Solid nutrient composition, method for preparing the same and use thereof

Abstract

The invention pertains to a solid nutrient composition, comprising at least one polyphosphate; at least 0.10 and at most 10.00 wt.% of iron, with reference to the total weight of said composition; and at least one pH reducing agent selected from the group consisting of solid acid, or salts thereof, hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP); wherein the solid acid is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetoacetic acid, tartaric acid, sulfosalicylic acid, and oxalic acid; wherein said composition is substantially free of organic chelating agents containing at least one amine group; and said composition has a Ppoly / Fe molar ratio of between 2.70 and 50.00 where Ppoly is a total number of moles of phosphorus in polyphosphate form and where Fe is a total number of moles of iron in said composition with the provisio that when the pH reducing agent is selected from hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoly / Fe molar ratio of the composition is between 4.00 to 50.00. The invention pertains further to an aqueous solution obtained by dissolving said solid nutrient composition, to a method for providing bioavailable iron to plants, to the use of said solid nutrient composition in a fertilizing composition and to the use in a foliar application of an aqueous solution according to the present invention.

Description

[0001] SOLID NUTRIENT COMPOSITION, METHOD FOR PREPARING THE SAME AND USE THEREOF

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the field of solid nutrient compositions, particularly for plant nutrition, more particularly for foliar and / or fertigation or field nutrition applications.

[0004] BACKGROUND OF THE INVENTION

[0005] Like all living organisms, plants need nutrients in order to grow and complete other activities of their life cycle. Modern agricultural practices often necessitate the use of fertilizers in order to bring the required amounts of nutrients to the plants.

[0006] It is common general knowledge that potassium, phosphate and iron are among the most important nutrients for plants. Indeed, iron is for example used in photosynthesis, respiration and many enzymatic processes. Iron is often available in the form of iron sulphate, which is readily soluble in water, but which cannot be readily absorbed by plants if the ferrous or ferric ions Fe in itself would precipitate, so that a supporting mechanism is needed for the iron to be bioavailable for plants.

[0007] Different strategies have been developed in order to try to overcome this issue. A common solution is to use organic chelating agents, in particular organic chelating agents containing at least one amine group, such as for example: ethylenediaminetetraacetic acid (EDTA) or ethylenediamine-N,N'- bis(2-hydroxyphenylacetic acid) (EDDHA), diethylenetriaminepentaacetic acid (DTPA), ethylenediamine- N,N'-bis(2-hydroxyphenylacetic acid) (HEDTA), N,N'-bis(2-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED), imidodisuccinic acid (IDHA), 2-[2-[bis(carboxymethyl)amino]ethyl-(2- hydroxyethyl)amino]acetic acid (HEEDTA), ethylenediaminedi(o-hydroxy-p-methylphenylacetic) acid (EDDHMA), ethylenediaminedi(2-hydroxy-5-sulfophenylacetic) acid (EDDHSA), and ethylenediaminedi(5- carboxy-2-hydroxyphenylacetic) acid (EDDCHA). The chelating agent forms stable and soluble complexes with the iron cations thus increasing their solubility. Of all the above mentioned chelating agents, EDTA is the most commonly used. However, many users are becoming reluctant to use synthetic organic chemicals in nutrient compositions, as some of these agents, such as EDTA, have a low biodegradability and have been shown to end up in deeper soil layers (EDTA application on agricultural soils affects microelement uptake of plants, E. Bloem et al., D0l:10.1016 / j.scitotenv.2016.10.153). Furthermore, when nutrient compositions are used in foliar and field nutrition applications, they will be subjected to UV radiations from the sun. However, it is known that at least some of the above chelating agents can degrade under sunlight because of UV radiations. As a result, the iron cations in the administered nutrient compositions are no longer chelated and will precipitate and cease to be bio-available to the plant.

[0008] Thus, several strategies were developed in the prior art to reduce or avoid altogether the use of organic chelating agents such as those mentioned above.

[0009] W02014 / 056690A1 and WO2014056688A1 use polyphosphates for complexing the Fe cations and render these cations bioavailable to organisms.

[0010] W02014 / 056690A1 discloses aqueous inorganic nutrient compositions comprising a polyphosphate and a source of iron and having a Ppoiy / Fe molar ratio of between 5 and 50 where Ppoiy represents a number of total moles of phosphorus in the form of polyphosphate and where Fe represents a number of total moles of iron. The compositions also have an N / Ptotai molar ratio of less than or equal to 0.2, where N represents the number of moles of ammonium and where Ptotai represents the number of moles of total phosphorus.

[0011] WO2014056688A1 discloses an inorganic solid nutrient composition comprising a polyphosphate, and at least one source of micronutrient Fe, the latter being present in a concentration of between 0.1 and 5 %. The polyphosphate can be a pyrophosphate and / or a tripolyphosphate. The molar ratio of Ppoiy / Fe can be between 5 and 50, where Ppoiydesignates the number of moles of phosphorus in the form of polyphosphate.

[0012] The compositions disclosed in these documents have the advantage over the compositions comprising the aforementioned organic chelating agents that polyphosphates do not degrade due to UV radiation and thus are not hindered by sunlight to render the Fe cations bio-available to the plant. The polyphosphates are also more biodegradable with respect to the organic chelating agents. Eventually, the polyphosphates will hydrolyse to a form that is absorbable by plants, such as in the form of orthophosphate.

[0013] While being promising, the nutrient compositions disclosed in said documents however also present some limitations. First of all, the ratio of Ppoiv / Fe is comparatively high, meaning that the amount of polyphosphates required to render the Fe cations bio-available to plants is quite significant. Polyphosphates being an expensive component, there is therefore a need for a composition using less polyphosphates per amount of Fe.

[0014] Moreover, the nutrient compositions described in the aforementioned documents often need to be dissolved in water before use and / or require the end user to adjust the pH before use. This usually requires the additional mixing of acids or bases with the nutrient composition which can be dangerous if handled by untrained users. Furthermore, such an action may need to be performed on a farm or in an agricultural environment which may not be equipped to store and handle acids or bases. There therefore is a need for a nutrient composition which does not require any further addition of acids or bases before use.

[0015] The compositions described in the aforementioned documents are meant to be used in applications such as hydroponics, relating to growing plants in a soilless environment by using water- soluble mineral nutrient solutions, and fertigation, relating to the practice of injecting water-soluble nutrients or fertilizers in an irrigation system. Alternatively, nutrients can also be delivered by foliar feeding, which refers to the practice of feeding plants by applying nutrients or fertilizer, which are in a liquid form, directly to the leaves. When used in such foliar applications, it has been observed that nutrient compositions may leave red-brown marks on the leaves, which are basically caused by Fe precipitates or by the natural colour of the chelate, formed as a result of non-absorption by the plant. Having Fe absorbed by the leaves of a plant may be considered a quite different technical challenge with respect to absorption via the root system of the plant.

[0016] Based on the above, there therefore is a need for a nutrient composition for delivering nutrients to plants, which composition contains Fe that is absorbable by and bio-available to plants and wherein the amount of Fe that is deliverable with regard to other particular components in the composition, such as complexing or chelating components, such as polyphosphates, is maximised. There is a need for said composition to be able to provide further nutritive elements to plants, and to be easy and safe to use, deliver and transport. Furthermore, there is a need for the nutrient composition to be deliverable (and the Fe therein to be bio-available) to the plant via different mechanisms, including via foliar application, fertigation, in soilless hydroponic or field environments. There is a further need for these nutrient compositions to be substantially free of chelating agents containing amine groups such as those components mentioned here above.

[0017] SUMMARY OF THE INVENTION

[0018] The inventors have surprisingly found that the solid nutrient composition according to the present invention fulfills the above mentioned needs and overcomes the above mentioned disadvantages.

