CN113207560B

CN113207560B - Alfalfa planting method by fully-biodegradable mulch film

Info

Publication number: CN113207560B
Application number: CN202110524743.9A
Authority: CN
Inventors: 朱德新; 汤小华; 韩庆辉; 黄岩
Original assignee: Beijing Baiqingyuan Animal Husbandry Technology Development Co ltd; Henan Qingyuan Tianren Biotechnology Co ltd
Current assignee: Beijing Baiqingyuan Animal Husbandry Technology Development Co ltd; Henan Qingyuan Tianren Biotechnology Co ltd
Priority date: 2021-05-14
Filing date: 2021-05-14
Publication date: 2023-04-25
Anticipated expiration: 2041-05-14
Also published as: CN113207560A

Abstract

The invention provides a alfalfa planting method with full-biodegradable mulch film, which adopts planting, field management and mowing, and comprises the following steps: seed selection, irrigation, base fertilizer application, soil preparation, narrow row hole sowing, field management and harvesting; the full-biodegradable mulching film comprises, by weight, 100 parts of full-biodegradable resin, 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate, wherein the performance of the full-biodegradable mulching film accords with the specification of national standard GB/T35795-2017 'full-biodegradable agricultural ground covering film', and the problems that the success rate of alfalfa planting in arid regions in northwest China is low, mulching film fragments are mixed into alfalfa grass during film covering planting are solved, and meanwhile the problems that the degradation rate and the mechanical strength of the biodegradable mulching film cannot be considered, and the damage to livestock caused by mistaking are solved.

Description

Alfalfa planting method by fully-biodegradable mulch film

Technical Field

The invention relates to the field of agricultural planting, in particular to a alfalfa planting method by covering a full-biodegradable mulch film.

Background

Alfalfa is an indispensable forage grass in modern animal husbandry, enjoys the special role of 'forage grass king', is the most important and best vegetable protein source especially in the dairy cow industry, and the practice at home and abroad repeatedly proves that the added alfalfa has the irreplaceable effect of any other feed for improving the milk yield of the dairy cows, reducing the unit cost of the milk and improving the health level of the dairy cows. In addition to dairy cows, the addition of a certain amount of alfalfa to herbivorous animal feeds such as beef cattle, mutton sheep and the like can also improve the growth speed of beef cattle, mutton sheep and the quality of meat. With the development of livestock industry in China, the quantity of imported high-quality alfalfa in China is increased year by year, the imported quantity of alfalfa hay in the last few years is maintained to be about 140 ten thousand tons, the annual import rate reaches more than 5 hundred million dollars, and the alfalfa hay import country is the biggest alfalfa grass import country worldwide.

The reason for the import of a large amount of alfalfa in China is that the high-quality alfalfa in China has small bed-remaining area and insufficient alfalfa yield, and meanwhile, the quality stability of the alfalfa in China is different from that of imported grass, and the reason is related to the alfalfa production area in China. The alfalfa in China is concentrated in northwest arid regions, the regions are low in rainfall and dry in climate, high-quality hay is easy to prepare, the quality of the produced alfalfa is high, but the regions are generally poor in soil conditions, drought and rainless in sowing seasons, complex and various in irrigation modes, large in wind and sand in spring and autumn and other climate factors which are unfavorable for alfalfa planting can influence the success rate of planting after sowing. The alfalfa seeds are small, the time from germination and seedling emergence to successful planting is enough, and the seedlings emerge unevenly; soil in northwest areas is mainly sandy soil, soil at seedling bases is easy to scrape off in windy weather, and seedling bases lose soil protection, so that alfalfa seedlings after emergence are dead. Therefore, although the northwest area is the main production area of high-quality alfalfa in China, the income and planting enthusiasm of alfalfa producers are affected due to the large planting difficulty and low planting success rate. In addition to low success rate of planting, another difficulty in alfalfa production is serious grass damage, because the alfalfa needs long time to germinate and grows slowly in seedling stage after emergence, the competition ability of alfalfa seedlings relative to weeds in newly planted alfalfa plots is poor, weeds grow faster than alfalfa, and the alfalfa seedlings are weak, so that 'weed cheating' frequently occurs to cause planting failure, even if the planting success affects the quality and price of alfalfa when a large amount of weeds are mixed into alfalfa during alfalfa harvesting, the conditions are very common when first grass mowing after the alfalfa planting success. The northwest arid region is used as the most suitable production region of high-quality alfalfa in China, and is also a traditional alfalfa planting region in China, and the planting yield of the alfalfa is higher than that of main grain crops, so that crops with better economic benefits can be brought, and the improvement of the alfalfa planting level has practical significance for improving the self-supporting capacity of the alfalfa in China and improving the yields of farmers in northwest arid regions.

In order to solve the difficult problem of alfalfa planting, researchers explore various new alfalfa planting technologies, wherein the water evaporation is reduced through plastic film mulching, the surface wind erosion caused by sand wind weather is reduced, and the success rate of alfalfa planting can be improved; meanwhile, the growth of weeds under the film is suppressed by the film-covered planting, the proportion of weeds in alfalfa is greatly reduced, the quality of alfalfa hay is improved, and accordingly the planting income of alfalfa can be improved. However, the used mulching film basically adopts the traditional polyethylene mulching film, the polyethylene mulching film in the alfalfa field cannot be cleaned and cannot be degraded while the planting success rate is improved and the proportion of weeds in first-crop hay is reduced, and mulching film fragments are easily mixed into the alfalfa hay in the mechanical operation process in the process of each mowing and tedding of the alfalfa hay, so that the hay quality is reduced. The serious thing is that once the mulching film fragments are eaten by livestock by mistake, intestinal obstruction of the livestock can be caused, and the life of the livestock is endangered when the mulching film fragments are seriously eaten by the livestock. Some researchers use biodegradable mulching films, but focus on avoiding pollution to the environment, and do not pay attention to the damage of the biodegradable mulching films to livestock, so that the yield of alfalfa planting is extremely difficult to increase by adopting the mulching films at present. In order to solve the problems, components of the mulching film for alfalfa planting need to be prepared, but in the actual situation, when a mulching film formula with a proper degradation period is obtained by adding starch, the mechanical strength of the mulching film is low and cannot be practically applied, and even if the mulching film is barely paved in a field, the strength is lost quickly and the mulching film breaks in advance; if the content of additives such as starch is reduced and the degradation period is prolonged, the cost is increased, and the problem similar to that of a polyethylene mulching film exists, namely the mulching film still remains in alfalfa plots for a certain time after the mulching film is successfully planted, large pieces of mulching film fragments are easily mixed into alfalfa grass in the process of each mowing and tedding of the alfalfa, and once the mulching film fragments are mistakenly eaten by livestock, the mulching film fragments are not degraded in intestines and stomach quickly, and the healthy growth of the livestock is still affected.

