Method for irrigation-free afforestation by utilizing shallow wet sand

Abstract

The invention relates to an irrigation-free afforestation method using shallow wet sand, and relates to the technical field of afforestation. The irrigation-free afforestation method using the shallow wet sand comprises the following steps that (1) after saline-alkali soil or sand dunes with the underground water burial depth smaller than 1.5 m is selected, field planting points are determined according to the shape like a Chinese character'pin ', stones in the field planting points are removed, and tree pits are dug; (2) afforestation is carried out in a deep seedling planting mode, seedlings which grow robustly, are free of plant diseases and insect pests and have complete root systems are selected and planted in the tree pits, soil burying and water supplementing are carried out after planting is completed, and shallow-layer wet-sand irrigation-free afforestation is completed. By means of the irrigation-free afforestation method through the shallow wet sand, dependence on fresh water resources and underground salt water resources can be effectively reduced, and therefore the water resource cost is effectively saved.

Description

Technical Field

[0001] The present invention relates to the technical field of afforestation, and particularly to a method for non-irrigated afforestation using shallow wet sand. Background Art

[0002] With the continuous growth of the population and the rapid development of industrialization and urbanization, the problem of global water shortage has become increasingly prominent. Especially in arid regions, due to the vulnerability of the ecological environment, the water shortage situation is particularly serious. This not only leads to difficulties in replenishing forest land on the edge of the desert and desert vegetation outside the oasis, but also intense competition for water resources between agriculture and forestry within the oasis. In addition, the cost per mu of afforestation irrigation is as high as 2,500 yuan, seriously hindering the ecological protection work carried out in the desert edge areas.

[0003] Although since the 1980s, people have successively carried out a number of experimental studies such as snow afforestation, runoff afforestation, and non-irrigated afforestation in arid and semi-arid regions with an annual rainfall of more than 100 mm, and achieved rich technical achievements. However, in the desert-oasis transition zone of extremely arid regions with an annual rainfall of less than 50 mm, there are large areas of saline-alkali land and sandy land with shallow groundwater. Traditionally, it has always relied on the method of irrigated afforestation. With the implementation of the desert edge battle, large-scale sand prevention and afforestation work needs to be carried out urgently, and there is an urgent need for the support of non-irrigated afforestation technology. At present, there are extremely limited research reports on non-irrigated afforestation in extremely arid regions, and there is a lack of technical specifications for reference. Summary of the Invention

[0004] In order to fill the gap in non-irrigated afforestation in extremely arid regions, the present invention provides a method for non-irrigated afforestation using shallow wet sand.

[0005] A method for non-irrigated afforestation using shallow wet sand provided by the present invention includes the following steps:

[0006] (1) After selecting saline-alkali land or sandy land with a groundwater depth of less than 1.5 m, determine the planting points in a "pin" shape, remove the stones in the planting points and dig good tree pits;

[0007] (2) Afforest by the method of deep planting seedlings, select seedlings with strong growth, no diseases and pests, and complete root systems, plant them in the tree pits, and after planting, cover with soil and replenish water to complete non-irrigated afforestation using shallow wet sand.

[0008] The present invention can ensure to a certain extent that the planted plants can absorb groundwater in saline-alkali land or the inter-dune land with a groundwater depth of less than 1.5 m after afforestation, effectively improving the survival rate of the planted plants after afforestation. Moreover, the method provided by the present invention can complete afforestation without irrigation, reducing the cost of afforestation and effectively promoting the process of afforestation in arid regions.

[0009] Preferably, the saline-alkali land or inter-dune land in step (1) is located in a desert-oasis transition zone, and the soil moisture content of the saline-alkali land or inter-dune land below 15 cm of the salt crust of the saline-alkali land or below 25 cm of the sand surface of the inter-dune land is greater than 10%.

[0010] The invention ensures the survival rate of plants by limiting the selection of afforestation land in extremely arid areas.

[0011] Preferably, the spacing between the planting points in step (1) is 2m×3m.

[0012] The present invention can effectively improve the survival rate of plants by limiting the spacing between planting points, and avoid the problem of plants competing for nutrients and water in the subsequent growth process.

[0013] Preferably, the depth of the tree pit in step (1) is ≥40 cm.

