FERTILIZER COMPOUND HAVING A GLASS MATRIX, PROCESS FOR THE PRODUCTION AND USES THEREOF

The present invention relates to a fertilizer compound having a glass matrix, a process for its production, and a fertilizer product based on said compound and relative uses thereof.

It is known that conventional fertilization can lead to the possible leaching of undesiderable compounds from soil to undergound water tables with the conseguent risk of water polluttion. In this case a restriction of using water for human and animal consuption can occur, as well as the utilization for agricultural purpose can lead to the alteration of biodiversity with conseguent harm of the environment. Polluting substances can be both inorganic and organic. Inorganic polluting substances results by the leaching from the soil of nitrogen compounds (particularly nitrates, the concentration of which can cause beyond certain limits the impossibility of a use of the water for drinking), or phosphatic compounds (in this case the main consequence can be eutrophication of internal waters marine water, nearby the coastlines, causing damages to the relative ecosystems including even the disappearance of living organisms or, at least, in less serious cases from an environmental point of view, the impossibility of a turistic exploitation of the polluted areas). In the case of inorganic polluting substances, the consequences of pollution can also be long lasting or at least more difficult to conflict, since molecules responsible for the contamination can come from organic synthesis unknown in nature; it is the case of the chelating substances used for application to plants of trace elements having a metallic nature.

At present, in order to avoid the aforementioned pollution risks, different expedients are used, amongst which the most common are the more frequent and gradual application of reduced amounts of nutrients or of chemical formulations allowing a slower release of them. In this last case, the fertilizer can be identified as a slow or controlled release fertilizer, the aim of which is exactly that of slowing down and prolong the fertilizing action of the product.

Amongst the slow or controlled release fertilizers those based on glass matrices are also known.

The problem of this kind of fertilizers is that they are realised so to release nutrients according to a preset time progress, i.e. according to programmes predetermined at the moment of their realisation. Nevertheless, plants needs are not constant and consequently, a product as those according to the prior art is unable to make available nutrients in soil only when plants actually need them.

In order to solve this problem, it was proposed, according to the European patent application EP-A-1 088 806, the realisation of a fertilizer compound having a glass matrix comprising a combination of forming oxides, modifier oxides and at least one inorganic trace element, wherein forming oxides, in an amount comprised between 9 and 22% by weight of the glass matrix, include phosphorus pentoxide (P ₂ O ₅ ), silica (Siθ2), and at least one of zirconium dioxide (ZrOa) and titanium dioxide (TiO ₂ ), modifier oxides of the glass matrix include potassium oxide (K ₂ O) and at least one of sodium oxide (Na ₂ O) and lithium oxide (Li ₂ O).

According to the aims of said patent application, it is possible to achieve a selective release of the nutrients having an immediate action since the beginning of the application and then going on following a definite schedule so as to proceed theoretically in relation both to the plant development and to the soil conditions.

Nevertheless, fertilizer compounds having a glass matrix according to the prior art and even according to the above mentioned European patent application EP-A-1 088 806 do not provide for an optimal solution and are sometimes unable to make trace elements contained therein available according to the plant needs. Particularly, some fertilizers having a glass matrix release trace elements contained therein, too slowly and only partially. In this context it is presented the solution according to the present invention the aim of which being that of providing an improved fertilizer compound having a glass matrix that, starting from studies on the plant nutrient absorption from the soil, according to their needs, and from the

investigation of the limits of the solutions according to the prior art, make it possible for the first time to obtain a fertilizer that can really release its nutritive elements only on the request of plants, according to their effective needs. Moreover, the present invention also relates to a method for producing said fertilizer compound having a glass matrix.

More particularly, the solution according to the present invention is based on the knowledge that plants are able to modify the rhizosphere, creating an environment more favorable for growth. Such modifications, mediated by the roots, mainly concerns mechanisms leading to an improvement in the acquisition of water and nutritive elements (e.g. H. Marschner, Mineral nutrition of higher plants, U.K. Academic Press, London, 1995).

