Solid fertilizer

Abstract

The present invention provides a solid fertilizer that has a slow-release function of gradually eluting a water-soluble fertilizer component and a marine degradation function of rapidly degrading a residue left after elution of the fertilizer component even when the residue flows into the ocean. A solid fertilizer according to the present invention comprises a mixture of a water-soluble fertilizer component, an alkali-soluble bio-resin, and plant fibers.

Description

Solid fertilizer

[0001] The present invention relates to solid fertilizers. This application claims priority based on Japanese Patent Application No. 2024-151717 filed in Japan on September 3, 2024, the content of which is incorporated herein by reference.

[0002] Coated fertilizers are known as slow-release fertilizers. A coated fertilizer is obtained by coating the surface of particles of a water-soluble fertilizer component such as urea with a film through which water and water vapor can penetrate. By changing the thickness and properties of the film, the dissolution rate and dissolution period of the fertilizer component can be adjusted. As coated fertilizers, those using resins such as polyolefin resins, ethylene-vinyl acetate copolymers, and alkyd resins in the film are mainstream (Patent Documents 1, 2).

[0003] Japanese Patent Application Laid-Open No. 4-202079 Japanese Patent Publication No. 60-21952

[0004] However, the above-mentioned coated fertilizers have a problem that the film shell, which is the residue after the dissolution of the fertilizer component, remains in the environment for a long time. In particular, if the film shell flows out with water from fields such as paddy fields and flows into the ocean and remains there for a long time, it may have an adverse effect on marine organisms such as fish. Therefore, there is a need for a new slow-release fertilizer that can be used as an alternative to coated fertilizers and whose residue is rapidly decomposed even if it flows into the ocean.

[0005] An object of the present invention is to provide a solid fertilizer having a slow-release function in which a water-soluble fertilizer component is gradually eluted and a marine degradable function in which the residue after the elution of the fertilizer component is rapidly decomposed even if it flows into the ocean.

[0006] The present invention has the following embodiments: [1] A solid fertilizer comprising a mixture of a water-soluble fertilizer component, an alkali-soluble bio-resin, and plant fibers. [2] The solid fertilizer according to [1], wherein the bio-resin is poorly soluble in water or water-insoluble. [3] The solid fertilizer according to [1] or [2], wherein the bio-resin is soluble in alcohol. [4] The solid fertilizer according to any one of [1] to [3], wherein the bio-resin is at least one selected from the group consisting of rosin and shellac. [5] The solid fertilizer according to any one of [1] to [4], wherein the bio-resin content is 2 to 25% by mass relative to the total mass of the solid fertilizer. [6] The solid fertilizer according to any one of [1] to [5], wherein the plant fibers are pulp. [7] The solid fertilizer according to any one of [1] to [6], wherein the plant fibers content is 2 to 25% by mass relative to the total mass of the solid fertilizer. [8] The solid fertilizer according to any one of [1] to [7], wherein the fertilizer component contains urea. [9] A solid fertilizer according to any one of [1] to [8], wherein the content of the fertilizer component is 50 to 96% by mass relative to the total mass of the solid fertilizer.

[10] A solid fertilizer according to any one of [1] to [9], further comprising a specific gravity adjusting material.

[11] A solid fertilizer according to

[10] , wherein the specific gravity adjusting material has a higher specific gravity than the bio-resin.

[12] A solid fertilizer according to any one of [1] to

[11] , wherein the ratio of the bio-resin on the surface of the solid fertilizer and its vicinity is greater than the ratio of the bio-resin in the center of the solid fertilizer.

[13] A solid fertilizer according to any one of [1] to

[12] , which is granular.

[14] A solid fertilizer according to any one of [1] to

[13] , which is for paddy rice or field crops.

[0007] According to the present invention, it is possible to provide a solid fertilizer that has a slow-release function in which water-soluble fertilizer components are gradually released, and a marine-degradable function in which the residue after the release of fertilizer components is rapidly decomposed even if it flows into the ocean.

[0008] This graph shows the evaluation results of the solid fertilizers in Examples 1 and 2 and Comparative Example 1.

[0009] In this specification, the "~" indicating a numerical range means that the numbers before and after it are included as the lower and upper limits. The lower and upper limits of the numerical ranges disclosed herein can be arbitrarily combined to form new numerical ranges.

