Preparation and application of a modified biochar composite enzyme agent for coastal saline-alkali soil improver

Abstract

The present invention discloses a method for preparing a coastal saline-alkali land modifier using a modified biochar composite enzyme agent, wherein the raw material formula of the modifier is: 10-20 parts of modified biochar composite enzyme agent, 150-200 parts of organic fertilizer, and 1-2 parts of microbial agent by weight, wherein the modified biochar composite enzyme agent is to dry the biochar after acid leaching and mixing with ferrous chloride, and then add glutathione reductase enzyme liquid for adsorption and immobilization, and finally filter and dry and dehydrate to obtain. The modifier application method includes: plowing the soil 20-30cm, plowing the soil 20-30cm and spreading the modifier according to the amount of 400-600kg / mu, and maintaining 20-45 days after rotary tillage. The modifier and application method of the present invention can achieve the purpose of improving saline-alkali land, and achieve the purpose of rapidly reducing the salt content of saline-alkali land, increasing the aggregate content and organic matter content, and improving the germination rate of crops at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of saline-alkali land improvement, and particularly relates to the preparation and application of an improver which is specially used for improving the structure of coastal saline-alkali soil, reducing salinity, increasing soil organic matter and improving crop germination rate. Background Art

[0002] Coastal saline-alkali soil is soil that develops on saline silt. Its salt accumulation process precedes the soil formation process. The salt mainly comes from seawater, mainly chloride [1]. Coastal tidal flat land is an important land reserve resource that can be used at present. However, coastal reclamation areas are affected by seawater mixing during the land formation process. The soil has high salt content, poor structure and low fertility, which seriously restricts the sustainable agricultural production in coastal areas [2]. At present, a lot of research work has been carried out at home and abroad on the improvement and utilization of saline-alkali soil. The main measures include engineering measures, such as terraced fields, sand pillars, water conservancy, underground pipes for salt drainage, and salt water freezing irrigation; physical and chemical measures, such as surface covering, isolation, and application of soil conditioners; biological measures, such as planting salt-tolerant plants and screening salt-tolerant bacteria, whose main function is to drain salt, reduce salt or eliminate the impact of salt on plant cultivation.

[0003] my country has carried out a lot of experiments and research on saline-alkali soil improvement. Among them, biological improvement agents for improving the rhizosphere microenvironment are a new method for saline-alkali land management and utilization that has attracted much attention in recent years. Compared with other measures, such as chemical improvers, biological improvement agents for saline-alkali soil have the advantages of low cost, wide source of materials, easy use, promotion of crop root system, accelerated formation of aggregate structure, green and safe process, environmental friendliness and no side effects.

[0004] In the prior art, there are many suitable improving agents for saline-alkali land in the northwest and northeast regions, but there are few improving agents suitable for coastal saline-alkali soil, which use modified biochar composite glutathione reductase and organic fertilizer as carriers and add microbial agents.

[0005] When faced with environmental stresses such as drought and salt damage, a large amount of reactive oxygen (such as superoxide anions, hydrogen peroxide, etc.) will accumulate in crops. These oxidative substances will damage plant cells, leading to growth stunting and even death. Glutathione reductase is a key enzyme in the glutathione antioxidant cycle. It can promote the removal of free radicals in plants by maintaining a high concentration of glutathione, thereby improving the antioxidant capacity of plants and helping plants maintain normal metabolism and growth under adverse environmental conditions. In addition, high light conditions during photosynthesis will cause a large amount of reactive oxygen to be produced in chloroplasts. If the reactive oxygen accumulates too much, it will inhibit the normal progress of photosynthesis. The addition of glutathione reductase helps maintain the balance of glutathione in chloroplasts, reduce photooxidative damage, and improve photosynthetic efficiency, thereby promoting the growth and yield of crops. Summary of the invention

[0006] One of the problems to be solved by the present invention is to prepare modified biochar improvers using waste biomass to address the practical problems of soil compaction, high salinity, and poor soil fertility in coastal saline-alkali soil, and to use the structural characteristics of the modified biochar itself to quickly form a granular structure in the saline-alkali soil, thereby achieving the purpose of improving the structure and reducing the salt content; at the same time, the loose structure of the biochar is used to provide an action space for organic fertilizers and microorganisms, thereby increasing the organic matter content of the soil and improving fertility. In addition, by adsorbing and fixing glutathione reductase through modified biochar, the purpose of supplementing glutathione reductase in vitro is achieved, reducing the oxidative damage to cells caused by salt stress and improving the efficiency of photosynthesis, thereby helping crops maintain normal growth in a saline-alkali environment.

