Laminated body for raising rice seedlings, mat seedlings, rice seedling raising box, and method for manufacturing rice seedling raising box

Abstract

The present invention relates to a laminate for a paddy rice seedling nursery, said laminate including a bed soil layer and a cover soil layer, wherein one or both of the bed soil layer and the cover soil layer is a water-absorbing resin layer that includes a particulate water-absorbing resin, the water-absorbing resin is disposed such that at least some paddy rice can come into contact with the water-absorbing resin, and the water-absorbing resin content in the laminate for a paddy rice seedling nursery is 1 to 5,000 g / m2.

Description

[Technical Field]

[0001] The present invention relates to a laminate for raising rice seedlings, which comprises a bed soil layer and a cover soil layer. [Background technology]

[0002] With the aging of agricultural workers, there is an increasing demand for reducing the burden of agricultural work. Furthermore, with the chronic depletion of water resources, there is a demand for the effective and appropriate use of agricultural water, and for the establishment of technologies for maintaining or increasing agricultural yields even with smaller irrigation volumes or less frequent irrigation than before. Rice seedlings are usually raised in seedling boxes containing culture soil and seeds, but these boxes are heavy and require irrigation multiple times a day, placing a heavy burden on agricultural workers.

[0003] In an attempt to solve these problems, the use of superabsorbent polymers has been investigated (see, for example, Patent Document 1). Superabsorbent polymers can hold an extremely large amount of water, tens to hundreds of times their own weight, and therefore offer the advantage of reducing the weight of the culture soil and / or the load of irrigation. Patent Documents 1 and 2 disclose the use of a water-absorbent polymer mixed with granular culture soil as a culture medium for raising rice seedlings. However, when a water-absorbent resin and granular culture soil are premixed, differences in density and particle size between the water-absorbent resin and the culture soil can cause the water-absorbent resin and the culture soil to separate during transportation or storage, or due to vibration in the hopper of a seed drill, making it difficult to introduce a consistent composition into seedling trays. Meanwhile, Patent Document 2 discloses the use of granular culture soil containing water-absorbent resin, which is premixed with soil and water-absorbent resin and then granulated. However, when water-absorbent resin is present inside the granular culture soil, the water absorption rate decreases, reducing the productivity of seedling tray production. Furthermore, the expansion of the water-absorbent resin causes the granular culture soil to collapse, reducing the permeability of the medium. It has also been shown that direct contact with water-absorbent resin can adversely affect seed germination or plant growth (especially root growth) (Patent Document 3 or Non-Patent Document 1).

[0004] As a means for solving such problems, Patent Document 4 discloses a sheet-like composition in which a water-absorbent resin is sandwiched between paper or the like, and discloses that the root growth is not inhibited because the water-absorbent resin does not come into direct contact with the roots. Furthermore, Patent Document 5 discloses a seedling raising box in which a water-absorbent resin layer is provided on the bottom surface, and a culture soil layer, a seed layer, and a culture soil layer are arranged on top of that in that order. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 64-51028 [Patent Document 2] Japanese Patent Application Publication No. 56-8619 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-148163 [Patent Document 4] Japanese Patent Application Publication No. 6-217636 [Patent Document 5] Utility Model Registration No. 3193812 [Non-patent literature]

[0006] [Non-Patent Document 1] Sugimura, Y. et al., Use of superabsorbent polymers as greening materials, Greening Technology, 9(2), 11-15, 1983 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the sheet containing the water-absorbent resin disclosed in Patent Document 4 cannot be used to make seedling trays using the hopper of a seed drill, making it difficult to manufacture a large number of seedling trays. Furthermore, if the sheet is easily disintegrated by water, direct contact between the roots and the water-absorbent resin will hinder growth, while if the sheet is too strong, it will interfere with planting using a rice transplanter. The method of Patent Document 5 not only complicates the manufacturing process, but also has little effect in reducing the weight of the seedling raising boxes by reducing the amount of culture soil.

[0008] In view of these, the problem that the invention aims to solve is to provide a laminate for raising rice seedlings that solves the problems of the past, i.e., a laminate for raising rice seedlings that reduces the burden of agricultural work (for example, weight reduction and / or reduction of irrigation load) while not inhibiting the growth of rice. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have conducted detailed studies on a laminate for raising rice seedlings, and have completed the present invention. That is, the present invention includes the following preferred embodiments. [1] A laminated body for raising paddy rice seedlings, comprising a bed soil layer and a cover soil layer, wherein one or both of the bed soil layer and the cover soil layer is a water-absorbent resin layer containing a particulate water-absorbent resin, and the water-absorbent resin is arranged so that at least a part of the paddy rice can come into contact with the water-absorbent resin, and the content of the water-absorbent resin in the laminated body for raising paddy rice seedlings is 1 to 5000 g / m 2 This is a laminate for raising rice seedlings. [2] The layered product for raising rice seedlings according to [1], wherein the content of the soil in the water-absorbent resin layer is 20% by mass or less based on the mass of the water-absorbent resin layer. [3] The content (X1) (g / m) of the water-absorbent resin in the bed soil layer 2 ) and the content (X2) (g / m ) of the water-absorbent resin in the covering layer 2 ) is the following formula: Content (X2) / Content (X1)≦0.2 or Content (X2) / Content (X1)≧5 The layered product for raising rice seedlings according to [1] or [2] above, which satisfies the above. [4] The content (X2) of the water-absorbent resin in the covering layer is 70 g / m 2 The layered product for raising rice seedlings according to any one of [1] to [3] above, which is as follows: [5] The layered product for raising rice seedlings according to any one of [1] to [4], wherein the water-absorbent resin layer contains more than 80% by mass of the water-absorbent resin based on the mass of each layer. [6] The laminated body for raising rice seedlings contains water, and the water content is 300 to 15,000 g / m2 The layered product for raising rice seedlings according to any one of [1] to [5] above, [7] In the water-absorbent resin layer, the content (X) of the water-absorbent resin (g / m 2 ) and water content (Y) (g / m 2 ) is represented by the following formula (I): 5≦Content (Y) / Content (X)≦500 (I) The layered product for raising rice seedlings according to any one of [1] to [6] above, which satisfies the above. [8] One of the bed soil layer and the covering soil layer is the water-absorbent resin layer, and the other is a culture soil layer containing more than 20% by mass of culture soil based on the mass of the layer, and the content of the culture soil layer in the layered product for raising rice seedlings is 1000 to 50000 g / m 2 The layered product for raising rice seedlings according to any one of [1] to [7] above, [9] The layered product for raising rice seedlings according to [8], wherein the bed soil layer is the water-absorbent resin layer.

[10] The layered product for raising rice seedlings according to [8] or [9], wherein the culture soil is granular and has an average particle size of 0.2 to 20 mm.

[11] The layered product for raising rice seedlings according to any one of [1] to

[10] above, wherein the thickness of the bed soil layer is 0.01 to 100 mm.

[12] The layered product for raising rice seedlings according to any one of [1] to

[11] above, wherein the thickness of the covering soil layer is 0.1 to 100 mm.

[13] The laminate for raising rice seedlings according to any one of [1] to

[12] above, wherein the water-absorbent resin has a volume average particle size of 1 to 10,000 μm.

[14] The laminate for raising rice seedlings according to any one of [1] to

[13] above, wherein the water-absorbent resin contains a carboxyl group.

[15] The laminate for raising rice seedlings according to any one of [1] to

[14] above, wherein the water-absorbent resin has potassium ions as counter cations.

[16] The laminate for raising rice seedlings according to any one of [1] to

[15] above, wherein the water-absorbent resin is a vinyl alcohol polymer.

[17] The laminate for raising rice seedlings described in

[16] , wherein the vinyl alcohol units of the vinyl alcohol polymer are acetalized with one or more acetalizing agents selected from the group consisting of glyoxylic acid and glyoxylic acid derivatives.

[18] A laminate for raising rice seedlings as described in

[16] or

[17] , wherein the vinyl alcohol polymer contains one or more monomer structural units selected from the group consisting of acrylic acid, methacrylic acid, and derivatives thereof.

[19] A laminate for raising rice seedlings according to any one of [1] to

[18] , wherein in a mixture of the water-absorbing resin and pure water having a mass 50 times that of the water-absorbing resin, the pure water having a water potential of 0 to 3 accounts for 10 mass% or more based on the mass of the pure water in the mixture.

[20] A layered product for raising rice seedlings according to any one of [1] to

[19] , wherein the bed soil layer or the covering soil layer further contains one or more components selected from the group consisting of peat moss, coco peat, rice husks, vermiculite, perlite, fertilizers and pesticides.

[21] The layered product for raising rice seedlings according to any one of [1] to

[20] above, further comprising rice.

[22] The layered product for raising rice seedlings described in

[21] , wherein the rice is in the form of seeds.

[23] A layered product for raising rice seedlings as described in

[22] , wherein the rice seeds are present in an area within 20 mm from the boundary line between the bed soil layer and the covering soil layer.

[24] The content of the rice seeds is 50 to 5,000 g / m 2 The layered product for raising rice seedlings according to

[22] or

[23] above.

[25] The layered product for raising rice seedlings described in

[21] , wherein the rice is in the state of seedlings.

[26] The mass of the laminate for raising rice seedlings is 28 kg / m 2 The laminate for raising rice seedlings according to any one of [1] to

[25] above, which is as follows:

[27] A mat seedling comprising the layered product for raising rice seedlings described in

[25] .

[28] A paddy rice seedling raising box into which the laminate for raising paddy rice seedlings according to any one of [1] to

[26] above and water have been introduced.

[29] A method for manufacturing a rice seedling raising box into which a layered structure for raising rice seedlings including a bed soil layer and a covering soil layer is introduced, The method includes the steps of introducing bed soil into a paddy rice seedling raising box, sowing paddy rice in the form of seeds, and introducing cover soil, wherein one or both of the bed soil and the cover soil contains a particulate water-absorbent resin, and the water-absorbent resin is arranged so that at least a part of the paddy rice comes into contact with the water-absorbent resin, and the content of the water-absorbent resin in the layered body for raising paddy rice seedlings is 1 to 5000 g / m 2 That's the method.

[30] The method described in

[29] , wherein one or both of the bed soil and the cover soil contains more than 80% by mass of the water-absorbent resin based on the mass of each soil.

[31] The method according to

[29] or

[30] , wherein the bed soil and / or cover soil is introduced using a hopper. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a laminate for raising rice seedlings that solves the conventional problems, i.e., a laminate for raising rice seedlings that reduces the burden of agricultural work (e.g., weight reduction and / or reduction of irrigation load) while not inhibiting the growth of rice. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing a configuration of one embodiment of a laminate for raising rice seedlings of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

[0013] The layered product for raising rice seedlings of the present invention is a medium for raising rice seedlings, which comprises a bed soil layer and a cover soil layer. One or both of the bed soil layer and the cover soil layer is a water-absorbent polymer layer containing a particulate water-absorbent polymer, and the water-absorbent polymer is arranged so that at least a part of the rice plants can come into contact with the water-absorbent polymer. The content of the water-absorbent polymer in the layered product for raising rice seedlings is 1 to 5,000 g / m.2 is. As shown in Figure 1, a layered body 1 for raising rice seedlings according to one embodiment of the present invention includes a bed soil layer 2 and a cover soil layer 3. In Figure 1, the dimensions and proportions of each component have been adjusted appropriately to make the drawing easier to see.

