Method and equipment for dissolved oxygen enrichment of irrigation water for plant cultivation

Abstract

A method and equipment for plant cultivation, where the plants are supplied with water, over irrigation phases of specific duration spread over a 24 h day, which water has a given content of dissolved oxygen, characterized in that use is made of a system for boosting the injection of oxygen (or of an oxygen-containing gas mixture) in the irrigation water over a first period, of given duration, of one or some of the irrigation phases in question, and in that the remainder of the time of said irrigation phase(s) in question is characterized by a content of dissolved oxygen in the water which is nominal, i.e. lower than the boosted content of the first period.

Description

Process and installation for enriching irrigation water for plant crops with dissolved oxygen

[0001] The present invention relates to the cultivation of plants and in particular the cultivation of plants in greenhouses and above ground.

[0002] But the technical solution proposed within the framework of the present invention applies more generally to any method of carrying out a cultivation of plants, and in particular a cultivation in a controlled environment: in a greenhouse, in a cellar, away from light, in soilless mode, and in particular in hydroponics, aquaponics, aeroponics, bioponics or other mode.

[0003] So let's consider the case of greenhouse production, grown in soilless mode.

[0004] These productions are gaining ground all over the world, in rich and poor countries alike. They are one of the solutions to provide future generations with healthy, risk-free food. To achieve this, they use scarce natural resources such as water and fertilizers in the most efficient way possible.

[0005] For example, it is generally considered that growing one kilo of tomatoes in the open field uses around 60 litres of water, whereas in greenhouses and when grown in soilless conditions, water requirements are limited to around 15 litres.

[0006] In the case of a state-of-the-art greenhouse, it is even possible to make an additional saving of 4 liters per kilo. These savings are the result of more efficient water use thanks to control of the oxygen content of nutrient solutions.

[0007] Oxygen enrichment of irrigation water for soilless crops also helps increase production yield:

[0008] It is well known why plant roots not only need water but also need oxygen, and in particular the fact that when the oxygen content in the soil is insufficient, the absorption of water by the plant is limited and the plant's susceptibility to diseases is increased.

[0009] It is also known that enriching irrigation water with oxygen in the air limits the content to a maximum of 10 mg / L, while enriching it with dissolved oxygen using pure oxygen (O2) makes it possible to achieve much higher contents (typically 40 mg / l).

[0010] The systems used to achieve this enrichment are very varied, including porous materials, static mixers and other commercially available oxygenators, such as those offered by the company FOX (“France Oxygénation”).

[0011] However, we know that these devices are actually sold for applications in the field of water treatment, or even for fish farming. And so they are, in fact, designed to operate continuously.

[0012] However, in this area of ​​soilless cultivation, irrigation is not carried out continuously, it responds to cycles corresponding to the needs of the plants, depending in particular on the temperature and the brightness prevailing in the greenhouse. Watering is then done discontinuously to ensure that the roots return to the air, with injection and pause cycles etc.

[0013] In practice, we observe that the procedures commonly followed include fairly short watering phases, of the order of 10 minutes, and if at the beginning of the season watering is carried out approximately 4 times per day, at the end of the cultivation we can reach 24 waterings per day.

[0014] In practice, difficulties are then noted in the field in controlling the supply of oxygen to the plant. The experiments carried out by the Applicant have made it possible to understand the origin of these difficulties and to make, within the framework of the present invention, proposals for resolving these difficulties.

[0015] Because in fact, when a producer site launches a watering phase, for a given period of time, for example 10 minutes, it also launches the simultaneous injection of oxygen, for example pure oxygen (but it can also be a gas mixture containing oxygen, preferably a mixture containing at least 25% oxygen), into the water reaching the plants, but the oxygenation equipment available on the market, which we recalled above, all require a certain time to reach the set value of dissolved oxygen in the water concerned, for example to reach 35 mg / l, and this “delay” time can reach 5 to 10 minutes, or even 15 minutes in certain cases.

[0016] As we can see, this technical characteristic has a negative impact on plants, since existing systems do not provide them with the oxygen content they require during a given irrigation phase.

[0017] It is therefore the merit of the present invention to have assessed these difficulties and to propose here a technical solution which can be synthesized in the following way: According to the present invention, it is proposed to "boost" the injection of oxygen during a first part, of given duration, of an irrigation phase considered (of one of the phases or of several of the irrigation phases of the crop considered, and preferably at least for an irrigation phase following an irrigation stop (restart)); By way of illustration to better understand the invention, on a given irrigation phase of 10 minutes, where the aim is to provide the plant with a dissolved oxygen content (setpoint) of 35 or 40 mg / liter, a "boost" of the oxygen injection will be carried out during the first 30 seconds of the irrigation phase, i.e the implementation of a dissolved oxygen content which is higher than the target setpoint;In other words, two oxygen flow rates are set up in the irrigation water for a given phase: a boost flow rate (or "increased" flow rate) for a given boost period (for example 30 seconds), then after this first period, an oxygen flow rate which can be described as "nominal" i.e. at the setpoint is adopted during the remainder of the irrigation phase in question;According to an advantageous method of implementing such a double flow rate, an installation is implemented comprising a flow sensor, located on the water supply line to the greenhouse (or to the crop more generally regardless of the cultivation method used), and two oxygen supply lines or a mixture containing oxygen in the water supply line, each oxygen supply line being equipped with a flow meter in series with a solenoid valve, one of the two solenoid valves being time-delayed.And so, when irrigation starts, the flow sensor detects the passage of water, and it orders the opening of the two solenoid valves, only one being timed, for example to a value of 30 seconds. And so, the gas arrives through the two gas lines, then after 30 seconds the timed line stops (closes) and the gas then only passes through the second line for the remainder of the irrigation phase considered. According to one of the embodiments of the invention, the duration of said period of time during which the oxygen content is boosted is located in a time range in seconds from 0.5 to 1.5 times the water flow rate in m. 3 / h, so for illustration purposes, for a water flow rate of 38m 3 / h, the boost time will be in the range of 38 x 0.5= 19 seconds and 38 x 1.5= 57 seconds.