Disclosure of Invention

In order to solve the problems, the invention provides the alfalfa planting method covered by the biodegradable plastic film, which can simultaneously solve the problems that the success rate of alfalfa planting in northwest arid regions is low and the mulching film fragments are mixed into alfalfa, and simultaneously solve the problem that the biodegradable plastic film cannot simultaneously take the degradation rate and the mechanical strength into consideration.

In order to achieve the above purpose, the invention provides a alfalfa planting method with full-biodegradable mulch film, which adopts full-biodegradable mulch film to plant, field management and mowing, and comprises the following steps:

(1) Seed selection: selecting alfalfa seeds, wherein the autumn dormancy level of the alfalfa seeds is 0-1 level higher than that of the alfalfa seeds required by the planting area in a non-film-covering planting mode;

(2) Irrigation: the water content of the soil during sowing is 5-20%, and the soil is in a range suitable for germination and emergence of alfalfa seeds;

(3) Applying a base fertilizer: the base fertilizer is one or a combination of organic fertilizer and inorganic fertilizer, and the application amount of the base fertilizer is lower than 10-20% of that of the planting mode without film coating;

(4) Preparing land: rotary tillage and soil preparation are required, the tidied alfalfa plots are required to be leveled, the soil blocks are basically smaller than 3 cm, and the influence of large soil blocks on seedling emergence due to the fact that large soil blocks press planting openings of films after transplanting is avoided;

(5) And (3) narrow row hill-drop: in the alfalfa sowing season, paving a full biodegradable mulch film, punching holes on the film after the row spacing and plant spacing are adjusted, sowing the alfalfa seeds in the step (1) in the holes, wherein the depth of the alfalfa seeds is 1-2cm, and covering a layer of soil strips with the thickness of 2-3 cm on the biodegradable mulch film between alfalfa sowing rows;

(6) And (3) field management: water management is carried out after sowing and before first mowing, and sprinkling irrigation, drip irrigation under a film or flood irrigation with small water is adopted to ensure that the water content of the soil is 20-35%;

(7) Harvesting: in the harvesting season of alfalfa, mechanically mowing, mechanically turning grass and picking up and bundling the alfalfa to form an alfalfa bundle; the mechanical mowing refers to mowing the alfalfa by mowing machinery and reserving stubble of 5-15 cm when each stubble of alfalfa is mowed; the moisture content of the alfalfa bundle is 20-25%.

Optionally, the alfalfa seeding season is spring or autumn; the spring refers to a period of 3-5 months; the autumn refers to at least 40 days before the local initial frost period.

Optionally, in spring of alfalfa seeding season, the fully biodegradable mulch film accords with the rule of national standard GB/T35795-2017 of fully biodegradable agricultural ground covering film, the thickness is standard 0.006-0.015mm, and the mulch film is black or colorless and transparent.

Optionally, the fully biodegradable mulching film comprises, by weight, 100 parts of fully biodegradable resin, 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate.

Alternatively, the fully biodegradable resin includes one or a combination of polylactic acid (PLA), polybutylene adipate/terephthalate (PBAT), polybutylene succinate (PBS), polybutylene succinate-adipate (PBSA), and polymethylethylene carbonate (PPC).

Optionally, the preparation method of the modified calcium carbonate comprises the following steps: (1) Weighing 100 parts of nano calcium carbonate powder according to the parts by weight, adding 10 parts of an absolute ethanol solution of a compound coupling agent with the concentration of 20wt%, continuously stirring and heating in a high-speed stirrer for 1-2h at the rotating speed of 1000-2000 r/min, filtering at the temperature of 70-80 ℃, and drying at the temperature of 100-120 ℃ to obtain primary treated calcium carbonate powder; wherein the components of the composite coupling agent are aluminum zirconate coupling agent, gamma-methacryloxypropyl trimethoxy silane and titanate coupling agent, and the weight ratio is 1:1:1; (2) Adding 100 parts of primary treated calcium carbonate powder, 5-10 parts of sodium silicate and 50-100 parts of deionized water into a reaction bottle, slowly adding 2.5wt% of mixed solution of hydrochloric acid and oxalic acid to adjust the pH value of the mixed system of the substances to 6.9-7.0, grinding in a ball mill, filtering and drying to obtain silica sol coated calcium carbonate powder; wherein the mass ratio of hydrochloric acid to oxalic acid is 1:1; (3) According to the parts by weight, 10 parts of hydroxyethyl methacrylate, 2 parts of polycaprolactone diol, 15 parts of toluene diisocyanate and 0.1 part of stannous octoate are sequentially added into 100 parts of silica sol coated calcium carbonate powder, uniformly stirred, reacted for 5-6 hours under the conditions of stirring and temperature control of 95-105 ℃ in a sealed autoclave, naturally cooled, decompressed and taken, and the materials are put into a vacuum drying oven, and dried at the temperature of 100-120 ℃ under the vacuum degree of 0.01-0.1Mpa, so as to obtain the modified calcium carbonate.

Optionally, the preparation method of the modified starch comprises the following steps: (1) paste mixing: adding starch raw materials into sodium hydroxide solution with pH of 8-9, mixing and stirring to form starch slurry, heating to 80-90 ℃ to form pasty starch slurry, wherein the mass concentration of starch in the starch slurry is 50-80%; (2) modification reaction: adding 10 parts of toluene diisocyanate and ethylene-vinyl acetate copolymer mixed emulsion, 0.2-1 part of stannous octoate and 2-4 parts of polyvinyl alcohol aqueous solution into 100 parts of pasty starch slurry according to the weight ratio, and then reacting for 10-20 hours at 75-105 ℃ to obtain modified starch slurry; wherein the mass ratio of toluene diisocyanate to ethylene-vinyl acetate copolymer is 1:0.2-1, and the concentration of the mixed emulsion is 20-40wt%; the concentration of the polyvinyl alcohol aqueous solution is 10-20wt%; (3) post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the drying temperature is 80-90 ℃.

Optionally, the preparation method of the fully biodegradable mulch film comprises the following steps: (1) Mixing 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate in a ball mill according to the weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding for 1-2 hours at the temperature of 80-100 ℃, and drying to obtain starch/calcium carbonate composite filler;

(2) According to the weight ratio, raw materials comprising the starch/calcium carbonate composite filler, 100 parts of full-biodegradable resin and 10-30 parts of auxiliary agent are weighed according to a set proportion, added into a mixing hopper, uniformly stirred, and then fed into a single screw extruder with an exhaust function for blow molding;

(3) The blow-molded film enters a traction station, and is rolled into a full-biodegradable plastic mulch film with the thickness of 0.006-0.015mm in a rolling machine through post-treatment processes such as edge cutting, thickness measurement, corona treatment and the like.

