JP4621480B2 - Water-retaining agent for plant growth comprising a hydrogel-forming polymer - Google Patents

Description

  The present invention relates to a water-retaining agent for plant growth that can exhibit a function as a water supply source during plant growth.

  Conventionally, natural soil has been mostly used for the growth and production of indoor and outdoor plants. However, natural soils have been required to have higher performance for water retention. In recent years, as a new plant cultivation base, various hydrogel-forming polymeric water retention materials that absorb a large amount of water. Has been proposed and used (see, for example, Patent Document 1).

JP 2000-308412 A

  However, although the conventionally known hydrogel-forming polymeric water-retaining material has exhibited an excellent effect on water retention, it is essential to use an alkali metal as a polymerization stabilizer in terms of molecular structure. As a result, the content of alkali metal is inevitably high, and when the plant is in direct contact, germination and growth are greatly hindered.

  Therefore, in the present invention, without inhibiting the germination and rooting of such plants, a water retention agent for plant growth that exhibits good water retention ability and is highly versatile in various surrounding environments, and using this The produced water retention material for plant cultivation is provided.

In order to solve the conventional problems as described above, in the present invention, various identifications were made on the hydrogel-forming polymer electrolyte constituting the water-retaining agent for plant growth.
That is, the polymer carrier has an acidic neutralized salt, the alkali metal content per gram dry weight is less than 0.3 mmol / g, and 25 ° C. ion-exchanged water per gram dry weight. The ratio of the water absorption capacity (A) of ion exchange water at 25 ° C. to the water absorption capacity (B) of a 1 wt% aqueous solution of calcium chloride is [(A) / (B)]. , 15 or less.

  According to the present invention, the water retention agent for plant growth comprising a hydrogel-forming polymer has an acidic neutralized salt in the molecule, and the content of alkali metal per 1 g of dry weight is 0.3 mmol / The water absorption capacity of 25 ° C. ion exchange water per gram of dry weight is 10 times or more, the water absorption capacity (A) of 25 ° C. ion exchange water, and the water absorption capacity of a 1% by weight calcium chloride aqueous solution. By specifying that the ratio [(A) / (B)] to (B) is 15 or less, germination rooting inhibition is not caused even when the plant is in direct contact, and good water retention It was possible to make it highly versatile and capable of performing stable functions in various surrounding environments.

A specific embodiment of the water-retaining agent for plant growth comprising the hydrogel-forming polymer of the present invention will be described. The present invention is not limited to the examples given below.
In the following, the hydrogel-forming polymer electrolyte refers to a polymer that has the property of forming a hydrogel by retaining water therein.
The “hydrogel” refers to a gel containing at least a polymer electrolyte and water supported or held in the structure (dispersed liquid).

The hydrogel-forming polymer electrolyte constituting the water-retaining agent for plant growth of the present invention will be described in detail.
First, the hydrogel-forming polymer of the present invention has an alkali metal ion content of less than 0.3 mmol / g, more preferably less than 0.1 mmol / g, per gram of dry weight. Shall.
In the present invention, it is not necessary to use an alkali metal as a polymerization stabilizer in the synthesis process of the hydrogel-forming polymer electrolyte, as will be described later. Only typical ones will be included.
If the alkali metal content exceeds 0.3 mmol / g, the influence of the plant calcium ion and the substitution reaction increases, which causes calcium deficiency and inhibits plant growth. Such a problem does not occur.

The hydrogel-forming polymer of the present invention has a water absorption ratio of 25 ° C. ion-exchanged water per gram of dry weight of 10 times or more, more preferably 20 times or more.
This is because if the water absorption ratio is less than 10 times, a practical water retention effect cannot be exhibited as a water retention material for plant growth.

In addition, the hydrogel-forming polymer of the present invention has a ratio of the water absorption capacity (A) of ion-exchanged water at 25 ° C. to the water absorption capacity (B) of a 1% by weight calcium chloride aqueous solution [(A) / ( B)] is 15 or less, more preferably 10 or less.
By selecting the ratio of water absorption ratio in this way, there is little fluctuation in water absorption capacity due to changes in the surrounding environment, good water retention capacity can be obtained by various soil types, and versatility is extremely wide and versatile It can be.

Specifically, the hydrogel-forming polymer of the present invention has a pH of 5 to 9, more preferably 6 to 8 after absorption of ion-exchanged water at 25 ° C.
By selecting the pH within the above numerical range, it was confirmed that practically sufficient germination and growth of plants were ensured.

