JP7652133B2 - Seed coating method and coated seeds - Google Patents

Description

The present invention relates to a seed coating method for coating seeds with a seed coating agent containing iron-based powder, and to coated seeds coated with the seed coating agent.

With the aging of agricultural workers and the globalization of agricultural product distribution, labor-saving in farm work and reduction in agricultural production costs have become issues that need to be resolved. To address these issues, for example, in rice cultivation, direct seeding methods in which seeds are sown directly in fields are becoming more widespread, with the aim of eliminating the labor of raising seedlings and transplanting. Among these methods, the method of using seeds coated with iron powder to increase the seed's specific gravity has attracted attention for its benefits of preventing seeds from floating or being washed away in paddy fields and preventing bird damage.

As a method for coating seeds with iron powder, for example, Patent Document 1 discloses a method in which the coated rice seeds are thinly spread, the oxidation reaction of the iron powder is continued for 12 hours at a room temperature of 25°C while humidified air is blown into the seeds, and then the seeds are dried at 40°C.

Patent Document 2 also discloses a method for producing iron-powder-coated rice seeds that are single-grained by applying silica gel to rice seeds with an iron-powder coating layer to suppress aggregation of the coated seeds. In Patent Document 2, the oxidation reaction of the iron powder is promoted by passing humidified air at a relative humidity of 80% or more and a temperature of 10 to 30°C through the seeds.

Furthermore, Patent Document 3 discloses a method of coating seeds by spraying a spray solution with a pH of 3.0 or more and 6.5 or less, and oxidizing iron-based powder at an ambient temperature of 31°C or more and 45°C or less. In Patent Document 3, to prevent heat generation, the seeds are thinly spread on a tray or the like to promote the oxidation reaction, and the oxidation process can be completed in about two hours.

JP 2005-192458 A JP 2014-221009 A JP 2019-213465 A

In Patent Document 1, the oxidation time requires about 12 to 24 hours, and there is a problem that the disintegration rate increases if the oxidation is inappropriate.

In addition, Patent Document 2 states that the amount of water sprayed to oxidize the iron powder should be appropriate, but it takes a long time, about 8 hours, to oxidize the iron powder, and there is a problem that oxidation does not progress sufficiently in a short time, causing the coating to peel off.

In Patent Document 3, the pH of the spray solution and the ambient temperature must be strictly controlled to prevent the seeds from dying, and although rusting progresses in a relatively short time of about two hours, the seeds are prone to coagulation and adhesion due to a rapid oxidation reaction, making sowing difficult. In other words, in exchange for the shorter sowing time, there is a problem with single-grain sowing.
Even if the seed is well-divided into single kernels, if the seed coating layer is thick, the seed temperature rises during drying. To counter this, thinning the seed layer thickness to dissipate heat is an effective way to suppress the seed temperature, but this requires a large working space, which is an issue.

The present invention has been made to solve these problems, and aims to provide a seed coating method that can suppress an increase in seed temperature during drying, and coated seeds that are coated with a seed coating agent using this seed coating method.

The inventors conducted extensive research to solve the above problems and came to the following findings.
Various coating methods were implemented and investigated to suppress the rise in seed temperature during drying of seeds coated with a seed coating agent (hereinafter simply referred to as "coated seeds"). As a result, it was found that the rise in temperature was effectively suppressed by spraying an aqueous solution of polyvinyl alcohol resin during the oxidation reaction in which water and a gas with an oxygen concentration of 15 to 30% are supplied to the flowing seeds during and/or after coating. It was also found that the dust emitted from the seeds was effectively reduced.

The present invention is based on the above findings and has the following configuration.
(1) The seed coating method of the present invention is a seed coating method in which a seed coating agent containing an iron-based powder is attached to a seed, and while flowing, a gas having an oxygen concentration of 15 to 30% is supplied to oxidize the iron-based powder and form a coating layer on the surface of the seed, and is characterized in that an aqueous solution of a polyvinyl alcohol-based resin is supplied in the step of attaching the seed coating agent and/or the step of forming the coating layer.