Optionally, the auxiliary agent comprises one or a combination of a plasticizer, a nucleating agent, a chain extender, an opening agent, a lubricant, an antiblocking agent, an antistatic agent, a light absorber or an antioxidant.

The beneficial effects of the invention are as follows:

1. the invention adopts the full-biodegradable mulching film to plant alfalfa, can keep better soil moisture content in the period from germination to emergence after the mulching film is covered, and simultaneously protects the soil under the film from wind erosion, thereby having beneficial effects of guaranteeing germination and emergence of alfalfa seeds and improving the success rate of plant alfalfa, and particularly, can plant high-quality alfalfa in areas with poor conditions.

2. The invention selects the biodegradable mulch film of a specific type for alfalfa planting, which not only can improve the planting success rate, but also can reduce the influence of the mulch film on the quality of alfalfa. According to different sowing seasons, the type of biodegradable mulching film with shorter effective life is selected according to the requirements of GB/T35795-2017 'full-biodegradable ground covering agricultural film', black mulching film with shorter effective service life and high water permeability is selected for spring planting, the spring is the season of weed germination and has higher competitiveness than alfalfa seedlings in the seedling stage of alfalfa, and the black mulching film has the strongest effect of inhibiting weeds due to the non-light transmittance. The grower can select according to specific planting time, in particular, the transparent mulching film can be used for enhancing the heating effect before the final frost period, the freezing injury of low temperature such as cold in the spring to alfalfa seedlings is reduced, the competitiveness of the alfalfa seedlings to weeds is improved, and the black mulching film is used for the spring sowing time rather than the black mulching film, so that the effect of inhibiting the weeds is enhanced; the mulching film with medium effective life is selected in autumn, so that the safety of alfalfa in winter is ensured. The specific biodegradable mulching film type with the effective service life is selected, so that the mulching film is degraded as soon as possible after the mulching film is planted, and the quality of alfalfa grass is reduced or avoided by mixing the mulching film fragments into the alfalfa grass after the alfalfa is mowed. The type of the full-biodegradable mulching film with high water permeability is selected to improve the air permeability of the mulching film, thereby being beneficial to improving the activity of alfalfa root systems and promoting the growth of seedlings.

3. The invention can improve the autumn sleep level of the variety selected in the alfalfa planting area. The autumn sleep level is an index reflecting that alfalfa enters sleep and does not grow any more before the low temperature in autumn, and the autumn sleep level indicates that the entering sleep time is late, the growing period is longer, and therefore the yield is generally higher. The invention adopts the specific biodegradable mulch film for planting, has high emergence rate after sowing, stronger competition force relative to weeds after emergence, stronger plants, more developed alfalfa root systems after successful planting, more root storage nutrients before autumn and winter entering autumn and sleep and stronger overwintering capability, thereby improving the autumn and sleep level of selected varieties by 0.5-1 level.

4. According to the invention, narrow row hill seeding is adopted, a layer of soil strips with the thickness of 2-3 cm is covered on the film between alfalfa seeding rows, the alfalfa seeds are guaranteed to be 1-2cm deep, a thicker soil layer is covered between the rows, the mulching film can be prevented from being blown away, shifted or broken by wind, a guarantee measure is provided for the service life of the mulching film, meanwhile, the root system soil penetration depth of the planting in the current year is improved, the overwintering capability is improved, the risk is reduced, the possibility that the mulching film is mixed into alfalfa is further reduced by covering soil on the inter-row film, and therefore, the guarantee is provided for the quality of alfalfa.

5. When the alfalfa is mowed for the first time, the high stubble height is reserved, the high stubble plays a role in supporting the cut alfalfa, the proportion of the alfalfa directly contacting the mulching film is reduced, the inserting depth of the mechanical turnings is well controlled, damage to the mulching film is reduced, the mulching film fragments are prevented from being mixed into the alfalfa, the quality of the alfalfa is reduced, and the probability of the alfalfa fragments mixed into the mulching film fragments is reduced when livestock eat the alfalfa by mistake.

6. The mulching film adopts full-biodegradable resin, and the degraded mulching film is mainly water and carbon dioxide, and is harmless substance; in addition, the used full-biodegradable resin contains starch modified by modifying agents such as polyvinyl alcohol and the like, and the polyvinyl alcohol and the starch have the characteristics of high hydroxyl content, strong water absorption and water solubility, and the crushed residual film which is not completely degraded after being crushed in soil has the advantages of improving the viscosity and water storage rate of local sandy soil and improving the soil moisture content of northwest dry sandy soil due to the high water absorption rate or cohesiveness of the polyvinyl alcohol and the starch. The invention utilizes the modifier such as isocyanate and the like to successfully form a bridge between the polyvinyl alcohol and the starch, so that the polyvinyl alcohol and the starch form an integral structure with groups similar to biodegradable resin in nature, thereby not only reducing the adverse effect of the starch on the mechanical property of the film, but also improving the compatibility of the starch and the like on the biodegradable mulch film.

7. The biodegradable mulch film is prepared by setting the addition amount of modified starch and modified calcium carbonate in a certain range according to the climate conditions in northwest areas and the planting conditions of alfalfa to obtain a mulch film formula which is suitable for the growth cycle of alfalfa; in addition, the mulch film has good mechanical strength in the early stage of alfalfa planting, has good soil moisture conservation and grass inhibition effects, accelerates the film-free process in the later degradation speed, and reduces the possibility of mixing residual film into alfalfa grass during mowing.

Drawings

FIG. 1 is a schematic diagram of the specifications of alfalfa planting according to the present invention.

FIG. 2 shows the degradation of the mulch film in the next year of green turning of alfalfa in example 1.

FIG. 3 shows the degradation of the mulch film at the next year of green turning of alfalfa in comparative example 1.

Reference numerals: 1-soil layer; 2-mulching film; 3-row spacing; 4-plant spacing; 5-a soil covering belt; 6-alfalfa sowing holes; 7-machine walking.

Detailed Description

The following detailed description of the present invention will provide further details in order to make the above-mentioned objects, features and advantages of the present invention more comprehensible.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways other than those described herein, and persons skilled in the art will readily appreciate that the present invention is not limited to the specific embodiments disclosed below.