[0014] The present invention can place the root system in moist soil by limiting the depth of the tree pit, and also shorten the distance between the plant root system and groundwater to a certain extent, further improving the survival rate of the plant.

[0015] Preferably, the soil in step (2) is buried to 5-8 cm above the original root of the seedling and is firmly tamp down.

[0016] The present invention can effectively improve the water and moisture retention effect of seedlings by limiting the parameters of soil burying, thereby improving the survival rate of the seedlings.

[0017] Preferably, the seedlings in step (2) are Tamarix chinensis, Halostachys salsa or Lycium ruthenicum; the seedlings are selected from 2-year-old seedlings or 1-year-old cuttings, and the seedling height of the seedlings is ≥60 cm.

[0018] The present invention clarifies the salt tolerance and drought tolerance of the selected plants by limiting the seedlings to three salt- and drought-tolerant shrubs, namely Tamarix chinensis, Halostachys chinensis or Lycium ruthenicum, thereby ensuring the survival rate and preservation rate. At the same time, the present invention limits the source of the seedlings to ensure that the seedlings have good vitality and avoid poor seedling status caused by changes in location and growth environment.

[0019] Preferably, the surface salt crust of the seedlings in step (2) needs to be peeled off before planting and transported out of the planting area, and the thickness of the surface salt crust is ≥5 cm.

[0020] The present invention can effectively reduce the salt content in the seedling planting environment by limiting the need to peel off the surface salt crust before seedling planting, thereby avoiding the decline in the growth state of the seedlings due to the influence of salt.

[0021] Preferably, after step (1) is completed, the step further includes filling the gel fertilizer into the tree pit, wherein the gel fertilizer comprises the following raw materials: cow dung, straw, starch, cyclodextrin, super absorbent resin, methacrylic acid, ammonium persulfate, N,N-methylenebisacrylamide and anti-transpiration agent.

[0022] The gel fertilizer used in the present invention contains an anti-transpiration agent, which can inhibit the transpiration of seedlings and prevent the seedlings from losing water continuously in a high temperature environment. At the same time, the gel fertilizer provided by the present invention can retain moisture and water, and can achieve slow release of water to prevent water loss. In addition, the gel fertilizer provided by the present invention can also provide the seedlings with the necessary nutrients for growth, further improving the filling condition of the seedlings.

[0023] Preferably, the preparation method of the gel fertilizer comprises the following steps:

[0024] A. adding the anti-transpiration agent into a saturated cyclodextrin aqueous solution, stirring the solution sufficiently, cooling and crystallizing the solution, and obtaining a gel fertilizer core layer;

[0025] B. After mixing cow dung and straw evenly, a fermentation raw material is obtained, EM bacterial agent is added to the fermentation raw material, mixed evenly, and then fermented for 6-8 days to obtain a fermented fertilizer, the fermented fertilizer is cut into concave semi-fermented fertilizers, and the gel fertilizer core layer is filled into the concave inner layer of the concave semi-fermented fertilizer;

[0026] C. Mix starch and water thoroughly, heat and stir to obtain a paste-like starch solution, cool to room temperature, add super absorbent resin, methacrylic acid, ammonium persulfate and N,N-methylenebisacrylamide, mix well, and heat in a water bath to obtain a gel;

[0027] D. Apply the gel on the surface of the concave semi-fermented fertilizer and dry it until the moisture content of the gel is 8-12% to obtain gel fertilizer.

[0028] Due to the special environmental influence of high daytime ambient temperature and low nighttime ambient temperature in arid areas, groundwater can be absorbed and fixed to the soil surface by plants at night, while the surface soil will be evaporated during the day. When the water is absorbed and fixed to the soil surface by seedlings at night, the gel fertilizer provided by the present invention will be fully moistened by water from the outside to the inside. Under the action of water, the semi-fermented fertilizer continues to ferment, and the nutrients produced by the fermentation process are absorbed by the seedlings along with the water, and the carbon dioxide produced by the fermentation process is released, which increases the content of carbon dioxide in the seedling growth environment, thereby partially reducing the respiration of the seedlings at night, and thereby increasing the moisture content of the seedling growth environment. At the same time, the gel fertilizer provided by the present invention coats the anti-transpiration agent in cyclodextrin. When the cyclodextrin contacts water, the coating structure is destroyed, and the anti-transpiration agent is partially dissolved in the water and absorbed by the seedlings, which can provide a certain anti-transpiration effect for the seedlings during the day, and prevent the seedlings from losing a large amount of water due to transpiration.

