CN113207560A

CN113207560A - Alfalfa planting method with full-biodegradable mulching film covering

Info

Publication number: CN113207560A
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: 2021-08-06
Anticipated expiration: 2041-05-14
Also published as: CN113207560B

Abstract

The invention provides an alfalfa planting method with full-biodegradable mulching film mulching, which adopts planting, field management and mowing and comprises the following steps: selecting seeds, irrigating, applying base fertilizer, preparing soil, performing narrow-row hole sowing, managing in the field and harvesting; the full-biodegradable mulching film comprises 100 parts of full-biodegradable resin, 20-40 parts of modified starch and 30-50 parts of modified calcium carbonate in parts by weight, and the performance of the full-biodegradable mulching film meets the specification of the national standard GB/T35795-2017 full-biodegradable agricultural ground covering film.

Description

Alfalfa planting method with full-biodegradable mulching film covering

Technical Field

The invention relates to the field of agricultural planting, in particular to a method for planting alfalfa with full-biodegradable mulching film mulching.

Background

Alfalfa is an indispensable forage grass in modern animal husbandry, enjoys the special status of the king of pasture, is the most important and the best plant protein source particularly in the dairy cow industry, and practices at home and abroad prove that the addition of alfalfa has the effect which cannot be replaced by any other feed for improving the milk yield of dairy cows, reducing the unit cost of milk and improving the health level of the dairy cows. Besides the dairy cows, the growth speed of the beef cattle and the mutton sheep and the quality of the meat can also be improved by adding a certain amount of alfalfa into the herbivorous animal feed of the beef cattle, the mutton sheep and the like. With the development of animal husbandry in China, the number of high-quality alfalfa imported in China is increased in successive years, the import amount of alfalfa hay is kept about 140 million tons in recent years, the annual import amount reaches more than 5 hundred million dollars, and the alfalfa is the largest world imported alfalfa.

The reason for mass import of alfalfa in China is that the area of a high-quality alfalfa staying bed in China is small, the yield of alfalfa is insufficient, and meanwhile, the quality stability of alfalfa in China is different from that of imported alfalfa, and the reason is related to the alfalfa production area in China. China alfalfa is concentrated in northwest arid areas, the rainfall capacity of the areas is low, the climate is dry, high-quality hay is easy to prepare, and the quality of the produced alfalfa is high, but the areas generally have adverse climate factors on alfalfa planting, such as poor soil conditions, drought and rain in a sowing season, complex and various irrigation modes, large wind and sand in spring and autumn, and the like, and the success rate of planting after sowing can be influenced. The alfalfa seeds are small, the time from germination and seedling emergence to successful planting is enough, and the seedling emergence is uneven; soil in northwest areas is mainly sandy soil, soil at the base of seedlings is easily scraped off in windy weather, and the seedlings of alfalfa after emergence are dry and dead due to the loss of soil protection at the base of the seedlings. Therefore, although the northwest region is the main producing area of the high-quality alfalfa in China, the income and planting enthusiasm of alfalfa producers are affected due to high planting difficulty and low planting success rate. In addition to low success rate of planting, another difficulty in alfalfa production is serious weed damage, which is common when the first crop of alfalfa is cut after successful planting, due to the long germination time of alfalfa, slow growth and development in the seedling stage after emergence of seedlings, poor competition ability of alfalfa seedlings relative to weeds in newly planted alfalfa plots, faster weed growth than alfalfa, weak alfalfa seedlings, and frequent occurrence of "weed cheating" which leads to failed planting, even if a large amount of weeds are mixed into alfalfa when the planting is successful, which affects the quality and price of alfalfa. The northwest arid region is used as the most suitable production region of the high-quality alfalfa in China, and the region is also the traditional alfalfa planting region in China, the income of the planted alfalfa is higher than that of the main grain crops, and the crop with better economic benefit can be brought, so that the improvement of the alfalfa planting level has practical significance for improving the alfalfa self-feeding capability in China and improving the income of farmers in the northwest arid region.

In order to solve the problem of alfalfa establishment, researchers explore various new alfalfa planting technologies, wherein water evaporation is reduced through mulching film covering, earth surface wind erosion caused by windy and sandy weather is reduced, and the alfalfa establishment success rate can be improved; meanwhile, the growth of weeds under the film is suppressed by film mulching planting, the proportion of weeds contained in the alfalfa is greatly reduced, the quality of the alfalfa hay is improved, and accordingly the alfalfa planting income can be improved. However, the mulching film is basically the traditional polyethylene mulching film, the polyethylene mulching film in the alfalfa land can not be cleaned and degraded while the planting success rate is improved and the proportion of weeds in the first crop of hay is reduced, and fragments of the mulching film are easily mixed into the alfalfa hay in the mechanical operation process in the process of mowing and tedding the alfalfa hay each time, so that the hay quality is reduced. In particular, the fragments of the mulching film can cause intestinal obstruction of livestock once being eaten by the livestock by mistake, and the life of the livestock is seriously threatened. Some researchers only focus on avoiding the pollution to the environment and do not pay attention to the damage of the biodegradable mulching film to livestock although adopting the biodegradable mulching film, so that the yield of the alfalfa planting is extremely difficult to increase by adopting a mulching film mode at present. In order to solve the problems, the components of the mulching film for alfalfa planting need to be blended, 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 very low, so that the mulching film cannot be practically applied, and the mulching film can lose strength quickly and break in advance even if being reluctantly paved in a field; if the content of additives such as starch and the like is reduced and the degradation period of the mulching film formula is prolonged, the cost is increased and the mulching film formula is similar to a polyethylene mulching film, namely, the mulching film still remains in an alfalfa land for a certain time after the mulching film is successfully built and planted, large pieces of mulching film fragments are easily mixed into alfalfa grass in the process of cutting and tedding the hay of alfalfa each time, and once the mulching film fragments are eaten by livestock by mistake, the mulching film fragments can not be degraded in intestines and stomach quickly, and the healthy growth of the livestock can still be influenced.

