Technical Field [0001] The present invention relates to a steelmaking slag-coated seed in which the 10 periphery of a seed is coated with steelmaking slag powder and a method for producing the same. 15 Background Ati [0002] Rice is a very important food consumed as the staple food by approximately two billion people in the world. In Japan, it is important that rice be able to be stably produced and supplied and the self-sufficiency rate be enhanced. Further, regions such as Southeast Asia, where rice is the staple food, are experiencing significant economic development, and it is of increasing importance to perform rice 20 cultivation stably and achieve stable supply of rice in these regions. [0003] Methods of rice cultivation include a cultivation method in which seeds (seed rice) are germinated, the seedlings are grown, and the seedlings are planted, and a cultivation method based on direct sowing in which seeds (seed rice) are 25 directly sown. In Japan, rice cultivation based on rice planting is the mainstream because homogeneous, good quality rice can be harvested. However, seedling raising that germinates rice seeds (seed rice) and grows the seedlings and rice planting that plants the seedlings require labor power, and are great factors in cost. [0004] 30 Further, because of falls in the price of rice in recent years, a technology to reduce cost and labor for rice farming in paddy fields is rapidly required. In view of 5 PCT/JP2016/070993 21100 the fact that thus far nee fanning has started from producing seedlings and performing rice planting, the reduction of the time and effort of seedling production leads to a great reduction of labor. [0005] The production of rice by direct sowing cultivation can omit seedling raising and rice planting working; therefore, can reduce the amounts of labor power, materials used, etc., and can suppress the cost for rice production. Among the types of direct sowing cultivation of rice, iron coating direct sowing cultivation in which iron-coated seeds are surface-sown is particularly well known. Unlike in the case 10 of transplanting cultivation, the iron-coated seed can be prepared in advance, and therefore the time required for a series of working for sowing in spring can be shortened by performing iron coating treatment in the agricultural off-season during winter. Furthermore, there is no need to use a nursery box during seedling raising. In addition, as well as the reduction of labor power for production, there are various 15 unique advantages derived from the iron coating. For example, since the specific gravity of the iron-coated seed is large, the occurrence of floating can be prevented, and the runoff of seeds can be prevented. Furthermore, the iron layer of the surface of the seed is very strong, and therefore the occurrence of damage by birds, that is, being eaten by birds can be suppressed. 20 [0006] Thus far, technological development has been advanced for the iron coating direct sowing cultivation (e.g., Patent Literature 1). For the seed production of iron coating direct oowing ~ultivation, a form in which the surface of the seed is coated with a mixture of iron powder and plaster of Paris and the surface is further coated 25 with plaster of Paris as a finish layer has been conventionally employed. This is because the iron powder is oxidized into rust on the surface of the seed by combination with the oxidation promotion capacity that the plaster of Paris has, and the rust acts as glue and sufficiently fixes the coating layer to the seed. 30 [0007] Patent Literature 1 mentions that the peeled-off amount is not changed even when a finish layer of plaster of Paris, which has so far been considered necessary, is 5 PCT/JP2016/070993 3/100 not formed, and the particle size of the peeled-off metal powder is smaller than in the case where a finish layer is formed; and a finish layer is not formed on the seed of Patent Literature 1. Citation List Patent Literature [0008] Patent Literature 1: JP 2014-l13128A 10 Summary oflnvention Technical Problem [0009] However, in regard to technologies of producing an iron-coated seed including the technology of Patent Literature 1, iron powder is difficult to obtain in 15 some regions, and the price is around 500,000 yen per ton; thus, the source material cost of the iron-coated seed has been very high. [0010] The present invention has been made in order to address such a problem, and an object of the present invention is to provide a steelmaking slag-coated seed 20 that can be directly sown and can be produced at low cost, and a method for producing the same. 25 Solution to Problem · [0011] The present invention includes roughly two aspects, and according to one aspect of the present invention, there is provided a steelmaking slag-coated seed including: a seed; and a steelmaking slag layer fanned on an outside of the seed, in which the steelmaking slag layer is a covering layer made of steelmaking slag powder obtained by pulverizing steelmaking slag, and the steelmaking slag contains 30 10 mass% or more iron and 30 mass% or more calcium relative to all components of the steelmaking slag. PCT/JP2016/070993 4/100 [0012] Further, the seed may be a seed of a rice plant. [0013] Further, the steelmaking slag may contain 10 mass% to 30 mass% iron and 5 30 mass% to 50 mass% calcium relative to all the components of the steelmaking slag. [0014] Further, the steelmaking slag powder may have a particle size of 600 j.lm or less, and may contain powder with a particle size of 45 j.lm or less at 20% or more. 10 [0015] A method for producing a steelmaking slag-coated seed including a seed and a steelmaking slag layer formed on a surface of the seed according to the above aspect includes: a steelmaking slag pulverization process of pulverizing, as steelmaking slag serving as a material of the steelmaking slag layer, steelmaking slag 15 containing 10 mass% or more iron and 30 mass% or more calcium relative to all components of the steelmaking slag into powder; a seed soaking process of incorporating water into a seed before coating; and a steelmaking slag coating process of mixing steelmaking slag powder obtained in the steelmaking slag pulverization process and a seed obtained in the seed soaking process and thereby 20 forming a steelmaking slag layer made of the steelmaking slag powder on a surface of the seed. 25 [0016] Further, the seed may be a seed of a rice plant. [0017] Further, in the steelmaking slag pulverization process, the steelmaking slag may be pulverized into steelmaking slag powder with a particle size of 600 j.lm or less. [0018] Further, the steelmaking slag powder obtained in the steelmaking slag 30 pulverization process may contain powder with a particle size of 45 j.lm or less at 20% or more. PCT/JP20 16/070993 5/100 [0019] Further, according to another aspect of the present invention, there is provided a steelmaking slag-coated seed, in which a seed is covered with steelmaking slag powder containing 25 mass% or more and 50 mass% or less CaO 5 and 8 mass% or more and 30 mass% or less Si02. [0020] Further, the steelmaking slag powder may further contain 1 mass% or more and 20 mass% or less MgO, 1 mass% or more and 25 mass% or less Ah03, 5 mass% or more and 35 mass% or less Fe, l mass% or more and 8 mass% or less Mn, and 0.1 10 mass% or more and 5 mass% or less P20 5. [0021] A steelmaking slag-coated seed according to the present invention may be covered with one or both of dephosphorization slag and decarburization slag that are kinds of steelmaking slag powder. 15 [0022] Further, the steelmaking slag powder may have a particle size of 600 f!m or less. [0023] Further, the seed may be covered with a mixture of the steelmaking slag 20 powder and one or both of gypsum and iron powder. [0024] Further, the seed may be a seed covered with starch. [0025] Further, a surface of the seed may be further covered with gypsum. 25 [0026] Further, a covering portion of the seed may further contain molasses. [0027] A method for producing a steelmaking slag-coated seed according to the above aspect includes: covering a seed with a mixture obtained by mixing 30 steelmaking slag powder containing 25 mass% or more and 50 mass% or less CaO and 8 mass% or more and 30 mass% or less Si02, and water; and solidifying the PCT/JP2016/070993 6/100 mixture. [0028] Further, the steelmaking slag powder may further contain I mass% or more and 20 mass% or less MgO, I mass% or more and 25 mass% or less Ah03, 5 mass% 5 or more and 35 mass% or less Fe, 1 mass% or more and 8 mass% or less Mn, and 0.1 mass% or more and 5 mass% or less P20 5. [0029] The method for producing a steelmaking slag-coated seed includes: covering a seed with a mixture. obtained by mixing one or both of dephosphorization 10 slag and decarburization slag that are kinds of steelmaking slag powder, and water; and solidifying the mixture. [0030] Further, in the method for producing a steelmaking slag-coated seed, the seed may be covered with a mixture obtained by mixing the steelmaking slag powder, 15 water, and one or both of gypswn and iron powder, and the mixture may be solidified. [0031] 20 25 Further, the mass ratio of water in the mixture may be 1 0 mass% or more and 80 mass% or less relative to the total mass of the mixture. [0032] Further, the water may be water containing 10 mass% or more and 50 mass% or less molasses. [0033] [0034] gypswn. [0035] Further, a seed ·soaked in a starch aqueous solution may be used as the seed. Further, a surface of the solidified mixture may be further covered with Further, a surface of the solidified mixture may be further wetted with water containing 0.5 mass% or more and 5 mass% or less sodium alginate, and then the 30 solidified mixture may be dried. Advantageous Effects of Invention [0036] 71100 PCT/JP2016/070993 According to the present invention, by covering a seed with steelmaking slag containing specific components, it becomes possible to produce a steehnaking 5 slag-coated seed that can be directly sown and can be produced at low cost. Brief Description of Drawings [0037] [FIG. 1] FIG. 1 is a schematic diagram showing an example of a steelmaking slag- 10 coated seed according to a first embodiment of the present invention. [FIG. 2] FIG. 2 is a flow chart showing a process of a method for producing a steelmaking slag-coated seed according to the embodiment. [FIG. 3] FIG. 3 is a photograph of steelmaking slag-coated seeds of Example 1 of the first embodiment. 15 [FIG. 4] FIG. 4 is a photograph of iron-coated seeds of Comparative Example 1 of the embodiment. [FIG. 5] FIG. 5 is photographs showing results of a water soaking experiment of the embodiment. [FIG. 6] FIG. 6 is photographs showing results of a germination experiment of the 20 embodiment in which soil covering was performed. [FIG. 7] FIG. 7 is photographs showing results of a germination experiment of the embodiment in which soil covering was not performed. [FIG. 8] FIG. Sis-photographs showing a state of roots of the embodiment that came out after sowing. 