Method for root fertilization in cultivated plants

A method of root fertilization in cultivated plants, particularly in the field of hydrophonics is provided wherein water is finely impregnated with a gas mixture of carbon dioxide and pure oxygen, whereby the mixing ratio of the carbon dioxide and the pure oxygen corresponds approximately to the natural solution ratio of carbon dioxide and oxygen in normally clean water at atmospheric pressure and room temperature and whereby the individual gaseous phases, respectively their inflow to the gas mixture, can be controlled when required from the gas mixing area.

The invention relates to a method for the fertilization of roots in 
cultivated plants, especially in hydrocultures, wherein water or an 
aqueous fertilizer solution is impregnated with a mixture of CO.sub.2 and 
O.sub.2 and directed towards the root area of the cultivated plants. 
From the German open specification No. 35 03 710 there is known a method 
for the fertilization of leaves in cultivated plants using CO.sub.2 
-impregnated water, wherein CO.sub.2 is added to the water up to a content 
corresponding approximately to the natural saturation of the water. In 
order to impregnate with CO.sub.2, large qunatities of water are necessary 
for spraying and fertilization in horticulture or in agriculture. In the 
most stable and economical way, the U.S. Pat. No. 4,675,165 teaches a 
method and an installation for the impregnation of water with CO.sub.2. 
The installation proposed for carrying out the method has a straight flow 
channel open at the exit end, whose other end is connectable to a source 
of water under pressure, particularly to the usual water supply system. In 
operation, the flow channel is filled up completely over its entire length 
and its entire cross section by a quiet, nearly turbulence-free water 
stream. At several locations, interspersed in the direction of flow, the 
flow cross-section widens suddenly over an annular shoulder of small size, 
of for instance 1 mm or even less. The outer flow portions of the water 
stream, flowing over this shoulder are thereby considerably accelerated in 
this limited shoulder area relative to the flow in the same flow cross 
section. As a result there is a corresponding pressure drop in this 
narrowly limited area downstream of the shoulder. In this area, the flow 
channel has several open bores, distributed circumferentially, whose width 
corresponds approximately to the width of the annular shoulder. At the 
outer end, the bores abut a gas chamber connected to a compressed-gas 
source for pure CO.sub.2. In operation the water is supplied to the flow 
channel at the usual temperature and under the usual pressure of the water 
source, particularly of the water supply system. The pressure of the gas 
in the CO.sub.2 gas chamber is set to a value which is slightly lower than 
the static pressure of the water stream in the flow channel. If the latter 
is, for instance, equivalent to 3 bar, the pressure of the gas in the 
chamber is kept, for instance, at approximately 2.5 bar. In the shoulder 
areas, the CO.sub.2 -gas from the gas chamber enters the outer water flow 
portions, due to the pressure fall limited to these locations. This way, a 
negative-pressure impregnation of the water with CO.sub.2 -gas, confined 
to these narrow locations, is obtained, resulting in a very stable fine 
impregnation of the water with CO.sub.2. The number of the successive 
shoulder areas determines among other things the content of the carbon 
dioxide gas absorbed by the water. Thereby, the CO.sub.2 -content of the 
water is preferably kept at values under 3 g per liter of water, 
advantageously within the range of 0.05 and 2.5 g per liter of water. 
This water finely impregnated with CO.sub.2 is immediately, or after the 
addition of fertilizers and/or plant protection substances, directed to 
the soil either directly, e.g. through sprinklers, or finely misted or 
sprayed with common spraying devices for the fertilization of leaves. 
In this manner the required quantities of CO.sub.2 and H.sub.2 CO.sub.3 
necessary for a healthy growth, for a natural resistance against diseases 
and pests and for crop increase can be introduced into the soil or into 
the plants in a simple and economical manner. It is essential in this case 
that the content of carbon dioxide in the water be considerably higher 
than normally found in the water coming from the supply system. On the 
other hand, the natural absorption capacity of normal, clean water at 
environmental temperature and atmospheric pressure must not be 
significantly increased. This requirement is based on the fact that even 
small amounts of carbon dioxide insure the desired effect and that when 
the CO.sub.2 -content is limited, the losses of CO.sub.2 remain very low 
during the distribution of the finely impregnated water in the sprinkler- 
or spraying systems. 