Disclosure of Invention

In order to solve the problems, the invention provides an alfalfa planting method covered by a biodegradable mulching film, which can simultaneously solve the problems of low alfalfa planting success rate in northwest arid regions and alfalfa grass mixed with fragments of the mulching film planting mulching film, and simultaneously solves the problem that the biodegradable mulching film cannot simultaneously consider both the degradation rate and the mechanical strength.

In order to achieve the purpose, the invention provides an alfalfa planting method by covering a film with a full-biodegradable mulching film, which selects the full-biodegradable mulching film, and adopts the following 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-mulching planting mode;

(2) irrigation: the water content of the soil during sowing is 5-20%, and the water content 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 or inorganic fertilizer, and the application amount of the base fertilizer is 10-20% lower than that of a non-film-covering planting mode;

(4) land preparation: rotary tillage and soil preparation, wherein the prepared alfalfa land is required to be flat, the soil blocks are basically smaller than 3 cm, and the influence of the large soil blocks on the film planting opening after transplanting to seedling emergence is avoided;

(5) narrow row hill planting: in the alfalfa seeding season, paving a full-biodegradable mulching film, adjusting the row spacing and the plant spacing, punching holes on the film to form holes, seeding 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 mulching film between the alfalfa seeding rows;

(6) field management: carrying out water management after sowing and before the first mowing, and ensuring that the water content of the soil is 20-35% by adopting spray irrigation, drip irrigation under the film or small water flood irrigation;

(7) harvesting: in the alfalfa harvesting season, mechanically mowing, mechanically turning grass and picking and bundling the alfalfa to form an alfalfa bundle; the mechanical mowing means that when each batch of alfalfa is mowed, a mowing machine is adopted to cut the alfalfa and 5-15 cm of stubbles are reserved; the water content of the alfalfa bale 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 first frost period.

Optionally, when the alfalfa is sowed in spring, the fully biodegradable mulching film meets the specification of national standard GB/T35795-2017 'fully biodegradable agricultural ground covering film', the thickness of the fully biodegradable mulching film is 0.006-0.015mm, and the mulching film is black or colorless and transparent.

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

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

Optionally, the preparation method of the modified calcium carbonate comprises the following steps: (1) weighing 100 parts of nano calcium carbonate powder by mass, adding 10 parts of an absolute ethanol solution of a composite coupling agent with the concentration of 20 wt%, continuously stirring and heating for 1-2h in a high-speed stirrer at the rotation speed of 1000-; 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 treatment calcium carbonate powder, 5-10 parts of sodium silicate and 50-100 parts of deionized water into a reaction bottle, slowly adding a mixed solution of 2.5 wt% hydrochloric acid and oxalic acid to adjust the pH value of the substance mixed system 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 the hydrochloric acid to the oxalic acid is 1: 1; (3) according to the mass parts, 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 and are uniformly stirred, the mixture is stirred and reacts for 5 to 6 hours under the condition of controlling the temperature to be 95 to 105 ℃ in a sealed high-pressure kettle, the mixture is naturally cooled, the material is taken under reduced pressure, the material is placed into a vacuum drying box, the vacuum degree is kept to be 0.01 to 0.1Mpa, and the temperature is kept to be 100 ℃ and the temperature is kept to be 120 ℃ for drying, so that the modified calcium carbonate is obtained.

Optionally, the preparation method of the modified starch comprises the following steps: (1) paste mixing: adding starch raw materials into a sodium hydroxide solution with the pH value of 8-9, mixing and stirring the mixture to form starch slurry, and heating the starch slurry 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 at 75-105 ℃ for 10-20h to obtain modified starch slurry; wherein the mass ratio of the toluene diisocyanate to the ethylene-vinyl acetate copolymer is 1: 0.2-1, and the concentration of the mixed emulsion is 20-40 wt%; the concentration of the polyvinyl alcohol aqueous solution is 10-20 wt%; (3) and (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 full-biodegradable mulching 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 a weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding at the temperature of 80-100 ℃ for 1-2 hours, and drying to obtain a starch/calcium carbonate composite filler;

(2) weighing raw materials comprising the starch/calcium carbonate composite filler, 100 parts of full-biodegradable resin and 10-30 parts of auxiliary agent according to a weight ratio, adding the raw materials into a mixing hopper according to a set proportion, uniformly stirring, feeding into a single-screw extruder with an exhaust function, and performing blow molding;

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

Optionally, the auxiliaries include one or a combination of plasticizers, nucleating agents, chain extenders, opening agents, lubricants, antiblocking agents, antistatic agents, light absorbers, or antioxidants.