[0019] In an aspect of the present invention, there is provided a solid nutrient composition, comprising o at least one polyphosphate; o at least 0.10 wt.% and at most 10.00 wt.% of iron, with reference to the total weight of said composition; o at least one pH reducing agent; wherein said pH reducing agent is selected from the group consisting of a solid acid, or a salt thereof, hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP); and wherein the solid acid is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetoacetic acid, tartaric acid, sulfosalicylic acid, and oxalic acid; wherein said composition has a Ppoiy / Fe molar ratio of between 2.70 and 50.00 wherein Ppoiyis a total number of moles of phosphorus in polyphosphate form and wherein Fe is a total number of moles of iron in said composition with the provisio that when the pH reducing agent is selected from hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoiy / Fe molar ratio of the composition is between 4.00 to 50.00; wherein said composition is substantially free of organic chelating agents containing at least one amine group.

[0020] It is an advantage of the solid nutrient composition according to the invention that relatively few polyphosphate needs to be used to render the Fe cations bioavailable to plant organisms. Indeed, typically, high Fe concentrations require high amounts of Ppoiyfor the Fe to be complexed. However, this would result in an increased amount of Ptotai which is not always permitted in each application. It has now advantageously been found that by adding at least one pH reducing agent, as described herein, the combination of said at least one polyphosphate and said at least one pH reducing agent allows to provide a composition wherein the weight of Fe in the composition, which Fe is bioavailable to plants, may be as high as 10 wt.% with reference to the total weight of the composition. It has been found that such high concentration of Fe cannot be reached by use of only said polyphosphates or by use of only said at least one pH reducing agent. In other words, by use of a combination of said two components, it has been found that the concentration of Fe, which Fe is bioavailable to plants, in the composition can be increased to such concentrations, without necessarily increasing the Ptotai of the composition, which concentrations are not attainable by use of only one of said two components. Furthermore, the Ppoiy / Fe ratio can be reduced to a level, which is not attainable by use of only one of said two components, while keeping the Fe bioavailable to plants and therefore from precipitating when used in a solution. It is therein to be noted that the concentration of the relatively expensive polyphosphate component can advantageously be reduced, wherein the relatively cheap at least one reducing agent, as described herein, does not harm or cause any disadvantages to the plant, soil or environment. It is a further advantage of the solid nutrient composition according to the invention that the composition is free or substantially free of any organic chelating agents containing at least one amine group. Advantageously, no organic chelating agents having low biodegradability are dispersed in the environment. Should such organic chelating agents eventually degrade in the soil or in the environment, amine groups would be released, which is also avoided in the present invention.

[0021] It is a further advantage of the composition according to the invention that it is in a solid form, making it relatively easy to ship or transport the composition to a point of use where it can be dissolved in water prior to being used in a fertilizer application. It is a further advantage of the composition being in solid form that it can be stored for at least a period of 6 months at room temperature (meaning between 15 and 35°C, preferably a temperature of 20°C) in a dry place (meaning having a relative humidity of 60% or less), preferably for at least 1 year.

[0022] In an aspect of the invention, there is provided an aqueous solution obtained by dissolving the solid nutrient composition described herein in an aqueous solvent wherein said aqueous solution has a pH of at least 3.0 and at most 7.5, preferably at least 3.5 and at most 7.5, more preferably at least 3.5 and at most 6.0, or at least 4.0 and at most 6.5, more preferably at least 4.0 and at most 5.5, more preferably at least 3.5 and at most 5.3, even more preferably at least 3.5 and at most 4.6, wherein said pH can be measured by dissolving 2 wt% of said solid nutrient composition in the aqueous solvent , thereby forming said aqueous solution.

[0023] Alternatively, said aqueous solution obtained by dissolving the solid nutrient composition described herein, in an aqueous solvent wherein the weight ratio of the solid nutrient composition to the aqueous solvent is comprised between 1:50 and 1:10. Preferably, the aqueous solution has a pH of at least 3.5 and at most 7.0, more preferably at least 4.0 and at most 5.0, wherein said pH can be measured by dissolving 10 wt% of said solid nutrient composition in the aqueous solvent, thereby forming said aqueous solution.

[0024] Among aqueous solvents suitable for use in the present invention mention may be notably made of water and water-based solutions. Preferably, the aqueous solvent is water.

[0025] It is an advantage of the aqueous solution that it can be used directly or as part of a fertilizing composition (fertilizer composition), wherein no acid or base needs to be added to the solid nutrient composition in order to obtain said aqueous solution. A pH regulator may however be added to the aqueous solution. It is a further advantage of said aqueous solution that it can be used in foliar, fertigation and / or field nutrition applications, wherein foliar application may be a preferred way of applying said aqueous solution. It has advantageously been found that such aqueous solutions as described herein only have a low percentage of insoluble matter, wherein essentially no precipitation is witnessed in the aqueous solution. It is a further advantage of the aqueous solution that it has a pH which allows the Fe cations to be absorbed by the root system or the leaves of the plant.

[0026] The present invention also concerns a method for providing bioavailable iron to plants and a use of the solid nutrient composition and the aqueous solution as described herein in a fertilizing composition for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

[0027] An aspect of the invention relates to the use of the solid nutrient composition according to the present invention in a foliar application.

[0028] An aspect of the invention relates to the use of the aqueous solution according to the present invention in a foliar application. More in particular, the invention relates to the use of the aqueous solution according to the present invention in a foliar application for plant nutrition, i.e. for delivering nutrients to organisms, more in particular plants.

[0029] It is an advantage of the solid nutrient composition and of the aqueous solution according to the invention that it can be used as or in a fertilizer composition, thereby allowing sufficient amounts of iron to be available to plants, which bioavailable iron is applicable to the plants by foliar application. It is further advantage of the aqueous solution that no or essentially no organic chelating agents, having at least one amine group, are necessary to provide iron in sufficient quantities to plants in a foliar application.

[0030] DETAILED DESCRIPTION

[0031] In the context of the present invention, the term "comprising" should not be interpreted as excluding features or elements other than those explicitly mentioned. It should be construed as specifying the presence of the features or elements indicated, but does not exclude the presence or addition of one or more other features or elements. Thus, the scope of the expression "a method comprising steps A and B" should not be limited to methods consisting only of steps A and B. Similarly, a composition comprising components A and B should not be limited to compositions consisting only of components A and B. Accordingly, the terms "comprising" and "including" encompass the terms more restrictive "consisting essentially of" and "consisting of".

[0032] In the context of the present invention, if an element or component is said to be selected from a list of recited elements or components, it should be understood that the element or component can also be any one of the individual recited elements or components in said list, or can also be selected from a group consisting of any two or more of the explicitly listed elements or components. An aspect of the invention relates to a solid nutrient composition for delivering nutrients to organisms, more in particular plants. Said solid nutrient composition can be used in or form part of an aqueous solution for application on plants. Such nutrients include Fe and may further refer to other mineral micronutrients, as well as to macronutrients such as phosphorous.

[0033] Micronutrients, such as iron, boron, manganese, zinc, copper, nickel and molybdenum, need to be present in plants, albeit in lower concentrations than macronutrients such as carbon, oxygen, hydrogen, nitrogen, phosphorus and the like. Among these micronutrients, iron is the one of which the plant requires the highest concentration (around 100 mg / kg of dry tissue). Such elements need to be bioavailable, essentially meaning herein that an element which is considered bioavailable can readily be solubilised in a solution so that organisms, in particular plants, can take them or absorb them and assimilate or process them further. Fe which is in a form that is not bioavailable will form precipitates. The formation of precipitates needs to be avoided as these cannot be absorbed and can negatively affect plant health, e.g. by yellowing of the leaves due to chlorosis. However, iron is a micronutrient that is well known for being an element that is particularly difficult to solubilise. When being without chelating agents, iron cations will typically precipitate.

[0034] The chelating capacities of polyphosphates have been described in literature. It has been found that the chelating effect of polyphosphates with respect to Fe cations is limited by the concentration of Fe in the solution applied to the plants and by the cost of the relatively expensive polyphosphates.

[0035] It has now been found that by addition of a pH reducing agent, and more in particular through the interaction of said pH reducing agent and said polyphosphate, the ratio Ppoiy / Fe can be significantly reduced and that the pH of the resulting aqueous solution is maintained equal to or lower than 7.5 in the entire range of Ppoiy / Fe ratio, namely between 2.70 and 50.00.

