CN115413446A

CN115413446A - Alfalfa drought-resistant seedling-protecting type biological water-retaining agent pill seed and preparation method thereof

Info

Publication number: CN115413446A
Application number: CN202211136512.1A
Authority: CN
Inventors: 毛培胜; 贾志程; 欧成明; 赵海君; 李曼莉; 张文旭
Original assignee: China Agricultural University
Current assignee: China Agricultural University
Priority date: 2022-09-19
Filing date: 2022-09-19
Publication date: 2022-12-02

Abstract

A drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seed comprises three layers: the first layer is a nucleating layer, the second layer is a water retention layer and the third layer is a film forming layer; the alfalfa seed water-retaining film comprises a first layer, a second layer and a third layer, wherein the first layer is a nucleating layer coated outside a alfalfa seed and consists of powder and an adhesive; the alfalfa seeds are subjected to the pill coating treatment, so that the drought resistance and seedling protection capability of alfalfa seedlings under drought can be improved, the successful establishment and planting of the alfalfa are facilitated, and the seed sowing amount and the watering amount of seeds in arid and semi-arid regions are reduced.

Description

Alfalfa drought-resistant seedling-protecting type biological water-retaining agent pill seed and preparation method thereof

Technical Field

The invention relates to treatment of seeds before sowing of alfalfa seeds, and mainly relates to a seed coating formula and a processing method.

Background

Alfalfa (Medicago sativa L.) as an excellent perennial leguminous forage has the characteristics of high yield and nutritional value, good palatability, strong adaptability and the like, has the reputation of the king of pasture, and is one of the most extensive forage grasses cultivated at home and abroad. With the rapid development of the economy of China and the increase of the demand of livestock products such as beef mutton, milk and the like caused by the change of the dietary structure, the development of the grassland animal husbandry has more and more requirements on high-quality forage products such as alfalfa and the like, and the production of the alfalfa becomes increasingly important. However, in the alfalfa cultivation process, the phenomena of low emergence rate and irregular emergence often occur, which are caused by various factors. In recent years, due to the influence of global warming and increasingly deficient water resources, drought becomes a worldwide problem, and the problems of seasonal drought and aggravation of soil salinization degree in China are increasingly prominent. Alfalfa is mostly planted in arid and semi-arid regions in China. Many studies report that drought stress is one of the important natural factors affecting plant growth. During sowing, drought is an undesirable important factor which causes low emergence rate, weak seedlings and the like.

At present, the tolerance of plants under drought stress is mainly improved by two ways, and one way is to utilize the traditional breeding means or molecular biotechnology means to cultivate drought-tolerant varieties. This includes traditional crossbreeding and emerging mutation breeding and genetic engineering breeding, but it takes a long time and is costly. And secondly, the drought tolerance of the plants is improved by adjusting the agronomic measures, including seeding time, planting density, exogenous substance induction, soil management and the like. Has the advantages of quick response, obvious effect and the like. Researches show that the water-retaining agent can improve the germination rate and the emergence rate of the alfalfa under the drought stress. The water-retaining agent can utilize the principle of water absorption and slow release to form a micro reservoir around the alfalfa seeds, store redundant water, slowly release the water to the seeds, and reduce the risk that the seeds cannot germinate and emerge due to drought. However, excessive application of water-retaining agents is likely to cause environmental problems and damage to seeds. The mode of application of the water-retaining agent is therefore of critical importance.

The seed coating is one of seed treatment technologies, and a proper amount of nutrient substances and protective substances are supplied to the seeds, so that the use amount of chemical fertilizers and medicines is reduced, adverse factors are resisted, and the germination of the seeds is promoted. Meanwhile, the physical structure and size of the seeds are improved, the mechanical sowing of precision agriculture is facilitated, and the method is an important engineering technology for sustainable development of agriculture.