The invention has the following beneficial effects:

1. the method adopts the full-biodegradable mulching film to cover the film for planting the alfalfa, can keep better soil moisture content from germination to seedling emergence after the film is covered, simultaneously protects the soil below the film from being eroded by wind, has beneficial effects of ensuring germination and seedling emergence of alfalfa seeds and improving the success rate of planting the alfalfa, and particularly can plant high-quality alfalfa in regions with poor conditions.

2. The method selects the specific type of biodegradable mulching film for alfalfa planting, can improve the planting success rate, and can reduce the influence of the mulching film on the quality of alfalfa. According to different sowing seasons, according to the requirements of GB/T35795-2017 'full-biodegradable ground cover agricultural film', a type of biodegradable mulching film with short effective life is selected, a black mulching film with short effective service life and high water permeability is selected for planting in spring, the black mulching film is a season in which weeds are germinated and has higher competitiveness than alfalfa seedlings in the seedling stage in spring, and the black mulching film has the strongest effect of inhibiting the weeds due to the light impermeability. The grower can also select according to the specific planting time, particularly, the transparent mulching film can be selected for seeding before the final frost period to strengthen the heating effect, the freezing damage of low temperature such as late spring coldness and the like to the alfalfa seedlings is reduced, the competitiveness of the alfalfa seedlings to weeds is improved, and the black mulching film is selected at the late spring sowing time, so that the effect of inhibiting the weeds is strengthened; in autumn, a mulching film with a medium effective life is selected, so that the safety of the alfalfa in winter is ensured. The type of the biodegradable mulching film with specific effective service life is selected to ensure that the mulching film is degraded as soon as possible after the mulching film is planted, and the degradation of alfalfa quality caused by the fact that fragments of the mulching film are mixed into alfalfa after the alfalfa is cut is reduced or avoided. The fully biodegradable mulching film with high water permeability is selected to improve the air permeability of the mulching film, so that the activity of the alfalfa root system is improved, and the growth of seedlings is promoted.

3. The invention can improve the autumn dormancy level of the variety selected in the alfalfa planting area. The autumn dormancy level is an index reflecting that alfalfa enters dormancy at low temperature in autumn and does not grow any more, and the high autumn dormancy level indicates that the alfalfa enters dormancy later, and the growing period is longer, so that the yield is generally higher. The method adopts specific biodegradable mulching film to cover the film for planting, the emergence rate after sowing is high, the competitiveness of the seedling after emergence is stronger than that of weeds, the plant is stronger, the root system of the alfalfa is more developed after successful planting, more nutrients are stored in the root part before the autumn sleep enters the autumn sleep in autumn and winter, and the overwintering capability is stronger, so that the autumn sleep grade of the selected variety can be improved by 0.5-1 grade.

4. The method adopts narrow-row hole sowing, coats a layer of soil strips with the thickness of 2-3 cm on the film between the sowing rows of the alfalfa, ensures the depth of the alfalfa seeds to be 1-2cm, coats a thicker soil layer between the rows, can avoid the mulching film from being blown away, shifted or broken by wind, provides a guarantee measure for the service life of the mulching film, simultaneously improves the root system soil penetration depth in the current planting year, improves the overwintering capacity, reduces the risk, and further reduces the possibility that the mulching film is mixed into the alfalfa due to the soil covering on the film between the rows, thereby providing guarantee for the quality of the alfalfa.

5. When the alfalfa is mowed for the first time, the higher stubble height is reserved, the higher stubble plays a role in supporting the cut alfalfa, the proportion that the alfalfa directly contacts the mulching film is reduced, the insertion depth of mechanical grass turning is well controlled, damage to the mulching film is reduced, mulching film fragments are prevented from being mixed into the alfalfa, the quality of the alfalfa is reduced, and the probability that livestock mistakenly eat the alfalfa mixed into the bundling mulching film fragments is reduced.

6. The mulching film adopts full-biodegradable resin, and mainly contains moisture and carbon dioxide after being degraded, and is harmless; in addition, all the used fully biodegradable resins contain starch modified by modifiers such as polyvinyl alcohol and the like, the polyvinyl alcohol and the starch have large content of hydroxyl groups, the water absorption is strong, and the fully biodegradable resins have the characteristic of water solubility, and crushed residual membranes which are not completely degraded after being crushed in soil improve the viscosity and water storage rate of local sandy soil and the soil moisture of northwest dry sandy soil due to high water absorption rate or caking property of the polyvinyl alcohol and the starch. According to the invention, the modifier such as isocyanate is used for successfully forming a bridge between the polyvinyl alcohol and the starch, so that the overall structure formed by the polyvinyl alcohol and the starch has a group similar to the biodegradable resin in property, the adverse effect of the starch on the mechanical property of the film is reduced, and the compatibility of the starch and the like on the biodegradable mulching film is improved.

7. Setting the addition amount of modified starch and modified calcium carbonate in a certain range according to the climatic conditions of the northwest region and the planting conditions of the alfalfa to obtain a mulching film formula which is suitable for the growth period of the alfalfa; in addition, the mulching film has good mechanical strength in the early stage of alfalfa planting, has good soil moisture preservation and weed suppression effects, accelerates the non-film process at the later stage of degradation, and reduces the possibility that residual film is mixed into alfalfa during mowing.