[0010] The solid fertilizer according to one embodiment of the present invention is a mixture of water-soluble fertilizer components, alkali-soluble bioresin, and plant fibers. The use of the solid fertilizer is not particularly limited and can be used for various plants in rice paddies, fields, orchards, landscaping, parks, ornamental plants, plant factories, etc. The following explanation will describe rice paddies, which are highly likely to flow into the ocean, as a representative example.

[0011] When the solid fertilizer of this embodiment is applied to fields such as paddy fields, moisture from the field comes into contact with the surface of the solid fertilizer and penetrates into the interior of the solid fertilizer via the plant fibers. The fertilizer components of the solid fertilizer dissolve due to the moisture that penetrates through the plant fibers and gradually leach out through the plant fibers. The leaching rate and duration of the fertilizer components can be adjusted by the ratio of fertilizer components to bioresin and plant fibers, the type of bioresin, the composition of the bioresin, etc. Furthermore, because the bioresin is alkali-soluble, even if the residue left after the fertilizer components have leached out of the solid fertilizer flows into the ocean, the bioresin dissolves in seawater. As the bioresin dissolves, the remaining plant fibers disperse. Even if marine organisms such as fish ingest the residue before the bioresin dissolves, the bioresin dissolves in their digestive system. Therefore, it is possible to prevent the residue from remaining in the ocean or in the bodies of marine organisms for a long time.

[0012] (Water-soluble fertilizer components) Any water-soluble fertilizer component is acceptable, and can be appropriately selected from known fertilizer components.

[0013] The fertilizer components may include nitrogenous fertilizers, phosphate fertilizers, potassium fertilizers, and trace elements such as calcium, magnesium, sulfur, iron, manganese, molybdenum, copper, zinc, and boron. Specifically, examples of nitrogenous fertilizers include ammonium sulfate, urea, ammonium nitrate, isobutyraldehyde condensed urea, and acetaldehyde condensed urea. Examples of phosphate fertilizers include superphosphate, fused phosphate fertilizer, and calcined phosphate fertilizer. Examples of potassium fertilizers include potassium sulfate, potassium chloride, and potassium silicate fertilizer. There are no particular limitations on the form of these fertilizers. Furthermore, high-grade compound fertilizers or blended fertilizers with a total component content of 30% by mass or more of the three main elements are also acceptable, as well as organic fertilizers. Fertilizers with added nitrification inhibitors or pesticides are also acceptable. One type of fertilizer component may be used alone, or two or more types may be used in combination. In one embodiment, the fertilizer component may include urea.

[0014] (Alkali-soluble bio-resins) Bio-resins refer to natural resins, resins derived from natural components, and their derivatives. Examples include rosin, shellac, casein, animal glue, collagen, polylactic acid, polyhydroxyalkanoic acid, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polybutylene succinate adipate (PBSA), polybutylene succinate (bio-PBS), polybutylene adipate terephthalate (bio-PBST), and their derivatives. Among these, alkali-soluble resins can be used. In particular, alkali-soluble resins that dissolve in seawater with a pH of 8.2 to 8.5 are preferred. Examples include rosin, shellac, casein, animal glue, collagen, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polybutylene succinate adipate (PBSA), and their derivatives.

[0015] It is preferable that the bio-resin is poorly soluble in water or water-insoluble. When the bio-resin near the surface of solid fertilizer dissolves in paddy fields, etc., the exposed fertilizer components leach out. If the bio-resin is poorly soluble in water or water-insoluble, the bio-resin will hardly dissolve or not dissolve at all. Moisture gradually penetrates into the solid fertilizer through the gaps in the composite portion of plant fibers and bio-resin, which are essential components of solid fertilizer. As the fertilizer components inside the solid fertilizer dissolve due to the penetrating moisture, the fertilizer components leach out through the gaps in the composite portion of plant fibers and bio-resin. Because the bio-resin is poorly soluble in water or water-insoluble, the bio-resin and plant fibers maintain their structure and do not immediately disintegrate, allowing the fertilizer components to leach out gradually. As a result, the leaching period of fertilizer components is extended, resulting in a solid fertilizer with excellent slow-release properties. On the other hand, as the leaching of fertilizer components progresses, the solid fertilizer will lose its structural shape and disintegrate.