25 [FIG. 9] FIG. 9 is a photograph showing a state of seeds of the embodiment that were sown by scattering on a paddy field from the air. [FIG. 1 0] FIG. 10 is photographs showing growth conditions of rice plants of the embodiment. [FIG. 11] FIG. 11 is a diagram showing adhered weight in cases of different particle 30 size distributions ofthe embodiment. [FIG. 12] FIG. 12 is photographs showing a difference between a coarse grade and a PCT/JP2016/070993 8/100 fine grade of steelmaking slag powder of the embodiment. [FIG. 13] FIG. 13 is a diagram showing adhered weight to seeds in cases of different kinds of slag of the embodiment. [FIG. 14] FIG. 14 is photographs showing a state of adhesion to seeds in cases of 5 different kinds of slag of the embodiment. [FIG. 15] FIG. 15 is a graph showing results of Test Example 2 of a second embodiment of the present invention. [FIG. 16] FIG. 16 is a graph showing results of Test Example 2 of the embodiment. [FIG. 17] FIG. 17 is a graph showing results of Test Example 3 of the embodiment. 10 [FIG. 18] FIG. 18 is a graph showing results of Test Example 3 of the embodiment. [FIG. 19] FIG. 19 is a graph showing results of Test Example 4 of the embodiment. [FIG. 20] FIG. 20 is a graph showing results of Test Example 5 of the embodiment. Description of Embodiments 15 [0038] Hereinafter, (a) preferred embodiment(s) of the present invention will be described in detail with reference to the appended drawings. In this specification and the appended drawings, structural elements that have substantially the same function and structure are denoted with the same reference numerals, and repeated 20 explanation ofthese structural elements is omitted. [0039] The present invention is a steelmaking slag-coated seed in which a seed is coated using steelmaking slag powder containing specific components. The present invention specifically includes a first embodiment and a second embodiment. In the 25 following, a description is given for each of the first embodiment and the second embodiment separately. [0040] < 1. First embodiment> A steelmaking slag -coated seed according to the first embodiment of the 30 present invention is a steelmaking slag-coated seed including a seed and a steelmaking slag layer formed on the outside of the seed, in which the steelmaking PCT/JP2016/070993 9/100 slag layer is a covenng layer made of steelmaking slag powder obtained by pulverizing steelmaking slag, and the steelmaking slag contains 10 mass% or more iron and 30 mass% or more calcium relative to all the components of the steelmaking slag. 5 [0041] In a conventional iron powder-coated seed, it has been necessary to perform mixing with plaster of Paris when performing iron coating treatment because iron powder alone does not cohere favorably. However, iron powder and plaster of Paris are greatly different in specific gravity, and are therefore difficult to uniformly mix 10 together; consequently, there has been a case where non-uniformity occurs in coating or coating iron powder falls off after drying. In this case, the occurrence of floating and damage by birds cannot be sufficiently suppressed, and the yield of rice plants is reduced. Furthermore, after iron coating treatment, a curing period of approximately 5 days is needed in order to alleviate heat generation due to the 15 oxidation reaction of iron. The heat generation has the advantage of causing disease germs growing naturally on the seed to disappear, but on the other hand excessive heat generation may cause quality degradation. [0042] Furthermore, in iron coating direct sowing cultivation, usually the worker 20 (farmer) oneself who performs direct sowing cultivation performs the iron powder coating treatment and the curing on seeds described above; hence, the difficulty of coating and a long curing period are a matter of concern to the worker, and lead to large time and·effort. 25 [0043] For materials other than iron, a technology in which steelmaking slag as a material containing minerals is used as a coating material is proposed. However, even in the case where steelmaking slag is used as a coating material, depending on the kind of steelmaking slag (in particular, the components), a sufficient adhered amount is not obtained, the supply of minerals etc. cannot be expected so much, and 30 the occurrence of damage by birds etc. cannot be sufficiently suppressed, either. Furthermore, since steelmaking slag has a smaller specific gravity than iron powder, PCT/JP20 16/070993 10/100 the weight of the coated seed is reduced when a sufficient adhered amount is not obtained. In this case, it is feared that during aerial scattering the seeds may not get into the soil sufficiently, and floating and damage by birds may occur. [0044] 5 A steelmaking slag-coated seed according to the present embodiment includes a seed and a steelmaking slag layer formed on the outside of the seed, and uses, as steelmaking slag that forms the steelmaking slag layer, a material containing prescribed components among various kinds of steelmaking slag; and can therefore include a sufficient amount of a uniform coating layer (steelmaking slag layer) on the 10 outside of the seed. [0045] Thus, in the present embodiment, since steelmaking slag is used as a coating material, the cost of the source material is greatly suppressed as compared to the case of an iron-coated seed using iron powder or the like as a coating material. 15 Furthermore, a large part of the iron in the steelmaking slag has already been oxidized; thus, as compared to the case of an iron-coated seed, the time of heat generation due to coating treatment is short and a long curing period is not needed, and sowing working can be started in a short period. As a result of these, the steelmaking slag-coated seed of the present embodiment can be produced with less 20 time and effort of the worker and at lower cost than an iron-coated seed. [0046] Furthermore, also minerals such as iron, silicic acid, calcium, manganese, magnesium, and boron dissolved out from the steelmaking slag during the growth period of a rice plant or the like contribute to growth, and therefore the costs of 25 materials etc. for growth are greatly suppressed. [0047] Furthermore, when steelmaking slag powder is used after being finely pulverized to 600 jlm or less in advance, seed coating can be performed without using an additional solidifying agent, and the material cost can be reduced. In 30 particular, when powder with a pmiicle size of 45 Jlm or less is contained at 20% or more, the steelmaking slag powder is fixed to the seed more firmly. PCT/JP2016/070993 11/100 [0048] Steelmaking slag can be easily made uniform by simply performing pulverization. Therefore, the powder hardly flies about at the time of performing coating on the seed; thus, a seed covered with a steelmaking slag layer with high 5 uniformity can be obtained. [0049] A steelmaking slag -coated seed according to the first embodiment of the present invention will now be specifically described on the basis of FIG. I. FIG. 1 is a schematic diagram showing an example of the steelmaking slag-coated seed 10 according to the present embodiment. As shown in FIG. 1, a steelmaking slagcoated seed 1 according to the present embodiment includes a seed 2 and a steelmaking slag layer 3. The steelmaking slag layer 3 is a covering layer (coating layer) made of steelmaking slag powder obtained by pulverizing steelmaking slag. In the example shown in FIG. 1, the steelmaking slag layer 3 is formed directly on 15 the surface of the seed 2; but an intermediate layer may be additionally provided between the seed 2 and the steelmaking slag layer 3 to the extent that the object of the present embodiment is not impaired, as necessary. [0050] The seed 2 is not particularly limited as long as it is a seed of a crop for 20 direct sowing cultivation. In the present embodiment, mainly a seed of a rice plant is dealt with. As the kind of the rice plant, the japonica variety, the indica variety, or the like may be used. In the steelmaking slag-coated seed l in which the seed 2 is provided with the steelmaking slag layer 3, the specific gravity of the steelmaking slag powder that forms the steelmaking slag layer 3 is higher than the specific gravity 25 of water, and a sufficient amount of steelmaking slag powder is adhered; hence, the capability of the seed to sink into the water is increased. Therefore, the occurrence of floating (floating rice) and damage by birds can be prevented. Furthermore, the steelmaking slag layer 3 formed on the surface of the seed 2 is very hard, and therefore exhibits strong resistance to damage by birds. 30 [0051] The steelmaking slag-coated seed can be used mainly for direct sowing PCT/JP2016/070993 12/100 cultivation. The time of performing steelmaking slag coating is not particularly limited as long as it is before performing sowing such as direct sowing. However, since the steelmaking slag-coated seed can be prepared in advance unlike in the case of transplanting cultivation, steelmaking slag coating treatment may be performed in 5 the agricultural off-season during winter, and thereby the time required for a series of working for sowing in spring can be shortened. [0052] The steelmaking slag-coated seed according to the present embodiment is distinctive in that it uses steelmaking slag powder as a material that covers the seed. 10 Steelmaking slag is slag obtained as a by-product in a process that removes impurities from pig iron produced in a blast furnace and adds a secondary material such as quicklime or silica stone to produce steel with high processability; and the components etc. of steelmaking slag vary with the type and process of the steelmaking method. The market selling price of fertilizers processed using 15 steelmaking slag as a source material is 20,000 yen to 50,000 yen per ton, which is much less expensive than the price of iron powder. [0053] In the present embodiment, a kind of steelmaking slag that contains soluble lime as a main component and contains, as other components, iron, soluble silicic 20 acid, soluble magnesia, citric acid-soluble phosphoric acid, citric acid-soluble manganese, citric acid-soluble boron, etc. is used as the steelmaking slag. In particular, steelmaking slag powder containing l 0 mass% or more iron and 30 mass% or more In a steelmaking slag-coated seed according to the second embodiment of the present invention, a seed is covered with steelmaking slag powder containing 25 20 mass% or more and 50 mass% or less CaO and 8 mass% or more and 30 mass% or less Si02. [0070] In order to enable direct sowing of seeds, various technologies of covering a seed with iron powder have so far been reported. However, in these technologies, 25 there has been a problem that seed covering using iron powder involves some cost for metal iron powder. [0071] Furthermore, in seed covering using iron powder or triiron tetroxide, there has been also a problem that the element from which a fertilizer effect can be 30 expected is only iron. [0072] PCT/JP2016/070993 18/100 Furthermore, fine iron powder with a minute particle size such as for use in seed covering has had also a problem that it requires attention to ignition, dust explosion, and the like, and involves some cost for safety measures when the general farmer handles it. 5 [0073] In view of the problems mentioned above, the present inventors conducted extensive studies of using, as a coating material of a seed, steel slag, which is produced as a by-product in a steel production process and which is relatively low in material cost, has a fertilizer effect, and is usable as a covering material. 