[0036] For this purpose, there is provided a solid nutrient composition, comprising o at least one polyphosphate; o at least 0.10 wt.% and at most 10.00 wt.% of iron, with reference to the total weight of said composition; o at least one pH reducing agent; wherein said pH reducing agent is selected from the group consisting of a solid acid, or salts thereof, hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP); and; wherein the solid acid is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetoacetic acid, tartaric acid, sulfosalicylic acid, and oxalic acid; wherein said composition has a Ppoiy / Fe molar ratio of between 2.70 and 50.00 wherein Ppoiy is a total number of moles of phosphorus in polyphosphate form and wherein Fe is a total number of moles of iron in said composition; with the provisio that when the pH reducing agent is selected from hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoiy / Fe molar ratio of the composition is between 4.00 to 50.00; wherein said composition is substantially free of organic chelating agents containing at least one amine group.

[0037] In embodiments according to the invention, said at least one polyphosphate relates to a component or components which are different from the iron source providing the iron (Fe) for the composition, and from said at least one pH reducing agent. Furthermore, it will be understood that the iron source providing the iron for the composition relates to a component or components that are different from said at least one pH reducing agent. Hence, it will be clear to the skilled person that there is no overlap between said at least one polyphosphate, said iron, and said at least one pH reducing agent.

[0038] According to the invention, the composition is substantially free from organic chelating agents containing at least one amine group. For the purpose of the invention, it will be understood that the composition can be considered to be substantially free from said organic chelating agents containing at least one amine group, when said composition comprises at most 1.00 wt.%, preferably at most 0.50 wt.%, more preferably at most 0.10 wt.%, and most preferably at most 0.010 wt.% of said organic chelating agents containing at least one amine group, with reference to the total weight of the composition. In embodiments, the composition contains no organic chelating agents containing at least one amine group, except for amounts of chelating agents that may have been present in a component used for preparing the composition. Such amounts present in a component used for preparing the composition may relate to trace amounts and the composition will be considered herein to be free of said chelating agents.

[0039] For the purpose of the invention, at least the compounds EDTA, EDDHA, DTPA, HEDTA, HBED, IDHA, HEEDTA, EDDHMA, EDDHSA and EDDCHA are considered to be organic chelating agents containing at least one amine group.

[0040] According to the present invention, the solid nutrient composition comprises at least one polyphosphate. For the purpose of the invention, the term "polyphosphate" refers herein to a salt of a polyphosphoric acid, wherein the term "polyphosphoric acid" refers herein to compounds having the general formula: HO[P;OH);O)O]... / wherein n>l. When n equals 1, the polyphosphoric acid can also be called "pyrophosphoric acid" herein, and its salts "pyrophosphates". When n equals 3, the polyphosphoric acid can also be called "tripolyphosphoric acid" herein, and its salts "tripolyphosphates". It will however be understood that the term "polyphosphoric acid" may also relate herein to and thus may include any compound of formula (1), wherein n equals, or is higher than, three.

[0041] Preferably, said at least one polyphosphate is selected from the group formed by sodium and potassium polyphosphates, which are for the purpose of the invention typically used in powder or granule form.

[0042] In particular embodiments according to the invention, said at least one polyphosphate is selected from the group formed by pyrophosphates and tripolyphosphates, such as tetrapotassium pyrophosphate (TKPP), potassium tripolyphosphate (KTPP), sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), and mixtures thereof.

[0043] It has been found that pyrophosphates and tripolyphosphates are particularly suited to ensure the bioavailability of iron. However, this does not exclude the presence of polyphosphate chains of longer length in the at least one polyphosphate component.

[0044] It is thereby to be noted that the sodium and potassium polyphosphates as mentioned herein contribute, in addition to their role as chelating agents for iron, to the supply of macronutrients needed by plant organisms. Indeed, said potassium polyphosphates advantageously ensure the supply of potassium (K) and phosphorus (P) in useful forms that can be absorbed by plant organisms.

[0045] In embodiments according to the invention, when expressed in the form of phosphorous pentoxide P2O5, the composition contains at least 0.5 wt.%, preferably at least 2 wt.%, more preferably at least 5 wt.%, even more preferably at least 7 wt.%, preferably at least 10 wt.%, preferably at least 13 wt.%, more preferably at least 17 wt.%, even more preferably at least 20 wt.%, preferably at least 23 wt.%, more preferably at least 1 wt.%, and most preferably at least 30 wt.% of phosphorus containing compounds, as expressed in the form of phosphorous pentoxide P2O5, with reference to the total weight of the composition. It will further be understood that the composition contains at most 60 wt.%, preferably at most 50 wt.%, more preferably at most 47 wt.%, even more preferably at most 44 wt.%, preferably at most 42 wt.%, and most preferably at most 40 wt.% of phosphorus containing compounds when expressed in the form of P2O5, with reference to the total weight of the composition. It is thereby to be noted that regardless of the selection of the type of polyphosphates and mixtures thereof, it is common practice in the industry to express the total amount of phosphorus containing compounds in a composition in terms of phosphorus pentoxide, or P2O5. In embodiments according to the invention, the solid nutrient composition contains between 0.5 wt.% and 35 wt.% of polyphosphates, expressed as P2O5, preferably between 1.0 wt.% and 35 wt.%, more preferably between 3 wt.% and 32 wt.%, preferably between 8 wt.% and 30 wt.% polyphosphates, and more preferably between 10 wt.% and 25 wt.% polyphosphates, with regard to the total weight of the composition.

[0046] According to the present invention, the solid nutrient composition comprises iron, which iron is provided by at least one iron source. Preferably, said at least one iron source is selected from the group formed by FezfSO^a.xHjO wherein x is a molar coefficient being at least 0 and at most 9, MFefSC hlZF O where M is Na or K, FefNOah.xF O wherein x is a molar coefficient being at least 0 and at most 9, FeCh.xF O wherein x is a molar coefficient being at least 0 and at most 6, Fe4(P2O7)3, FePC .xF O wherein x is a molar coefficient being at least 0 and at most 4, FeSC .xF O wherein x is a molar coefficient being at least 0 and at most 7, FeCL.xF O wherein x is a molar coefficient being at least 0 and at most 4, FeO.xFhO wherein x is a molar coefficient being at least 0 and at most 1, Fe(NH4)PO4.H2O, iron oxysulphate, and the mixtures thereof.

[0047] According to the present invention, said solid nutrient composition comprises said at least one iron source, wherein the composition has at least 0.10 and at most 10.00 wt.% of iron, with reference to the total weight of said composition. It will be understood that the term iron refers herein to or is expressed as atomic iron (Fe).

[0048] In embodiments of the composition according to the invention, the composition comprises at least 0.20 wt.%, preferably at least 0.50 wt.%, more preferably at least 0.70 wt.%, even more preferably at least 1.00 wt.%, more preferably at least 1.50 wt.%, even more preferably at least 2.00 wt.%, more preferably at least 2.50 wt.%, and most preferably at least 3.00 wt.% of iron (Fe), with reference to the total weight of the composition. It will be further understood that the composition comprises at most 9.50 wt.%, preferably at most 9.00 wt.%, more preferably at most 8.50 wt.%, even more preferably at most 8.00 wt.%, more preferably at most 7.50 wt.%, even more preferably at most 6.50 wt.%, more preferably at most 6.00 wt.%, even more preferably at most 5.50 wt.% and most preferably at most 5.00 wt.% of iron (expressed in Fe content), with reference to the total weight of the composition.

[0049] According to the present invention, the solid nutrient composition has a Ppoiy / Fe molar ratio from 2.70 to 50.00 where Ppoiy corresponds to the total number of moles of phosphorus that are present in the composition in polyphosphate form and where Fe is a total number of moles of iron in said composition.

[0050] In embodiments of the composition according to the invention, said solid nutrient composition has a Ppoiy / Fe molar ratio of at least 3.00, preferably at least 4.00, preferably at least 5.00, preferably at least 6.00, more preferably at least 7.00, more preferably at least 7.5, and most preferably at least 10.0. It is further understood that said composition preferably has a Ppoiy / Fe molar ratio of at most 45.0, preferably at most 40.0, more preferably at most 35.0, even more preferably at most 30.0, and most preferably at most 15.0.