[0007] The second problem to be solved by the present invention is to provide a method for improving coastal saline-alkali soil by using improved biochar composite enzyme agent, thereby improving the germination rate and yield of crops.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0009] A saline-alkali soil conditioner prepared by a modified biochar composite enzyme agent, wherein the total salt content of the saline-alkali soil conditioner is in the range of 2‰-15‰, and is characterized in that, by weight: 10-20 parts of the modified biochar composite enzyme agent, 150-200 parts of organic fertilizer, and 1-2 parts of microbial agent, wherein the modified biochar composite enzyme agent is obtained by acid leaching the biochar, mixing it with ferrous chloride for dehydration and drying, and then adding glutathione reductase enzyme solution for adsorption and immobilization.

[0010] The modified biochar composite enzyme agent is biochar prepared from biomass, which is crushed into fine particles or powder, then mixed with an acid solution with a concentration of 10-20 wt.%, filtered, mixed with ferrous chloride, dehydrated and dried, and then glutathione reductase enzyme solution is added for adsorption and immobilization, and first filtered and then dried and dehydrated to obtain the modified biochar composite enzyme agent.

[0011] According to the present invention, the source of the biochar in the modified biochar composite enzyme agent is biochar prepared from agricultural waste such as rice husks and straws, without any particular limitation; as a preferred aspect of the present invention, straw biochar is used.

[0012] According to the present invention, the biochar is mixed with an acid solution for reaction for 2-3 hours, which can greatly improve the porosity of the biochar and improve the adsorption performance. After acid leaching, it is mixed with ferrous chloride for 12-24 hours, so that ferrous chloride can be adsorbed in its pores and surface through physical and chemical effects, providing iron ions for the formation of the soil structure skeleton.

[0013] The acid leaching can be any commonly used acid, such as hydrochloric acid, sulfuric acid, nitric acid, etc., without any particular limitation.

[0014] As a preferred aspect of the present invention, a hydrochloric acid solution with a concentration of 10-20 wt.% is used for the acidification treatment. The acidification treatment can be carried out at room temperature or at a temperature higher than the ambient temperature.

[0015] Furthermore, the glutathione reductase of the present invention is glutathione reductase CcGR derived from Coptis chinensis, and its amino acid sequence is shown in SEQ ID NO.1.

[0016] Furthermore, in a specific preferred aspect of the present invention, the modified biochar can be prepared by the following steps: preparing the straw biochar into powder or small particles and passing them through a 60-mesh sieve, then mixing and reacting with a 10-20 wt.% hydrochloric acid solution, stirring and then mixing with a 50-60 wt.% ferrous chloride aqueous solution, stirring and drying to obtain the modified biochar.

[0017] The dosage relationship of biochar and acid solution is 1:5~35 (g:mL).

[0018] According to the present invention, the organic fertilizer is in powder form after passing through a 10-mesh sieve, has an organic matter content of ≥50 wt.%, a moisture content of ≤30 wt.%, and a pH of 6-8.

[0019] Furthermore, the matrix of the organic fertilizer described in the present invention can be cow dung, sheep dung, straw, sludge, etc.; in a preferred aspect of the present invention, the organic fertilizer is cow dung organic fertilizer.

[0020] According to the present invention, the microbial agent is a composite agent formed by mixing multiple microbial agents, which at least contains Bacillus megaterium or Bacillus subtilis.

[0021] Further, the total effective viable count of the microorganisms of the present invention is ≥10 billion / g, and the number of each effective bacterium is ≥2 billion / g. These beneficial bacteria coordinate with each other to promote plant growth, and at the same time, combined with modified biochar, promote the formation of a large agglomeration structure in the soil. As a preferred embodiment of the present invention, the beneficial bacteria agent is composed of 20-30 parts of Bacillus megaterium, 20-30 parts of Bacillus subtilis, 20-30 parts of Bacillus gelatinus, and 15-25 parts of nitrogen-fixing bacteria in parts by weight.