[0016] Examples of alkali-soluble and poorly water-soluble or water-insoluble bioresins include rosin, shellac, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polybutylene succinate adipate (PBSA), and derivatives thereof. Rosin, shellac, and their derivatives are preferred materials, and it is more preferable that at least one is selected from the group consisting of rosin and shellac.

[0017] The bio-resin may be soluble in alcohol. When producing solid fertilizer by dissolving the bio-resin in alcohol, examples of alcohol include ethanol, isopropyl alcohol, methanol, etc., and can be appropriately selected depending on the fertilizer components to be used. For example, urea does not dissolve in isopropyl alcohol, so if the fertilizer contains urea, it is preferable that the bio-resin is soluble in isopropyl alcohol.

[0018] From this viewpoint, at least one bio-resin selected from the group consisting of rosin and shellac is preferred, and rosin is more preferred from the viewpoint of raw material cost. Rosin is a compound derived from pine. The pine is not particularly limited, and examples include Merkus pine, slash pine, and horsehair pine. These may be used individually or in combination of two or more. The rosin is not particularly limited, and examples include known unmodified rosin and its derivatives. Examples of unmodified rosin include crude rosin and purified rosin. Examples of crude rosin include gum rosin, tall rosin, and wood rosin. Examples of purified rosin include purified crude rosin. Examples of rosin derivatives include hydrogenated rosin, disproportionated rosin, and polymerized rosin. These may be used individually or in combination of two or more. Alkali solubility, etc., may be adjusted by adjusting the molecular weight or modifying with substituents. The bio-resin may be used individually or in combination of two or more.

[0019] (Plant Fibers) Plant fibers regulate the amount of fertilizer components released. They also contribute to improving the strength of solid fertilizers as aggregates.

[0020] Examples of plant fibers include woody fibers, seed hair fibers, bast fibers, leaf vein fibers, and fruit fibers from plant bodies. Examples of plant bodies include conifers, broad-leaved trees, bamboo, kenaf, cotton, hemp, reeds, and straw. As raw materials for plant fibers, for example, plant trunks, stems, branches, leaves, and roots can be used. Waste materials such as bagasse, rice husks, tea leaves, coffee grounds, sawdust, wood shavings, and herbivore feces may also be used. In addition, recycled paper, cardboard, corrugated cardboard, shredded paper, or recycled thread scraps, yarn, woven fabrics, nonwoven fabrics, and gypsum board may be used. The raw materials for plant fibers are not particularly limited as long as they are fibrous in the state of solid fertilizer, and may be processed into any size and shape by cutting, crushing, grinding, or pulverizing. For example, they may be processed into pulp, or into cellulose powder or cellulose nanofibers. Plant fibers may be used individually or in combination of two or more types. From the standpoint of stable production, cost, versatility, and sustainability, pulp is preferred. The following explanation will use pulp as a representative example, but is not limited to pulp.

[0021] Examples of pulp include chemical pulp, mechanical pulp, recycled paper pulp, and non-wood pulp.

[0022] Examples of chemical pulps include coniferous chemical pulp and hardwood chemical pulp. Examples of coniferous chemical pulps include unbleached coniferous kraft pulp (NUKP), bleached coniferous kraft pulp (NBKP), semi-bleached coniferous kraft pulp (NSBKP), and sulfite coniferous pulp (NSP). Examples of hardwood chemical pulps include unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), semi-bleached hardwood kraft pulp (LSBKP), and sulfite hardwood pulp (LSP).

[0023] Examples of mechanical pulps include stone ground pulp (SGP), pressure stone ground pulp (PGW), refiner ground pulp (RGP), thermo ground pulp (TGP), chemiground pulp (CGP), wood pulp (GP), and thermomechanical pulp (TMP). Examples of recycled paper pulp include disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, and disintegrated, deinked and bleached recycled paper pulp. Examples of recycled paper used as raw material for recycled paper pulp include brown recycled paper, kraft envelope recycled paper, magazine recycled paper, newspaper recycled paper, flyer recycled paper, office recycled paper, corrugated cardboard recycled paper, white recycled paper, Kent recycled paper, imitation recycled paper, and land deed recycled paper. Furthermore, recycled paper derived from household paper products such as tissue paper and paper hand towels, recycled paper derived from printed coated paper such as art paper, coated paper, and cast coated paper, and recycled paper derived from waste gypsum board can also be used. Waste paper derived from coated printing paper and waste gypsum board contains a large amount of calcium, and can be used to make solid fertilizer containing calcium. Examples of non-wood pulp include various types of pulp, such as pulp chemically or mechanically produced from non-wood fibers such as kenaf, cotton, hemp, reeds, and straw.

