CN112624807B

CN112624807B - Cadmium-reducing agent for rice, seed soaking liquid, preparation method and seed soaking method

Info

Publication number: CN112624807B
Application number: CN202110050320.8A
Authority: CN
Inventors: 谢杰; 董爱琴; 李建国; 杨涛; 陈院华; 徐昌旭
Original assignee: Institute of Soil Fertilizer Resources and Environment of Jiangxi Academy of Agricultural Sciences
Current assignee: Institute of Soil Fertilizer Resources and Environment of Jiangxi Academy of Agricultural Sciences
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2022-12-16
Anticipated expiration: 2041-01-14
Also published as: CN112624807A

Abstract

The invention belongs to the technical field of rice production, and particularly relates to a cadmium reduction agent for rice, a seed soaking liquid, a preparation method and a seed soaking method. The medicament comprises metal salt, wherein the metal salt is at least one of ferrous sulfate, ferric chloride, ferrous chloride, manganese nitrate, manganese sulfate, zinc chloride, zinc nitrate and zinc sulfate. When the agent is used for soaking rice seeds, the absorption capacity of the rice to cadmium can be reduced, and the germination potential of the rice seeds can be improved. The metal salt is used as competitive adsorption particles of heavy metal cadmium, can enter rice seeds in advance during seed soaking, improves the concentration of competitive metal ions in rice seed cells, reduces the absorption of the rice to cadmium in soil through competing with cadmium ions for a transport channel in a rice root system membrane transport protein, can stimulate the expression of stress-resistant genes in the rice seeds, accelerates the germination of the rice seeds, improves the germination vigor and shortens the germination accelerating time of the rice.

Description

Cadmium-reducing agent for rice, seed soaking liquid, preparation method and seed soaking method

Technical Field

The invention belongs to the technical field of rice production, and particularly relates to a cadmium reduction agent for rice, a seed soaking liquid, a preparation method and a seed soaking method.

Background

In recent years, with the development of industry and the use of agricultural input products in large quantities, the world faces more and more serious soil environment safety problems, and the attention on heavy metal pollution is the most. The method is subject to the nervous cultivated land level in China, and the adoption of simple and rough desertion measures for the soil polluted by heavy metal obviously brings huge hidden troubles to the grain safety. In order to reduce the absorption of heavy metals by crops and ensure the safety of food on the premise of not influencing the productivity of soil, the common technical means comprise reducing the activity of heavy metals in soil and reducing the absorption capacity of heavy metals by crops.

The efficient and cheap reduction of the absorption of heavy metals by crops is a current research hotspot. Soil heavy metal passivation materials produced by taking various materials as raw materials are diversified, but the problems of high cost, large manpower input and repeated application are often caused, and certain influence is brought to the soil structure and the environment bearing capacity. The absorption capacity of crops to heavy metals is reduced through certain measures, the absorption of crops such as rice and the like to heavy metal cadmium is reduced on the premise of not damaging the soil structure and the original productivity, and the method gradually becomes a new research direction for safe utilization of cadmium-polluted farmlands at present.

Chinese patent CN110066202A discloses a foliage spraying agent for reducing cadmium content of rice, which consists of sodium selenite and a pesticide fertilizer infiltration agent, and achieves the effect of reducing the cadmium content of the rice by spraying the rice for three times. Chinese patent document CN105613577A discloses a foliar spray agent, which comprises a plurality of components such as silicon micropowder, methoxysilane, thiocyanate, cosolvent, surfactant and the like, and the foliar spray agent is sprayed on rice foliar for a plurality of times to achieve the effect of reducing cadmium. Chinese patent document CN107759349A discloses a multi-nutrient compound foliar fertilizer for preventing and controlling the accumulation of cadmium in rice, a preparation method and application thereof. Chinese patent document CN105724428A discloses a foliar blocking agent for accurately regulating and controlling expression of genes related to cadmium absorption and transport of rice, and the cadmium content of rice is reduced by adopting a spraying mode. However, the method of spraying on the leaf surface can not obviously reduce the safe planting cost of the rice, and the method of spraying for many times in different periods of rice growth also brings higher labor cost, and the raw materials of the existing method are complex and expensive, thereby limiting popularization and application. Therefore, it is very important to develop a method for reducing the cadmium absorption capacity of rice with simple technology, low cost, safety and high efficiency.