[0022] The preparation method of the microbial agent is as follows: Bacillus megaterium, Bacillus subtilis, Bacillus jelly and nitrogen-fixing bacteria can all be purchased commercially, and their bacterial powders are activated and propagated separately to prepare powders, and the propagation method is carried out according to a known method or a method recommended by the merchant, and the bacterial agents are mixed according to a proportion to obtain the microbial agent. The present invention also provides a preparation method of the coastal saline-alkali soil improver described in the above technical solution, the steps are:

[0023] (1) Mixing biochar and acid solution and reacting for 2-3 hours;

[0024] (2) mixing the biochar treated by acid leaching in step (1) with a ferrous chloride solution and reacting for 12-24 hours, dehydrating and drying, and then grinding into modified biochar powder;

[0025] (3) adding the modified biochar powder of step (2) into the glutathione reductase enzyme solution, stirring and mixing, and then standing at room temperature for 12-24 hours to allow the modified biochar to fully adsorb and fix it, then washing with potassium phosphate buffer, first filtering and then drying and dehydrating to obtain modified biochar composite enzyme agent powder;

[0026] (4) sieving the organic fertilizer to obtain powdered organic fertilizer;

[0027] (5) The powders obtained in (3) and (4) are thoroughly mixed, and the bacterial agent is added and stirred to obtain a mixture.

[0028] The biochar and acid solution were mixed and reacted at a mass volume ratio of 1:5~35 (g:mL).

[0029] The biochar after acid leaching was mixed with ferrous chloride solution at a mass volume ratio of 1:10~50 (g:mL) for reaction.

[0030] Furthermore, the modified biochar and glutathione reductase enzyme solution were stirred and mixed at a ratio of 1:20~60 (g:mL), and then kept at room temperature for 12-24 hours to allow the modified biochar to fully adsorb and fix it. The mixture was then washed with 100mM, pH7.0 potassium phosphate buffer, filtered and then dried to obtain modified biochar composite enzyme powder with a protein loading of 80mg / g carrier.

[0031] Furthermore, the protein concentration of the glutathione reductase enzyme solution is 10-15 mg / ml.

[0032] According to the present invention, a method for improving saline-alkali soil comprises: tilling the soil by 20-30 cm, spreading the saline-alkali soil improver of the present invention at an amount of 400-600 kg / mu, mixing it evenly with 0-20 cm soil with a rotary tiller, and leaving it for more than 20-45 days.

[0033] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0034] (1) The biochar described in the present invention has a wide range of sources and can be used to comprehensively utilize agricultural waste, turning waste into treasure. At the same time, the biochar has a high porosity, which can loosen the soil and retain water. Ferrous chloride contains divalent iron ions, which can form a soil aggregate skeleton during oxidation, promote aggregate formation and stability, and reduce soil salinity. In addition to loosening the soil and providing organic matter and nutrients to the soil, organic fertilizer also provides a suitable living environment for the growth of microorganisms; microbial agents can quickly decompose organic matter to improve soil fertility, and at the same time, the polysaccharides secreted by beneficial bacteria form more stable aggregate particles with modified activated carbon.

[0035] (2) The present invention adds glutathione reductase to obtain a composite enzyme agent after being adsorbed and immobilized on modified biochar, which can enhance the antioxidant system of plants, alleviate saline-alkali environmental stress, improve photosynthesis efficiency, and promote the growth of crops.

[0036] (3) The improver of the present invention comprehensively utilizes the combined effects of physics, chemistry and biology to improve the soil, and has high efficiency and significant effect. The modified biochar and organic fertilizer used in the present invention are widely available, low in price, and will not cause secondary pollution to the environment.

[0037] (4) The present invention has conducted a large number of laboratory and field tests on the selection and dosage of the three raw materials, and conducted rigorous analysis of the test results. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The SDS-PAGE electrophoresis diagram of the supernatant of the recombinant bacterial fermentation; M: protein molecular weight standard; 1: supernatant of the recombinant bacteria without induction treatment; 2: supernatant of the recombinant bacteria after induced expression. DETAILED DESCRIPTION

[0039] The following specific embodiments are further explanations of the present invention, but do not mean that the content of the present invention is limited to the scope of the examples given.

[0040] The strain sources used in the following examples are as follows

[0041] strain Buy from manufacturers Product Number Bacillus megaterium Shanghai Chen Microbiology Technology Co., Ltd. GDMCC 1.460 Bacillus subtilis Jiangsu Yinyimei Biotechnology Co., Ltd. none Nitrogen-fixing bacteria Mingzhou Biotechnology BMZ123084 Bacillus gelatinosa Weifang Yihao Biotechnology Co., Ltd. none

[0042] Example 1: Artificial synthesis and expression verification of glutathione reductase