Drawings

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

FIG. 2 shows the membrane degradation in the event of the alfalfa reversion in the next year in example 1.

FIG. 3 shows the membrane degradation of comparative example 1 during the next year of alfalfa reversion.

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

Detailed Description

The present invention will be described in detail with reference to the following embodiments in order to make the aforementioned objects, features and advantages of the 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 than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

Referring to fig. 1, the alfalfa planting method by covering a film with the full-biodegradable mulching film selects the full-biodegradable mulching film, and comprises the following 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-mulching planting mode; (2) irrigation: the water content of the soil during sowing is 5-20%, and the water content 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 or inorganic fertilizer, and the application amount of the base fertilizer is 10-20% lower than that of a non-film-covering planting mode; (4) land preparation: rotary tillage and soil preparation, wherein the prepared alfalfa land is required to be flat, the soil blocks are basically smaller than 3 cm, and the influence of the large soil blocks on the film planting opening after transplanting to seedling emergence is avoided; (5) narrow row hill planting: in the alfalfa seeding season, paving a full-biodegradable mulching film, adjusting the row spacing and the plant spacing, punching holes on the film to form holes, seeding 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 mulching film between the alfalfa seeding rows; (6) field management: carrying out water management after sowing and before the first mowing, and ensuring that the water content of the soil is 20-35% by adopting spray irrigation, drip irrigation under the film or small water flood irrigation; (7) harvesting: in the alfalfa harvesting season, mechanically mowing, mechanically turning grass and picking and bundling the alfalfa to form an alfalfa bundle; the mechanical mowing means that when each batch of alfalfa is mowed, a mowing machine is adopted to cut the alfalfa and 5-15 cm of stubbles are reserved; the water content of the alfalfa bale is 20-25%.

In the alfalfa planting method of the full-biodegradable mulch film mulching according to the present invention, 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 first frost period.

In the alfalfa planting method of the full-biodegradable plastic film mulching film, the full-biodegradable plastic film is in accordance with the specification of the national standard GB/T35795-2017 'full-biodegradable agricultural ground covering film' in spring of the alfalfa seeding season, the thickness of the full-biodegradable plastic film mulching film is black or colorless and transparent.

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

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

In the alfalfa planting method of the full-biodegradable plastic film mulching film, the preparation method of the modified calcium carbonate comprises the following steps: (1) weighing 100 parts of nano calcium carbonate powder by mass, adding 10 parts of an absolute ethanol solution of a composite coupling agent with the concentration of 20 wt%, continuously stirring and heating for 1-2h in a high-speed stirrer at the rotation speed of 1000-; 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 treatment calcium carbonate powder, 5-10 parts of sodium silicate and 50-100 parts of deionized water into a reaction bottle, slowly adding a mixed solution of 2.5 wt% hydrochloric acid and oxalic acid to adjust the pH value of the substance mixed system 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 the hydrochloric acid to the oxalic acid is 1: 1; (3) according to the mass parts, 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 and are uniformly stirred, the mixture is stirred and reacts for 5 to 6 hours under the condition of controlling the temperature to be 95 to 105 ℃ in a sealed high-pressure kettle, the mixture is naturally cooled, the material is taken under reduced pressure, the material is placed into a vacuum drying box, the vacuum degree is kept to be 0.01 to 0.1Mpa, and the temperature is kept to be 100 ℃ and the temperature is kept to be 120 ℃ for drying, so that the modified calcium carbonate is obtained.

In the alfalfa planting method of the full-biodegradable plastic film mulching film, the preparation method of the modified starch comprises the following steps: (1) paste mixing: adding starch raw materials into a sodium hydroxide solution with the pH value of 8-9, mixing and stirring the mixture to form starch slurry, and heating the starch slurry 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 at 75-105 ℃ for 10-20h to obtain modified starch slurry; wherein the mass ratio of the toluene diisocyanate to the ethylene-vinyl acetate copolymer is 1: 0.2-1, and the concentration of the mixed emulsion is 20-40 wt%; the concentration of the polyvinyl alcohol aqueous solution is 10-20 wt%; (3) and (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 plastic film mulching film, the preparation method of the full-biodegradable plastic film mulching 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 a weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding at the temperature of 80-100 ℃ for 1-2 hours, and drying to obtain a starch/calcium carbonate composite filler;

In the alfalfa planting method of the full-biodegradable plastic film mulching film, the auxiliary agent comprises 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 absorbing agent or an antioxidant.

In the alfalfa planting method of the full-biodegradable plastic film mulching film, the row spacing of sowing is 12-20 cm, the plant spacing is 4-20 cm, the hole diameter of the hole is 3-6 cm, the sowing depth is 1-2cm, and the sowing amount of each hole is 5-10 alfalfa seeds; the width of the soil-covering belt 5 is 5-10 cm, the thickness of the soil-covering belt is 2-3 cm, the width of the soil-covering belt is at least 5 cm smaller than the row spacing of the alfalfa, and the soil-covering belt cannot cover the alfalfa seeding position.

In the alfalfa planting method of the full-biodegradable plastic film mulching, the paving of the full-biodegradable plastic film is completed by using a film mulching machine.