[0014] When the layered structure for raising rice seedlings contains seeds, in the present invention, the layer below the seeds is referred to as the bed soil layer, and the layer above the seeds is referred to as the cover soil layer. When the layered structure for raising rice seedlings does not contain seeds, the layer below the boundary line of the layer closest to the center of the layer in the thickness direction of the layered structure for raising rice seedlings is referred to as the bed soil layer, and the layer above the boundary line is referred to as the cover soil layer. The bed soil layer and the cover soil layer are each preferably a single layer, but may be multiple layers.

[0015] The thickness of the bed soil layer is preferably 0.01 to 100 mm, more preferably 0.05 to 30 mm, even more preferably 1 to 15 mm, and particularly preferably 2 to 10 mm. When the thickness of the bed soil layer is within the above range, water retention is likely to be high, and well-grown seedlings are likely to be obtained. The thickness of the covering soil layer is preferably 0.1 to 100 mm, more preferably 1 to 50 mm, even more preferably 2 to 20 mm, and particularly preferably 3 to 10 mm. When the thickness of the covering soil layer is within the above range, root uprising and exposure after emergence are less likely to occur, making it easier to obtain well-grown seedlings. The thickness of the bed soil layer and the cover soil layer can be determined by the method described in the Examples below. In the present invention, the thickness of the bed soil layer and the cover soil layer refers to the value in a water-absorbed state. In the present invention, "water-absorbed state" refers to the state in which the rice seedling raising laminate contains water. For example, a rice seedling raising laminate after irrigation and a rice seedling raising box into which water has been introduced and the rice seedling raising laminate and water are in a water-absorbed state. More specifically, it is preferable to measure the thickness when the water-absorbent resin contains water (when the expansion of the water-absorbent resin due to water absorption has been completed). On the other hand, the content of the water-absorbent resin, the content of the culture soil, the culture soil layer, and the fertilizer described later, the average particle size of the granular culture soil described later, and the volume average particle size of the granular water-absorbent resin described later each refer to values ​​in a dry state. In the present invention, the "dry state" means a state in which the water-absorbent resin and the culture soil do not contain volatile components such as water or organic solvents. For example, the water-absorbent resin and the culture soil can be brought into a dry state by vacuum drying at 40°C until the mass of the water-absorbent resin and the culture soil becomes constant.

[0016] In a preferred embodiment of the present invention, the content (X1) (g / m) of the water-absorbent resin in the bed soil layer 2 ) and the content (X2) (g / m ) of the water-absorbent resin in the covering layer 2 ) is the following formula: Content (X2) / Content (X1)≦0.2 or Content (X2) / Content (X1)≧5 The ratio of content (X2) / content (X1) is more preferably 0.1 or less or 10 or more, further preferably 0.05 or less or 50 or more, and particularly preferably 0.01 or less or 100 or more. If only one of the content (X2) and the content (X1) is 0 g / m 2 It can be said that the above formula is satisfied even in this case. When the content (X2) / content (X1) is equal to or less than the upper limit or equal to or more than the lower limit, water retention and breathability tend to be high, and good growth of paddy rice is likely to be obtained. Here, the contents (X1) and (X2) of the water-absorbent resin mean values ​​in a dry state, as described above.

[0017] In a preferred embodiment of the present invention, the content (X2) of the water-absorbent resin in the covering layer is 70 g / m 2 Less than 50 g / m 2 Less than 30 g / m, more preferably 2 More preferably, 20 g / m or less 2 Below 10 g / m, particularly preferably 2 or less, even more preferably 5 g / m 2 More particularly preferably 1 g / m or less 2 or less, 0 g / m 2When the content (X2) is equal to or less than the upper limit, the air permeability is high and good growth of paddy rice is likely to be achieved.

[0018] [Water absorbent resin layer] One or both of the bed soil layer and the cover soil layer is a water-absorbent resin layer containing a particulate water-absorbent resin. That is, the water-absorbent resin may be contained in either the bed soil layer or the cover soil layer, or in both the bed soil layer and the cover soil layer. From the viewpoints of germination, good growth, and suppression of exposure and root uprooting, it is preferable that the water-absorbent resin be contained in the bed soil layer. When a water-absorbent resin is used in both the bed soil layer and the cover soil layer, the water-absorbent resin used in the bed soil layer and the water-absorbent resin used in the cover soil layer may be the same or different. The content of the water-absorbent resin in each water-absorbent resin layer is preferably more than 80% by mass, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the mass of each water-absorbent resin layer. The content of the water-absorbent resin in the water-absorbent resin layer may be 100% by mass, that is, the water-absorbent resin layer may consist solely of a water-absorbent resin. In the present invention, even when the bed soil layer and / or the covering soil layer are water-absorbent resin layers consisting only of a water-absorbent resin, such layers are referred to as the "bed soil layer" and / or the "covering soil layer", respectively. When one or both of the bed soil layer and the covering soil layer are water-absorbent resin layers, the burden of agricultural work can be reduced.

[0019] Rice seedling raising media are required to promote good rice seed emergence and growth. Specifically, seeds are required to sown in the rice seedling raising media and germinate after a certain period (usually about two days) in a germination chamber. After a certain period (usually about two to three weeks), the roots of the grown rice plants are required to intertwine and spread out, resulting in a mat of seedlings suitable for placement in a rice transplanter. Therefore, the inventors have discovered that the amount of water-absorbent resin per unit area of ​​the rice seedling raising media is extremely important. Too little water-absorbent resin reduces the strength of the gel-state water-absorbent resin and increases the amount of water not absorbed by the water-absorbent resin. This leads to seed burial, inhibiting oxygen supply to the seeds and potentially preventing seed emergence. On the other hand, too much water-absorbent resin strongly retains water in the water-absorbent resin, reducing the water potential of the medium and impeding water supply to the seeds. The present invention focuses on and specifies the content of a specific water-absorbent resin. That is, in the present invention, the content of the water-absorbent resin per unit area of ​​the laminate for raising rice seedlings is 1 to 5000 g / m 2 If the content is within this range, seeds can germinate and grow well even when they are in contact with the water-absorbent resin, and the burden of agricultural work can be reduced. The content of the water-absorbent resin in the laminate for raising rice seedlings is preferably 1 to 3000 g / m 2 , more preferably 5 to 2000 g / m 2 , and more preferably 10 to 1000 g / m 2 , particularly preferably 50 to 500 g / m 2 , more preferably 100 to 300 g / m 2 When the content is within the above range, better seed emergence and growth and further reduction in the burden of agricultural work are likely to be achieved. The content of the water-absorbent resin in the laminate for raising rice seedlings can be determined by the method described in the Examples below. In the present invention, the area of ​​the laminate for raising rice seedlings means the area of ​​the upper surface of the laminate for raising rice seedlings (the surface of the covered soil that is exposed above the ground).

[0020] The water-absorbent resin is arranged so that at least a portion of the rice plants can come into contact with the water-absorbent resin. If at least a portion of the rice plants cannot come into contact with the water-absorbent resin, for example, if a sheet or soil is present between the rice seeds and the water-absorbent resin, the structure of the layered body for raising rice seedlings becomes complicated, and it becomes impossible to prepare a rice seedling raising box using the hopper of a seed sowing machine, which reduces the productivity of the layered body for raising rice seedlings or the rice seedling raising box.

[0021] [Water absorbent resin] The water-absorbent resin in the present invention is not particularly limited. Examples of water-absorbent resins that can be used include acrylate polymers, isobutylene-maleate copolymers, starch-acrylate copolymers, carboxymethylcellulose polymers, acrylate-acrylamide copolymers, vinyl acetate-acrylate copolymers, saponified acrylonitrile polymers, saponified starch-acrylonitrile copolymers, polysaccharide-acrylate copolymers, alginate polymers, sulfonate polymers, vinyl acetate-maleic anhydride copolymers, N-vinylacetamide polymers, acrylamide polymers, ethylene glycol polymers, and vinyl alcohol polymers. These polymers can be used alone or in combination of two or more.

[0022] From the viewpoint of easily exhibiting excellent water absorption or water absorption rate, the water-absorbent resin preferably contains a carboxyl group. Examples of such water-absorbent resins include acrylate polymers, isobutylene-maleate copolymers, starch-acrylate copolymers, carboxymethylcellulose polymers, acrylate-acrylamide copolymers, vinyl acetate-acrylate copolymers, polysaccharide-acrylate copolymers, vinyl acetate-maleic anhydride copolymers, acrylamide polymers, and vinyl alcohol polymers having a carboxyl group.

[0023] From the viewpoint of easily achieving a superior water absorption rate and from the viewpoint of rice growth, the water-absorbent resin preferably has potassium ions as counter cations.

[0024] From the viewpoints of ease of production and water retention, the water-absorbent resin preferably contains an acrylate polymer, an acrylate-acrylamide copolymer, or a vinyl alcohol polymer, and more preferably an acrylate polymer, an acrylate-acrylamide copolymer, or a vinyl alcohol polymer. Furthermore, from the viewpoints of weather resistance and the ability to supply retained water to paddy rice (water potential), the water-absorbent resin further preferably contains a vinyl alcohol polymer, and in one preferred embodiment, the water-absorbent resin is a vinyl alcohol polymer.

[0025] Rice plants and culture media have water potentials that correspond to their ability to adsorb water or their moisture content, and the stronger the ability to adsorb water, the lower the water potential tends to be. Water tends to move from a high water potential to a low water potential, so if the water potential of the culture media is not higher than that of the rice, it will be difficult for the rice to absorb the water and it will be prone to withering. Water in the culture media with a water potential (pF) of 0 to 3 is called available water and is easily available to the rice.

[0026] Therefore, in a preferred embodiment of the present invention, in a mixture of a water-absorbent resin and pure water having a mass 50 times that of the water-absorbent resin, the amount of pure water having a water potential of 0 to 3 is 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and particularly preferably 40% by mass or more, based on the mass of the pure water in the mixture. There are no particular limitations on the upper limit of the content of pure water having a water potential of 0 to 3 in the mixture. The content of pure water having a water potential of 0 to 3 in the mixture is usually 80% by mass or less. The above content can be achieved, for example, by using a vinyl alcohol polymer, a polyethylene glycol polymer, or a mixture thereof as the water-absorbent resin. The above content can be measured by the method described in the Examples below.

[0027] The pure water absorption capacity of the water-absorbent resin is preferably 5 g / g or more, more preferably 10 g / g or more, even more preferably 30 g / g or more, even more preferably 50 g / g or more, and even more preferably 80 g / g or more, relative to the mass of the water-absorbent resin, and is preferably 2000 g / g or less, more preferably 1000 g / g or less, even more preferably 500 g / g or less, even more preferably 300 g / g or less, and even more preferably 200 g / g or less. When the pure water absorption capacity of the water-absorbent resin is equal to or greater than the above-mentioned lower limit, the amount of water that can be retained by the water-absorbent resin layer increases, which tends to enhance the effect of reducing the amount of irrigation and the frequency of irrigation. When the pure water absorption capacity of the water-absorbent resin is equal to or less than the above-mentioned upper limit, excessive swelling can be prevented, thereby preventing seed displacement or overflow of the rice seedling raising laminate from the seedling raising box, and the available water when the water-absorbent resin is dried tends to increase. The pure water absorption of the water-absorbent resin can be adjusted to be equal to or greater than the above-mentioned lower limit or equal to or less than the above-mentioned upper limit by optimizing the amount of carboxyl groups, the degree of crosslinking, the crosslink distribution, and the shape of the water-absorbent resin. The pure water absorption of the water-absorbent resin can be measured by the method described in the Examples below.