Chinese patent document CN110934152A discloses a seed soaking agent for reducing cadmium and arsenic content in rice seeds, which is a solution containing sodium selenite and sodium metasilicate, the seed soaking agent is used for soaking the rice seeds before sowing, but the sodium selenite belongs to a highly toxic substance, rat orally takes LD50 of 7mg/kg, so that a large safety risk exists, the application scene is limited, the seed soaking agent cannot be popularized and used in farmers, and the method has a low effect of reducing the cadmium content of the rice seeds and needs to be further improved.

Disclosure of Invention

Therefore, the invention aims to overcome the defects that the rice seed soaking liquid in the prior art has high toxicity and can not be popularized and used, the cadmium reduction effect of the soaking liquid needs to be further improved and the like, and provides a rice cadmium reduction medicament, a rice cadmium reduction soaking liquid, a preparation method thereof and a seed soaking method.

Therefore, the invention provides the following technical scheme.

The invention provides a rice cadmium reduction medicament, which comprises metal salt;

the metal salt is at least one of ferrous sulfate, ferric chloride, ferrous chloride, manganese nitrate, manganese sulfate, zinc chloride, zinc nitrate and zinc sulfate.

The medicament comprises the following components in percentage by mass (6-8): ferrous sulfate and manganese chloride of (2-4); or the like, or, alternatively,

the medicament comprises the following components in percentage by mass (2-3): the ferrous chloride and the zinc nitrate of (1-2); or the like, or a combination thereof,

the medicament comprises the following components in percentage by mass (3-4): (2-4) manganese nitrate and zinc sulfate.

The medicament is powder.

The invention also provides a rice cadmium reduction seed soaking liquid which comprises a solvent and the medicament.

The seed soaking liquid comprises the following components in percentage by mass of 1: (10-50) a pharmaceutical agent and a solvent.

The seed soaking liquid comprises the following components in percentage by mass of 1: (10-30) a pharmaceutical agent and a solvent.

The solvent is water.

The invention also provides a preparation method of the seed soaking liquid, which comprises the steps of uniformly mixing and dissolving the medicament and the solvent to obtain the seed soaking liquid.

Further, the present invention provides a seed soaking method using the above seed soaking liquid or the seed soaking liquid prepared by the above preparation method, comprising the steps of,

soaking rice in the seed soaking liquid for 20-30h, taking out, stacking together, and allowing the rice to germinate.

Further, the temperature of the seed soaking is 25-30 ℃ in the seed soaking process.

The medicament and the seed soaking liquid provided by the invention can be suitable for but not limited to a plurality of early and late rice products such as Zhongjiazao 17, huanghua clay, taiyou 398, yuenongsimiao, wufengyou Huazhan, zhongzao 33, xiangzaixian 45 and Quanyou 33, and play a role in reducing cadmium for most rice varieties.

The technical scheme of the invention has the following advantages:

1. the cadmium reduction medicament for the rice comprises metal salt, wherein the metal salt is at least one of ferrous sulfate, ferric chloride, ferrous chloride, manganese nitrate, manganese sulfate, zinc chloride, zinc nitrate and zinc sulfate. When the agent is used for soaking rice seeds, the absorption capacity of the rice to cadmium can be reduced, and the germination potential of the rice seeds can be improved. The metal salt is used as competitive adsorption particles of heavy metal cadmium, can enter rice seeds in advance during seed soaking, improves the concentration of competitive metal ions in rice seed cells, reduces the absorption of the rice to cadmium in soil through competing with cadmium ions for a transport channel in a rice root system membrane transport protein, can stimulate the expression of stress-resistant genes in the rice seeds, accelerates the germination of the rice seeds, improves the germination vigor and shortens the germination accelerating time of the rice.