The water-retaining agent is a high molecular polymer with super-strong water absorption and retention capacity, is nontoxic and harmless, can be degraded and biologically decomposed into CO ₂ 、H ₂ O and K ⁺ Stable physical and chemical properties and long service life. Water is absorbed by chemical adsorption, physical adsorption and net adsorption, and after absorbing water, the water-retaining agent becomes a hydrogel state and then is slowly released according to the demand of plants for water. The water absorption and slow release characteristics of the water retention agent can be extended to multiple functions. For example, water retention agents are used with fertilizers, pesticides, and rooting powders, and then slowly released to significantly increase ingredient utilization. The water-retaining agent can form a micro reservoir around the seeds and has the functions of protecting the seedlings and resisting drought. The influence of the dosage of the water-retaining agent on seed germination is different from species to species, and the proper amount of the water-retaining agent has a promoting effect on the germination of typical desert plant seeds, so that the seed germination capacity is improved, and the plant survival rate is increased. Appropriate amount of water-retaining agent can also promote germination of alfalfa, sea buckthorn (Hippophae rhamnoides L.) and Caragana korshinskii Kom and growth of seedling. Under mild drought stress, the use of the high water-absorbing polymer can improve the water utilization rate of cowpea (Vigna anguillata (Linn.) Walp.) in adverse environment and optimize the yield of the cowpea. The water-retaining agent is mainly applied by mixing soil and serving as a culture medium or directly adopting root dipping, seed soaking, seed coating and the like. The principle of applying the water-retaining agent in the seed coating mode is that after the water-retaining agent with a certain concentration is prepared and mixed with seeds, a layer of protective film can be formed on the surfaces of the seeds, so that the influence of stimulation factors on the seeds can be effectively prevented, and the seeds can be provided with nutrient components and required water, which is very beneficial to the preservation and the germination of the seeds. 5 percent ofThe chemical water-retaining agent with the concentration can promote the seed germination of caragana microphylla, chinese pine, sea buckthorn (Hippophae rhamnoides L.) and wild jujube (Ziziphus acidojuba C.Y.Cheng et M.J.Liu) seeds, has a certain promotion effect on the growth of seedlings in the later period, and can also increase the surface area of the root systems of the seedlings. There are two problems in the application of water-retaining agents: the chemical water-retaining agent is continuously accumulated in the soil, thereby causing soil problems and environmental problems; the research on the pelleting formula of the water-retaining agent is less, and particularly, the application of the biomass water-retaining agent is less, and the application is less reported in alfalfa.

Disclosure of Invention

The inventors of the present invention believe that drought stress is a major abiotic stress that causes osmotic stress to the plant, which prevents the plant from developing properly. The germination process of the seeds is very sensitive to moisture, and the vitality of the seedlings determines whether the field planting can be successful and the yield of the plants. Therefore, the invention adopts the environment-friendly biomass water-retaining agent to carry out the pill-coating treatment on the alfalfa seeds to improve the drought-resisting and seedling-protecting capability of the alfalfa seedlings under the drought, is beneficial to successful alfalfa establishment, reduces the seed sowing amount and the watering amount of the seeds in the arid and semi-arid regions, and promotes the sustainable development of agriculture.

The first aspect of the invention provides a drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seed, wherein the whole seed pill has three layers: the first layer is a nucleating layer, the second layer is a water retention layer and the third layer is a film forming layer.

The first layer is a nucleating layer coated outside the alfalfa seeds and is composed of powder, wherein the powder is bentonite or talcum powder, and the proportion of the bentonite and the talcum powder is as follows: 2-1, wherein the thickness of the nucleation layer is as follows: 0.10-0.12mm.

The second floor is the cladding at the outer guarantor's water layer of nucleation layer, guarantor's water layer comprises powder and water-retaining agent, the powder is bentonite or talcum powder, the ratio of powder and water-retaining agent is: 6-10, the thickness of water conservation layer is: 0.1-0.13mm.

The third layer is a film forming layer coated outside the water retention layer, the film forming layer is composed of powder or/and a binder, and the ratio of the powder to the binder is as follows: 1g and 1ml, and the thickness of the film forming layer is as follows: 0.04-0.06mm.

Preferably, the powder is bentonite or talcum powder.

Preferably, the water retaining agent is a biomass water retaining agent (SB) or a Huashen water retaining agent (HB), and the particle size of the water retaining agent is 200 meshes. The Huashen water retention agent is a contrast water retention agent, and actually the drought-resistant seedling-protecting type biological water retention agent is a biomass water retention agent for alfalfa coated seeds.

