COMPOSITION FOR COATING SUBSTRATES

Abstract

The present invention provides an aqueous dispersion comprising (a) an active agent, which is a humic substance, and (b) pyrogenic silica, wherein: the weight percent of the active agent relative to the total weight of the dispersion is between 1 and 50%; and the weight ratio of the active agent to the pyrogenic silica is between 1.5:1 and 75:1, particularly between 1.5:1 and 60:1. The invention also provides a method for its preparation, as well as its use in coating a substrate, and the resulting coated substrate. The dispersion of the invention allows for an increased amount of humic substances without adversely affecting the stability of the granule (in terms of dust and caking).

Description

COMPOSITION FOR COATING SUBSTRATES FIELD OF INVENTION The invention relates generally to the field of formulation and use of fertilizer compositions for agricultural use. In particular, the present invention relates to a stable, high-load aqueous dispersion comprising (a) an active agent that is a humic substance and (b) pyrogenic silica, as well as a process for its preparation, its use as a coating, a process for coating a substrate, and the resulting coated substrate, such as a coated fertilizer or seed. BACKGROUND OF THE INVENTION Modern agriculture has shifted towards high yields, high quality, efficiency, and pollution-free production. The development of new fertilizers is essential for this progress. Humic substance, a natural organic compound, is a key component of humus (the main organic fraction of soil), peat, and coal (and is also found in many mountain streams, depleted lakes, and ocean water). A typical humic substance is a mixture of many molecules, some of which are based on a core unit of aromatic rings with phenolic and carboxylic substituents bonded together. The functional groups that contribute most to the surface charge and reactivity of humic substances are the phenolic and carboxylic groups. Humic acids behave as mixtures of dibasic acids, with a pKa value around 4 for the protonation of carboxyl groups and around 8 for the protonation of phenolate groups. Another important characteristic is charge density. The molecules can form a supramolecular structure held together by non-covalent forces, such as Van der Waals forces, π bonds, and C-π interactions. The presence of carboxylate and phenolate groups gives humic acids the ability to form complexes with ions such as Mg²⁺, Ca²⁺, Fe²⁺, and Fe³⁺.Many humic acids have two or more of these groups arranged to allow the formation of chelate complexes. Complex formation (chelation) is an important aspect of the biological role of humic acids in regulating the bioavailability of metal ions. Due to the special properties of humic substances, efforts have focused on their use to enrich fertilizer granules through coating. In this coating process, the humic substance is dissolved in a liquid carrier. Significant drawbacks to this technology have been identified. One is the deterioration of the granule due to the use of a liquid carrier if large quantities of it are added. Another is that a high concentration of humic substance is required to achieve the desired agronomic effect. Therefore, there is a need to provide a formulation based on humic substances that overcomes the above limitations. BRIEF DESCRIPTION OF THE INVENTION The present inventors have discovered that pyrogenic silica can stably disperse a large load of humic substance. As illustrated below, when a commercially available hydrophobic pyrogenic silica dispersion was used, it was found to successfully disperse more than 20% by weight of humic substance relative to the total weight of the dispersion. Specifically, Table 1 shows approximately 22.1% and Table 2 approximately 34–36%. Table 2 also illustrates that this technical effect of high loading is not limited to a particular hydrophobic fumed silica or to the fact that the starting fumed silica is used as a liquid or as a solid: the results of a high loading were substantially the same using the same source of fumed silica, one in the form of a dispersion and the other in the form of a powder. The inventors have also discovered that the coating could be efficiently applied to fertilizer granules, thus providing a homogeneous distribution of the coating ingredients over the entire fertilizer, while keeping the granules intact. Thus, the present invention provides, in a first aspect of the invention, an aqueous dispersion comprising (a) an active agent that is a humic substance and (b) pyrogenic silica, wherein: - the percentage by weight of the active agent with respect to the total weight of the dispersion is between 1 and 50%; and - the weight ratio between the active agent and the pyrogenic silica is between 1.5:1 and 75:1, particularly from 1.5:1 to 60:1. Commercially available concentrated humic substance solutions comprise up to approximately 15% humic substance. Thus, the present invention, based on the use of a dispersion using fumed silica, can provide humic substance dispersions with a higher loading (at least approximately 50% higher) than those currently available. This remarkable increase in humic loading is achieved by using an excess of humic