Method for promoting decomposition of straw returned to field

Abstract

The present application belongs to the technical field of straw decomposition and soil improvement, and particularly relates to a method for promoting decomposition of straw returned to field. The present application forms a biological community of diazotrophs by applying artificial cultivation of nitrogen-fixing blue-green algae to a rice field, uses the diazotrophs to increase soil nitrogen by biological nitrogen fixation, and reduces the amount of nitrogen fertilizer applied. Meanwhile, the diazotrophs can also improve the activity of soil decomposing bacteria by secreting active substances such as extracellular enzymes, accelerate the conversion of straw source carbon to soil microbial source carbon, regulate the carbon-nitrogen balance of soil, and reduce the adverse effects on crops. On the other hand, the present application can reduce greenhouse gas emissions, and achieve rapid accumulation of soil organic matter and improvement of soil fertility.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of straw decomposition and soil improvement, and particularly relates to a method for promoting decomposition of straw returned to field. BACKGROUND

[0002] Straw returning to field is a method of directly or after piling up for decomposition, and is one of important measures for soil fertility cultivation and farmland quality improvement. The method can avoid air pollution caused by straw burning and has the effects of increasing fertilizer and yield. The straw returning to field methods include direct returning to field, decomposition returning to field, and returning to field through the stomach, etc. The direct returning to field is the most simple returning to field method, which is simple to operate, has less labor input and low cost. However, there are problems such as long decomposition period, nitrogen competition between straw and crops in the process of straw decomposition, slow increase of soil organic matter, and difficulty in playing the potential of straw returning to field and producing greenhouse gas emission.

[0003] The existing technical measures for accelerating decomposition of straw returned to field include: increasing nitrogen fertilizer to adjust soil carbon-nitrogen balance and reducing the influence of nitrogen consumption in the process of straw decomposition on crops, but it is easy to increase ammonia volatilization, denitrification and other nitrogen losses, which has adverse effects on the ecological environment and increases the cost; adding decomposition bacteria, but the activity of decomposition bacteria is affected by soil temperature, humidity, pH value and nutrient content, and the reproduction activity, fermentation capacity and enzyme activity of the decomposition microbial strains are inhibited, which affects the decomposition efficiency; returning green manure and straw to field together, which can reduce the amount of nitrogen fertilizer, but planting green manure in rice-wheat rotation area will lead to the failure of planting winter wheat, and the total grain yield is greatly reduced; at the same time, the carbon-nitrogen ratio of straw is too high, and too much carbon brought in by straw returning to field leads to imbalance of soil carbon-nitrogen; in addition, the soil microorganisms reproduce a lot after straw returning to field, and the nitrogen is consumed by the growth and metabolism of the microorganisms, which further aggravates the imbalance of carbon-nitrogen. It can be seen that the existing technical measures for accelerating decomposition of straw returned to field still have the problems of imbalance of carbon-nitrogen and inability to improve soil fertility. SUMMARY

[0004] The present application aims to provide a method for promoting decomposition of straw returned to field, which can promote straw decomposition, adjust carbon-nitrogen balance and improve soil fertility.

[0005] The present application provides a method for promoting decomposition of straw returned to field, which comprises the following steps:

[0006] Planting rice in the field of straw returning to field, and keeping the depth of field surface water of the field at 2-3 cm;

[0007] At the rice seedling greening period, applying nitrogen-fixing cyanobacteria to the field for the first time; the application amount of the nitrogen-fixing cyanobacteria is not less than (1.5-2) x 10 11 cells / ha;

[0008] The nitrogen-fixing blue algae is applied again after 20-25 days from the first application, and the amount of the nitrogen-fixing blue algae applied again is (1-3)×10 10 cells / ha.