These mechanisms, particularly important in situations of lack of nutrients, when the requests of the plant lead to a greater mobilization of the elements also from non-soluble source, are carried out through the release of organic acids, mainly citric, oxalic, malic acid and of amino acids. To this regard, reference is also made to the text adopted and written in collaboration by the professors of agricultural chemistry from all the Italian Faculties of Agriculture "Fondamenti di chimica del suolo", supervised by Paolo Sequi, edited by Patron Editore, 2005, in chapter 6 7/ suolo, Ia pianta e Ia rizosfera" by Maurizio Cocucci, Zeno Varanini and Roberto Pinton (pag. 175-206). The acidification of the rhizosphere gives a contribution to the mobilization of the elements, such as for example phosphorus and iron (F. D. Dakota and D.A. Phillips, Root exudates as mediator of mineral acquisition in low-nutrient environments, Plant and Soil 245:35-47, 2002).

Nevertheless, for some compounds, such as for example for iron phosphate, the solubility product is so low that it can not be considered useful for the nutrition of plants, and even if these compounds are present in the soil in considerable amounts, they can not be absorbed by the roots. The natural mechanism just described can be completely inadequate or anyway insufficient in order to satisfy vegetal needs, since non-soluble

salts are difficult to attack even for compounds of the kind released by the roots, since they are considerably crystallized or obstructed by other compounds of a different nature. Actually, the mechanism exerted, by the root secretions is unable to make soluble most of the mineral forms of nutrients indispensable for a good vegetal growth.

These and other results are achieved according to the present invention by proposing a new fertilizer having a glass matrix studied with the purpose of making soluble the nutrients depending on the plant needs. Thus, the aim of the invention was not that of improving the release at low speed of the nutrients, or the control of the rate of release from the fertilizer, but the possibility of an effective supply of the nutrients when requested by the plant, through the release of organic substances having chelating or complexing properties by the roots.

Further, it is in particular the theoretic solubilization of the aforementioned citric acid that was ideally used for improving the different steps of the production process of the product of the invention. In our fertilizer having a glass matrix, following the solubilization of iron and other metals, to which phosphates are chemically bonded, the phosphates themselves can be released in the solution of soil and becoming available for the plant.

Another aspect of the invention is to assure that the roots cannot meet any physical obstacles that can stop their lack signal emission, or, if desired, the specific secretion of chelating substances and natural complexing agents. Further, according to the method of the present invention, many limits of the method for producing fertilizers having a glass matrix at present on trade were surpassed. In fact, according to the production methods already known, many compounds of iron, and of other metals, produced through a fusion process and a subsequent step of cooling or crystallization of the melt mass can not be solubilized by organic acids of the kind of citric acid and therefore cannot be used by root secretions. This phenomenon was considered as due to the formation of spinels, commonly produced also in nature through the crystallization of volcanic

magma and having an empirical formula of the kind Me ²⁺ Me ³⁺ ₂ 0 ₄ , characterised by its minimum solubility and the difficulty for external agents to attack the structure of the corresponding minerals.

The method according to the invention, uses therefore reactive substances the composition of which allows for avoiding the formation of products of this kind.

It is therefore a specific object of the present invention a fertilizer compound having a glass matrix having the following percentage composition expressed by weight: phosphorus (as P ₂ O ₅ ) in the range 2- 45%, potassium (as K ₂ O) in the range 2-45%, other secondary macronutrients (calcium, magnesium, sulphur and if necessary sodium) and trace elements.

Preferably, according to the invention, among the aforesaid trace elements the following compounds are present, alone or in mixture thereof, according to the following amounts by weight: 0 - 22% ZnO; 0 -

38% Fe ₂ O ₃ ; O - 18% B ₂ O ₃ ; O - 18% MnO; O - 12% Co ₃ O ₄ ; O - 18% CuO; O -

16% MoO ₃ .

According to a particularly preferred embodiment of the invention, said compound has the following percentage composition by weight: 0,50 - 30% SiO ₂ , 0,00 - 20% AI ₂ O ₃ , 3,00 - 37,40% CaO, 0,50 - 22,90% MgO,

0 - 10,45% Na ₂ O, 2,00 - 45,00% K ₂ O, 0,00 - 22,00% ZnO, 0,030 -

4,00% ZrO ₂ , 0,001 - 4,0% TiO ₂ , 0,00 - 38% Fe ₂ O ₃ , 0 - 18% B ₂ O ₃ , 2,00 -

45,00% P ₂ O ₅ , 0,00 - 18% MnO, 0 - 12% Co ₃ O ₄ 0 - 18% CuO ₁ 0 - 16%

MoO ₃ , 0,00 - 10% SO ₃ . However, minimum percentage of some components can be detected, due to possible impurities of the raw materials.