The second aspect of the invention provides a preparation method of the drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seeds, which comprises the following steps:

step 1: selecting alfalfa seeds, powder and a water-retaining agent;

step 2: preparing 0.5-1% and 1-1.5% sodium carboxymethylcellulose aqueous solution;

and step 3: preparing alfalfa coating seeds:

first layer (nucleation layer): weighing 5g of clean alfalfa seeds, pouring the alfalfa seeds into a coating machine, adjusting the rotating speed to 650-690 range, enabling the seeds to roll at a constant speed along the clamping grooves, and enabling the seeds to touch the baffle plate to have a certain falling height (about 2 cm), so that the powder and the adhesive are in full contact. Thereafter, the atomizing disk was secured within the chuck slot, and a small amount (about 0.4 ml) of 1.0% CMC binder was added to the in-slot atomizing disk to wet the seed surfaces with no sticking between the seeds. Then, powder is added, and the rotating speed is slightly reduced; when the seeds are observed to return to the constant rolling speed, a small amount of adhesive is continuously dropped. The above procedure was repeated until the formulation powder was added (table 2). The binder and powder are added alternately during the coating process, following the principle of a few times.

Second layer (water-retaining layer): after the first layer of powder is added, the seeds are idled for 2-3min, and then the rotating speed is properly increased to 690-700. The powders were mixed well according to formula table 2. The addition of 1% CMC in water solution binder and the second layer of powder was continued alternately. In the process, a small amount of adhesive and powder are added for multiple times, the adhesive is added firstly, a proper amount of powder is added when the surface of the seeds is wet on the premise of ensuring that the seeds are not adhered together, the powder is uniformly coated on the surface of the seeds, and the operations are repeated until the formula powder is completely added. The dosage of the second layer of the adhesive is about 6 to 8ml, 0.4 to 0.5ml of the adhesive is used each time, and about 0.7g of the powder is used.

Third layer (film-forming layer): after the second layer is finished, the seeds are idled for 2-4min, then 1.5 percent of CMC binder and the powder of the third layer are added according to the formula, and the steps are alternately carried out, and an appropriate amount of powder is added when the surface of the seeds is wet on the premise of ensuring that the seeds are not adhered together, wherein about 0.4-0.5ml of the binder is added each time, and 0.5-0.7g of the powder is added. The seed rolling time can be properly prolonged (rolling for 30-40s after adding the binder and the powder each time, adding the binder and the powder to improve the hardness and smoothness of the seeds, idling for 3min after the formula powder is completely added, stopping the machine, taking the seeds, sieving the seeds, leaving the seeds with proper size, and drying the pelleted seeds in an oven after coating.

And after the third layer of pelleting is finished, the alfalfa seeds are taken out, and the pelleted seeds with the size of 14-9 meshes and the size of 1.4-2.0 mm are screened and reserved. And (3) putting the pelletized seeds into an oven to dry for 0.5h at the drying temperature of 35 ℃, or naturally airing (24 h).

The third aspect of the invention is the field experiment and the application of the alfalfa coated seeds prepared by the invention, which are suitable for drought.

Concrete technical solution of the invention

1 screening of water-retaining agent formula and development of pill coating formula

The biomass water retention agent (SB) and the Huashen water retention agent (HB) are selected as coating materials. The biomass water-retaining agent is used as a novel environment-friendly material, is extracted from banana peel and is environment-friendly. Huashen Baoji water-retaining agent is used as a contrast material for agricultural and forestry water retention in the market, is generally used by a method of soil mixing and the like, and is synthesized by chemical substances.

Referring to the technology of pelleting small-sized seeds, the whole pelleting layer has three layers. The first layer is a nucleating layer (bentonite and talcum powder); adding a water-retaining agent into the second layer; the third layer is a film forming period. Take 5g of alfalfa naked seeds as an example. The overall coating design pattern is shown in figure 1.

2 screening of alfalfa seeds for drought gradient

In order to verify the performance of the pill coating under drought, drought is simulated by adopting a sand culture water control method, the germination rate is taken as an index, and the optimum drought gradient screening is carried out by using naked seeds.

3 Water-retaining agent pill coat for seedling germination and seedling vitality under drought

The measured indexes include germination characteristics, antioxidant enzyme indexes, chlorophyll indexes and drought resistance indexes. The germination characteristic indexes include: germination rate (emergence rate), germination index, fresh weight, etc. The indexes of antioxidant enzyme are as follows: catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD). Chlorophyll index: chlorophyll a, chlorophyll b and total chlorophyll. Drought indexes include: proline content, soluble protein content and relative conductivity.