10 Conventionally, neutral materials such as iron powder have been used as covering materials of a seed, and materials with strong alkalinity have been considered not suitable for covering materials of a seed; but the present inventors have found that a seed can be germinated also by using a certain kind of steelmaking slag, although it has alkalinity with a pH of approximately 11, as a covering material of the seed. 15 The present inventors have found that the growth of a plant can be promoted by using such steelmaking slag as a covering material by virtue of minerals supplied from the steelmaking slag. [0074] That is, the steelmaking slag-coated seed according to the present 20 embodiment has been thought up on the basis of the findings mentioned above, and can suppress the material cost as compared to conventional coated seeds covered with metal iron powder or iron oxide. Furthermore, the steelmaking slag-coated seed according tB the present embodiment has a feriilizer effect, and can be directly sown. 25 [0075] [With regard to steelmaking slag powder] Next, steelmaking slag powder used for covering in the steelmaking slagcoated seed according to the second embodiment of the present invention is described in detail. 30 [0076] Steelmaking slag IS produced m a large amount as a by-product in the PCT/JP2016/070993 19/100 ironmaking industry, and the composition of steelmaking slag is analyzed and managed. Steelmaking slag contains various fertilizer-effective elements such as Ca, Si, Mg, Mn, Fe, and P, and is used as a fertilizer source material. In Japan, as fertilizers using steelmaking slag as a source material, there are fertilizers falling 5 under the standards of the slag silicate fertilizer, the slag phosphate fertilizer, the byproduct lime fertilizer, and the special fertilizer (the iron-containing substance) provided by Fertilizers Regulation Act. Approximately 10 million tons of steelmaking slag is produced per year in Japan alone, and steelmaking slag can be obtained inexpensively. 10 [0077] 15 Steelmaking slag is a material that has no fear of ignition or dust explosion and is inexpensive as compared to iron powder, and has been conventionally used for fertilizer uses as well. [0078] In the present embodiment, examples of the steelmaking slag used for the covering of a seed include, as well as steelmaking slag containing prescribed components like that described in detail below, dephosphorization slag, decarburization slag, and the like, which are kinds of steelmaking slag produced as a by-product from a steel production process. Dephosphorization slag is slag 20 containing phosphorus that is produced as a by-product by adding lime, iron oxide, or the like as a dephosphorizing agent to molten iron and blowing a gas such as oxygen into the material in order to remove phosphorus contained in the molten iron, and is a kind In the following, first, Examples corresponding to the first embodiment of 5 PCT/JP2016/070993 35/100 the present invention are described, along with Comparative Examples. However, the technical scope of the present embodiment is not limited to Examples described below. [0128] As Example 1, usmg nee seeds (variety: Koshihikari), a pulverization process, a seed soaking process, a steelmaking slag coating process, and a drying process were sequentially performed by the procedure shown in FIG. 2 to provide the seed with a steehnaking slag coating. A coating machine was used in the steelmaking slag coating process. The steelmaking slag-coated seed of Example 1 10 has a structure in which the surface of the seed is covered with steelmaking slag powder. The component ratio of the steelmaking slag powder used is shown in Table 1, and the pH and the specific gravity are shown in Table 2. The particle size distribution of the steelmaking slag powder used is of "the medium grade" shown in Tables 4 to 7 described later. 15 [0129] As Comparative Example 1, using rice seeds of the same variety, a seed soaking process, an iron coating process, a finish layer coating process, and an oxidation and drying process were sequentially performed to provide the seed with an iron coating. A similar apparatus to the apparatus of Example 1 was used in the 20 iron coating process. The iron-coated seed of Comparative Example 1 has a structure in which the surface of the seed is covered with a mixture layer made of iron powder and plaster of Paris and further the surface of the mixture layer is covered with a finish layer made of plaster of Paris. [0130] 25 [Table 1] (Table 1) Contained amount [mass%] [0131] [Table 2] Soluble silicic acid 10.0 Soluble lime Soluble magnesia 40.3 4.96 Citric acid Citric acid- Citric acidsoluble Iron soluble soluble phosphoric acid manganese boron 1.65 25.5 2.57 0.02 PCT/JP20 16/070993 36/100 (Table 2) I Steelmaking slag Qowder I Soecif~H !!ravitv I 12.2 2.2 I [0132] FIG. 3 shows a photograph of steelmaking slag-coated seeds of Example 1, 5 and FIG. 4 shows a photograph of iron-coated seeds of Comparative Example 1. As shown in FIG. 3, it can be seen that, in Example 1, the seed is in a state of being uniformly coated with a steelmaking slag layer. On the other hand, in Comparative Example 1, the iron of the coating layer has turned into red rust due to oxidation, and it cannot be said that the coating layer is sufficiently uniform. 10 [0133] The weight of the coated seed of each of Example I and Comparative Example 1 was measured; in Example I, the weight was 1.9 g per 10 seeds, whereas in Comparative Example 1, the weight was 1.8 g per 10 seeds. That is, it is presumed that the adhered weight is a little higher in the case of Example 1 than in 15 the case of Comparative Example 1. In the steelmaking slag powder, components with smaller specific gravities than iron are contained in large amounts in addition to iron, unlike in the iron powder; thus, the specific gravity of the steelmaking slagcoated seed is smaller than the specific gravity of the iron-coated seed. In view of the difference in adhered weight and specific gravity, it can be said that the 20 steelmaking slag-coated seed has a capability to sink into the water equal to or more than that of the iron-coated seed. [0134] Next, a water soaking experiment of the coated seed of each of Example 1 and Comparative Example 1 was performed. 10 steelmaking slag-coated seeds of 25 Example 1 were put into one of two beakers and 10 iron-coated seeds of Comparative Example 1 were put into the other beaker, water was poured into each beaker, and the change in the state of each coated seed was observed. FIG. 5 shows the results of the water soaking experiments of Example I (the upper figure) and Comparative Example 1 (the lower figure). As shown in FIG. 5, in the steelmaking 30 slag-coated seeds of Example 1, the peeling-off of the steelmaking slag layer was PCT/JP2016/070993 37/100 seen in some seeds. On the other hand, in the iron-coated seeds of Comparative Example 1, the dusted iron powder fell off partially. [0135] Next, for the coated seed of each of Example 1 and Comparative Example 1, 5 the germination rate in the case where soil covering was performed on the seed was investigated. I 00 steelmaking slag-coated seeds of Example I were sown into the soil interior of one of two indoor soil areas and were subjected to soil covering; and I 00 iron-coated seeds of Comparative Example 1 were sown into the soil interior of the other soil area and were subjected to soil covering. Table 3 shows the 10 germination rates on the 26th day after sowing and on the 34th day after sowing according to Example I and Comparative Example 1. FIG. 6 shows the results of the 26th day after sowing in the experiments of Example I (the upper figure) and Comparative Example I (the lower figure). [0136] 15 [Table 3] (Table 3) Example 1 Comparative Examole 1 [0137] Germination rate (26th day after sowing) f%1 33 2 Germination rate (34th day after sowing) f%1 37 2 As shown in Table 3 and FIG. 6, in the case of Example I, the germination 20 of 33 seeds, that is, seeds of 33% of all the seeds was observed. On the other hand, in the case of Comparative Example 1, the germination of 2 seeds, that is, seeds of 2% of all the seeds was observed. On the 34th day after sowing, in the case of Example I the germination of 37 seeds, that is, seeds of 37% of all the seeds was observed, whereas in the case of Comparative Example I the germination of 2 seeds, 25 that is, seeds of 2% of all the seeds was observed. From this, the germination rate of the steelmaking slag-coated seed shows a value approximately 20 times higher than the value in the case of the iron-coated seed, and it can be said that the steelmaking slag-coated seed is advantageous in germination in the case where soil covering is performed on the seed. PCT/JP2016/070993 38/100 [0138] Next, for the coated seed of each of Example 1 and Comparative Example 1, the germination rate in the case where soil covering was not performed on the seed was investigated. Some of the soil was put into one of two identical plastic bottles, 5 and 20 steelmaking slag-coated seeds of Example 1 were sown on the surface of the soil in the bottle; the same amount of the soil was put into the other plastic bottle, and 20 iron-coated seeds of Comparative Example 1 were sown on the surface of the soil in the bottle. Soil covering was not performed on either of the seeds of Example 1 and Comparative Example l. FIG. 7 shows the results of the 26th day 10 after sowing in the experiments of Example 1 (the upper figure) and Comparative Example 1 (the lower figure). [0139] As shown in FIG. 7, in the case of Example 1, the germination of 19 seeds, that is, seeds of 95% of all the seeds was observed. On the other hand, in the case 15 of Comparative Example 1, the germination of 18 seeds, that is, seeds of 90% of all the seeds was observed. From this, it can be said that, in the case where soil covering is not performed on the seed, the germination rate of the steelmaking slagcoated seed is equal to or more than the germination rate of the iron-coated seed. This is presumed to be due to the fact that mineral components dissolved out from 20 the steelmaking slag are composed of, in addition to iron, various kinds of components such as silicic acid, calcium, manganese, magnesium, and boron, and consequently special mineral supply effects are exhibited for the seed. [0140] Next, the state of roots of the rice plant obtained by germination in a state 25 where soil covering was performed on the coated seed of each of Example 1 and Comparative Example I was investigated. FIG. 8 shows photographs of rice plants obtained in the experiments of Example 1 (the upper figure) and Comparative Example 1 (the lower figure). As shown in FIG. 8, in the case of Example l, the germination was rapid, and also the elongation of roots was rapid. On the other 30 hand, in the case of Comparative Example 1, the germinate was slow, and also the elongation of roots was slow. PCT/JP2016/070993 39/100 [0 141] Next, steelmaking slag-coated seeds of Example l were scattered on a paddy field from the air, and the state of the surface of the paddy field after sowing was investigated. The scattering was performed from a point at an altitude of 5 m 5 using a helicopter for scattering. FIG. 9 shows the state of the surface of the paddy field after sowing. As shown in FIG. 9, it has been revealed that the scattered steelmaking slag-coated seeds were sown at a point in the soil approximately 4 em deep from the soil surface. It has also been revealed that, even after germination, the steelmaking slag layer did not peel off from the seed but remained adhered to the 10 seed. [0142) FIG. 10 shows growth conditions when the cultivation of rice plants was performed. The upper figure of FIG. 10 is a photograph showing a test zone in which the cultivation of rice plants using steelmaking slag-coated seeds of the 15 present invention was performed, and the lower figure of FIG. lO is a photograph showing a practice zone in which the cultivation of rice plants was performed by an ordinary method (transplanting). As shown in FIG. 10, it can be said that the method of sowing steelmaking slag-coated seeds by scattering from the air is useful as a means for preventing the occurrence of damage by birds and floating rice. 20 [0143] Next, the optimum conditions of seed coating were investigated from the difference in coating performance due to the difference in particle size distribution. 