(2) The seed coating method according to the present invention is characterized in that a seed coating agent containing an iron-based powder and a polyvinyl alcohol-based resin powder is attached to the seeds while being sprayed with water, and gas having an oxygen concentration of 15 to 30% is supplied while being fluidized to oxidize the iron-based powder and form a coating layer on the surface of the seeds.

(3) Furthermore, in the above (1) or (2), the seed coating agent is characterized by containing a pro-oxidant.

(4) The coated seed according to the present invention is characterized in that a coating layer is formed on the seed surface by the seed coating method described in (1) or (2) above.

(5) The coated seed according to the present invention is characterized in that a coating layer is formed on the seed surface by the seed coating method described in (3) above.

In the present invention, in a seed coating method in which seeds are fluidized using a seed coating agent containing iron-based powder while gas with an oxygen concentration of 15 to 30% is supplied, an aqueous solution of polyvinyl alcohol-based resin is supplied to suppress an increase in seed temperature during drying, thereby reducing the area required for drying work and avoiding a decrease in seed germination rate due to heat generation.

The seed coating method according to the embodiment of the present invention involves coating the surface of a seed with a seed coating agent containing iron-based powder. Hereinafter, the seeds to be coated with the seed coating agent in the present invention and the seed coating agent will be described. Hereinafter, mass% will be abbreviated as %.

<Seeds>
The seeds of rice are preferably used as the target of the present invention. There is no particular restriction on the variety of rice, and any of japonica, indica, and javanica rice can be used. Rice is often cultivated in paddy fields in hot and humid regions, so the effects of the present invention can be achieved.

<Seed coating agent>
The seed coating agent used in this embodiment contains an iron-based powder, and the iron-based powder may be iron powder, iron oxide powder, or a mixture of iron powder and iron oxide powder.
The seed coating agent may further contain a binder (pro-oxidant), a pro-oxidant, a separating agent, water, a polyvinyl alcohol-based resin and/or an aqueous solution thereof, and a third component.

<Iron powder>
As the iron powder, powder of pure iron or alloy iron can be used.
Examples of methods for producing iron powder include a reduction method in which mill scale or iron ore is reduced, and an atomization method in which water or gas is injected into molten steel at high speed.

<Iron oxide powder>
As the iron oxide powder, iron oxide or partial iron oxide powder can be used. Examples of iron oxide include magnetite (Fe3O4), hematite (Fe2O3), wustite (FeO), and amorphous. The ratio of each is not particularly limited as long as it is within the range of the present invention. However, from the viewpoint of economy, mill scale is preferably used.

The amount of the iron-based powder used is not particularly limited, but is preferably 5% or more and 800% or less, more preferably 10% or more and 500% or less, based on the amount of the seeds (dry rice grains).
Although the particle size of the iron-based powder is not particularly specified, it is preferable for uniform coating that the iron-based powder having a particle size of 150 μm or less accounts for 80% or more of the total iron-based powder mass. The particle size distribution of the iron-based powder can be evaluated by sieving using the method specified in JIS Z2510-2004.
The iron-based powder may be any of the above iron powders, iron oxide powders, and mixtures of iron powder and iron oxide powder, mixed with other metal powders. However, from the viewpoint of rust formation, the iron-based powder preferably contains 20% or more of metallic iron, and more preferably 40% or more.

<Binding agent>
In the present invention, the binder is an oxidation promoter, and is composed of sulfates and/or chlorides. The sulfates are calcium sulfate, potassium sulfate, magnesium sulfate, and hydrates thereof. The chlorides are sodium chloride, potassium chloride, calcium chloride, magnesium chloride, and hydrates thereof. In particular, calcined gypsum (calcium sulfate 1/2 hydrate) and gypsum (calcium sulfate dihydrate) are preferred. The calcined gypsum and gypsum may be a mixture or a mixture. An anhydride may also be used for each binder.
The mass ratio of the binder to the iron-based powder is not particularly determined, but in order to facilitate the progression of rust, it is preferably 0.1% to 33%.