substance relative to the amount of fumed silica dispersed in the composition of the invention. As also shown below, the high-load humic compositions of the invention are stable (despite the high load of humic substances in the coating), homogeneous, and dryable. In addition to the above, it was also found that the dispersions of the invention can be used easily and efficiently for coating fertilizer granules without adversely affecting the physicochemical properties of the fertilizers. As shown below, no significant caking or dusting was observed when the granules were coated with the dispersion of the invention. Therefore, the invention represents a major advance in the field of agrochemicals. In a second aspect, the present invention provides a procedure for preparing an aqueous dispersion as defined in the first aspect of the invention, comprising the step of mixing the pyrogenic silica with the active agent. In a third aspect, the present invention provides for the use of an aqueous dispersion as defined in the first aspect of the invention to coat a substrate. In a fourth aspect, the present invention provides the use of an aqueous dispersion as defined in the first aspect of the invention as a plant growth stimulant. In a fifth aspect, the present invention provides a method for coating a substrate selected from a fertilizer granule and a seed, comprising the method of applying the aqueous dispersion as defined in the first aspect of the invention onto the surface of the substrate. Finally, in a sixth aspect, the present invention provides a coated fertilizer granule or seed obtainable by the procedure defined in the fourth aspect of the invention. DETAILED DESCRIPTION OF THE INVENTION All terms as used in this application, unless otherwise stated, shall have their ordinary meaning as known in the prior art. More specific definitions for certain terms used in this application are set forth below and are intended to be applied consistently throughout the specification and claims, unless a more comprehensive definition is expressly provided. Furthermore, for the purposes of this invention, any given range includes both the lower and upper limits of that range. Given ranges, such as temperatures, times, weights, and the like, are to be regarded as approximate unless specifically stated. In a first aspect, the present invention provides an aqueous dispersion comprising a humic substance and a pyrogenic silica. In the present invention, the term dispersion is to be understood as a system in which discrete particles of pyrogenic silica are dispersed in a continuous phase of another material (i.e., a polar solvent, such as water). In the present invention, the term humic substance (HS) is to be understood as an organic complex comprising major components of humus, the principal organic fraction of soil, peat, and coal (and also a component of many mountain streams, dystrophic lakes, and ocean water). Humic substances are involved in many processes in natural soils and waters: for example, soil erosion, plant nutrition, pH buffering, trace metal mobility and toxicity, bioavailability, degradation and transport of hydrophobic organic chemicals, formation of disinfection byproducts during water treatment, and heterotrophic production in wastewater ecosystems. Consequently, humic substances have received attention from scientists in a wide variety of disciplines. According to information provided by the International Humic Substances Society (IHSS), humic substances in soils and sediments can be divided into three main fractions: humic acids (HA or HAs), fulvic acids (FA or FAs), and humins. HA and FA are extracted from soil and other solid-phase sources using a strong base (NaOH or KOH). Humic acids are insoluble at low pH and precipitate upon the addition of a strong acid (adjust to pH 1 with HCl). Humins cannot be extracted with either a strong base or a strong acid. Aquatic soil samples contain only hydrohalic acids (HA) and fulvic acids (FA). The HA is typically removed from the water by lowering the pH to 1 and decanting it. The remaining extract is then passed through a hydrophobic resin that retains the fulvic acids, while eluting any adulterants. These adulterants are subsequently extracted from the resin using an alkaline solution. Resin column separation is used to separate the FA from non-humic materials (amino acids, peptides, sugars, etc.) extracted from the soils. At low pH, the FA is adsorbed onto the resin, while the non-humic materials pass through the column. In one embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the humic substance comprises humic acid, or alternatively, fulvic acid, or alternatively, a combination of humic and fulvic acids. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the humic substance comprises humic acid in a weight percentage relative to the total weight of humic substance in the range of 5 to 90%, preferably between 25 and 85%, more preferably between 80 and 83%, more preferably 82%, and fulvic acid in a weight percentage relative to the total weight of humic substance in the range of 10 to 95%, the sum of both ingredients being 100% by weight.In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the humic substance comprises humic acid in a weight percentage relative to the total weight of humic substance in the range of 10 to 30%, and fulvic acid in a weight percentage relative to the total weight of humic substance in the range of 70 to 90%, the sum of the ingredients being 100% by weight. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the humic substance comprises humic acid in a weight percentage relative to the total weight of humic substance in the range of 5 to 90%, 10 to 90%, 25 to 85%, or 80 to 83%.In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the humic substance comprises humic acid in a weight percentage relative to the total weight of the humic substance of approximately 82%. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the humic substance comprises fulvic acid in a weight percentage relative to the total weight of the humic substance in the range of 10 to 95% or 70 to 90%. In the present invention, the term pyrogenic silica (CAS number 112945-52-5) may also be called fumed silica because it is produced in a flame, and refers to microscopic droplets of amorphous silica fused into three-dimensional secondary particles in a branched, chain-like form, which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and a large surface area. Its three-dimensional structure results in increased viscosity and thixotropic behavior when used as a thickener or reinforcing filler. In one embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the pyrogenic silica is a hydrophobic pyrogenic silica. In the present invention, the term "hydrophobic fumed silica" means a fumed silica that repels a mass of water and is characterized by having hydrophobic groups chemically bonded to its surface. The hydrophobic groups are typically alkyl chains or polydimethylsiloxane, hexamethyldisilazane, dimethyldichlorosilane, and combinations thereof. Many manufacturers supply hydrophobic fumed silicas, such as Evonik (Aerodisp™) or Cabot, Corp. (Cab-O-Sperse™). In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the weight percent of the active agent relative to the total weight of the dispersion is between 10 and 50% by weight, between 10 and 40% by weight, between 15 and 50% by weight, between 20 and 50% by weight, or between 19 and 40% by weight. In one embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, CCQQ LO / ZZnZ / q / Yli The % by weight of the active agent with respect to the total weight of dispersion is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49% or 50% by weight. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the weight ratio between the active agent and the pyrogenic silica is between 2:1 and 70:1, between 2:1 and 55:1, preferably between 10:1 and 65:1, preferably between 15:1 and 60:1, between 20:1 and 45:1 or between 30:1 and 40:1. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the weight ratio between the active agent and the pyrogenic silica is 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, 30:1, 31:1, 32:1, 33:1, 34:1, 35:1, 36:1, 37:1, 38:1, 39:1, 40:1,41:1,42:1,43:1,44:1,45:1,46:1,47:1,48:1,49:1,50:1,51:1,52:1,53:1,54:1,55:1,56:1,57:1,58:1,59:1, 60:1,61:1,62:1,63:1,64:1,65:1,66:1,67:1,68:1,69:1, 70:1,71:1, 72:1,73:1,74:1 or 75:1. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the weight % of the active agent with respect to the total weight of the dispersion is 10-50%, and the weight ratio between the active agent and the pyrogenic silica is between 2:1 and 70:1, between 10:1 and 65:1 or between 15:1 and 60:1. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the weight % of the active agent with respect to the total weight of the dispersion is 10-40%, and the weight ratio between the active agent and the pyrogenic silica is between 2:1 and 70:1, between 10:1 and 65:1 or between 15:1 and 60:1. In another embodiment of the first aspect of the invention, optionally in combination with any of the embodiments provided above or below, the aqueous dispersion further comprises one or more agriculturally acceptable agents. In the present invention, the expression agriculturally acceptable agent comprises chelates, macronutrients, micronutrients, amino acids, plant hormones, plant extracts, crop protectants, biopolymers and microorganisms, among others. The term "agriculturally acceptable" applied to a material or composition in this document means that it is not unacceptably harmful or toxic to a plant or its environment, and is safe for the user or other persons who may be exposed to the material when used as described in this document. Illustrative non-limiting examples of chelates and chelating agents are ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA) and ethylenediamine-N,N'-bis-2-hydroxyphenylacetic acid (EDDHA). Non-exhaustive, illustrative examples of plant protection products include insecticides, fungicides, and nematicides. Non-limiting, illustrative examples of macronutrients are nitrogen, potassium, calcium, magnesium, phosphorus, and sulfur. Non-limiting, illustrative examples of micronutrients include boron, zinc, copper, manganese, iron, and molybdenum. Non-limiting illustrative examples of amino acids are glutamate, glutamine, aspartate, and derived amino acids. Non-limiting illustrative examples of plant