Referring to fig. 1, the alfalfa planting method using the fully biodegradable mulching film according to the present invention adopts the steps of planting, field management and mowing: (1) seed selection: selecting alfalfa seeds, wherein the autumn dormancy level of the alfalfa seeds is 0-1 level higher than that of the alfalfa seeds required by the planting area in a non-film-covering planting mode; (2) irrigation: the water content of the soil during sowing is 5-20%, and the soil is in a range suitable for germination and emergence of alfalfa seeds; (3) applying a base fertilizer: the base fertilizer is one or a combination of organic fertilizer and inorganic fertilizer, and the application amount of the base fertilizer is lower than 10-20% of that of the planting mode without film coating; (4) soil preparation: rotary tillage and soil preparation are required, the tidied alfalfa plots are required to be leveled, the soil blocks are basically smaller than 3 cm, and the influence of large soil blocks on seedling emergence due to the fact that large soil blocks press planting openings of films after transplanting is avoided; and (5) narrow row hill-drop: in the alfalfa sowing season, paving a full biodegradable mulch film, punching holes on the film after the row spacing and plant spacing are adjusted, sowing the alfalfa seeds in the step (1) in the holes, wherein the depth of the alfalfa seeds is 1-2cm, and covering a layer of soil strips with the thickness of 2-3 cm on the biodegradable mulch film between alfalfa sowing rows; (6) field management: water management is carried out after sowing and before first mowing, and sprinkling irrigation, drip irrigation under a film or flood irrigation with small water is adopted to ensure that the water content of the soil is 20-35%; (7) harvesting: in the harvesting season of alfalfa, mechanically mowing, mechanically turning grass and picking up and bundling the alfalfa to form an alfalfa bundle; the mechanical mowing refers to mowing the alfalfa by mowing machinery and reserving stubble of 5-15 cm when each stubble of alfalfa is mowed; the moisture content of the alfalfa bundle is 20-25%.

In the alfalfa planting method of the full-biodegradable mulch film according to the present invention, the alfalfa planting season is spring or autumn; the spring refers to a period of 3-5 months; the autumn refers to at least 40 days before the local initial frost period.

In the alfalfa planting method of the full-biodegradable mulching film, the full-biodegradable mulching film accords with the national standard GB/T35795-2017 of full-biodegradable agricultural mulching film in spring of alfalfa sowing season, the thickness is 0.006-0.015mm, and the mulching film is black or colorless and transparent.

In the alfalfa planting method of the full-biodegradable mulch film according to the invention, the components of the full-biodegradable mulch film comprise 100 parts of full-biodegradable resin, 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate in parts by weight.

In the alfalfa planting method of the fully biodegradable mulch film according to the present invention, the fully biodegradable resin includes one or a combination of polylactic acid (PLA), polybutylene adipate/terephthalate (PBAT), polybutylene succinate (PBS), polybutylene succinate-butylene adipate (PBSA), and polymethylethylene carbonate (PPC).

In the alfalfa planting method covered by the full-biodegradable mulch film according to the invention, the preparation method of the modified calcium carbonate comprises the following steps: (1) Weighing 100 parts of nano calcium carbonate powder according to the parts by weight, adding 10 parts of an absolute ethanol solution of a compound coupling agent with the concentration of 20wt%, continuously stirring and heating in a high-speed stirrer for 1-2h at the rotating speed of 1000-2000 r/min, filtering at the temperature of 70-80 ℃, and drying at the temperature of 100-120 ℃ to obtain primary treated calcium carbonate powder; wherein the components of the composite coupling agent are aluminum zirconate coupling agent, gamma-methacryloxypropyl trimethoxy silane and titanate coupling agent, and the weight ratio is 1:1:1; (2) Adding 100 parts of primary treated calcium carbonate powder, 5-10 parts of sodium silicate and 50-100 parts of deionized water into a reaction bottle, slowly adding 2.5wt% of mixed solution of hydrochloric acid and oxalic acid to adjust the pH value of the mixed system of the substances to 6.9-7.0, grinding in a ball mill, filtering and drying to obtain silica sol coated calcium carbonate powder; wherein the mass ratio of hydrochloric acid to oxalic acid is 1:1; (3) According to the parts by weight, 10 parts of hydroxyethyl methacrylate, 2 parts of polycaprolactone diol, 15 parts of toluene diisocyanate and 0.1 part of stannous octoate are sequentially added into 100 parts of silica sol coated calcium carbonate powder, uniformly stirred, reacted for 5-6 hours under the conditions of stirring and temperature control of 95-105 ℃ in a sealed autoclave, naturally cooled, decompressed and taken, and the materials are put into a vacuum drying oven, and dried at the temperature of 100-120 ℃ under the vacuum degree of 0.01-0.1Mpa, so as to obtain the modified calcium carbonate.

In the alfalfa planting method of the full-biodegradable mulch film according to the present invention, the preparation method of the modified starch comprises the following steps: (1) paste mixing: adding starch raw materials into sodium hydroxide solution with pH of 8-9, mixing and stirring to form starch slurry, heating to 80-90 ℃ to form pasty starch slurry, wherein the mass concentration of starch in the starch slurry is 50-80%; (2) modification reaction: adding 10 parts of toluene diisocyanate and ethylene-vinyl acetate copolymer mixed emulsion, 0.2-1 part of stannous octoate and 2-4 parts of polyvinyl alcohol aqueous solution into 100 parts of pasty starch slurry according to the weight ratio, and then reacting for 10-20 hours at 75-105 ℃ to obtain modified starch slurry; wherein the mass ratio of toluene diisocyanate to ethylene-vinyl acetate copolymer is 1:0.2-1, and the concentration of the mixed emulsion is 20-40wt%; the concentration of the polyvinyl alcohol aqueous solution is 10-20wt%; (3) post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the drying temperature is 80-90 ℃.

In the alfalfa planting method of the full-biodegradable mulch film according to the present invention, the preparation method of the full-biodegradable mulch film comprises the steps of: (1) Mixing 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate in a ball mill according to the weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding for 1-2 hours at the temperature of 80-100 ℃, and drying to obtain starch/calcium carbonate composite filler;

In the alfalfa planting method of the fully biodegradable mulch film according to the present invention, the auxiliary agent includes one or a combination of a plasticizer, a nucleating agent, a chain extender, an opening agent, a lubricant, an anti-blocking agent, an antistatic agent, a light absorber, or an antioxidant.

In the alfalfa planting method of the full-biodegradable mulch film according to the invention, the row spacing 3 of the sowing is 12-20 cm, the plant spacing 4 is 10-20 cm, the aperture of the punching is 3-6 cm, the sowing depth is 1-2 cm, and the sowing amount of each hole is 5-10 alfalfa seeds; the width of the earthing band 5 is 5-10 cm, the thickness is 2-3 cm, the width is at least 5 cm smaller than the alfalfa spacing, and the earthing band cannot cover the alfalfa sowing positions.

In the alfalfa planting method of the full-biodegradable mulch film according to the present invention, the laying of the full-biodegradable mulch film is accomplished with a mulch film laying machine.

In the alfalfa planting method of the full-biodegradable mulch film according to the present invention, the full-biodegradable mulch film is laid, punched into holes on the film, alfalfa seeds are sown in the holes, and soil is covered on the full-biodegradable mulch film between the alfalfa rows.

