Method for increasing grassland carbon sink by sowing mixed green manure

Abstract

A method for increasing grassland carbon sequestration by sowing mixed green manure relates to the technical field of grassland carbon sequestration and carbon sequestration, and selects perennial leguminous plants lespedeza and medicago sativa for sowing based on the ecological characteristics of grassland. The two kinds of green manure belong to types capable of growing rapidly and can effectively resist competition of local plants so as to rapidly cover the ground, nitrogen in the atmosphere is fixed through leguminous plants, and the grassland soil structure is rapidly improved and grassland plant growth is promoted. The method is simple to operate, rapid and efficient, and has better popularization value.

Description

Technical Field

[0001] The invention relates to the field of grassland carbon sink, and in particular to a method for increasing grassland carbon sink by sowing mixed green manure. Background Art

[0002] Grassland ecosystems are one of the most widely distributed terrestrial ecosystems on Earth, covering about 31% of the world's land area. Grasslands not only provide important feed resources for animal husbandry, but also play a key role in ecological balance. Against the backdrop of global warming posing severe challenges to human survival and development, the global terrestrial ecosystem carbon cycle has become a hot topic for scientists around the world. Therefore, in recent years, the carbon sequestration capacity of grassland ecosystems has received increasing attention. Improving the carbon sequestration capacity of grasslands will not only help mitigate climate change, but also improve soil health, promote biodiversity and enhance the resilience of ecosystems. Grassland ecosystems have a wide distribution area on the surface, and the proportion of underground biomass is high. Compared with forest ecosystems, grasslands have higher vegetation coverage and shorter vegetation growth cycles, and have huge carbon sequestration potential. Therefore, they occupy an important position in the study of carbon cycles.

[0003] Grassland ecosystems store carbon mainly through plant photosynthesis, soil organic carbon accumulation, root carbon input, and soil microbial activity. Grassland plants absorb carbon dioxide from the atmosphere through photosynthesis, convert it into organic carbon, and store it in the plant body and root system; their litter (such as dead grass, leaves) and root secretions enter the soil and can be decomposed by microorganisms to form soil organic carbon, fixing carbon in the soil. Therefore, grassland soils usually have a high organic carbon content, especially in deep soil.

[0004] In the existing technology, there are various carbon enhancement schemes for different environments, such as reforestation, selective logging, and application of fertilizers to increase forest carbon sinks. Not only are the sink efficiency low, but the cost is also high. There is still a lack of an efficient carbon fixation technology that can target grasslands. Summary of the invention

[0005] The purpose of the present invention is to provide a method for increasing grassland carbon sink by sowing mixed green manure, which is simple and quick to operate, can effectively improve the nitrogen fixation effect of grassland, thereby enhancing the soil carbon sink function, and has good promotion value.

[0006] The embodiment of the present invention is achieved as follows:

[0007] A method for increasing grassland carbon sink by sowing mixed green manure, characterized by comprising:

[0008] Plant Lespedeza and Medicago sativa in the grassland.

[0009] The beneficial effects of the embodiments of the present invention are:

[0010] The present invention provides a method for increasing grassland carbon sink by sowing mixed green manure, which selects perennial legume plants Lespedeza and Medicago sativa for sowing based on the ecological characteristics of the grassland itself. Both green manures are fast-growing types, which can effectively resist the competition of native plants, thereby quickly covering the ground, and then using legume plants to fix nitrogen in the atmosphere to achieve rapid improvement of grassland soil structure and promote grassland plant growth. The method is simple to operate, fast and efficient, and has good promotion value. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0012] The following is a detailed description of a method for increasing grassland carbon sink by sowing mixed green manure according to an embodiment of the present invention.

[0013] An embodiment of the present invention provides a method for increasing grassland carbon sequestration by sowing mixed green manure, which comprises:

[0014] Plant Lespedeza and Medicago sativa in the grassland.

[0015] There have been many studies on increasing the organic carbon content in the soil by planting green manure in the existing technology. However, traditional green manure planting usually adopts the practice of in-situ harvesting and plowing to return the field. There are problems such as low carbon sequestration efficiency, high economic and labor costs, and being unfavorable to improving soil fertility in terms of grassland soil carbon sequestration and sink. At the same time, the practice of in-situ harvesting and plowing to return the field will destroy the soil structure, which is not conducive to the formation of soil aggregates, and will hinder grassland soil carbon sequestration and emission reduction.