hormones include auxins, gibberellins, cytokinins, ethylene, and abscisic acid. Non-limiting, illustrative examples of plant extracts include those derived from seaweed, essential oils, and neem extracts. Non-limiting, illustrative examples of biopolymers include chitosan, proteins, peptides, carrageenans, cellulose, starch, polyvinylpyrrolidone, alkylated polyvinylpyrrolidone, polyvinyl acetates, polyvinyl acetate copolymers, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyacrylates, styrene butadiene, polyurethane, carnauba wax, paraffin wax, beeswax, polyethylene wax, polypropylene wax, methylcellulose, and ethylcellulose. Non-limiting illustrative examples of microorganisms are bacteria (e.g., Phizobium, Bacillus, Pseudomonas) and fungi (e.g., Aspergillus, Trichoderma, Penicillium). All the modalities provided under the first aspect of the invention, relating to pyrogenic silica, active agent, weight percentages, ratios and the possible inclusion of other acceptable agricultural agents, are also modalities of the other aspects provided in this application. In a second aspect, the present invention provides a procedure for preparing an aqueous dispersion as defined in the first aspect of the invention. In one embodiment of the second aspect of the invention, optionally in combination with any of the embodiments provided above, the fumed silica, which is mixed with the humic substance, is in liquid form. In an alternative embodiment of the second aspect of the invention, optionally in combination with any of the embodiments provided above, the fumed silica is in powder form and is then mixed with the humic substance (also in powder form) before preparing the aqueous dispersion. In a third aspect, the present invention provides for the use of an aqueous dispersion as defined in the first aspect of the invention to coat a substrate. In the present invention, the term substrate encompasses inert carriers (such as limestone), fertilizer granules, and plant parts, such as seeds, rhizomes, cuttings, or shoots. In one embodiment of the third aspect of the invention, optionally in combination with any of the embodiments provided above or below, the substrate is a fertilizer granule, an inert carrier, or a seed. In the present invention, the term fertilizer granule means a particle or agglomeration of particles containing nutrients to enhance plant growth. For the purposes of the present invention, fertilizer grains and granules may be used synonymously, as the differences between the two relate only to the size of the particle or particle agglomeration. A fertilizer granule is a material of natural or synthetic origin used to distribute essential nutrients to plants and crops. Any granule containing nutrients and capable of accepting a coating is suitable for the purposes of the present invention. The granule may, in certain embodiments, include one or more of the primary nutrients, and the nutrients may be derived from one or more fertilizer sources such as urea and muriate of potash. Thus, fertilizer granules may comprise nitrogen, phosphorus, or potassium sources such as ammonium nitrate, ammonium sulfate, ammonium sulfonitrate, calcium nitrate, calcium ammonium nitrate (NAC), urea, urea-formaldehyde, monoammonium phosphate (MAP), diammonium phosphate (DAP), polyphosphate compounds, phosphate rock, single superphosphate (SPS), triple superphosphate, potassium nitrate, potassium chloride, or potassium sulfate (SOP).Combinations comprising the above may also be used. In certain embodiments, the granulated materials are generally of uniform size and easy to handle, which facilitates the coating procedure of the present invention. The granules are also generally water-soluble to allow for release and dissolution in the soil and to enable timely absorption by plant roots. The dispersion of the invention may be applied to any commercially available fertilizer granule. In a fifth aspect, the present invention provides a method for coating a substrate selected from a fertilizer granule and seed, the method comprising applying the aqueous dispersion as defined in the first aspect of the invention onto the surface of the substrate. The substrate to be coated can be mixed using any conventional mixing equipment (e.g., a batch or continuous mixer) suitable for handling liquid and dry components. Furthermore, the mixing operation can be customized or performed near the application point to fully meet the varying nutrient requirements of different soil types. Coated fertilizer / seed can be prepared using various methods. Fertilizer granules can be coated by spray coating (e.g., top, bottom, or side spray coating), drum coating, pan coating, fluidized bed coating, continuous pouring coating, or any other method known to those skilled in the art. This can be done in a batch or continuous process. The granules can be coated with a single layer in a single application, or they can be coated with multiple layers of the same coating material, such as two, three, four, five, or more layers, or alternatively, with a different material.Thus, the granule or seed of the invention may include a single coating of the dispersion of the invention in direct contact with the surface of the granule / seed