METHOD FOR PRODUCING AN INORGANIC IRON NUTRITIONAL COMPOSITION

Abstract

A plant fertigation process comprising the formation of a series of stock solutions, feeding each of the stock solutions into a dilution system to form a fertigation solution, feeding a fertigation device by means of a transfer device, supplying said fertigation device with said fertigation solution, and the addition of iron and at least one polyphosphate.

Description

[0001] The present invention relates to a method for implementing an inorganic iron nutrient composition according to claim 1. Reference is also made to the corresponding device for fertigation of plants.

[0002] Whether for human, animal, plant or microorganism nutrition, the assimilation of minerals (macro- and micronutrients) is essential to the life cycles of these different organisms.

[0003] Indeed, it is known that macronutrients (carbon, hydrogen, oxygen, nitrogen, potassium, sodium, calcium, magnesium, phosphorus, and sulfur) must be present in optimal quantities for plants to develop optimally. Micronutrients, or trace elements, present in lower concentrations than macronutrients in plants, include, for example, chlorine, iron, boron, manganese, zinc, copper, nickel, and molybdenum, and are also very important. If any of these micronutrients are deficient or present in too low a concentration, deficiency diseases can result, directly impacting plant growth and therefore crop yields.

[0004] Furthermore, in order to be absorbed and assimilated, these nutrients must be bioavailable, that is, able to be completely solubilized in a solution from which these organisms can draw and assimilate them.

[0005] Among these micronutrients, iron is the one for which the plant requires the highest concentration (around 100 mg / kg of dry tissue), this element being necessary for the synthesis of chlorophyll which is itself essential for photosynthesis, which is directly linked to the growth and "survival" of plants.

[0006] However, iron is a micronutrient well known for being particularly poorly solubilizable. One method used to solubilize iron involves complexing it with synthetic organic chelates. However, these chelating agents are increasingly controversial because they are not biodegradable and, in particular, promote the resolubilization of heavy metals in surface waters.

[0007] It is for this reason that inorganic iron-based nutritional compositions have been developed (see for example international patent applications WO 2014 / 056690 and WO 2014 / 056688), these compositions contain at least one source of iron and a polyphosphate.

[0008] Nowadays, horticulturalists and farmers are increasingly using fertigation, a technique that optimizes water and nutrient supply efficiently and ecologically. However, in a fertigation system, it is essential that the minerals be completely dissolved in the irrigation solution to be present as ions that can be absorbed by plants, as minerals in solid form are not readily available to plants.

[0009] Current fertigation processes typically involve preparing one or more stock solutions by dissolving solid fertilizers or by mixing / diluting liquid fertilizers. Each of these stock solutions is then added to the irrigation water, either in a dilution tank or directly into the irrigation line, to form a fertigation solution. A fertigation device (such as a drip irrigation system) is then supplied with this solution via a transfer device. This device then provides a continuous supply of fertilizer to plants grown hydroponically, on substrates, in soil, aeroponics, or using the nutrient film technique.

[0010] Such processes and devices are described in documents DE2729417 and US8690982 in which phosphoric acid is added as a nutrient.

[0011] When growers decide to opt for alternatives without organic iron chelates and to use inorganic iron-based nutrient compositions, it is typically necessary to introduce this iron source into a stock solution of a chosen composition and then inject this stock solution into the irrigation solution. Various implementation methods can be proposed.

[0012] For example, one could consider injecting the aqueous nutrient composition of patent application WO2014056690, either as is or diluted with water, directly into the irrigation solution, with this nutrient composition then acting as a stock solution. The same type of stock solution can be obtained by dissolving the solid nutrient composition of application WO2014056688 in water separately from other fertilizers. Another possibility is to introduce inorganic nutrient compositions based on solid or liquid iron into one of the stock solutions already used to provide the other nutrients required by the plants.

[0013] Unfortunately, this application of inorganic iron-based nutrient compositions is problematic for many growers. A chemical precipitation phenomenon frequently occurs during the feeding stage of the stock solution containing the iron source into the irrigation solution. The resulting solid phase, composed primarily of calcium phosphate, carries with it a significant amount of iron, which is thus lost.

[0014] This precipitation phenomenon leads to iron deficiencies and also results in fouling and even blockages of the devices used to dose and inject the stock solution into the irrigation solution or fertigation solution. Blockage is particularly significant in the case of the venturi system commonly used by growers to dose stock solutions, where a portion of the calcium-rich irrigation solution is typically used as a suction fluid. Blockage of the venturi device can lead to a complete halt in iron dosing if the problem is not detected promptly, with potentially disastrous consequences for the crop.

[0015] Upon further diagnosis, it was also observed that the precipitate, once formed, struggles to resolubilize in the irrigation solution, even when the solution's pH falls within the range typically recommended for fertigation (pH 5.5–5.8). Consequently, the residence time of the solution in the mixing tank (when present) is insufficient to dissolve the precipitate. Furthermore, any storage tanks for the irrigation solution and the irrigation line downstream of the mixing tank are not sufficiently agitated to allow the precipitate to dissolve further.