[0028] <Vinyl alcohol polymer> Examples of the vinyl alcohol polymer (hereinafter sometimes referred to as the vinyl alcohol polymer (A)) include polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and those in which the vinyl alcohol unit is acetalized with an acetalizing agent. As mentioned above, from the viewpoint of easily exhibiting excellent water absorption or water absorption rate, the vinyl alcohol polymer (A) preferably has a carboxyl group. The content of the vinyl alcohol polymer (A) in the water absorbent resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, and may be 100% by mass.

[0029] When the vinyl alcohol polymer (A) has a carboxyl group, examples of the vinyl alcohol polymer (A) include (i) a saponified copolymer of a vinyl ester and one or more selected from a monomer having a carboxyl group and a derivative of the monomer; (ii) a reaction product of a vinyl alcohol polymer and a compound (B) having a functional group (b1) capable of reacting with a hydroxyl group and a carboxyl group and / or a functional group (b2) capable of being derived to a carboxyl group; and the like.

[0030] In the above (i), the monomer having a carboxyl group is not particularly limited, but examples thereof include acrylic acid, methacrylic acid, itaconic acid, maleic acid, etc. Furthermore, derivatives of the above-mentioned monomer having a carboxyl group include anhydrides, esters, neutralized products, etc. of the monomer, such as methyl acrylate, methyl methacrylate, dimethyl itaconate, monomethyl maleate, and maleic anhydride.

[0031] In the above (i), the vinyl ester is not particularly limited, but examples thereof include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl valerate, vinyl stearate, vinyl benzoate, vinyl trifluoroacetate, and vinyl pivalate, with vinyl acetate being preferred.

[0032] The method for producing the saponified product (i) above is not particularly limited, and the product can be produced by carrying out a known polymerization reaction of one or more selected from a monomer having a carboxyl group and a derivative of the monomer with a vinyl ester using a known polymerization initiator, and then carrying out a saponification reaction by a known method.

[0033] In the compound (B) used in the above (ii) having a functional group (b1) capable of reacting with a hydroxyl group and a functional group (b2) capable of being derived to a carboxyl group, the functional group (b1) capable of reacting with a hydroxyl group is not particularly limited, and examples thereof include an aldehyde group, a carboxyl group, an amino group, and derivatives of these functional groups. Among these, from the viewpoint of ease of production or durability of the water-absorbent resin, an aldehyde group and a derivative of an aldehyde group are preferred. That is, as the compound (B), an aldehyde having a carboxyl group and / or a derivative of the aldehyde is preferred.

[0034] That is, the reaction product of the above (ii) is preferably a vinyl alcohol polymer in which at least a part of the vinyl alcohol units is acetalized with one or more selected from aldehydes having a carboxyl group and / or derivatives of the aldehydes [hereinafter, this may be referred to as vinyl alcohol polymer (A-1)].

[0035] The aldehyde having a carboxyl group, which is the compound (B), is not particularly limited, and examples thereof include glyoxylic acid, 2-formylpropanoic acid, 3-formylpropanoic acid, and phthalaldehyde acid. Among these, glyoxylic acid is preferred from the viewpoints of availability and biodegradability. Furthermore, derivatives of the aldehyde having a carboxyl group, which is the compound (B), include anhydrides, hydrates, esters, acetals, and neutralization products of the aldehyde, such as glyoxylates, glyoxylic acid monohydrate, glyoxylic acid esters, and glyoxylic acid dimethyl acetal. Therefore, in a preferred embodiment of the present invention, the vinyl alcohol units of the vinyl alcohol polymer are acetalized with one or more acetalizing agents selected from the group consisting of glyoxylic acid and glyoxylic acid derivatives.

[0036] Counter cations of the glyoxylate salts include alkali metal ions such as sodium ion, potassium ion, and lithium ion; alkaline earth metal ions such as calcium ion and magnesium ion; and organic cations such as ammonium ion and alkylammonium ion. Among these, potassium ion, calcium ion, and magnesium ion are preferred from the viewpoint of easily achieving a superior water absorption rate. Calcium ion is more preferred from the viewpoint of easily maintaining water absorption upon contact with divalent ions contained in the soil, and potassium ion is more preferred from the viewpoint of rice growth.

[0037] Examples of the glyoxylate ester include methyl glyoxylate, ethyl glyoxylate, propyl glyoxylate, isopropyl glyoxylate, butyl glyoxylate, isobutyl glyoxylate, sec-butyl glyoxylate, tert-butyl glyoxylate, hexyl glyoxylate, octyl glyoxylate, and 2-ethylhexyl glyoxylate.

[0038] The method for producing the vinyl alcohol polymer (A-1) is not particularly limited, and the vinyl alcohol polymer (A-1) can be produced by acetalizing at least a portion of the vinyl alcohol units of a vinyl alcohol polymer produced by a known method with one or more selected from an aldehyde having a carboxyl group and a derivative of the aldehyde, in the presence or absence of a catalyst.

[0039] Examples of the catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; organic acids such as carboxylic acids and sulfonic acids; and solid acids such as cation exchange resins and heteropolyacids. These catalysts may be used alone or in combination. Glyoxylic acid is also an acid that promotes the acetalization reaction, and therefore also acts as a catalyst when producing the vinyl alcohol polymer (A-1). In other words, from the viewpoint of ease of post-reaction treatment, a method of using glyoxylic acid as the aldehyde having a carboxyl group when producing the vinyl alcohol polymer (A-1) is preferred.

[0040] The vinyl alcohol polymer used as raw material in the production of vinyl alcohol polymer (A-1) may be any of industrially produced commercial products; those produced by carrying out a known polymerization reaction using a known polymerization initiator in the presence of vinyl carboxylate such as vinyl acetate and other monomers as needed, followed by a known method of saponification; those produced by cationic polymerization and hydrolysis of vinyl ether; those produced by direct polymerization of acetaldehyde; etc., but preferably those produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. The saponification degree of the vinyl alcohol polymer used as raw material is preferably 30 mol% or more, more preferably 60 mol% or more, and in one embodiment of the present invention, from the viewpoint of easily introducing an appropriate amount of carboxyl groups, more preferably 80 mol% or more.

[0041] The degree of acetalization of the vinyl alcohol polymer (A-1) is preferably 0.01 mol% or more and 85 mol% or less. When the degree of acetalization is within this range, water absorbency is easily improved. From the above viewpoints, the degree of acetalization is preferably 0.1 mol% or more, more preferably 1 mol% or more, even more preferably 5 mol% or more, still more preferably 8 mol% or more, particularly preferably 10 mol% or more, and is preferably 80 mol% or less, more preferably 70 mol% or less, even more preferably 60 mol% or less, still more preferably 50 mol% or less, particularly preferably 45 mol% or less, and even more preferably 40 mol% or less.

[0042] From the viewpoint of easily suppressing the elution of the water-absorbent resin during the raising of rice seedlings, in the production of the vinyl alcohol polymer (A-1), an acetalization reaction may be carried out using an aldehyde other than the aldehyde having a carboxyl group and its derivatives in combination. Examples of such an aldehyde include aliphatic aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, i-butyraldehyde, sec-butyraldehyde, and tert-butyraldehyde; and aromatic aldehydes such as benzaldehyde, anisaldehyde, cinnamic aldehyde, 4-benzyloxybenzaldehyde, 3-benzyloxybenzaldehyde, 4-amyloxybenzaldehyde, and 3-amyloxybenzaldehyde. Among these, formaldehyde, acetaldehyde, and n-butylaldehyde are preferred from the viewpoint of ease of production or the water absorbency of the resulting water-absorbent resin. When other aldehydes are used in combination, there are no particular limitations on the amount used, but the amount is usually 0.01 to 30 mol %, preferably 0.1 to 10 mol %, and more preferably 1 to 5 mol % based on the total amount of the aldehyde having a carboxylic acid and its derivative. When the amount of other aldehyde used is equal to or less than the upper limit, the water absorbency of the resulting water-absorbent resin tends to be excellent, while when the amount is equal to or greater than the lower limit, the effect of suppressing leaching of the water-absorbent resin during rice seedling raising, which is achieved by using other aldehydes in combination, is easily obtained. The other aldehydes may be used in the form of derivatives such as acetals.

[0043] In one embodiment of the present invention, when the vinyl alcohol polymer (A) has carboxyl groups, some or all of the carboxyl groups may be in the form of a carboxylate. Examples of counter cations of the carboxylate include alkali metal ions such as lithium ion, sodium ion, potassium ion, rubidium ion, and cesium ion; alkaline earth metal ions such as magnesium ion, calcium ion, strontium ion, and barium ion; other metal ions such as aluminum ion and zinc ion; and onium cations such as ammonium ion, imidazolium ions, pyridinium ions, and phosphonium ions. Among these, potassium ion, calcium ion, and ammonium ion are preferred, with calcium ion being more preferred from the viewpoint of easily maintaining water absorption upon contact with divalent ions contained in soil, and potassium ion being more preferred from the viewpoint of rice growth. Therefore, in a preferred embodiment of the present invention, the vinyl alcohol polymer (A) has a potassium ion as a counter cation. Examples of methods for producing a vinyl alcohol polymer (A) in which some or all of the carboxyl groups are carboxylates include the above method (i) using a neutralized product of a monomer having a carboxyl group; the above method (ii) using a neutralized product of a compound having a carboxyl group and a functional group reactive with a hydroxyl group; and a method in which a vinyl alcohol polymer (A) having a carboxyl group is produced by the above-mentioned various methods and then neutralized; among these, the above method (ii) is preferred.

[0044] In one embodiment of the present invention, when the vinyl alcohol polymer (A) contains carboxyl groups, the amount of carboxyl groups in the vinyl alcohol polymer (A) is preferably 0.1 mol% or more, more preferably 1 mol% or more, particularly preferably 3 mol% or more, and most preferably 5 mol% or more, based on the total structural units of the vinyl alcohol polymer (A). It is preferably 80 mol% or less, more preferably 50 mol% or less, more preferably 40 mol% or less, more preferably 30 mol% or less, even more preferably 25 mol% or less, particularly preferably 20 mol% or less, and most preferably less than 18 mol%. When the amount of carboxyl groups is equal to or greater than the lower limit, the water absorbency of the water-absorbent resin of the present invention is more likely to be excellent. When the amount of carboxyl groups is equal to or less than the upper limit, the water absorbency is more likely to be maintained even when the resin comes into contact with divalent ions contained in soil. Furthermore, the amount of carboxyl groups derived from acrylic acid or a salt thereof, based on the total structural units of the vinyl alcohol polymer, is preferably 20 mol% or less, more preferably 15 mol% or less, particularly preferably 10 mol% or less, and may even be 0 mol%. When the amount of carboxyl groups derived from acrylic acid or a salt thereof among the carboxyl groups is not more than the upper limit, better weather resistance (particularly ultraviolet resistance) is easily obtained. When some or all of the carboxyl groups contained in the vinyl alcohol polymer (A) are in the form of carboxylates, the amount of carboxyl groups mentioned above is the amount of carboxyl groups and carboxylates or the amount of carboxylates.

[0045] The amount of the carboxyl groups in the vinyl alcohol polymer (A) and the amount of the carboxyl groups derived from acrylic acid or a salt thereof among the carboxyl groups can be determined, for example, by the following method: 13 It can be measured by C-NMR (nuclear magnetic resonance spectroscopy), FTIR (Fourier transform infrared spectroscopy), acid-base titration, etc. In the present invention, the term "structural unit" refers to a repeating unit that constitutes a polymer; for example, a vinyl alcohol unit is counted as "1 unit," and a structure in which two vinyl alcohol units are acetalized is counted as "2 units."