When the agent provided by the invention is used for soaking rice seeds, the germination accelerating time of the rice seeds can be shortened, the germination accelerating cost is reduced, the agricultural production efficiency is improved, and the additional labor cost is not increased; the metal salt in the pesticide provided by the invention is a non-toxic or low-toxicity compound, does not harm personnel, is cheap and easy to obtain, is a metal component contained in soil, does not bring new pollution to the soil, and is suitable for popularization and application in farmers. The medicament provided by the invention has a good cadmium reduction effect on multiple rice varieties and good adaptability. In addition, the rice cadmium reduction medicament provided by the invention is convenient to transport.

2. When the metal salt comprises a mixture of ferrous sulfate and manganese chloride, or a mixture of ferrous chloride and zinc nitrate, or a mixture of manganese nitrate and zinc sulfate, or ferrous sulfate, the medicament is prepared into a seed soaking solution, and after the rice seeds are soaked, the obtained brown rice has low cadmium content and especially obvious cadmium reduction effect.

3. The cadmium-reducing rice seed soaking liquid provided by the invention comprises the medicament and the solvent, and can reduce the absorption capacity of rice to cadmium and improve the germination vigor of rice seeds after the rice seeds are soaked by the seed soaking liquid. The metal salt is used as competitive adsorption particles of heavy metal cadmium, can enter the rice seeds in advance during seed soaking, improves the concentration of competitive metal ions in rice seed cells, reduces the absorption of the rice to cadmium in soil by competing with cadmium ions for a transport channel in rice root system membrane transport protein, can stimulate the expression of stress-resistant genes in the rice seeds through the metal salt, accelerates the germination of the rice seeds, improves the germination vigor, and shortens the germination accelerating time of the rice.

The invention adopts the seed soaking liquid with specific concentration, and greatly reduces the cadmium content in the rice seeds by reducing the absorption of heavy metal cadmium by the rice root system, and the cadmium reduction effect can reach 75 percent to the maximum. In addition, the rice seed soaking liquid provided by the invention can achieve the aim of safe production of rice in farmland polluted by medium and light cadmium, and compared with other seed soaking agents, the rice seed soaking liquid can achieve the condition of suitable sowing and is reduced by at least 2 days.

4. The seed soaking method of the seed soaking liquid provided by the invention comprises the steps of soaking rice in the seed soaking liquid for 20-30h, fishing out, stacking together and allowing the rice to germinate. The seed soaking time is too long, the respiration of the rice seeds is inhibited, the germination is seriously influenced, the soaking time is too short, the rice seeds do not absorb water, and the germination rate is influenced. In addition, the seed soaking method is simple and convenient, strong in operability, free of additional labor cost, capable of shortening the germination accelerating time of the rice seeds after seed soaking, and capable of improving agricultural production efficiency, and after multiple tests, the time for the rice seeds to reach the suitable sowing condition (the root length is more than 1 cm) is at least shortened by 2 days compared with other seed soaking solutions.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 shows germination of rice seeds in test example 4 of the present invention;

FIG. 2 shows the rice seedlings of test example 4 of the present invention.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

The examples do not indicate specific experimental procedures or conditions, and can be performed according to the procedures or conditions of the conventional experimental procedures described in the literature in the field. The reagents or instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.

Example 1

The embodiment provides a cadmium reduction medicament for rice and a seed soaking liquid containing the same, wherein the medicament comprises 5g of ferrous sulfate and 3g of manganese chloride; the seed soaking liquid comprises 5g of ferrous sulfate, 3g of manganese chloride and 200g of water.

Example 2

The embodiment provides a rice cadmium reduction medicament and a seed soaking liquid containing the same, wherein the medicament comprises 5g of ferrous sulfate and 3g of manganese chloride; the seed soaking liquid comprises 5g of ferrous sulfate, 3g of manganese chloride and 88g of water.

Example 3

The embodiment provides a cadmium reduction medicament for rice and a seed soaking liquid containing the cadmium reduction medicament, wherein the medicament comprises 5g of ferric chloride and 3g of manganese sulfate; the seed soaking liquid comprises 5g of ferric chloride, 3g of manganese sulfate and 320g of water.

Example 4

The embodiment provides a cadmium reduction medicament for rice and a seed soaking liquid containing the same, wherein the medicament comprises 5g of ferrous sulfate; the seed soaking liquid comprises 5g of ferrous sulfate and 150g of water.

