~ 20 for growin~ plants~without soil by means of a plant nutrient ;
- medium circulating in a closed system, wherein plant nutrients ;~
~;~ consumed are replaced by the addition of concentrated stock
solutions depending on the measured pH concentration of the
plant nutrient medium, nitrogen being supplied in the form Oe
nitrate nitrogen on a decrease of the pH below a predetermined
value in order to increase the pH value as a result of the
plants takin~ up nitrate ni-trogen, and nitrogen being supplied
:,
; in the form of ammonium nitrogen on an increase of the pH
above the predetermined value in order tb decrease the pH
value as a result of the plants taking up ammonium nitrogen,
the potassium content of the plant nutrition medium being
preferably maintained at 100 to 150~ of the nitrogen con-
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tent of the plant nu-tr,it.ion medium.
In broadest scope, -the present invention provides
a method of ~rowin~ plants in a circulating liquid nutrient
medium, which method comprises:
measurlng the conductivity and the pH of the nutrient
medium;
adding a stock nutxient solutio~ to the nutrient
medium to replenish the nutrient salt content of the medium
- when the conductivity of the medium ~alls to a first pre~
determined value;
the s~ock nutrient solution having a relatively con-
stant concentration of the elemental nutrients required by
the plan-ts for growth;
the stock nutrient solution hav.ing a relatively
constant pH, and
varying the source of nitrogen in the stock solution
, in response to the pH of the nutrient medium with the
content of nitrate nitrogen heing increased when the pH ~ -
~ of the nutrient medium falls below a predetermlned pH value
2Q and the content of ammonium nitrogen being increased when
the pH of the nutrient medium rises above said predetermined
pH value; ' '~
whereby the plants increase the production of basic ~ ,
emiss.ion products from the plant roots when the pH of the ~ '
nutrient medium falls below the predetermined pH value and '~
the plants increase the production of acidic emission pro- '
ducts from the plant roots when the pH of the nutrient ,
medium rises above the predetermined pH level.
; The present invention also provides apparatus for
30- growing plants in the absence of soil comprising:
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~ILl)4~3;Z7~)
means providing a circulating liquid pla~t
n~trient medium;
means to measure the conductivity of the ~
nutrient meclium; :.
means to measure the pH of the nutrient medium;
means providing a source of a stock nutrient
solution;
first control means actuatable by the means
to measure the conductivity of the nutrient medium;
the first control means being actuated to .
feed stock nutrient solution to the
nutr.ient medium when the conductivity of said medium
falls to a first predetermined value; .
: second control means actuatable by the means
;: to measure the pH of the nutrient medium; ~' ' !
the second control means being actuated to
vary the content of nitrate nitrogen and to vary the content
:: of ammonium nitrogen in the stock solution with the content ;~
of nitrate nitrogen being lncreased when the pH of the .
2a nutrient medium falls below a predetermined pH value and
with the content of ammonium nitrogen being increased when
the pH of the nutrient increases above the predetermined :~'
pH value.
In order to illustrate-the invention a preferred
: emhodiment thereof will be described in detail in the following
with reference being made to the accompanyi.ng drawings: :~
Fig. 1 discloses diagrammatically apparatus :
for use with the method according to the invention,and
Fig. 2 shows a somewhat modified embodiment
3~ of the apparatus for use with th~ method according to the
invention.
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'rhe apparatus disclosed comprises a tank 10
for nutrient medium which is provided with an output
conduit 11 having a liquid pump 12 by means of which nutrient
medium is pumped from the tank to channels 11' or flat tubes
or hoses made of plas-tic foil, the plants being "planted"
in these channel or tubes so that their root systems are
situated more or less in the plant nutrient medium circulating
therethrough. There is no soil in the channelbut there
may be sui~able material therein which absorbs nutrient
medium. If channels are used they are preferably covered
with plastic foil 13' or the like in order to reduce direct
evaporation therefrom. The root system of a plant thus
extends into the channelor tubes and the plant takes its
nourishment throuyh its root system directly from the nutrient
medium. The nutrient medium is of course supplied in large
excess to the channels and returns to the tank through a
return conduit 13. A conduit 14 is connected to the tank ~
for the supply of raw water and this supply is controlled ~ - ;
by means of solenoid valve 15. For the supply of concentrated
~ 20 nutrient stock solutlon there is conduit 16 having solenoid
;; valve 17 which has two inputs, one through conduit I8
provided wlth solenoid valve 19, from vessel 20, and the ~-
other through conduit 21 provided with solenoid valve 22,
vessel 23. The solenoid valves 19 and 22 are controlled
by pH meter 24, the test probe 25-of which is immersed
into the nutrient medium in tank 10, while the solenoid
valves 15 ahd 17 are controlled by means of conductivity
meter 26, the test probes 27 of which are also immersed
into the nutrient medium in the tank 10, as well as by float
3Q controlled level guard 28 for maintaining a predetermined
liquid level in the tank. The tank lS provided with spill-
~~~ way 29 and with one or more perforated tube or hose conduits 30
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which extend along the bottom o~ the tank and ~re connect-
ed to a compressor for blowinc3 air lnto -the nutrient
medium from below for oxygenatin~ the nutrient medium
and for providing turbulence and stirring of the nutrient
medium so that the medium will have uniform concentration
and composition. Carbon dioxide can be blown into the medium
instead of air so that the plants will take up carbon dio-
xide through the root system; for the rest carbon dioxide
is taken up through the leaves. It is also possible to
introduce air as well as carbon dioxide or a mixture thereof
into the medium.