A specific configuration of the hydrogel-forming polymer electrolyte that satisfies the various conditions as described above will be described.
In the present invention, the hydrogel-forming polymer electrolyte has a hydrophilic ionic group in the polymer skeleton in order to improve water retention. Examples of the ionic group include a sulfonic acid group, a sulfonic acid group, a carboxylic acid group, and a carboxylic acid group.
In addition, the hydrogel-forming polymer electrolyte of the present invention has an acidic neutralized salt in the polymer carrier. In other words, there is a basic counter ion to neutralize the sulfonic acid group and carboxylic acid group to form a sulfonic acid group and a carboxylic acid group, respectively. Specifically, calcium ions, magnesium ions, and iron ions are applied. it can.
The basic counter ion is most preferably calcium ion that does not inhibit the growth of the plant.
On the other hand, when alkali metal or ammonia is applied as a basic counter ion, substitution with calcium ion occurs, which causes deficiency of plant calcium ion and causes growth inhibition.
That is, in order to make the pH of the hydrogel near neutral, a sulfonate group or a carboxylate group is preferable, but a sulfonate group that can be easily neutralized with calcium ions is most preferable.

The amount of ionic groups such as sulfonate groups, that is, the amount of acidic neutralized salt introduced is preferably 5 to 95 mol%, more preferably 10 to 70 mol% of the entire monomer unit of the hydrogel-forming polymer. It is desirable.
When the introduction ratio is less than 5 mol%, the portion of the molecular chain that inevitably contributes to the water absorption ability is reduced, so that sufficient water absorption ability cannot be obtained. Dissolves in water.

  Next, a method for producing the hydrogel-forming polymer electrolyte of the present invention having the above-described configuration will be specifically described.

(1) Concentrated sulfuric acid treatment of a styrene polymer containing a predetermined amount of acrylonitrile groups Styrene containing 5 to 80 mol%, preferably 10 to 60 mol%, more preferably 20 to 50 mol% of acrylonitrile units in the polymer Polymer (specifically, ABS resin (acrylonitrile-butadiene-styrene resin), SAN resin (styrene-acrylonitrile resin), ASA resin (acrylonitrile-styrene-acrylate resin), ACS resin (acrylonitrile-chlorinated polyethylene-styrene resin) ), AAS resin (acrylonitrile-acrylic-styrene resin) etc.] treated with hot concentrated sulfuric acid (nitrile group is hydrolyzed and converted to amide group or carboxyl group, and benzene ring in styrene group is sulfonated) In the molecule, sulfo A water retention material (gel form) having acid groups is obtained.
Then, the obtained gel is filtered, and the pH is adjusted to 5 to 9 with a calcium hydroxide aqueous solution or the like, followed by filtration and drying again to obtain a powdery water retaining material.
The content of ionic groups [sulfonic acid (salt) groups and carboxylic acid (salt) groups] contained in the water retention material can be adjusted by examining conditions such as reaction time, reaction temperature, and sulfuric acid concentration.

The weight average molecular weight (Mw) of a styrenic polymer containing a predetermined amount of acrylonitrile groups is generally 1,000 to 20,000,000, more preferably 10,000 to 1,000,000.
When the molecular weight is less than 1,000, it becomes water-soluble after the hot sulfuric acid treatment, and a gel-like water retaining material cannot be obtained. On the other hand, when the molecular weight is larger than 20,000,000, hot concentrated sulfuric acid This is because hydrolysis and sulfonation reaction are difficult to proceed during the treatment.
The styrenic polymer containing a predetermined amount of acrylonitrile groups may be a virgin material, a used waste plastic, or a recovered material discharged from a factory. From the viewpoint of effective use of resources, it is desirable to apply waste materials and recovered materials.

(2) 1 selected from monomers having an ionic group of a carboxylic acid group or a sulfonic acid group and other hydrophilic group monomers (acrylamide, N-methylpyrrolidone, etc.) and / or monomers that become water-soluble by hydrolysis (acrylonitrile, etc.) More than one type of monomer and a crosslinking agent (monomer) are polymerized, and if necessary, hydrolysis is performed.
In addition, you may make block polymer by adding starch and a cellulose beforehand in a polymerization system.
The neutralization reaction with basic ions may be performed in the monomer state (before polymerization) or in the polymer state (after polymerization). In addition, the quantity of the ionic group contained in a water retention agent can be adjusted with the preparation amount of various monomers before superposition | polymerization.