However, for healthy growth of the plants, particularly the roots, a 
sufficient proportion of carbon dioxide and carbonic acid in the soil is 
not the only necessary factor. The soil has also to be supplied 
sufficiently with oxygen. Since in the upper soil strata, the atmospheric 
pressure and the gas composition are approximately equal to that of the 
atmosphere, an insufficiency of carbon dioxide gas leads also to an oxygen 
insufficiency. The soil air contains as known 20.93 vol-% O.sub.2 0.03 
vol.-% CO.sub.2 and 78.10 vol-% N. In a good humus soil, up to 5 kg of 
carbon dioxide gas is produced per hectare, and according to the Gay 
Lussac law, exchanged against proportional amounts of oxygen. Use of water 
finely impregnated with carbon dioxide gas also insures the supply of 
oxygen to the root area of soil-cultivated plants. 
The relationship becomes much more problematic, however, in the case of 
hydroponic applications or hydrocultures. Here the roots are not 
surrounded by gas-containing soil, but only by water or by solutions 
containing nutrients. It is known that also in this field of application, 
the fine impregnation with carbon dioxide gas of the water used for 
hydroculture and the therefrom resulting adjustable content of chemically 
bound oxygen in the water is responsible for the health and growth of the 
cultures. This way, from the German open specification No. 26 41 945 a 
method for the soil-free cultivation of plants is known, wherein a 
plant-nutrient solution is guided in a closed circuit, wherein the used-up 
plant nutrients are replaced by supplying one or the other from two 
concentrated supply solutions, depending on the measured pH-value of the 
plant-nutrient solution, and wherein, with the aid of one or several pipe- 
or hose ducts, carbon dioxide under pressure is blown into the nutrient 
solution, so that the plants can absorb the carbon dioxide through their 
roots. 
With respect to the gas exchange between CO.sub.2 and O.sub.2, the 
conditions existing in the water are completely different from the ones in 
the atmosphere. For instance, normally clean water at atmospheric pressure 
and at room temperature can absorb 0.88 l carbon dioxide gas, but only 
0.03 l oxygen. Thus, when the water or the nutrient solution are 
impregnated with CO.sub.2, there is danger that the absorbed carbon 
dioxide in the water will drive out the oxygen from the water, and will 
generally deprive the roots of the necessary supply of oxygen. 
In the last-mentioned method reported German open specification No. 26 41 
945 it is also known to blow air instead of the CO.sub.2 -gas or in 
addition thereto into the nutrient solution, through the perforations in 
the pipe- or hose ducts, in order to supply the nutrient solution also 
with oxygen. This known method is complicated and also does not lead to 
any certain and reproducible results. Also the supply of pure oxygen, 
based on the measurement of the content of carbon dioxide gas and oxygen, 
as well as the control of the oxygen supply and the corresponding control 
installations are cumbersome and costly and can hardly be used in 
practice. This applies also to the known case (compare European 
publication No. 0 062 966) wherein the fertilizer solution pumped in a 
closed circuit is atomized in a pressure container, containing oxygen and 
carbon dioxyde gas. There is intended achievement, through atomizing of 
the fluid in the pressure container, of corresponding impregnation of the 
fluid with the gases. In addition to the high capital costs required by 
the method, a disadvantage of the known method is that the gas content can 
hardly be accurately controlled and in the cultivated areas the gas losses 
are considerable.

In opposition thereto, it is the object of the present invention to further 
develop a method which can supply in a simple and cost-efficient manner 
the CO.sub.2, H.sub.2 CO.sub.3 and O.sub.2 to the root areas of cultivated 
plants, especially hydrocultures, so that the process can be safe and 
properly supervisable. 