[0016] Nitrogen is an important component of chlorophyll, and chlorophyll is a key molecule in photosynthesis. With enough nitrogen, plants can synthesize more chlorophyll, thereby improving the efficiency of photosynthesis and increasing carbon fixation. Therefore, plant nitrogen fixation can improve the availability of nitrogen, promote photosynthesis and the assimilation and accumulation of carbon, and play an important role in plant growth and the carbon cycle of the ecosystem. The raw Lespedeza and alfalfa used in the present invention both belong to leguminous plants, have good nitrogen fixation ability, can establish a symbiotic relationship with nitrogen-fixing bacteria, fix nitrogen in the atmosphere into ammonia available to plants, and convert it into amino acids, proteins and other nitrogen-containing organic matter, providing nitrogen nutrients required for plant growth. Secondly, plants can also be allowed to synthesize more chlorophyll, improve the efficiency of photosynthesis, thereby fixing carbon to a greater extent, and improving the overall carbon fixation efficiency of grassland.

[0017] In addition, compared to forests, planting green manure in grasslands has relative advantages. Grasslands are usually located in flat or gently sloping areas, with shallow soil and sufficient water conservation conditions. Green manure is easy to plant and plow on grasslands, which helps to quickly improve soil fertility and carbon storage. Forests are generally distributed in complex terrains such as mountains and hills, with deep soil and rich organic matter. Green manure in forests needs to consider the influence of tree roots and terrain. Usually, it can only increase soil nitrogen content and carbon sequestration through intercropping or interplanting. Because forest plants have developed root systems, it is suitable to plant legumes such as Robinia and Beech, which can penetrate deep into the root system to improve soil structure. Therefore, planting green manure on grasslands to fix nitrogen and promote carbon has certain terrain advantages and planting advantages.

[0018] After comprehensive consideration, the present invention combines various factors such as soil conditions, climate, topography, economic costs, etc. in grassland areas, and specially selects perennial legume Lespedeza and perennial legume Alfalfa for planting. First of all, both Lespedeza and Alfalfa have the characteristics of fast growth and large-scale survival, can effectively resist the competition of native plants, and can quickly cover the ground. On this basis, relying on the symbiosis of Lespedeza and Alfalfa with rhizobia, nitrogen in the atmosphere is converted into nitrogen that can be used by plants through biological nitrogen fixation, and soil nitrogen is increased to promote the growth of grassland plants, thereby quickly improving the carbon sink efficiency of grassland.

[0019] In addition, Lespedeza is cold-resistant, barren-resistant, acid-resistant, salt-resistant, and mowing-resistant. It has a strong adaptability to the soil environment and can be widely used in grassland soil improvement to increase the carbon absorption capacity of marginal land. Lespedeza can grow up to 3 meters in height and its root system can reach 3 meters underground. It is a leguminous shrub with a high height and deep root system. Alfalfa has higher requirements for the soil environment and its growth height generally reaches about 1 meter. The root system depth is generally 1-2 meters underground. The mixed planting of the two leguminous plants can absorb photosynthetically active radiation at different heights, improve photosynthetic utilization, and improve soil structure at different depths, thereby promoting the improvement of vegetation carbon and the accumulation rate of soil nitrogen and carbon. Therefore, Lespedeza and alfalfa can form a multi-level vegetation structure at different growth heights and root system depths, synergistically improve photosynthesis efficiency, improve soil structure, improve soil water retention capacity and erosion resistance, and increase the organic carbon content in the soil. At the same time, a diverse vegetation combination can increase the biodiversity of the grassland, improve the stability of the ecosystem, and thus enhance the long-term carbon storage capacity of the grassland.

[0020] Optionally, the sowing ratio of Lespedeza bicolor to Medicago sativa L. is 1:1.8 to 2.5. Under this ratio, the synergistic effect of the two plants is better, which can greatly improve the carbon fixation effect.