[0051] In a certain embodiment of the invention, the solid nutrient composition has a Ppoiy / Fe molar ratio from 2.7 to 4.95, where Ppoiy corresponds to the total number of moles of phosphorus that are present in the composition in polyphosphate form and where Fe is a total number of moles of iron in said composition. In embodiments of the composition according to the invention, said solid nutrient composition has a Ppoiy / Fe molar ratio of at least 2.7, more preferably at least 3.0. It is further understood that said solid nutrient composition preferably has a Ppoiy / Fe molar ratio of at most 4.8, preferably at most 4.6, more preferably at most 4.4, even more preferably at most 4.2, and most preferably at most 4.0.

[0052] The value for Ppoiy may be obtained by analysing the value of Ptotai, wherein Ptotai relates to the number of moles of total phosphorus in the composition, and Portho, wherein Portho relates to the number of moles of phosphorous in orthophosphate form, by applying the equation Ppoiy=Ptotai -Portho-

[0053] According to the present invention, the solid nutrient composition comprises at least one pH reducing agent.

[0054] In embodiments according to the invention, the term "at least one pH reducing agent" may refer to compounds which have an acidifying effect on an aqueous solution comprising said solid composition, e.g. in a solution containing 1-15 wt.% of said solid composition, such that the addition of at least one of said compounds results in the pH of the solution to be lower or more acidic than without said at least one of said compounds.

[0055] In embodiments according to the invention, said at least one pH reducing agent is an organic acid, or salts thereof. Alternatively or additionally said at least one pH reducing agent is an inorganic acid, or salts thereof.

[0056] According to the present invention, said pH reducing agent is selected from the group consisting of a solid acid or salt thereof, hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP) and the solid acid is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetoacetic acid, tartaric acid, sulfosalicylic acid, and oxalic acid. Preferably, the solid acid is citric acid.

[0057] According to the present invention when the pH reducing agent is selected from the group consisting of hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoiy / Fe molar ratio of the composition is between 4.00 to 50.00. In other words, when the pH reducing agent is only selected from the group consisting of hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoiy / Fe molar ratio of the composition is between 4.00 to 50.00.

[0058] The inventors have found that when the Ppoiy / Fe molar ratio is below 4.00, using a pH reducing which is a solid acid or salts thereof as described above, allows to increase the iron content in the composition while reaching an acceptable pH for a safe use in foliar, fertigation and / or field nutrition applications. Without being bound to this theory, the inventors believe that a pH reducing agent being a solid acid or salts thereof have a chelating effect on iron. Additionally, when the Ppoiy / Fe molar ratio of the composition is between 4.00 to 50.00, the use of a pH reducing agent selected from the group consisting of hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), allows to reach an acceptable pH for a safe use in foliar, fertigation and / or field nutrition applications.

[0059] Advantageously, the pH reducing agent is a solid acid, preferably the solid acid is citric acid and the PPoiy / Fe molar ratio of the composition is between 2.70 to 50.00, preferably between 2.70 to 30.00, preferably between 2.70 to 20.00, more preferably 2.70 to 10.00 or between 2.70 and 4.95.

[0060] Advantageously, said at least one pH reducing agent, has a concentration of between 5 wt.% and 90 wt.%, with reference to the total weight of the composition.

[0061] Preferably, the composition preferably contains at least 7 wt.%, more preferably at least 10 wt.%, even more preferably at least 15 wt.%, and most preferably at least 20 wt.%, of said pH reducing agent, with reference to the total weight of the composition. It will further be understood that the composition preferably contains at most 85 wt.%, preferably at most 75 wt.%, preferably at most 65 wt.%, more preferably at most 55 wt.%, more preferably at most 50 wt.%, even more preferably at most 45 wt.%, and most preferably at least 40 wt.%, of said pH reducing agent, with reference to the total weight of the composition.

[0062] In embodiments according to the present invention, the composition comprises between 5 wt.% and 85 wt.%, preferably between 7 wt.% and 75 wt.%, preferably 10 wt.% and 65 wt.%, preferably between 10 wt.% and 55 wt.%, preferably between 10 wt.% and 50 wt.%, more preferably between 10 wt.% and 45 wt.%, more preferably between 10 wt.% and 40 wt.%, of said pH reducing agent, with reference to the total weight of the composition.

[0063] In a particular embodiment of the invention, the concentration of the at least one pH reducing agent, may depend on the choice of the pH reducing agent. For example, when using an organic acid, or salts thereof, the concentration can be lower than for the case when salts of inorganic acids are used, for the purpose of obtaining the effect of solubilizing and making Fe bioavailable to plants as described herein.

[0064] In this particular embodiment, when the solid nutrient composition comprises at least one pH reducing agent, selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetyl acetonic acid, tartaric acid, sulfosalicylic acid, oxalic acid, and salts thereof, and mixtures thereof, the composition may contain at least 5 wt.%, more preferably at least 10 wt.%, even more preferably at least 15 wt.%, and most preferably at least 20 wt.%, of said pH reducing agent, with reference to the total weight of the composition. It will further be understood that the composition preferably contains at most 55 wt.%, more preferably at most 50 wt.%, even more preferably at most 45 wt.%, and most preferably at least 40 wt.%, of said pH reducing agent, with reference to the total weight of the composition.

[0065] In another particular embodiment of the composition according to the present invention, when the solid nutrient composition comprises at least one pH reducing agent selected from the group consisting of salts of hemipotassium phosphate (HKP), and / or monopotassium phosphate (MKP); and potassium sulphate (SOP); and mixtures thereof, the composition may contain at least 30 wt.%, more preferably at least 40 wt.%, even more preferably at least 50 wt.%, preferably at least 55 wt.%, and most preferably at least 60 wt.%, of said pH reducing agent, with reference to the total weight of the composition. It will further be understood that the composition preferably contains at most 95 wt.%, more preferably at most 90 wt.%, even more preferably at most 85 wt.%, more preferably at most 80 wt.%, and most preferably at least 75 wt.%, of said pH reducing agent, with reference to the total weight of the composition.

[0066] In embodiments of the composition according to the present invention, said at least one pH reducing agent relates to a mixture of citric acid and MKP, or a mixture of citric acid and SOP, or a mixture of citric acid and HKP.

[0067] It has been found that the combination of said at least one pH reducing agent and said at least one polyphosphate at the concentrations described herein, allows for a ratio between the iron content and the polyphosphate content in the composition, that ensures a sufficiently fast dissolution rate of the solid composition and allows the iron to be maintained essentially entirely or entirely in solution in the final nutrient medium. This is even so despite the presence in water of other ions such as Ca2+and Mg2+which compete with iron via their own complexing or chelating reactions with the polyphosphates.

[0068] In embodiments of the composition according to the present invention, the solid nutrient composition has a molar ratio N / Ptotai of 0.2 or less, wherein N is the number of moles of nitrogen, and which may be close to zero or be zero. It has been found that using a minimal amount of nitrogen has several advantages, as accumulation of nitrogen ions is prevented and pH of solutions of the composition can be more easily controlled. Such embodiments typically comprise compositions wherein no nitrogen coming from ammonium (e.g. ammonium polyphosphate or ammonium phosphate) is needed in the composition.

[0069] In embodiments of the composition according to the present invention, the solid nutrient composition also comprises phosphorus in orthophosphate form in a molar ratio of Portho / Ptotai of between 0 and 0.95, preferably between 0.10 and 0.95, more preferably between 0.10 and 0.80, more preferably between 0.15 and 0.70, or between 0.10 and 0.70, more preferably between 0.20 and 0.60, or between 0.10 and 0.60, preferably between 0.15 and 0.40, more preferably between 0.20 and 0.30, wherein Portho represents the number of phosphorus moles in orthophosphate form and wherein Ptotai represents the total number of phosphorus moles.

[0070] It will be appreciated by the person skilled in the art that the molar ratio of Portho / Ptotai may depend on the choice of said at least one pH reducing agent. It may also depend of other additives added to the composition.