Drawings

FIG. 1 is a schematic diagram of alfalfa seed coating design;

FIG. 2 photo of water-retaining agent pill seed of different types and contents;

FIG. 3 shows the emergence rate of alfalfa seeds under conditions of sand culture simulated drought treatment;

FIG. 4 germination characteristics of pelleted seeds under drought stress. A: the rate of emergence; b: a germination index; c: fresh weight;

FIG. 5 antioxidase index of pellet seeds under drought stress. A: POD enzyme activity; b: SOD enzyme activity; c: CAT enzyme activity;

FIG. 6 drought resistance index of the pelleted seedlings under drought stress. A: (ii) proline; b: relative conductivity; c: a soluble protein;

FIG. 7 chlorophyll content of pelleted seedlings under drought stress. A: chlorophyll a; b: chlorophyll b; c: total chlorophyll;

FIG. 8 principal component analysis of pill-coated seedlings under drought stress. A, a 3D picture of a main component; b: a variable contribution graph.

Detailed Description

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the exemplary embodiments below do not represent all implementations consistent with the present disclosure. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the disclosure, as detailed in the appended claims.

Example 1

Screening of water-retaining agent formula and development of pill coating formula

Referring to the technology of pelleting small-sized seeds, the whole pelleting layer has three layers. The first layer is the nucleation period (bentonite and talc); the second layer is added with effective substances and increases the rolling period; the third layer is a film forming period. Take 5g of alfalfa naked seeds as an example. The formulation of the second layer of the pellet is shown in table 2. CK2 is used as a control, namely the water retention agent is not added to the second layer of the pill coat.

Before pelleting, the water-retaining agent is crushed and sieved by a 200-mesh sieve, and then is uniformly mixed with bentonite and talcum powder according to the formula shown in the table 2.

TABLE 2 Water-loss reducer pill coating formula

Referring to the method for pelleting seeds of small size with tonicity (2017) and with some modifications, the procedure for coating the seeds of pellets according to the formulation of table 2 is as follows:

first layer (nucleation layer): weighing 5g of clean alfalfa seeds, pouring the alfalfa seeds into a coating machine, adjusting the rotating speed to 650-690 range, enabling the seeds to roll at a constant speed along the clamping grooves, enabling the seeds to touch the baffle plate to have a certain falling height (about 2-2.5 cm), and enabling the powder and the adhesive to be in full contact. The atomizing disk was then secured in the chuck slot and a small amount (about 0.4-0.45 ml) of 1.0% CMC binder was added to the in-slot atomizing disk to wet the seed surfaces and not block the seeds from one another. Then, powder is added, and the rotating speed is slightly reduced; when the seeds are observed to return to the constant rolling speed, a small amount of adhesive is continuously dropped. The above procedure was repeated until the formulation powder was added (table 2). The binder and powder are added alternately during the coating process, following the principle of a few times.

Second layer (water-retaining layer): after the first layer of powder is added, the seeds are idled for 2-3min, and then the rotating speed is properly increased to 690-700. The powders were mixed well according to formula table 2. The addition of 1% CMC in water solution binder and the second layer of powder was continued alternately. In the process, a small amount of adhesive and powder are added for multiple times, the adhesive is added firstly, a proper amount of powder is added when the surface of the seeds is wet on the premise of ensuring that the seeds are not adhered together, the powder is uniformly coated on the surface of the seeds, and the operations are repeated until the formula powder is completely added. The dosage of the second layer of the adhesive is about 6 to 8ml, 0.4 to 0.5ml of the adhesive is used each time, and about 0.7 to 0.8g of the powder is used.

Third layer (film-forming layer): after the second layer is finished, the seeds are idled for 2-4min, then 1.5 percent of CMC binder and the powder of the third layer are added according to the formula, and the steps are alternately carried out, and an appropriate amount of powder is added when the surface of the seeds is wet on the premise of ensuring that the seeds are not adhered together, wherein about 0.4-0.5ml of the binder is added each time, and 0.5-0.55g of the powder is added. The seed rolling time can be properly prolonged (rolling for 30-50s after adding the binder and the powder each time, adding the binder and the powder to improve the hardness and smoothness of the seeds, idling for 3-5min after the formula powder is completely added, stopping the machine, taking the seeds, sieving the seeds, leaving the seeds with proper size, and drying the pelleted seeds in an oven after coating.

And taking out the alfalfa seeds after the pelleting of the third layer is finished, and screening and reserving 9-14 meshes of pelleted seeds. And (4) putting the pelletized seeds into an oven to be dried for 0.5h at the drying temperature of 35 ℃, or naturally airing (24 h). The final water-retaining agent pill seed is shown in figure 2.