[0009] Preferably, the nitrogen-fixing blue algae is applied in the form of a nitrogen-fixing blue algae suspension, and the nitrogen-fixing blue algae suspension is prepared by using a blue algae culture solution as a solvent and comprises the following components: nitrogen-fixing blue algae with an effective algae cell concentration of not less than 1×10 6 cells / mL, 1.0-2.0 g / L of NaCl, 0.05-0.1 g / L of MgCl2 and 1.5-2.5 g / L of a homogenizing agent.

[0010] Preferably, the nitrogen-fixing blue algae comprises Nostoc and Anabaena, and the cell quantity ratio of the Nostoc to the Anabaena is (10-15):(5-10).

[0011] Preferably, the homogenizing agent comprises agar powder, dextran and sodium alginate, and the mass ratio of the agar powder, the dextran and the sodium alginate is (10-15):(4-6):(1-1.5).

[0012] Preferably, the straw comprises wheat straw and / or rice straw.

[0013] Preferably, the method further comprises the following steps before the rice is planted: sequentially applying base fertilizer, rotary tillage and water irrigation after the straw is applied to the field.

[0014] Preferably, the rotary tillage has a depth of 8-15 cm, and the water irrigation is performed for 2-4 days until the water depth reaches 2-3 cm.

[0015] Preferably, the application of the base fertilizer comprises application of nitrogen fertilizer and phosphorus fertilizer, and the application amount of the nitrogen fertilizer and the phosphorus fertilizer is applied according to the base fertilizer application standard of the rice planting land.

[0016] Preferably, the preparation method of the nitrogen-fixing blue algae suspension comprises the following steps: centrifuging nitrogen-fixing blue algae cultured to the logarithmic growth phase to obtain nitrogen-fixing blue algae slurry;

[0017] mixing the nitrogen-fixing blue algae slurry, the blue algae culture solution, the homogenizing agent, NaCl and MgCl2 to obtain the nitrogen-fixing blue algae suspension.

[0018] Preferably, the blue algae culture solution comprises WC medium.

[0019] Beneficial effects:

[0020] The application provides a method for promoting the decomposition of straw applied to a field, which comprises the following steps: planting rice in a field where straw is applied to the field and keeping the water depth of the field at 2-3 cm; applying nitrogen-fixing blue algae to the field at the rice seedling greening period, and the application amount of the nitrogen-fixing blue algae is not less than (1.5-2)×1011 The present application forms a diazotrophic symbiotic colony by applying the nitrogen-fixing blue algae to the rice field, uses the symbiotic colony to increase soil nitrogen by biological nitrogen fixation, and reduces the amount of nitrogen fertilizer application; meanwhile, the symbiotic colony can also improve the activity of soil decomposing bacteria by secreting active substances such as extracellular enzymes, accelerate the conversion of straw carbon to soil microbial carbon, regulate the soil carbon-nitrogen balance, reduce the adverse effects on crops, reduce greenhouse gas emissions, and achieve rapid accumulation of soil organic matter and improvement of soil fertility. DETAILED DESCRIPTION

[0021] The present application provides a method for promoting the decomposition of straw returned to the field, comprising the following steps:

[0022] Rice is planted in the field where the straw is returned to the field, and the depth of the field surface water of the field is kept at 2-3 cm;

[0023] At the rice seedling greening period, nitrogen-fixing blue algae are applied to the rice field; the application amount of the nitrogen-fixing blue algae is not less than (1.5-2) × 10 11 cells / ha;

[0024] The nitrogen-fixing blue algae are supplemented and applied again 20-25 days after the first application, and the supplemented application amount is (1-3) × 10 10 cells / ha.

[0025] The present application preferably selects a rice-wheat rotation or double-cropping rice planting area, and the wheat straw or rice straw is returned to the field at the time of wheat harvesting in the rice-wheat rotation planting area or at the time of rice harvesting in the double-cropping rice planting area. In the present application, when the straw is returned to the field, the straw is preferably crushed to 3-5 cm.