In the alfalfa planting method of the full-biodegradable plastic film mulching film, the full-biodegradable plastic film mulching, punching holes on the film to form holes, sowing alfalfa seeds in the holes and covering soil on the full-biodegradable plastic film among alfalfa rows are completed while hole sowing.

The method for planting alfalfa with fully biodegradable plastic film mulching of the present invention is specifically described below with reference to specific examples. The auxiliary agent in each embodiment is a combination of glycerol and an antioxidant 1010, and the mass ratio is 10: 1.

Example 1

As shown in the specification of figure 1, the experiment of planting alfalfa through full-biodegradable mulching film covering is carried out in Zhangye city of Gansu province within 3 months and 27 days.

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 a 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 a starch/calcium carbonate composite filler; (2) weighing raw materials comprising the starch/calcium carbonate composite filler, 100 parts of full-biodegradable resin (the mass ratio of polylactic acid (PLA) to polybutylene adipate/terephthalate (PBAT) is 0.1:1), 30 parts of auxiliary agent, 1 part of carbon black and the like according to a set proportion, adding the raw materials into a mixing hopper, uniformly stirring, feeding into a single-screw extruder with an exhaust function, and performing blow molding; (3) the film formed by blow molding enters a traction station, and is rolled into a full-biodegradable plastic mulching film with the thickness of 0.015mm by a rolling machine through the post-treatment processes of edge cutting, thickness measurement, corona treatment and the like.

The preparation method of the modified starch comprises the following steps: (1) paste mixing: adding a starch raw material into a sodium hydroxide solution with the pH value of 9, mixing and stirring to form starch slurry, and 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 at 105 ℃ for 20 hours to obtain modified starch slurry; wherein the mass ratio of the toluene diisocyanate to the ethylene-vinyl acetate copolymer is 1:1, and the concentration of the mixed emulsion is 40 wt%; the concentration of the polyvinyl alcohol aqueous solution is 20 wt%; (3) and (3) post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the temperature of the drying was 90 ℃.

The preparation method of the modified calcium carbonate comprises the following steps: (1) weighing 100 parts of nano calcium carbonate powder by mass, adding 10 parts of an absolute ethanol solution of a composite coupling agent with the concentration of 20 wt%, continuously stirring and heating for 2 hours in a high-speed stirrer at the rotating speed of 2000 r/min and the temperature of 80 ℃, filtering, 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 treatment calcium carbonate powder, 10 parts of sodium silicate and 100 parts of deionized water into a reaction bottle, slowly adding a mixed solution of 2.5 wt% hydrochloric acid and oxalic acid to adjust the pH value of the substance mixed system to 7.0, grinding in a ball mill, filtering and drying to obtain silica sol coated calcium carbonate powder; wherein the mass ratio of the hydrochloric acid to the oxalic acid is 1: 1; (3) according to the mass parts, 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 and are uniformly stirred, the mixture is stirred and reacted for 6 hours under the condition of controlling the temperature to be 105 ℃ in a sealed high-pressure kettle, the mixture is naturally cooled, the material is taken under reduced pressure, the material is placed into a vacuum drying oven, the vacuum degree is kept to be 0.1Mpa, and the temperature is kept to be 120 ℃ for drying, so that the modified calcium carbonate is obtained.

The performance indexes of the full-biodegradable mulching film are as follows: the effective life period is classified into class I, the water vapor transmission rate is classified into class C, the thickness is 0.015mm, and the color of the mulching film is black.

(II) a planting method of the film-covered alfalfa: fully irrigating winter water before the winter comes in the previous year, and utilizing the soil in winter high-cold weather to freeze and lock water so as to reduce loss; after thawing the soil with the depth of more than 10 cm on the surface of the soil at the bottom of 3 months, preparing the soil and sowing, uniformly spreading 25 kg of diammonium phosphate, 5 kg of potassium sulfate and 10 kg of phosphorus nitrate per mu before soil preparation, then rotating the soil by a rotary cultivator to uniformly mix fertilizers with the soil, finishing the soil into flat ground without large soil blocks on the surface of the soil, and properly compacting a soil layer 1; the alfalfa variety is selected from the alfalfa variety Adina of the autumn sleep level 4 (the local more common bred variety Gannong No. 3 is the autumn sleep level 3.0); sowing in an alfalfa sowing hole 6 of a full-biodegradable mulching film 2 with an effective width of 1.68 m by using a hole sowing machine with a film covering and soil pressing device, wherein the operation width is 1.8 m, the film covering and soil pressing device is arranged, 12 rows are sowed on the film, the row spacing 3 of the film covering hole sowing machine is adjusted to 14 cm, the plant spacing 4 is adjusted to 10 cm, the sowing depth is adjusted to 2cm, the width of a soil covering belt 5 is 10 cm, the thickness is 2-3 cm, an earthing device is a strip type earthing strip, the earthing strip is positioned between the alfalfa rows, no earthing is carried out between the plants, and the field condition after sowing is shown in figure 1; after sowing, paying attention to water management, and supplementing soil water by flood irrigation with small water when the soil is over-dry; the alfalfa continuously enters the flowering period in 8 months, the height of the alfalfa reaches more than 60 cm, meanwhile, when the rainy weather is forecasted for at least 5 days, the first mowing is carried out by the mower, the mowing height of the mower is adjusted before operation, and the stubble is kept at 15 cm; drying in the sun for 4 days after cutting, and turning over the grass for 1 time by a grass turner in the middle to dry the grass layer uniformly; and (4) after the alfalfa grass reaches the preset water content, bundling the alfalfa grass into bundles by using a picking and bundling machine, and timely moving the alfalfa grass out of the field. The full-biodegradable mulching film is basically degraded after the hay is harvested in the next year after the hay is harvested twice in winter, no degradable mulching film residue is basically left between the fields, and the hay harvesting operation is not affected.