Particularly, in the composition according to the invention, said trace elements are present as a whole in a percentage range by weight comprised between 1% and 65% over the total of the glass matrix, wherein said amounts of trace elements refer to the respective oxides.

The invention further relates to a method for the production of a fertilizer compound as defined hereinabove, comprising the following steps:

- mixing a plurality of precursors of the chemical compounds comprised in the final fertilizer compound, in a powder or pellet state;

- melting the mixture thus obtained at a temperature ranging between 1100 ⁰ C and 1600 ⁰ C; - cooling the melt mixture;

- grinding of the solid-vitreous and granular product obtained by the preceding step.

Preferably, according to the invention, said precursors comprise the following compounds in percentage amounts by weight: 0 - 55% kaolinite clay (AI ₂ Si ₂ O ₅ (OH) ₄ ), 0,10 - 10% zirconium flour (ZrSiO ₄ ), 0,00 - 22,00% zinc oxide (ZnO), 0 - 18% colemanite (Ca ₂ B ₆ On -5H ₂ O), 0 - 30% potassium feldspar (K ₂ AIO ₂ (SiO ₂ ) ₃ ), 0 - 35% potassium carbonate (K ₂ CO ₃ ), 0 - 30% dolomite (MgCa(CO ₃ ) ₂ ), 0 - 30% calcium carbonate (CaCO ₃ ), 0 - 40,00% iron carbonate (FeCO ₃ ), 0,00 - 20% iron sulfate (FeSO ₄ ), 0,00 - 23% hydrate copper carbonate (CuCO ₃ Cu(OH) ₂ ), 0 - 40,00% manganese carbonate (MnCO ₃ ), 0 - 16 % molybdenum oxide (MoO ₃ ), 0,00 - 50% monoammonic ammonium phosphate (NH ₄ H ₂ PO ₄ ), 0 - 12% cobalt oxide (Co ₃ O ₄ ) and 0,00 - 50% dipotassium phosphate (K ₂ HPO ₄ ). In the composition according to the invention natural raw materials from mines and/or chemical products obtained by synthesis and/or pyrolisis reactions can be optionally used.

Still according to the invention, said step of melting of the mixture is realised by introducing the mixture in a continuous or batch melting oven, electric and/or with free flame. Further, according to the invention, said cooling step occurs through percolating said melt mixture from the the melting oven to water.

Always according to the invention, said cooling step occurs by conveying said melt mixture between two cooled cylinders made of steel. The invention further relates to a fertilizer product comprising the fertilizer having a glass matrix as defined hereinabove together with disperding agents and/or fertilizers or organic soil ameliorants able to modify the surrounding physical environment of root exploration and/or

with biostimulating substances that promote the plant growth and particularly of their roots.

Further, the invention relates to a container for a fertilizer product that can be positioned in suitable locations close to the plants, for example in the soil located under the drips of the irrigation apparatuses, in order to address root growth toward the nutrients.

Lastly, the invention relates to the use of a fertilizer compound as defined hereinabove for the nutrition of soilless cultivations.

In order to assure the roots cannot run into physical obstacles that could restrain their emission of deficiency signals, for example for the use in vegetable and flower cultivations, the product according to the present invention can be mixed together with fertilizers or soil ameliorants having the physical consistency of a sponge, such as for example vinasses from wine and distillery waste treatment, so as to facilitate the development of the roots closer to the fertilizer having a glass matrix that is solubilised according to the real needs.

This preferential development of the roots in a favorable physical environment can be further facilitated by adding biostimulating substances to the substrate promoting the development of roots and, obviously, of the whole plant. It is an interaction involving a further sinergy that can make even more evident and easier to appreciate the use of nutrients provided by the fertilizer having a glass matrix according to the invention.

In the case of cultivations taking advantage by localised irrigation, such as drip irrigation, the fertilizer having a glass matrix according to the present invention, or its mixture together with spongy substances and other additives, is preferably provided under the drips or other irrigators, already constituting a sort of a attraction for the roots, thus constituting sort of a "drinking trough" for plants, obtaining from it, together with water, also the nutrients they need. Even in the very different environment of soilless cultivations, commonly used particularly in the field of nursery gardening, in an equally typical way, the fertilizers having a glass matrix of the present invention can be determinant to completely remove any risk of pollution on the one

hand, since only the necessary amount of nutrients for the plant is added to the solution, and to avoid any problem of recycling, analytical calculation and restoring of the necessary nutrients on the other hand.