The average particle size of the binder is not particularly specified, but 1 to 150 μm is preferable. If the average particle size of the binder is less than 1 μm, a large number of agglomerated particles will be generated during the coating process, significantly reducing workability. On the other hand, if the average particle size of the binder exceeds 150 μm, the adhesion to the iron-based powder will decrease, and the strength of the coating layer will tend to decrease.

<Pro-oxidant>
As the oxidation promoter, it is preferable to use a carboxylic acid in addition to the above-mentioned binder. The form of the carboxylic acid is not particularly limited as long as it has two or more carboxy groups in one molecule, and carboxylic acids and/or their salts, as well as their anhydrides, hydrates, and isomers, can be used. Two or more kinds of carboxylic acids can also be used in combination.
Examples of the carboxylic acid include citric acid, tartaric acid, malic acid, succinic acid, and ethylenediaminetetraacetic acid.

Examples of carboxylates include trisodium citrate, disodium hydrogen citrate, tripotassium citrate, potassium dihydrogen citrate, diammonium hydrogen citrate, triammonium citrate, sodium tartrate, sodium hydrogen malate, sodium malate, disodium succinate, and mono-, di-, and tetrasodium salts of ethylenediaminetetraacetic acid.

Examples of the metal carboxylate include iron citrate, calcium citrate, ammonium iron citrate, and ammonium iron ethylenediaminetetraacetate. However, metal salts other than iron can also be used and are within the scope of the present invention. In addition, these carboxylic acids, carboxylates, and metal carboxylates include anhydrides and hydrates.
The coating layer is preferably smoothed when a carboxylic acid having two or more carboxy groups in one molecule is contained or added. The reason for this is thought to be that the acid dissolves iron powder and generates and stabilizes a large amount of divalent iron by its chelating effect, which spreads over the entire seed surface and then converts to trivalent iron and fixes it. The occurrence of the above-mentioned reaction can also be inferred from the fact that, when the seed coating agent of this embodiment is used, the coated seeds first take on a green to black color tone, and then change to a red to brown color tone.

The amount of the organic acid in the seed coating agent is 0.01% by mass or more and 6% by mass or less based on the iron-based powder. If the amount is less than 0.01% by mass, the effect of the present invention is reduced, and if the amount is more than 6% by mass, the chelating effect makes it difficult for rust to progress, and the coating layer becomes weak due to the increased amount of components other than iron.
The amount of carboxylic acid is calculated in the form of a carboxy group (COOH), excluding water of hydration and cationic components.
It is preferable to use a binder and a carboxylic acid as an oxidation promoter in combination, but the use of either one alone will facilitate the oxidation of the iron-based powder and is within the scope of the present invention.

<Polyvinyl alcohol resin>
As the polyvinyl alcohol-based resin used in the seed coating agent according to the present embodiment, polyvinyl alcohol and/or its copolymer, or a mixture thereof is preferably used.
The degree of saponification of the polyvinyl alcohol resin is not particularly limited, but the preferred range is 50 to 100 mol%. The lower the degree of saponification, the easier it is to dissolve in water, and the work required for dissolution can be simplified. The degree of saponification of the polyvinyl alcohol resin can be measured in accordance with JIS K6726-1994.

On the other hand, there is no particular restriction on the degree of polymerization of the polyvinyl alcohol resin, but it is preferably 2000 or less, more preferably 950 or less, and even more preferably 800 or less. A lower degree of polymerization leads to lower viscosity, which improves workability. Reducing the aqueous solution concentration to lower the viscosity is also an effective method. The degree of polymerization of polyvinyl alcohol can be measured in accordance with JIS K6726-1994.

In the case of copolymers, ethylene, propylene, butylene, etc. are preferred as hydrophobic groups, with ethylene being particularly preferred. The content of these hydrophobic groups is preferably 0.1 to 15% by weight. Whether the form of the copolymer of the polyvinyl alcohol resin with the hydrophobic group is block or random, it can be applied to the copolymer of the present invention.