[0043] The glutathione reductase CcGR (NCBI accession number: KAF9605959.1) from Coptis chinensis was synthesized by entrusting Sangon Biotech (Shanghai) Co., Ltd., and its nucleotide sequence was obtained by artificial synthesis after codon optimization based on its amino acid sequence (shown in SEQ ID NO.1). Restriction endonucleases EcoR I and Hind III were selected, and the obtained glutathione reductase CcGR gene was inserted into the expression plasmid pET-28a(+), thereby generating a recombinant expression vector 28a-CcGR. The recombinant expression vector was transformed into Escherichia coli E.coli BL21(DE3) by conventional transformation methods, and the genetically engineered bacteria E.coli BL21(DE3)-28a-CcGR containing glutathione reductase CcGR was obtained and stored in an ultra-low temperature refrigerator at -80°C.

[0044] Two strains of E. coli BL21 (DE3) -28a-CcGR recombinant genetic engineering bacteria were selected and inoculated into 10 ml LB medium containing kanamycin (50 μg / mL) resistance. They were first cultured at 37°C and 200 rpm until the bacterial OD600 reached 0.6. 0.2 mM IPTG inducer was added to one tube, and the other tube was not induced. They were then transferred to 16°C and 200 rpm for shaking flask induction expression. After 12 hours of induction culture, the bacteria were collected by centrifugation, resuspended with 100 mM pH 7.0 potassium phosphate and ultrasonically broken. The supernatant crude enzyme solution after centrifugation was used to prepare samples for SDS-PAGE protein electrophoresis. The results showed that the recombinant bacteria after induced expression had a band between 44-66 kDa consistent with the theoretical molecular weight of CcGR 60 KDa ( Figure 1 ).

[0045] Example 2: Preparation of glutathione reductase enzyme solution

[0046] The above-mentioned recombinant expression genetic engineering strain E.coli BL21-28a-CcGR was inoculated into a 50mL shaking tube containing 10mL LB liquid medium (LB (g / L): peptone 10, sodium chloride 10, yeast extract 5) containing kanamycin, and cultured on a shaker at 37°C for 12 hours at a speed of 200 rpm. Then, the culture solution was inoculated with 2% of the inoculation amount into a 2000mL shaking flask containing 400mL induction medium TB (TB (g / l): yeast powder 25, tryptone 15, sodium chloride 10, glucose 2, lactose 3), and cultured at 200rpm, 37°C for 2 hours. When the OD600 reached about 0.6, the culture was inducing at 30°C for 16 hours and centrifuged to collect the bacteria. The bacteria were washed once with an appropriate amount of 100 mM, pH 7.0 potassium phosphate buffer, then resuspended, broken by ultrasound, and centrifuged to obtain the supernatant as the crude enzyme solution. The protein content was determined using the BCA kit method and then placed in a 4°C refrigerator. It can be used for subsequent enzyme activity determination and preparation of modified biocarbon complex enzyme agents.

[0047] Example 3: Preparation of saline-alkali soil conditioner

[0048] The saline-alkali soil improver used in the present invention has the following main preparation process:

[0049] (1) Preparation of modified biochar: Local straw was thermally cracked into biochar at 400-450°C using high-temperature pyrolysis technology, and the biochar was ground through a 60-mesh sieve. The biochar powder was mixed with 20 wt.% hydrochloric acid at a ratio of 1:10 (g:mL) and allowed to stand at room temperature for 3 hours. The acid-leached biochar was mixed with 50 wt.% ferrous chloride solution at a ratio of 1:25 (g:mL) for 18 hours, dried and passed through a 60-mesh sieve to obtain modified biochar.

[0050] (2) The modified biochar was mixed with the glutathione reductase solution (protein concentration 10-15 mg / ml) prepared in Example 1 at a ratio of 1:30 (g:mL), and then allowed to stand at room temperature for 18 h to allow the modified biochar to fully adsorb and fix it. The mixture was then washed with 100 mM, pH 6.0-7.0 potassium phosphate buffer, filtered and then dried to obtain a modified biochar composite enzyme powder with a protein loading of 80 mg / g modified biochar carrier.

[0051] (2) Preparation of organic fertilizer: Pass the cow dung organic fertilizer through a 10-mesh sieve, with an organic matter content of ≥50 wt.%, a moisture content of ≤30 wt.%, and a pH of 6-8.

[0052] (3) Preparation of microbial agents: The microorganisms used are Bacillus megaterium, Bacillus subtilis, Bacillus gellinga and Azotobacter rotundifolia. The total effective viable bacteria count is ≥ 10 billion / g. The number of each effective bacterium in the beneficial bacteria agent is ≥ 2 billion / g. The weight ratio is 25:25:25:20. All of them are purchased from the market.