[0071] In a particular embodiment of the composition according to the present invention, the solid nutrient composition comprises at least one pH reducing agent selected from solid acid or salts thereof, as detailed above, potassium sulphate (SOP); and mixtures thereof. In such embodiments, the molar ratio Portho / Ptotai may be preferably between 0.15 and 0.40, more preferably from 0.20 to 0.30.

[0072] In another particular embodiment of the composition according to the present invention, the solid nutrient composition comprises at least pH reducing agent selected from the group consisting of hemipotassium phosphate (HKP), and / or monopotassium phosphate (MKP); and mixtures thereof. In such embodiments, the molar ratio Portho / Ptotai may be between 0.10 and 0.90, preferably between 0.15 and 0.70, more preferably from 0.20 to 0.60.

[0073] In embodiments according to the invention, the solid nutrient composition is water-soluble or is substantially soluble in water or in an aqueous solution, meaning, for the purpose of the invention, that it has, after being dissolved in a sufficient amount of water, a percentage of insoluble matter of less than 5 wt.%, preferably less than 2 wt.%, more preferably less than 0.2 wt.%, and most preferably less than 0.1 wt.%, with reference to the total weight of the composition. In preferred embodiments according to the invention, after dissolution in water, a loss of iron during the change of iron in solid state to its dissolved form can be noted which is less than 5 wt.%, preferably less than 2 wt.%, more preferably less than 0.2 wt.%, and most preferably less than 0.1 wt.%, with reference to the total weight of iron in the composition. It is preferred that the amount of insoluble matter of the composition is as low as possible and that there is preferably no precipitation. Preferably, the amount of insoluble is measured in an aqueous solution obtained by dissolving the solid nutrient composition in water, wherein the weight ratio of the solid nutrient to the water is 1:10. In other words, the amount of insoluble is measured on an aqueous solution obtained by dissolving the solid nutrient composition in water, wherein the amount of solid nutrient composition in the aqueous solution is 10.00 wt.%, relative to the total weight of the aqueous solution. It is understood that the skilled person in the art will measure the amount of insoluble according to standard and general practice known by said skilled person in the art. Preferably, unless otherwise mentioned or indicated, according to the present invention, the measurement of insoluble is performed at room temperature, by weighting 20.00 g of a sample of the composition (mE). Then, the method comprises dissolving this sample by adding 200 ml of ultrapure water and agitating during 10 minutes for forming an aqueous solution. The aqueous solution is then filtered on a 0.45 pm filter which is then rinsed with 150 ml of water. The filter is placed in an oven at 105 °C for 30 minutes. Finally, the filter is cooled to room temperature in a desiccator. The cooled filter is weighted.

[0074] The insoluble content in wt.% is: 100

[0075] Wherein mE: mass of the sample of the composition mo: mass of the filter before filtration mi: mass of the filter after filtration and cooling

[0076] In embodiments according to the invention, the solid nutrient composition further comprises at least one of trisodium phosphate (TSP), tricalcium phosphate (TCP). Preferably, said solid nutrient composition comprises said TSP and / or TCP in an individual concentration of at most 1.00 wt%, preferably at most 0.90 wt.%, and most preferably at most 0.80 wt.%, with reference to the total weight of the composition.

[0077] In embodiments according to the invention, the solid nutrient composition further comprises monoammonium phosphate (MAP) in an amount between 5 wt.% and 85 wt.%, preferably between 7 wt.% and 75 wt.%, preferably 10 wt.% and 65 wt.%, preferably between 10 wt.% and 55 wt.%, preferably between 10 wt.% and 50 wt.%, more preferably between 10 wt.% and 45 wt.%, more preferably between 10 wt.% and 40 wt.%, with reference to the total weight of the composition.

[0078] In embodiments according to the invention, the solid nutrient composition further comprises an anticaking agent. It will be appreciated by the skilled in the art that, although such compounds may contain an amine group, they do not qualify as an organic chelating agent.

[0079] In embodiments according to the invention, the solid nutrient composition further comprises at least one additional source of micronutrients selected from the group formed by sources of B, Mn, Zn, Cu, Mo, Co and the mixtures thereof. Preferably, said at least one additional source of micronutrients is contained in an atomic ratio relative to Fe of between 0.1 and 5 for B, between 0.05 and 2.5 for Mn, between 0.01 and 1 for Zn, between 0.005 and 0.25 for Cu and Mo, and between 0.001 and 0.1 for Co.

[0080] It has been found that such contents of micronutrients ensure optimal, adequate supplies of minerals i.e. according to the true needs of living organisms and of plants in particular. However, these contents can be modified in relation to application or the stage of plant development which, depending on morphology and growth phase, requires variable proportions of the different macro and micronutrients.

[0081] It is further understood that all definitions and preferences, as described above, equally apply for all further embodiments, as described below.

[0082] In an aspect of the invention, there is provided an aqueous solution obtained by dissolving said solid nutrient composition as described herein, in an aqueous solvent wherein the weight ratio of the solid nutrient composition to the aqueous solvent is comprised between 1:50 and 1:10. Among aqueous solvents suitable for use in the present invention mention may be notably made of water and waterbased solutions. Preferably, the aqueous solvent is water.

[0083] Alternatively, the aqueous solution is obtained by dissolving the at least one polyphosphate, as detailed above, the at least one source of iron, as detailed above and the at least one pH reducing agent, as detailed above, independently in the aqueous solvent in order to reach an aqueous solution having a Ppoiy / Fe molar ratio of between 2.70 and 50.00.

[0084] Preferably, said aqueous solution has a pH of at least 3.0 and at most 7.5, preferably between 3.5 and 7.5, preferably between 3.5 and 6.0, or between 4.0 and 6.5, more preferably between 4.0 and 5.5, more preferably between 3.5 and 5.3, even more preferably between 3.5 and 4.6. In embodiments, said pH is measured by dissolving 2 wt% (weight ratio of 1:50) of said solid nutrient composition in water, thereby forming said aqueous solution. In alternative embodiments, said pH is measured by dissolving 10 wt% (weight ratio of 1:10) of said solid nutrient composition in water, thereby forming said aqueous solution. In embodiments of the aqueous solution according to the invention, said aqueous solution has a solution turbidity of less than 50 NTU (Nephelometric Turbidity Unit), preferably less than 40 NTU, more preferably less than 30 NTU and most preferably less than 20 NTU and at a defined concentration of 2 wt% of said solid nutrient composition in water.

[0085] It has been found that solutions having a turbidity of 50 NTU and less can be administered to plants via foliar application as the solid particles in the solution will not clog any hardware parts of a plant feeding system. In embodiments of the aqueous solution according to the invention, said aqueous solution further comprises at least one of a surfactant, a wetting agent, and / or a penetrant. It will be appreciated by the skilled in the art that, although such compounds may contain an amine group, they do not qualify as an organic chelating agent.

[0086] In preferred embodiments of the aqueous solution, the solution has a percentage of insolubles of less than 5 wt.%, preferably less than 2 wt.%, more preferably less than 0.2% by weight relative to the weight of the solid nutrient composition, and most preferably less than 0.1% by weight relative to the weight of the solid nutrient composition, measured as detailed above. It is understood that any order of dissolving of the various components as comprised in the composition, as detailed above, is acceptable.

[0087] In an embodiment according to the present invention, the at least one polyphosphate, as detailed above, the at least one source of iron, as detailed above and the at least one pH reducing agent, as detailed above, are mixed, in no particular order, before being dissolved in water.

[0088] In alternative embodiments according to the invention, said aqueous solution is obtained by dissolving, in no particular order, said at least one polyphosphate and said at least one source of iron in water. In embodiments, said at least one pH reducing agent, is furthermore dissolved in said water. In embodiments, at least one of the non-aqueous components making up the aqueous solution, such as said at least one polyphosphate and / or said at least one source of iron, is a liquid or is in liquid state, and is added, in no particular order with regard to the other components, to obtain the aqueous solution. In embodiments, at least one of the non-aqueous components making up the aqueous solution, such as said at least one polyphosphate and / or said at least one source of iron, is a solid or is in a suspension, and is added, in no particular order with regard to the other components, to obtain the aqueous solution.