[0016] This precipitation problem is clearly linked to the basic pH of the stock solutions naturally obtained from these iron-based inorganic nutrient compositions. As stated in claim 12 of patent application WO 2014 / 056690, the preferred pH range for the aqueous phase nutrient composition is from 7 to 10.8, where the storage stability of the solution is optimal.

[0017] On the other hand, as shown in Examples 1 and 2 of patent application WO 2014 / 056688, the solid nutrient composition also yields typically basic pH values ​​after being dissolved in water. It is possible to lower the pH of these stock solutions by adding a certain amount of acid, but to date it is not clear whether there is a pH range for these stock solutions that would avoid the precipitation problem described above without creating other difficulties.

[0018] Lowering the pH of the stock solution containing said iron source tends to reduce its storage stability, and this for two different reasons.

[0019] First, the protonation reaction that polyphosphates undergo when the pH of the solution is lowered generally reduces their complexing power towards metallic cations such as iron.

[0020] On the other hand, it is also well known that a decrease in pH increases the rate of polyphosphate hydrolysis, the disappearance of which leads to iron precipitation. However, the stock solutions in question must be able to be stored for several weeks without precipitation at storage temperatures of up to 40°C in horticultural greenhouses, knowing that this high temperature further accelerates polyphosphate hydrolysis.

[0021] The chemical stability data we have for irrigation solutions cannot be extrapolated to the case of stock solutions, which are typically 100 to 10,000 times more concentrated and have much longer storage times than irrigation solutions, whose consumption time rarely exceeds 1 or 2 days.

[0022] The invention aims to overcome these drawbacks of the prior art by providing an optimal method for implementing iron and at least one polyphosphate in fertigation devices.

[0023] To solve this problem, the invention provides a method for fertigating plants comprising the provision of a series of stock solutions comprising a stock solution comprising iron and at least one polyphosphate, at basic pH or at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5, formed by the addition of iron and at least one polyphosphate to an aqueous phase, feeding each of the stock solutions into a dilution system, to form a fertigation solution, feeding a fertigation device by means of a transfer device, supplying said fertigation device with said fertigation solution.with the condition that if said stock solution is at basic pH, a sufficient quantity of acid is added to said dilution system before feeding said stock solution, and sufficiently intensive mixing conditions at a feeding point of said stock solution in said dilution system are ensured so that said fertigation solution has a pH below 6.2.

[0024] By studying the stability of said solutions as a function of their pH, and then testing the new implementation method according to the invention in all kinds of configurations including venturi devices

[0025] operating with a recycling of the irrigation solution, it has been surprisingly shown that the aforementioned pH range avoids the precipitation problem encountered when feeding one or more stock solutions into the irrigation solution while maintaining sufficient storage stability of the stock solution series itself.

[0026] Furthermore, the pH range is sufficiently wide to ensure the robustness of the implementation method according to the present invention, despite the numerous parameters that can influence the pH of the stock solution series or the fertigation solution and disrupt their adjustment: the concentrations in the stock solution series and the fertigation solution, the potential buffering effect of other constituents, and the various dosing errors that can occur, particularly with regard to the acid added or left in excess to lower the solution's pH. These errors can be especially significant in the case of liquid fertilizers, where it is often a matter of neutralizing basic solutions with other acidic solutions, and where a small excess of either solution can create substantial pH variations.

[0027] Indeed, according to the present invention, the aforementioned pH range in the stock solution into which the iron and said at least one polyphosphate are fed makes it possible to avoid the precipitation problem encountered when feeding the stock solution into the irrigation solution, while maintaining sufficient storage stability of the solution.

[0028] In a variant of the process according to the present invention, although, as mentioned above, the precipitation problem described above tends to exclude any other implementation process that would feed a basic stock solution comprising iron, it is also provided that said at least one solution of iron and at least one polyphosphate at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5, is a solution of iron and at least one polyphosphate at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5, preferably less than or equal to 5.8 and is the fertigation solution.

[0029] Indeed, the slightest exceedance of pH above 6.2, even localized at the point of supply of said stock solution in the irrigation solution, seems sufficient to cause the problem given the persistence of the precipitate once formed.

[0030] However, surprisingly, it has been shown in the variant of the process according to the present invention that the precipitation phenomenon in question can nevertheless be avoided, for example by ensuring a sufficiently rapid dispersion of said basic mother solution comprising iron at the feed point and by dosing a sufficient quantity of acid upstream of the feed point so that the resulting mixture is below pH 6.2, preferably below pH 6.0 and preferably below pH 5.8.

[0031] A dispersing turbine or other intensive mixing device, whether static or dynamic, can be installed in the mixing tank or irrigation line to create the necessary dispersing effect at the supply point. Alternatively, this implementation method can be implemented by selecting a supply point within the mixing tank that provides sufficiently intensive mixing conditions.

[0032] The suitability of the mixing conditions at the feeding point can be verified by measuring the solubilized iron content according to the analytical method described in the patent applications mentioned above.