[0021] Furthermore, the planting density of Lespedeza is 3 to 5 g / m2 The planting density of alfalfa is 5-10g / m 2 Because the two plants grow fast, the planting density needs to be controlled. Within this sowing amount range, the planting density of Lespedeza and Medicago sativa is appropriate, which not only has a higher carbon fixation efficiency, but also can better ensure the survival rate.

[0022] Optionally, the sowing time of Lespedeza and Medicago sativa is from March to April or from September to October each year. Since Lespedeza and Medicago sativa grow fast, there is no need to consider the competition of native plants. Selecting March to April or from September to October can avoid extreme high temperature or cold seasons and maximize the growth advantages of the two plants.

[0023] When sowing, choose a large area with fertile soil, evenly distributed grassland plants, and a sowing depth of 0.5 to 2 cm. In addition, due to the competitive advantages of the two plants, it can also be mixed with native forage grasses. After sowing, the soil in the sowing area can be lightly compacted with a light roller or foot to ensure good contact between the seeds and the soil.

[0024] Furthermore, before sowing, the seeds of Lespedeza and Medicago sativa are pretreated by soaking in warm water, which can break the dormancy period of the seeds and promote germination. During soaking, the water temperature is 40-50°C and the soaking time is 2-5 hours. Under this condition, the germination rate of the seeds is relatively high.

[0025] In addition, the present invention further comprises uniformly mixing the pretreated seeds with a liquid inoculum of nitrogen-fixing bacteria. Optionally, the nitrogen-fixing bacteria is rhizobium; after mixing, ensure that the surface of each seed is covered with the liquid inoculum of rhizobium.

[0026] After sowing, water appropriately according to weather conditions. Check the planting area regularly and remove competitive weeds in time to ensure the healthy growth of Lespedeza and alfalfa. Appropriate tillage can be carried out in the later stage to improve the fertility of the grassland soil. Regularly monitor and evaluate the growth of the plants, and record the coverage rate, growth height, carbon content and health status. If the survival rate is low, appropriate replanting is required in the grassland to ensure that the green manure reaches a certain density in the grassland.

[0027] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0028] Example 1

[0029] This embodiment provides a method for increasing grassland carbon sink by sowing mixed green manure, which includes:

[0030] S1. Selection of nitrogen-fixing plants:

[0031] Purchase certified Lespedeza and Alfalfa seeds to ensure that the germination rate of seeds is above 90%.

[0032] S2. Soil preparation:

[0033] Choose a large area with fertile soil, evenly distributed grassland plants, and good coverage for sowing, and make appropriate trenches or holes without causing too much damage to the area to ensure that the seeds can directly and quickly contact the soil.

[0034] S3. Seed weighing and pretreatment:

[0035] According to the size of the grassland, weigh 5g / m of Lespedeza seeds. 2 , Alfalfa seeds 10g / m 2 . Soak the seeds in 40℃ warm water for 6 hours before sowing to break the seed dormancy and promote germination.

[0036] S4. Inoculation of nitrogen-fixing bacteria:

[0037] Take out the pre-treated seeds, mix them with the purchased rhizobium liquid inoculant, and gently stir the seeds to ensure that the surface of each seed is covered with the rhizobium inoculant.

[0038] S5. Seed sowing:

[0039] The inoculated seeds were sown within 24 hours. The no-till broadcast method was used in late March to ensure that the seeds were evenly spread over the sowing area, with a sowing depth of about 1 cm. After sowing, the sowing area was lightly compacted by foot to ensure that the seeds were in full contact with the soil.

[0040] S6. Management and maintenance:

[0041] After sowing, water appropriately according to weather conditions. Check the planting area regularly and remove competitive weeds in time to ensure the healthy growth of Lespedeza and alfalfa. Appropriate tillage can be carried out in the later stage to improve the fertility of the grassland soil.

[0042] S7. Monitoring and Evaluation:

[0043] Regularly monitor and evaluate the growth of plants, record coverage, growth height, carbon content and health status. If the survival rate is low, appropriate replanting is required in the grassland to ensure that Lespedeza and alfalfa reach a certain density in the grassland.

[0044] In this embodiment, the germination rate of Lespedeza seeds is 88%; the germination rate of alfalfa seeds is 89%.