[0026] After the straw is returned to the field, the present application preferably applies base fertilizer on the field where the straw is returned to the field, and the base fertilizer preferably comprises nitrogen fertilizer and phosphorus fertilizer, and the application amount of the base fertilizer is preferably applied according to the standard of base fertilizer application in the rice planting area.

[0027] After the base fertilizer is applied, the present application preferably performs rotary tillage and irrigation on the field where the base fertilizer is applied. The depth of the rotary tillage is preferably 8-15 cm, and more preferably 10 cm. The depth of the field surface after irrigation is preferably 2-3 cm, and more preferably 2 cm; and the irrigation time is preferably 2-4 days, and more preferably 3 days.

[0028] After the irrigation, the present application preferably transplants rice seedlings in the field where the irrigation is performed, and keeps the depth of the field surface water at 2-3 cm.

[0029] After the rice seedlings turn green, the present application applies nitrogen-fixing blue algae to the rice field; the application amount of the nitrogen-fixing blue algae is not less than (1.5-2) × 10 11Cells / ha, preferably (1.8–2) × 10⁻⁶. 11 Cells / ha. This invention is suitable for rice seedlings during the greening stage, when the seedlings are relatively small, allowing the surrounding organisms to receive sufficient light and grow rapidly. It avoids the problem of excessively large seedlings blocking light, which is detrimental to the growth of the surrounding organisms. In addition, this period is also the stage of rapid decomposition of straw, and the nitrogen fixation by cyanobacteria can supplement nitrogen.

[0030] The nitrogen-fixing cyanobacteria described in this invention are preferably applied in the form of a nitrogen-fixing cyanobacteria suspension; the nitrogen-fixing cyanobacteria suspension uses cyanobacteria culture medium as a solvent and includes the following components: an effective algal cell concentration of not less than 1×10⁻⁶. 6 Nitrogen-fixing cyanobacteria per mL, 1.0–2.0 g / L NaCl, 0.05–0.1 g / L MgCl2, and 1.5–2.5 g / L homogenizer.

[0031] The nitrogen-fixing cyanobacteria of this invention preferably include *Nostoc commune* and *Anabaena*, with a cell number ratio of *Nostoc commune* to *Anabaena* preferably being (10-15):(5-10), more preferably 15:10. The cyanobacteria culture medium of this invention is preferably WC medium. The concentration of NaCl in this invention is preferably 2.0 g / L; the concentration of MgCl2 is preferably 0.1 g / L; and the concentration of the homogenizing agent is preferably 2 g / L. The homogenizing agent of this invention preferably includes agar powder, dextran, and sodium alginate, with a mass ratio of agar powder, dextran, and sodium alginate preferably being (10-15):(4-6):(1-1.5), more preferably 12:5:1. The homogenizing agent of this invention can maintain the uniformity of the nitrogen-fixing cyanobacteria cells during the preservation of the nitrogen-fixing cyanobacteria suspension. Based on the nitrogen-fixing cyanobacteria suspension, the preferred application rate of the nitrogen-fixing cyanobacteria suspension of the present invention is 150-200 L / ha, more preferably 180-200 L / ha.

[0032] The preferred method for preparing the nitrogen-fixing cyanobacteria suspension of the present invention includes the following steps: centrifuging nitrogen-fixing cyanobacteria cultured to the logarithmic growth phase to obtain nitrogen-fixing cyanobacteria sludge;

[0033] The nitrogen-fixing cyanobacterial mud, cyanobacterial culture medium, homogenizer, NaCl and MgCl2 are mixed to obtain the nitrogen-fixing cyanobacterial suspension.

[0034] In this invention, *Nostoc commune* and *Anabaena globulus* are preferably cultured separately to the logarithmic growth phase to obtain *Nostoc commune* culture medium and *Anabaena globulus* culture medium, respectively. The culture media for the expanded culture of *Nostoc commune* and *Anabaena globulus* are preferably WC medium; the temperatures are preferably 23–25°C, more preferably 25°C and 25°C, respectively; the photoperiods are preferably 12L:12D, and the light intensity is preferably 2000–3000 lux, more preferably 2500 lux.