The polyvinyl alcohol resin and its copolymer in the coated seeds coated with the seed coating agent of the present invention can be analyzed by mechanically peeling or scraping the coating layer, immersing the resultant in hot water at about 95° C. for about 1 hour, and extracting the resin. Extraction from coated seeds is also possible if there are no operational problems.
The mass ratio of the polyvinyl alcohol-based resin to the iron-based powder is preferably 0.01% by mass or more and 20% by mass or less. If it is less than 0.01% by mass, the effect of suppressing the rise in seed temperature is reduced, and if it exceeds 20% by mass, the supply operation time becomes longer.

The polyvinyl alcohol resin and its copolymer are preferably dissolved in water before use. Those with a high degree of saponification may be dissolved by heating. The raw material form of the polyvinyl alcohol resin before dissolution is not limited. The concentration is not particularly specified as long as the aqueous solution is stable, but is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass from the viewpoint of workability.
The timing of supplying the aqueous solution of polyvinyl alcohol resin is not particularly limited. In addition to the method of supplying the aqueous solution from the beginning to the end of coating, the method of supplying the aqueous solution (regardless of concentration) in the first half of coating and supplying water in the second half of coating, or the method of supplying water in the first half of coating and supplying the aqueous solution (regardless of concentration) in the second half of coating can also be adopted, and are within the scope of the present invention. In addition, supplying the aqueous solution while appropriately changing the concentration rather than keeping it constant can also obtain the same effect, and is therefore within the scope of the present invention.

The reason why the seed temperature rise can be suppressed by supplying an aqueous solution of polyvinyl alcohol resin is believed to be as follows. The iron-based powder forms a coating due to rusting, and heat is generated in the process. The polyvinyl alcohol resin maintains rusting because it is water-soluble, but has high gas barrier properties, which slows down oxidation during rusting. In addition, since it has many hydroxyl groups, it is thought that it can be combined with rust to form a high-quality coating. For this reason, it is thought that it was possible to suppress the seed temperature rise while forming a composite coating with rust. Even when oxidation is promoted by methods such as adding an oxidation promoter, increasing the mixing temperature, or increasing the oxygen concentration, the present invention is thought to be able to effectively suppress the seed temperature.
Since polyvinyl alcohol resin also acts as a binder, it is believed that the dust reduction effect will also be improved.

In the above explanation, the polyvinyl alcohol-based resin is supplied in advance as an aqueous solution, but in the present invention, the polyvinyl alcohol-based resin may be contained in the seed coating agent without being prepared as an aqueous solution in advance.
That is, finely granulated polyvinyl alcohol resin is mixed into a seed coating agent, and the seeds are coated with the seed coating agent. Then, water is sprayed during coating to turn the polyvinyl alcohol resin on the seed surface into an aqueous solution in situ during coating. In this case, since there is a large density difference between the iron powder and the polyvinyl alcohol resin, the effect can be improved by increasing the dispersibility in the coating agent by making the polyvinyl alcohol resin finer, and by increasing the solubility by using a resin with a low degree of saponification.

Additionally, the seed coating composition of the present invention may contain other finishing agents and third components, as described below.
<Finishing agent>
The finishing agent is applied to the seeds as the outermost layer and prevents the seeds from fusing together when the seed coating agent is oxidized. However, since the seed coating method of the present embodiment has the effect of suppressing the fusing of the seeds together, the use of the finishing agent is not essential.
When a finishing agent is used to further prevent the seeds from fusing together during the oxidation treatment, gypsum, silica gel, etc. can be preferably used.

<Third Component>
The seed coating agent may contain a third component to the extent that it does not impair the effects of the present invention. The third component includes inevitable impurities and additives intentionally added for the purpose of achieving some effect, and in any case, the amount of the third component contained is preferably up to about 30% by weight based on the seed coating agent.

<Coating amount>
The amount of the seed coating agent to be applied to the seeds is not particularly limited, but may be 5 to 800 parts by mass per 100 parts by mass of dry seeds. In order to obtain a sufficient seed specific gravity, the amount may be appropriately adjusted, and a coating amount of about 10 to 500 parts by mass is preferably applied.