[0033] The present invention therefore also provides a method for implementing basic stock solutions comprising iron and at least one polyphosphate which does not require bringing said stock solutions into the pH range claimed above.

[0034] Preferably, in the process according to the present invention, said addition of iron and at least one polyphosphate is carried out by feeding separately or together, a source of iron and a source of at least one polyphosphate, each source being, independently of each other, in the form of a solid, a solution or a suspension.

[0035] In another preferred embodiment of the present invention, said addition of iron and at least one polyphosphate is carried out by feeding a composition containing iron and at least one polyphosphate, in solid form, solution or suspension.

[0036] In a variant of the process according to the present invention, said at least an addition of iron and at least one polyphosphate to an aqueous phase with a formation of at least one solution of iron and at least one polyphosphate at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5 is an addition of a pre-solution of iron and at least one polyphosphate to a stock solution, which forms the solution of iron and at least one polyphosphate at a pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5.

[0037] In another variant of the process according to the present invention, said at least one solution of iron and at least one polyphosphate at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5 is a solution of iron and at least one polyphosphate at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5 added to at least one stock solution of said series of stock solutions.

[0038] Advantageously, in the process according to the present invention, said at least one stock solution of said series of stock solutions containing iron and at least one polyphosphate also contains ions selected from the group consisting of sulfates, phosphates of any type, nitrates, chlorides, potassium, ammonium, sodium and mixtures thereof.

[0039] According to a preferred embodiment of the present invention, said at least one mother solution of said series of mother solutions containing iron and at least one polyphosphate, does not contain magnesium ion.

[0040] According to yet another embodiment, iron and said at least one polyphosphate are added to an aqueous phase to form a stock pre-solution comprising iron and at least one polyphosphate, said stock pre-solution comprising iron and at least one polyphosphate then being added to another aqueous phase to form said at least one solution of iron and at least one polyphosphate at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5.

[0041] More particularly, in the process according to the present invention, said at least one mother solution of said series of mother solutions or said pre-mother solution containing iron and at least one polyphosphate, contains micronutrients selected from the group consisting of boron, manganese, zinc, copper, molybdenum, cobalt and mixtures thereof, preferably in an atomic ratio with respect to Fe between 0.1 and 5 for B, 0.05 and 2.5 for Mn, 0.01 and 1 for Zn, 0.005 and 0.25 for Cu and Mo and between 0.001 and 0.1 for Co.

[0042] Advantageously, in the plant fertigation process according to the present invention, the pH of said mother solution or of one of said mother solutions or of said pre-mother solution or of the fertigation solution containing iron and at least one polyphosphate is adjusted by adding an acid chosen from the group consisting of mineral acids, such as, for example, nitric acid, sulfuric acid, phosphoric acid and mixtures thereof.

[0043] Advantageously, said fertigation solution has a molar concentration, expressed in millimole / L (mM) of phosphorus (P) between 0.05 and 5 mM, preferably between 0.5 and 3 mM, advantageously between 1 and 2 mM.

[0044] The process according to the present invention comprises, in a preferred mode, an oxidation of said at least one solution of iron and at least one polyphosphate and / or of said pre-mother solution containing iron and at least one polyphosphate.

[0045] For example, commonly used oxidation treatments include: air bubbling using a disperser located at the bottom of the tank (the air can come from a compressor or a simple pump), agitation of the liquid surface under air, and the addition of oxidants such as oxygen, air, hydrogen peroxide, and bleach.

[0046] The duration of the oxidation treatment varies between a few hours and several days depending on the size of the tank and the aeration system used.

[0047] In yet another advantageous embodiment of the process according to the invention, iron and said at least one polyphosphate are added in a ratio P poly / Fe of between 5 and 50, preferably between 8 and 32, where Fe represents the total number of moles of iron and where P poly represents the number of moles of phosphorus in the form of polyphosphate.

[0048] More particularly, in the process according to the present invention, said at least one polyphosphate comprises potassium tripolyphosphate, and / or tetrapotassium pyrophosphate, and / or potassium tripolyphosphate, and / or sodium tripolyphosphate, and / or sodium acid pyrophosphate, and / or tetrasodium pyrophosphate, and / or ammonium pyrophosphate, and / or ammonium polyphosphate, or mixtures thereof

[0049] More particularly, in said solution of iron and at least one polyphosphate, the molar ratio P ortho / P total, with P ortho the number of moles of P in ortho form and P total the total number of moles of P, between 0 and 0.95, preferably 0 to 0.3.

[0050] In a particularly preferred embodiment, each feeding step of each of the stock solutions into the dilution system is a venturi-drive transfer step of said stock solution by means of a fertigation solution flow derived from the discharge of said transfer device which allows feeding the fertigation device in which the pH of the fertigation solution is less than 6.2.

[0051] Advantageously, and more particularly when iron and said at least one polyphosphate are added to the fertigation solution, said fertigation solution is at a pH below 6.0 and preferably below 5.8.