[0035] After obtaining the Nostoc culture solution and the Anabaena culture solution, the Nostoc culture solution and the Anabaena culture solution are preferably centrifuged respectively to obtain Nostoc slurry and Anabaena slurry. The present application does not have special limitations on the conditions of the centrifugation, and the conventional centrifugation conditions in the art can be used.

[0036] After obtaining the Nostoc slurry and the Anabaena slurry, the Nostoc slurry, the Anabaena slurry, the cyanobacteria culture solution, the homogenizing agent, NaCl and MgCl2 are preferably mixed to adjust the pH value to obtain the nitrogen-fixing cyanobacteria suspension. The present application preferably uses 1:1 hydrochloric acid to adjust the pH value, and the pH value is preferably 4.5-5.5, and more preferably 4.

[0037] After 20-25 days of the first application of the nitrogen-fixing cyanobacteria, the nitrogen-fixing cyanobacteria are applied again, and the application amount is (1-3) x 10 10 cells / ha, that is, the nitrogen-fixing cyanobacteria suspension is applied, and the application amount is preferably (10-30) L / ha.

[0038] The present application forms a nitrogen-fixing symbiotic organism community by applying nitrogen-fixing cyanobacteria to a rice field, uses the symbiotic organisms to increase soil nitrogen through biological nitrogen fixation, and reduces the amount of nitrogen fertilizer; at the same time, the symbiotic organisms can also improve the activity of soil decomposing bacteria by secreting active substances such as extracellular enzymes, accelerate the conversion of straw source carbon to soil microbial source carbon, regulate the carbon-nitrogen balance of the soil, reduce the adverse effects on crops, reduce greenhouse gas emissions, and achieve rapid accumulation of soil organic matter and improvement of soil fertility, and improve rice yield.

[0039] In order to further illustrate the present application, the technical solutions provided by the present application are described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0040] Unless otherwise specified, the materials and reagents used in the examples of the present application are obtained through conventional commercial channels in the art; during the growth of rice, the irrigation and drainage time and frequency are performed according to the growth needs of rice.

[0041] Example 1

[0042] A method for promoting the decomposition of straw returned to the field, the steps are as follows:

[0043] The experiment was carried out in a rice field in Jurong City, Jiangsu Province

[0044] (1) Select rice-wheat rotation area and divide it into 6 experimental plots of 5m x 5m. After the wheat is harvested, the straw is crushed to 3-5cm. Meanwhile, a buried bag experiment is set up. The experiment is as follows: a certain amount of straw is put in a nylon bag, the bag is about 10cm long, and all of it is buried in the 0-15cm surface soil. Six replicates are set up in each plot, and on the 30th and 60th day, three of them are taken out, washed, dried, weighed, and the rate of straw decomposition is calculated.

[0045] (2) After the straw is applied to the field, base fertilizer is applied. The amount of nitrogen and phosphorus fertilizer applied is based on the conventional amount in the region, i.e. 150kg N / ha of nitrogen fertilizer and 60kg P / ha of phosphorus fertilizer. A rotary tiller is used to rotary till the rice planting area to a depth of 10cm, then water is poured to a depth of 3cm.

[0046] (3) After 3 days of watering, rice seedlings are transplanted to the rice planting area, and the water depth is maintained at 2cm.

[0047] (4) After the rice seedlings turn green, the nitrogen-fixing blue-green algae suspension composed of nostoc and anabaena is uniformly sprayed into the water. The cell number ratio of nostoc to anabaena is 10:5, and the amount of nitrogen-fixing blue-green algae suspension sprayed is 200L / ha. During the growth of rice, the irrigation and drainage time and frequency are carried out according to the needs of rice growth. Specifically, at the end of the tillering stage, the water is drained and the field is dried, then water is poured after 3-7 days, and the water is drained at the end of the filling stage.