[0018] And as will be clear to those skilled in the art, the installation solution described above is extremely advantageous because it is very inexpensive.

[0019] Because in fact we could think at first glance of another embodiment of this oxygen boost, using a Mass Flow Regulator ("MFR" in the industrial gas sector), coupled with a regulator, where when the contactor detects the water flow it orders via the regulator an oxygen flow for example twice the demand for 30 seconds, then the regulator lowers the flow to settle on a nominal demand (not boosted).

[0020] It is therefore clear that this latter solution, which is very reliable and very luxurious, is also incredibly more expensive and is therefore not preferred according to the present invention.

[0021] The invention then relates to a method for growing plants, where the plants are supplied with water during irrigation phases of determined duration, spread over a 24-hour day, water which has a given dissolved oxygen content, characterized in that:

[0022] - a system is implemented for boosting the injection of oxygen or a gas mixture containing oxygen into the irrigation water during a first period, of given duration, of one or some of the irrigation phases considered, by the fact that the oxygen content in the water during said first period is higher than a given setpoint; and in that

[0023] - the remainder of the time of said irrigation phase(s) considered (of which a first period is boosted) is characterized by a dissolved oxygen content in the water which is equal to said setpoint, i.e. which is thus lower than the boosted content of the first period.

Claims

A plant cultivation process, where plants are supplied with water during irrigation phases of determined duration, distributed over a 24-hour day, water which has a given dissolved oxygen content, characterized in that: - a system is implemented to boost the injection of oxygen or a gaseous mixture containing oxygen into the irrigation water during a first period, of given duration, of one or some of the irrigation phases considered, by the fact that the oxygen content in the water during said first period is greater than a given setpoint; and in that - the remainder of the time of said or said irrigation phase(s) considered, the first period of which has been boosted, is characterized by a dissolved oxygen content in the water which is equal to said setpoint, i.e. which is thus less than the boosted content of the first period. A method according to claim 1, characterized in that the duration of said first period of time during which the oxygen content is boosted is within a time range in seconds of 0.5 to 1.5 times the water flow rate in m³ 3 / h feeding the culture during the phase considered. A method according to claim 1 or 2, characterized in that the system for boosting oxygen injection into irrigation water comprises an installation including: a flow sensor, located on the water supply line to the crop, and two supply lines for oxygen or a mixture containing oxygen into the water supply line, each supply line for oxygen or the mixture being equipped with a flow meter in series with a solenoid valve, one of the two solenoid valves being time-delayed, and in that at the start of an irrigation phase, the first period of which is boosted with oxygen, the flow sensor detects the passage of water and orders the opening of both solenoid valves, only one of which is time-delayed for said first period of given duration, thus allowing the gas to arrive via both gas lines, and then, at the expiration of said first period of given duration, the time-delayed line closes.and that the gas then passes only through the second line for the remainder of the irrigation phase under consideration. A method according to any one of the preceding claims, characterized in that said plant cultivation is cultivation in a controlled environment, among the following methods: in a greenhouse, in a cellar protected from light, in soilless mode, in hydroponic mode, aquaponic mode, aeroponic mode, or even bioponic mode or other. A method according to any one of the preceding claims characterized in that the oxygen injection is boosted during a first part, of a given duration, of at least one or some of the irrigation phases following a cessation of irrigation. A method according to any one of claims 1 to 4, characterized in that the oxygen injection is boosted during a first part, of a given duration, of all the irrigation phases spread over 24 hours. Plant cultivation installation where plants are supplied with water during irrigation phases of determined duration, distributed over a 24-hour day, water which has a given dissolved oxygen content, comprising: at least one irrigation water supply line to the crop; means for injecting oxygen or a gas containing oxygen into the irrigation water; characterized in that the installation includes a flow sensor, located on the water supply line to the crop, and in that the means for injecting oxygen or a mixture containing oxygen include two supply lines for oxygen or a mixture containing oxygen into the water supply line, each gas supply line being equipped with a flow meter in series with a solenoid valve, one of the two solenoid valves being timed. Installation according to claim 7, characterized in that said plant cultivation is a controlled environment cultivation, among the following methods: in a greenhouse, in a cellar protected from light, in soilless mode, in hydroponic mode, aquaponic mode, aeroponic mode, or even bioponic mode or other.