[0052] Preferably, in this case, the iron and said at least one polyphosphate are added to said fertigation solution at a feeding point exhibiting sufficiently intense mixing conditions to avoid any precipitation.

[0053] Advantageously, said stock solutions comprising iron and at least one polyphosphate have an iron concentration of 0.15 mM to 500 mM.

[0054] Advantageously, said stock solutions comprising iron and at least one polyphosphate constitute a solid inorganic composition containing iron and at least one polyphosphate dissolved in water or in an aqueous solution (fertigation solution or drainage solution) or a liquid inorganic composition comprising iron and at least one polyphosphate.

[0055] Advantageously, said stock pre-solutions comprising iron and at least one polyphosphate constitute a solid inorganic composition containing iron and at least one polyphosphate dissolved in one of said stock pre-solutions or a liquid inorganic composition comprising iron and at least one polyphosphate.

[0056] Preferably, said at least one source of iron is chosen from the group consisting of Fe2(SO4)3.xH2O where x represents a molar coefficient between 0 and 9, MFe(SO4)2.12H2O where M represents Na or K, Fe(NO3)3.xH2O where x represents a molar coefficient between 0 and 9, FeCl3.xH2O where x represents a molar coefficient between 0 and 6, Fe4(P2O7)3, FePO4.xH2O where x represents a molar coefficient between 0 and 4, FeSO4.xH2O where x represents a molar coefficient between 0 and 7, FeCl2.xH2O where x represents a molar coefficient between 0 and 4, FeO.xH2O where x represents a molar coefficient between 0 and 1, Fe(NH4)PO4.H2O, iron oxysulfate and their mixtures.

[0057] Advantageously, feed water, stock solutions or pre-stock solutions, or fertigation solutions can be filtered by any commonly used means or device such as, for example, sand filters, ...

[0058] Other embodiments of the process according to the invention are indicated in the attached claims. In the drawings, the figure 1 schematically represents one embodiment of the first method according to the present invention. figure 2 schematically represents one embodiment of the second embodiment of the process according to the present invention. figure 3 schematically represents one embodiment of the third embodiment of the process according to the present invention. figure 4 schematically represents one embodiment of the fourth embodiment of the process according to the present invention. figure 5 schematically represents one embodiment of the fifth embodiment of the process according to the present invention.

[0059] In the figures, identical or analogous elements bear the same references.

[0060] The plant fertigation process according to the present invention comprises a provision of a series of stock solutions A, B... in a series of stock solution tanks 1, 2,..., a feeding of each of the stock solutions (A, B,...) into a dilution system 6, to form a fertigation solution F, a feeding of a fertigation device 7 by means of a transfer device 8, supplying said fertigation device 7 with said fertigation solution F, an addition of iron and at least one polyphosphate to an aqueous phase with the formation of at least one solution D of iron and at least one polyphosphate at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably a pH greater than or equal to 5.5.

[0061] In a preferred embodiment of the invention, the process makes it possible to achieve an iron yield at the outlet of the tubing 9 of the fertigation system 7 of more than 85%, preferably more than 90%. Iron yield is defined as the concentration of soluble iron measured at the outlet of the tubing 9 of the fertigation system 7 (or just before the fertigation solution comes into contact with the substrate(s) and the plant(s)) relative to the theoretical iron concentration at that point. The theoretical iron concentration is calculated based on the initial iron concentration (stock solution or pre-stock solution) and the dilution factor of the fertigation solution preparation step F.

[0062] In a first embodiment of the process according to the invention illustrated in the figure 1The said series of stock solutions comprises a first stock solution A in a first stock solution tank 1 and a second stock solution B in a second stock solution tank 2. The first stock solution A comprises calcium nutrients, preferably in the form of nitrate or chloride, and magnesium nutrients, preferably in the form of nitrate. The second stock solution B comprises sulfate and phosphate anions, and mixtures thereof, as well as iron and at least one polyphosphate, fed, for example, by a hopper P in solid form. The second stock solution B is the solution D of iron and at least one polyphosphate having a pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably greater than 5.5, by adjusting the pH using pH adjustment means 10 connected to the second tank 2 with acid.

[0063] Naturally, depending on the fertigation systems available to horticulturalists or farmers and the possibilities for adapting them, the process according to the invention can be implemented in various ways. The first, mentioned above, aims to adapt the conventional process by introducing calcium and magnesium nutrients into the first tank, while the other nutrients, including iron and at least one polyphosphate, are introduced into the second tank.

[0064] In this embodiment, the only ions with which the inorganic nutrient composition, comprising iron and at least one polyphosphate, is incompatible are calcium and magnesium. These are isolated in the first stock solution A in the first stock solution vessel 1, while the inorganic nutrient composition is implemented in the second stock solution B in the second stock solution vessel 2, for example, with monopotassium phosphate (MKP), potassium nitrate (KNO₃), or potassium sulfate (K₂SO₄). However, magnesium, which is often found as sulfate in the second stock solution B in conventional processes, is now supplied as nitrate in the first stock solution A.