Example 2

As shown in the specification of figure 1, an experiment of planting alfalfa in a full-biodegradable mulching film was carried out at 22 months 8 in Tongliao City of inner Mongolia autonomous region.

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 a 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 a starch/calcium carbonate composite filler; (2) weighing 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 (propylene carbonate) (PPC) according to a weight ratio of 1: 0.1: 0.1) and 10 parts of auxiliary agent according to a set proportion, adding the raw materials into a mixing hopper, uniformly stirring, feeding the raw materials into a single-screw extruder with an exhaust function, and performing blow molding; (3) the film formed by blow molding enters a traction station, and is rolled into a full-biodegradable plastic mulching film with the thickness of 0.006mm by a rolling machine through the post-treatment processes of 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 a sodium hydroxide solution with the pH value of 8, mixing and stirring to form starch slurry, and 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 the toluene diisocyanate to the ethylene-vinyl acetate copolymer is 1:0.2, and the concentration of the mixed emulsion is 20 wt%; the concentration of the polyvinyl alcohol aqueous solution is 10 wt%; (3) and (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 by mass, adding 10 parts of an absolute ethanol solution of a composite coupling agent with the concentration of 20 wt%, continuously stirring and heating for 1h in a high-speed stirrer at the rotation speed of 1000 revolutions per minute and the temperature of 70 ℃, filtering, and drying at 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 2.5 wt% hydrochloric acid and oxalic acid to adjust the pH value of the substance mixed system 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 the hydrochloric acid to the oxalic acid is 1: 1; (3) according to the mass parts, 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 and are uniformly stirred, the mixture is stirred and reacted for 5 hours under the condition of controlling the temperature to be 95 ℃ in a sealed high-pressure kettle, the mixture is naturally cooled, the material is taken under reduced pressure, the material is placed into a vacuum drying oven, the vacuum degree is kept to be 0.01MPa, and the temperature is kept to be 100 ℃ for drying, so that the modified calcium carbonate is obtained.

The performance indexes of the mulching film are as follows: the effective life period is classified into III types, the water vapor transmission rate is classified into A type, the thickness is 0.006mm, and the color of the mulching film is transparent.

(II) a planting method of the film-covered alfalfa: irrigating water before planting, preparing soil after irrigating water for three days, sowing, applying 25 kg of diammonium phosphate and 15 kg of potassium sulfate to each mu of land before land preparation, then rotating the land by using a rotary cultivator to uniformly mix fertilizers to the soil, uniformly mixing the fertilizers to the flat land without large soil blocks on the surface of the soil, and properly compacting a soil layer 1; the alfalfa variety is selected from 3.4 grade variety "Bai Yun 341" (the local variety of Luohan alfalfa in the year, autumn sleeping grade is about 2.5 grade); sowing in an alfalfa sowing hole 6 of a full-biodegradable mulching film 2 with an effective width of 1.68 m by using a hole sowing machine with an operation width of 1.4 m and a mulching and soil pressing device, adjusting the row spacing 3 of the mulching hole sowing machine to 13 cm, the plant spacing 4 to 10 cm, the sowing depth to 1.5 cm and the width of an earthing strip 5 to 8 cm before sowing, wherein the earthing device is used for strip earthing, the earthing strip is positioned between the alfalfa rows, and no earthing is performed between the plants; after sowing, sprinkling by using a pointer type sprinkling irrigation machine, continuously sprinkling irrigation when the soil is dry, stopping sprinkling irrigation when the water penetration depth reaches 20 cm, and stopping irrigation when the water penetration reaches 50 cm during the last winter water irrigation in winter; the alfalfa planted in the current year is not mowed, the alfalfa continuously enters the flowering period in the 6 th late month of the next year, the height reaches 70-80 cm, meanwhile, when the rainy weather is forecasted for at least 5 days, the first mowed is carried out by the mower, the mowing height is adjusted by the mower before the operation, the stubble is kept at 15 cm, and the stubble height can be properly reduced according to the degradation of the residual situation of the mulching film, such as land blocks with few residual films, from the second mowed; drying in the sun for 6 days after cutting, and turning over the grass for 2 times by a grass turner in the middle to dry the grass layer uniformly; and (4) after the alfalfa grass reaches the preset water content, bundling the alfalfa grass into bundles by using a picking and bundling machine, and timely moving the alfalfa grass out of the field. And (5) when the third crop is mowed, the degraded mulching film reaches a high degradation degree, and after the field residual film is less, the mowing and the grass collection can be carried out according to a normal mode.

Example 3

As shown in FIG. 1, the experiment of planting alfalfa in the full-biodegradable mulching film was conducted in 5 days 4 months in Gaozhuangxiang, Ping Luo county, the autonomous region in Ningxia. The soil is medium alkaline soil, and the pH value of the soil is between 8.0 and 8.3.