The alfalfa planting method covered by the full-biodegradable mulch film of the invention is specifically described below with reference to specific examples. The auxiliary agent of each embodiment is the combination of glycerin and antioxidant 1010, and the mass ratio is 10:1.

Example 1

As shown in the specification of FIG. 1, experiments of planting alfalfa by fully-biodegradable mulch film covered on day 27 of 3 months in Gansu province, zhangye city were performed.

Firstly, preparing a full-biodegradable mulching film: (1) Mixing 20 parts of modified starch and 30 parts of modified calcium carbonate in a ball mill according to the weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding for 1-2 hours at the temperature of 100 ℃, and drying to obtain starch/calcium carbonate composite filler; (2) According to the weight ratio, raw materials comprising the starch/calcium carbonate composite filler, 100 parts of full-biodegradable resin (polylactic acid (PLA) and polybutylene adipate/terephthalate (PBAT) in a mass ratio of 0.1:1), 30 parts of auxiliary agent, 1 part of carbon black and the like are weighed according to a set proportion, added into a mixing hopper, uniformly stirred, and then fed into a single screw extruder with an exhaust function for blow molding; (3) The blow-molded film enters a traction station, and is rolled into a full-biodegradable plastic mulch film with the thickness of 0.015mm in a rolling machine through post-treatment processes such as edge cutting, thickness measurement, corona treatment and the like.

The preparation method of the modified starch comprises the following steps: (1) paste mixing: adding starch raw materials into sodium hydroxide solution with pH of 9, mixing and stirring to form starch slurry, heating to 90 ℃ to form pasty starch slurry, wherein the mass concentration of starch in the starch slurry is 80%; (2) modification reaction: adding 10 parts of toluene diisocyanate and ethylene-vinyl acetate copolymer mixed emulsion, 1 part of stannous octoate and 4 parts of polyvinyl alcohol aqueous solution into 100 parts of pasty starch slurry according to the weight ratio, and then reacting for 20 hours at 105 ℃ to obtain modified starch slurry; wherein the mass ratio of toluene diisocyanate to ethylene-vinyl acetate copolymer is 1:1, and the concentration of the mixed emulsion is 40wt%; the concentration of the polyvinyl alcohol aqueous solution is 20wt%; (3) post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the temperature of the drying is 90 ℃.

The preparation method of the modified calcium carbonate comprises the following steps: (1) Weighing 100 parts of nano calcium carbonate powder according to the parts by weight, adding 10 parts of an absolute ethanol solution of a compound coupling agent with the concentration of 20wt%, continuously stirring and heating for 2 hours in a high-speed stirrer, rotating at 2000 rpm, filtering at 80 ℃, and drying at 120 ℃ to obtain primary treated calcium carbonate powder; wherein the components of the composite coupling agent are aluminum zirconate coupling agent, gamma-methacryloxypropyl trimethoxy silane and titanate coupling agent, and the weight ratio is 1:1:1; (2) Adding 100 parts of primary treated calcium carbonate powder, 10 parts of sodium silicate and 100 parts of deionized water into a reaction bottle, slowly adding a mixed solution of hydrochloric acid and oxalic acid with the weight percent of 2.5 to adjust the pH value of a mixed system of the materials to 7.0, grinding in a ball mill, filtering and drying to obtain silica sol coated calcium carbonate powder; wherein the mass ratio of hydrochloric acid to oxalic acid is 1:1; (3) 10 parts of hydroxyethyl methacrylate, 2 parts of polycaprolactone diol, 15 parts of toluene diisocyanate and 0.1 part of stannous octoate are sequentially added into 100 parts of silica sol coated calcium carbonate powder according to parts by weight, uniformly stirred, reacted for 6 hours in a sealed autoclave under the conditions of stirring and temperature control of 105 ℃, naturally cooled, taken out under reduced pressure, and the materials are placed into a vacuum drying oven, and dried at the temperature of 120 ℃ under the vacuum degree of 0.1Mpa, so as to obtain the modified calcium carbonate.

Performance index of the fully biodegradable mulch: the effective life cycle is classified into class I, the water vapor transmittance is classified into class C, the thickness is 0.015 mm, and the color of the mulching film is black.

(II) planting method of alfalfa covered by plastic film: the winter water is filled before winter in the previous year, and the soil in the severe cold weather in winter is utilized to freeze and lock water, so that the loss is reduced; preparing soil and sowing after thawing more than 10 cm on the bottom soil surface for 3 months, uniformly scattering 25 kg of diammine phosphate, 5 kg of potassium sulfate and 10 kg of phosphorus nitrate per mu before preparing the soil, then rotating the soil by a rotary cultivator to uniformly mix the fertilizer into the soil, preparing the soil into a flat land without large soil blocks on the soil surface, and properly compacting the soil layer 1; the alfalfa variety adopts an autumn sleep grade 4 alfalfa variety Adina (the local more common bred variety Gannong No. 3 is autumn sleep grade 3.0); sowing in alfalfa sowing holes 6 of a full-biodegradable mulch film 2 with the effective width of the film of 1.68 meters by using a hill planter with the operation width of 1.8 meters and the covering film and soil pressing device, sowing 12 rows on the film, adjusting the row spacing 3 of the covering film hill planter to 14 cm, the plant spacing 4 to 10 cm, the sowing depth to 2 cm and the width of a soil covering belt 5 to 10 cm before sowing, and 2-3 cm in thickness, wherein the soil covering device is strip-type soil covering, soil covering strips are positioned among alfalfa rows, no soil covering is arranged among plants, and the field condition after sowing is completed is shown in figure 1; after sowing, paying attention to water management, and supplementing water to soil by flooding irrigation with small water when soil is overdry; the alfalfa enters a flowering period successively in 8 months, the height reaches more than 60 cm, and at the same time, the mower is used for mowing for the first time when the rainless weather is forecasted for at least 5 days, and the mowing height is adjusted by the mower before operation, so that the stubble is left at 15 cm; after cutting, airing for 4 days according to weather conditions, and turning grass for 1 time by using a grass turning machine in the middle to uniformly dry the grass layer up and down; after the alfalfa reaches the preset water content, the alfalfa is baled by a pickup baler and is removed from the field in time. The whole biodegradable mulch is basically degraded when the plants are cut twice in the same year and the hay is harvested after winter, and the mulch residue is basically not degraded between the lands and the hay harvesting operation is not influenced.

Example 2

As shown in fig. 1, experiments were performed on alfalfa planted in 8 months 22 of the Liaoning city in the inner Mongolian autonomous region.