Water-retaining agent pill coating quality evaluation

And (4) measuring and evaluating the coating performance and activity indexes of the coated seeds after coating. According to the standard of the pill coating, the single seed rate and the cracking rate are more than 98 percent, which shows that the pill coating is qualified, and the process is qualified. Furthermore, the coating does not significantly reduce the germination rate. In summary, the process of the pill coating was acceptable (table 3).

TABLE 3 evaluation of seed quality of alfalfa water-retaining agent pill coat

Screening of alfalfa seed drought stress suitable conditions

To verify the role of the pelleted coating in drought, drought stress was simulated using sand-culture controlled water. The results show that when the moisture content of the sand culture water control treatment is 5%, the germination rate of the seeds is remarkably reduced to about 70% (figure 3). Thus, a substrate moisture content of 5% was selected as a drought stress condition.

Validation of water-retaining agent pill coating under drought stress

Selecting sand culture water control to simulate drought, and keeping the water content of the matrix at 5% (mass ratio of water to matrix). The specific treatments are listed in Table 4, with CK0, CK1 and CK2 as controls.

TABLE 4 drought treatment of pelleted seeds

And (3) measuring germination performance, antioxidant enzyme activity, drought resistance index and chlorophyll content index. The germination performance includes: germination rate, germination index and fresh weight; the indexes of antioxidant enzyme are as follows: CAT enzyme activity, SOD enzyme activity and POD enzyme activity; drought resistance index: proline content, conductivity and soluble protein content.

The result of germination performance indexes shows that the water-retaining agent with proper concentration can improve the rate of emergence, but has no obvious difference. HB inhibits seed emergence at high concentrations. SB1 was increased by 7.2% relative to both CK1 and CK2 emergence rates (FIG. 4A). SB1 significantly increased germination index (P < 0.05) compared to CK1 (fig. 4B). At the same time, all concentrations of water retention agent significantly increased the fresh weight of seedlings (P < 0.05) compared to CK1, with SB significantly higher than HB, where SB1 and SB2 were the highest (fig. 4C).

The antioxidase index results showed that the POD enzyme activities of SB1, SB2 and HB0.5 were significantly reduced compared to the POD enzyme activities of the controls CK1 and CK2, and were close to the POD enzyme activity of CKO (not subjected to drought stress) (FIG. 5A). The SOD enzyme activity of SB1 was lowest compared to control CK1 and CK2, and was consistent with CK0 (fig. 5B). The concentration of SB1 in the CAT enzyme activity is far lower than that of CK1, CK2 and other water-retaining agent treatments, and the level of the CAT enzyme activity is close to that of CK0 (figure 5C).

Drought resistance index results showed that proline content of SB1 and HB0.5 was lowest compared to other treatments, close to CK0 (fig. 6A). The relative conductivity of SB1 was the lowest with CK1, CK2 and other processes (fig. 6B). The soluble protein content SB1 is significantly higher than CK1 and CK2 (P < 0.05) while also being highest in the different water retention agent addition levels (fig. 6C).

For the chlorophyll index, the results show that SB significantly increased the chlorophyll a and chlorophyll b content (P < 0.05) over CK1 and CK2 at all three levels, with SB1 being the highest (fig. 7a, b). While the three contents of total chlorophyll SB were significantly higher than CK1 and CK2 (P < 0.05) (fig. 7C).

And (4) performing principal component analysis and membership function analysis by combining the indexes. The result shows that the main component can obviously distinguish the seedling after the water-retaining agent pill coating from the CK1 and CK2 contrast, which shows that the water-retaining agent pill coating is effective under sand culture drought. The results of the analysis of the contribution of the main component variables show that the indexes of fresh weight (weight), soluble Protein (SP), SOD, CAT, germination Index (GI), proline (Pro) and Vitality Index (VI) are important (fig. 8).

And selecting important indexes to perform membership function analysis so as to comprehensively evaluate the performances of different water-retaining agent coating formulas. The results show that SB1 has the best overall performance among SB. Among HB, HB0.5 water-retaining agents gave the best overall results, with higher membership function values than the controls CK1, CK2 (Table 5). And the SB1 membership function value is higher than HB0.5. The membership functions for all coating formulations were from high to low: CK0> SB1> SB2> HB0.5> SB0.5> CK2> HB1> HB2> CK1.