[0045] Example 2

[0046] This embodiment provides a method for increasing grassland carbon sink by sowing mixed green manure, which includes:

[0047] S1. Selection of nitrogen-fixing plants:

[0048] Purchase certified Lespedeza and Alfalfa seeds to ensure that the germination rate of seeds is above 90%.

[0049] S2. Soil preparation:

[0050] Choose a large area with fertile soil, evenly distributed grassland plants, and good coverage for sowing, and make appropriate trenches or holes without causing too much damage to the area to ensure that the seeds can directly and quickly contact the soil.

[0051] S3. Seed weighing and pretreatment:

[0052] According to the size of the grassland, weigh 3g / m of Lespedeza seeds. 2 , Alfalfa seeds 7.5g / m 2 . Soak the seeds in 50℃ warm water for 3 hours before sowing to break the seed dormancy and promote germination.

[0053] S4. Inoculation of nitrogen-fixing bacteria:

[0054] Take out the pre-treated seeds, mix them with the purchased rhizobium liquid inoculant, and gently stir the seeds to ensure that the surface of each seed is covered with the rhizobium inoculant.

[0055] S5. Seed sowing:

[0056] The inoculated seeds are sown within 24 hours. The no-till broadcast method is used in late September to ensure that the seeds are evenly spread in the sowing area, and the sowing depth is about 1 cm. After sowing, the sowing area is lightly compacted by foot to ensure that the seeds are in full contact with the soil.

[0057] S6. Management and maintenance:

[0058] After sowing, water appropriately according to weather conditions. Check the planting area regularly and remove competitive weeds in time to ensure the healthy growth of Lespedeza and alfalfa. Appropriate tillage can be carried out in the later stage to improve the fertility of the grassland soil.

[0059] S7. Monitoring and Evaluation:

[0060] Regularly monitor and evaluate the growth of plants, record coverage, growth height, carbon content and health status. If the survival rate is low, appropriate replanting is required in the grassland to ensure that Lespedeza and alfalfa reach a certain density in the grassland.

[0061] In this embodiment, the germination rate of Lespedeza seeds is 89%; the germination rate of alfalfa seeds is 87%.

[0062] Example 3

[0063] This embodiment provides a method for increasing grassland carbon sink by sowing mixed green manure, which includes:

[0064] S1. Selection of nitrogen-fixing plants:

[0065] Purchase certified Lespedeza and Alfalfa seeds to ensure that the germination rate of seeds is above 90%.

[0066] S2. Soil preparation:

[0067] Choose a large area with fertile soil, evenly distributed grassland plants, and good coverage for sowing, and make appropriate trenches or holes without causing too much damage to the area to ensure that the seeds can directly and quickly contact the soil.

[0068] S3. Seed weighing and pretreatment:

[0069] According to the size of the grassland, weigh 4g / m of Lespedeza seeds. 2 , Alfalfa seeds 8g / m 2 . Soak the seeds in 45℃ warm water for 4 hours before sowing to break the seed dormancy and promote germination.

[0070] S4. Inoculation of nitrogen-fixing bacteria:

[0071] Take out the pre-treated seeds, mix them with the purchased rhizobium liquid inoculant, and gently stir the seeds to ensure that the surface of each seed is covered with the rhizobium inoculant.

[0072] S5. Seed sowing:

[0073] The inoculated seeds are sown within 24 hours. In early April, the seeds are sown using the no-till broadcast method to ensure that the seeds are evenly spread over the sowing area, with a sowing depth of about 1.5 cm. After sowing, the sowing area is lightly compacted by foot to ensure that the seeds are in full contact with the soil.

[0074] S6. Management and maintenance:

[0075] After sowing, water appropriately according to weather conditions. Check the planting area regularly and remove competitive weeds in time to ensure the healthy growth of Lespedeza and alfalfa. Appropriate tillage can be carried out in the later stage to improve the fertility of the grassland soil.

[0076] S7. Monitoring and Evaluation:

[0077] Regularly monitor and evaluate the growth of plants, record coverage, growth height, carbon content and health status. If the survival rate is low, appropriate replanting is required in the grassland to ensure that Lespedeza and alfalfa reach a certain density in the grassland.