[0053] (4) Preparation of modified biochar compound enzyme agent improver: 15 parts of modified biochar compound enzyme agent, 180 parts of organic fertilizer, and 1 part of microbial agent.

[0054] Example 4: Enzyme activity detection of modified biochar composite enzyme agent

[0055] In order to confirm that the modified biochar composite enzyme in Example 3 above has glutathione reductase activity, it is necessary to detect its enzyme activity. The detection principle is: CcGR can reduce oxidized glutathione (GSSG) to reduced glutathione (GSH), and this reaction requires NADPH as a reducing agent. During the reaction, NADPH is oxidized to NADP⁺, accompanied by a decrease in absorbance at a wavelength of 340 nm. Therefore, by monitoring the change in absorbance at 340 nm, the enzyme activity of CcGR can be evaluated. Also using the glutathione reductase activity detection kit purchased from Shenggong Company-ultraviolet colorimetry (item number D799261), the enzyme activity was detected according to the operating instructions provided, and the enzyme activity of the modified biochar composite enzyme reached 500U / mg carrier.

[0056] Example 5: Application of saline-alkali soil conditioner

[0057] The moderate saline-alkali soil of the coastal tidal flat was selected. The location is located in the Tongzhou Bay saline-alkali land improvement demonstration area in Nantong City. The soil of the test site is sandy loam. The total salt content of the 0-20cm soil in the test site is 5.68-10.13‰, the average content is 8.72‰, the pH value is 8.37 on average, the average organic matter is 4.17g / kg, the total nitrogen is 0.276 g / kg, the available potassium is 285mg / kg, the available phosphorus is 3.90mg / kg, and the average content of soil macroaggregates with a diameter of ≥0.25mm is 0.79%. The test time is from April 2023 to September 2023. The test plot has been placed since it was reclaimed in 2014. The test site is divided into 9 areas of the same size, each of which is 0.04 mu in size. Each plot is separated by a 40cm deep and 30cm wide ditch. The first 8 plots are normally plowed and the amendment is added. The 9th area is used as the blank soil of the control group, which is only plowed without adding amendments.

[0058] Application of the modifier: plough the soil to a depth of 30 cm and apply 600 kg / mu of the modifier described in Example 2. After rotary tilling evenly, water the soil thoroughly and keep it for 30 days.

[0059] Crop trial planting: corn, which will be planted starting in 2023. 100 corns will be planted in each area, watered every 5 days, and the number of germinations will be counted every other day. After corn planting, the soil macroaggregate content, organic matter and fertility indicators will be measured.

[0060] Comparative Example 1

[0061] The preparation of the coastal saline-alkali soil conditioner in this comparative example is basically the same as that in Example 3, except that the biochar is not modified.

[0062] Comparative Example 2

[0063] The preparation of the coastal saline-alkali soil conditioner in this comparative example is basically the same as that in Example 3, except that the biochar is only acid-leached and then glutathione reductase solution is added for immobilization and compounding, without reacting with ferrous chloride.

[0064] Comparative Example 3

[0065] The preparation of the coastal saline-alkali soil improver of this comparative example is basically the same as that of Example 3, except that the biochar is acid-leached and reacted with ferrous chloride, and no glutathione reductase solution is added for immobilization and compounding.

[0066] Comparative Example 4

[0067] The preparation of the coastal saline-alkali soil conditioner in this comparative example is basically the same as that in Example 3, except that no organic fertilizer is added.

[0068] Comparative Example 5

[0069] The preparation of the coastal saline-alkali soil conditioner in this comparative example is basically the same as that in Example 3, except that the organic fertilizer is prepared from sludge, wherein the water content is 40 wt.%, and the organic matter content is 40 wt.%.

[0070] Comparative Example 6

[0071] The preparation of the coastal saline-alkali soil conditioner of this comparative example is basically the same as that of Example 3, except that the composition is: Bacillus megaterium, Bacillus gelatinus and round brown nitrogen-fixing bacteria, and the weight ratio thereof is 25:25:20.

[0072] Comparative Example 7

[0073] The preparation of the coastal saline-alkali soil conditioner in this comparative example is basically the same as that in Example 3, except that the composition is: Bacillus subtilis, Bacillus gellinga and round brown nitrogen-fixing bacteria, and the weight ratio thereof is 25:25:20.