[0029] In addition, the gel fertilizer provided by the present invention has good water absorption and moisture retention effects. After the moisture on the soil surface is evaporated during the day, the moisture in the gel fertilizer can still be retained for a period of time and slowly released into the soil, continuously providing moisture for the growth of seedlings.

[0030] Preferably, the weight proportions of starch, super absorbent resin, methacrylic acid, ammonium persulfate, and N,N-methylenebisacryl in step C are as follows:

[0031] 10-30 parts of starch, 10-20 parts of super absorbent resin, 100-150 parts of methacrylic acid, 0.5-1.5 parts of ammonium persulfate and 1-2 parts of N,N-methylenebisacrylamide.

[0032] Preferably, the mass ratio of the gel fertilizer core layer, the concave semi-fermented fertilizer and the gel is 1:(30-40):(10-20).

[0034] Preferably, the mass volume ratio of the anti-transpiration agent to the saturated cyclodextrin aqueous solution is (10-20) g:1L.

[0035] Preferably, the dosage of the EM bacterial agent in the concave-shaped fermented fertilizer is (0.01-0.03) wt%.

[0036] Preferably, the mass ratio of the cow dung to the straw is (1-3):1.

[0037] The present invention can effectively prevent the gel from being too dense to release water and from being too loose to be formed by limiting the mass ratio of starch, super absorbent resin, methacrylic acid, ammonium persulfate and N,N-methylenebisacryloyl.

[0038] In the present invention, the super absorbent resin is a super absorbent resin SAP, which can further improve the water absorption of the gel and release the absorbed water when the roots of the seedlings are short of water.

[0039] In summary, the present invention includes at least one of the following beneficial technical effects:

[0040] 1. The present invention proposes an innovative afforestation strategy, namely, implementing irrigation-free afforestation technology on the wet sand layer of saline-alkali land and desertified land. The present invention reduces the dependence on freshwater resources and underground salt water resources, effectively saves water resource costs, and takes the example of 400 cubic meters of irrigation per mu of afforestation in arid areas. If the ecological water price is 0.178 yuan / cubic meter, the water cost per mu can be saved by 71.2 yuan. At the same time, the method of afforestation without irrigation using shallow wet sand provided by the present invention does not require expensive irrigation materials, further saves irrigation costs, and can save about 1,500 yuan per mu. Therefore, the method of afforestation without irrigation using shallow wet sand provided by the present invention not only saves costs, but also expands the space for afforestation in the desert edge area, and sets a new benchmark for the demonstration and promotion of afforestation technology in arid areas. DETAILED DESCRIPTION

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the present invention will be briefly introduced below in combination with the description of the embodiments or the prior art. Obviously, the following descriptions are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these embodiments without creative work. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention.

[0042] The present invention is further described in detail below with reference to the embodiments.

[0043] Preparation Example 1:

[0044] A method for preparing a gel fertilizer comprises the following steps:

[0045] A. Add 10 g of hydroxysulfonic acid into 1 L of saturated cyclodextrin aqueous solution, stir thoroughly at 30° C., cool and crystallize to obtain a gel fertilizer core layer;

[0046] B. Mix cow dung and straw in a mass ratio of 3:1 to obtain a fermentation raw material, add EM bacterial agent in an amount of 0.01% by weight of the fermentation raw material to the fermentation raw material, mix evenly, and ferment for 7 days to obtain a fermentation fertilizer, cut the fermentation fertilizer into concave semi-fermented fertilizers, and fill the gel fertilizer core layer into the concave inner layer of the concave semi-fermented fertilizer;

[0047] C. Mix starch and water thoroughly, heat and stir to obtain a paste-like starch solution, cool to room temperature, add super absorbent resin, methacrylic acid, ammonium persulfate and N, N-methylenebisacrylamide, mix evenly, and heat in a water bath to obtain a gel, wherein the gel comprises 10 parts of starch, 10 parts of super absorbent resin, 100 parts of methacrylic acid, 0.5 parts of ammonium persulfate and 1 part of N, N-methylenebisacrylamide;

[0048] D. Apply the gel on the surface of the concave semi-fermented fertilizer and dry it until the moisture content of the gel is 8% to obtain the gel fertilizer, and make the mass ratio of the gel fertilizer core layer, the concave semi-fermented fertilizer and the gel be 1:30:10.

