Method and application of spartina alterniflora hydrothermal carbon in preventing and controlling ammonia volatilization of soil in coastal salinized area and improving soil quality

Abstract

The invention relates to a method and application of spartina alterniflora hydrothermal carbon in preventing and controlling ammonia volatilization of soil in a coastal salinized area and improving soil quality, and belongs to the technical field of agriculture. According to the present invention, the two-phase catalysis preparation method using the spartina alterniflora as the biomass and adopting the bimetallic / clay mineral has advantages of short reaction time, low energy consumption, large product specific surface area and no aging; when the hydrothermal carbon is applied to coastal area salinized soil, the soil ammonium nitrate conversion process is influenced by adsorbing NH4 < + > in the soil and improving the metabolic activity of microorganisms, and the ammonia volatilization of the salinized soil is reduced by 59.0% or above; meanwhile, the total nitrogen content of the soil is increased to 57.6%-60.4%, and the utilization efficiency of the nitrogen fertilizer is remarkably improved. Besides, the hydrothermal carbon effectively increases the content of organic matters in soil by 204.6% and has a certain promotion effect on the rice yield, and the rice yield can be respectively increased by 12.0% and 10.6% by the application amount of the spartina alterniflora hydrothermal carbon of 0.5% and 1.5%. In combination with an ammonia volatilization inhibition effect and a rice yield increasing effect, 0.5% of hydrothermal carbon application amount is recommended. The method is suitable for the agricultural land in the saline soil area with the requirements for preventing and controlling non-point source pollution and improving the soil quality.

Description

Technical Field

[0001] The invention relates to a method and application of Spartina alterniflora hydrothermal charcoal in preventing and controlling soil ammonia volatilization and improving soil quality in coastal saline areas, and belongs to the technical field of improving saline soil in coastal areas with hydrothermal biochar. Background Art

[0002] Soil salinization refers to the accumulation of soluble salt ions on the soil surface, which leads to the destruction of soil structure and deterioration of quality, and ultimately leads to a decrease in crop yields. my country has a large total area of ​​saline soil, which is an important reserve arable land resource. Therefore, the use of reasonable soil conditioners to improve the degree of salinization and increase crop yields is of great strategic significance for my country's arable land resource security and agricultural sustainable development. At present, many measures such as irrigation and drainage regulation, chemical improvement and biological measures have been used to improve saline soil. Chemical improvement methods are widely used because of their quick effect and flexibility. For example, Chinese patent application number: CN202111594140.2, the application publication date is May 13, 2022, which discloses a method for improving coastal saline-alkali land, mixing a soil combination conditioner with soil at a vertical depth of 0.8 to 1.8 m from the surface of the saline-alkali land; such as Chinese patent application number: CN202410179776.8, the application publication date is April 30, 2024, which discloses an "organic mineral mixture and its use in improving saline-alkali land and raising seedlings", with an application amount of 4000 to 10000 kg / mu. The above saline soil improvement methods are effective, but the former has too deep a tillage depth and the latter has too large an application amount, which has certain limitations in actual agricultural production. Therefore, it is of great practical significance to develop a convenient, low-cost, environmentally friendly, and fully functional improver.

[0003] In the process of agricultural production, nitrogen fertilizer is often required to ensure crop yield. However, nitrogen fertilizer is converted into ammonium nitrate through microbial metabolism in the soil, and some nitrogen will be lost through ammonia volatilization, runoff and leaching. According to statistics, the overall utilization rate of nitrogen fertilizer in farmland is only 30%-40%, and ammonia volatilization is the main way of nitrogen loss from surface fertilization. Controlling ammonia volatilization in saline soil to reduce nutrient loss and reduce environmental non-point source pollution in farmland production has become one of the current focuses in the field of agricultural technology. For example, Chinese patent application number: CN201811566576.9, application publication date February 23, 2021, discloses "a method for using rice straw biochar to ensure production and increase production and reduce ammonia volatilization emissions". The application of biochar in rice fields can promote rice production and inhibit ammonia volatilization. However, the biochar is generated by pyrolysis and is alkaline, which is not suitable for saline soil, especially ammonia volatilization is more serious in coastal saline soil with poor soil structure. Therefore, it is necessary to find a soil conditioner suitable for coastal saline soil to control ammonia volatilization.

[0004] Hydrochar is a solid product obtained by dehydrating and decarboxylating biomass at high temperature. It has good regulating functions on soil structure, fertility and nutrients. Studies have found that hydrochar itself is acidic, has rich functional groups and a large specific surface area, can reduce soil pH, adsorb salt ions, and reduce the degree of soil salinization. Therefore, it is widely used in saline soil improvement. However, some organic matter produced by hydrochar during pyrolysis is not conducive to plant growth, resulting in a decrease in the productivity of the improved soil. Chinese patent application number: CN202211170326.X, application publication date December 9, 2022, discloses "a method for iron-aluminum modification of kitchen waste biochar", and iron-aluminum modification increases the specific surface area and surface functional groups of biochar, and enhances adsorption capacity. However, it is worth noting that the catalytic enhancement of the decomposition of organic matter by metal salt solution can easily lead to the loss of C of hydrochar, which reduces the nutrients of hydrochar and makes it difficult to provide organic matter and other nutrients to the soil; its preparation method is usually a multi-step method of preparation + modification, which is complicated and not conducive to large-scale production.