[0048] The preparation steps of the nitrogen-fixing blue-green algae suspension are as follows: the nostoc and anabaena strains (purchased from the Chinese Academy of Sciences Freshwater Algae Culture Collection) are respectively cultured in WC medium at 23-25℃ with 12 hours of light (light intensity of 2500 lux) and 12 hours of darkness to the logarithmic phase to obtain nostoc and anabaena culture solutions; the nostoc and anabaena culture solutions are centrifuged to obtain nostoc and anabaena algae mud respectively; the nostoc and anabaena algae mud are mixed with WC medium to obtain a suspension, and a homogenizing agent (agar powder, dextrose and sodium alginate in a mass ratio of 12:5:1), NaCl and MgCl2 are added to the suspension, and 1:1 hydrochloric acid is used to adjust the pH of the suspension to 4 to obtain the nitrogen-fixing blue-green algae suspension, wherein the effective algae cell number of nostoc and anabaena is 1.2 x 10 6 ML, the concentration of the homogenizing agent is 2g / L, the concentration of NaCl is 2.0g / L, and the concentration of MgCl2 is 0.1g / L.

[0049] (5) After 20 days of spraying the nitrogen-fixing blue-green algae suspension, the nitrogen-fixing blue-green algae suspension is supplemented and applied at a rate of 10L / ha.

[0050] (6) 30 days and 60 days after the first addition of the cyanobacteria suspension, surface 0-20 cm soil samples and straw in the nylon bags were collected to determine the straw decomposition rate, soil total organic carbon content, and the composition of the plexus community in the rice field. The soil total organic carbon and other soil properties were determined according to the Soil Agricultural Chemistry Analysis Method; the straw decomposition rate was determined by weighing the change in weight before and after straw decomposition; and the composition of the plexus community was determined by amplicon sequencing. The rice yield in each experimental plot was determined after the rice was harvested (120 days after the addition of the cyanobacteria suspension).

[0051] Comparative Example 1

[0052] The test was performed in the same planting area according to the method of Example 1, with the addition of 10 kg / ha of nitrogen fertilizer at the rice seedling stage but without spraying the cyanobacteria suspension as Comparative Example 1, and the rest was the same as Example 1.

[0053] Table 1: Test results of the plexus community accelerating straw decomposition in Example 1 and Comparative Example 1

[0054]

[0055] Note: Comparative-1, Comparative-2, and Comparative-3 in Table 1 represent the three experimental plots in Comparative Example 1, and represent three biological replicates. Implementation-1, Implementation-2, and Implementation-3 represent the three experimental plots in Example 1, and represent three biological replicates. When evaluating the technical effect, the average value of the three biological replicates was taken.

[0056] As shown in Table 1, the determination results of the plexus community in the rice field, straw decomposition rate, and soil total organic carbon content showed that the relative abundance of cyanobacteria in the plexus community in Example 1 reached 34.7% 30 days after spraying the cyanobacteria suspension, which was much higher than 22.7% in Comparative Example 1.

[0057] The plexus community disappeared 60 days after the first spraying due to reasons such as field drying and rice growth, but its influence on straw decomposition and soil organic carbon persisted. For example, the straw decomposition rate during the rice growing season reached 76.3%, which was much higher than 61.3% in Comparative Example 1; and the total organic carbon content in the surface soil was 18.6 g / kg, which was significantly higher than 17.1 g / kg in Comparative Example 1.

[0058] The average yield of rice in Example 1 reached 9105 kg / ha, which was higher than the average yield of 8952 kg / ha in Comparative Example 1.