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 a 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 a starch/calcium carbonate composite filler; (2) weighing raw materials comprising the starch/calcium carbonate composite filler, 100 parts of full-biodegradable resin (poly (adipic acid)/polybutylene terephthalate (PBAT) and poly (butylene succinate) (PBS) in a mass ratio of 1:1), 20 parts of an auxiliary agent and 0.1 part of carbon black according to a set proportion, adding the raw materials into a mixing hopper, uniformly stirring, feeding into a single-screw extruder with an exhaust function, and performing blow molding; (3) the film formed by blow molding enters a traction station, and is rolled into a full-biodegradable plastic mulching film with the thickness of 0.008mm in a rolling machine through the post-treatment processes of 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 a sodium hydroxide solution with the pH value of 8.5, mixing and stirring to form starch slurry, heating to 85 ℃ to form 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 the toluene diisocyanate to the ethylene-vinyl acetate copolymer is 1:0.6, and the concentration of the mixed emulsion is 30 wt%; the concentration of the polyvinyl alcohol aqueous solution is 15 wt%; (3) and (3) post-treatment: drying, grinding and screening the modified starch slurry to obtain modified starch; the temperature of the drying was 85 ℃.

The preparation method of the modified calcium carbonate comprises the following steps: (1) weighing 100 parts of nano calcium carbonate powder by mass, adding 10 parts of an absolute ethanol solution of a composite coupling agent with the concentration of 20 wt%, continuously stirring and heating for 1.5 hours in a high-speed stirrer at the rotation speed of 1500 rpm and the temperature of 75 ℃, filtering, and drying at 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 2.5 wt% hydrochloric acid and oxalic acid to adjust the pH value of the substance mixed system 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 the hydrochloric acid to the oxalic acid is 1: 1; (3) according to the mass parts, 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 and are uniformly stirred, the mixture is reacted for 5.5 hours in a sealed high-pressure kettle under the conditions of keeping stirring and controlling the temperature to be 100 ℃, the mixture is naturally cooled, the material is taken under reduced pressure, the material is placed into a vacuum drying box, and the vacuum degree is kept to be 0.05Mpa and the temperature is kept to be 110 ℃ for drying, so that the modified calcium carbonate is obtained.

The performance indexes of the mulching film are as follows: the service life is classified into type II, the water vapor transmission rate is classified into type B, the thickness is 0.008mm, and the mulching film is a black mulching film with the light transmittance of 13%;

(II) a planting method of the film-covered alfalfa: the alfalfa variety is selected from a 5.5-grade autumn sleeping variety, namely 'long voyage' (the variety 'Adina' with a large local planting area is in 4.5-grade autumn sleeping); the ground is high in underground water level, the soil is filled with winter water for the first year, the soil is unfrozen at the depth of 20 cm in 4 months and 5 days, the soil moisture content is proper, 15 kg of ammonium sulfate is applied to each mu of the ground before land preparation for neutralizing the soil alkalinity and providing the nitrogen requirement in the seedling stage, 20 kg of dipotassium phosphate is applied, then a rotary cultivator is used for rotating the ground, the fertilizer is uniformly mixed to the soil, the surface of the soil is provided with a flat ground without large soil blocks, the soil layer 1 is properly pressed, and the large soil blocks are crushed; covering film, covering soil belt and sowing by using a film covering seeder with an operation width of 1.4 m and a film covering and soil compacting device, wherein the soil covering device is used for covering soil in a strip mode, the distance between the soil covering belt and the punching and sowing device is 13 cm, the plant spacing is adjusted to 10 cm, the width of the soil covering belt is adjusted to 5 cm, the thickness of the soil covering belt is adjusted to 2-3 cm, the seeder walks in a machine traveling device 7, and the sowing depth is adjusted to 1.5 cm; irrigating when water comes from the irrigation channel after sowing. After the planting is successfully established, mowing is respectively carried out for three times in 18 days in 6 months, 25 days in 7 months and 2 days in 9 months, the mowing height of the mower is adjusted before mowing, and the heights of the three stubbles left are respectively 15 cm, 12 cm and 10 cm; and (4) after the alfalfa grass reaches the preset water content, bundling the alfalfa grass into bundles by using a picking and bundling machine, and timely moving the alfalfa grass out of the field.

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 was as in example 1 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 the modified calcium carbonate were not used to prepare a starch/calcium carbonate composite filler.

And (3) performance testing:

1. measurement of tensile Strength and elongation at Break

According to the test conditions for films and sheets, part 3 of the national Standard "determination of tensile Properties of plastics" (GB \ T1040.3-2006): the dumbbell specimens have a length of 150mm, a narrow parallel width of 10mm, a drawing speed of 200mm/min and a room temperature of 25 ℃.

2. Determination of Right Angle tear Strength

Quote QB/T1130-1991 "Plastic Right Angle tear Performance test method", tensile speed 200mm/min, room temperature 25 ℃.

3. Degradation during alfalfa planting

The examples and comparative examples were compared in the same plot and no mulch was visually observed as complete degradation.