[0065] The pH of the second stock solution B must be greater than 4.5, preferably greater than 5.0, and advantageously greater than 5.5, to ensure the stability of the iron during storage. On the other hand, if the pH of this second stock solution does not exceed 6.2, any risk of precipitation during the dilution step is eliminated, as explained above.

[0066] The other trace elements or micronutrients (B, Mn, Zn, Mo, Co, Cu and their mixtures) can be introduced into both the first stock solution A and the second stock solution B; however, in view of the pH conditions imposed in the second stock solution B, it is preferable to introduce them into the first stock solution A.

[0067] In a second embodiment according to the present invention illustrated in the figure 2The series of stock solutions comprises a first stock solution A contained in a first stock solution tank 1 and a second stock solution B contained in a second stock solution tank 2. The first stock solution A comprises calcium nutrients, preferably in the form of nitrate or chloride, and magnesium nutrients, preferably in the form of nitrate. The second stock solution B comprises sulfate and phosphate anions and mixtures thereof, as well as iron and at least one polyphosphate. The iron and the at least one polyphosphate are supplied from a pre-stock solution C contained in a pre-stock solution tank 3 to the second stock solution B in the second stock solution tank 2 by means of a transfer tube 11 connected on one side to the pre-solution tank 3 and on the other side to the second stock solution tank 2. pH adjustment means 10 are connected directly to the pre-stock solution tank 3.The pre-stock solution C has sufficient acidity to ensure a pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably greater than 5.5 in the said second stock solution B.

[0068] In this particular embodiment of the process according to the present invention, a pre-stock solution C comprising iron and at least one polyphosphate is provided for subsequent transfer into the second stock solution B as a solution. In this case, the pH of the pre-stock solution C is directly adjusted by adding acid such that the pH of said second stock solution B is between 4.5 and 6.2, more particularly between 5.0 and 6.0, preferably greater than 5.5. This can be achieved in various ways, such as by adjusting the pH of the pre-stock solution C to a predetermined pH using pH adjustment means 10, so that the pH in the second stock solution B is within the required range of 4.5 to 6.2, more particularly between 5.0 and 6.0, preferably greater than 5.5.In this case, the second stock solution B is the solution of iron and at least one polyphosphate at a pH within the required range mentioned above (B=D). Another method involves adjusting the pH in the second stock solution B as well, in which case the second cuvette 2 is also connected to pH adjustment means 10 (not shown), or by ensuring that the second stock solution B has a pH between 4.5 and 6.2, more particularly between 5.0 and 6.0, preferably greater than 5.5, as does the pre-stock solution C. In this latter case, the pre-stock solution C is solution D (C=D) containing iron and at least one polyphosphate at a pH between 4.5 and 6.2, more particularly between 5.0 and 6.0, preferably greater than 5.5, but also the second stock solution B (B=D).

[0069] In a third particular embodiment of the process according to the present invention illustrated in the figure 3The series of stock solutions comprises a first stock solution A in a first stock solution tank 1 and a second stock solution B in a second stock solution tank 2. The first stock solution A in the first stock solution tank 1 comprises calcium nutrients, preferably in the form of nitrate or chloride, and magnesium nutrients, preferably in the form of nitrate. The second stock solution B in the second stock solution tank comprises sulfate and phosphate anions and mixtures thereof, as well as iron and at least one polyphosphate. The iron and at least one polyphosphate are supplied from a pre-stock solution C contained in a pre-solution tank 3 to the second stock solution B by means of a transfer tube 11 connected on one side to the pre-solution tank 3 and on the other side to the second stock solution tank 2. The pH adjustment means 10 are connected to the second stock solution tank 2.The second stock solution B is then said solution D (B=D) of iron and at least one polyphosphate having the pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably greater than 5.5, by adjusting it with acid.

[0070] In this particular embodiment of the process according to the present invention, a stock pre-solution C comprising iron and at least one polyphosphate is provided for subsequent transfer into the second stock solution B as a solution. In this case, the pH of the second stock solution B, into which the pre-solution is added, is directly adjusted to a value between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, more particularly greater than 5.5, by means of an acid addition.

[0071] Advantageously, in the second and third embodiments, the pre-stock solution C comprises iron and at least one polyphosphate and has a P poly / Fe ratio between 5 and 50 and preferably between 8 and 32, where Fe represents the total number of moles of iron and where P poly represents the number of moles of phosphorus in the form of polyphosphate.

[0072] Preferably, in the second and third embodiments, the pre-stock solution C is formed from a nutritive inorganic composition based on iron and at least one solid or liquid polyphosphate.

[0073] Preferably, in the second and third embodiments, the pre-stock solution C is formed from an iron source and at least one solid or liquid polyphosphate added independently or not.