[0024] Pulp may be used alone or in combination of two or more types. Among the above, recycled paper pulp is preferred from an environmental perspective.

[0025] The pulp is preferably fluffy pulp. Fluffing is the process of mechanically breaking down the raw pulp into fibers. Fluffing the pulp tends to improve its mixability when manufacturing solid fertilizers. There are no particular restrictions on the equipment used for fluffing; for example, known defibrillators used in the manufacture of absorbent materials such as disposable diapers, and defibrillators that utilize friction or shear force as mechanical treatment can be used. Specifically, a defibrillator having a toothed cylinder can be suitably used (see Japanese Patent No. 2521577). The shape of the raw pulp subjected to mechanical treatment is not particularly limited, but pulp in sheet form (so-called pulp sheets) or pulp that has been filtered into sheets and then wound into rolls is preferred because it is easier to handle.

[0026] (Specific Gravity Adjusting Material) The solid fertilizer of this embodiment may further contain a specific gravity adjusting material as needed. From the viewpoint of suppressing the runoff of the solid fertilizer with water from paddy fields, etc., during the leaching period of fertilizer components, it is preferable that the specific gravity adjusting material increases the specific gravity of the solid fertilizer compared to when the solid fertilizer does not contain a specific gravity adjusting material.

[0027] Examples of gravity-adjusting materials used to increase the specific gravity of solid fertilizers include materials with a higher specific gravity than bio-resin. The specific gravity of bio-resin is generally around 0.8 to 1. By including a gravity-adjusting material with a higher specific gravity than this, the solid fertilizer becomes less likely to float in water, thus reducing the likelihood of it flowing out of rice paddies and other areas. For example, the specific gravity of a gravity-adjusting material used to increase the specific gravity of solid fertilizer is 3.5 to 6.

[0028] Examples of specific gravity adjusting materials include various powders such as iron oxide, graphite, and sand. The specific gravity adjusting material may also be a fertilizer component (excluding water-soluble fertilizer components). For example, iron oxide, because it contains iron, also functions as a fertilizer component.

[0029] As a specific gravity adjusting material, at least one powder selected from the group consisting of iron oxide, graphite, and sand is preferred. Including such a powder as a specific gravity adjusting material has advantages such as increasing the specific gravity of the solid fertilizer, making the raw materials easier to handle during the manufacture of the solid fertilizer, and preventing the solid fertilizer from sticking together when stored in a high-temperature environment. In particular, including iron oxide is effective in preventing root rot in rice plants. The specific gravity adjusting material may be used alone or in combination of two or more types.

[0030] (Other Components) The solid fertilizer of this embodiment may further contain other components besides the fertilizer components, bio-resin, plant fibers, and specific gravity adjusting materials mentioned above, as needed. These other components may be components known as fertilizer components and can be appropriately selected depending on the intended use of the solid fertilizer. Examples of other components include additives such as chemicals, insecticides, and preservatives. These additives are preferably made from natural materials. The other components may be used individually or in combination of two or more. From an environmental standpoint, it is preferable that the solid fertilizer of this embodiment does not contain resins other than alkali-soluble bio-resin.

[0031] The amount of fertilizer components in the solid fertilizer may be, for example, 50 to 96% by mass, 70 to 95% by mass, or 80 to 90% by mass, relative to the total mass of the solid fertilizer.

[0032] The bio-resin content in the solid fertilizer may be 2 to 25% by mass, 2 to 20% by mass, or 5 to 15% by mass, relative to the total mass of the solid fertilizer. When the bio-resin content is above the lower limit, the strength of the solid fertilizer tends to be stronger and the amount of fertilizer components leached out tends to be lower. When the bio-resin content is below the upper limit, a larger amount of fertilizer components can be retained.