Example 5

The embodiment provides a cadmium reduction agent for rice and a seed soaking liquid containing the same, wherein the agent comprises 4g of ferrous chloride and 2g of zinc nitrate; the seed soaking liquid comprises 4g of ferrous chloride, 2g of zinc nitrate and 90g of water.

Example 6

The embodiment provides a rice cadmium reduction medicament and a seed soaking liquid containing the same, wherein the medicament comprises 1g of manganese nitrate and 1g of zinc sulfate; the seed soaking liquid comprises 1g of manganese nitrate, 1g of zinc sulfate and 100g of water.

Comparative example 1

The present comparative example provides a medicament and a seed soak containing the medicament, wherein the medicament includes 5g ferrous sulfate and 3g manganese chloride; the seed soaking liquid comprises 5g of ferrous sulfate, 3g of manganese chloride and 40g of water.

Comparative example 2

The present comparative example provides a medicament and an infusion solution comprising the medicament, wherein the medicament comprises 8g of calcium chloride; the seed soaking solution comprises 8g of calcium chloride and 200g of water.

Comparative example 3

The present comparative example provides a medicament and a seed soaking solution containing the same, wherein the medicament comprises 8g of sodium silicate; the seed soaking liquid comprises 8g of sodium silicate and 200g of water.

Comparative example 4

The present comparative example provides a medicament and an infusion solution comprising the medicament, wherein the medicament comprises 8g potassium sulfate; the seed soaking liquid comprises 8g of potassium sulfate and 200g of water.

Comparative example 5

This comparative example used clear water as the seed soak.

Test example 1

This test example provides a seed soaking method of the seed soaking liquid of examples 1 to 6 and comparative examples 1 to 5, comprising the steps of,

soaking rice seeds in the seed soaking liquid of the examples 1-6 and the comparative examples 1-5 for 24 hours respectively, wherein the seed soaking temperature is 29 +/-1 ℃, then fishing out the seeds to the open space for natural germination acceleration, keeping the environmental temperature at 20 +/-1 ℃ in the germination acceleration process, properly turning over the seeds according to the actual environment to avoid burning and decaying the seeds, and recording the germination rate and the average root length of the rice seeds on the 3 rd day and the 5 th day of the germination acceleration process respectively; among them, the rice variety of test examples 1 to 4 was Zhongjiazao 17.

After the rice seed root length exceeds 1cm, sowing the rice seed into a seedling bed, normally raising the rice seedling, after the condition suitable for planting is reached, transplanting the rice seedling into a cadmium-polluted field block, and adopting the same agricultural management measures and water management conditions for all experimental treatments. After rice is ripe, a rice sample is collected, husked, the brown rice part of the rice is taken, crushed, and the cadmium content in the brown rice is determined by adopting a triacid digestion-graphite furnace atomic absorption method according to the method of determination of cadmium in GB 5009.15-2014 national standard food for food safety and the cadmium reduction effect is evaluated. The rice germination rate and root length recording results are shown in table 1, and the cadmium content testing results in the brown rice are shown in table 2. Examples 1-6 and comparative examples 1-5 are labeled A-K, respectively.

TABLE 1 statistics of seed soaking and germination of rice seeds in test example 1

Number of	A	B	C	D	E	F	G	H	I	J	K
												3d average root length (mm)	9	14	10	9	10	9	3	5	6	7	7
5d average root length (mm)	14	19	17	15	18	15	5	9	11	10	11
												3d germination (%)	51	56	39	42	53	40	11	42	35	40	45
5d Germination (%)	72	78	61	64	73	62	19	59	51	49	57

TABLE 2 test results of cadmium content in brown rice obtained in test example 1

Note: "-" indicates no cadmium reduction effect, as in tables 4 and 6.

As can be seen from Table 1, after the rice seeds are soaked in the seed soaking liquid of examples 1-6 and comparative examples 1-5 for 24 hours, the seeds reach suitable sowing conditions after 3 days of pregermination, and the germination rate is 39-56%. The radicle length of the rice seeds soaked in the example 1-6 after 5 days of pregermination is far beyond the sowing condition, and the rice seeds soaked in the comparative example 2-5 just reach the sowing condition. The seed soaking liquids obtained in examples 1 to 6 contribute to the improvement of the germination rate and the growth of the root system of rice seeds.