3 kinds of steelmaking slag with different particle size distributions were prepared, and the seed coating performance was evaluated by the adhered weight (g/100 seeds). 25 The steelmaking slag used was classified into 3 kinds of the coarse grade, the medium grade, and the fine grade in accordance with the pulverization method. As shown in Table 4, the coarse grade includes under-1-mm-sieve products, the medium grade includes ball-mill-pulverized products, and the fine grade includes mortarpulverized products of under-sieve products of the medium grade. For the particle 30 size distribution, pa1iicles with particle sizes in the range of more than 0.045 mm were measured with a low tap sieve shaker, and particles with particle sizes in the PCT/JP2016/070993 40/100 range of 0.045 mm or less were measured by the laser diffraction scattering method. The adhered weight was estimated by wetting 100 rice seeds ( unhulled rice) with water, putting the rice seeds into a beaker, coating the rice seeds with steelmaking slag while rotating the beaker, performing drying, and weighing the steelmaking 5 slag-coated seeds collected after the drying. [0144] [Table 4] (Table 4) Coarse e:rade Medium grade Fine grade 10 [0145] Details Under-1-mm-sieve products of powderv fertilizer Pulverized with ball mill Pulverized products of medium grade were further pulverized with mortar The particle size distribution was measured; the results of the frequency in particle size ranges are shown in Table 5 and Table 6. In order to adhere the steelmaking slag powder to the seed without using an additional solidifying agent, it is preferable that the frequency in the particle size range of 45 [tiD or less be 20% or 15 more. From this point of view and Table 5, the medium grade and the fine grade are suitable as a coating agent. Further, as shown in Table 6, it has been found that the particle size distribution is shifted to the small particle size side with transition from the coarse grade to the medium grade to the fine grade. [0146] 20 [Table 5] (Table 5) Sample name Coarse grade Medium grade fir1e grade [0147] [Table 6] 25 (Table 6) +2mm 0.0 0.0 0.0 -lmm -0.5"mm -0.25mm 0.0 21.3 23.7 1.2 1.5 5.1 0.8 0.9 7.2 Frequency [%] - -0_15mm -0_10mm -0_075mm -0.045mm -0.045mm 20.9 13.2 6.9 7.0 7.0 -- 14_4 13.3 i 2.5 7.7 44.3 16.0 17.9 12_4 5.9 38.9 PCT/JP2016/070993 411100 Sample name Cumulative frequency Cumulative frequency Cumulative frequency Measurement method 10% lower limit value Lu m] 50% median value [tJ m] 90% upper limft value [/.I m] Coarse grade 14.12 33_42 54.97 J!SR1629 Medium grade 5.140 24.17 53.13 Laser dHfraction scattering method Apparatus: MT3000 manufactured Fine grade 4.637 22.96 51.67 by Nikkiso Co., Ltd [0148] The adhered weight was measured; as shown in Table 7 and FIG. 11, the result was that the adhered weight was 0.5 g/100 seeds in the coarse grade, 2.3 g/100 5 seeds in the medium grade, and 6.8 g/1 00 seeds in the fine grade, and the adhered weight increased as the steelmaking slag powder was pulverized more finely. In the section of evaluation of Table 7, the triangle sign stands for a little poor, the circle sign for good, and the double circle sign for the best. [0149] 10 [Table 7] (Table 7) Coarse grncle Medium grade Fine gr<.lde [0 150] Before treatment (g/100 .seeds) 2.8 2.8 2.8 After treatment (g/100 Adhered weight (g/100 Evaluation seeds) seeds) 3.3 0.5 b, 5.1 2.3 0 9.6 8.8 © FIG. 12 shows photographs of steelmaking slag-coated seeds produced with 15 steelmaking slag powder of the coarse grade and the fine grade. As shown in FIG. 12, the steelmaking slag-coated seeds produced with steelmaking slag powder of the fine grade have formed a plumper external appearance than in the case of the coarse grade, and it -can be said that the adhered weight increases as the steelmaking slag powder is pulverized more finely. 20 [0151] Next, the difference in seed coating performance due to the difference in the contained amounts of iron and calcium of the steelmaking slag was evaluated by the adhered weight (g/100 seeds). As the test material for coating the surface of the seed, varieties of steelmaking slag 1 to 3 of different components, blast furnace slag, 25 iron powder, and iron powder +plaster of Paris of the contained amounts of iron and calcium shown in Table 8 were used. The varieties of steelmaking slag 1 and 2 PCT/JP2016/070993 42/100 contain the amount of iron and the amount of calcium prescribed in the present embodiment. In each of the varieties of slag mentioned above, silicic acid, lime, magnesia, phosphoric acid, manganese, boron, aluminum, carbon, oxygen, etc. are contained in addition to iron and calcium. Among the test materials mentioned 5 above, the test materials excluding iron powder + plaster of Paris were finely pulverized witb a mortar, and the particle sizes of the test materials were equalized. The coating method for the materials other than iron powder + plaster of Paris is the same as Example 1 described above. The results of measurement of the adhered weight of the materials are shown in Table 9 and FIG. 13. In the section of 10 evaluation of Table 9, the "X" sign stands for poor, the triangle sign for a little poor, and the circle sign for good. 15 [0152] [Table 8] (Table 8) Name of test material Steelmaking slag 1 Steelmaking slag 2 Steelmaking slag 3 Blast furnace slag Iron powder Iron powder + plaster of Paris · [0153] [Table 9] (Table 9) Contained amount of iron [mass%] 25 12 8 0 100 90 Name of test material Before treatment (g/100 After treatment (g/1 00 Specific gravity (each seeds) seeds) test material) Steelma~ing slag 1 2.0 '·" LS Steelmaking slag 2 3.0 <.5 L5 Steelmaking slag 3 3.0 <.0 '' Blast fumace slag '" " u !ron powder " +-· 3.5 '' Iron powder+ plaster of Paris 2.8 '·' <.0 20 [0154] Contained amount of calcium [mass%] 42 43 39 42 0 3 Adhered weight (g/1 00 Adhered volume seeds) (cm'/100 seeds) Evaluation L9 LOG 0 L5 1.00 0 LO 0.71 0.2 0.15 o.• 0.02 3.3 0.83 0 Iron powder + plaster of Paris was used for seed coating as it was without PCT/JP2016/070993 43/100 fine pulverization. For iron powder + plaster of Paris, 10 parts by weight of iron powder and 1 part by weight of plaster of Paris relative to 100 parts by weight of seeds wetted with water were added and mixed, and the surface of the seed was coated using the mixture mentioned above; further, 24 hours later, plaster of Paris 5 was added at a ratio of 0.5 parts by weight while being wetted again with a sprayer, and thereby the surface of the iron powder + plaster of Paris layer was coated; thus, coated seeds were obtained. [0155] As shown in Table 9 and FIG. 13, the adhered weight per 100 seeds was 10 larger in the conventional method (iron powder + plaster of Paris) than in steehnaking slag 1 and steelmaking slag 2; but in terms of the adhered volume per 100 g, steelmaking slag 1 and steelmaking slag 2 were superior to the conventional method (iron powder+ plaster of Paris). Steelmaking slag 3, blast furnace slag, and iron powder were inferior to iron powder + plaster of Paris in both adhered weight 15 and adhered volume. [0156] From these, it can be said that, as compared to the case of iron powder + plaster of Paris, steelmaking slag I and steelmaking slag 2, although the adhered weight is small, have good efficiency of adhesion to the surface of the seed when the 20 specific gravity is taken into account, and were able to be uniformly adhered over a wide range of the surface of the seed even when only a small amount was used. On the other hand, it can be said that, for iron powder + plaster of Paris, although the adhered weight is largest, the adhered volume is small and the efficiency of adhesion to the surface of the seed is not good when the specific gravity is taken into account. 25 [0157] As shown in FIG. 14, the uniformity of the adhesion of the steelmaking slag powder to the seed varied with the kind of slag, that is, the contained amounts of iron and calcium. Steelmaking slag 1, steelmaking slag 2, and iron + plaster of Paris adhered to the seed almost uniformly. However, steelmaking slag 3 adhered to only 30 part of the seed. Further, blast furnace slag alone and iron powder alone hardly adhered to the seed. PCT/JP20 16/070993 44/100 [0158) Next, Examples corresponding to the second embodiment of the present invention are described, along with Comparative Examples. However, the technical 5 scope of the present embodiment is not limited to Examples described below. In the following, "the steelmaking slag-coated seed" is also referred to as a "covered rice seed. 11 10 [0159) [Test Example 1] Using 9 kinds of slag of the composition show.n in Table 10, sieved-out particles adjusted to a maximum particle size of less than 600 rtm were prepared. Samples A, C, D, E, and F are steelmaking slag obtained from a converter of a steel process. Sample B is steelmaking slag obtained from a molten iron preliminary treatment process. Sample G is dephosphorization slag, and sample H is 15 decarburization slag. Sample I is a preparation in which 50 mass% sample G and 50 mass% sample H are mixed together. [0160) All of the compositions of 5 kinds of steehnaking slag of sample A to sample E among these samples were a composition in which the contained amount of 20 CaO was 25 mass% or more and 50 mass% or less and the contained amount of Si02 was 8 mass% or more and 30 mass% or less. The compositions of the 5 kinds of steelmaking slag of sample A to sample E further satisfied a composition in which the contained amount of MgO was l mass% or more and 20 mass% or less, the contained amount of Ah03 was l mass% or more and 25 mass% or less, the 25 contained amount of Fe was 5 mass% or more and 35 mass% or less, the contained amount ofMn was l mass% or more and 8 mass% or less, and the contained amount ofP20 5 was 0.1 mass% or more and 5 mass% or less. [0 161) On the other hand, sample F contains 55% CaO and IS neither 30 dephosphorization slag nor decarburization slag, and is therefore a sample of steelmaking slag outside the range of the present embodiment. PCT/JP2016/070993 45/100 [0162] Sample G contains 35.0% Si02 and does not fall under the composition of steelmaking slag mentioned above, but is dephosphorization slag and is a sample within the range of the present embodiment. Sample H is decarburization slag and 5 is a sample within the range of tbe present embodiment. Sample I is a mixture of dephosphorization slag and decarburization slag and is a sample within the range of the present embodiment. 