Based on this method of this invention, CO.sub.2 and O.sub.2 is supplied to 
the water or the nutrient solution, in a stable mixing proportion. Since 
the two gases already present an initially stable mixing ratio, there is 
no need for neither test probes to measuring the CO.sub.2 -content or 
O.sub.2 -content in the water, nor a closed circuit through which the 
water or the aqueous fertilizer solution must be guided. Also, it is not 
necessary to provide a special dosing installation, or a control device 
acting between the probes and the dosing installation. The arrangement 
required for carrying out the method is therefore extremely simple, 
supervisable and insures in a cost-efficient manner perfectly reproducible 
results. 
Further, it is essential that a constant mixing ratio between the gases be 
maintained, which corresponds to the natural proportion of these gases in 
clean water at room temperature. This way it is avoided that one gas 
expells the other from the solution. Thereby very stable conditions are 
achieved, which of course have a decisive influence on the reproducibility 
of the results. 
It is particularly favorable for plant growth that in their root area 
practically natural conditions are maintained. Due to the absence of the 
expelling effect, no gas is lost from the fluid and this also contributes 
to cost savings. 
A further important feature of the invention is that the CO.sub.2 -content 
is limited to values under 3 g per liter of water. Particularly 
advantageous is a range within 0.05 g per liter and 2.5 g per liter of 
water. The limitation of the CO.sub.2 -content leads automatically to a 
corresponding limitation of the O.sub.2 -content, due to their natural 
proportions in the water. Normal tap water contains the gases in amounts 
considerably lower than the natural dissolving capacity. Therefore, with 
the new method the water can to a considerable extent be adjustedly 
enriched with these gases, and thereby each value up to the maximal value 
can be set securely and reproducibly. Due to the predetermination of the 
upper limit of the gas content, gas loss can be prevented, even when the 
water or the aqueous fertilizer solution are violently or turbulently 
agitated. 
The method of impregnation of the water with the gas mixture is also 
important for the stability of the gas content of the water. Hereby, the 
already known method of impregnation of the previously mentioned U.S. Pat. 
No. 4,675,165 can be advantageously used. This impregnation method is 
indispensable in order to achieve the desired purpose, since only the 
thereby conditioned stable dissolution of the gases in the water can lead 
to the mentioned advantages and can insure the required reproducibility of 
results. 
From the U.S. Pat. No. 4,675,175, dosage valves for various flow quantities 
are known in the installations for the controlled irrigation of soil-free 
plant cultivation with the aid of fertilizer solutions. In these known 
installations the problem is to achieve stable conditions while using 
various water sources (well water, rain water). For this, the pH-values 
and values of electrical conductibility of the fertilizer solution are 
established. Based on these values, the target values are set for the 
preparation of the fertilizer solution. The installation also has a 
CO.sub.2 -dosage device. In order to take into account the various water 
qualities, the therefor provided dosage valves are differently laid out 
with respect to their flow rate, so that by opening one or several of the 
individual valves, each time different mixing proportions of well water 
and rain water can be obtained. 
By contrast, the new method supplies to the area containing the gases to be 
mixed CO.sub.2 and O.sub.2 in the predetermined stable proportions, 
whereby the mixing ratio of CO.sub.2 to O.sub.2 in the gas mixture is 
advantageously kept at a stable value of 30:1. 
In order to prepare the mixture, the CO.sub.2 and O.sub.2 can be supplied 
to the chamber containing the gas mixture each as a pure gas and 
individually, as well as under equal pressure but in different amounts per 
unit time. For this purpose, the two gases can be supplied advantageously 
to the chamber over flow cross sections whose size is adjusted according 
to the mixing ratio. 
Advantageous results could already be observed when instead of the 
preferred mixing ratio, the mixture of CO.sub.2 :O.sub.2 ranges between 
20:1 and 40:1. 
The water which has been finely impregnated in this manner can be used for 
irrigation. However it is used preferentially in hydroculture and in 
hydroponics. For this purpose, there can be added to the water impregnated 
as above, the required nutrients and trace elements. 
If the nourishing water already from the start contains CO.sub.2 or O.sub.2 
gases in a higher proportion, or the requirement of specific plants for 
one of the individual gases differs from the normal requirement, the 
supply of these individual gases can be controlled, for instance by 
changing the cross section of the supply flow to the gas chamber.