[0059] Example 2

[0060] A method for promoting the decomposition of straw returned to the field, comprising the following steps:

[0061] The experiment was carried out in a rice field in Fusui County, Guangxi Zhuang Autonomous Region

[0062] (1) Select double cropping rice area and divide it into 6 experimental plots of 5m x 5m. After the early rice is harvested, the rice straw is crushed to 3-5 cm. Meanwhile, a bagging experiment is set up. The bagging experiment is as follows: a certain amount of straw is put in a nylon bag, the bag is about 10 cm long, and all of it is buried in the 0-15 cm surface soil. Six replicates are set up in each experimental plot, and three are taken out on the 30th and 60th days.

[0063] (2) After the straw is applied, base fertilizer is applied. The amount of nitrogen and phosphorus fertilizer applied is based on the conventional amount of fertilizer used in the area for late rice, i.e. 190 kg N / ha of nitrogen fertilizer and 65 kg P / ha of phosphorus fertilizer. A rotary cultivator is used to rotary till the rice planting area to a depth of 10 cm, then water is poured to a depth of 3 cm.

[0064] (3) After 3 days of watering, rice seedlings are transplanted to the rice planting area, and the water depth is maintained at 2 cm.

[0065] (4) After the rice seedlings turn green, active nitrogen-fixing blue-green algae liquid composed of nostoc and anabaena is uniformly sprayed into the water. The ratio of nostoc to anabaena is 15:5, and the amount of active algae liquid sprayed is 180 kg / ha. During the growth of the rice, the irrigation and drainage time and frequency are based on the needs of the rice growth. Specifically, at the end of the rice tillering period, the water is drained and the field is dried, then watered 3-7 days later, and drained at the end of the grain filling period.

[0066] The preparation steps of the nitrogen-fixing blue-green algae suspension are as follows: nostoc and anabaena strains (purchased from the Chinese Academy of Sciences Freshwater Algae Culture Collection) are respectively cultured in WC medium at 23-25°C with 12 hours of light (light intensity of 2500 lux) and 12 hours of darkness until the logarithmic phase, obtaining nostoc and anabaena culture liquids; the nostoc and anabaena culture liquids are centrifuged to obtain nostoc and anabaena algae mud; the nostoc and anabaena algae mud are mixed with WC medium to obtain a suspension, and a homogenizing agent (agar powder, dextrose and sodium alginate in a mass ratio of 12:5:1), NaCl and MgCl2 are added to the suspension, and 1:1 hydrochloric acid is used to adjust the pH of the suspension to 4, obtaining a nitrogen-fixing blue-green algae suspension, wherein the effective algae cell number of nostoc and anabaena is 1.3 x 10 6 individuals / mL, the concentration of the homogenizing agent is 2 g / L, the concentration of NaCl is 2.0 g / L, and the concentration of MgCl2 is 0.1 g / L.

[0067] (5) After 25 days of spraying the nitrogen-fixing blue-green algae suspension, active blue-green algae liquid is added again, with an addition amount of 20 L / ha.

[0068] (6) 30 days and 60 days after the first addition of the active blue-green algae liquid, surface 0-20 cm soil samples and straw in the nylon bags are collected, the straw in the nylon bags is used to determine the straw decomposition rate, the soil is used to determine the total organic carbon content of the soil, and the composition of the paddy field microflora is determined by the method of Example 1. The rice yield of each experimental plot is determined after the rice is harvested.

[0069] Comparative Example 2

[0070] The method of Example 2 is used to perform a test in the same planting area, nitrogen fertilizer 10 kg / ha is added in the rice seedling stage but no blue-green algae suspension is sprayed as Comparative Example 2, and the rest is the same as Example 2.

[0071] Table 2 Test results of the microflora accelerating straw decomposition in Example 2 and Comparative Example 2

[0072]

[0073] Note: Comparative-1, Comparative-2 and Comparative-3 in Table 2 respectively represent the three experimental plots in Comparative Example 2, and represent three biological replicates. Implementation-1, Implementation-2 and Implementation-3 respectively represent the three experimental plots in Example 2, and represent three biological replicates. When evaluating the technical effect, the average value of the three biological replicates is taken.