[0049] Preparation Example 2:

[0050] A method for preparing a gel fertilizer comprises the following steps:

[0051] A. Add 20 g of hydroxysulfonic acid into 1 L of saturated cyclodextrin aqueous solution, stir thoroughly at 30°C, cool and crystallize to obtain a gel fertilizer core layer;

[0052] B. Mix cow dung and straw in a mass ratio of 2:1 to obtain a fermentation raw material, add 0.03% of the weight of the fermentation raw material to the fermentation raw material, mix evenly, and ferment for 7 days to obtain a fermentation fertilizer, cut the fermentation fertilizer into concave semi-fermented fertilizer, and fill the gel fertilizer core layer into the concave inner layer of the concave semi-fermented fertilizer;

[0053] C. Mix starch and water thoroughly, heat and stir to obtain a paste-like starch solution, cool to room temperature, add super absorbent resin, methacrylic acid, ammonium persulfate and N, N-methylenebisacrylamide, mix evenly, and heat in a water bath to obtain a gel, wherein the gel comprises 30 parts of starch, 20 parts of super absorbent resin, 150 parts of methacrylic acid, 1.5 parts of ammonium persulfate and 2 parts of N, N-methylenebisacrylamide;

[0054] D. Apply the gel on the surface of the concave semi-fermented fertilizer and dry it until the moisture content of the gel is 12% to obtain the gel fertilizer, and make the mass ratio of the gel fertilizer core layer, the concave semi-fermented fertilizer and the gel be 1:40:20.

[0055] Preparation Example 3:

[0056] A method for preparing a gel fertilizer comprises the following steps:

[0057] A. Add 10g of sodium azide into 1L of saturated cyclodextrin aqueous solution, stir thoroughly at 30°C, cool and crystallize to obtain a gel fertilizer core layer;

[0058] B. Mix cow dung and straw in a mass ratio of 1:1 to obtain a fermentation raw material, add 0.03% of the weight of the fermentation raw material to the fermentation raw material, mix evenly, and ferment for 7 days to obtain a fermented fertilizer, cut the fermented fertilizer into concave semi-fermented fertilizer, and fill the gel fertilizer core layer into the concave inner layer of the concave semi-fermented fertilizer;

[0059] C. Mix starch and water thoroughly, heat and stir to obtain a pasty starch solution. After cooling to room temperature, add superabsorbent resin, methacrylic acid, ammonium persulfate, and N,N'-methylenebisacrylamide and mix evenly. Heat in a water bath to obtain a gel, where there are 20 parts of starch, 15 parts of superabsorbent resin, 125 parts of methacrylic acid, 1 part of ammonium persulfate, and 1.5 parts of N,N'-methylenebisacrylamide;

[0060] D. Apply the gel to the surface of the concave semi-fermented fertilizer and dry it until the water content of the gel is 10%. Obtain the gel fertilizer, and the mass ratio of the core layer of the gel fertilizer, the concave semi-fermented fertilizer, and the gel is 1:35:15.

[0061] Example 1:

[0062] A method for afforestation using shallow wet sand without irrigation, comprising the following steps:

[0063] (1) After selecting saline-alkali land with a groundwater depth less than 1.5 m, determine the planting points in a "pin" shape, remove the stones in the planting points and dig tree pits with a depth of 40 cm. Among them, the spacing of the planting points is 2 m × 3 m;

[0064] (2) Peel off the surface salt crust with a thickness of 5 cm and transport it out of the planting area. Afforest by the method of deep-planting seedlings. Select 2-year-old Tamarix ramosissima seedlings with strong growth, no pests and diseases, and complete root systems and plant them in the tree pits. After planting, bury the soil to 5 cm above the original root and stem of the seedlings, and tamp it down. Water each plant, and the water consumption for watering is 20 kg, thus completing the afforestation using shallow wet sand without irrigation.