By way of generalisation, the features of the process for the production of fertilizers having a glass matrix according to the present invention provide for a first step according to which the raw materials being used, in a dust or pellet state, are separately weighed and subsequently put in a mixer in order to make the composition omogeneous in line with the stoichiometric amounts of raw materials. The obtained mixture is put in a melting oven, which can be continuous or batch, with free flame and/or electric, and it is melt at a temperature ranging between 1100 ⁰ C and 1600 ⁰ C. As the heating of the mixture in the oven proceeds, the chemical reactions of the different elements start involving the formation of an homogeneous glass matrix, in a viscous liquid state.

The obtained material is percolated from the melting oven to water to cool it, or as an alternative it is conveyed between two cooled cylinders made of steel and has a solid-vitreous and granular aspect, with granules of different dimensions, depending on the cooling system being used. The material cooled as hereinabove is then ground, in order to obtain the desired particle-size characteristics, i.e. the one which is more suitable for the subsequent applications.

The invention will be described hereinbelow for illustrative, non limitative purposes, by making reference in particular to some illustrative examples. Example 1.

In order to realise a fertilizer compound having a glass matrix, the reactants listed in Table 1 were used, the Table also indicating their respective amounts, as percentage concentrations by weight.

Table 1

Starting materials were weighted according to the proportions listed in the table and mixed together. The obtained composition was conveyed to a melting plant constituted by a pot made of refractary material fed up with gaseous methane, suitable for melting up to 30 kg of material for each used. The temperature was raised up to 1400 ⁰ C for some hours, i.e. until an homogeneous melt mass is obtained, being sufficiently fluid to be percolated into water through the nozzle below.

The cooled glass was dried and subsequently ground in order to obtain particle-size dimensions suitable for use in agriculture.

The product obtained accordingly was examined and showed the chemical composition summarized in Table 2, wherein relative amounts of each compound are expressed as percentage amount by weight. Table 2

The product of the invention is constituted by complexed salts originating by the reaction of phosphorus, silicon and boron anions with cations of the metals added to the composition. The products in excess are mainly constituted by CO ₂ and H ₂ O.

The chemical composition of the starting materials, their physical state, the quality of mixture, as well as the melting conditions, decisively affect the availability of all the ions on place, comprising trace elements, with respect to the exudates of the plant itself. Example 2.

By the same method of preparation of Example 1 the compounds listed in Table 3 were mixed, their amounts being expressed as a percentage by weight. Table 3

The product obtained showed the chemical composition of the following Table 4. Table 4

Example 3.

By the same method of preparation of Example 1 the compounds listed in Table 5 were employed for the reaction, their amounts being expressed as a percentage by weight. Table 5

The product obtained accordingly showed the chemical composition of the following Table 6. Table 6

Example 4.

By the same method of preparation of Example 1 the compounds listed in the following Table 7 were mixed, their composition being expressed as a percentage by weight. Table 7

The product obtained accordingly showed the chemical composition summarized in the following Table 8. Table 8

Example 5.

By the same method of preparation of Example 1 the compounds listed in the following Table 9 were mixed for the reaction. Table 9

The product obtained accordingly showed the chemical composition summarized in the following Table 10. Table 10

Example 6.

By the same method of preparation of Example 1, in order to realise a fertilizer compound having a glass matrix the compounds listed in the following Table 11 were carried to react, the respective amounts being expressed as percentage concentrations by weight. Table 11

The product obtained accordingly showed the chemical composition summarized in the following Table 12. Table 12

Example 7.

By the same method of preparation of Example 1 the compounds listed in the following Table 13 were used for reaction. Table 13

The product obtained accordingly showed the chemical composition summarized in the following Table 14. Table 14

Example 8.

By the same method of preparation of Example 1 reaction was obtained by the compounds listed in the following Table 15, the starting materials being used satisfying the criteria requested for the application in organic agriculture. Table 15

The product obtained accordingly was examined and showed the chemical composition summarized in the following Table 16, wherein relative amounts of each compound are expressed as percentage amount by weight. Table 16

Zn, Mo and Co oxides were obtained through a thermal treatment of natural mineral sulfides, a method allowed for the preparation of starting materials to be used in organic agriculture. All the remaining starting materials being used came from natural mines. Example 9.