[0074] As can be seen from Table 2, the determination results of the paddy field microflora, straw decomposition rate, total organic carbon content of the soil and the like show that the relative abundance of cyanobacteria in the microflora in Example 2 reaches 36.3% after spraying the active algae liquid for 30 days, which is much higher than 21.7% in Comparative Example 2.

[0075] Until 60 days after spraying, the microflora is eliminated due to reasons such as field drying and rice growth, but its influence on straw decomposition and soil organic carbon continues to exist. For example, the straw decomposition rate in the rice growth season reaches 74.7%, which is much higher than 55.9% in Comparative Example 2; the total organic carbon content of the surface soil is 24.9 g / kg, which is obviously higher than 23.9 g / kg in Comparative Example 2.

[0076] The average yield of rice in Example 2 reaches 8957 kg / ha, which is higher than the average yield of 8779 kg / ha in Comparative Example 1.

[0077] From the above examples, it can be concluded that the method provided by the present application can effectively promote straw decomposition, regulate carbon-nitrogen balance, improve soil fertility and rice yield.

[0078] Although the above examples have made a detailed description of the present application, it is only a part of the examples of the present application, not all the examples, and other examples can be obtained under the premise of no creativity according to the present examples, which all belong to the protection scope of the present application.

Claims

1. A method for promoting decomposition of straw incorporated into the field, characterized by, The method comprises the following steps: planting rice in a field with straw returning, keeping the water depth of the field at 2-3 cm; applying nitrogen-fixing cyanobacteria to the field for the first time at the rice seedling turning green stage, the nitrogen-fixing cyanobacteria being in a suspension form, the nitrogen-fixing cyanobacteria being in a ratio of (10-15) : (5-10) in terms of the number of cells of Nostoc and Anabaena; The application amount is not less than (1.5~2)×10 11 cells / ha; The nitrogen-fixing blue-green algae is supplemented again after 20-25 days from the first application, with a supplemental application amount of (1-3) x 10 10 cells / ha. the homogenizing agent comprising agar powder, dextrose and sodium alginate, the mass ratio of the agar powder, the dextrose and the sodium alginate being (10-15) : (4-6) : (1-1.5).

2. The method of claim 1, wherein, The nitrogen-fixing blue-green algae is applied in the form of a nitrogen-fixing blue-green algae suspension; the nitrogen-fixing blue-green algae suspension uses a blue-green algae culture solution as a solvent and comprises the following components: nitrogen-fixing blue-green algae with an effective algal cell concentration of not less than 1×10 6 0.05-0.1 g / L of MgCl2 and 1.5-2.5 g / L of a homogenizing agent.

3. The method of claim 2, wherein, the straw comprising wheat straw and / or rice straw.

4. The method of claim 1, wherein, The method further comprises, before planting rice, sequentially applying base fertilizer, rotary tillage and water irrigation after the straw returning.

5. The method of claim 2, wherein, The rotary tillage has a depth of 8-15 cm, and the water irrigation is performed to reach a water depth of 2-3 cm and has a time of 2-4 days.

6. The method of claim 5, wherein, The application of the base fertilizer comprises applying nitrogen fertilizer and phosphorus fertilizer, and the application amount of the nitrogen fertilizer and the phosphorus fertilizer is applied according to the standard of base fertilizer application for rice planting land.

7. The method of claim 5, wherein, The preparation method of the nitrogen-fixing cyanobacteria suspension comprises centrifuging nitrogen-fixing cyanobacteria cultured to the logarithmic growth phase to obtain cyanobacteria slurry; 8. The method of claim 2, wherein, mixing the cyanobacteria slurry, cyanobacteria culture solution, homogenizing agent, NaCl and MgCl2 to obtain the nitrogen-fixing cyanobacteria suspension. The cyanobacteria culture solution comprises WC culture medium.

9. The method of claim 8, wherein, ​

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