[0046] The content of vinyl alcohol structural units in the vinyl alcohol polymer (A) is preferably more than 20 mol%, more preferably 50 mol% or more, and even more preferably 60 mol% or more, and is preferably 98 mol% or less, more preferably 95 mol% or less, and even more preferably 90 mol% or less, based on the total structural units of the vinyl alcohol polymer (A). The content of the vinyl alcohol structural units can be measured, for example, by Fourier transform infrared spectroscopy (FTIR), solid state 13 It can be measured by C-NMR (nuclear magnetic resonance spectroscopy) or can be calculated from the amount of acetic anhydride consumed when reacted with a certain amount of acetic anhydride.

[0047] The vinyl alcohol polymer (A) may contain other structural units besides vinyl alcohol units. Examples of such other structural units include structural units derived from vinyl carboxylates such as vinyl acetate and vinyl pivalate; structural units derived from olefins such as ethylene, 1-butene, and isobutylene; and structural units derived from acrylic acid and its derivatives, methacrylic acid and its derivatives, acrylamide and its derivatives, methacrylamide and its derivatives, maleic acid and its derivatives, and maleimide derivatives. One or more of the other structural units may be contained. Accordingly, in a preferred embodiment of the present invention, the vinyl alcohol polymer contains one or more monomer structural units selected from the group consisting of acrylic acid, methacrylic acid, and their derivatives. The content of the other structural units is preferably 50 mol% or less, more preferably 30 mol% or less, and even more preferably 15 mol% or less, based on the total structural units of the vinyl alcohol polymer (A), and may even be 0 mol%. When the content of the other structural units is equal to or less than the upper limit, the water-absorbent resin of the present invention is likely to achieve superior water absorption and water absorption rate.

[0048] The viscosity-average degree of polymerization of the vinyl alcohol polymer (A) is not particularly limited, but from the viewpoint of ease of production, it is preferably 20,000 or less, more preferably 10,000 or less, even more preferably 4,000 or less, and particularly preferably 3,000 or less. On the other hand, from the viewpoint of the mechanical properties and resistance to elution in water of the water-absorbent resin, it is preferably 100 or more, more preferably 200 or more, and even more preferably 400 or more. The viscosity-average degree of polymerization of the vinyl alcohol polymer (A) can be measured, for example, by a method in accordance with JIS K 6726.

[0049] The water-absorbent resin of the present invention preferably contains a crosslinked structure from the viewpoint of preventing elution of the water-absorbent resin during rice seedling raising. When the water-absorbent resin of the present invention contains a crosslinked structure, it becomes a gel state when absorbing water. The form of the crosslinked structure is not particularly limited, and examples thereof include crosslinked structures by ester bonds, ether bonds, acetal bonds, carbon-carbon bonds, etc.

[0050] An example of the ester bond is an ester bond formed between hydroxyl groups of the vinyl alcohol polymer (A) when the vinyl alcohol polymer (A) has a carboxyl group. An example of the ether bond is an ether bond formed by dehydration condensation between hydroxyl groups of the vinyl alcohol polymer (A). An example of the acetal bond is an acetal bond formed by acetalization reaction between hydroxyl groups of two vinyl alcohol polymers (A) and an aldehyde having a carboxyl group when the vinyl alcohol polymer (A) is produced using the aldehyde. An example of the carbon-carbon bond is a carbon-carbon bond formed by coupling between carbon radicals of the vinyl alcohol polymer (A) when the water-absorbing resin is irradiated with active energy rays. These crosslinked structures may be contained alone or in combination. Among these, crosslinked structures formed by ester bonds and acetal bonds are preferred from the viewpoint of ease of production, and crosslinked structures formed by acetal bonds are more preferred from the viewpoints of water retention and UV resistance during rice seedling raising. Such a crosslinked structure may be formed simultaneously with the acetalization reaction or in a separate step in the step of acetalizing at least a portion of the vinyl alcohol units with, for example, one or more selected from aldehydes having a carboxyl group and their aldehyde derivatives. In the present invention, however, it is preferable to form the crosslinked structure by further adding a crosslinking agent.

[0051] Examples of crosslinking agents include glyoxal, malonaldehyde, succinaldehyde, glutaraldehyde, 1,9-nonanedial, adipaldehyde, malealdehyde, tartaraldehyde, citrualdehyde, phthalaldehyde, isophthalaldehyde, and terephthalaldehyde.

[0052] When a crosslinking agent is added, the amount of the crosslinking agent in the vinyl alcohol polymer (A) is preferably 0.001 mol% or more, more preferably 0.005 mol% or more, even more preferably 0.01 mol% or more, still more preferably 0.03 mol% or more, from the viewpoint of easily maintaining water retention in soil, and is preferably 0.5 mol% or less, more preferably 0.4 mol% or less, even more preferably 0.3 mol% or less.

[0053] The water-absorbent resin contained in the laminate for raising rice seedlings of the present invention is composed of one or more polymers or contains additives in addition to one or more polymers. Examples of such additives include polysaccharides such as starch, modified starch, sodium alginate, chitin, chitosan, cellulose and its derivatives; polyethylene, polypropylene, ethylene-propylene copolymer, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene-styrene copolymer, polyvinyl chloride, polycarbonate resin, polyethylene terephthalate, polybutylene terephthalate, polylactic acid, polysuccinic acid, polyamide 6, polyamide 6·6, polyamide 6·10, polyamide 11, polyamide 12, polyamide 6·12, polyhexamethylenediamine terephthalamide, polyhexamethylenediamine isophthalamide, polynonamethylenediamine terephthalamide, polyphenylene ether, polyoxymethylene, polyethylene glycol, polypropylene glycol, polytrimethylene glycol, polytetramethylene glycol, polyurethane, Resins such as polyvinyl acetate, ethylene-vinyl acetate copolymer, polyacrylic acid, polyacrylic acid ester, polyacrylate, polymethacrylic acid, polymethacrylic acid ester, polymethacrylate, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylate copolymer, and ethylene-methacrylate copolymer; rubbers and elastomers such as natural rubber, synthetic isoprene rubber, chloroprene rubber, silicone rubber, fluororubber, urethane rubber, acrylic rubber, styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer, ester-based thermoplastic elastomer, urethane-based thermoplastic elastomer, and amide-based thermoplastic elastomer; UV absorbers, antioxidants, light stabilizers, plasticizers, organic solvents, defoamers, thickeners, surfactants, lubricants, mildew inhibitors, and antistatic agents. These additives can be used alone or in combination of two or more. When the water-absorbing resin contains additives, the total content thereof may be within a range that does not impair the effects of the present invention, and is usually 30% by mass or less, preferably 20% by mass or less, based on the total mass of the water-absorbing resin.

[0054] The water-absorbent resin contained in the laminate for raising rice seedlings of the present invention is particulate. If the water-absorbent resin is not particulate, for example, in sheet form, it becomes impossible to prepare rice seedling raising boxes using the hopper of a seed sowing machine, resulting in a decrease in productivity of the rice seedling raising boxes. The water-absorbent resin of the present invention preferably has a volume-average particle diameter of 1 to 10,000 μm. The volume-average particle diameter is more preferably 10 μm or more, even more preferably 30 μm or more, particularly preferably 50 μm or more, more preferably 1,000 μm or less, even more preferably 500 μm or less, and particularly preferably 300 μm or less. When the volume-average particle diameter is equal to or greater than the lower limit, excellent handleability is easily obtained, and when it is equal to or less than the upper limit, excellent water absorption rate is easily obtained. The volume-average particle diameter can be measured by laser diffraction / scattering.

[0055] [Optional ingredients] The water-absorbent resin layer may contain optional components other than the water-absorbent resin. Examples of such optional components include resins other than the water-absorbent resin, the culture soil described below, and optional components (other than the water-absorbent resin) that may be contained in the culture soil layer described below. Examples of resins other than the water-absorbent resin include polyethylene, polypropylene, alkyd resin, phenolic resin, polyethylene glycol, polyacrylic acid, polyacrylate, polyacrylamide, and polyurethane.

[0056] When the water-absorbent resin layer contains the above-mentioned optional components, the total content thereof is 20% by mass or less, preferably 10% by mass or less, and more preferably 5% by mass or less, based on the total mass of the water-absorbent resin layer. In a preferred embodiment of the present invention, the content of the culture soil in the water-absorbent resin layer is 20% by mass or less, preferably 10% by mass or less, more preferably 5% by mass or less, and may be 0% by mass, based on the mass of the water-absorbent resin layer. In this embodiment, when a seedling tray is prepared using a seeding machine, the water-absorbent resin and the culture soil are unlikely to separate due to vibrations during operation of the seeding machine, and as a result, the introduction error of the water-absorbent resin is reduced, making it easier to achieve stable seeding work.

[0057] When the laminated body for raising rice seedlings contains water, the water content per unit area of ​​the laminated body for raising rice seedlings is preferably 300 to 15,000 g / m 2 , more preferably 1000 to 10000 g / m 2 , particularly preferably 2000 to 8000 g / m 2 When the water content is within the above range, good germination and growth of seeds are likely to be achieved. The water content can be adjusted to within the above range by mixing water with the components constituting the bed soil layer and / or the components constituting the cover soil layer before preparing each layer, or by irrigating the bed soil layer and / or the cover soil layer with water after preparing them.

[0058] When the layered body for raising rice seedlings contains water, preferably, the water-absorbent resin layer has a water-absorbent resin content (X) (g / m 2 ) and water content (Y) (g / m 2 ) is represented by the following formula (I): 5≦Content (Y) / Content (X)≦500 (I) The ratio of content (Y) / content (X) is more preferably 10 or more, even more preferably 15 or more, particularly preferably 20 or more, and more preferably 200 or less, even more preferably 100 or less, particularly preferably 60 or less. When the ratio of content (Y) / content (X) is equal to or more than the lower limit and equal to or less than the upper limit, better germination and growth of seeds is likely to be achieved. As mentioned above, the water-absorbent resin content (X) here means the value in a dry state.

[0059] [Cultivating soil layer] In one embodiment of the present invention, when one of the bed soil layer and the cover soil layer is a water-absorbent resin layer, the other is a culture soil layer containing more than 20% by mass of culture soil based on the mass of the layer, and the content of the culture soil layer in the layered product for raising rice seedlings is 1000 to 50000 g / m 2When the rice seedling raising laminated body includes a culture soil layer, roots grow into the gaps in the culture soil and tend to intertwine appropriately, which results in favorable strength for the mat seedlings. Furthermore, the gaps in the culture soil make it easier to obtain excellent drainage and breathability for the rice seedling raising laminated body. When the water-absorbent resin layer or the culture soil layer includes a water-absorbent resin and culture soil, the layer with a higher content of water-absorbent resin than the culture soil is called the water-absorbent resin layer, and the layer with a higher content of culture soil than the water-absorbent resin is called the culture soil layer.

[0060] From the viewpoint of easily obtaining a desirable strength of the mat seedlings, in a preferred embodiment of the present invention, the bed soil layer is a water-absorbent resin layer. In a further preferred embodiment, the bed soil layer is a water-absorbent resin layer and the covering soil layer is a culture soil layer.

[0061] The content of the soil layer in the laminate for raising rice seedlings is preferably 1000 to 50000 g / m 2 and more preferably 2000 to 10000 g / m 2 and particularly preferably 3000 to 10000 g / m 2 When the content of the culture soil layer is within the above range, in addition to the effects of the strength of the mat seedlings and the drainage and breathability of the layered product for raising rice seedlings, it is easy to obtain the effect of reducing the burden of farm work.