Here, the content of the alkali metal in the water retention agent can be quantified by analyzing the material dissolved in an inorganic acid by atomic absorption after ashing the dried product with an electric furnace or the like.
Alternatively, after the dried product is put into a mixture of sulfuric acid and nitric acid and subjected to pressure decomposition using a microwave decomposition apparatus, the decomposition solution can be quantified by ICP mass spectrometry.
About content of an ionic group, in the case of a sulfonic acid (salt) group, it can quantify by an ion chromatograph measurement after the process by a combustion flask method.
In the case of a carboxyl group, it can be quantified by CHN elemental analysis, enzymatic method, fluorescent derivatization method and the like.

  As a method of measuring the water absorption ratio in ion-exchanged water, first, a certain amount (Ag) of a dry water retaining material is weighed and immersed in an excessive amount of ion-exchanged water (electric conductivity 5 μS / cm or less) at 25 ° C. Let the water retention agent swell for 30 minutes. Next, after removing excess water by filtration, the weight (Bg) of the water retention material swollen by water absorption is measured, and the water absorption magnification is obtained from water absorption magnification = (B−A) / A. The water absorption capacity in a 1% by weight calcium chloride aqueous solution is also determined by the same method.

  The pH of the water-retaining agent (hydrogel) can be measured by directly introducing a pH test paper or a pH meter into the hydrogel when 20 weight times of ion-exchanged water is added to the dry water-retaining agent.

  By using each measurement method as described above and producing while confirming, the present invention has a very low alkali metal content, a pH range suitable for plant growth, and extremely excellent water absorption. Thus, a water retention agent comprising a hydrogel-forming polymer electrolyte having properties can be obtained.

  The hydrogel-forming polymer electrolyte in the present invention may be used as it is as a water-retaining material for plant growth, or may be used by mixing with the following plant growth support.

  As the plant growth carrier, those generally used as substances suitable for plant growth can be applied and are not particularly limited. Examples of substances suitable for plant growth include water-insoluble solid substances such as powders of inorganic substances and / or organic substances, porous bodies, pellets, fibers, and foams.

  Examples of the inorganic substances include inorganic powders (soil, sand, fly ash, diatomaceous earth, clay, talc, kaolin, bentonite, dolomite, calcium carbonate, alumina, etc.), inorganic fibers (rock wool, glass fibers, etc.), inorganic porous bodies [Filton (porous ceramic, kuntan), vermiculite, pumice, volcanic ash, zeolite, shirasu balloon, etc.], inorganic foam (perlite, etc.) and the like.

  Examples of the organic substances include organic powders [coconut shells, rice straw, peanut shells, mandarin shells, wood chips, wood powders, dried coconut powder, synthetic resin powders (polyethylene powder, polypropylene powder, polystyrene powder, polycarbonate powder, SAN Powder, ABS powder, ethylene-vinyl acetate copolymer powder, etc.)], organic fiber [natural fiber (cellulosic (cotton, sawdust, straw, etc.) and others, grass charcoal, wool, etc.), artificial fiber (rayon, Cellulose-based materials such as acetate), synthetic fibers (polyamide, polyester, acrylic, etc.), pulp (mechanical pulp (pulverized wood pulp, aspulled pulp, etc.), chemical pulp (sulfite pulp, soda pulp, sulfate pulp, Nitrate pulp, chlorine pulp, etc.), semi-chemical pulp, recycled pulp ( For example, mechanically pulverized or pulverized paper made from pulp once, or recycled waste paper pulp that is mechanically crushed or pulverized waste paper)), other waste materials (waste material produced from the manufacture of paper diapers, etc.), etc. ], Organic porous body (coconut shell activated carbon, etc.), organic foam [cereals, synthetic resin or rubber foam (polystyrene foam, polyvinyl acetal sponge, rubber sponge, polyethylene foam, polypropylene foam, urethane foam, etc.)] And organic pellets [rubber and synthetic resin pellets] and the like.

  The above-mentioned plant growth carrier can be used alone or in combination of a plurality of kinds as necessary. Among these, preferable examples include inorganic porous bodies, inorganic foams, organic fibers, rubbers, and synthetic resins.