[0074] In a fourth preferred embodiment of the method according to the present invention illustrated in the figure 4said series of stock solutions comprises a first stock solution A in a first stock solution 1 tank, a second stock solution B in a second stock solution 2 tank, and a third stock solution E in a third stock solution 5 tank. The first stock solution A comprises calcium nutrients, preferably in the form of nitrate or chloride, the second stock solution B comprises sulfate and phosphate anions or mixtures thereof, and said third stock solution E comprises iron and at least one polyphosphate; the magnesium nutrients being able to be supplied in said first stock solution A or in said second stock solution B; said third stock solution E being said solution D (E = D) of iron and at least one polyphosphate having a pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably greater than 5.5 by adjustment thereof with acid.

[0075] In this embodiment, a third stock solution E comprising iron and at least one polyphosphate is formed separately (for example, in a third stock solution tank 5 or from pre-stock solutions (not shown) fed into the third stock solution tank 5). It is then fed, not into the second stock solution B, but directly into the fertigation solution F, into the dilution tank 6 or into the irrigation line 12, using, for example, its own transfer device 13. However, in this embodiment, the pH will be adjusted to a value between 4.5 and 6.2, advantageously greater than or equal to 5.0 and less than or equal to 6.0, preferably greater than 5.5, by the pH adjustment means 10 connected to the third tank 5, in particular by adding acid to the third stock solution E.Although this embodiment requires two additional pieces of equipment—a tank 5 for preparing a third stock solution E and an additional dosing system 13 or 14 for adding this solution to the dilution tank 6 or the irrigation line 8—it is nevertheless less demanding from a chemical standpoint. In particular, the magnesium nutrients can be supplied in the form of sulfates or nitrates in the second stock solution B.

[0076] The various stock solutions or pre-stock solutions of the aforementioned embodiments are transferred from one tank to another by means of any conventional solution transfer system (11, 14, 8, 13) such as pumps, venturi, gravity, ....

[0077] In an advantageous embodiment of the invention, each feeding step of each of the stock solutions (A, B, E) of the above embodiments, in a dilution tank 6 or in an irrigation line 12 is a venturi drive transfer step of said stock solution by means of a fertigation solution flow derived from the discharge of said transfer device 8 which allows to feed the fertigation device 7 (not illustrated).

[0078] All stages of the process, regardless of the method of implementation envisaged, are carried out at ambient temperature, i.e. without strict temperature control in the tanks of the said mother solutions or pre-mother solutions, i.e. at temperatures fluctuating between 10 and 40°C depending on whether the preparation installation is installed in the open air or in a greenhouse.

[0079] Advantageously, in the present invention, for example in embodiments 1, 2, 3, or 4, oxidation of the stock solutions or pre-stock solutions can be achieved by oxidation means 15, particularly to prevent the precipitation or co-precipitation of certain micronutrients such as copper. Indeed, in the absence of oxidation, micronutrients such as copper can precipitate with iron and other ions such as pyrophosphates. Conventional oxidation techniques can be implemented with known oxidizing agents such as oxygen, air, hydrogen peroxide, bleach, etc.

[0080] For example, commonly used oxidation treatments include: air bubbling using a disperser located at the bottom of the tank (the air can come from a compressor or a simple pump), agitation of the liquid surface under air, ....

[0081] The duration of the oxidation treatment varies between a few hours and several days depending on the size of the tank and the aeration system used.

[0082] Advantageously, regardless of embodiment 1, 2, 3 or 4, a second pH adjustment means 10 may be present in the dilution tank 6 (not shown).

[0083] In a fifth embodiment of the process according to the present invention, illustrated in the figure 5, said series of stock solutions includes a first stock solution A contained in a first stock solution vat 1, a second stock solution B contained in a second stock solution vat 2 and a third stock solution E contained in a third stock solution vat 5.The first stock solution A comprises the calcium nutrients, preferably in the form of nitrate or chloride, the second stock solution B comprises the sulfate and phosphate anions and said third stock solution E comprises iron and at least one polyphosphate; the magnesium nutrients being able to be supplied in said first A or in said second stock solution B; the mixing conditions being sufficiently intensive at the point of supply of said third stock solution E in said fertigation solution F so as to prevent any precipitation of calcium phosphate; said fertigation solution F being at a pH below 6.2, preferably below 6.0 and preferably below 5.8 after said supply of the third stock solution E.

[0084] In this embodiment, a stock solution E comprising iron and at least one polyphosphate is formed separately. This stock solution may have a basic pH and is fed directly into the fertigation solution F, into the dilution system 6, or into the irrigation line 12 to which pH adjustment means 10 are connected (which, in this particular embodiment, also include means for ensuring sufficiently intensive mixing conditions at the feed point 16 of said third stock solution E into said fertigation solution F). Advantageously, in the fifth embodiment, mixing conditions can be ensured by any conventional means of agitation at the injection point of said third stock solution E, such as agitators, recirculators, gas bubblers, etc.

[0085] However, in this embodiment, the sufficient quantity of acid will be added before feeding said third solution E into the dilution device (dilution tank 6 or irrigation line 12).

[0086] In this particular embodiment, the fertigation solution F is the solution D of iron and at least one polyphosphate in the required pH range, i.e. 4.5 and 6.2, more particularly between 5.0 and 6.0, preferably greater than 5.5, but less than or equal to 5.8.