10 [0163] [Table 10] (Table 1 0) -- Sample A Sample B Sample C SampleD Sample E Sample F Sample G Sample H Sample I [0164] Composition of 9 kinds of slag (mass%) CaO Si02 MgO Al 20 3 30.7 17.5 16.5 16.5 36.8 17.5 1.7 1.6 43.7 12.5 5.6 4.4 27.1 17.7 15.0 21.0 40.9 13.0 8.4 2.1 55.0 15.6 6.3 3.8 38.2 35.0 3.3 4.7 39.5 8.5 2.8 5.6 38.9 21.8 3.1 5.2 Fe Mn P20 5 6.2 1.2 0.17 30.6 1.6 2.00 17.7 3.5 1.88 9.0 1.2 0.14 19.1 3.0 2.82 10.3 2.3 1.45 9.4 2.0 1.23 15.1 2.1 1.47 12.3 2.1 1.35 Water was added to each of the 9 kinds of samples with a sieved particle size adjusted to less than 600 11m so that the mass ratio of water in the mixture of each sample and water might be 30%, and mixing was performed. A rice seed 15 (variety: "Fusakogane") -was put into the mixture of each sample and water and mixing was performed, and the rice seed was covered with the sample mentioned above. The mass of each sample used for covering was equivalent to 0.6 on the assumption that the mass of the rice seed is 1. The covered rice seed was air-dried for 3 hours in a well-ventilated state. Thus, a rice seed covered with each of the rice 20 seed coating materials mentioned above was produced. The surface of the produced rice seed was entirely covered with the sample mentioned above. [0165] A sodium chloride aqueous solution (specific gravity: 1.4) was prepared, PCT/JP2016/070993 46/100 and it was investigated whether the rice seed covered with each of the 9 kinds of slag mentioned above and a not -covered rice seed settled or not. As shown in the results of Table 11, the not-covered rice seed did not settle, whereas the rice seed covered with each of the varieties of slag of sample A to sample I settled. Thus, it has been 5 found that the settleability of the rice seed is increased by covering the rice seed with various kinds of slag like those mentioned above. [0166] [Table 11] 10 [0167] [Test Example 2] A piece of circular filter paper (diameter: 11 em) was laid over a plastic laboratory dish with a diameter of 11 em. Distilled water was added, and the piece of filter paper was shallowly immersed in the distilled water. 25 rice seeds that 15 were covered with each of the 9 kinds of slag of the composition shown in Table 10 by a similar method to Test Example 1 were put on the piece of filter paper shallowly immersed in the distilled water that was put in a laboratory dish different from sample to sample. As a control, a laboratory dish was prepared also for not-covered rice seeds that were not covered with steelmaking slag, and similarly 25 seeds were 20 put on a piece of filter paper shallowly immersed in distilled water. Each laboratory dish was placed into a constant temperature oven of 30°C in a state where an upper cover was laid on the ·laboratory dish, and a germination test was performed. On the 7th day, the number of genninated seeds was measured for the laboratory dish of each sample, and the germination rate was calculated. For the germinated seed, the 25 length of the radicle and the seedling was measured. [0168] Table 12 below shows the results of the number of germinated seeds and the germination rate. [0169] 30 [Table 12] PCT/JP2016/070993 (Ta' 12} Number of germinated seeds (seeds) Germination rate (%) [0 170] 47/100 Number of erminated seeds and ermination rote Sample D- Sample E- Sample F- Sample G- Sample Hcovered Sample I Not-covered Sample A- Sample B- Sample Cseed covered seed covered seed covered seed covered seed covered seed covered seed covered seed covered seed seed 21 19 22 " " 21 84 76 88 80 88 84 Although steelmaking slag is a material exhibiting alkalinity around a pH of 11, the rice seeds covered with each of sample A to sample E within the range of the 5 present embodiment have a ge1mination rate around 80%, similarly to the notcovered rice seeds; and it has been found that the rice seeds covered with the steelmaking slag coating material within the range of the present embodiment have a germination rate at approximately the same level as the not-covered rice seeds of a control. On the other hand, in sample F, since it is steelmaking slag having strong 10 alkalinity in which the contained amount of CaO is as high as 55%, the germination rate was 60%, which was lower than the germination rate of the not-covered rice seeds. In sample G, which is dephosphorization slag, sample H, which is decarburization slag, and sample I, which was prepared by miXIng both dephosphorization slag and decarburization slag, the germination rate was 84%, 15 which was equal to the germination rate of the not-covered rice seeds. [0171] FIG. 15 shows the average value of the measurement results of the lengths of the germinated radicles of the seeds covered with each sample and the not -covered seeds serving as a control, by comparison on a graph. FIG. 15 shows also the 20 standard deviation. [0172] FIG. 16 shows the average value of the measurement results of the lengths of the germinated seedlings of the seeds covered with each sample and the notcovered seeds serving as a control, by comparison on a graph. FIG. 16 shows also 25 the standard deviation. [0173] As shown in the results of FIG. 15 and FIG. 16, in the seeds covered with 5 kinds of slag of sample A to sample E within the range of the present embodiment, both the growth of the radicle and the growth of the seedling after germination were PCT/JP2016/070993 48/100 more promoted than in the not-covered seeds of a control. In the rice seeds covered with sample G, which is dephosphorization slag, sample H, which is decarburization slag, and sample I prepared by mixing both dephosphorization slag and decarburization slag, both the growth of the radicle and the growth of the seedling 5 after germination were more promoted than in the not-covered rice seeds of a control. On the other hand, in the rice seeds covered with sample F in which the contained amount of CaO is as high as 55%, both the growth of the radicle and the growth of the seedling were suppressed as compared to the rice seeds covered with sample A to sample E, sample G, sample H, and sample I. However, both the growth of the 10 radicle and the growth of the seedling were more promoted than in the not-covered rice seeds. [0174] Thus, it has been found that the germination rate of the rice seeds covered with steelmaking slag of a composition in which the contained amount of CaO is 25 15 mass% or more and 50 mass% or less, the contained amount of Si02 is 10 mass% or more and 30 mass% or less, the contained amount of MgO is 1 mass% or more and 20 mass% or less, the contained amount of Ah03 is 1 mass% or more and 25 mass% or less, the contained amount of Fe is 5 mass% or more and 35 mass% or less, the contained amount of Mn is 1 mass% or more and 8 mass% or less, and the contained 20 amount of P205 is 0.1 mass% or more and 5 mass% or less is substantially equal to the germination rate of the not-covered seeds of a control, and the growth of roots and the seedling after germination can be promoted as compared to the not-covered rice seeds. It has also been found that the germination rate of the rice seeds covered with dephosphorization slag, decarburization slag, and a mixture of both 25 dephosphorization slag and decarburization slag is substantially equal to the germination rate of the not-covered rice seeds of a control, and the growth of roots and the seedling after germination can be promoted. [0175] [Test Example 3] 30 A piece of circular filter paper (diameter: ll ern) was laid over a plastic laboratory dish with a diameter of 11 em. Distilled water was added, and the piece PCT/JP2016/070993 49/100 of filter paper was shallowly immersed in the distilled water. 25 rice seeds covered with sample B with a maximum particle size of 600 11m having the composition shown in Table 10 and 25 rice seeds covered with powder of pure iron with a maximum particle size of 600 11m likewise were put individually on the pieces of 5 filter paper shallowly immersed in the distilled water in different laboratory dishes. As a control, a laboratory dish was prepared also for not-covered rice seeds that were not covered with steelmaking slag, and similarly 25 seeds were put on a piece of filter paper shallowly immersed in distilled water. Each laboratory dish was placed into a constant temperature oven of 3 0°C in a state where an upper cover was laid on 10 the laboratory dish, and a germination test was performed. On the 7th day, the number of germinated seeds was measured for the laboratory dish of each sample, and the germination rate was calculated. For the germinated seed, the length of the radicle and the seedling was measured. 15 [0176] Table 13 below shows the results of the number of germinated seeds and the germination rate. [0177] [Table 13] (T a bl e 13) Number of germinated seeds (seeds) Germination rate (%) N um be r of germmate d see ds an d germ1natlo n rate Not-covered Sample B- Iron powderseed covered seed covered seed 21 22 20 84 88 80 20 [0178] 25 The rice seeds covered with sample B within the range of the present embodiment had a higher germination rate than the not -covered seeds and the iron powder-covered seeds. [0179] FIG. 17 shows the average value of the measurement results of the lengths of the germinated radicles, by comparison on a graph. FIG. 17 shows also the PCT/JP20 16/070993 50/100 standard deviation. [0 180] FIG. 18 shows the average value of the measurement results of the lengths of the germinated seedlings, by comparison on a graph. FIG. 18 shows also the 5 standard deviation. [0181] As shown in the results of FIG. 17 and FIG. 18, in the seeds covered with sample B within the range of the present embodiment, both the growth of the radicle and the growth of the seedling after germination were more promoted than in the not- 10 covered seeds and the iron powder-covered seeds. [0182] Thus, it has been found that, by covering the rice seed with steelmaking slag of a composition in which the contained amount of CaO is 25 mass% or more and 50 mass% or less, the contained amount of Si02 is 10 mass% or more and 30 mass% or 15 less, the contained amount of MgO is 1 mass% or more and 20 mass% or less, the contained amount of Ah03 is 1 mass% or more and 25 mass% or less, the contained amount of Fe is 5 mass% or more and 35 mass% or less, the contained amount ofMn is l mass% or more and 8 mass% or less, and the contained amount of P20 5 is 0.1 mass% or more and 5 mass% or less, a steelmaking slag-coated seed with good 20 growth is obtained less expensively than by covering the rice seed with iron powder. [0183] [Test Example 4] (comparison to iron powder) A piece ·of circular filter paper (diameter: 11 em) was laid over a plastic laboratory dish with a diameter of 11 em. Distilled water was added, and the piece 25 of filter paper was shallowly immersed in the distilled water. 