As shown in Table 2, the cadmium content of the brown rice obtained by soaking the rice seeds in the seed soaking liquid obtained in examples 1 to 6 is low, and the cadmium reduction rate of the seed soaking liquid obtained in examples 1 to 6 is 45.7 to 74.6 percent compared with that of the brown rice obtained by soaking the rice seeds in water; in addition, the cadmium reduction rate of the seed soaking liquid obtained in the comparative examples 1 to 5 is less than 40%, and the cadmium content exceeds the food safety standard (< 0.2 mg/kg).

Test example 2

This test example provides a seed soaking method of the seed soaking liquid of examples 1 to 6 and comparative examples 1 to 5, comprising the steps of:

respectively soaking rice seeds in the seed soaking liquid of the embodiments 1-6 and the comparative examples 1-5 for 48 hours at the temperature of 29 +/-1 ℃, then fishing out the seeds to the open ground for natural germination acceleration, keeping the environmental temperature at 20 +/-1 ℃ in the germination acceleration process, properly turning over the seeds according to the actual environment to avoid burning and rotting the seeds, and respectively recording the germination rate and the average root length of the rice seeds on the 3 rd day and the 5 th day of the germination acceleration process.

After the rice seed root length exceeds 1cm, sowing the rice seed into a seedling bed, normally raising the rice seedling, after the condition suitable for planting is reached, transplanting the rice seedling into a cadmium-polluted field block, and adopting the same agricultural management measures and water management conditions for all experimental treatments. After rice is ripe, a rice sample is collected, husked and the brown rice part is taken, crushed, and the cadmium content in the brown rice is determined by adopting a triacid digestion-graphite furnace atomic absorption method according to the method of determination of cadmium in GB 5009.15-2014 national standard food for food safety and the cadmium reduction effect is evaluated. The rice germination rate and root length recording results are shown in table 3, and the cadmium content testing results in the brown rice are shown in table 4.

TABLE 3 statistics of the germination of rice seeds in test example 2

Numbering	A	B	C	D	E	F	G	H	I	J	K
												3d average root length (mm)	7	3	6	4	3	7	3	6	6	6	7
5d average root length (mm)	12	7	10	8	7	12	7	10	10	9	11
												3d Germination (%)	12	7	31	15	20	30	11	31	31	33	41
5d Germination (%)	15	20	21	45	24	48	19	47	47	45	55

TABLE 4 test results of cadmium content in brown rice obtained in test example 2

Table 3 shows that the germination rate of rice is seriously affected by changing the seed soaking time to 48 hours, and the average root length and the germination rate are more remarkably reduced as the seed soaking liquid concentration is higher, in this test example, examples 1 to 6 are seriously reduced as compared with the germination rate and the average root length of test example 1. The seed soaking time is too long, the respiration of the rice seeds is inhibited, and the high-concentration seed soaking agent has an inhibiting effect on the germination of the rice seeds.

In Table 4, after the rice seeds are soaked in the seed soaking liquid of examples 1 to 6, the cadmium reduction rate of the brown rice is 41 to 67.3 percent, the cadmium content of most of the rice seeds does not meet the national food standard, and the cadmium content of comparative examples 1 to 5 is high. The seed soaking time cannot improve the cadmium reduction effect.

Test example 3

soaking rice seeds in the seed soaking liquid of the examples 1-6 and the comparative examples 1-5 for 12 hours respectively, wherein the seed soaking temperature is 29 +/-1 ℃, then fishing out the seeds to the open space for natural germination acceleration, keeping the environmental temperature at 20 +/-1 ℃ in the germination acceleration process, properly turning over the seeds according to the actual environment to avoid burning and decaying the seeds, and recording the germination rate and the average root length of the rice seeds on the 3 rd day and the 5 th day of the germination acceleration process respectively.