[0087] For example, in one variant, said series of stock solution tanks comprises a first stock solution tank, a second stock solution tank, and a third stock solution tank, said iron and at least one polyphosphate supply means being connected to said third tank, said pH adjustment means being connected to said dilution system or to one of said first or second stock solution tanks.

[0088] It is understood that the present invention is in no way limited to the embodiments described above and that many modifications can be made to it without departing from the scope of the attached claims. Examples.-

[0089] The implementation of mineral nutrient compositions based on iron and at least one polyphosphate has been tested in various fertigation processes, the most representative examples of the present invention and the problem it has solved are given below. Test procedure

[0090] The fertigation solution is continuously prepared in a standard 1000-liter dilution tank through which the irrigation water flows. Nutrients are added to this dilution tank via three different stock solutions: one containing the iron and polyphosphate source, and the other two containing all the remaining nutrients. Comparative Example 1.-

[0091] The stock solution containing iron and at least one polyphosphate is that of Example 1 of patent application WO2014 / 056688. This solution, with an Fe content of 10 mmole / kg, is characterized by a basic pH of 9.4 in which no precipitate appears after 4 weeks of storage at room temperature or higher temperature (40°C).

[0092] Each stock solution is dosed using a specific venturi system. A small fraction of the fertigation solution is drawn from the irrigation pump outlet to serve as the entrainment fluid for each venturi. The pH of the fertigation solution is continuously adjusted between 5.4 and 5.7 by the automatic addition of nitric acid directly into the dilution tank. A severe precipitation problem occurs at the outlet of the venturi used to dose the stock solution containing iron and at least one polyphosphate after a few hours of operation.

[0093] The solid particles thus formed partially deposit on the tube walls and eventually completely block the passage. Furthermore, the solid calcium orthophosphate precipitate that causes this fouling carries away a significant fraction of the iron through chemical co-precipitation. This can lead to severe iron deficiency in cultivated plants if the problem is not detected quickly enough. Analysis of the fertigation solution collected by drip irrigation showed that the resulting iron loss before the venturi blockage was already at least 20% of the calculated theoretical iron concentration that should have been present in the fertigation solution. This theoretical value was correctly achieved with a diluted solution prepared in the same proportions in the laboratory to simulate the process. Comparative Example 2.-

[0094] A variation of Comparative Example 1 was implemented by replacing the venturi system dedicated to the stock solution containing iron and at least one polyphosphate with a volumetric dosing pump. In this case, the stock solution containing iron and at least one polyphosphate flows directly into the dilution tank without being partially diluted by the fertigation solution in the transfer system. During this second trial, the iron yield obtained by drip irrigation was particularly inconsistent, with losses of up to 40% observed at times. Comparative Example 3.-

[0095] In a second variation of Comparative Example 1, the stock solution containing iron and at least one polyphosphate is adjusted to pH 7.0 by adding nitric acid before being used with the venturi dosing system, with the other operating conditions being identical to those of Comparative Example 1. As in Comparative Example 1, the stability of the stock solution is satisfactory: no precipitate is observed after 4 weeks of storage at room temperature or at 40°C. However, such acidification of the stock solution is not sufficient to prevent the venturi from clogging after a few days. Comparative Example 4.-

[0096] A variation of Comparative Example 3 was carried out by increasing the acidification of the stock solution containing iron and at least one polyphosphate to pH 4.0. A precipitate then appeared in the stock solution containing iron and at least one polyphosphate after a few days. Analyses of the filtered stock solution containing iron and at least one polyphosphate allowed for the measurement of the proportion of iron remaining in solution. The results revealed significant iron losses in the stock solution containing iron and at least one polyphosphate, reaching 20% ​​and 55%, respectively, after 1 and 4 weeks of storage at room temperature. Example 1.-

[0097] In this test, the stock solution containing iron and at least one polyphosphate, as described in Example 1 of patent application WO2014 / 056688, was acidified with nitric acid to a pH of 6.0 before being transferred via a venturi-type transfer system into the dilution tank. The results obtained are satisfactory in all respects: the fouling problem at the venturi outlet was eliminated, and the soluble iron content of the fertigation solution, collected drop by drop, was consistently equal to the calculated value, within the margin of error. Finally, the stock solution containing iron and at least one polyphosphate is stable: no iron loss through chemical precipitation occurred during four weeks of storage at room temperature or at 40°C. Example 2.-

[0098] Example 1 was reproduced by replacing the transfer system of Example 1 with a volumetric pump. The iron yield at the drip level still exceeds 90%. Example 3

[0099] Example 1 was reproduced by acidifying the stock solution containing iron and at least one polyphosphate to pH 5.0. The storage stability of the stock solution is maintained for up to 4 weeks at room temperature.