or, alternatively, in contact with an intermediate coating made of one or more additional ingredients (such as humic acid or excipients). After applying the liquid coating material to the core, the coated core is allowed to cool and / or dry so that the coating material solidifies, forming a solid layer surrounding the core. This procedure can be repeated one or more times to produce multiple layers of the same or different coating materials surrounding the core. Alternatively, the coating material can be dissolved or suspended in a solvent, applied to the granules, and the solvent evaporated. This procedure can be repeated one or more times to produce multiple layers of the same or different coating materials surrounding the core. Alternatively, the coating can be applied to a fertilizer or seed that already comprises a coating prepared with additional ingredients in powder form (such as humic acid (in addition to that already included in the dispersion), excipients, etc.). In one embodiment, optionally in combination with any of the embodiments provided above or below, the fertilizer or seed granule comprises a single coating of the dispersion of the invention. In another embodiment, optionally in combination with any of the embodiments CCQQI 0 / 7707 / 3 / Yl· provided above or below, the fertilizer granule or seed comprises a single layer of the dispersion of the invention and is obtained by continuously pouring the dispersion of the invention onto the surface of the fertilizer (either in a batch or in a continuous process). In this embodiment, the surface of the starting fertilizer (i.e., before coating with the dispersion) may already be coated with one or more additional ingredients in powder form. The resulting coated fertilizer granule or seed can be further coated with one or more layers comprising other ingredients or with the dispersion of the invention. This additional layer(s) can be applied in liquid or powder form. In one embodiment of the fifth aspect of the invention, the process comprises applying the liquid dispersion of the invention and then applying a powder of the additional ingredient(s) of interest to the resulting liquid coating. Alternatively, the process comprises applying the powder of the additional ingredient(s) and then coating the resulting powder coating with the dispersion of the invention. Depending on the coating technique ultimately selected, it may be necessary to adjust the viscosity of the aqueous dispersion of the invention before application. A person skilled in the art can routinely perform this task effortlessly. In one embodiment of the procedure of the fifth aspect of the invention, optionally in combination with any of the embodiments provided above or below, the viscosity adjustment is made by adding water; or, alternatively, by adding an aqueous solution comprising one or more agriculturally acceptable agents as defined above. In one embodiment of the fifth aspect of the present invention, optionally in combination with any of the embodiments provided above or below, the aqueous dispersion is applied to the substrate surface by dripping or spraying. In another embodiment of the fifth aspect of the present invention, optionally in combination with any of the embodiments provided above or below, the aqueous dispersion is applied to a portion of the substrate surface. Alternatively, in another embodiment of the fifth aspect of the present invention, optionally in combination with any of the embodiments provided above or below, the aqueous dispersion is applied to the entire substrate surface. There are no significant restrictions during the coating stage, other than the surface only being moistened to the point of agglomeration. If the procedure involves the subsequent addition of powder, it can be added until the wetted surface is completely saturated (no more powder will be absorbed). In another embodiment of the fifth aspect of the present invention, optionally in combination with any of the embodiments provided above or below, after application of the dispersion, one or both of the following steps are performed: (a) adding humic substance powder and / or one or more excipients selected from: a drying agent (such as a desiccant), an anti-caking agent, a lubricating agent, an anti-adherent agent, a slip agent, or a combination thereof, or one or more plant trace elements, or a combination thereof; and (b) drying the impregnated substrate. In another embodiment of the fifth aspect of the present invention, optionally in combination with any of the embodiments provided above or below, after application of the dispersion, the process further comprises CCQQI n / 77D7 / =l / Yl· (i) adding powdered humic substance, and (ii) adding one or more excipients. In another embodiment of the fifth aspect of the present invention, optionally in combination with any of the embodiments provided above or below, after the application of the dispersion, the process further comprises (i) adding powdered humic substance, and (ii) adding one or more drying agents. In another embodiment of the fifth aspect of the present invention, optionally in combination with any of the embodiments provided above or below, steps (i) and (ii), as defined