[0033] The plant fiber content in solid fertilizer may be 2 to 25% by mass, 2 to 15% by mass, or 5 to 15% by mass, relative to the total mass of the solid fertilizer. When the plant fiber content is above the lower limit, the strength of the solid fertilizer tends to be greater, and the amount of fertilizer components released tends to be greater. When the plant fiber content is below the upper limit, a larger amount of fertilizer components can be retained.

[0034] If the solid fertilizer contains a specific gravity adjusting material, the amount of the specific gravity adjusting material in the solid fertilizer may be, for example, 0.1 to 1.5% by mass or 0.2 to 1% by mass, relative to the total mass of the solid fertilizer.

[0035] The specific gravity of the solid fertilizer is preferably 1 to 1.5, and more preferably 1.05 to 1.5. If the specific gravity of the solid fertilizer is above the lower limit, it is less likely to run off from fields such as paddy fields during the leaching period of fertilizer components. On the other hand, if the specific gravity of the solid fertilizer is below the upper limit, it is easier to prevent the residue after the leaching of fertilizer components from flowing into the ocean. Therefore, the usefulness of the solid fertilizer of this embodiment is high when the specific gravity of the solid fertilizer is below the upper limit.

[0036] The shape of the solid fertilizer is not particularly limited and may be the same as that of known solid fertilizers. The solid fertilizer may typically be granular. If the solid fertilizer is granular, the average particle size of the solid fertilizer may be the same as that of known granular fertilizers, for example, 1.5 to 5 mm or 2 to 4 mm.

[0037] The distribution of fertilizer components, bio-resin, and plant fibers within the solid fertilizer may be uniform or non-uniform. From the viewpoint of ensuring a sufficient content of fertilizer components while suppressing the leaching of fertilizer components, it is preferable that the ratio of bio-resin on and near the surface of the solid fertilizer (for example, within a range of 1.0 mm from the surface of the solid fertilizer) is relatively higher than the ratio of bio-resin in the center of the solid fertilizer (for example, in a region 2.0 mm or more away from the surface of the solid fertilizer). Furthermore, it is preferable that the ratio of fertilizer components in the center of the solid fertilizer is relatively higher than the ratio of fertilizer components on and near the surface of the solid fertilizer. Here, the ratios of fertilizer components and bio-resin are the ratios of the solid content mass of fertilizer components and bio-resin to the solid content mass of the solid fertilizer.

[0038] (Methods for Manufacturing Solid Fertilizers) Examples of methods for manufacturing solid fertilizers include the following methods (1), (2), and (3). However, the methods for manufacturing solid fertilizers are not limited to these and can be modified as appropriate.

[0039] <Manufacturing Method (1)> A method in which a raw material containing fertilizer components and plant fibers is granulated by adding a binder such as water or alcohol as appropriate, and the resulting granules are sprayed with a solution of bio-resin dissolved in a solvent and dried.

[0040] The raw materials may include a specific gravity adjusting material and other components. The granulation method is not particularly limited, and known granulation methods such as the fluidized bed granulation method and the rolling granulation method can be adopted. When the bioresin is soluble in alcohol, the solvent for dissolving the bioresin can be selected from, for example, ethanol, isopropyl alcohol, and methanol. A solvent that does not dissolve the fertilizer components when the bioresin is dissolved and sprayed onto the granulated product is preferred. The drying conditions only need to be able to remove the solvent, and it is preferably dried under conditions below the flash point according to the solvent used, and the temperature conditions can be set as appropriate.

[0041] The solution sprayed onto the granulated product penetrates from the surface of the granulated product to the inside. The solid fertilizer thus obtained is considered to have a higher ratio of bioresin on the surface and in its vicinity than the ratio of bioresin in the central part, and a higher ratio of fertilizer components in the central part than the ratio of fertilizer components on the surface and in its vicinity. By adjusting the ratio of the bioresin on the surface and in its vicinity, the slow-release function of the fertilizer components can be adjusted.

[0042] <Manufacturing Method (2)> A method of granulating a raw material containing a fertilizer component, plant fiber, and bioresin by appropriately adding a binder such as water or alcohol.