[0065] Example 2:

[0066] A method for afforestation using shallow wet sand without irrigation, comprising the following steps:

[0067] (1) After selecting the inter-dune land with a groundwater depth less than 1.5 m, determine the planting points in a "pin" shape, remove the stones in the planting points and dig tree pits with a depth of 60 cm. Among them, the spacing of the planting points is 2 m × 3 m;

[0068] (2) Peel off the surface salt crust with a thickness of 6 cm and transport it out of the planting area. Afforest by the method of deep-planting seedlings. Select 1-year-old Halostachys caspica cuttings with strong growth, no pests and diseases, and complete root systems and plant them in the tree pits. After planting, bury the soil to 8 cm above the original root and stem of the seedlings, and tamp it down. Water each plant, and the water consumption for watering is 20 kg, thus completing the afforestation using shallow wet sand without irrigation.

[0069] Example 3:

[0070] (1) After selecting saline-alkali land with a groundwater depth less than 1.5 m, determine the planting points in a "pin" shape, remove the stones within the planting points and dig tree pits with a depth of 40 cm. Among them, the spacing between the planting points is 2 m × 3 m;

[0071] (2) Peel off the surface salt crust with a thickness of 5 cm and transport it out of the planting area. Fill the gel fertilizer in Preparation Example 1 into the tree pits. Afforest by the method of deep planting seedlings. Select 2-year-old Lycium ruthenicum Murr. seedlings with strong growth, no diseases and pests, and complete root systems and plant them in the tree pits. After planting, cover the soil. Cover the soil to 5 cm above the original rootstock of the seedlings and tamp it down. Water each plant, and the water consumption for watering is 20 kg, and complete the shallow-layer wet sand non-irrigation afforestation.

[0072] Example 4:

[0073] A method for non-irrigation afforestation using shallow-layer wet sand, comprising the following steps:

[0074] (1) After selecting the inter-dune land with a groundwater depth less than 1.5 m, determine the planting points in a "pin" shape, remove the stones within the planting points and dig tree pits with a depth of 60 cm. Among them, the spacing between the planting points is 2 m × 3 m;

[0075] (2) Peel off the surface salt crust with a thickness of 6 cm and transport it out of the planting area. Fill the gel fertilizer in Preparation Example 2 into the tree pits. Afforest by the method of deep planting seedlings. Select 1-year-old Tamarix chinensis Lour. cuttings with strong growth, no diseases and pests, and complete root systems and plant them in the tree pits. After planting, cover the soil. Cover the soil to 8 cm above the original rootstock of the seedlings and tamp it down. Water each plant, and the water consumption for watering is 20 kg, and complete the shallow-layer wet sand non-irrigation afforestation.

[0076] Detect the soil water content at the planting points of the seedlings in Examples 1-4, and the obtained data are shown in Table 1:

[0077] Table 1 Changes in soil water content at the planting points of the seedlings in Examples 1-4

[0078] project Water content on day 5 Water content on day 10 Water content on day 15 Example 1 6％ 14％ 25％ Example 2 6％ 15％ 24％ Example 3 4％ 13％ 27％ Example 4 5％ 12％ 27％

[0079] It can be seen from Table 1 that the method of afforestation using shallow wet sand without irrigation provided by the present invention can effectively ensure that the growth environment of the seedlings has sufficient moisture, and by comparing Examples 1 and 2 with Examples 3 and 4, it can be seen that after the gel fertilizer is added, the water content in the soil will decrease during the early growth of the seedlings. This is because the gel fertilizer does not contain moisture in the early stage of planting and needs to absorb moisture in the soil to provide a longer water release effect. It can also be seen from Table 1 that after the seedlings have grown for a period of time, the soil of the seedlings to which the gel fertilizer has been added contains more moisture. This is because the gel fertilizer has fully absorbed water and can continue to exert the effect of moisturizing and retaining water in the subsequent growth process.

[0080] The method of afforestation without irrigation using shallow wet sand provided in Examples 1-4 was used to carry out a seedling planting experiment in arid areas. The survival rate of each group was counted two months after the seedlings were planted, and the data obtained are shown in Table 2:

[0081] Table 2 Statistical table of survival rate of seedlings in seedling planting experiment of Example 1-4

[0082] project Seedling survival rate Example 1 97.57％ Example 2 96.13％ Example 3 98.87％ Example 4 98.02％

[0083] As can be seen from Table 2, the method of afforestation without irrigation using shallow wet sand provided by the present invention can effectively ensure the survival rate of seedlings. Therefore, the present invention realizes the implementation of non-irrigation afforestation technology on the wet sand layer of saline-alkali land and desertified land, reduces the dependence on fresh water resources and underground salt water resources, expands the space for afforestation in desert edge areas, and sets a new benchmark for the demonstration and promotion of afforestation technology in arid areas.