Firstly, preparing a full-biodegradable mulching film: (1) Mixing 40 parts of modified starch and 50 parts of modified calcium carbonate in a ball mill according to the weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding for 1 hour at the temperature of 80 ℃, and drying to obtain starch/calcium carbonate composite filler; (2) According to the weight ratio, raw materials comprising the starch/calcium carbonate composite filler, 100 parts of full-biodegradable resin (poly (butylene adipate/terephthalate) (PBAT), poly (butylene succinate-butylene adipate) (PBSA) and poly (methyl ethylene carbonate) (PPC)) and 10 parts of auxiliary agent in a mass ratio of 1:0.1:0.1 are weighed according to the set ratio, added into a mixing hopper, uniformly stirred, and then fed into a single screw extruder with an exhaust function for blow molding; (3) The blow-molded film enters a traction station, and is rolled into a full-biodegradable plastic mulch film with the thickness of 0.006mm in a rolling machine through post-treatment processes such as edge cutting, thickness measurement, corona treatment and the like.

The preparation method of the modified starch comprises the following steps: (1) paste mixing: adding starch raw materials into sodium hydroxide solution with pH of 8, mixing and stirring to form starch slurry, heating to 80 ℃ to form pasty starch slurry, wherein the mass concentration of starch in the starch slurry is 50%; (2) modification reaction: adding 10 parts of toluene diisocyanate and ethylene-vinyl acetate copolymer mixed emulsion, 0.2 part of stannous octoate and 2 parts of polyvinyl alcohol aqueous solution into 100 parts of pasty starch slurry according to the weight ratio, and then reacting at 75 ℃ for 10 hours to obtain modified starch slurry; wherein the mass ratio of toluene diisocyanate to ethylene-vinyl acetate copolymer is 1:0.2, and the concentration of the mixed emulsion is 20wt%; the concentration of the polyvinyl alcohol aqueous solution is 10wt%; (3) post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the temperature of the drying was 80 ℃.

The preparation method of the modified calcium carbonate comprises the following steps: (1) Weighing 100 parts of nano calcium carbonate powder according to the parts by weight, adding 10 parts of an absolute ethanol solution of a compound coupling agent with the concentration of 20wt%, continuously stirring and heating for 1h in a high-speed stirrer at the rotating speed of 1000 revolutions per minute, filtering at the temperature of 70 ℃, and drying at the temperature of 100 ℃ to obtain primary treated calcium carbonate powder; wherein the components of the composite coupling agent are aluminum zirconate coupling agent, gamma-methacryloxypropyl trimethoxy silane and titanate coupling agent, and the weight ratio is 1:1:1; (2) Adding 100 parts of primary treated calcium carbonate powder, 5 parts of sodium silicate and 50 parts of deionized water into a reaction bottle, slowly adding a mixed solution of hydrochloric acid and oxalic acid with the weight percent of 2.5 to adjust the pH value of a mixed system of the materials to be 6.9-7.0, grinding in a ball mill, filtering and drying to obtain silica sol coated calcium carbonate powder; wherein the mass ratio of hydrochloric acid to oxalic acid is 1:1; (3) According to the parts by weight, 10 parts of hydroxyethyl methacrylate, 2 parts of polycaprolactone diol, 15 parts of toluene diisocyanate and 0.1 part of stannous octoate are sequentially added into 100 parts of silica sol coated calcium carbonate powder, uniformly stirred, reacted for 5 hours under the conditions of stirring and temperature control of 95 ℃ in a sealed autoclave, naturally cooled, decompressed and taken, and the materials are placed into a vacuum drying box, and dried at the temperature of 100 ℃ under the vacuum degree of 0.01Mpa, so as to obtain the modified calcium carbonate.

Performance indexes of the mulching film: class III is classified in the effective life cycle, the water vapor transmittance is classified as class A, the thickness is 0.006mm, and the color of the mulching film is transparent.

(II) planting method of alfalfa covered by plastic film: irrigation is carried out before planting, soil preparation and sowing are carried out after three days of irrigation, 25 kg of diammonium phosphate and 15 kg of potassium sulfate are applied to each mu of land before soil preparation, then a rotary cultivator is used for rotary tillage, fertilizers are uniformly mixed into soil, the soil surface is flat without large soil blocks, and soil layer 1 is properly compacted; the alfalfa variety adopts a 3.4 grade variety 'the alfalfa 341' (the local variety of the current year, namely, the Chinese alfalfa decocted in autumn sleep grade is about 2.5 grade); sowing in alfalfa sowing holes 6 of a full-biodegradable mulch film 2 with the effective width of 1.68 meters by using a hill planter with the operation width of 1.4 meters and a film covering and soil pressing device, adjusting the row spacing 3 of the film covering hill planter to 13 cm, the plant spacing 4 to 10 cm, the sowing depth to 1.5 cm and the width of a soil covering belt 5 to 8 cm before sowing, wherein the soil covering device is strip-type soil covering, soil covering strips are positioned among alfalfa rows, and soil covering is not carried out among plants; after sowing, adopting a pointer type sprinkler to carry out sprinkling irrigation, continuously sprinkling irrigation when soil is arid, stopping sprinkling irrigation when the water penetration depth reaches 20 cm, and stopping irrigation after the water penetration reaches 50 cm when the water irrigation is carried out for the last time in winter; the alfalfa is not mowed in the current year, the alfalfa enters the flowering period successively in the next 6 th and the height reaches 70-80 cm, meanwhile, the mower is used for carrying out first mowing when the rainless weather is forecast for at least 5 days, the mowing height is adjusted by the mower before the operation, the stubble remaining reaches 15 cm, and the stubble remaining height can be properly reduced from the second mowing to the land with few residual mulch degrading conditions such as residual mulch; after cutting, airing for 6 days according to weather conditions, and turning grass for 2 times by a grass turning machine in the middle to uniformly dry the grass layer up and down; after the alfalfa reaches the preset water content, the alfalfa is baled by a pickup baler and is removed from the field in time. When the third crop is mowed, the mulching film is degraded to a high degradation degree, and after the residual film in the field is less, the grass can be mowed and harvested in a normal mode.

Example 3

As indicated in fig. 1, experiments were performed on alfalfa planted with full-biodegradable mulch films at 5 days of 4 months in the ning-summer autonomous region, run No. Gao Zhuangxiang. The soil is medium alkaline soil, and the pH value of the soil is 8.0-8.3.

Firstly, preparing a full-biodegradable mulching film: (1) Mixing 30 parts of modified starch and 40 parts of modified calcium carbonate in a ball mill according to the weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding for 1.5 hours at the temperature of 80-100 ℃, and drying to obtain starch/calcium carbonate composite filler; (2) According to the weight ratio, raw materials comprising the starch/calcium carbonate composite filler, 100 parts of full-biodegradable resin (poly (adipic acid)/butylene terephthalate) (PBAT) and poly (butylene succinate) (PBS), wherein the mass ratio is 1:1), 20 parts of auxiliary agent and 0.1 part of carbon black are weighed according to the set proportion, added into a mixing hopper, uniformly stirred, and then fed into a single screw extruder with an exhaust function for blow molding; (3) The blow-molded film enters a traction station, and is rolled into a full-biodegradable plastic mulch film with the thickness of 0.008mm in a rolling machine through post-treatment processes such as edge cutting, thickness measurement, corona treatment and the like.