[0043] If a method of spraying and drying a solution of the bioresin dissolved in a solvent onto the obtained granulated product is adopted, the manufacturing method (2) can be carried out in the same manner as the manufacturing method (1) except that a part of the bioresin is contained in the raw material. Since the solution sprayed onto the granulated product penetrates from the surface of the granulated product to the inside, the solid fertilizer obtained is considered to have a higher ratio of bioresin on the surface and in its vicinity than the ratio of bioresin in the central part, and a higher ratio of fertilizer components in the central part than the ratio of fertilizer components on the surface and in its vicinity. By spraying a solution of the bioresin dissolved in a solvent, the slow-release function of the fertilizer components can be adjusted.

[0044] <Manufacturing Method (3)> A method of mixing a raw material containing a fertilizer component, plant fiber, bioresin, and a solvent for dissolving the bioresin, kneading the obtained mixture under heating, and pelletizing the obtained kneaded product.

[0045] Kneading can be carried out using a known kneader such as a kneader or a kneading extruder. The heating temperature during kneading is preferably set to be below the flash point temperature of the solvent or solvent used. After being discharged from the kneader, the kneaded product is pelletized using a pelletizer or the like. The pelletized kneaded product may be used as a solid fertilizer as it is, or may be granulated using a granulator to obtain a solid fertilizer. In the case of this production method, during granulation, the solvent that had dissolved the bioresin evaporates from the surface. At this time, if a highly volatile solvent is used, the bioresin moves rapidly from the inside to the surface together with the solvent, so it is considered that in the obtained solid fertilizer, the ratio of the bioresin on the surface and in its vicinity is higher than the ratio of the bioresin in the central part, and the ratio of the fertilizer component in the central part is higher than the ratio of the fertilizer component on the surface and in its vicinity. By selecting the solvent to be used, the slow-release function of the fertilizer component can be adjusted.

[0046] (Use) The solid fertilizer of the present embodiment is used for cultivating plants. In cultivating plants, the solid fertilizer of the present embodiment can be used in the same manner as conventional coated fertilizers. Before applying the solid fertilizer of the present embodiment to the field, the solid fertilizer of the present embodiment and other fertilizers may be mixed in advance to form a compound fertilizer.

[0047] The plants cultivated using the solid fertilizer of the present embodiment are not particularly limited, but rice is preferable in terms of the relatively high possibility that the residue after elution of the fertilizer component flows into the ocean and the high usefulness of applying the present invention.

[0048] Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited by the following examples.

[0049] <Comparative Example 1> Commercially available powdered urea ("Kozakai M" manufactured by Sakai Pharmaceutical Co., Ltd., Japanese Pharmacopoeia urea) was used as the solid fertilizer of Comparative Example 1.

[0050] <Comparative Example 2> Commercially available coated fertilizer ("LP Coat S100" manufactured by Jaycam Agri Co., Ltd., urea-based fertilizer coated with a polyolefin resin) was used as the solid fertilizer of Comparative Example 2.

[0051] <Example 1> A solid fertilizer with the composition shown in Table 1 was manufactured using the following procedure. A pulp sheet (pulp type: recycled newspaper pulp) was filled with a fluffer to obtain fluff pulp. The obtained fluff pulp was mixed with a solution of powdered urea (Kozakai-M, manufactured by Kozakai Pharmaceutical Co., Ltd., Japanese Pharmacopoeia urea) and rosin from Fujifilm Wako Pure Chemical Industries, Ltd., with a solid content concentration of 60% using IPA (isopropyl alcohol). The mixture was then put into a pellet manufacturing apparatus (Imoto Seisakusho Co., Ltd., IMC-9415) and kneaded at 60°C using a single-screw kneader attached to the preceding stage. Subsequently, the mixture was granulated to a diameter of 4-5 mm using the attached pellet manufacturing machine to obtain solid fertilizer. The average particle size of the obtained solid fertilizer was 4.5 mm and the specific gravity was 1.0.

[0052] <Example 2> A solid fertilizer with the composition shown in Table 1 was obtained in the same manner as in Example 1, except that powdered iron oxide was mixed with a solution of fluff pulp, powdered urea, and rosin. The average particle size of the obtained solid fertilizer was 4.5 mm and the specific gravity was 1.15.