<Seed coating method>
Next, the seed coating method according to the present embodiment will be specifically described.
The seed coating method according to the present embodiment is a method for coating the surface of a seed with a seed coating agent containing an iron-based powder, and includes a step of supplying the seed coating agent, an aqueous polyvinyl alcohol resin solution, and a gas to flowing seeds to oxidize the iron-based powder and form a coating layer on the surface of the seeds. Water may be added appropriately in the step of attaching the seed coating agent and the step of forming the coating layer.

There are no limitations on the specific method for the process of attaching the seed coating agent to the surface of the seeds (hereinafter also referred to as "coating"). For example, as shown in the "Iron-Coated Flooded Direct Seeding Manual 2010 (compiled by the Kinki-Chugoku-Shikoku Agricultural Research Center, National Agriculture and Food Research Organization)," any method may be used, including manual coating and methods using a conventionally known mixer.

As the mixer, for example, a mixing blade type mixer (such as a Henschel mixer or concrete mixer) or a container rotation type mixer (such as a V-type mixer, a double cone mixer, an inclined rotation type pan mixer, or a rotary hoe type mixer) can be used. A concrete mixer without the mixing blades can also be preferably used.
When applying the seed coating agent using these mixers, the iron-based powder and seeds, as well as binders, separators, and additives as necessary, are placed into the mixer, and the mixer is rotated while spraying water and/or a water-based treatment liquid.

In the step of forming the coating layer, while the seeds to which the seed coating agent is attached are in a flowing state, an aqueous polyvinyl alcohol-based resin solution and a gas having an oxygen concentration of 15 to 30% are supplied to oxidize the iron-based powder, thereby forming a coating layer (film) on the surface of the seeds. Note that water may be supplied in addition to the aqueous polyvinyl alcohol-based resin solution.
The step of forming the coating layer will be specifically described below.

<Flow>
Fluidity can be achieved by rolling, rocking, vibrating, etc., but essentially requires that the seeds are not stationary.
As a method for fluidizing the seeds, it is preferable to use a granulator or mixer used in the step of attaching the seed coating agent to the surface of the seeds, since this simplifies the work, but a different mixer may also be used. Also, after the seed coating agent is attached to the surface of the seeds using a mixer, the seeds may be transferred to a vibrator and shaken to form a coating layer. Fluidizing the seeds during the oxidation treatment can prevent the seeds from colliding with each other and separating to cause the seeds to aggregate, thereby obtaining single-grained seeds.

<Polyvinyl alcohol resin aqueous solution>
The method of supplying the polyvinyl alcohol-based resin aqueous solution may be either a method of adding it directly to the seeds or a method of including it in the air. For example, a method of adding it to the seeds or the inside of a mixer using a spray, a mister, a cup, etc., or a method of supplying it as humidified air containing steam, mist, or water droplets. It is preferable that the seeds to be coated are in a wet state during the oxidation treatment. The same applies when water is supplied in addition to the polyvinyl alcohol-based resin aqueous solution.

The total amount of water and polyvinyl alcohol resin aqueous solution is not particularly determined as long as the effects of the present invention are obtained, but it is preferably 10 to 1000% relative to the iron-based powder, more preferably 20 to 500%, and even more preferably 50 to 200%. If it is less than 10%, rusting will be insufficient and the coating layer will peel off. If it exceeds 1000%, it will take a long time to dry, which will result in a problem of longer working hours.

Furthermore, if a large amount of water or polyvinyl alcohol-based resin aqueous solution is supplied at once, the seeds will clump together, so it is preferable to supply the water or polyvinyl alcohol-based resin aqueous solution in multiple batches while keeping the amount of water to a level that allows the seeds to flow as single grains and while keeping the seeds wet.
The pH of the spray water is not particularly determined as long as the effects of the present invention are obtained, but it is advisable to avoid strongly acidic or strongly alkaline water since they may damage the seeds.