[0089] In an aspect of the invention, there is provided a method for providing bioavailable iron to plants, the method comprising a mixing of the at least one polyphosphate, as detailed above, the at least one source of iron, as detailed above and the at least one pH reducing agent, as detailed above. Furthermore, it is understood that any order of mixing of the various components as comprised in the composition, as detailed above, is acceptable.

[0090] It is further understood that all definitions and preferences as described above equally apply for this embodiment and all further embodiments, as described below.

[0091] Typically said mixing of the at least one polyphosphate, as detailed above, the at least one source of iron, as detailed above and the at least one pH reducing agent, as detailed above, may be carried out by using traditional mixers and blenders, high intensity mixers and electric stirrers. It is understood that the skilled person in the art will carry out said mixing according to general practice such as notably using optimal times, speeds, weights, volumes and batch quantities.

[0092] In an aspect of the invention, there is provided a method for providing bioavailable iron to plants, the method comprising the steps of: o Providing at least one polyphosphate, wherein said at least one polyphosphate is preferably selected from the group containing tetrapotassium pyrophosphate (TKPP), potassium tripolyphosphate (KTPP), sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), and mixtures thereof; o Providing at least one source of iron; o Providing at least one pH reducing agent selected from the group consisting of a solid acid, or salts thereof, hemipotassium phosphate (HKP) having the chemical formula KHsfPC h, monopotassium phosphate (MKP) having the chemical formula KH2PO4; potassium sulphate (SOP) having the chemical formula K2SO4; and mixtures thereof; wherein said at least one solid acid, is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetyl acetonic acid, tartaric acid, sulfosalicylic acid, oxalic acid; and o Mixing said at least one polyphosphate, said at least one source of iron and said at least one pH reducing agent, to form a solid nutrient composition, wherein said mixture comprises at least 0.10 wt.% and at most 10.00 wt.% of iron, with reference to the total weight of said composition.

[0093] In embodiments of the method, said at least one source of iron is selected from the following: Fe2(SO4)3.xH2O wherein x is a molar coefficient being at least 0 and at most 9, MFe(SO4)212H2O where M is Na or K, FefNOah-x^O wherein x is a molar coefficient being at least 0 and at most 9, FeCfe.xHzO wherein x is a molar coefficient being at least 0 and at most 6, Fe4(P2O7)3, FePC .x^O wherein x is a molar coefficient being at least 0 and at most 4, FeSC .x^O wherein x is a molar coefficient being at least 0 and at most 7, FeCL.x^O wherein x is a molar coefficient being at least 0 and at most 4, FeO.xH2O wherein x is a molar coefficient being at least 0 and at most 1, Fe(NH4)PO4.H2O, iron oxysulphate, and the mixtures thereof.

[0094] In embodiments of the method, said at least one polyphosphate, said at least one source of iron and / or said at least one pH reducing agent, are applied in the composition in concentrations and in mutual ratios as described herein. In embodiments of the method according to the invention, said method further comprises the step of: o Dissolving said solid nutrient composition with an aqueous solvent to form an aqueous solution, having a pH of at least 3.0 and at most 7.5, and o Applying said aqueous solution to plants.

[0095] Preferably, the aqueous solvent is water.

[0096] Preferably, the application is foliar application.

[0097] In embodiments of the method according to the invention, said pH values are obtained by diluting said solid nutrient composition with water to form an aqueous solution, wherein said composition has a concentration of 2 wt.%.

[0098] In alternative embodiments of the method according to the invention, said pH values are obtained by diluting said solid nutrient composition with water to form an aqueous solution, wherein said composition has a concentration of 10 wt.%.

[0099] In embodiments of the method according to the invention, said pH is preferably between 3.5 and 7.5, preferably between 3.5 and 6.0, or between 4.0 and 6.5, more preferably between 4.0 and 5.5, more preferably between 3.5 and 5.3, even more preferably between 3.5 and 4.6.

[0100] In another aspect of the invention, it is provided an aqueous solution, for use in a foliar application, wherein said aqueous solution is obtained by dissolving the nutrient composition according to the invention in an aqueous solvent, preferably in water. Advantageously, in this aqueous solution, the weight ratio of the solid nutrient composition to the aqueous solvent is comprised between 1:50 and 1:10. Among aqueous solvents suitable for use in the present invention mention may be notably made of water and water-based solutions. Preferably, the aqueous solvent is water.

[0101] It is further understood that all definitions and preferences, as described above, equally apply for the aqueous solution, for use in a foliar application.

[0102] Experimental section

[0103] In order to more clearly define the invention, the following examples are set forth. These examples are illustrative only and are not limiting as to the scope of the invention.

[0104] Figure 1 illustrates the curative effect of feeding kale with a fertilizer composition according to invention.

[0105] Figure 2 illustrates the curative effect of feeding arugula with a fertilizer composition according to invention.

[0106] Figure 3 illustrates the effect of preventively feeding kale with a fertilizer composition according to the invention. Figure 4 illustrates the effect of preventively feeding arugula with a fertilizer composition according to the invention.

[0107] Figure 5 illustrates the iron content in a mixed sample of kale and arugula subjected to the preventive greening, and in harvested plants.

[0108] General procedure for preparing solid nutrient compositions according to the present invention

[0109] The exact compositions of the Examples and of the Comparative Examples, with respect to the type of components contained therein and the related quantities thereof, are described in Tables 1 - 3 below.

[0110] For forming the solid nutrient compositions of the Examples and the Comparative Examples, the different components were typically mixed without any particular order, one by one, in a churn mixer having a volume of 20 1, for twenty minutes after adding the ultimate component when 1 kg of the composition was produced, and for one hour after adding the ultimate component when 10 kg of the composition was produced.

[0111] General analytical test methods

[0112] Tests were conducted under laboratory conditions to determine the following properties of the solid nutrient compositions of the Examples and the Comparative Examples, as described herein:

[0113] Dissolution and evaluation of precipitation;

[0114] - Turbidity (NTU);

[0115] - pH .

[0116] Dissolution and evaluation of precipitation

[0117] The solid nutrient compositions according to the present invention, as detailed above, were added to demineralized water in a beaker at 20 °C in amounts corresponding to a weight ratio of 1 part of the solid nutrient composition to 50 parts demineralized water, thereby forming an aqueous solution. The aqueous solution was stirred magnetically for 15 minutes at 400 rpm. The obtained aqueous solution was subsequently filtered over Nitrocellulose filters Porafil NC (50 mm 0) with pores of 0.45 pm. The filter was then rinsed with 150 ml of water. The filter was placed in an oven at 105 °C for 30 minutes. Finally, the filter was cooled to room temperature in a desiccator and visibly evaluated for the presence of insoluble matters.

[0118] Turbidity

[0119] The turbidity measurements were carried out by using a laboratory nephelometer (Hanna Instruments HI83414).

[0120] The solid nutrient compositions according to the present invention, as detailed above, were added to demineralized water in a beaker at 20 °C in amounts corresponding to a weight ratio of 1 part of the solid nutrient composition to 50 parts demineralized water, thereby forming an aqueous solution. The aqueous solution was stirred magnetically for 15 minutes at 400 rpm. After the given stir time and with the solution still having a temperature between 20 °C and 1 °C, the turbidity of the aqueous solution was measured. The typical unit for the measurement of turbidity is the Nephelometric Turbidity Unit (NTU). pH

[0121] The pH measurements were carried out by using a laboratory pH meter (Knick Portamess 911 - battery-operated).The solid nutrient compositions according to the present invention, as detailed above, were added to demineralized water in a beaker at 20 °C in amounts corresponding to a weight ratio of 1 part of the solid nutrient composition to 50 parts demineralized water, thereby forming an aqueous solution.

[0122] The aqueous solution was stirred magnetically for 15 minutes at 400 rpm. After the given stir time and with the solution still having a temperature between 20 °C and 1 °C, the pH of the aqueous solution was measured.