[0078] In this embodiment, the germination rate of Lespedeza seeds is 90%; the germination rate of alfalfa seeds is 89%.

[0079] Comparative Example 1

[0080] This comparative example provides a method for increasing grassland carbon sink by sowing mixed green manure, and the specific method is basically the same as that of Example 1, except that Lespedeza bicolor is not planted, and only Medicago sativa is planted.

[0081] In this comparative example, the germination rate of alfalfa seeds was 91%.

[0082] Comparative Example 2

[0083] This comparative example provides a method for increasing grassland carbon sink by sowing mixed green manure, and the specific method is basically the same as that of Example 1, except that only Lespedeza bicolor is planted instead of alfalfa.

[0084] In this comparative example, the germination rate of Lespedeza seeds was 88%.

[0085] Comparative Example 3

[0086] This comparative example provides a method for increasing grassland carbon sink by sowing mixed green manure, and the specific method is basically the same as that of Example 1, except that Lespedeza is replaced by an equal amount of Robinia pseudoacacia.

[0087] In this comparative example, the germination rate of Lespedeza seeds was 80%; the germination rate of alfalfa seeds was 90%.

[0088] Comparative Example 4

[0089] This comparative example provides a method for increasing grassland carbon sink by sowing mixed green manure, and the specific method is basically the same as that of Example 1, except that alfalfa is replaced with an equal amount of beech.

[0090] In this comparative example, the germination rate of the seeds of Echinops eriophorum was 81%; and the germination rate of the seeds of Lespedeza chinensis was 91%.

[0091] Comparative Example 5

[0092] This comparative example provides a method for increasing grassland carbon sink by sowing mixed green manure. The specific method is basically the same as that in Example 1, except that the sowing rate of Lespedeza is increased to 10 g / m 2 The sowing rate of alfalfa was increased to 20g / m 2 .

[0093] In this comparative example, the germination rate of Lespedeza seeds was 91%; the germination rate of alfalfa seeds was 90%.

[0094] Comparative Example 6

[0095] This comparative example provides a method for increasing grassland carbon sink by sowing mixed green manure. The specific method is basically the same as that in Example 1, except that the sowing rate of Lespedeza is reduced to 2.5 g / m 2 , the sowing rate of alfalfa was reduced to 5g / m 2 .

[0096] In this comparative example, the germination rate of Lespedeza seeds was 87%; the germination rate of alfalfa seeds was 91%.

[0097] Comparative Example 7

[0098] This comparative example provides a method for increasing grassland carbon sink by sowing mixed green manure, and the specific method is basically the same as that of Example 1, except that no pretreatment is performed in step S3.

[0099] In this comparative example, the germination rate of Lespedeza seeds was 80%; the germination rate of alfalfa seeds was 75%.

[0100] Test example

[0101] The method of increasing grassland carbon sink by sowing mixed green manure provided in Examples 1 to 3 and Comparative Examples 1 to 7 was adopted to sow seeds in respective experimental plots, and the experimental plots without planting green manure were used as blank cases. After one year of planting and cultivation, the surface soil of the experimental plots was sampled, and data of the samples were measured, and the annual nitrogen and carbon fixation effects were evaluated. The measurement results are shown in Table 1.

[0102] Table 1 Comparison of nitrogen fixation and carbon promotion effects of grassland water and fertilizer management

[0103]

[0104]

[0105] As can be seen from Table 1, after using the methods of Examples 1 to 3 of the present invention, the annual total carbon fixation of soil green manure reaches 4.6 to 5.5 tons / hectare, and under the influence of the nitrogen fixation effect of green manure, the annual carbon fixation of the grassland itself can be increased by 1.6 to 1.9 tons / hectare. This shows that nitrogen fixation has a significant effect on promoting carbon, and can significantly enhance the carbon sink function of grassland soil.

[0106] In contrast, in Example 1, where Medicago sativa was planted alone, the total annual carbon fixation was only 2.5 tons / hectare; in Example 2, where Lespedeza was planted alone, the total annual carbon fixation was only 1.4 tons / hectare. In Example 1, in the case of mixed sowing, the annual carbon fixation of each green manure was significantly higher than that of each green manure when planted alone, indicating that in the case of mixed sowing, the two green manures have a synergistic effect.