<Gas to be supplied>
The oxygen concentration of the gas to be supplied is preferably 15 to 30%. If it is less than 15%, oxidation is suppressed and there is a risk of oxygen deficiency, which can be a problem in terms of work. If it exceeds 30%, further oxidation may be promoted, but there are many issues such as the cost of adding oxygen and the difficulty of controlling heat generation due to overheating. More preferably, the oxygen concentration is 18 to 25%. In addition to oxygen, mainly nitrogen is contained, but gases such as H ₂ , He, Ne, Ar, Kr, and Xe are also included in the scope of this patent. Moisture is naturally contained, and a dew point of -50 to 80°C is preferable, and a dew point of -40 to 50°C is more preferably applicable. In terms of obtaining gas and work, it is preferable to use air in the atmosphere as it is as the gas, and to humidify the air in the atmosphere with steam or the like. A method of separately introducing steam into a mixing device such as a mixer can also obtain the same effect, and is therefore within the scope of this invention.
As a method for supplying the gas having an oxygen concentration of 15 to 30%, a blower, a fan, various dryers, a hot air blower, etc. can be used.
The temperature of the gas to be supplied is not particularly limited as long as the effects of the present invention can be obtained, but is preferably −20 to 200° C., more preferably 0 to 150° C., and even more preferably 46 to 100° C. In the present invention, water is supplied simultaneously with the gas, so that even when a high-temperature gas is supplied, the seed temperature does not increase due to the heat of evaporation, and the seed temperature can be kept lower than the temperature of the gas to be supplied.

However, from the viewpoint of promoting the oxidation of the iron-based powder, a higher atmospheric temperature is preferable, and it is preferable to supply gas so that the atmospheric temperature becomes 46° C. or higher.
Here, the atmospheric temperature refers to the temperature of the gas supplied toward the seeds in the vicinity of the seeds, and is the temperature of the gas at a location approximately 1 to 15 cm away from the seeds.
However, in order to maintain germination, the seed temperature should be kept below 50° C., more preferably below 40° C. Also, to prevent the seeds from freezing and the development of rust, the seed temperature should be kept above 0° C., more preferably above 10° C.

The wind speed of the gas to be supplied is not particularly limited as long as the effects of the present invention can be obtained, but is preferably 0.1 to 15 m/sec, and more preferably 0.5 to 10 m/sec. If it is less than 0.1 m/sec, the oxidation reaction and cooling do not proceed, and the effects of the present invention cannot be obtained. If it exceeds 15 m/sec, the seeds and the seed coating agent will be scattered. As long as the effects of the present invention can be obtained, the wind speed may be strong or weak, but it is sufficient to consider the average value over about 1 to 30 seconds.
The wind speed can be measured near the seeds using a hot wire anemometer. In the case of a pan-type granulator, pot mixer, etc., it can be measured near the position where the seeds stay in a stationary state. It is preferable to perform the measurement with seeds present as dummy, but it is also acceptable to perform the measurement without seeds as long as the positional relationship is the same. It is also possible to substitute a method of measuring at the outlet of the air duct of a hot air blower. In the case of a closed space device such as a V-type mixer, it is sufficient to temporarily remove the supply air duct and measure at the outlet of the air duct.

When water and gas are supplied to iron-based powder to carry out oxidation treatment, the iron-based powder generates heat due to the oxidation reaction, and the seed temperature rises. For example, if water and gas are supplied to seeds that are stacked and stationary to carry out oxidation treatment, the seed temperature may rise too much, resulting in reduced germination.

For this reason, in the past, the seeds were spread thinly on a tray or a tray to a thickness of about 1 cm or less, and then oxidized by spraying water under conditions that could sufficiently dissipate the heat of the seeds. Alternatively, the coated seeds were packed in a mesh bag, and cooled by spraying water and circulating humid air.
In addition, supplying hot air will promote oxidation, but in that case too, there is the same concern as above that the rise in seed temperature will reduce germination and cause the seeds to clump together.

In this embodiment, an oxidation treatment is carried out by supplying an aqueous polyvinyl alcohol resin solution and gas to the flowing seeds, so that the seed temperature is kept at a maximum of about 50°C even when measured using a contact thermometer, and the rise in seed temperature can be kept low.
Furthermore, as described above, even when high-temperature gas is supplied, the polyvinyl alcohol-based resin aqueous solution is also supplied at the same time as the gas, so the seed temperature does not increase due to the heat of evaporation, and the seed temperature can be kept lower than the temperature of the gas supplied. Therefore, the adverse effect on germination in this embodiment is extremely small.