[0053]

[0054] <Evaluation> "Evaluation 1: Evaluation of the slow-release properties of fertilizer" The following evaluations were performed on the solid fertilizers of Comparative Example 1 and Examples 1-2. 2.0 g of solid fertilizer (in urea equivalent) was added to 20 cc of water with a pH of 7.0, and left to stand for 30 days at 23°C. The pH of the water was measured during this time. The pH rises as urea dissolves. Table 2 shows the pH at 1 hour, 1 day, 2 days, 3 days, 5 days, 10 days, 15 days, 20 days, 25 days, and 30 days after adding the solid fertilizer. Figure 1 shows a graph with elapsed time on the horizontal axis and pH on the vertical axis.

[0055]

[0056] "Evaluation 2: Evaluation of Marine Degradability" The following evaluations were performed on the solid fertilizers of Comparative Example 2 and Examples 1-2. 2.0 g of solid fertilizer (in urea equivalent) was added to 20 cc of water with a pH of 7.0 and left to stand for 30 days at 23°C. Red Sea Salt (manufactured by MMC Planning Co., Ltd. Red Sea Division, artificial seawater base) was added to the tank to a salinity of 30 ppt and stirred to obtain artificial seawater with a pH of 8.4. Ten granules of solid fertilizer that were beginning to disintegrate after being left to stand in water for 30 days were placed in a 30-mesh net and their mass was measured. These were then immersed in the artificial seawater and left to stand for 70 days. After that, the mass of the dissolved residue was measured. From the measurement results, the mass loss rate (approximate weight loss after 70 days) was calculated using the formula: ["Dry mass of dissolved residue before immersion in artificial seawater - Dry mass of dissolved residue after immersion in artificial seawater" / Dry mass of dissolved residue before immersion in artificial seawater × 100], and the marine degradability was evaluated according to the following criteria. The results are shown in Table 3. A: Mass loss rate of 80% or more. B: Mass loss rate of 10% by mass or more and less than 80% by mass. C: Mass loss rate of less than 10%.

[0057]

[0058] From the above results, it was confirmed that the solid fertilizers of Examples 1 and 2 have a slow-release function in which water-soluble fertilizer components are gradually released, and a marine-degradable function in which the residue after the release of fertilizer components is rapidly decomposed even if it flows into the ocean.

[0059] The solid fertilizer of the present invention has a slow-release function in which water-soluble fertilizer components are gradually released, and a marine-degradable function in which the residue after the release of fertilizer components is rapidly decomposed even if it flows into the ocean.

Claims

1. A solid fertilizer containing a mixture of water-soluble fertilizer components, alkali-soluble bio-resin, and plant fibers.

2. The solid fertilizer according to claim 1, wherein the bio-resin is poorly soluble in water or water-insoluble.

3. The solid fertilizer according to claim 1 or 2, wherein the bio-resin is soluble in alcohol.

4. The solid fertilizer according to claim 1 or 2, wherein the bio-resin is at least one selected from the group consisting of rosin and shellac.

5. The solid fertilizer according to claim 1 or 2, wherein the bio-resin content is 2 to 25% by mass relative to the total mass of the solid fertilizer.

6. The solid fertilizer according to claim 1 or 2, wherein the plant fiber is pulp.

7. The solid fertilizer according to claim 1 or 2, wherein the content of the plant fiber is 2 to 25% by mass relative to the total mass of the solid fertilizer.

8. The solid fertilizer according to claim 1 or 2, wherein the fertilizer component includes urea.

9. The solid fertilizer according to claim 1 or 2, wherein the content of the fertilizer component is 50 to 96% by mass relative to the total mass of the solid fertilizer.

10. The solid fertilizer according to claim 1 or 2, further comprising a specific gravity adjusting material.

11. The solid fertilizer according to claim 10, wherein the specific gravity adjusting material has a higher specific gravity than the bio-resin.

12. The solid fertilizer according to claim 1 or 2, wherein the ratio of the bio-resin on the surface of the solid fertilizer and its vicinity is greater than the ratio of the bio-resin in the center of the solid fertilizer.

13. A solid fertilizer according to claim 1 or 2, which is granular.

14. The solid fertilizer according to claim 1 or 2, which is for use in paddy rice or field crops.

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