[0074] Table 1 Various indicators of soil after improvement

[0075]

[0076] It can be seen from the above test results that the use of the improver and improvement method of the present invention can increase the aggregate content, improve the soil structure, and reduce the soil salt content, which is consistent with the goal of improving saline-alkali land.

[0077] Furthermore, conventional corn planting and management were carried out on the improved soil, the number of corn germination was recorded, and the surface biomass was counted after one month of growth. The number of germination was observed and counted 10 days after planting.

[0078] Table 2 Statistics of corn planting under different implementation conditions

[0079]

[0080] The above test results show that the germination rate of crops planted is greatly improved after adding the improver. The improver and the improvement method of the present invention can successfully improve the saline-alkali land with significant improvement effect.

[0081] SEQ ID NO.1

[0082] MMASSVGAAPKTTLTSSTFHNLYNKIPSLPSHFLPNPYSSPSFKHLKSLSNTRCFHNKHQYRHFTVEASDSSNGSEPPRHYDFDLFTIGAGSGGVRASRFAANYGASVAICELPFATISSDSTGGVGGTCVLRGCVPKKL LVYASKYSHDIEESGGFGWKYETNPTHDWSTLMAHKNAELNRLTGIYKNILKNANVKLIEGRGKIVDPHTVDVDGKRYSTRHILISVGGRPFIPDIPGSEYAIDSDAALDLPSRPKRIAIVGGGYIALEFAGIFNGLGSD VHVFIRQKKVLRGFDEEVRDFVTEQMSVRGIEFHTEESPEAILKAQDGSLSLKTNKETLDGFSHIMFATGRRPNTKNLGLEEVGVKFKKNGAIEVDEYSLSSVPSIWAVGDATDRVNLTPVALMEGAAFAKTVFGNEPSK PDYRNVPSAVFSQPPIGQVGLSEEQAIQEYGDIDVFTSNFRPLKATLSGLPDRVFMKIIVCAKTNKVIGLHMCGDDSPEIVQGFAVKTGLTKADFDTTVGIHPTAAEELVTMRTPTRKIRKSPPSEGKADTESKATAGV

Claims

1. A saline-alkali land improver, characterized in that: The composition is composed of the following raw materials by weight: 10-20 parts of modified biochar composite enzyme agent, 150-200 parts of organic fertilizer, and 1-2 parts of microbial agent; wherein the modified biochar composite enzyme agent is prepared by the following steps: (a) mixing the biochar with a 10-20wt.% hydrochloric acid solution at a mass volume ratio of 1:5-35 (g:mL), reacting at room temperature for 2-3 hours, and filtering to obtain the acid-leached biochar; (b) mixing the acid-leached biochar of step (a) with 50-60 wt.% ferrous chloride solution at a mass volume ratio of 1:10-50 (g:mL), reacting at room temperature for 12-24 hours, and dehydrating and drying to obtain ferrous chloride-modified biochar; (c) mixing the ferrous chloride modified biochar of step (b) with a glutathione reductase CcGR enzyme solution derived from Coptis chinensis at a mass volume ratio of 1:20-60 (g:mL), wherein the amino acid sequence of the glutathione reductase CcGR is as shown in SEQ ID NO.1, and the protein concentration of the enzyme solution is 10-15 mg / mL, adsorbing at room temperature for 12-24 hours, filtering and drying, and obtaining a modified biochar composite enzyme agent with a protein loading of 80 mg / g carrier; The microbial agent is composed of 20-30 parts of Bacillus megaterium, 20-30 parts of Acinetobacter, 20-30 parts of Bacillus gelatinus and 15-25 parts of nitrogen-fixing bacteria, and the total effective viable count is ≥10 billion / g; The organic fertilizer is selected from at least one of cow dung, sheep dung, straw and sludge, with an organic matter content of ≥50wt.%, a moisture content of ≤30wt.%, and a pH of 6-8.

2. The method for preparing the saline-alkali land improving agent according to claim 1, characterized in that: The following steps are involved: (1) Passing the organic fertilizer through a 10-mesh sieve to obtain powdered organic fertilizer; (2) Mix the modified biochar complex enzyme agent according to claim 1 and the powdered organic fertilizer of step (1) in proportion, add the microbial agent, and stir until uniform.

3. Use of the saline-alkali land improver according to claim 1 in improving coastal saline-alkali soil, characterized in that: After the soil is ploughed to 20-30 cm, the improver is spread at 400-600 kg / mu, and the soil is tilled evenly and maintained for 20-45 days.

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