[0062] The content of the culture soil in the culture soil layer is preferably more than 20% by mass, more preferably 50% by mass or more, and particularly preferably 70% by mass or more, based on the mass of the culture soil layer. The upper limit of the content is not particularly limited, and the content may be 100% by mass or less. When the content is equal to or greater than the lower limit, it is easy to obtain the above-mentioned strength of the mat seedlings and the effects of the drainage and breathability of the layered product for raising rice seedlings.

[0063] [Cultivating soil] The soil is not particularly limited, and any soil commonly used in the art can be used. From the viewpoint of obtaining better drainage and breathability, the culture soil is preferably granular. When the culture soil is granular, its average particle size is preferably 0.2 to 20 mm, more preferably 0.5 to 10 mm, and particularly preferably 1 to 5 mm. To adjust the average particle size of the granular culture soil within the above range, commercially available granular culture soil for paddy rice can be used after sieving. Granular culture soil can be produced by granulation methods such as compression granulation, extrusion granulation, tumbling granulation, and fluidized bed granulation. The average particle size of the granular culture soil can be determined by the method described in the Examples below.

[0064] [Optional ingredients] The culture soil layer may contain optional components other than the culture soil. Such optional components can be incorporated into the culture soil layer by the following methods: a method of pre-mixing the culture soil raw materials with the optional components and granulating the mixture; a method of spraying a solution or dispersion of the optional components onto the granulated culture soil; a method of pre-mixing an optional component (e.g., a water-absorbent resin) with another optional component (e.g., a fertilizer or pesticide) and mixing the resulting mixture with the culture soil; a method of spraying a solution or dispersion of another optional component (e.g., a fertilizer or pesticide) onto a mixture of an optional component (e.g., a water-absorbent resin) and the culture soil.

[0065] Examples of such optional components include the above-mentioned water-absorbent resins, resins other than the above-mentioned water-absorbent resins, animal and plant substances such as peat, grass peat, peat, peat moss, coco peat, rice husks, humus enzyme materials, charcoal, calcined diatomaceous earth granules, shell fossil powder, shell powder, crab shells, VA mycorrhizal fungi, and microbial materials, minerals such as vermiculite, perlite, bentonite, natural zeolite, synthetic zeolite, gypsum, fly ash, rock wool, kaolinite, smectite, montmorillonite, sericite, chlorite, glauconite, and talc, fertilizers such as bark compost, and combinations of one or more of these. These optional components may be disinfected or sterilized before use, as necessary, and may be used together with a pH adjuster or a pesticide.

[0066] Therefore, in one preferred embodiment of the present invention, the bed soil layer or cover soil layer further comprises one or more components selected from the group consisting of peat moss, coco peat, rice husks, vermiculite, perlite, fertilizers and pesticides.

[0067] When the soil layer contains the above-mentioned optional components, the total content thereof may be within a range that does not impair the effects of the present invention, and is typically 80% by mass or less, preferably 50% by mass or less, and more preferably 30% by mass or less, relative to the total mass of the soil layer.

[0068] Examples of fertilizers include the three major fertilizers: nitrogen-based fertilizers, phosphorus-based fertilizers, and potassium-based fertilizers; fertilizers containing essential plant elements such as calcium, magnesium, sulfur, iron, copper, manganese, zinc, boron, molybdenum, chlorine, and nickel; and composts such as bark compost, cow manure, pig manure, chicken manure, food waste, and pruning waste. Nitrogen-based fertilizers include ammonium sulfate, ammonium chloride, ammonium nitrate, sodium nitrate, calcium nitrate, humic acid ammonium fertilizer, urea, lime nitrogen, ammonium nitrate calcium, sodium ammonium nitrate, and magnesium nitrate fertilizer. Phosphorus-based fertilizers include superphosphate, calcium hydroxide, fused phosphate fertilizer, humic acid phosphate fertilizer, burnt phosphorus, burnt phosphorus, phosphorus starch, magnesium superphosphate, mixed phosphate fertilizer, by-product phosphate fertilizer, and high-concentration phosphoric acid. Potassium-based fertilizers include potassium sulfate, potassium chloride, potassium magnesium sulfate, potassium carbonate, potassium bicarbonate, and potassium silicate. These fertilizers may be used in solid, paste, liquid, or solution form, or as coated fertilizers. Examples of pesticides include insecticides, fungicides, insecticides and fungicides, herbicides, rodenticides, antiseptics, and plant growth regulators.

[0069] When the laminated sheet for raising rice seedlings of the present invention contains a fertilizer, in a preferred embodiment, the fertilizer is used as a coated fertilizer. The coated fertilizer is a fertilizer coated with a resin. Examples of resins include polyolefins. When a coated fertilizer is used, the fertilizer can be continuously supplied to the soil as the resin decomposes. Furthermore, when the coated fertilizer is granular, the strength of the resulting mat seedlings tends to be higher. The average particle size of the coated fertilizer is preferably 1 mm to 10 mm, more preferably 3 mm to 6 mm. When a coated fertilizer is used, the content of the coated fertilizer in the laminated sheet for raising rice seedlings is preferably 10 to 99.99 mass%, more preferably 15 to 90 mass%, particularly preferably 20 to 80 mass%, and most preferably 30 to 60 mass%. When a coated fertilizer is used, the content of the bed soil in the laminated sheet for raising rice seedlings may be 20 to 80 mass%.

[0070] Seeds can be sown in the laminate for raising rice seedlings of the present invention. Thus, in one embodiment of the present invention, the laminate for raising rice seedlings of the present invention further contains rice. In another embodiment of the present invention, the rice is in the form of seeds, and in another embodiment of the present invention, the rice is in the form of seedlings.

[0071] The content of rice in the seed state per unit area of ​​the laminated body for raising rice seedlings is preferably 50 to 5000 g / m 2 , more preferably 500 to 3000 g / m 2 , particularly preferably 1000 to 2000 g / m 2 When the content is within the above range, it is easy to obtain sufficient strength for the mat seedlings.

[0072] As described above, in the present invention, in an embodiment in which the rice seedling raising laminate contains rice seeds, the layer below the seeds is referred to as the bed soil layer, and the layer above the seeds is referred to as the cover soil layer. That is, in this embodiment, it is intended that rice seeds be sown at the boundary between the bed soil layer and the cover soil layer. For example, if the water absorption rate of the rice seedling raising laminate or the water-absorbent resin is insufficient or if the water content of the bed soil layer is high, the sown rice seeds may not be able to remain on the boundary line. However, the rice seedling raising laminate or the water-absorbent resin of the present invention exhibits excellent water absorption rate and can retain a large amount of water, allowing the sown rice seeds to remain near the boundary line. The rice seeds are present preferably within a region of 20 mm, more preferably within 10 mm, even more preferably within 5 mm, and particularly preferably within 2 mm of the boundary line between the bed soil layer and the cover soil layer.

[0073] The mass of the laminated body for raising rice seedlings of the present invention is preferably 28 kg / m 2 Less than or equal to 20 kg / m 2 or less, more preferably 15 kg / m 2 Below 10 kg / m, particularly preferably 2 The "mass of the laminate for raising rice seedlings" means the total mass of the components of the laminate for raising rice seedlings per unit area of ​​the laminate for raising rice seedlings, i.e., the total mass of the bed soil and covering soil, and optionally optional components such as water, rice, and fertilizer, per unit area of ​​the laminate for raising rice seedlings.

[0074] In the examples described below, in addition to the "mass of the laminated sheet for raising rice seedlings," we also used the "total mass of materials," which is more practical, as a method for evaluating the mass of the laminated sheet for raising rice seedlings. As described in the examples below, "total mass of materials" refers to the sum of the total mass (total mass of bed soil, covering soil, and optional components such as water, rice, and fertilizer) per rice seedling raising box and the mass of the rice seedling raising box. While sowing and transplanting have been mechanized, tasks such as loading and unloading seedlings into and from seedling storage rooms and placing seedlings in rice transplanters are still largely done by hand. Therefore, the lighter the total mass of materials, the less burdensome the agricultural work. According to the Japanese Labor Standards Act, women's routine heavy-duty handling work must be less than 20 kg. If the total mass of materials is 5 kg, only three boxes can be carried simultaneously. The total mass of materials is preferably less than 4 kg, in which case five boxes can be carried simultaneously. The total mass of the materials is more preferably less than 3 kg, in which case 6 boxes can be carried at the same time, and even more preferably less than 2 kg, in which case 10 boxes can be carried at the same time. Therefore, the total mass of the materials in the present invention is preferably 4000 g / box or less, more preferably 3000 g / box or less, and particularly preferably 2000 g / box or less.

[0075] The present invention also relates to mat seedlings containing the laminate for raising rice seedlings of the present invention. By including a water-absorbent resin in the laminate for raising rice seedlings of the present invention, weight reduction and / or a reduction in irrigation load can be achieved. Because the content of the water-absorbent resin in the laminate for raising rice seedlings of the present invention is optimized, sown seeds germinate and grow well, and the roots of the rice plants can grow sufficiently and intertwine with each other. This allows the mat seedlings of the present invention to have properties suitable for setting in a rice transplanter (e.g., tensile strength, ease of attachment to the rice transplanter, ease of scraping, seedling stand during scraping, and resistance to crumbling during scraping, etc.).

[0076] The tensile strength of the mat seedlings is an indicator of how resilient the mat seedlings are to crumbling; the higher this tensile strength, the better the workability when placing the mat seedlings in a rice transplanter. The tensile strength of the mat seedlings can be measured by the method described in the Examples below, and is preferably 0.3 kgf / 10 cm (2.9 N / 10 cm) or more, more preferably 0.5 kgf / 10 cm (4.9 N / 10 cm) or more, and even more preferably 1.0 kgf / 10 cm (9.8 N / 10 cm) or more. When the tensile strength of the mat seedlings is above the lower limit, the mat seedlings are less likely to crumble even when the above-ground parts of the mat seedlings are lifted with both hands. The tensile strength of the mat seedlings is particularly preferably 1.5 kgf / 10 cm (14.7 N / 10 cm) or more, and in this case, the seedlings are less likely to crumble even when the above-ground parts of the mat seedlings are lifted with one hand.

[0077] Seeds are often sown in rice seedling raising boxes into which a laminated sheet for raising rice seedlings has been introduced. Accordingly, the present invention also relates to the laminated sheet for raising rice seedlings of the present invention and a rice seedling raising box into which water has been introduced. The rice seed content is typically 100 to 500 g per rice seedling raising box (usually 28 cm long x 58 cm wide). When the amount of seeds per box is as high as 250 to 500 g, the amount of water lost through transpiration during seedling raising increases. However, because the laminated sheet for raising rice seedlings of the present invention has good water retention properties, even in such cases, the use of the laminated sheet for raising rice seedlings of the present invention makes it possible to reduce the irrigation load.

[0078] The rice seedling raising box can be produced, for example, by the following method, which is also within the scope of the present invention: A method for manufacturing a paddy rice seedling raising box into which a laminate for raising paddy rice seedlings containing a bed soil layer and a cover soil layer has been introduced, the method comprising the steps of introducing bed soil into the paddy rice seedling raising box, sowing paddy rice in the form of seeds, and introducing cover soil, wherein one or both of the bed soil and the cover soil contain a particulate water-absorbent resin, the water-absorbent resin being arranged so that at least a part of the paddy rice can come into contact with the water-absorbent resin, and the content of the water-absorbent resin in the laminate for raising paddy rice seedlings is 1 to 5000 g / m 2 That's the method.