In this embodiment, a granulator or mixer is used to appropriately spray water and an aqueous solution of a polyvinyl alcohol-based resin to adhere the seed coating agent to the surface of the seeds, and the granulator or mixer used in the previous step is subsequently used to fluidize the seeds with the seed coating agent attached, and water, the aqueous solution of a polyvinyl alcohol-based resin, and gas are supplied to the fluidized seeds.
The aqueous polyvinyl alcohol resin solution may be supplied in either the step of adhering the seed coating agent to the surface of the seeds or the subsequent step of fluidizing the seeds, or in both steps.
Water may be supplied as needed.

After supplying the water, polyvinyl alcohol resin aqueous solution, and gas, the gas supply continued in the mixer, and the seeds were removed after they had dried to a certain extent. After that, the seeds were transferred to a tray or the like and spread out, and excess water was removed and dried in preparation for seed storage. At this time, a small amount of unadhered powder may be produced, but this can be removed by gently sifting, and the removed powder can be used for the next coating.

According to this embodiment, it was possible to obtain single seeds without the seeds clumping together. In addition, the strength of the coating layer and the germination of the seeds were good. The time required for the process of forming the coating layer was less than one hour, and the time required for the oxidation treatment was shortened. Furthermore, the rise in seed temperature during drying was effectively suppressed, and the workability was improved by reducing the drying work area.

The above is an example in which a step of adhering a seed coating agent to the surface of a seed is followed by a step of oxidizing the iron-based powder (forming a coating layer), but the present invention is not limited to this, and the step of adhering a seed coating agent to the surface of a seed and the step of oxidizing the iron-based powder may be carried out simultaneously.
For example, when rotating a mixer containing a seed coating agent and seeds, gas can be supplied along with an aqueous polyvinyl alcohol resin solution (water may be added), thereby simultaneously carrying out the process of adhering the seed coating agent to the seed surface and the process of oxidizing the iron-based powder.
The above case also achieves the effects of the present invention and is therefore within the scope of the present invention, but it is more preferable to carry out a step of oxidizing the iron-based powder (forming a coating layer) after the step of adhering the seed coating agent to the surface of the seed.

In the above seed coating method, the method of supplying the polyvinyl alcohol-based resin as an aqueous solution has been described. However, as mentioned above, the polyvinyl alcohol-based resin may be in the form of a powder and mixed into the seed coating agent. In this case, the seed coating method is carried out as follows.
A seed coating agent containing iron-based powder and polyvinyl alcohol-based resin powder is attached to seeds while spraying water, and gas is supplied while the seeds are fluidized to oxidize the iron-based powder and form a coating layer on the surface of the seeds.

An experiment was carried out to confirm the effect of the present invention, and the experiment will be described below.
In the experiment, rice seeds were coated with a seed coating agent using the seed coating method according to the present invention, and the coated seeds were subjected to an evaluation test.
The step of applying the seed coating agent to the surface of the seeds in the invention examples and comparative examples was carried out in accordance with the method described in the above-mentioned "Iron-Coated Flooded Direct Seeding Manual 2010." Specifically, the steps are as follows.

First, seeds (dry rice grains) and seed coating agent were prepared.
Next, using an inclined rotating pan-type granulator or the like, the seed coating agent was applied to 400 g of seeds (dry rice grains) in several batches while spraying an appropriate amount of water and/or an aqueous solution of a polyvinyl alcohol-based resin.

In the process of oxidizing the iron-based powder (forming a coating layer) in the invention examples, the equipment used in the above process was used continuously, and water and a polyvinyl alcohol-based resin aqueous solution were sprayed onto the flowing seeds while air was supplied to them by a hot air blower. Unless otherwise specified, tap water was used as the water. The gas supplied was atmospheric air (oxygen concentration 21%, dew point 10°C), and its temperature was the temperature of the gas supplied near the blowing nozzle of the hot air blower, measured at a position 5 cm from the seeds.
The seeds coated with the seed coating agent were loaded into a 3 cm thick frame in a tray (seed layer thickness: 3 cm), dried, and then lightly sieved through a sieve with 2 mm openings before being sowed.