The preparation method of the modified starch comprises the following steps: (1) paste mixing: adding starch raw materials into sodium hydroxide solution with pH of 8.5, mixing and stirring to obtain starch slurry, and heating to 85 ℃ to obtain pasty starch slurry, wherein the mass concentration of starch in the starch slurry is 60%; (2) modification reaction: adding 10 parts of toluene diisocyanate and ethylene-vinyl acetate copolymer mixed emulsion, 0.6 part of stannous octoate and 3 parts of polyvinyl alcohol aqueous solution into 100 parts of pasty starch slurry according to the weight ratio, and then reacting at 90 ℃ for 15 hours to obtain modified starch slurry; wherein the mass ratio of toluene diisocyanate to ethylene-vinyl acetate copolymer is 1:0.6, and the concentration of the mixed emulsion is 30wt%; the concentration of the polyvinyl alcohol aqueous solution is 15wt%; (3) post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the temperature of the drying is 85 ℃.

The preparation method of the modified calcium carbonate comprises the following steps: (1) Weighing 100 parts of nano calcium carbonate powder according to the parts by weight, adding 10 parts of an absolute ethanol solution of a compound coupling agent with the concentration of 20wt%, continuously stirring and heating in a high-speed stirrer for 1.5 hours at the rotating speed of 1500 rpm, filtering at the temperature of 75 ℃, and drying at the temperature of 110 ℃ to obtain primary treated calcium carbonate powder; wherein the components of the composite coupling agent are aluminum zirconate coupling agent, gamma-methacryloxypropyl trimethoxy silane and titanate coupling agent, and the weight ratio is 1:1:1; (2) Adding 100 parts of primary treated calcium carbonate powder, 7 parts of sodium silicate and 80 parts of deionized water into a reaction bottle, slowly adding a mixed solution of hydrochloric acid and oxalic acid with the weight percent of 2.5 to adjust the pH value of the mixed system of the materials to be 6.9-7.0, grinding in a ball mill, filtering and drying to obtain silica sol coated calcium carbonate powder; wherein the mass ratio of hydrochloric acid to oxalic acid is 1:1; (3) 10 parts of hydroxyethyl methacrylate, 2 parts of polycaprolactone diol, 15 parts of toluene diisocyanate and 0.1 part of stannous octoate are sequentially added into 100 parts of silica sol coated calcium carbonate powder according to parts by weight, uniformly stirred, reacted for 5.5 hours under the conditions of stirring and controlling the temperature to be 100 ℃ in a sealed autoclave, naturally cooled, decompressed and taken, and the materials are placed into a vacuum drying oven, and dried at the temperature of 110 ℃ under the vacuum degree of 0.05Mpa, so as to obtain the modified calcium carbonate.

Performance indexes of the mulching film: class II is classified in the effective life cycle, the water vapor transmittance is classified as class B, the thickness is 0.008 mm, and the mulching film is a black mulching film with 13% of light transmittance;

(II) planting method of alfalfa covered by plastic film: the alfalfa variety adopts a autumn sleep grade 5.5 grade variety 'long voyage' (a variety 'Adina' Qiu Mian 4.5.5 grade with larger local planting area); the underground water level of the soil is high, winter water is fully filled in the soil after the first year, the soil is thawed at a depth of 20 cm for 4 months and 5 days, the soil moisture content is proper, 15 kg of ammonium sulfate is applied to each mu of land before soil preparation for neutralizing the alkalinity of the soil and providing nitrogen demand in the seedling stage, 20 kg of dipotassium phosphate is applied, then a rotary cultivator is used for rotary-tillage, so that the fertilizer is uniformly mixed into the soil, the soil surface is flat without large soil blocks, the soil layer 1 is properly compacted, and the large soil blocks are crushed; covering film, covering soil with a covering film planter with a working width of 1.4 m and a covering film and soil pressing device, sowing, wherein the covering soil device is strip-type covering soil, the distance between the covering soil and a punching sowing device is 13 cm, the plant spacing 4 is adjusted to 10 cm, the width of the covering soil is adjusted to 5 cm, the thickness is adjusted to 2-3 cm, the planter is arranged in a planter travel 7, and the sowing depth is adjusted to 1.5 cm; irrigation is carried out when irrigation canal comes from the water after sowing. After the planting is successful, mowing is carried out for three times respectively in 18 days of 6 months, 25 days of 7 months and 2 days of 9 months, the mowing height is adjusted by the mowing machine before mowing, and the stubble remaining heights of three stubbles are respectively 15 cm, 12 cm and 10 cm; after the alfalfa reaches the preset water content, the alfalfa is baled by a pickup baler and is removed from the field in time.

Comparative example 1

The planting method was the same as in example 1, except that the mulching film was a polyethylene film.

Comparative example 2

The planting method was the same as in example 2, except that the mulching film was a polyethylene film.

Comparative example 3

The planting method was the same as in example 3, except that the mulching film was a polyethylene film.

Comparative example 4

The procedure of example 1 was repeated except that the starch and calcium carbonate were not modified.

Comparative example 5

The procedure of example 1 was repeated except that the modified starch and modified calcium carbonate were not used to prepare the starch/calcium carbonate composite filler.

Performance test:

1. determination of tensile Strength and elongation at Break

Test conditions for films and sheets according to the national Standard "determination of Plastic tensile Properties" (GB\T 1040.3-2006) section 3: the dumbbell bar was 150mm long, 10mm narrow parallel width, 200mm/min stretch speed, 25 ℃ room temperature.

2. Determination of Right angle tear Strength

QB/T1130-1991 test method for Right-angle tear Property of Plastic, stretching speed 200mm/min, room temperature 25℃was cited.

3. Degradation of alfalfa during planting

The examples and comparative examples were compared in the same field to visually see that no mulch film was completely degraded.