[0079] In a preferred embodiment of the present invention, the content of the water-absorbent polymer in each soil (bed soil or covering soil) is preferably more than 80% by mass, more preferably 90% by mass or more, and particularly preferably 95% by mass or more, based on the mass of each soil. The content of the water-absorbent polymer in each soil may be 100% by mass, that is, each soil may consist solely of the water-absorbent polymer. Both soils (bed soil and covering soil) may satisfy the above-mentioned water-absorbent polymer content, but it is more preferable that only one of the bed soil and covering soil satisfies the above-mentioned water-absorbent polymer content. By ensuring that the content is equal to or greater than the above-mentioned lower limit, the burden of agricultural work can be reduced.

[0080] The production of rice seedling raising boxes is usually carried out on an assembly line using a belt conveyor or the like. For this reason, a certain level of water absorption rate is required for the rice seedling raising laminate or water-absorbent resin. The rice seedling raising laminate or water-absorbent resin of the present invention can exhibit an excellent water absorption rate that fully meets this requirement. Furthermore, in assembly line production, bed soil and / or cover soil are often introduced using a hopper or the like. Therefore, in a preferred embodiment of the present invention, in the above-mentioned method of the present invention, the bed soil and / or cover soil is introduced using a hopper. By using a hopper to produce rice seedling raising boxes into which a rice seedling raising laminate comprising a bed soil layer and a cover soil layer has been introduced, the productivity of the rice seedling raising laminate or rice seedling raising boxes can be increased. [Example]

[0081] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0082] [Evaluation items and evaluation methods] (1) Content of water-absorbent resin, water, soil layer or rice seeds in the laminate for raising rice seedlings The content of water-absorbent resin, water, soil layer or rice seeds in the laminate for raising rice seedlings (g / m 2 ) is the mass (g) of the water-absorbent resin, water, soil layer or rice seeds contained in the layered product for raising rice seedlings, multiplied by the area (m 2 ) was calculated by dividing by (2) Average particle size of granular soil Thirty particles were randomly selected from the granular soil, and the diameter of each particle was measured using a vernier caliper. The average diameter was taken as the average particle size of the granular soil. If the particle was not spherical, the average of the longest and shortest sides was taken as the diameter of the particle. (3) Thickness of the bed soil layer and the covering soil layer Using a ruler, the thickness from the bottom of the bed soil layer (usually the bottom of the seedling box) to the top of the bed soil layer was measured and recorded as the thickness of the bed soil layer. Also, using a ruler, the thickness from the bottom of the cover soil layer to the top of the cover soil layer was measured and recorded as the thickness of the cover soil layer. Both measurements were performed after the seedling boxes were made, and the values ​​were measured in a water-absorbed state. (4) Volume average particle diameter of water-absorbent resin The volume average particle size of the water-absorbent resin was measured using a laser diffraction / scattering particle size distribution measuring device. (5) In a mixture of water-absorbent resin and pure water of 50 times its mass, the proportion of pure water having a water potential of 0 to 3, W 2.4 g of a sample mixture that had absorbed 50 times the mass of the water-absorbent resin in pure water was introduced into a syringe, and this syringe was fixed inside a centrifuge tube so that it was 10.2 cm from the center of a small centrifuge "H-36" manufactured by Kokusan Co., Ltd. The centrifuge was rotated at 2200 rpm for 60 minutes, and W was calculated based on the following formula. However, if the cross-linked copolymer could not absorb 50 times the mass of pure water, 2.4 g of resin that had saturated with water was introduced into the syringe. W = [{(mass of sample mixture before centrifugation) - (mass of sample mixture after centrifugation)} / (mass of sample mixture before centrifugation)] × 100 (6) Position of rice seeds in the rice seedling raising laminate The vertical distance from the boundary between the bed soil layer and the cover soil layer to the center of the rice seed was measured using a ruler. This procedure was performed on a total of 10 randomly selected rice seeds, and if 9 or more of them were located within 5 mm of the boundary, it was judged to be "present." (7) Mass of the laminated body for raising rice seedlings Mass of laminated body for raising rice seedlings (kg / m 2) is the total mass (kg) of the components constituting the layered structure for raising rice seedlings (bed soil and covering soil, and optionally water, rice, fertilizer, etc.) divided by the area (m 2 ) was calculated by dividing by

[0083] [Water absorption, shipping and growth surveys of laminated sheets for raising rice seedlings] (8) Time to complete water absorption during irrigation The time from the end of shower irrigation until the water surface in the rice seedling box disappeared and the bed soil was exposed (water absorption completion time) was measured. If seeds are sown with the water surface still present, the position of the germinated rice grains (rice seeds) will shift, reducing the uniformity of germination in the rice seedling box. Therefore, the shorter the water absorption completion time, the higher the productivity of seedling box production. The water absorption completion time is preferably 12 seconds or less. (9) Total mass of materials The total mass of materials (g / box) was calculated by adding up the mass of bed soil, mass of covering soil, mass of fertilizer, amount of water irrigated to bed soil, amount of water irrigated for leveling, mass of rice seedling boxes, and mass of germinated rice.

[0084] (10) Shipment survey (2 days after sowing) (10-1) Germination rate The number of sprouts that had emerged above the covered soil (N1) was counted visually. The number of germinated rice seeds sown (N2) was used to calculate the emergence rate according to the following formula. Germination rate [%]=(N1 / N2)×100 If the emergence rate is 0%, the laminate is not suitable for raising rice seedlings. (10-2) Compatibility with seed drills The water-absorbent resin was placed in the bed soil hopper of a seed drill (Kubota Corporation, SR4500). If the water-absorbent resin could be dispensed through the hopper, the seed drill's suitability was rated "A," and if it could not be dispensed, the seed drill's suitability was rated "B." (10-3) Mold growth The occurrence of mold was visually observed and evaluated according to the following criteria. A: No mold growth was observed. B: Mold growth was confirmed, but the area of ​​the upper surface of the layered product for raising rice seedlings that was covered with mold was 5% or less. C: Mold growth was confirmed, and the area of ​​the upper surface of the layered product for raising rice seedlings covered with mold was greater than 5%. (10-4) Number of exposed rice grains (N3) The number of exposed grains was counted visually. (10-5) Number of uprooted grains (N4) The number of rice grains with roots raised was counted visually. (11) Shipment survey (11 days after sowing) (11-1) NDVI value The NDVI (Normalized Difference Vegetation Index) values ​​of the seedlings were measured using a GreenSeeker handheld crop sensor (manufactured by Nikon Trimble Co., Ltd.). A higher value indicates more vigorous seedlings.

[0085] (12) Growth survey (any day between 15 and 22 days after sowing) (12-1) Plant height The length from the top surface of the rice seedling raising layered structure to the top of the seedling was measured for 10 seedlings randomly sampled, and the average value was used as the plant height. (12-2) Leaf color The leaf color of 10 randomly sampled seedlings was measured using a leaf color scale (manufactured by Fujidaira Kogyo Co., Ltd.), and the average value was used as the leaf color. (12-3) Leaf age The leaf age of 10 randomly sampled seedlings was measured visually, and the average value was used as the leaf age. (12-4) Tensile strength of mat seedlings The mat seedlings were cut into strips measuring 10cm x 20cm, one of the short sides was fixed (fixed area: 10cm x 4cm), and the other side was connected to a spring balance (connected area: 10cm x 4cm). The spring balance was pulled until the mat seedlings broke, and the maximum stress was measured.

[0086] (13) Pure water absorption According to JIS K 7223, the pure water absorption amount of the water-absorbent resin used in the examples and comparative examples was measured, and the pure water absorption amount per unit mass of the sample [g / g] was calculated based on the following formula. Pure water absorption amount [g / g] = [(sample mass after absorbing pure water) - (sample mass before absorbing pure water)] / (Sample mass before absorbing pure water) Here, the "mass of the sample before absorbing pure water" is a value measured using 0.1 g of water-absorbent resin.

[0087] [Materials used] Granular soil A: New Clean soil, fertilizer content N-P2O5-K2O=0.5-0.8-0.5g / kg, average particle size 2.7mm ·Granular soil B: Manufactured by Arashikita Shoji, does not contain fertilizer, average particle size 3.3mm Coco peat: Green soils Peat moss: T&H Vermiculite: SK Agri Co., Ltd. Rice husks

[0088] Water-absorbent resin A: Synthesized by the method described below in [Synthesis of water-absorbent resin A]. Water-absorbent resin B: Synthesized using the method described below in [Synthesis of water-absorbent resin B]. Water-absorbent resin C: Synthesized by the method described below in [Synthesis of water-absorbent resin C]. Water-absorbent resin D: AQUAKEEP (polyacrylate gel) manufactured by Sumitomo Seika Chemicals Co., Ltd. Water-absorbent resin E: Aquacork (polyethylene glycol gel) manufactured by Sumitomo Seika Chemicals Co., Ltd. Water-absorbent resin F: KI gel (isobutylene-maleate gel) manufactured by Kuraray Co., Ltd. Water-absorbent resin G: Aquasorb 3005KB (polyacrylamide gel) manufactured by SNF Holding Company

[0089] [Table 1]

[0090] [Synthetic raw materials] Glyoxylic acid monohydrate, 40% by weight glyoxal aqueous solution, 25% by weight glutaraldehyde aqueous solution, acetonitrile, methanol, vinyl acetate, sodium hydroxide, methyl acrylate, and azobisisobutyronitrile; manufactured by Wako Pure Chemical Industries, Ltd. Polyvinyl alcohol A: ELVANOL® 71-30 manufactured by Kuraray America, Inc.

[0091] [Synthesis of water-absorbent resin A] A 500 mL four-neck separable flask equipped with a reflux condenser and a stirring blade was charged with 12.55 g of glyoxylic acid monohydrate, 0.11 g of 40% by weight glyoxal aqueous solution, 12.55 g of ion-exchanged water, 150 mL of acetonitrile, and 40.0 g of polyvinyl alcohol A, and the mixture was stirred at 23°C for 1 hour. The resulting mixture was heated to 70°C, and 16.87 g of 25% by weight sulfuric acid aqueous solution was added dropwise over 10 minutes. The mixture was then allowed to react for 6 hours while maintaining the temperature at 70°C. After cooling to 30°C, 150 mL of ion-exchanged water was added, and the resin was removed by filtration. The filtered resin was then washed five times with 200 mL of methanol. The washed resin was then charged to a 500 mL four-neck separable flask equipped with a reflux condenser and a stirring blade. 180 mL of methanol, 11.6 mL of ion-exchanged water, and 16.8 mL of 8 mol / L potassium hydroxide aqueous solution were added, and the mixture was allowed to react under reflux for 2 hours. The resin was filtered off, washed six times with 200 mL of methanol, and vacuum dried at 40° C. for six hours to obtain the desired vinyl alcohol polymer (referred to as "water-absorbent resin A").