In this example, experiments were conducted by changing the types and amounts of the raw materials for the seed coating agent, namely iron powder, iron oxide powder, binder, carboxylic acid, finishing agent, water or aqueous polyvinyl alcohol resin solution.
Table 1 shows the type and amount of each raw material contained in the seed coating agent used in the experiment, and Tables 2 to 6 show the type of each raw material used in the seed coating agent (Table 2: iron powder, Table 3: iron oxide powder, Table 4: binders and finishing agents, Table 5: carboxylic acids, Table 6: polyvinyl alcohol resins).
In addition, Example 12 in Table 1 is an example in which the polyvinyl alcohol-based resin is not added as an aqueous solution but is instead finely granulated and contained in the seed coating agent. Examples 13 and 14 are examples in which the oxygen concentration of the gas supplied is changed. Examples 15 and 16 are examples in which the method of adding the aqueous polyvinyl alcohol-based resin solution is changed. Example 17 is an example in which the dew point of the gas supplied is changed.

The seed temperature during seed drying was measured for the coated seeds coated with the seed coating agent under the conditions of the invention example and comparative example shown in Table 1, as shown below.

<Seed temperature (MAX)>
400 g of seeds were coated and oxidized at the ratios shown in Table 1. Next, a 3 cm thick resin frame was formed in a tray on a 3 cm thick insulating material, and the treated seeds were placed in the frame and left for about half a day so that the layer thickness was 3 cm. At this time, a temperature sensor was attached to the surface of the tray in the center of the lower seed layer, and the temperature change was recorded every 10 minutes with a logger, and the maximum temperature reached was read.

evaluation:
◎: 50℃ or less 〇: Over 50℃ to 65℃ △: Over 65℃ to 80℃ ×: Over 80℃

<Dust>
After the above temperature measurement, the seeds were shaken for 30 seconds using a sieve with 2 mm openings, and the weight loss rate was measured.
The weight loss rate was judged as follows: 1% or less: ◎; over 1% to 3%: ○; over 3% to 5%: △; over 5%: ×.

As shown in Table 1, in Examples 1 to 17, in which the seed coating method according to the present invention was used, the rise in seed temperature was suppressed. As a result, the decrease in germination rate was slight or almost nonexistent. Dust was also suppressed.
As described above, it has been demonstrated that the seed coating method of the present invention can significantly shorten the oxidation time compared to conventional methods, can produce single-grain coated seeds with sufficient coating layer strength, suppresses dust, and can prevent the seed temperature from increasing during drying, without significantly reducing the germination rate.

Claims (5)

A seed coating method comprising the steps of: attaching a seed coating agent containing an iron-based powder to a seed; and supplying a gas having an oxygen concentration of 15 to 30% while flowing the seed coating agent to oxidize the iron-based powder and form a coating layer on the surface of the seed, comprising:
A seed coating method characterized in that, in the step of applying the seed coating agent and/or the step of forming the coating layer, an aqueous solution of a polyvinyl alcohol-based resin is supplied and the gas is supplied using a blower, a fan, various types of dryers, or a hot air blower. A seed coating method characterized by attaching a seed coating agent containing iron-based powder and polyvinyl alcohol-based resin powder to seeds while spraying with water, and supplying gas with an oxygen concentration of 15 to 30% using an air blower, fan, various dryers, or hot air blower while fluidizing the seeds, thereby oxidizing the iron-based powder and forming a coating layer on the surface of the seeds. The seed coating method according to claim 1 or 2, characterized in that the seed coating agent contains a pro-oxidant. A method for producing coated seeds, comprising forming a coating layer on the surface of a seed by the seed coating method according to claim 1 or 2. A method for producing coated seeds , comprising forming a coating layer on the surface of a seed by the seed coating method according to claim 3.