In a cultivation of pear trees, located in an area being characterised by calcareous soils, wherein severe phenomena of iron chlorosis and zinc chlorosis were evident, amounts corresponding to 20

kg/ha of chelates, containing 6% iron in the soil, were administered, to alternating rows, plus five leaf treatments with a solution containing 7% iron and 1 ,4% zinc. The fertilizer having a glass matrix corresponding to the formulation of Example 2, at a rate of 40 kg/ha, was applied to the other rows.

According to the test made by normal chelates the main result was immediate but transient: in some cases ten days after the leaf application it was necessary a new application to avoid the reappearance of the symptoms of deficiency. The same symptoms of deficiency always and anyway came up again to the same extent during the following year in the rows of pear trees treated with chelates.

In the rows treated with the fertilizer having a glass matrix of the invention, the symptoms of deficiency gradually but definitively disappeared, and did not came up again during the following two years, so that the preexisting deficiency of iron and zinc could be considered as disappeared. Example 10

Field cultivations of cabbage and spinach, showing deficiency symptoms from lack of iron, were treated with mixtures with a ratio of 2:1 and 1 :1 of anaerobically produced wine vinasse and the fertilizer having a glass matrix of example 8 (in an amount equivalent to 40 kg/ha of fertilizer having a glass matrix).

The results were compared with those obtained by adjacent cultivations of the same two crops, with applications of 1 q/ha of mineral superphosphate 19%, 1 q/ha of potassium sulfate 50% and a common iron chelate repeated two times.

The efficiency of the fertilizer having a glass matrix of the invention looked similar to that of the conventional fertilizers, except for iron, which is sometimes slightly slower in reacting, even if it is much longer lasting with reference to the cultivations to which the common iron chelate was administered.

The following year the same cultivation of cabbages and spinach was cultivated on the same fields, without any application of fertilizers. The

crops appeared to be luxuriant in the field wherein the previous year the fertilizer having a glass matrix of the invention was applied, while they come out to be scrubby and showed signs of iron deficiency in the field wherein conventional fertilizers together with common chelates had been applied. To sum up, by means of the fertilizers having a glass matrix of the invention even fertilization with superphosphate and potassium sulfate was found superfluous. Example 11.

In a cultivation of peach trees, drip irrigated and located in soils wherein symptoms of iron, zinc and manganese deficiency could be observed, some perforated containers were positioned containing peat and an amount of fertilizer having a glass matrix according to the invention corresponding to 50 g per plant, with a chemical composition as that of example 8. The containers were positioned in the soil in correspondence of drips.

During the five years following the positioning of the containers no symptoms of deficiency appeared and all allow to foresee that they are not going to appear even during the following years, whereas in adjacent cultivations symptoms of deficiency had a permanent character and were faced with a positive outcome even if extremely discontinuous with time by means of administrations of conventional chelates.

During a dry year preceded by exceptionally rainy conditions with water stagnation on the surface of the soil, the plants showed signs of sufference, thus biostimulating agents were administered to the soil in correspondence of the drips. The plants in correspondence of which the containers were positioned registered a vigorous and immediate vegetative recovery, whereas in those of the adjacent fields the treatment remained substantially without any apparent effect. An inspection made by realising a cutting in the soil having a 50 cm depth showed that in the first case a very important development of the roots in correspondence and inside the containers could be noticed, whereas in the adjacent fields a similar increase of concentration of the roots in correspondence of the drips of the irrigation plant did not be occur.

Example 12.

Two flower cultivations were carried out during a complete season on soilless system on substrates, in a case with a conventional monitoring of the nutrient solutions and a continuous addition of the macro and microelements up to the conventional level and in the second case adding an excess of fertilizer having a glass matrix according to the invention as a source of phosphorus, potassium, secondary nutrients and trace elements.

In the second case, the analysis of the nutrient solutions did not show appreciable concentrations of most of the elements and making it superfluous in similar cases for the future, differently from the first case.

In both cases no relevant differences were observed and the plants developped luxuriant without any problem of nutritional deficiency.

It is evident that the fertilizer having a glass matrix was able to respond to the nutritional need of the plants independently from the analysed mineral content of the nutrient solution, without any problem of pollution and recycle of the solutions and without any need of a continuous analytical control thereof. Thus, the nutritional functions in question was related to both phosphorus and potassium and also to all the other applied secondary nutrients and trace elements.

The present invention was described for illustrative, non limitative purposes, according to its preferred embodiments, but it has to be understood that any variations and/or modifications can be made by the skilled in the art without escaping the correspondent scope, as defined by the enclosed claims.