[0084] The above are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for afforestation using shallow wet sand without irrigation, characterized in that: It includes the following steps: (1) After selecting saline-alkali land or the inter-dune land where the groundwater depth is less than 1.5 m, determine the planting points in a "pin" shape, remove the stones within the planting points and dig tree pits; (2) Afforest by means of deep-planting seedlings. Select seedlings that are robust, disease-free and pest-free and have complete root systems, plant them in the tree pits, cover them with soil after planting and supply water, thus completing the shallow-layer wet-sand irrigation-free afforestation.

2. A method for afforestation using shallow wet sand without irrigation according to claim 1, characterized in that: In step (1), the saline-alkali land or the inter-dune land is located in the desert-oasis transition zone, and the soil water content below 15 cm of the saline crust of the saline-alkali land or below 25 cm of the sand surface of the inter-dune land is greater than 10%.

3. The method for afforestation using shallow wet sand without irrigation according to claim 1, characterized in that: In step (1), the spacing between the planting points is 2 m × 3 m.

4. The method for afforestation using shallow wet sand without irrigation according to claim 1, characterized in that: In step (1), the depth of the tree pit is ≥ 40 cm.

5. The method for afforestation using shallow wet sand without irrigation according to claim 1, characterized in that: In step (2), the requirement for covering with soil is to cover to a position 5 - 8 cm above the original root and stem of the seedling, and ensure it is tamped down.

6. The method for afforestation using shallow wet sand without irrigation according to claim 1, characterized in that: In step (2), the seedlings are Tamarix chinensis, Halostachys caspica or Lycium ruthenicum; the seedlings are selected from 2-year-old seedlings or 1-year-old cuttings, and the seedling height is ≥ 60 cm.

7. The method for afforestation using shallow wet sand without irrigation according to claim 1, characterized in that: Before planting the seedlings in step (2), the surface saline crust needs to be peeled off and transported out of the planting area, and the thickness of the peeled surface saline crust is ≥ 5 cm.

8. The method for afforestation using shallow wet sand without irrigation according to claim 1, characterized in that: After step (1) is completed, it also includes filling gel fertilizer into the tree pits. The gel fertilizer includes the following raw materials: cow dung, straw, starch, cyclodextrin, superabsorbent resin, methacrylic acid, ammonium persulfate, N,N-methylenebisacrylamide and an antitranspirant.

9. A method for afforestation using shallow wet sand without irrigation according to claim 8, characterized in that: The preparation method of the gel fertilizer includes the following steps: A. Add the antitranspirant to the saturated cyclodextrin aqueous solution, stir well, then cool and crystallize to obtain the core layer of the gel fertilizer; B. Mix cow dung and straw evenly to obtain the fermentation raw material. Add EM microbial agents to the fermentation raw material, mix evenly and ferment for 6 - 8 days to obtain the fermented fertilizer. Cut the fermented fertilizer into concave semi-fermented fertilizer, and fill the core layer of the gel fertilizer into the concave inner layer of the concave semi-fermented fertilizer; C. Mix starch and water充分, heat and stir to obtain a paste-like starch solution. After cooling to room temperature, add superabsorbent resin, methacrylic acid, ammonium persulfate and N,N-methylenebisacrylamide, mix evenly, and heat in a water bath to obtain a gel; D. Apply the gel on the surface of the concave semi-fermented fertilizer, and dry it until the water content of the gel is 8 - 12% to obtain the gel fertilizer.

10. A method for afforestation using shallow wet sand without irrigation according to claim 9, characterized in that: In step C, the weight parts of starch, superabsorbent resin, methacrylic acid, ammonium persulfate and N,N-methylenebisacrylamide are as follows: Starch 10 - 30 parts, superabsorbent resin 10 - 20 parts, methacrylic acid 100 - 150 parts, ammonium persulfate 0.5 - 1.5 parts and N,N-methylenebisacrylamide 1 - 2 parts.