According to the invention the method is - ~,
operated with two concentrated stock nutrient solutions
which are received in vessels 20 and 23, respectively~
These stock solutions preferably both have a pH value of
about 5.8 and thus ~oth are acid. The relative composition
of the two stock solutions ;s as follows;
-Vessel 20 Vessel 23 -
- N 100 lon ; ~ ~
P 15 15
K 123 123
Ca 32 74
Mg 20 20
As far as the stock solution in vessel 20 is
concerned the nitrogen can compr~se a mixture of 80%
C~(NO3)2 and 20 % NH4NO3, while the nitro~en of the solution
in the vessel 23 can compr~se solely 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 used because the plant does
not take up more calcium than it requires. The excess is -
harmles-s to the plants according to the tests made. As will
be seen the potassium content is preferably high, i.e. 100-
2~0
-1S0% on the average 125~, of the ni-tro~en content of the
nutrient medium. This potassium content is consIderably
higher than the content prescribed according to Swedish
patent 323,255 whereIn the potassium content is limited
to 40-100% of the nitrogen content.
When the plants take up Ca(NO3)2 from the
nutrient solution the roots of the plants will give oEf OH
and HCO3 - which are both basic and therefore this emission
from the plants increases the pH value. On the other hand
when the plants take up NII4NO3 the roots of the plants giye ~;
off an H ion which decreases the pH of the nutrient
medium. By measuring the pH by means o~ meter 24, the two
solenoid valves 19 and 22 are controlled in such a way that -
the valve 19 is open for connection throu~h conduit 18 from ~
.
vessel 20 to solenoid valve 17 when the pH i5 abo~e a pre- -
determined value which is the nomlnal value of the pH con-
centration of the nutrlent medium in the tank 10, while
solenoid valve 21 is opened to connect vessel 23 with sole-
noid valve 17 when the pH of the nutrient ~edium in the tank
2Q 10 lS below the predetermined value. Thus, either connection
from vessel 20 or from vesse~l 23 to the solenoid valve
17 is maintained but the supply oP concentrated solution
from one or the other of these two vessels- is controlled
not by the pH value of the nutrient medium in the tank 10
but by the conductivity~of this medium; thus, the pH deter-
~ines the vessel from which the~solution will be supplied
but this will be supplied as required in accordance with
the conductivity of the nutrient medium in tank 10.~ When ,
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~ the medium in tank 10 is decreased in nutrient salts - ~-
contained therein, the conductivity decreases which is measured
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by the conductivity meter 26 and solenoid valve 17 is opened
at a predetermined value for the supply of nutrient solution
to the tank. If the concentration of nutrient substances in
the nutrient solution should be too high, which is not incon-
ceivable when evaporation from the cannels or the plants is
high, solenoid valve 15 will be opened at a predetermined ~ -
upper value of the conductivity for the supply of raw water
to the tank. Any excess solution will drain off through
spillway 29. The necessary amount of sulfur can be supplied
1~ with the raw water. The supply of raw water also is controlled
depending on float con-trolled level guard 28 so that a pre~
determined liquid level is always maintained in the tank.
If the concentration of nutrient subs-tances in the solution
is altered by refill depending on the level guard, the con-
ductivity measurements, and the pH value as measured by
means of the pH meter wlll determine if stock solution from
vessel 20 or that from vessel 23 will be supplied.