As described above, when a water retention material is constituted by combining a hydrogel-forming polymer electrolyte and a plant growth carrier, these weight ratios are appropriately selected depending on the type and the optimal moisture content of the plant. In general, however, the hydrogel-forming polymer: carrier = 0.01: 99.09 to 90:10, preferably 0.1: 99.1 to 80:20, : 99-70: 30, 5: 95-60: 40 are desirable.
If the content of the hydrogel-forming polymer electrolyte is less than 0.01, the water retention capacity is practically insufficient, and if it is 90 or more, the cost increases.

Note that a binder may be applied when the hydrogel-forming polymer electrolyte and the plant-growing carrier are mixed.
As the binder, conventionally known materials can be applied. For example, natural polymers or semi-synthetic polymers can be applied regardless of whether they are water-soluble or water-insoluble.
Examples of natural polymers include starch (starch, etc.), animal proteins (gelatin, casein, collagen, etc.), animal proteins (soy protein, wheat protein, etc.), fibrin (wood cellulose, etc.), seaweed extract (agar, etc.) , Carrageenan, etc.), plant seed mucilage (guar gum, locust bean gum, tamarind seed gum, etc.), plant leaf mucilage (arabic gum, tragacanth gum, etc.), plant fruit mucilage (pectin etc.), microbial production mucilage (xanthan gum, Pullulan, curdlan, dextran, dulan gum, etc.), plant rhizome mucilage (konjaknanman, etc.) and the like.
Semi-synthetic polymers include cellulose derivatives (methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, carboxymethyl cellulose, methyl hydroxypropyl cellulose, etc.), starch derivatives (soluble starch, carboxymethyl starch, methyl starch, etc.), and alginic acid derivatives ( Alginate, propylene glycol alginate, etc.).
These can be used by utilizing thermoplasticity rather than as an aqueous system. The thermoplastic softening point is the same as that of the thermoplastic resin described above.

  As a method of blending the above-described hydrogel-forming polymer electrolyte and the plant-growing carrier, the above-mentioned binder may be used as necessary. (1) Polymer electrolyte and plant-growing (2) A method of pressure-molding a stirred mixture of carriers into a pellet in a mold of an appropriate shape and size, (2) A method of pressure-molding the mixture, and cutting and grinding to an appropriate size, (3) (4) The method of (4) and (3), wherein the surface of the cut and pulverized product obtained in (2) is coated with a hydrogel-forming polymer and, if necessary, a binder and then pressure-molded again, and then cut and pulverized A method of pressure-molding the material before pressure molding into a pellet shape in a mold of an appropriate shape and size, (5) Once pressure-molded into a sheet shape, rod shape or block shape, then to an appropriate size Cutting or pulverizing method, (6) Mixture of sheet, rod or block (7) A method of heat-molding the mixture into a pellet in a mold of an appropriate shape and size, (8) Foaming the mixture into a sheet, rod or block Then, a method of cutting or pulverizing can be used.

As a mixing apparatus, any conventionally known apparatus can be applied as long as the mixture can be mixed uniformly. Examples thereof include a hessell mixer, a ribbon blender, a planetary mixer, a tumbler, and a universal mixer.
Moreover, in order to knead | mix a mixture, the apparatus which can knead | mix knead | mixing under a shearing force, such as a twin-screw extruder, a single screw extruder, a kneader, a Banbury mixer, a kneader, an open roll, is applicable.

The water-retaining agent for plant growth of the present invention includes fertilizers, agricultural chemicals, insecticides, bactericides, deodorants, fragrances, fungicides, antiseptics, anti-blocking agents, surfactants and the like as necessary. Various drugs may be added.
These agents only need to be present in the water retention material for plant growth of the present invention, and may be added in advance to the plant growth support and / or hydrogel-forming polymer electrolyte, or molded. You may add before and after a process.
Although the water-retaining agent for plant growth of the present invention may be colored or not colored, it is preferably colored with a pigment and / or a dye from the viewpoint of visual effects.

Hereinafter, specific samples of the water-retaining agent for plant cultivation according to the present invention and the water-retaining material produced using the same were prepared and tested for characteristics.
In addition, this invention is not limited to each Example shown below.