The results of the performance tests of the products obtained in the above examples and comparative examples are given in the following table:

TABLE 1

TABLE 2

	Tensile Strength/N	Elongation at break/%	Tear Strength/N
				Example 1	4	400	1.5
Comparative example 4	1.2	300	0.8
				Comparative example 5	1.4	350	0.9

From the above examples and the comparison of fig. 2 and 3, it can be seen that the full biodegradable plastic film provided in the present invention, both the modified starch and the modified calcium carbonate greatly affect the tensile strength, the elongation at break and the tear strength of the mulch film; in addition, unlike the gradual degradation of the biodegradable mulching film in the prior art, the strength change is small in the early degradation period, the strength of the biodegradable mulching film has a relatively stable strength platform period, and the strength can be rapidly reduced after a certain degradation degree is achieved, so that the mulching film is broken into small blocks, good coverage characteristics can be successfully maintained in a crop growth period, the harvesting and the next planting of crops are not affected when the crops are harvested and tidied on the ground, and the figure 2 shows that the non-membranization area of the fully biodegradable mulching film is about 70% compared with that of the polyethylene mulching film when the alfalfa is turned green in the next year, and the degree of being mixed into mulching film grass when the alfalfa is harvested is greatly reduced. The biodegradable mulch film is suitable for planting alfalfa in northwest areas, and can meet the requirements because the weather is relatively dry, the influence of water on the mulch film is relatively small, and whether the modified starch and the modified calcium carbonate are subjected to advanced composite treatment is not required.

While certain specific embodiments of the invention have been described in detail by way of example, it will be appreciated by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the invention. It will be appreciated by those skilled in the art that modifications may be made to the above embodiments without departing from the scope and spirit of the invention. The scope of the invention is defined by the appended claims.

Claims

1. A alfalfa planting method with full-biodegradable mulching film is characterized in that the full-biodegradable mulching film is selected, and the following steps of planting, field management and mowing are adopted:

(1) Seed selection: selecting alfalfa seeds, wherein the autumn dormancy level of the alfalfa seeds is higher than the 1 level of the alfalfa seeds required by the planting area in a non-film-covering planting mode;

(4) Preparing land: rotary tillage and soil preparation are required, the tidied alfalfa plots are required to be leveled, the soil blocks are less than 3 cm, and the influence of large soil blocks to the planting openings of the pressing films after transplanting on seedling emergence is avoided;

(5) And (3) narrow row hill-drop: in the alfalfa sowing season, paving a full-biodegradable mulch film, punching holes on the film after the row spacing and plant spacing are adjusted, sowing the alfalfa seeds in the step (1) in the holes, wherein the depth of the alfalfa seeds is 1-2cm, and covering a layer of soil strips with the thickness of 2-3 cm on the full-biodegradable mulch film between alfalfa sowing rows;

(7) Harvesting: in the harvesting season of alfalfa, mechanically mowing, mechanically turning grass and picking up and bundling the alfalfa to form an alfalfa bundle; the mechanical mowing refers to mowing the alfalfa by mowing machinery and reserving stubble of 5-15 cm when each stubble of alfalfa is mowed; the moisture content of the alfalfa bundle is 20-25%;

when the alfalfa sowing season is spring, the full-biodegradable mulching film meets the national standard GB/T35795-2017 of full-biodegradable agricultural ground covering film, the thickness is 0.006-0.015mm, and the mulching film is black or colorless and transparent;

the fully biodegradable mulching film comprises, by weight, 100 parts of fully biodegradable resin, 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate;

The preparation method of the modified calcium carbonate comprises the following steps:

(1) Weighing 100 parts of nano calcium carbonate powder according to the parts by weight, adding 10 parts of an absolute ethanol solution of a compound coupling agent with the concentration of 20wt%, continuously stirring and heating in a high-speed stirrer for 1-2h at the rotating speed of 1000-2000 r/min, filtering at the temperature of 70-80 ℃, and drying at the temperature of 100-120 ℃ to obtain primary treated calcium carbonate powder; wherein the components of the composite coupling agent are aluminum zirconate coupling agent, gamma-methacryloxypropyl trimethoxy silane and titanate coupling agent, and the weight ratio is 1:1:1;

(2) Adding 100 parts of primary treated calcium carbonate powder, 5-10 parts of sodium silicate and 50-100 parts of deionized water into a reaction bottle, slowly adding 2.5wt% of mixed solution of hydrochloric acid and oxalic acid to adjust the pH value of the mixed system of the substances to 6.9-7.0, grinding in a ball mill, filtering and drying to obtain silica sol coated calcium carbonate powder; wherein the mass ratio of hydrochloric acid to oxalic acid is 1:1;

(3) According to the parts by weight, 10 parts of hydroxyethyl methacrylate, 2 parts of polycaprolactone diol, 15 parts of toluene diisocyanate and 0.1 part of stannous octoate are sequentially added into 100 parts of silica sol coated calcium carbonate powder, uniformly stirred, reacted for 5-6 hours under the conditions of stirring and temperature control of 95-105 ℃ in a sealed autoclave, naturally cooled, decompressed and taken, and the materials are put into a vacuum drying oven, and dried at the temperature of 100-120 ℃ under the vacuum degree of 0.01-0.1Mpa, so as to obtain modified calcium carbonate;

The preparation method of the modified starch comprises the following steps:

(1) Paste mixing: adding starch raw materials into sodium hydroxide solution with pH of 8-9, mixing and stirring to form starch slurry, heating to 80-90 ℃ to form pasty starch slurry, wherein the mass concentration of starch in the starch slurry is 50-80%;

(2) Modification reaction: adding 10 parts of toluene diisocyanate and ethylene-vinyl acetate copolymer mixed emulsion, 0.2-1 part of stannous octoate and 2-4 parts of polyvinyl alcohol aqueous solution into 100 parts of pasty starch slurry according to the weight ratio, and then reacting for 10-20 hours at 75-105 ℃ to obtain modified starch slurry; wherein the mass ratio of toluene diisocyanate to ethylene-vinyl acetate copolymer is 1:0.2-1, and the concentration of the mixed emulsion is 20-40wt%; the concentration of the polyvinyl alcohol aqueous solution is 10-20wt%;

(3) Post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the temperature of the drying is 80-90 ℃;

the alfalfa sowing season is spring or autumn; the spring refers to a period of 3-5 months; the autumn refers to at least 40 days before the local frost period;

the fully biodegradable resin comprises one or a combination of polylactic acid (PLA), poly (adipic acid)/butylene terephthalate (PBAT), poly (butylene succinate) (PBS), poly (butylene succinate) -adipate (PBSA) and poly (methyl ethylene carbonate) (PPC).

2. The alfalfa planting method of a fully biodegradable mulch film according to claim 1, wherein the method for preparing the fully biodegradable mulch film comprises the steps of:

(1) Mixing 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate in a ball mill according to the weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding for 1-2 hours at the temperature of 80-100 ℃, and drying to obtain starch/calcium carbonate composite filler;

(3) The blow-molded film enters a traction station, and is rolled into a full-biodegradable plastic mulch film with the thickness of 0.006-0.015mm in a rolling machine through the post-treatment process of edge cutting, thickness measurement and corona treatment.

3. The alfalfa planting method of fully biodegradable mulch film according to claim 2, wherein the adjuvant comprises one or a combination of plasticizers, nucleating agents, chain extenders, openers, lubricants, anti-blocking agents, antistatic agents, light absorbers or antioxidants.