25 rice seeds that were covered with steelmaking slag sample C with a maximum particle size of 600 J.lm having the composition shown in Table 10 by the method described in Test Example 1 and 25 rice seeds covered with powder of pure iron with a maximum particle size of 600 J.lm likewise were put individually on the pieces of filter paper 30 shallowly immersed in the distilled water in different laboratory dishes. As a control, a laboratory dish was prepared also for not -covered rice seeds that were not PCT/JP2016/070993 51/100 covered with steelmaking slag, and similarly 20 seeds were put on a piece of filter paper shallowly immersed in distilled water. Each laboratory dish was placed into a constant temperature oven of 30°C in a state where an upper cover was laid on the laboratory dish, and a germination test was performed. On the 7th day, the number 5 of germinated seeds was measured for the laboratory dish of each sample, and the germination rate was calculated. For the germinated seed, the length of the radicle was measured. [0184] Table 14 below shows the results of the number of germinated seeds and the 10 germination rate. 15 20 [0 185] [Table 14] (T a bl e 14) ·.. . .. Number of germinated seeds (seeds) Germination rate (%) [0186] N urn be r of e:erm.m a t e d see d s an d germm· af 10 nrate Not-covered Sample C- Iron powderseed covered seed covered seed 18 18 17 90 90 85 The rice seeds covered with steelmaking slag sample C within the range of the present embodiment had a germination rate substantially equal to the germination rate of the not -covered seeds, and had a germination rate higher than the germination rate of the iron powder-covered seeds. [0 187] FIG. 19 shows the average value of the measurement results of the lengths of the germinated radicles, by comparison on a graph. [0 188] The seeds covered with steelmaking slag sample C within the range of the present emhodiment exhibited a growth of the radicle substantially equal to that of 25 the not -covered seeds. On the other hand, in the iron powder-covered seeds, the growth of the radicle after germination was significantly poor. PCT/JP2016/070993 52/100 [0189] The pH of the water left in the laboratory dish was investigated; the water of the laboratory dish of the not-covered seeds had a pH of 5.8, and the water of the laboratory dish of the rice seeds covered with sample C had a pH of 8.0; on the other 5 hand, the water of the laboratory dish of the iron powder-covered seeds had a pH of 4.0 and was acidified. It is presumed that iron was dissolved to form iron hydroxide and was thereby acidified, and the acidified condition inhibited the growth of the radicle after germination of the iron powder-covered seed. 10 [0190] Thus, it has been found that, by covering the rice seed with steelmaking slag of a composition in which the contained amount of CaO is 25 mass% or more and 50 mass% or less, the contained amount of Si02 is 10 mass% or more and 30 mass% or less, the contained amount of MgO is 1 mass% or more and 20 mass% or less, the contained amount of Ah03 is I mass% or more and 25 mass% or less, the contained 15 amount of Fe is 5 mass% or more and 35 mass% or less, the contained amount ofMn is 1 mass% or more and 8 mass% or less, and the contained amount of P20 5 is 0.1 mass% or more and 5 mass% or less, a steelmaking slag-coated seed with good growth is obtained less expensively than by covering the rice seed with iron powder. It has also been revealed that, in the iron powder-covered seed, acidification in 20 association with iron hydroxide formation inhibits the growth of the radicle, depending on conditions. [0191] [Test Example 5J{!ong-term storage) Rice seeds that were covered with steelmaking slag sample C with a 25 maximum particle size of 600 flm having the composition shown in Table 10 by the method described in Test Example 1 and not-covered rice seeds of a control were stored in a dark place at room temperature. The germination rates of steelmaking slag-coated seeds covered with sample C after drying at room temperature for 3 hours (0 days) and steelmaking slag-coated seeds stored for I month, 2 months, 3 30 months, 4 months, 5 months, and 6 months were investigated. For comparison, also the germination rates of not -covered rice seeds stored in the same environments were PCT/JP2016/070993 53/100 investigated. The investigation of the germination rate is based on the following method. [0192] A germination test was performed at the time point when each of the storage 5 periods of 0 days, 1 month, 2 months, 3 months, 4 months, 5 months, and 6 months has elapsed. [0193) A piece of circular filter paper (diameter: 11 em) was laid over a plastic laboratory dish with a diameter of II em. Distilled water was added, and the piece 10 of filter paper was shallowly immersed in the distilled water. 20 steelmaking slagcoated seeds were put on the piece of filter paper shallowly immersed in the distilled water. As a control, a laboratory dish was prepared also for not-covered rice seeds that were not covered with steelmaking slag, and similarly 20 seeds were put on a piece of filter paper shallowly immersed in distilled water. Each laboratory dish 15 was placed into a constant temperature oven of 30°C in a state where an upper cover was laid on the laboratory dish, and a germination test was performed. On the 7th day, the number of germinated seeds was measured for the laboratory dish of each sample, and the germination rate was calculated. 20 [0194] FIG. 20 shows the results of the stored period and the germination rate. [0195] Although steelmaking slag sample C is alkaline, the results of the germination test have revealed that the rice seed covered with sample C can genninate well even after it is stored for 6 months. Thus, the steelmaking slag- 25 coated seed according to the present embodiment can be stored for a long period. [0196] [Test Example 6) (starch treatment) 40 Koshihikari seeds were soaked for I 0 minutes in a liquid in which starch was suspended in water to set the concentration to 50 mass%. The seeds were 30 extracted from the starch suspension; the seeds were stirred in a suspension of sample C in which steelmaking slag sample C described in Test Example l was PCT/JP2016/070993 54/100 suspended at 66 mass% in water, and thus the seeds were covered with sample C; and the covered seeds were extracted, and were dried at room temperature for 24 hours. As a control, also 40 rice seeds that were not soaked in a suspension of starch were stirred in a suspension of sample C in which steelmaking slag sample C 5 described in Test Example 1 was suspended at 66 mass% in water, and thus seeds on which starch treatment was not performed were prepared. [0197] The average value of the mass per seed of the starch-treated seeds covered with sample C and the not-starch-treated seeds covered with sample C, and the 10 average value of the mass per seed of not-covered seeds are shown in Table 15 below. Further, the mass of the not -covered seed was subtracted from the mass of the rice seed covered with sample C to calculate the mass of the covering substance, and the results are shown in Table 15 as well. Also the ratio of the mass of the covering substance to the mass of the not-covered seed is shown. 15 [0198] [Table 15] Table15 Mass of rice seed-and mass of covering substance per rice seed ---------- ------------ - Starch-treated rice seed Not-starch-treated rice ---- ---- --------- -- Not-covered rice seed - covered with sample C seed covered with sample C ------ Mass of rice seed 0.0567 0.0422 0.0283 (g) Mass of covering substance 0.0284 O.o139 - (g) Mass of covering substance/ 1.00 0.49 - Mass of not-covered seed [0199] In the not-starch-treated seed, the ratio of the mass of the covering substance 20 to the mass of the not-covered seed was 0.49, whereas in the starch-treated seed, the ratio of the mass of the covering substance to the mass of the not-covered seed was increased to 1, and the adhered amount of the covering substance was able to be increased. [0200] 25 20 starch-treated rice seeds covered with sample C and 20 not-stmch-treated PCT/JP2016/070993 55/100 rice seeds covered with sample C that were produced by being covered with sample C and then dried at room temperature for 24 hours were naturally dropped once onto an iron plate from a position at a height of 20 em. The rice seeds dropped on the iron plate were collected, and the mass was measured to investigate the mass of the 5 covering substance per seed after dropping; the results (average value) are shown in Table 16 below. [0201) Further, the ratio of the mass of the covering substance after dropping to the mass of the covering substance before dropping was calculated, and the results are 10 shown in Table 16 below as well. 15 [0202) [Table 16) (Ta bl e 16) --- Mass of covering substance after dropping (g) Mass of covering substance after dropping/ Mass of covering substance before dropping [0203) Effe ct on mass o f covenng su b stance bby dr opp1ng onto 1ro n plate Starch-treated rice seed Not-starch-treated rice covered with sample C seed covered with sample C 0.0262 0.0083 0.92 0.60 The ratio of the mass of the covering substance after dropping to the mass of the covering substance before dropping was a larger value in the case where starch treatment was performed than in the case where starch treatment was not performed. Thus, it has been found that, by starch treatment, the fixability of the covering substance was increased, and the covering substance became less likely to peel off. 20 [0204) A germination test was performed usmg covered nee seeds that were covered with sample C and then dried at room temperature for 24 hours. A piece of circular filter paper (diameter: 11 em) was laid over a plastic laboratory dish with a diameter of ll em. Distilled water was added, and the piece of filter paper was 25 shallowly immersed in the distilled water. 20 starch-treated covered rice seeds and PCT/JP2016/070993 561100 20 not-starch-treated covered rice seeds were put individually on the pieces of filter paper shallowly immersed in the distilled water. As a control, a laboratory dish was prepared also for not-covered rice seeds that were not covered with steelmaking slag, and similarly 20 seeds were put on a piece of filter paper shallowly immersed in 5 distilled water. Each laboratory dish was placed into a constant temperature oven of 30°C in a state where an upper cover was laid on the laboratory dish, and a germination test was performed. On the 7th day, the number of germinated seeds was measured for the laboratory dish of each sample, and the germination rate was calculated. A germination test was similarly performed using the not-covered rice 10 seeds as a control. Table 17 below is the results of the germination rate. 15 [0205] [Table 17] (Ta bl e 17) . ~ .. Germination rate (%) [0206] Re su Its ofgerrnmatlon rate Starch-treated rice seed Not-starch-treated rice Not-covered rice seed covered with sample C seed covered with sample C 85 85 85 The starch-treated covered rice seeds showed a high germination rate substantially equal to the germination rates of the not-starch-treated covered rice seeds and the not-covered rice seeds. [0207] Thus, it has been revealed that, by covering a starch-treated rice seed with 20 steelmaking slag, tbe mass ·of the covering substance can be increased, and yet the germination rate can be kept at a high value. [0208] [Test Example 7] (gypsum outer covering) 80 Koshihikari seeds were stirred in a suspension of sample C in which 25 steelmaking slag san1ple C described in Test Example 1 was suspended at 66 mass% in water, and thus the seeds were covered with sample C; and the covered seeds were extracted, and were dried at room temperature for 24 hours. Of the 80 seeds covered with sample C, 40 seeds were further subjected to outer covering with PCT/JP2016/070993 57/100 gypsum. The outer covering with gypsum was performed in the following manner. [0209] 40 seeds covered with sample C were soaked in a suspension of gypsum in which hemihydrate gypsum was suspended at 30 mass% in water, were quickly 5 extracted, and were dried at room temperature for 24 hours; thus, 40 seeds in which the outside of the covering of sample C was further outer-covered with gypsum were produced. [0210] Table 18 below shows the average mass per seed of the rice seeds covered 10 only with sample C, the rice seeds covered with sample C and further covered with gypsum on the outside, and not -covered rice seeds. Further, the mass of the notcovered seed was subtracted from the mass of the covered rice seed to calculate the mass of the covering substance, and the results are shown in Table 18 as well. Also the ratio of the mass of the covering substance to the mass of the not -covered seed is 15 shown. 