Claims

1. A method for fertigation of plants comprising - a provision of a series of stock solutions comprising a stock solution comprising iron and at least one polyphosphate, at basic pH or at pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and lower than or equal to 6.0, preferably a pH greater than or equal to 5.5, formed by adding iron and at least one polyphosphate to an aqueous phase, - feeding each of the stock solutions into a diluting system to form a fertigation solution, - feeding a fertigation device by means of a transfer device, supplying said fertigation device with said fertigation solution, with the proviso that if said stock solution is at basic pH, a sufficient amount of acid is added to said diluting system prior to feeding said stock solution, and sufficiently intensive mixing conditions at a point of feeding said stock solution to said diluting system are provided so that said fertigation solution has a pH below 6.2.

2. The method for fertigation of plants according to claim 1, wherein one of said at least one iron solution and at least one polyphosphate at a pH between 4.5 and 6.2, advantageously greater than or equal to 5,0 and lower than or equal to 6.0, preferably a pH greater than or equal to 5.5 has a pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and lower than or equal to 6.0, preferably a pH greater than or equal to 5.5 and lower than or equal to 5.8 and is the fertigation solution.

3. The method for the fertigation of plants according to claim 1 or claim 2, wherein said addition of iron and at least one polyphosphate is carried out by feeding separately or together a source of iron and a source of at least one polyphosphate, each source being, independently of one another, in the form of a solid, a solution or a suspension.

4. The method for fertigation of plants according to claim 1 or claim 3 when it depends on claim 1, wherein at least one addition of iron and at least one polyphosphate to an aqueous phase with a formation of at least one iron solution and at least one polyphosphate at a pH of between 4.5 and 6.2, advantageously greater than or equal to 5.0 and lower than or equal to 6.0, preferably a pH greater than or equal to 5.5 is an addition of an iron stock pre-solution and at least one polyphosphate to a stock solution, which forms the iron solution and at least one polyphosphate at a pH between 4.5 and 6.2, advantageously greater than or equal to 5,0 and lower than or equal to 6.0, preferably a pH greater than or equal to 5.5.

5. The method for fertigation of plants according to claim 1 or 4, or claim 3 when it depends on claim 1, wherein said at least one iron solution and at least one polyphosphate at a pH of between 4.5 and 6.2, advantageously greater than or equal to 5.0 and lower than or equal to 6.0, preferably a pH greater than or equal to 5.5 is an iron stock pre-solution and at least one polyphosphate at a pH between 4.5 and 6.2, advantageously greater than or equal to 5.0 and lower than or equal to 6.0, preferably a pH greater than or equal to 5.5 added to at least one stock solution of said series of stock solutions.

6. The method for fertigation of plants according to any one of claims 1 to 5, wherein said addition of iron and at least one polyphosphate is carried out by feeding a composition containing iron and at least one polyphosphate, in solid, solution or suspension form.

7. The method for fertigation according to any one of claims 1 to 6, wherein said at least one stock solution of said series of stock solutions containing the iron and at least one polyphosphate also contains ions selected from the group consisting of sulfates, phosphates, nitrates, chlorides, potassium, sodium, ammonium and mixtures thereof.

8. The method for fertigation according to any one of claims 1 to 7, wherein said at least one stock solution of said series of stock solutions containing the iron and at least one polyphosphate or said stock pre-solution containing the iron and at least one polyphosphate, contains micronutrients selected from the group consisting of boron, manganese, zinc, copper, molybdenum, cobalt and mixtures thereof.

9. The method for fertigation of plants according to any one of claims 1 to 8, wherein the pH of said stock pre-solution or one of said stock solutions or fertigation solution is adjusted by adding an acid selected from the group consisting of mineral acids, such as for example nitric acid, sulfuric acid, phosphoric acid and mixtures thereof.

10. The method for fertigation of plants according to any one of claims 1 to 9, further comprising an oxidation of said stock solution containing the iron and at least one polyphosphate and / or of said stock pre-solution containing iron and at least one polyphosphate.

11. The method for fertigation of plants according to any one of claims 1 to 10, wherein iron and said at least one polyphosphate are added according to a ratio Ppoly / Fe of between 5 and 50, preferably between 8 and 32, wherein Fe represents the total molar number of iron and wherein Ppoly represents the molar number of phosphorus in the form of polyphosphate.

12. The method for fertigation of plants according to any one of the preceding claims, wherein said at least one polyphosphate comprises potassium tripolyphosphate, and / or tetrapotassium pyrophosphate, and / or potassium tripolyphosphate, and / or sodium tripolyphosphate, and / or sodium acid pyrophosphate, and / or tetrasodium pyrophosphate, and / or ammonium pyrophosphate, and / or ammonium polyphosphate or mixtures thereof.

13. The method for fertigation of plants according to any one of the preceding claims, wherein the pH of the fertigation solution is lower than 6.2.

14. The method for fertigation of plants according to any one of the preceding claims, wherein said fertigation solution is at a pH lower than 6 and preferably lower than 5.8.

15. The method for fertigation of plants according to any one of claims 3 and 6 to 14, when dependent on claim 2, wherein iron and said at least one polyphosphate are added to said fertigation solution at a feeding point having sufficiently intense mixing conditions to avoid any precipitation.