If the liquid level in the tank 10 were to be
lowered so far that the test probes 27 of the conductivity
meter were no longer immersed this would mean that the con-
ductivity meter would measure a resistance of indefinite
value which is equivalent to an order for supply of nutrient
solution from the vessel 20 or 23. This could happen if
leakage arose in the circulation system or if the supply of
water failed. If a concentrated nutrient solution were to
be c;rcu]ated to the plants this could be catastrophic and
the plants could be totally destroyed. In order to eliminate
this risk the level guard 28 is arranged so that it will
close solenoid valve 17 at an even lower level than that at
which the supply of water is started, although the conducti-
vity meter indicates opening of the solenoid valve.
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The control siynal from the level yuard to the solenQid v~lve
17 thus overricles the control signal trom the conductivity
meter 26 and closes the valve 17 so that no further concen-
trated nutrient solution will be supplied to the tank.
When the plants take up Ca~NO3)2from the nutrien-t
medium the pH value of the medium will increase as mentioned
before, and the supply of concentrated solution takes place
from vessel 20 when the concentration of the nutrient solution
in tank lO has decreased sufficiently for the supply to be
made~ When the pH decreases following a decrease of the
nitrogen content due to the plants taking up NH4NO3, solution
will be supplied instead from vessel 23 when required by the
conductivity measurement. Excess calcium, if any, does not
harm the plants as already mentioned.
Trace elements should also be used in the nutr-
ient solutions. Iron is one such trace element but it cannot,
as in known nutrient solutions for growing plants without
soil, be present as a nitrate because the iron would then
deposit in the nutrient solution and the plants would lack
iron. Thus iron must be supplied as an iron chelate. The
same is true for manganese.
The conductivity of the nutrient medium in the
tank 10 should range from 1400 to 4000~ S/cm and preferably
between 1600 and ]800~S/cm. The pH value should range from
5.7 to 6.5 and preferably should be 5.8 with a variation of
+ 0.1.
The use of the method according to the invention
has resulted in good growth of plants and a rich crop, in
many cases up to more than three times the crop obtained ~
3n when grown in the conventional manner usiny soil. The present ~ ~;
'~A' control involving use of two solutions in vessels 20 and 23
has turned out to be less sensitive than control using a basic
and an acid as well as a tl-lird, acid or neutral solution as
~L8~7~
proposed before accorcling to Swedis~ patent 331,61~. The
present methQd furnishes the plants with plant nutriment
as required for their growth ancl ~ruit setting without risk
of deviations in the balance o~ the plant nutrient medium
so as to provide a lack of nu-triment ~n some aspect or o-ther
whereby the plants are damaged occasionally or permaneantly.
The sys-tem can be completely automated and, as will be seen
from the embodiment descrihed, inherently prevents fail-ure
of raw water supply which would result in a dangerously ~igh
concentration in the nu-trient medium.
Conductivity meter 26, which receives signals
- from the test probes 27 thereof which are for example oxidized
platina electrodes, preferably is provided with thermistor
means for temperature compensation, and, as shown in
Figure 2, may be connected to am ampliEier 30 wherein the
nominal value of the conductivity of the nutrient medium in
the tank 10 can be ad~usted, It IS also connected to
amplifier 32 which in turn is connected to alarm apparatus
33 for emitting an alarm signal at a predetermined maximum
value of the conductivity, and to amplifier 34 also conn~
ected 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, depending on any discrepancy between the actual
value of the conductiv;ty and the nominal value thereof, to
a timer 35 which is connected to pH meter 24. This meter
receives a signal from the test probe 25.
Solenoid valves 17, lg and 22 in Fig. 1 are re-
-- placed in this case by two pumps 36 and 37 arranged to pump
stock nutrient solution from vessels 20 and 23, respectively,
to the tank 10, and one of these pumps is operated for a
predetermined time interval depending on the conductivity
10 .
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measured, by the timer 35. The pump which i5 operated is cle-
pendent on the measured p~-l value and is selected by the pH
meter 24.
~lo level guards 28a and 23b are provided, level
guard 28a being connected to solenoid valve 15 to close
this valve at a predetermined maximum level in the tank 10.
The ampliEier 32 is also connected to the solenoid valve
15 in order to open the valve when the conductivlty has reached
a predetermined maximum value. Level guard 28b is connected
to solenoid valve 15 to open it at a predetermined lowermost
liquid level in the tank 10 and is also connected to timer
; 35 to simultaneously stop the pump 36 or 37, which i.s operatin~
Thus it will be seen that the function is prin-
cipally -the same as has been described with reference to
Fig. 1.
The timer 35 is arranged to control the operation ~ ;
of the pump 36 or 37 in such a manner that the pump is
operated for intervals of S to 20 seconds and is allowed ~:
; to be deenergized between these intervals from 1 to 10
minutes. The timer includes means for manual presetting ;~
of these intervals which have to be ad~usted to the total
liquid volume of the system.
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