[Comparative Example 1]
Used 8 mm video cassette shell material (ABS resin waste: 50 mol% styrene unit, 39 mol% acrylonitrile unit and 11 mol% butadiene unit as a resin composition) The pulverized product was used as a resin raw material.
3 g of this resin pulverized product was added to 90 g of concentrated sulfuric acid (concentration: 97% by weight) and reacted at 80 ° C. for 60 minutes.
After completion of the reaction, the gel-like material in the system was filtered with a glass filter.
Next, after washing the filtrate twice with water, the filtrate was dried at 115 ° C. for 2 hours with a circulating drier to obtain a black dried product (water retaining agent sample).
When the quantitative analysis of sulfur by the combustion flask method was performed with respect to the said water retention agent sample, it was confirmed that content of a sulfonic acid group is 40 mol%.
The content of alkali metals (Na, K) was confirmed to be less than 0.1 mmol / g when measured by ICP mass spectrometry after pressure decomposition using a microwave decomposition apparatus.
The sample was added to 20 times by weight of ion-exchanged water (electric conductivity: 2.3 μS / cm), and the pH after 30 minutes (25 ° C.) was measured and found to be 2.0.

[Comparative Example 2]
The filtrate obtained in Comparative Example 1 (after washing twice with water) was poured into a large amount of water, and the pH was adjusted to 7 with sodium hydroxide.
The other conditions were the same as in Comparative Example 1 above to prepare a water retention material sample.
When a quantitative analysis was performed in the same manner as in Comparative Example 1, the content of the sulfonic acid group was 40 mol%.
The content of alkali metal (Na, K) was 0.5 mmol / g or more.
Similarly, the pH was measured and found to be 7.0.

[Comparative Example 3]
Instead of sodium hydroxide applied in Comparative Example 2, the pH was adjusted using potassium hydroxide.
Other conditions were the same as in Comparative Example 2 above, and a water retention material sample was prepared.
When a quantitative analysis was performed in the same manner as in Comparative Example 1, the content of the sulfonic acid group was 40 mol%.
The content of alkali metal (Na, K) was 0.5 mmol / g or more.
The pH was 7.0.

[Comparative Example 4]
A water absorbent resin (Na salt of carboxylic acid) used in commercially available paper diapers was used as a water retention material sample.
As a result of quantitative analysis in the same manner as in Comparative Example 1, the content of carboxylic acid groups was 97 mol%.
The content of alkali metal (Na, K) was 0.5 mmol / g or more.
The pH was 7.0.

[Example 1]
Instead of sodium hydroxide applied in Comparative Example 2, the pH was adjusted using calcium hydroxide.
The other conditions were the same as in Comparative Example 2, and a water retention material sample was prepared.
When a quantitative analysis was performed in the same manner as in Comparative Example 1, the content of the sulfonic acid group was 40 mol%.
The content of alkali metal (Na, K) was less than 0.1 mmol / g.
The pH was 7.0.

[Example 2]
Instead of used 8mm videocassette shell material, commercial videocassette (β tape) reel material (transparent part) (9SAN resin waste material: As resin composition, styrene unit is 56 mol%, acrylonitrile unit is 44 mol% Was used as a raw material.
Furthermore, pH was adjusted using calcium hydroxide as a neutralizing agent.
The other conditions were the same as in Comparative Example 2, and a water retention material sample was prepared.
When quantitative analysis was performed in the same manner as in Comparative Example 1, the content of sulfonic acid groups was 50 mol%.
The content of alkali metal (Na, K) was less than 0.1 mmol / g.
The pH was 7.0.

(Measurement of water absorption ratio)
Each sample was added to 20 times by weight of ion-exchanged water (electric conductivity: 2.3 μS / cm), the weight after 30 minutes (25 ° C.) was measured, and the water absorption ratio A was calculated.
Further, the water absorption ratio B of a 1% by weight calcium chloride aqueous solution with the same capacity as ion-exchanged water was measured.
A ratio (A / B) between the water absorption A in the ion-exchanged water and the water absorption B of the calcium chloride aqueous solution was calculated.

(Komatsuna growth experiment)
Each water-retaining material sample was swollen with 20 times weight of ion-exchanged water in a glass bottle, and then two komatsuna seeds were added to the upper surface of the gel.
Next, these glass bottles were allowed to stand for 140 hours in a thermostatic chamber (sunlight was inserted) at 25 ° C., and germination of Komatsuna was observed.
As an observation method, the lengths of germinated stems and roots were measured as two samples, and average values were obtained.

  Table 1 below shows the measurement results of the water absorption ratio of each sample and the measurement results of stem length and root length in the growth test of Komatsuna.

  From the results of Table 1 above, in Comparative Example 1, the contained ionic groups are not neutralized salts, and the gel pH is too low, so germination and rooting are inhibited, and the growth of Komatsuna is extremely poor. It did not have a function as a water retention agent.