[0123] Influence of the nature of the pH reducing agent

[0124] Examples 4 - 6 (Ex 4 - 6) and Examples 8 - 9 (Ex 8 - 9) according to the invention were prepared by mixing the respective components of the composition, as described in Table 1, according to the general procedure described above.

[0125] The Comparative Examples 1 - 3 (CE1 - CE3) do not contain any pH reducing agent. These Comparative Examples were prepared by mixing the respective components of the composition, as described in Table 1, according to the general procedure described above.

[0126] The Comparative Examples 7 and 10 (CE7 and CE10) were prepared by mixing the respective components of the composition, as described in Table 1, according to the general procedure described above. All the experimental results are shown below in Table 1 where all the composition have a P ortho / Ptotal Of 0.2.

[0127] Examples 11 and 12 according to the invention were prepared by mixing the respective components of the composition, as described in Table 2, according to the general procedure described above. The experimental results are shown below in Table 2, where all the composition have a Portho / ptotai of 0.6. Table 1: Influence of citric acid and MKP as pH reducing agents

[0128] In the table where the results are presented, as well as in the following examples:

[0129] - "P2O5" relates to the concentration in weight of phosphorus containing compounds in the composition, wherein said compounds are expressed in P2O5; relates to the total number of moles of phosphorus in polyphosphate form; relates to the number of moles of phosphorus in orthophosphate form; and relates to the total number of moles of phosphorus in the composition.

[0130] Table 1 demonstrates that the aqueous solutions prepared from the solid nutrient compositions without any pH reducing agent (i.e. CE1 - CE3), according to the testing methods, as described above, have pH values much higher than 7.5, which make them unsuitable to be used for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

[0131] Examples 4 - 6 according to the present invention differ from the Comparative Examples 1 - 3, respectively, in that Examples 4 - 6 contain 15.0 wt. % of citric acid (i.e. solid acid). The aqueous solutions prepared from the solid nutrient compositions of Examples 4 - 6, according to the testing methods, as described above, do not show any precipitation, have NTU values of less than 10 and pH values between 5.2 and 5.9, which make them suitable to be used for foliar application, for application in horticulture, hydroponics and / or fertigation and the like. Comparative Example 7 differs from Examples 4 - 6 according to the present invention, in that Comparative Example 7 has a Ppoiy / Fe molar ratio of 2.2. The aqueous solution prepared from the solid nutrient composition of Comparative Example 7 , according to the testing methods, as described above, suffers from the formation of precipitates and the measured NTU value was higher than 100 which make them unsuitable to be used for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

[0132] Examples 8 and 9 according to the present invention differ from the Examples 5 and 6, respectively, in that Examples 8 and 9 contain 15.0 wt. % of monopotassium phosphate (MKP) instead of 15.0 wt. % citric acid (i.e. solid acid) as pH reducing agent. The aqueous solutions prepared from the solid nutrient compositions of Examples 8 and 9, according to the testing methods, as described above, do not show any precipitation, have NTU values of less than 10 and pH values between 7.1 and 7.4 which make them suitable to be used for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

[0133] Comparative Example 10 differs from Examples 8 and 9 according to the present, in that Comparative Example 10 has a Ppoiy / Fe molar ratio of 3.5. The aqueous solution prepared from the solid nutrient composition of Comparative Example 10, according to the testing methods, as described above, suffers from the formation of precipitates and the measured NTU value was higher than 100 which make it unsuitable to be used for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

[0134] The experimental results in Table 1 clearly demonstrates that both citric acid as MKP can be used as pH reducing agents but the lower limit of the Ppoiy / Fe molar ratio can be reduced to a lower value when citric acid is used. It is clear from table 1 than when the pH reducing agent is selected from hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the PPoiy / Fe molar ratio of the composition is of at least 4.00.

[0135] Table 2: Influence of mixtures of HKP and MKP as pH reducing agent

[0136] The pH reducing agent in Examples 11 and 12 according to the present invention is a mixture of hemipotassium phosphate (HKP) and monopotassium phosphate (MKP). The aqueous solutions prepared from the solid nutrient compositions of Examples 11 and 12, according to the testing methods, as described above, do not show any precipitation, have NTU values of less than 10 and pH values between 4.3 and 5.3, which make them suitable to be used for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

[0137] Influence of the amount of the pH reducing agent

[0138] Examples 4, 13, and 14 (E4, E13, and E14) according to the invention were prepared by mixing the respective components of the composition, as described in Table 3, according to the general procedure described above.

[0139] The experimental results are shown below in Table 3, where all the composition have a P ortho / Ptotal Of 0.2.

[0140] Table 3: Influence of amounts of pH reducing agent

[0141] Examples 13 - 15 according to the present invention differ from Example 4, respectively, in that Examples 13 - 15 contain higher amounts of citric acid. The aqueous solutions prepared from the solid nutrient compositions of Examples 13 - 15, according to the testing methods, as described above, do not show any precipitation, have NTU values of less than 10 and pH values between 4.3 and 5.0, which make them suitable to be used for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

[0142] General procedure for manufacturing the fertilizer compositions

[0143] Two of the solid nutrient compositions previously described in Table 3, Example 13 and 14, were added to demineralized water in amounts corresponding to a weight ratio of 1 part of the solid nutrient composition to 50 parts demineralized water. The obtained aqueous solutions were filtered by use of Nitrocellulose filters Porafil NC (50 mm 0) with pores of 0.45 pm, thus obtaining the fertilizer compositions described in Table 4. Table 4: Fertilizer compositions

[0144] Curative regreening of plants

[0145] Arugula and kale plants were sown (Day 1) and raised into rockwool plugs in a greenhouse under optimal climate conditions during the summer in order to obtain leafy greens. Right after sowing the trays were covered with a plastic lid to create optimal germination circumstances. After 18 days, when the plants had 1 or two full grown leaves, the seedlings were transplanted into a hydroculture system, and subsequently at specific times fed by one of the fertilizer compositions described herein. The trial was set up with four replications (four plots) per treatment; the plant spacing was app. 32 plants / m2. Plots were laid out in complete randomized block design, each plot consisted of 48 plants which were irrigated continuously in said hydroculture system. The plants were thereby given nutrient water, comprising macro- and micronutrients but without iron to create deficient circumstances, wherein said iron was provided by said fertilizer composition.

[0146] The fertilizer compositions described in Table 4 were applied (sprayed) by foliar application on the plants on:

[0147] Day 33,

[0148] Day 36,

[0149] Day 40, Day 43,

[0150] Day 47,

[0151] Day 50,

[0152] Day 56.

[0153] Assessments on the crops took place at least three times during the trial, the timing was based on visibility of deficiency and visible reduced crop vigour.

[0154] For the purpose of the invention, the greening or regreening value herein is an appreciation in percentage of a surface of plant leaves having the same colour as a negative reference. A complete green leaf would then be given a value of 100; a yellow leaf showing Fe deficiency would receive a value of 0.

[0155] Figure 1 and Figure 2 show the curative effect of feeding with a fertilizer composition, as described here above, for kale and arugula respectively, wherein the fertilizer composition consisted of

[0156] 1) fertilizer 1 (water)

[0157] 2) fertilizer 2 (dosed at a concentration of 6.20 kg / ha), and

[0158] 3) fertilizer 3 (dosed at a concentration of 9.77 kg / ha).

[0159] The fertilizer 1 sprayed control plants remained yellow during the trial. A progressive regreening effect was visible both for kale and arugula for fertilizer 2 and fertilizer 3. It can be seen that Arugula reacts slightly better on a foliar application than kale thanks to the initial clear yellowing of the leaves which was absent for kale.

[0160] Preventive greening of plants

[0161] Arugula and kale plants were sown and raised into rockwool plugs in a greenhouse under optimal climate conditions during the summer in order to obtain leafy greens and transplanted into a hydroculture system, as described in the previous test. After being transplanted, the plants were immediately preventively subjected to irrigation with nutrient water and at specific times fed by one of the fertilizer compositions described herein.

[0162] The fertilizer compositions described in Table 4 were applied (sprayed) by foliar application on the plants on:

[0163] Day 19,

[0164] Day 26,

[0165] Day 29,

[0166] Day 33,

[0167] Day 40,

[0168] Day 47, Day 56.