[0092] [Synthesis of water-absorbent resin B] A reactor equipped with a stirrer, reflux condenser, nitrogen inlet, and initiator inlet was charged with 602 g of vinyl acetate, 1.21 g of methyl acrylate, and 254 g of methanol. The reactor was then purged with inert gas for 30 minutes while bubbling with nitrogen. The reactor was heated using a water bath, and when the internal temperature of the reactor reached 60 °C, 0.16 g of azobisisobutyronitrile (AIBN) was added as an initiator to initiate polymerization. Sampling was performed periodically to confirm the progress of the polymerization based on the solids concentration. The consumption rate, which is the total mass of vinyl acetate and methyl acrylate consumed in the polymerization relative to the total mass of vinyl acetate and methyl acrylate introduced, was calculated. When the consumption rate reached 4%, the internal temperature of the reactor was cooled to 30 °C to terminate the polymerization. The reactor was connected to a vacuum line, and the remaining vinyl acetate and methanol were distilled off under reduced pressure at 30 °C. While visually checking the inside of the reactor, when the viscosity increased, methanol was added appropriately while continuing distillation, and polyvinyl acetate containing 5.2 mol % of acrylic acid structural units was obtained. The content of acrylic acid structural units was 5.2 mol %. 13 Measurement was performed using C-NMR. Next, 1 g of the resulting polyvinyl acetate containing acrylic acid structural units and 18.2 g of methanol were added to the same reactor as above, and the polyvinyl acetate containing acrylic acid structural units was dissolved. The reactor was heated using a water bath, and the temperature was increased with stirring until the internal temperature of the reactor reached 70°C. 0.78 g of a methanol solution of sodium hydroxide (metacaustic, concentration 15% by mass) was added, and saponification was carried out at 70°C for 2 hours. The resulting solution was filtered to obtain polyvinyl alcohol containing 5.2 mol% of acrylic acid structural units (hereinafter referred to as "polyvinyl alcohol B"). A three-neck separable flask equipped with a reflux condenser and a stirring blade was charged with 58.9 g of acetonitrile, 6.28 g of ion-exchanged water, 0.171 g of a 25% by weight aqueous glutaraldehyde solution, and 20 g of polyvinyl alcohol B. The mixture was stirred at 23°C to disperse the polyvinyl alcohol B. 12.38 g of a 16.9% by weight aqueous sulfuric acid solution was added dropwise over 15 minutes, and the mixture was heated to 65°C and reacted for 6 hours. After the reaction, the resin was filtered and washed six times with 160 g of methanol. The washed resin was then charged to a three-neck separable flask equipped with a reflux condenser and a stirring blade. 71 g of methanol, 13.3 g of ion-exchanged water, and 5.7 g of potassium hydroxide were added, and the mixture was reacted at 65°C for 2 hours. After the reaction, the resin was filtered off, washed six times with 160 g of methanol, and vacuum dried at 40°C for 12 hours to obtain the desired vinyl alcohol polymer (referred to as "water-absorbent resin B").

[0093] [Synthesis of water-absorbent resin C] The target vinyl alcohol polymer (referred to as "water absorbent resin C") was obtained in the same manner as in [Synthesis of water absorbent resin B], except that the mass of the 25 mass % glutaraldehyde aqueous solution was changed from 0.171 g to 0.086 g.

[0094] Example 1 Water-absorbent resin A and pure water were mixed as bed soil and spread in a paddy rice seedling raising box (670 g) with internal dimensions of 58 cm x 28 cm. Germinated rice grains (variety: Koshihikari) were evenly spread, and then granular culture soil A was spread on top of them as cover soil, to prepare a paddy rice seedling raising box into which a laminated body for raising paddy rice seedlings and water were introduced. The above procedure was repeated two more times to prepare three identical paddy rice seedling raising boxes into which the same laminated body for raising paddy rice seedlings and water were introduced. After germination for 48 hours in a germination chamber at 30°C and 100% RH, a germination survey was conducted. Table 2 shows the results of Examples 1-1 to 1-15, where the content of the water-absorbent resin and the content of water (corresponding to the amount of pure water mixed; referred to as "amount of bed soil irrigation" in the table) in the laminated body for raising paddy rice seedlings were changed. In all of the Examples and Comparative Examples, germinated rice grains (variety: Koshihikari) were used, but different lots of germinated rice grains were used for each of Tables 2 to 9. In addition, the Examples and Comparative Examples were carried out on different days for each of Tables 2 to 9.

[0095] Comparative Example 1 A rice seedling raising box containing water and a layered product for raising rice seedlings was prepared in the same manner as in Example 1-1, except that granular soil A was used as bed soil instead of water absorbent resin A, and a shipping survey was conducted. The results are shown in Table 2.

[0096] Comparative Examples 2 and 3 A paddy rice seedling raising laminate and a paddy rice seedling raising box into which water was introduced were prepared in the same manner as in Example 1-1, except that the content of the water absorbent resin A in the paddy rice seedling raising laminate was changed, and a shipping survey was conducted. The results are shown in Table 2. In Comparative Example 2, the ratio of the introduced water to the content of the water-absorbent resin in the bed soil was excessive, causing the bed soil to become gelatinous. The germinated rice grains sank into the gelatinous bed soil, and although they were present within 5 mm of the boundary between the bed soil layer and the cover soil layer, they were not present within 2 mm of the boundary.

[0097] Comparative Example 4 A paddy rice seedling raising laminate and a paddy rice seedling raising box into which water was introduced were prepared in the same manner as in Example 1-11, except that instead of mixing the water absorbent resin A as bed soil with pure water and spreading the mixture in the paddy rice seedling raising box, a sheet-like water absorbent resin A was prepared by sandwiching the water absorbent resin A between two pieces of nonwoven fabric (Prowipe Soft High Wiper S150, manufactured by Daio Paper Co., Ltd.), and the sheet was spread in the paddy rice seedling raising box and pure water was added. The results are shown in Table 2.

[0098] Example 2 A paddy rice seedling raising laminate and a paddy rice seedling raising box into which water was introduced were prepared in the same manner as in Example 1-6, except that water absorbent resin B was used instead of water absorbent resin A as bed soil and the water content in the paddy rice seedling raising laminate was changed, and a shipping survey was conducted (Examples 2-1, 2-2, and 2-4 to 2-6). A paddy rice seedling raising laminate and a paddy rice seedling raising box into which water was introduced were prepared in the same manner as in Example 1-6, except that water absorbent resin B was used instead of water absorbent resin A as bed soil, and a shipping survey was conducted (Example 2-3). The results are shown in Table 3.

[0099] Comparative Example 5 A rice seedling raising box containing water and a layered product for raising rice seedlings was prepared in the same manner as in Example 2-6, except that granular soil A was used as the bed soil instead of water absorbent resin B, and a shipping survey was conducted. The results are shown in Table 3.

[0100] Example 3 Except for changing the mass of granular culture soil A used as covering soil, the rice seedling raising laminate and the rice seedling raising boxes into which water was introduced were prepared in the same manner as in Example 2, and a shipping survey was conducted. Table 4 shows the results of Examples 3-1 to 3-6, where the water content in the rice seedling raising laminate was changed.

[0101] Comparative Example 6 The rice seedling raising boxes with water introduced were prepared in the same manner as in Example 3-6, except that granular culture soil A was used as the bed soil instead of water absorbent resin B and the mass of the covering soil was changed, and a shipping survey was conducted. The results are shown in Table 4.

[0102] [Table 2]

[0103] [Table 3]

[0104] [Table 4]

[0105] As can be seen from Tables 2 to 4, the laminates for raising rice seedlings of the present invention (Examples 1-1 to 1-15, Examples 2-1 to 2-6, and Examples 3-1 to 3-6) have a lighter total mass of materials and a lighter mass of the laminates for raising rice seedlings than laminates that do not contain a water-absorbent resin (Comparative Examples 1, 5, and 6), and can reduce the burden of farm work. 2 When the range was not met (Comparative Examples 2 and 3), weight reduction was possible, but germination did not occur, and such laminates were not suitable as laminates for raising rice seedlings. When the effects of the water content [or water content (Y) / water absorbent resin content (X)] were compared among Examples with the same water-absorbent resin content (comparison between Example 1-3 and Example 1-4, comparison between Examples 1-6 to 1-9, comparison between Example 1-11 and Example 1-12, comparison between Examples 2-1 to 2-6, and comparison between Examples 3-1 to 3-6), the germination rate was high because the water content was within a certain range, and such a laminate was superior as a laminate for raising rice seedlings. When the water-absorbent resin was in particulate form (Examples 1-11), compatibility with the seed sowing machine was superior compared to when the water-absorbent resin was used in sheet form (Comparative Example 4). Furthermore, when the water-absorbent resin was in contact with at least a portion of the seeds (Examples 1-11), growth was superior compared to when there was no contact (Comparative Example 4). This is thought to be because water was efficiently supplied from the water-absorbent resin to the seeds.

[0106] Example 4 and Comparative Example 7 The bed soil listed in Table 5 was spread in a rice seedling raising box with internal dimensions of 58 cm x 28 cm. The rice seedling raising box with the bed soil spread was placed on a seeding plant (Kubota Corporation, Model No. SR4500) and transported by conveyor while being shower-watered at the bed soil irrigation rate listed in Table 5. Germinated rice grains (variety: Koshihikari) were evenly spread, followed by leveling irrigation at the leveling irrigation rate listed in Table 5. A rice seedling raising box containing a layered structure for raising rice seedlings and water was prepared by spreading the cover soil listed in Table 5 on top. Fertilizer (ammonium sulfate, calcium superphosphate, and potassium chloride) was added to the granular medium B, coco peat, peat moss, vermiculite, and rice husks in advance to achieve the fertilizer content listed in Table 5. The above procedure was repeated two more times to prepare three identical rice seedling raising boxes containing the layered structure for raising rice seedlings and water. Germination was allowed to occur for 48 hours in a germination chamber at 30°C and 100% RH, after which a storage inspection was conducted. The rice seedling raising boxes were then moved into a glasshouse and the seedlings were raised. Table 5 shows, as Examples 4-1 to 4-13, the results of the growth inspection when the type of bed soil and covering soil in the layered product for raising rice seedlings, as well as the water (amount of bed soil irrigation), water-absorbent resin, and culture soil contents were varied. Furthermore, as Comparative Example 7, the results of the growth inspection when granular culture soil B was used as the bed soil and covering soil are shown.

[0107] Example 5 and Comparative Example 8 Laminated bodies for raising rice seedlings and raising boxes for raising rice seedlings were prepared in the same manner as in Example 4, except that the bed soil and cover soil shown in Table 6 were used in the masses shown in Table 6 and the amount of water irrigation for the bed soil was changed from 500 to 1000 g / box to 1400 g / box, and a shipping inspection and growth inspection were carried out. The time to complete water absorption was also measured. The results are shown in Table 6 as Examples 5-1 to 5-3 and Comparative Example 8.

[0108] Example 6 and Comparative Example 9 Laminated bodies for raising rice seedlings and raising boxes for raising rice seedlings were prepared in the same manner as in Examples 4-9, except that the bed soil and cover soil shown in Table 7 were used in the masses shown in Table 7 and the amount of water irrigation for the bed soil was changed from 500 g / box to 1000 g / box, and a shipping inspection and growth inspection were conducted. The time until completion of water absorption was also measured. The results are shown in Table 7 as Examples 6-1 to 6-12 and Comparative Example 9. Fertilizers (ammonium sulfate, calcium superphosphate, and potassium chloride) were added in advance to granular culture soil B as cover soil so that the fertilizer content was the amount shown in Table 7.

[0109] Example 7 and Comparative Examples 10-11 A laminated body for raising rice seedlings and a rice seedling raising box were prepared in the same manner as in Example 5-1, and a shipping inspection and growth inspection were conducted (Example 7-1). A laminated body for raising rice seedlings and a rice seedling raising box were prepared in the same manner as in Example 5-1, except that the content of rice in the seed state was changed, and a shipping inspection and growth inspection were conducted (Example 7-2). Furthermore, a laminated body for raising rice seedlings and a rice seedling raising box were prepared in the same manner as in Comparative Example 8, and a shipping inspection and growth inspection were conducted (Comparative Example 10). A laminated body for raising rice seedlings and a rice seedling raising box were prepared in the same manner as in Comparative Example 8, except that the content of rice in the seed state was changed, and a shipping inspection and growth inspection were conducted (Comparative Example 11). The results are shown in Table 8.