The results of the performance tests on the products obtained in the above examples and comparative examples are shown 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

Through the comparison between the above examples and the accompanying fig. 2 and 3, it can be seen that the modified starch and the modified calcium carbonate of the fully biodegradable plastic film provided by the present invention greatly affect the tensile strength, elongation at break and tear strength of the mulching film; in addition, the mulching film is different from the prior art that the biodegradable mulching film is slowly degraded, the strength change in the early degradation stage is small, a relatively stable strength plateau stage is provided, after a certain degradation degree is reached, the strength can be rapidly reduced, so that the mulching film is broken into small blocks, good coverage characteristics can be successfully maintained in the crop growth period, when crops are harvested and land is cleared, the crop harvesting and the next planting are not influenced, and the attached figure 2 shows that the non-film area of the full-biodegradable mulching film is about 70% relative to a polyethylene mulching film when alfalfa is turned green in the next year, and the degree of mixing into mulching film grass when alfalfa is harvested is greatly reduced. The biodegradable mulching film is suitable for planting alfalfa in northwest regions, because the climate is relatively dry, the influence of moisture on the mulching film is relatively small, and whether the modified starch and the modified calcium carbonate are subjected to advanced composite treatment is not required, so that the mulching film meeting the requirements can still be achieved.

Although some specific embodiments of the present invention have been described in detail by way of illustration, it should be understood by those skilled in the art that the above illustration is only for the purpose of illustration and is 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 method for planting alfalfa covered with fully biodegradable mulching film is characterized in that the fully biodegradable mulching film is selected, and the following steps of planting, field management and mowing are adopted:

2. The method for growing alfalfa with fully biodegradable mulch film as claimed in claim 1, wherein 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 first frost period.

3. The method for planting alfalfa covered with fully biodegradable plastic film according to claim 1, wherein the fully biodegradable plastic film meets the regulations of national standard GB/T35795-2017 "fully biodegradable agricultural ground covering film" in spring of alfalfa seeding season, the thickness of the fully biodegradable plastic film is 0.006-0.015mm, and the plastic film is black or colorless and transparent.

4. The method for planting alfalfa covered with fully biodegradable plastic film according to claim 3, wherein the components of the fully biodegradable plastic film comprise, by weight, 100 parts of fully biodegradable resin, 20-40 parts of modified starch, and 30-50 parts of modified calcium carbonate.

5. The method for planting alfalfa as claimed in claim 4, wherein the fully biodegradable resin comprises one or a combination of polylactic acid (PLA), polybutylene adipate/terephthalate (PBAT), polybutylene succinate (PBS), polybutylene succinate-adipate (PBSA), and poly (methyl ethylene carbonate) (PPC).

6. The method for planting alfalfa covered with fully biodegradable plastic film as claimed in claim 4, wherein the preparation method of the modified calcium carbonate comprises the following steps:

(1) weighing 100 parts of nano calcium carbonate powder by mass, adding 10 parts of an absolute ethanol solution of a composite coupling agent with the concentration of 20 wt%, continuously stirring and heating for 1-2h in a high-speed stirrer at the rotation speed of 1000-; wherein the components of the composite coupling agent are aluminum zirconate coupling agent which is long in coupling length and easily causes basic seedling uncoupling agent when the soil water content is low, and the weight ratio of gamma-methacryloxypropyl trimethoxy silane to titanate coupling agent is 1:1: 1;

(2) adding 100 parts of primary treatment calcium carbonate powder, 5-10 parts of sodium silicate and 50-100 parts of deionized water into a reaction bottle, slowly adding a mixed solution of 2.5 wt% hydrochloric acid and oxalic acid to adjust the pH value of the substance mixed system 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 the hydrochloric acid to the oxalic acid is 1: 1;

(3) according to the mass parts, 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 and are uniformly stirred, the mixture is stirred and reacts for 5 to 6 hours under the condition of controlling the temperature to be 95 to 105 ℃ in a sealed high-pressure kettle, the mixture is naturally cooled, the material is taken under reduced pressure, the material is placed into a vacuum drying box, the vacuum degree is kept to be 0.01 to 0.1Mpa, and the temperature is kept to be 100 ℃ and the temperature is kept to be 120 ℃ for drying, so that the modified calcium carbonate is obtained.

7. The method for planting alfalfa covered with fully biodegradable plastic film as claimed in claim 4, wherein the method for preparing the modified starch comprises the following steps:

(1) paste mixing: adding starch raw materials into a sodium hydroxide solution with the pH value of 8-9, mixing and stirring the mixture to form starch slurry, and heating the starch slurry 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 at 75-105 ℃ for 10-20h to obtain modified starch slurry; wherein the mass ratio of the toluene diisocyanate to the ethylene-vinyl acetate copolymer is 1: 0.2-1, and the concentration of the mixed emulsion is 20-40 wt%; the concentration of the polyvinyl alcohol aqueous solution is 10-20 wt%;

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

8. The method for planting alfalfa covered with fully biodegradable mulch film according to claim 4, wherein the method for preparing 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 a weight ratio, adding 8 parts of absolute ethyl alcohol and 0.6 part of citric acid, grinding at the temperature of 80-100 ℃ for 1-2 hours, and drying to obtain a starch/calcium carbonate composite filler;

9. The method for growing alfalfa covered with biodegradable mulch film according to claim 8, wherein the auxiliary agent comprises 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.