herein, are performed one or more times. Non-limiting, illustrative examples of drying agents include diatomaceous earth, zeolites, anhydrous sodium sulfate, anhydrous calcium sulfate, biochar, activated carbon, and clay or mixtures thereof. Illustrative, non-limiting examples of excipients include stearic acid or its salts (such as sodium, calcium, magnesium and potassium stearate), sodium oleate, sodium benzoate, sodium chloride, sodium stearyl fumarate, magnesium lauryl sulfate, sodium stearyl fumarate, sucrose esters or fatty acids, zinc, polyethylene glycol, talc and mixtures thereof, and colloidal silicon dioxide. The drying stage can be carried out using any of the routine techniques well known to experts in the field. In a sixth aspect, the present invention provides a coated fertilizer obtainable by the procedure defined in the fifth aspect of the invention. In one embodiment of the fifth aspect of the invention, the coating has the active agent in a weight percentage between 0.005 and 3.5%, with respect to the total weight of the coated granule, preferably between 0.01 and 1.5%. In one embodiment of the fifth aspect of the invention, the coating has the active agent in a weight percentage between 0.05 and 3.5%, with respect to the total weight of the coated granule, preferably between 0.05 and 1.5%. Throughout the description and claims, the word "comprises" and its variants are not intended to exclude other technical features, additives, components, or steps. Furthermore, the word "comprises" includes the case "consists of." For those skilled in the art, other objects, advantages, and features of the invention will become apparent partly from the description and partly from the practice of the invention. The following examples are provided by way of illustration and are not intended to be limiting of the present invention. Moreover, the present invention covers all possible combinations of the particular and preferred embodiments indicated herein. Examples The selection process began with a hydrophilic and a hydrophobic fumed silica. When used as a powder, fumed silica requires very high shear rates to disperse in a solution. Fumed silica is readily dispersible in water, which facilitates its incorporation into a liquid. This option was chosen for selection purposes. Essay 1 In this test, the ability of a hydrophobic fumed silica dispersion (Aerodisp WR8520, EVONIK) to incorporate solid Humifirst® WG (Tradecorp) was tested. To this end, water and fumed silica were first mixed, and then the humic powder was added in portions until no more powder could be incorporated (i.e., a mass with a very high, almost solid viscosity was obtained). Table 1 below provides the achievable concentration of humic substances when fumed silica was used compared to the commercially available humic solution without fumed silica. Impact of pyrogenic silica on the achievable concentration of humic substances % of active substances in raw material Commercial Humifirst liquid (for comparative purposes) PCB078-1 (dispersion of the invention) Water, g Aerodisp WR8520, FS dispersion, g Humifirst l / l / G (powder), g 20% ​​of FS 65% of humic substances none 100 g 10 g 145 g % of humic powder 56% % of humic substances (HS) 15% 36.4% % of active pyrogenic silica (FS) (= 20% dispersion) - 0.8% FS:HS - 2.15:100 Coating appearance 30 μ wet film on flat substrate: - Glass - Leneta2A - Leneta N2A2 Translucent and dry to the touch To obtain an initial estimate of the coating quality, the dispersion was applied by stretching onto a flat substrate using a block coating apparatus that leaves a 30 µm wet film. To achieve a variety of surface characteristics, as is the case with fertilizer granules, the following flat substrates were selected: glass (float clair), Leneta 2A sheet, and Leneta N2A2 sheet. Each Leneta sheet was divided into a white and a black section. This resulted in five substrates with different surface characteristics in terms of surface tension and roughness. The objective at this stage was to verify film formation on various substrate surfaces and whether the liquid coating solution physically dried. The drying process was monitored by fingerprinting. The appearance of the dried film was visually observed, although aesthetics are not a critical parameter for a fertilizer coating. This solution was sprayed onto fertilizer granules (Urea 46 and CAN 27 were selected) in a small rotary mixer. Subsequently, mica drying powder was added to the wet granules, resulting in a physically dry fertilizer surface that appeared homogeneously coated with humic substances. After several weeks of storage under ambient conditions in a sealed bag, no caking was observed. In addition to achieving a solution capable of coating Urea 46 and CAN 27 fertilizers, an unexpected increase in the concentration of humic substances was observed with the hydrophobic pyrogenic silica dispersion, compared to the commercially available Humifirst® humic solution. In fact, the concentration of humic substances was found to be more than double the level in commercially available liquid Humifirst®, which contains 15% humic substances. This surprising increase in humic concentration is achieved by adding a small amount of pyrogenic