[0110] Example 8 and Comparative Examples 12 to 15 Laminated bodies for raising rice seedlings and raising boxes for raising rice seedlings were prepared in the same manner as in Example 5-1, except that the mass of the covering soil and the fertilizer content were changed, and a shipping survey and growth survey were conducted (Examples 8-1 to 8-4). Furthermore, laminated bodies for raising rice seedlings and raising boxes for raising rice seedlings were prepared in the same manner as in Comparative Example 8, except that the mass of the bed soil and covering soil and the fertilizer content were changed, and a shipping survey and growth survey were conducted (Comparative Examples 12 to 15). The NDVI values ​​and growth survey results when the irrigation management after emergence was changed are shown in Table 9.

[0111] [Table 5]

[0112] [Table 6]

[0113] [Table 7]

[0114] [Table 8]

[0115] [Table 9]

[0116] As can be seen from Tables 5 to 9, the laminates for raising rice seedlings of the present invention (Examples 4-1 to 4-13, Examples 5-1 to 5-3, Examples 6-1 to 6-12, Examples 7-1 to 7-2, and Examples 8-1 to 8-4) have a lighter total mass of materials and a lighter laminate for raising rice seedlings than laminates that do not contain a water-absorbent resin (Comparative Examples 7 to 15), thereby reducing the burden of agricultural work. When granular soil was used as the covering soil layer (Examples 4-1 to 4-3), the tensile strength of the mat seedlings was superior to when coco peat, peat moss, vermiculite, or rice husks were used (Examples 4-4 to 4-7).Furthermore, when a water-absorbent resin was used as the bed soil (Examples 4-1 to 4-3), the tensile strength of the mat seedlings was superior to when a water-absorbent resin was used as the covering soil (Examples 4-8 to 4-9).

[0117] As can be seen from Table 9, the rice seedling raising laminate of the present invention had a high NDVI value and good growth even when the irrigation frequency or amount was low, compared to when it did not contain a water-absorbent resin (comparison between Example 8-2 and Comparison Example 13, comparison between Example 8-3 and Comparison Example 14, comparison between Example 8-4 and Comparison Example 15).

[0118] Example 9 1840 g of water-absorbent resin B was loaded into a Suzutec SH2B seed drill. A polypropylene seedling box with internal dimensions of 16.2 cm x 18.8 cm was placed on top of the box, and the seed drill was run on top of the box in the longitudinal direction to load water-absorbent resin B into the box. The time when the resin volume in the seedling box decreased from approximately 100% to approximately 95% was defined as the initial running time. The seed drill was removed from the top of the seedling box and operated until approximately 20% of the resin volume remained. An empty seedling box of the same size was then placed on top of the box, and the seed drill was run on top of the box in the longitudinal direction to load water-absorbent resin B into the seedling box. The time when the resin volume in the seedling box decreased from approximately 20% to approximately 15% was defined as the final running time. The mass of water-absorbent resin B contained in each seedling box was measured, and the loading error of the water-absorbent resin was calculated using the following formula. The results are shown in Table 10. Addition error = {addition amount of water-absorbing resin B at the initial stage of running (g)} / {Amount of absorbent resin B added at the end of the run (g)} The closer the injection error is to 1, the smaller the difference in the amount of water-absorbent resin injected between seedling boxes when preparing seedling boxes using a seed drill, allowing for stable seeding work.

[0119] Example 10 Mixed soil was prepared by placing 40 g of water-absorbent resin B and 1800 g of granular soil A in a polyethylene bag and shaking. A seedling box containing mixed soil for the initial running time and a seedling box containing mixed soil for the final running time were prepared in the same manner as in Example 9, except that mixed soil was added to the seeding machine instead of water-absorbent resin B. The mixed soil contained in each seedling box was separated with a 600 μm sieve, and those with sizes of 600 μm or more were designated as granular soil A and those with sizes less than 600 μm as water-absorbent resin B. The addition error of water-absorbent resin B was calculated using the same formula as in Example 9. The results are shown in Table 10.

[0120] [Table 10]

[0121] As can be seen from Table 10, when the content of the culture soil in the water-absorbent resin layer based on the mass of the water-absorbent resin layer was 20 mass% or less (Example 9), when a seedling box was prepared using a seeding machine, the error in the addition of the water-absorbent resin was small, and stable seeding work could be performed. When the content of the culture soil in the water-absorbent resin layer based on the mass of the water-absorbent resin layer was more than 20 mass% (Example 10), the water-absorbent resin and the granular culture soil separated due to vibrations during seeding machine operation, and the error in the addition of the water-absorbent resin was large, and stable seeding work could not be performed for a long period of time. [Industrial Applicability]

[0122] The laminate for raising rice seedlings of the present invention reduces the burden of agricultural work while not inhibiting the growth of rice, and therefore can be suitably used as a medium for raising rice seedlings that meets the needs of farmers. [Explanation of symbols]

[0123] 1. Laminated body for raising rice seedlings 2 bed soil layer 3 Soil cover layer

Claims

1. A layered body for raising paddy rice seedlings, comprising a bed soil layer and a cover soil layer, wherein one or both of the bed soil layer and the cover soil layer is a water-absorbent polymer layer containing a particulate water-absorbent polymer, and the water-absorbent polymer is arranged so that at least a part of the paddy rice plants can come into contact with the water-absorbent polymer, and the content of the water-absorbent polymer in the layered body for raising paddy rice seedlings is 1 to 5000 g / m ２ a laminate for raising rice seedlings, wherein the water-absorbent resin comprises a vinyl alcohol-based polymer, and the vinyl alcohol-based polymer comprises one or more monomer constituent units selected from the group consisting of acrylic acid, methacrylic acid, and derivatives thereof; in a mixture of the water-absorbent resin and pure water in an amount 50 times the mass of the water-absorbent resin, the pure water having a water potential of 0 to 3 accounts for 20% by mass or more and 80% by mass or less based on the mass of the pure water in the mixture; and the content of culture soil in the water-absorbent resin layer is 20% by mass or less based on the mass of the water-absorbent resin layer.

2. The content (X1) of the water-absorbent resin in the bed soil layer (g / m ２ ) and the content (X2) (g / m ) of the water-absorbent resin in the covering layer ２ ) is represented by the following formula: Content (X2) / Content (X1)≦0.2 or Content (X2) / Content (X1)≧5 The layered product for raising rice seedlings according to claim 1, which satisfies the above.

3. The content (X2) of the water-absorbent resin in the covering layer is 70 g / m ２ The layered product for raising rice seedlings according to claim 1 or 2, which is as follows:

4. The layered product for raising rice seedlings according to any one of claims 1 to 3, wherein the water-absorbent resin layer contains more than 80% by mass of the water-absorbent resin based on the mass of the water-absorbent resin layer.

5. The layered body for raising rice seedlings contains water, and the water content is 300 to 15,000 g / m ２ The layered body for raising rice seedlings according to any one of claims 1 to 4.

6. In the water-absorbent resin layer, the content of the water-absorbent resin (X) (g / m ２ ) and water content (Y) (g / m ２ ) is represented by the following formula (I): 5≦Content (Y) / Content (X)≦500 (I) The layered product for raising rice seedlings according to any one of claims 1 to 5, which satisfies the above.

7. One of the bed soil layer and the covering soil layer is the water-absorbent resin layer, and the other is a culture soil layer containing more than 20% by mass of culture soil based on the mass of the culture soil layer, and the content of the culture soil layer in the layered body for raising rice seedlings is 1000 to 50000 g / m ２ The layered body for raising rice seedlings according to any one of claims 1 to 6.

8. 8. The layered product for raising rice seedlings according to claim 7, wherein the bed soil layer is the water-absorbent resin layer.

9. The layered product for raising rice seedlings according to claim 7 or 8, wherein the soil is granular and has an average particle size of 0.2 to 20 mm.

10. The layered product for raising rice seedlings according to any one of claims 1 to 9, wherein the thickness of the bed soil layer is 0.01 to 100 mm.

11. The layered product for raising rice seedlings according to any one of claims 1 to 10, wherein the thickness of the covering soil layer is 0.1 to 100 mm.

12. The layered product for raising rice seedlings according to any one of claims 1 to 11, wherein the volume average particle diameter of the water-absorbent resin is 1 to 10,000 µm.

13. The layered product for raising rice seedlings according to any one of claims 1 to 12, wherein the water-absorbent resin contains a carboxyl group.

14. The layered product for raising rice seedlings according to any one of claims 1 to 13, wherein the water-absorbent resin has potassium ions as counter cations.

15. The layered product for raising rice seedlings according to any one of claims 1 to 14, wherein the water-absorbent resin is a vinyl alcohol polymer.

16. The bed soil layer or the covering soil layer further contains one or more components selected from the group consisting of peat moss, coco peat, rice husks, vermiculite, perlite, fertilizers and pesticides. A layered product for raising rice seedlings according to any one of claims 1 to 15.

17. The layered product for raising rice seedlings according to any one of claims 1 to 16, further comprising rice.

18. The layered product for raising rice seedlings according to claim 17, wherein the rice is in the form of seeds.

19. 19. The layered product for raising rice seedlings according to claim 18, wherein the rice seeds are present in an area within 20 mm from a boundary line between the bed soil layer and the covering soil layer.

20. The content of rice in the seed state is 50 to 5000 g / m ２ The layered product for raising rice seedlings according to claim 18 or 19,

21. The layered product for raising rice seedlings according to claim 17, wherein the rice plants are in the state of seedlings.

22. The mass of the layered body for raising rice seedlings is 28 kg / m ２ The layered body for raising rice seedlings according to any one of claims 1 to 21, wherein:

23. A mat seedling comprising the laminate for raising rice seedlings according to claim 21.

24. A paddy rice seedling raising box having the laminate for raising paddy rice seedlings according to any one of claims 1 to 22 and water introduced therein.

25. A method for manufacturing a rice seedling raising box into which a rice seedling raising laminate including a bed soil layer and a cover soil layer is introduced, The method includes the steps of introducing bed soil into a paddy rice seedling raising box, sowing paddy rice in the form of seeds, and introducing cover soil, wherein one or both of the bed soil and the cover soil contains a particulate water-absorbent resin, and the water-absorbent resin is arranged so that at least a part of the paddy rice comes into contact with the water-absorbent resin, and the content of the water-absorbent resin in the paddy rice seedling raising laminate is 1 to 5000 g / m ２ wherein the water-absorbent resin comprises a vinyl alcohol-based polymer, and the vinyl alcohol-based polymer comprises one or more monomer constituent units selected from the group consisting of acrylic acid, methacrylic acid, and derivatives thereof; in a mixture of the water-absorbent resin and pure water having a mass 50 times that of the water-absorbent resin, the pure water having a water potential of 0 to 3 accounts for 20 mass % or more and 80 mass % or less based on the mass of the pure water in the mixture; and the content of culture soil in one or both of the bed soil and the cover soil containing the water-absorbent resin is 20 mass % or less based on the mass of the water-absorbent resin layer.

26. 26. The method of claim 25, wherein one or both of the bed soil and the cover soil comprises more than 80% by weight of the water-absorbent resin based on the weight of the bed soil or cover soil.

27. 27. The method according to claim 25 or 26, wherein the introduction of the bed soil and / or cover soil is carried out using a hopper.

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