20 [0211] [Table 18] Table 18 •. Mass of rice seed (g) Mass of covering substance (g) Mass of covering substance/ Mass of not-covered seed [0212] Mass of rice seed and mass of covering substance per rice seed Rice seed covered with Rice seed covered only with sample C and further Not-covered rice seed sample C covered with gypsum on outside 0.0428 0.0536 0.0278 0.0150 0.0258 - 0.54 0.93 - In the seed covered only with sample C, the ratio of the mass of the covering substance to the mass of the not-covered seed was 0.54, whereas in the seed covered with sample C and further covered with gypsum on the outside, the ratio of the mass of the covering substance to the mass of the not-covered seed was 0.93; thus, the adhered amount was able to be increased by being covered with sample C 25 and then further covered with gypsum from the outside. PCT/JP2016/070993 58/100 [0213] 20 rice seeds covered with sample C and 20 rice seeds covered with sample C and further covered with gypsum on the outside were naturally dropped once onto an iron plate from a position at a height of 20 em. The rice seeds dropped on the 5 iron plate were collected, and the mass was measured to investigate the mass of the covering substance per seed after dropping; the results (average value) are shown in Table 19 below. [0214] Further, the ratio of the mass of the covering substance after dropping to the 10 mass of the covering substance before dropping was calculated, and the results are shown in Table 19 below as well. [0215] [Table 19] (Table 19) ~ Mass of covering substance after dropping (g) Mass of covering substance after dropping/ Mass of covering substance before dropping 15 [0216] Effect on mass of coverinP substance bv drooninrr onto iro n plate Rice seed covered with Rice seed covered only with sample C and further sample C covered with gypsum on outside 0.01 0.0243 0.67 0.94 The ratio of the mass of the covering substance after dropping to the mass of the covering ·substance before dropping was a larger value in the case of being covered with sample C and further covered with gypsum on the outside than in the case of being covered only with sample C. Thus, it has been found that, by being 20 covered steelmaking slag and further covered with gypsum on the outside, the adhesiveness of the covering substance was increased, and the covering substance became less likely to peel off. [0217] 20 rice seeds covered only with sample C and 20 rice seeds covered with 25 sample C and then further covered with gypsum on the outside were used for a PCT/JP2016/070993 59/100 germination test. A piece of circular filter paper (diameter: 11 em) was laid over a plastic laboratory dish with a diameter of 11 em. Distilled water was added, and the piece of filter paper was shallowly immersed in the distilled water. 20 rice seeds covered only with sample C and 20 rice seeds covered with sample C and then 5 further covered with gypsum on the outside were put individually on the pieces of filter paper shallowly immersed in the distilled water. Each laboratory dish was placed into a constant temperature oven of 30°C in a state where an upper cover was laid on the laboratory dish, and a germination test was perfonned. On the 7th day, the number of germinated seeds was measured for the laboratory dish of each sample, 10 and the germination rate was calculated. Table 20 below is the results of the germination rate. [0218] [Table 20] (Ta bl e 20) . . . . . . . . . . . . . . . . . . . . . . Germination rate (%) Re su ts o f germination rate Rice seed covered with Rice seed covered only with sample C and further sample C covered with gypsum on outside 85 85 15 [0219] 20 The rice seeds covered with sample C and then covered with gypsum on the outside showed a high germination rate of 80% or more, which was substantially equal to the germination rate of the rice seeds covered only with sample C. [0220] Thus, it has been revealed that, when a rice seed is covered with steelmaking slag and then covered with gypsum on the outside, the mass per seed of the steelmaking slag -coated seed can be increased, and yet the germination rate can be kept high. [0221] 25 [Test Example 8] (use of gypsum as additive) Steelmaking slag sample C described in Test Example 1 and materials in PCT/JP2016/070993 60/100 which gypsum was added to sample Cat mass ratios of 90%:10%, 80%:20%, and 50%:50% were prepared. Each sample was suspended in water so that the ratio, to water, of sample C or each of the materials in which gypsum was added to sample C might be 66 mass%, 40 Koshihikari seeds were put into the suspension and stirred, 5 and the seeds were extracted and dried at room temperature for 24 hours; thus, rice seeds covered with sample C or each of the materials in which gypsum was added to sample C at different ratios were produced. [0222] Table 21 below shows the average mass per seed of the rice seeds covered 10 with sample C and each of the materials in which gypsum was added to sample Cat mass ratios of90%:10%, 80%:20%, and 50%:50%. Also the average mass per seed of not-covered rice seeds is shown. Further, the mass of the not-covered seed was subtracted from the mass of the covered rice seed to calculate the mass of the covering substance, and the results are shown in Table 21 as welL Also the ratio of 15 the mass of the covering substance to the mass of the not-covered seed is shown. [0223] [Table 21] 0 N .N. . ~ (Table 21) -------- ---------------------- Mass of rice seed (g) Mass of covering substance (g) Mass of covering substance/ Mass of not-covered seed MIVI d'>'> Ufl IIVt:: ::;t;:t;:dU adiniUd 111<:1'>'> VI VUVt:fl!l ::iUbU l>ldflL'tl tH rto..;t: :;;o::o::du Rice seed covered only with Sample C 90% + gypsum 1 0% Sample C 80% + gypsum 20% sample C covering covering 0.0417 0.0423 0.0410 0.0137 0.0143 0.0130 0.49 0.51 0.46 Sample C 50% + gypsum 50% Not-covered rice seed covering 0.0405 0.0280 0.0125 - 0.45 - 0, --~ 0 0 >-r::J 0 ~ N 0 >-' a> .0.., 0 ""w"" PCT/JP2016/070993 62/100 In the seed covered only with sample C, the ratio of the mass of the covering substance to the mass of the not-covered seed was 0.49; and also in the seed covered with each of the materials in which gypsum was added to sample C at mass ratios of 90%:10%, 80%:20%, and 50%:50%, the ratio of the mass of the covering 5 substance to the mass of the not -covered seed was almost the same value. Thus, it can be seen that a rice seed can be covered also when each of the materials in which gypsum is added to sample Cat mass ratios of90%:10%, 80%:20%, and 50%:50% is used, like in the case of sample C. 10 (0225] 20 rice seeds covered with sample C and 20 rice seeds covered with each of the materials in which gypsum was added to sample C at mass ratios of 90%:10%, 80%:20%, and 50%:50% were naturally dropped once onto an iron plate from a position at a height of 20 em. The seeds dropped on the iron plate were collected, and the mass was measured to investigate the mass of the covering substance after 15 dropping; and the ratio of the mass of the covering substance after dropping to the mass of the covering substance before dropping was calculated; the results are shown in Table 22 below. [0226] [Table 22] PCT/JP20 16/070993 63/100 E 0 w ~ '" ~ c + ·c ru "co' "0 ' >0 0 ""'' ~ 0 0 0 0"' 0 0 ru~ 0. E m "0 ' "' E 0 w ~ '" ~ + ·cc "co' co ru 0 "'! "0 ' >0 C> 0 00 0 0 0 ru ru ~ 0. -1: E m c .~ "' .B 0 ~ c E 0 0 ~ w ~ ·~ '" ~ "' + .§ e ru 0" ' r- 2 "0 ' >0 C> "0 ' m 0 0 ru 0 0 c ru !l 0. w E ~ m 0 ; "~' ·cc "•' ru ~ > c 0 0 0 ~ ~0 0 0 ru ww >r' ur~-u "0 ' ""''! m o E 0 0 E 0 mw 0 c ~ 0 ru ru ~ w 0 ru ru iii 0 iX M ..._ ~ c c~ ~ bn1 'i'i ~ 'i'i ~ c 0 ~ ·§ e c ' -~ {5 ·;::: -u ru~ ru > ' > ' > ru 0 ru o ru 0 ' 0 <:: '!;j1 0 ~ o.B ~ ·- 't~ ~ ru 0 ru 0~ o; w 0 w ru w ru w c w 0 w 0 "' • !l • c c ~ "' w "' !!~ ~• ~ w w 0 ~ ~ w 0 0 w w [0227] The ratio of the mass of the covering substance after dropping to the mass of the covering substance before dropping was almost the same value between the case 5 of being covered only with sample C and the case of being covered with each of the materials in which gypsum was added to sample C at mass ratios of 90%:10%, 80%:20%, and 50%:50%; thus, it has been found that a rice seed can be covered with a material in which gypsum is added to steelmaking slag. PCT/JP2016/070993 64/100 [0228] Drying was performed for 24 hours and it was checked that the entire covering substance was sufficiently solidified, and then a germination test was performed. A piece of circular filter paper (diameter: 11 em) was laid over a plastic 5 laboratory dish with a diameter of 11 em. Distilled water was added, and the piece of filter paper was shallowly immersed in the distilled water. 20 rice seeds covered only with sample C and 20 rice seeds covered with each of the materials in which gypsum was added to sample C were put individually on the pieces of filter paper shallowly immersed in the distilled water. Each laboratory dish was placed into a 10 constant temperature oven of 3 0°C in a state where an upper cover was laid on the laboratory dish, and a germination test was performed. On the 7th day, the number of germinated seeds was measured for the laboratory dish of each sample, and the germination rate was calculated. In addition to the germination test using the notstarch- treated rice seeds, also a germination test nsing rice seeds that were treated 15 with starch by the method described in Test Example 6 was similarly performed for companson. Table 23 below is the results of the germination rate. [0229] [Table 23] 65/100 [0230] E 0 u" Gi1" + ·;:: ~ ~ 0 0 ~ 0 0# 0 "u ~ E Sl 0 00 0 00 "00' PCT/JP2016/070993 0 "' 0 00 "00' "00' g~--~1-----+----~ i c :•8 .§c ! 0 ,13 0 " ~ ·cc ~ 0 0 0 z "00' "00' &~--~,~---+----~ 0 0 ·c In the case of being covered only with sample C and in the cases where the ratio at which gypsum was added to sample C was up to 80%:20%, the germination PCT/JP2016/070993 66/100 rate was 80% or more, which was a high germination rate like in the not-covered seeds, in both the not-starch-treated rice seeds and the starch-treated rice seeds. On the other hand, the germination rate of the seeds covered with the material in which the ratio at which gypsum was added to sample C was 50%:50% was 40% and 50%, 5 which were low. Thus, it is presumed that the upper limit of the ratio at which gypsum is added to steelmaking slag on the occasion when a material in which gypsum is added to steelmaking slag is used for the covering of a seed is appropriately 20%. [0231] 10 [Test Example 9] (use of iron powder as additive) Steelmaking slag sample C described in Test Example l, materials in which iron powder was added to sample C at mass ratios of 80%:20%, 50%:50%, and 20%:80%, and iron powder were prepared. Sample C, each of the materials in which iron powder was added to sample C, or iron powder was suspended in water 15 so that the ratio to water might be 66 mass%, 20 Koshihikari seeds were put into the suspension and stirred, and the seeds were extracted and dried at room temperature for 24 hours; thus, rice seeds covered only with sample C, rice seeds covered with each of the materials in which iron powder was added to sample C, and rice seeds covered only with iron powder were produced. Further, 20 Koshihikari seeds were 20 soaked for 10 minutes in a liquid in which starch was suspended in water so that the concentration might be 50 mass%, and then the seeds were extracted from the starch suspension; also the extracted 20 Koshihikari seeds were similarly put into a suspension of sample C, a suspension of each of the materials in which iron powder was added to sample C, or a suspension of iron powder and stirred, and the seeds 25 were extracted and dried at room temperature for 24 hours; thus, starch-treated rice seeds covered with sample C, starch-treated rice seed covered with each of the materials in which iron powder was added to sample C, and starch-treated rice seeds covered with iron powder were produced. 