[0107] In Comparative Example 3, Lespedeza was replaced with an equal amount of Robinia pseudoacacia, and the total annual carbon fixation of green manure reached 3.3 tons / hectare, of which the contribution of lucerne was 2.1 tons / hectare and the contribution of Robinia pseudoacacia was 1.2 tons / hectare. The total annual carbon fixation of the two green manures is significantly lower than the mixed sowing scheme of Example 1, and it can be seen that the annual carbon fixation of lucerne pseudoacacia is even lower than that of its single planting (Comparative Example 1), and its growth is suppressed by Robinia pseudoacacia. In Comparative Example 4, lucerne pseudoacacia was replaced with an equal amount of beech, and the total annual carbon fixation of green manure reached 3.6 tons / hectare, of which the contribution of Lespedeza pseudoacacia was 2.0 tons / hectare and the contribution of beech was 1.6 tons / hectare. Although the growth of Lespedeza pseudoacacia is improved compared to Comparative Example 2, the total annual carbon fixation of green manure still does not reach the level of Examples 1 to 3 of the present application. Moreover, the green manure combination of Comparative Examples 3 to 4 has a relatively poor promoting effect on the grassland itself, and the annual carbon fixation of the grassland itself is only increased by 0.6 to 0.7 tons / hectare.

[0108] Comparative Examples 5 and 6 investigated the effect of planting density on carbon fixation. It can be seen that when the sowing amount is doubled (Comparative Example 5), the annual total carbon fixation of green manure is also increased accordingly, but the growth of the grassland itself is suppressed, and the annual carbon fixation of the grassland itself increases by only 1.2 tons / hectare, and the annual carbon fixation of green manure and grassland increases by 6.5 tons / hectare, which is lower than the result of Example 1. It can be seen that increasing the sowing amount too much not only increases the cost, but also has an adverse effect. In Comparative Example 6, when the sowing amount is halved, the annual total carbon fixation of green manure and the increase in the annual carbon fixation of grassland also decrease significantly accordingly, and the optimal configuration of the present invention is not achieved.

[0109] In comparative example 7, no pretreatment was performed on the seeds, and the germination rate of the seeds was affected, which resulted in a significant decrease in the annual total carbon fixation of the green manure and the increase in the annual carbon fixation of the grassland. Therefore, ensuring the germination rate of the seeds is conducive to achieving better carbon fixation and carbon sink effects.

[0110] In summary, the present invention provides a method for increasing grassland carbon sink by sowing mixed green manure, which selects perennial legumes Lespedeza and Medicago sativa for sowing based on the ecological characteristics of the grassland itself. Both green manures are fast-growing types that can effectively resist the competition of native plants, thereby quickly covering the ground, and then using legumes to fix nitrogen in the atmosphere to achieve rapid improvement of grassland soil structure and promote grassland plant growth. The method is simple to operate, fast and efficient, and has good promotion value.

[0111] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for increasing grassland carbon sink by sowing mixed green manure, characterized in that: include: Plant Lespedeza and Medicago sativa in the grassland.

2. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 1, characterized in that: The sowing rate ratio of the Lespedeza bicolor to the Medicago sativa L. is 1:1.8-2.

5.

3. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 2, characterized in that: The planting density of the Lespedeza chinensis is 3 to 5 g / m 2 .

4. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 2, characterized in that: The planting density of the alfalfa plant is 5 to 10 g / m 2 .

5. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 3, characterized in that: The sowing time of the Lespedeza and the Medicago sativa is from March to April or from September to October every year.

6. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 1, characterized in that: When sowing, choose a large area with fertile soil, evenly distributed grass plants, and good coverage.

7. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 1, characterized in that: The sowing depth of the Lespedeza and the Medicago sativa L. is 0.5 to 2 cm.

8. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 1, characterized in that: Before sowing, the seeds of Lespedeza and Medicago sativa are pretreated by soaking them in warm water; during soaking, the water temperature is 40-50° C. and the soaking time is 2-5 hours.

9. The method for increasing grassland carbon sink by sowing mixed green manure according to claim 8, characterized in that: The pretreated seeds are uniformly mixed with a liquid inoculum of nitrogen-fixing bacteria.

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