Moreover, in Comparative Examples 2-4, since alkali metal content was too high, Ca deficiency of a plant body was caused by substitution, and the growth state of Komatsuna deteriorated.
Particularly in Comparative Example 4, the water absorption ratio B of the calcium chloride aqueous solution is low, the ratio (A / B) between the water absorption ratio A of the ion exchange water and the water absorption ratio B of the calcium chloride aqueous solution is extremely large, and the applicable range of soil selection is It turned out to be very narrow.
In this sample, the molecular chain has a carboxylic acid group as an ionic group, and Na ion is applied as an essential element for stabilizing the polymerization. Therefore, the content of Na ion is inevitably high. Upon substitution, the molecule caused a cross-linking reaction, resulting in significant degradation of water absorption.

(Sprout growth test of Komatsuna)
First, a water retention agent sample made of the following polymer was prepared.
Sample 1: Polymer three-dimensionally cross-linked poly N-vinylacetamide Sample 2: Polymer three-dimensionally cross-linked acrylic acid, partially Na neutralized salt.
Sample 3: Sulfonated ABS resin calcium salt Next, sprouting growth of Komatsuna was observed under the following conditions. After a predetermined time, the stem length and root length were measured, and the stem length / root length was calculated.
Test number: 1 sample 2 Absorption capacity: 20 times (ion-exchanged water)
Komatsuna seeds: 2 grains / sample Indoor temperature: 25-27 ° C
Elapsed time: 310 hours (about 13 days)

In FIGS. 1-3, the state of the Japanese mustard spinach after each growth test of the said samples 1-3 was shown.
When Sample 3 which is the water retention agent of the present invention was used, it was confirmed that the growth of Komatsuna was clearly better than the other samples, as shown in FIG.

The growth state of Komatsuna when Sample 1 is used is shown. The growth state of Komatsuna when Sample 2 is used is shown. The growth state of Komatsuna when sample 3 is used is shown.

Claims (9)

A water retention agent for plant growth comprising a hydrogel-forming polymer having an acidic neutralized salt on a polymer carrier,
The alkali metal content per gram dry weight is less than 0.3 mmol / g,
The water absorption ratio of 25 ° C. ion-exchanged water per 1 g of dry weight is 10 times or more,
The ratio [(A) / (B)] of the water absorption capacity (A) of ion-exchanged water at 25 ° C. and the water absorption capacity (B) of a 1% by weight calcium chloride aqueous solution is 15 or less. A water retention agent for plant growth comprising a hydrogel-forming polymer electrolyte.   The water retention agent for plant growth according to claim 1, wherein 20 parts by weight of ion-exchanged water with respect to 1 part by weight of dry water has a pH in an aqueous system at 25 ° C of 5.0 to 9.0. .   The water retention agent for plant cultivation according to claim 1, wherein at least one of the acidic neutralized salts is a sulfonate group.   The water retention water for plant growth according to claim 3, wherein the hydrogel-forming polymer electrolyte contains a modified resin obtained by sulfonating a styrene copolymer copolymerized with acrylonitrile. Agent.   The water-retaining agent for plant growth according to claim 4, wherein the styrene-based copolymer obtained by copolymerizing acrylonitrile is acrylonitrile in an amount of 5 to 80 mol% of the entire constituent units.   5. The water retention agent for growing a plant according to claim 4, wherein the sulfonate group formed by the sulfonation is contained in an amount of 5 to 95 mol% of the whole monomer unit of the hydrogel-forming polymer. .   The water-retaining agent for plant cultivation according to claim 4, wherein the acid neutralized salt is calcium sulfonate.   6. The water retention agent for plant growth according to claim 5, wherein the styrene copolymer obtained by copolymerizing acrylonitrile of the hydrogel-forming polymer electrolyte is a waste material. A water retention material for plant growth comprising a molded product of a mixture of a hydrogel-forming polymer electrolyte and a plant growth support,
The hydrogel-forming polymer electrolyte has an acidic neutralized salt on a polymer carrier,
The alkali metal content per gram dry weight is less than 0.3 mmol / g,
The water absorption ratio of 25 ° C. ion-exchanged water per 1 g of dry weight is 10 times or more,
The ratio [(A) / (B)] of the water absorption capacity (A) of ion-exchanged water at 25 ° C. and the water absorption capacity (B) of a 1% by weight calcium chloride aqueous solution is 15 or less. Water retention material for plant growth.

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