30 [0232] Table 24 below shows the average mass per seed of the not-starch-treated rice seeds covered with sample C, the not-starch-treated rice seeds covered with each PCT/JP2016/070993 67/100 of the materials in which iron powder was added to sample C at mass ratios of 80%:20%, 50%:50%, and 20%:80%, and the not-starch-treated rice seeds covered with iron powder. Also the average mass per seed of not -covered rice seeds is shown as well. Further, the mass of the not-covered seed was subtracted from the 5 mass of the covered rice seed to calculate the mass of the covering substance, and the results are shown in Table 24 as well. Also the ratio of the mass of the covering substance to the mass of the not -covered seed is shown. [0233] [Table 24] ~ 0 N "-'"' ~ (T,bl, 24) ------------------------- Mass of rice seed (g) Mass of covering substance (g) Mass of covering substance/ Mass of not-covered seed Mass of rice seed and mass of covering substance per rice seed (not starch-treated seed) Covered only with sample C Sample C 80% + iron powder Sample C 50% + iron powder Sample 0 20% + iron powder 20% covering 50% covering 80% covering 0_0420 0,0438 0.0475 0.0497 0.0140 0.0158 0.0195 0.0217 0.50 0.56 0.70 0.78 Covered only with iron Not-covered rice seed powder 0.0520 0.0280 0.0240 - 0.86 - 000 ~ ~ 0 0 '"0 Q ~ '"0 0,".. ".. "0_,' 0 ""w"' 5 PCT/JP2016/070993 69/100 As shown in Table 24, since iron powder has a larger specific gravity than steelmaking slag, the mass of the covering substance tended to become larger as the existence ratio of iron powder became larger. [0235] Table 25 below shows the average mass per seed of the starch-treated rice seeds covered with sample C, the starch-treated rice seeds covered with each of the materials in which iron powder was added to sample C at mass ratios of 80%:20%, 50%:50%, and 20%:80%, and the starch-treated rice seeds covered with iron powder. Further, the mass of the not -covered seed was subtracted from the mass of the 10 covered rice seed to calculate the mass of the covering substance, and the results are shown in Table 25 as well. Also the ratio of the mass of the covering substance to the mass of the not-covered seed is shown. [0236] [Table 25] ~ 0 N w c:::l (Table 25) . . ... . ·· ....... Mass of rice seed (g) Mass of covering substance (g) Mass of covering substance/ Mass of not-covered seed MIVI< :lO>O> Ufl IIVt;: l>t::t::dU a<:nllidU lila::.;, Ufl VUVt:::llll O>UbU: :>U:HIVt:: tH IIVt:: O>t::tldU (l, t;LdiLiihi-U O::o:Ht::U l;t;lt:JdU)) Covered only with sample C Sample C 80% + iron powder Sample C 50% + iron powder 20% covering 50% covering 0.0581 0.0602 0.0618 0.0301 0.0322 0.0338 1.08 1 .1 5 1 .21 Sample C 20% + iron powder Covered only with iron 80% covering powder 0.0634 0.0660 0.0354 0.0380 1.26 1.36 --.l 0 ~ ~ 0 0 '<::1 ~ "0 "0 " "O"'l _0, 0 ""c.o'' PCT/JP2016/070993 711100 In the starch-treated seed, the mass of the covering substance was a larger value than in the case of the not-starch-treated seed shown in Table 24. Thus, it can be seen that, by using a starch-treated seed, it becomes possible to produce not only a rice seed covered with steehnaking slag but also a rice seed in which iron powder is 5 added to steelmaking slag and a rice seed in which a larger amount of iron powder is adhered as a covering substance. [0238] 20 not-starch-treated rice seeds covered with sample C, 20 not-starchtreated rice seeds covered with each of the materials in which iron powder was added 10 to sample Cat mass ratios of 80%:20%, 50%:50%, and 20%:80%, and 20 not-starchtreated rice seeds covered with iron powder were naturally dropped once onto an iron plate from a position at a height of 20 em. The seeds dropped on the iron plate were collected, and the mass was measured to investigate the mass of the covering substance after dropping; and the ratio of the mass of the covering substance after 15 dropping to the mass of the covering substance before dropping was calculated; the results are shown in Table 26 below. claims. A steelmaking slag-coated seed comprising: a seed; and PCT/JP2016/070993 a steelmaking slag layer formed on an outside of the seed, wherein the steelmaking slag layer is a covering layer made of steelmaking slag powder obtained by pulverizing steelmaking slag, and the steelmaking slag contains 1 0 mass% or more iron and 3 0 mass% or more calcium relative to all components of the steelmaking slag.Claim2 The steelmaking slag-coated seed according to claim 1, wherein the seed is a seed of a rice plant. 15 Claim 3 The steelmaking slag-coated seed according to claim 1 or 2, wherein the steelmaking slag contains 10 mass% to 30 mass% iron and 30 mass% to 50 mass% calcium relative to all the components of the steelmaking slag. 20 Claim 4 25 A steelmaking slag-coated seed, wherein a seed is covered with steelmaking slag powder containing 25 mass% or more and 50 mass% or less CaO and 8 mass% or more and 30 mass% or less Si02. Claim 5 The steelmaking slag-coated seed according to claim 4, wherein the steelmaking slag powder fnrther contains 1 mass% or more and 20 mass% or less MgO, 1 mass% or more and 25 mass% or less Ah03, 5 mass% or 30 more and 35 mass% or less Fe, 1 mass% or more and 8 mass% or less Mn, and 0.1 mass% or more and 5 mass% or less P20 5. PCT/JP2016/070993 96/100 Claim 6 A steelmaking slag-coated seed, wherein a seed is covered with one or both of dephosphorization slag and 5 decarbnrization slag that are kinds of steelmaking slag powder. 10 15 20 Claim 7 Claim 8 The steelmaking slag-coated seed according to any one of claims 4 to 6, wherein the steelmaking slag powder has a particle size of 600 J.tm or less .. The steelmaking slag-coated seed according to any one of claims 1 to 7, wherein the steelmaking slag powder has a particle size of 600 J.tm or less, and contains powder with a particle size of 45 f!m or less at 20% or more. Claim 9 The steelmaking slag-coated seed according to any one of claims 4 to 8, wherein the seed is covered with a mixture of the steelmaking slag powder and one or both of gypsum and iron powder. Claim 10 The steelmaking slag-coated seed according to any one of claims 1 to 9, wherein the seed is a seed covered with starch. 25 Claim 11 30 The steelmaking slag-coated seed according to any one of claims 1 to I 0, wherein a surface of the seed is further covered with gypsum. Claim 12 The steelmaking slag-coated seed according to any one of claims 1 to ll, wherein a covering portion of the seed further contains molasses. 5 97/100 Claim 13 A method for producing a steelmaking slag-coated seed, the steelmaking slag-coated seed including a seed and PCT/JP2016/070993 a steelmaking slag layer formed on a surface of the seed, the method comprising: a steehnaking slag pulverization process of pulverizing, as steelmaking slag serving as a material of the steelmaking slag layer, steelmaking slag containing l 0 10 mass% or more iron and 30 mass% or more calcium relative to all components of the steelmaking slag into powder; a seed soaking process of incorporating water into a seed before coating; and a steehnaking slag coating process of mixing steelmaking slag powder 15 obtained in the steelmaking slag pulverization process and a seed obtained in the seed soaking process and thereby forming a steelmaking slag layer made of the steelmaking slag powder on a surface of the seed. 20 25 Claim 14 The method for producing a steelmaking slag-coated seed according to claim 13, wherein the seed is a seed of a rice plant. Claim 15 The method for producing a steelmaking slag-coated seed according to claim 13 or 14, wherein, in the steelmaking slag pulverization process, the steelmaking slag is pulverized into steelmaking slag powder with a particle size of 600 1-1m or less. 30 Claim 16 The method for producing a steelmaking slag-coated seed according to any 5 PCT/JP2016/070993 98/100 one of claims 13 to 15, wherein the steelmaking slag powder obtained in the steelmaking slag pulverization process contains powder with a particle size of 45 11m or less at 20% or more. Claim 17 A method for producing a steelmaking slag-coated seed comprising: covering a seed with a mixture obtained by mixing steelmaking slag powder containing 25 mass% or more and 50 mass% or less CaO and 8 mass% or more and 10 30 mass% or less Si02, and water; and solidifYing the mixture. Claim 18 The method for producing a steelmaking slag-coated seed according to 15 claim 17, 20 wherein the steelmaking slag powder further contains 1 mass% or more and 20 mass% or less MgO, 1 mass% or more and 25 mass% or less Ah03, 5 mass% or more and 35 mass% or less Fe, 1 mass% or more and 8 mass% or less Mn, and 0.1 mass% or more and 5 mass% or less P20 5. Claim 19 A method for producing a steelmaking slag-coated seed comprising: covering a seed with a mixture obtained by mixing one or both of dephosphorization slag and decarburization slag that are kinds of steelmaking slag 25 powder, and water; and solidifYing the mixture. Claim 20 The method for producing a steelmaking slag-coated seed according to any 30 one of claims 17 to 19, wherein the seed 1s covered with a mixture obtained by m1xmg the 5 PCTIJP20l61070993 991100 steelmaking slag powder, water, and one or both of gypsum and iron powder, and the mixture is solidified. Claim 21 The method for producing a steelmaking slag-coated seed according to any one of claims 17 to 20, wherein the mass ratio of water in the mixture is 10 mass% or more and 80 mass% or less relative to the total mass of the miA'Lure. 10 Claim 22 15 20 25 The method for producing a steelmaking slag -coated seed according to any one of claims 17 to 21, wherein the water is water containing 10 mass% or more and 50 mass% or less molasses. Claim23 The method for producing a steelmaking slag-coated seed according to any one of claims 17 to 22, wherein a seed soaked in a starch aqueous solution is used as the seed. Claim 24 The method for producing a steelmaking slag-coated seed according to any one of claims 17 to 23, wherein a surface ofthe solidified mixture is further covered with gypsum. Claim 25 The method for producing a steelmaking slag-coated seed according to any one of claims 17 to 24, wherein a smface of the solidified mixture is further wetted with water 30 containing 0.5 mass% or more and 5 mass% or less sodium alginate, and then the solidified mixture is dried.