silica (approximately 0.8% by weight). Essay 2 The test was performed using the hydrophobic fumed silica (FS) dispersion Aerodisp WR8520 and the hydrophobic fumed silica (FS) powder Aerosil R972: Table 2 CCQQI n / 77O7 / 3 / Yl· % of active substances in raw material Hydrophobic FS dispersion Aerodisp WR8520 Hydrophobic FS powder Aerosil R972 Water, g FS dispersion, g FS powder, g Humifirst WG (powder), g 20% ​​FS 100% FS 65% HS 100 10 74 100 2 68% Humic substances (HS) 26% 26% % of active pyrogenic silica (FS) 1.1% 1.2% FS:HS 4.2:100 4.6:100 Coating appearance 30 µm wet film on a translucent flat substrate, touch-dry film on - Glass - Leneta2A - Leneta N2A2 As previously stated, it was concluded that pyrogenic silica, regardless of whether it is originally in liquid or powder form, allows a significant increase in the concentration of humic substances compared to the commercially available Humifirst® liquid, which contains 15% humic substances. Essay 3 To verify the unexpected property of pyrogenic silica to increase the concentration of humic substances in a liquid solution, commonly recommended dispersing and wetting agents for pigment concentrates were used, as well as tap water, to carry out a comparison. For this purpose, humic powder (Humifirst WG (HF WG, Tradecorp)) was added in portions to the undiluted adjuvant. The organic humic powder was incorporated manually using a spatula. The experiment was stopped when the solution became too viscous and no longer flowed, or when the additional powder was no longer absorbed by the liquid. Table 3: Raw materials Product Family Product Name Active Ingredients, % by Weight Adjuvants Water Tap water Wetting Agent Additol VXW3208 50% Polymeric Non-Ionic Dispersant Pyrogenic Silica Dispersion Aerosil WR8520 20% FS Humic Powder High Humic Acid Level Humifirst WG 65% Humic Substances (53% Humic Acid and 12% Fulvic Acid) Table 4: Concentration of dust / humic substances achievable in the pure adjuvant Humifirst WG % of powder in the final solution % of humic substances in the final solution Adjuvant Aerodisp WR8520 44.0% 28.6% Additol 6208 32.0% 20.8% Water 24.2% 15.8% When Aerodisp WR8520 was used as an undiluted liquid compound, a 44% humic powder content was achieved. This outperformed the other liquid substances. For reasons of cost and efficiency, a 10 wt% aqueous dispersion of fumed silica (FS) was prepared. This diluted FS solution even allows for a humic formulation with 36.4% humic substances (see Table 2 above). However, the viscosity of the dispersion was found to be beyond the pumping capacity of most pumps available at fertilizer blending companies. For use as a coating on fertilizers, this high-viscosity solution needs to be diluted to a viscosity below 3600 cP. A pumpable solution was obtained with a 40% Humifirst WG powder level. To maintain the highest possible humic substance level, a diluted version of PCB078_1 (Table 1 above) was prepared using Humifirst liquid (Tradecorp). Table 5 % of active substances in raw material PCB 154-1 Water, g FS Dispersion (Aerodisp WR8520), g Humifirst® Liquid, g Humic Powder HF WG, g 20% ​​FS 15% humic substances 65% humic substances 36.4 3.6 20 40% humic substances 29% % of active pyrogenic silica 0.7% Final solution <3600 cP Coating appearance 30 µm wet film on translucent flat substrate, touch-dry film on - Glass - Leneta2A - Leneta N2A2 ccqq Ln / zznz / q / Yi Essay 4 The PCB151-4 dispersion (Table 5 above), containing 36% water, 3.6% pyrogenic silica dispersion, and 29% humic substances, was used to coat the CAN27+4 granular fertilizer (origin: Borealis). For this purpose, 400 g of fertilizer granules were added to a small rotary mixer. The mixer was set to rotation mode, and 2.5 g of the dispersion and 4 g of MU85F mica drying powder (Imerys) were added alternately and very rapidly. The liquid was added by spraying (using an aluminum water spray bottle), and the powder by pouring, while the mixer was running. After approximately 1 minute, a total of 10 g of humic dispersion and 16 g of drying powder were added. The 400 g of fertilizer granules, along with 10 g of liquid solution and 16 g of drying powder, were left to mix in the rotary mixer for one more minute.After a total procedure time of 2 minutes, the mixer was stopped and the resulting fertilizer was collected in an open aluminum box. It was visually concluded that the resulting coated fertilizer, enriched with 7.25 kg of humic substances per ton of fertilizer, exhibited a homogeneous coating. After 15 minutes, this coated fertilizer was stored in plastic bags at room temperature. After 21 days, dust release and caking were assessed. A powder equal to or less than 1 pm was determined, using a RETSCH ISO 3310 / 1 200x50 mm 1.00 mm stainless steel test sieve with certificate of conformity acc. EN 10204 2.1. It was found that there was a release of 0.8 g of powder, which means 0.18% of the total weight of the coated granule. The stored fertilizer sample showed no signs of caking. All granules exhibited free-flowing behavior (verified during the previous screening test). Therefore, it could be concluded that the coated granules of the invention, even carrying such a high load of humic substances, were extremely stable.