After the rice seed root length exceeds 1cm, sowing the rice seed into a seedling bed, normally raising the rice seedling, after the condition suitable for planting is reached, transplanting the rice seedling into a cadmium-polluted field block, and adopting the same agricultural management measures and water management conditions for all experimental treatments. After rice is ripe, a rice sample is collected, husked, the brown rice part of the rice is taken, crushed, and the cadmium content in the brown rice is determined by using a triacid digestion-graphite furnace atomic absorption method according to the method of determination of cadmium in GB 5009.15-2014 national standard food for food safety, and the cadmium reduction effect is evaluated. The rice germination rate and root length recording results are shown in table 5, and the cadmium content testing results in the brown rice are shown in table 6.

TABLE 5 statistics of the germination and seed soaking of the rice seeds in test example 3

Number of	A	B	C	D	E	F	G	H	I	J	K
												3d average root length (mm)	5	8	6	6	6	5	2	3	3	3	3
5d average root length (mm)	10	11	10	12	11	10	7	9	10	9	10
												3d Germination (%)	39	40	37	38	42	38	12	33	29	32	35
5d Germination (%)	55	61	47	49	62	48	15	53	42	41	45

TABLE 6 test results of cadmium content in brown rice obtained in test example 3

As can be seen from Table 5, the seed soaking time was 12 hours, the germination rate and average root length of rice seeds were significantly lower than those of test example 1, and after 5 days of germination acceleration, examples 1 to 6 reached sowing-suitable conditions, and the germination rate was 47% to 62%. Compared with the test example 1 comprehensively, the average root length and the germination rate of the test example 3 are lower than those of the test example 1, which indicates that the seed soaking time is 12 hours, the seed soaking is insufficient, and the germination of the rice seeds is influenced.

Table 6 shows that after the rice seeds are soaked in the seed soaking liquid of the examples 1 to 6, the cadmium reduction rate is between 40.9 and 67.3 percent, the cadmium reduction effect is slightly lower than that of the test example 1, the cadmium content of most brown rice does not meet the national food standard, the cadmium content of the comparative examples 1 to 5 is very high, and the cadmium reduction effect is reduced to a certain extent due to the shortened seed soaking time.

Comprehensively, the medicament and the seed soaking liquid provided by the invention are beneficial to improving the germination rate and the germination potential of rice seeds and reducing the cadmium content in brown rice; the optimal seed soaking time of the seed soaking liquid is 20-30h, and the average cadmium reduction rate of the brown rice is about 50% -75%.

Test example 4

The test example considers the influence of the mass ratio of the medicament to the solvent on the rice seed germination, the medicament comprises 5g of ferrous sulfate and 3g of manganese chloride, soaking seeds in the soaking liquid with the mass ratio of 1 to the solvent of 1, 50, 1.

Then the germinated seeds are transferred to an illumination incubator in a unified mode, constant-temperature illumination culture is carried out for 7 days, the seedling raising condition is shown in figure 2, the mass fraction of the pesticide in the seed soaking liquid is large, the height of rice seedlings is high, and the fact that the seed soaking agent with the specific formula can promote the germination of the rice seeds and accelerate the rice seedling raising process is shown.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.

Claims

1. The cadmium-reducing rice seed soaking liquid is characterized by consisting of a medicament and a solvent;

the medicament is prepared from the following components in percentage by mass (6-8): (2-4) ferrous sulfate and manganese chloride; or the like, or, alternatively,

the medicament is prepared from the following components in percentage by mass (2-3): (1-2) ferrous chloride and zinc nitrate;

the mass ratio of the medicament to the solvent is 1: (10-50);

the solvent is water.

2. The rice cadmium reduction seed soaking liquid according to claim 1, wherein the medicament is a powder.

3. The seed soaking liquid according to claim 1, wherein the seed soaking liquid comprises the following components in a mass ratio of 1: (10-30) a pharmaceutical agent and a solvent.

4. A method of preparing an infusion solution according to any one of claims 1 to 3, comprising mixing a pharmaceutical agent with a solvent and dissolving the mixture to obtain said infusion solution.

5. A seed soaking method using the seed soaking liquid according to any one of claims 1 to 3 or the seed soaking liquid prepared by the preparation method according to claim 4, comprising the steps of,

6. The seed soaking method according to claim 5, wherein the temperature of the seed soaking is 25-30 ℃ during seed soaking.