[0169] The fertilizer composition relate to the ones described in Table 4, namely:

[0170] 1) fertilizer 1 (water)

[0171] 2) fertilizer 2 (dosed at a concentration of 6.20 kg / ha), and

[0172] 3) fertilizer 3 (dosed at a concentration of 9.77 kg / ha).

[0173] Hence, for evaluating preventive greening of the plants, fertilizer compositions are applied on three different occasions in the first two week after transplanting the seedlings.

[0174] Figure 3 and Figure 4 show the effect of preventively feeding the plants with a fertilizer composition, as described here above, for kale and arugula respectively,

[0175] It is observed during the experiment that leaves remain green when treated with fertilizer 2 and fertilizer 3 while the leaves treated with the negative reference (fertilizer 1) turns yellow. The results are plant-dependent. In kale, little greening effect is visible. In arugula, progressive regreening is notable for the cases treated with an organic acid.

[0176] It is to be expected that curative and preventive greening can be increased by adding more additive like surfactants, wetting agents and penetrants to improve aspects such as the coverage of the leaf and the penetration of the leaf.

[0177] Nutrient analysis of plant leaves

[0178] During the two precedent tests (Curative regreening of plants and Preventive greening of plants), leaf samples were taken twice during the trial, more in particular wherein

[0179] 1) a mixed sample of kale and arugula subjected to the preventive greening was analysed on Day 32, when only preventive foliar applications had so far been performed; and

[0180] 2) leaf samples were taken at the end of the trial when the whole plants were harvested for fresh and dry weight measurements. For the water-sprayed references, green and yellow leaves were kept and analysed separately. The plant leaves were evaluated for their iron content.

[0181] The results are shown in Figure 5, wherein values are expressed in pmol Fe per kg dry material.

[0182] The reference root-fed leaves contain around 2000 pmol Fe per kg dry matter. The leaves of the plants treated by foliar application show clear Fe deficiency symptoms when receiving only water: the yellow leaves of the water-sprayed negative references contained typically between 900 and 1400 pmol Fe. However, it was found that their green parts show similar Fe levels as the root-fed leaves.

[0183] The foliar application of the fertilizers 1 and 2, both for preventive and curative purposes, have a clear positive effect on the Fe concentration of dry matter with an average of 4000-5000 pmol and a peak result of 8000 pmol.

Claims

CLAIMS1. A solid nutrient composition, comprising o at least one polyphosphate; o at least 0.10 and at most 10.00 wt.% of iron, with reference to the total weight of said composition; o at least one pH reducing agent; wherein said pH reducing agent is selected from the group consisting of a solid acid or salt thereof, hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP); and wherein the solid acid is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetoacetic acid, tartaric acid, sulfosalicylic acid, and oxalic acid; wherein said composition has a Ppoiy / Fe molar ratio of between 2.70 and 50.00 wherein Ppoiyis a total number of moles of phosphorus in polyphosphate form and wherein Fe is a total number of moles of iron in said composition, with the provisio that when the pH reducing agent is selected from hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoiy / Fe molar ratio of the composition is between 4.00 to 50.00;2. wherein said composition is substantially free of organic chelating agents containing at least one amine group. The solid nutrient composition according to claim 1, wherein the composition is substantially soluble in water and has, after dissolution in water, a percentage of insolubles of less than 0.2 wt.%, with reference to the total weight of the composition.

3. The solid nutrient composition according to any one of claims 1 or 2, wherein said at least one polyphosphate is selected from the group consisting of sodium and potassium polyphosphates.

4. The solid nutrient composition according to any one of previous claims, wherein said at least one polyphosphate is selected from the group consisting of pyrophosphates and tripolyphosphates, such as tetrapotassium pyrophosphate (TKPP), potassium tripolyphosphate (KTPP), sodium tripolyphosphate (STPP), and tetrasodium pyrophosphate (TSPP).

5. The solid nutrient composition according to any one of previous claims, wherein said at least one pH reducing agent is present in said composition in a concentration of at least 5 wt% and at most 55wt%, relative to the total weight of the composition.

6. The solid nutrient composition according to any one of previous claims, wherein said composition has a N / Ptotai molar ratio of 0.2 or less, wherein N is the number of moles of nitrogen and where Ptotai is the number of moles of phosphorus in the composition.

7. The solid nutrient composition according to any one of previous claims, further comprising phosphorus in orthophosphate form in a molar ratio P ortho / Ptotai of between 0.10 and 0.70, wherein Portho is the number of phosphorus moles in orthophosphate form in the composition.

8. An aqueous solution obtained by dissolving said solid nutrient composition according to any one of claims 1-7 in an aqueous solvent, wherein the weight ratio of the solid nutrient composition to the aqueous solvent is comprised between 1:50 and 1:10.

9. The aqueous solution according to claim 8, wherein said aqueous solution has a pH of at least 3.0 and at most 7.5.

10. The aqueous solution according to claim 8 or claim 9, wherein said aqueous solution has a solution turbidity being lower than 50 NTU, preferably lower than 20 NTU.

11. A method for providing bioavailable iron to plants, the method comprising the steps of o Providing at least one polyphosphate, wherein said at least one polyphosphate is preferably selected from the group containing tetrapotassium pyrophosphate (TKPP), potassium tripolyphosphate (KTPP), sodium tripolyphosphate (STPP), tetrasodium pyrophosphate (TSPP), and mixtures thereof; o Providing at least one source of iron; o Providing at least one pH reducing agent selected from the group consisting of solid acid, or salts thereof, hemipotassium phosphate (HKP) having the chemical formula KH5(PO4)2 and monopotassium phosphate (MKP) having the chemical formula KH2PO4, wherein said at least one solid acid is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetoacetic acid, tartaric acid, sulfosalicylic acid, oxalic acid; o Mixing said at least one polyphosphate, said at least one source of iron and said at least one pH reducing agent, to form a solid nutrient composition, wherein said solid nutrient composition (mixture) comprises at least 0.10 wt.% and at most 10.00 wt.% of iron, with reference to the total weight of said composition and wherein said solid nutrient composition has a Ppoiy / Fe molar ratio of between 2.70 and 50.00, wherein Ppoiyis a total number of moles of phosphorus in polyphosphate form and wherein Fe is a total number of moles of iron in said composition;with the provisio that when the pH reducing agent is selected from hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoiy / Fe molar ratio of the composition is between 4.00 to 50.00.

12. The method of claim 11, wherein said method further comprises the step of o Dissolving said solid nutrient composition in water to form an aqueous solution, having a pH of at least 3.5 and at most 7.5, and o Applying said aqueous solution to plants.

13. Use of said solid nutrient composition according to claims 1-8 or of said aqueous solution according to claims 9-10, in a fertilizing composition for foliar application, for application in horticulture, hydroponics and / or fertigation and the like.

14. Use in a foliar application of an aqueous solution according to claims 9 and 10.

15. Use in a foliar application of an aqueous solution, wherein said aqueous solution comprises: o at least one polyphosphate o at least one source of iron o at least one pH reducing agent; wherein said pH reducing agent is selected from the group consisting of a solid acid or salt thereof, hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP); and wherein the solid acid is selected from the group consisting of propionic acid, acrylic acid, lactic acid, pyruvic acid, butyric acid, succinic acid, fumaric acid, malic acid, itaconic acid, citric acid, gluconic acid, acetoacetic acid, tartaric acid, sulfosalicylic acid, and oxalic acid; wherein said aqueous solution has a Ppoiy / Fe molar ratio of between 2.70 and 50.00 wherein Ppoiy is a total number of moles of phosphorus in polyphosphate form and wherein Fe is a total number of moles of iron in said aqueous solution with the provisio that when the pH reducing agent is selected from hemipotassium phosphate (HKP), monopotassium phosphate (MKP), and potassium sulphate (SOP), the Ppoiv / Fe molar ratio of the aqueous solution is between 4.00 to 50.00; wherein said aqueous solution is substantially free of organic chelating agents containing at least one amine group.

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