Claims

1. An aqueous dispersion characterized in that it comprises an active agent which is a humic substance and pyrogenic silica, wherein: - the weight % of the active agent with respect to the total weight of the dispersion is between 1 and 50%; and - the weight ratio between the active agent and the pyrogenic silica is between 1.5:1 and 75:1, particularly from 1.5:1 to 60:

1.

2. The aqueous dispersion according to claim 1, further characterized in that the pyrogenic silica is hydrophobic pyrogenic silica.

3. The aqueous dispersion according to any of claims 1 and 2, further characterized in that the humic substance comprises humic acid or, alternatively, fulvic acid or, alternatively, a combination of humic and fulvic acids.

4. The aqueous dispersion according to any of claims 1 to 3, further characterized in that the humic substance comprises humic acid in a weight percentage relative to the total weight of the humic substance in the range of 5 to 90%, and fulvic acid is in a weight percentage relative to the total weight of the humic substance in the range of 10 to 95%, the sum of both ingredients being 100% by weight.

5. The aqueous dispersion according to any of claims 1 to 4, further characterized in that the weight percent of the active agent with respect to the total weight of the dispersion is between 10 and 50% by weight, between 15 and 50% by weight, or between 20 and 50% by weight.

6. The aqueous dispersion according to claim 5, further characterized in that the weight % of the active agent with respect to the total weight of the dispersion is between 10 and 40% by weight or between 19 and 40% by weight.

7. The aqueous dispersion according to claim 1, further characterized in that the weight ratio between the active agent and the pyrogenic silica is between 2:1 and 55:1 or between 15:1 and 60:

1.

8. The aqueous dispersion according to any of the preceding claims, further characterized in that it additionally comprises one or more biostimulants.

9. A process for preparing an aqueous dispersion as defined in any of the preceding claims, characterized in that it comprises the step of mixing hydrophobic fumed silica, preferably liquid or powdered hydrophobic fumed silica, with the active agent.

10. Use of an aqueous dispersion as defined in any of claims 1 to 8 to coat a substrate, preferably a fertilizer granule or seed.

11. The use of an aqueous dispersion as defined in any of claims 1 to 8 as a plant growth stimulant.

12. A method for coating a substrate selected from a fertilizer granule and a seed, characterized in that the method comprises applying the aqueous dispersion as defined in any of claims 1 to 8 onto the surface of the substrate.

13. The procedure according to claim 12, further characterized in that the aqueous dispersion is applied to the substrate surface by dripping or spraying.

14. A coated fertilizer or seed granule characterized in that it is obtainable by the process in accordance with any of claims 12 and 13.

15. The coated fertilizer or seed granule according to claim 14, further characterized in that the coating has the active agent in a weight percentage between 0.01 and 3.5% with respect to the total weight of the coated granule.