TABLE 5 drought-resistant comprehensive evaluation of seedlings with different water-retaining agent formulas

In conclusion, 1 g-2 g of biomass water-retaining agent is added into every 5g of alfalfa seeds for pelleting, so that the vigor and the drought resistance of alfalfa seedlings can be improved, and the pelleting formula can be used for drought resistance and seedling protection of alfalfa. Compared with common chemical water-retaining agents in markets such as Huashen, the water-retaining agent has no inhibiting effect on seedlings and is environment-friendly.

6 advantages of the invention

The technology improves the drought resistance and seedling protection capability of the alfalfa seeds during sowing;

the technology can be used for related enterprises to perform pelleting coating of the alfalfa seeds, so that the size of the seeds is increased, and the sowing is facilitated;

the invention has simple and convenient technical method, material saving, easy operation and program standardization.

Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

Claims

1. A drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seed comprises three layers: the first layer is a nucleating layer, the second layer is a water retention layer and the third layer is a film forming layer.

2. The drought-resistant seedling-protecting type biological water-retaining agent alfalfa coating seed as claimed in claim 1, wherein the first layer is a nucleation layer coated outside the alfalfa seed, and is composed of powder and adhesive, the powder is bentonite and talcum powder, and the ratio of the bentonite to the talcum powder is as follows: 2-1; the adhesive is 1.0-1.5% sodium carboxymethylcellulose aqueous solution, and the proportion of the powder and the adhesive is 1g.

3. The drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seed as claimed in claim 1, wherein the second layer is a water-retaining layer coated outside the nucleation layer, the water-retaining layer is composed of powder, a water-retaining agent and an adhesive, the powder is bentonite and talcum powder, and the ratio of the bentonite to the talcum powder is 2-1; the adhesive is 0.5-1.0% sodium carboxymethylcellulose aqueous solution, and the proportion of the powder and the adhesive is 1g; the powder and the water-retaining agent are mixed in proportion as follows: 6-10:1.

4. The drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seed as claimed in claim 1, wherein the third layer is a film-forming layer coated outside the water-retaining layer, the film-forming layer is composed of powder and an adhesive, the adhesive is a 1.0-1.5% sodium carboxymethylcellulose aqueous solution, the powder is talcum powder, and the ratio of the powder to the adhesive is as follows: 1g and 1ml.

5. The drought-resistant seedling-protecting type biological water-retaining agent alfalfa coating seed as claimed in claim 1, wherein the water-retaining agent is selected from biomass water-retaining agent (SB) and/or Huashen water-retaining agent (HB).

6. A preparation method of the drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seeds as claimed in any one of claims 1 to 5 comprises the following steps:

step 1: selecting alfalfa seeds, powder and a water-retaining agent;

step 2: preparing 1% and 1.5% sodium carboxymethylcellulose aqueous solutions;

and 3, step 3: preparation of alfalfa coated seeds comprising:

first layer, nucleation layer: weighing an appropriate amount of seeds, pouring the seeds into a coating machine, adjusting the rotating speed to enable the seeds to roll along the clamping groove at a constant speed, ensuring that the seeds have a certain falling height when the seeds touch the baffle, fixing the atomizing disk in the clamping groove, adding a small amount of 1 percent of CMC aqueous solution into the in-groove atomizing disk until the surface of the seeds is wet and the seeds are not adhered together, continuously adding 1.5 percent of CMC aqueous solution, and repeating the operation until the powder is added according to the proportion;

the second layer, water-retaining layer: after the first layer of powder is added, idling the seeds for 2-3min, then properly increasing the rotating speed, and continuously and alternately adding the binder and the powder according to the proportion; repeating the operations until the powder is added according to the proportion;

third layer, film-forming layer: after the second layer is finished, idling the seeds for 2-4min, then adding an adhesive and powder according to a formula, alternately performing, adding a proper amount of powder when the surfaces of the seeds are wet on the premise of ensuring that the seeds are not adhered together, properly prolonging the rolling time of the seeds, then adding the adhesive and the powder, stopping the machine to take the seeds and sieving the seeds after all the powder is added according to the proportion, and leaving the seeds with proper sizes;

and taking out the alfalfa seeds after the pelleting of the third layer, screening and reserving 9-14 meshes of pelleted seeds, and putting the pelleted seeds into an oven for drying or naturally airing.

7. The application of the drought-resistant seedling-protecting type biological water-retaining agent alfalfa coated seeds as claimed in any one of claims 1 to 6.