[0005] The problem of soil salinization in my country's coastal areas is serious, and in recent years, the growth of Spartina alterniflora, an invasive species in coastal areas, has continued to spread. If Spartina alterniflora is used as biomass for carbonization and the Spartina alterniflora biochar is used to improve local saline soil, ammonia volatilization can be controlled and soil fertility can be improved, which can generate more economic and environmental benefits. Summary of the invention

[0006] One object of the present invention is to provide a bimetallic / viscous hydrochar of Spartina alterniflora. Based on the demand for saline soil improvement in my country and the current situation where ammonia volatilization leads to serious nitrogen loss, the present invention proposes a method and application of hydrochar of Spartina alterniflora in preventing and controlling soil ammonia volatilization and improving soil quality in coastal saline areas. The use of metal salt solution catalysis can promote the pyrolysis reaction of biomass, intensify the decomposition of biomass organic matter, reduce the molecular weight of hydrochar organic matter, and make it harmless to plants when applied directly without aging. Minerals contribute to the stability of C in the hydrochar synthesis process. Combining metal catalysis with mineral stabilization to prepare hydrochar may be more suitable for soil improvement.

[0007] In order to achieve the above-mentioned invention object, the present invention provides a method for preventing soil ammonia volatilization and improving soil quality in coastal saline areas by hydrothermal charcoal of Spartina alterniflora. The preparation of hydrothermal charcoal of Spartina alterniflora comprises the following steps:

[0008] First, the Spartina alterniflora is dried, crushed and sieved, and then mixed with a bimetallic salt solution, and then a certain amount of clay mineral is added and mixed evenly; the mixture is placed in a sealed reactor, and the temperature is 215-225° C. and the pressure is 9-11 MPa for hydrothermal carbonization reaction for 0.5-1.5 hours, and after cooling to room temperature, the product is taken out from the reactor; the reactant is filtered to obtain a solid product, and the solid product is placed in an oven and dried at 70-90° C. to obtain the Spartina alterniflora hydrothermal carbon;

[0009] The particle size of the Spartina alterniflora after crushing is 0.6-1 cm, and the ratio of the Spartina alterniflora to the bimetallic catalyst solution after crushing is 1 g: (9-11) mL;

[0010] The bimetallic salt solution contains 4-6% aluminum sulfate and 4-6% iron sulfate (mass concentration);

[0011] The clay mineral is kaolin, and the addition ratio is 0.3-0.7% (mass fraction).

[0012] In a preferred embodiment, the Spartina alterniflora hydrothermal charcoal does not need to be aged before use.

[0013] In a preferred embodiment, the mixture is placed in a sealed reactor, subjected to hydrothermal carbonization reaction at a temperature of 220° C. and a pressure of 10 MPa for 1 hour, and then cooled to room temperature.

[0014] In a preferred embodiment, the ratio of the crushed Spartina alterniflora to the bimetallic catalyst solution is 1 g:10 mL.

[0015] Furthermore, the bimetallic salt solution contains 5% aluminum sulfate and 5% iron sulfate (mass concentration); the clay mineral is kaolin, and the addition ratio is 0.5% (mass fraction).

[0016] Preferably, the carbonization process selects a higher carbonization pressure and a simple one-pot method for catalytic preparation, which can significantly increase the hydrothermal carbonization rate of biomass, shorten the preparation time and simplify the operation method.

[0017] Preferably, the catalyst for the carbonization process is a bimetallic catalytic solution of 5% aluminum sulfate and 5% ferric sulfate. Metal salts such as aluminum sulfate and ferric sulfate can not only play a catalytic role in the biomass carbonization process, but can also be loaded on the surface of hydrothermal carbon to change its surface structure and improve its own performance; acidic conditions can reduce the macromolecular polycyclic organic matter in the hydrothermal carbon and reduce the negative effects on plants. This preparation method significantly increases the specific surface area of ​​hydrothermal carbon by about 5 times. After application, the hydrothermal carbon significantly reduces ammonia volatilization during rice growth, and does not require aging. There is no side effect of rice growth after direct application.

[0018] Preferably, 0.5% kaolinite mineral powder is added during the carbonization process, which has a good fixation effect on the organic matter and nutrient elements in the biomass raw materials, helps to reduce the nutrient loss during the hydrothermal carbonization process, and enhances the improvement effect of hydrothermal charcoal. Compared with the preparation by pure water, the ash content and nutrient element content (C, O, Mg, K, Ca) of the hydrothermal charcoal prepared in the present invention are greatly increased, and after application, the soil organic matter content and rice yield are significantly improved.

[0019] Another object of the present invention is to disclose an application of Spartina alterniflora hydrocharcoal in preventing soil ammonia volatilization and improving soil quality in coastal saline areas. Before rice planting, the Spartina alterniflora hydrocharcoal is first mixed with the surface layer of saline soil in a mass ratio of (0.5-1.5):100, and the surface layer refers to a soil layer with a thickness of 10 cm to 14 cm from the soil surface downward; after rice transplanting, basal fertilizer, tillering fertilizer and ear fertilizer are applied normally; after the basal fertilizer period, soil salt is discharged in combination with water management.

[0020] In a preferred embodiment, the method of draining salt from the soil after the basal fertilizer period in combination with water management is as follows: draining salt after the basal fertilizer period so that the soluble salt concentration is about 2000 μS / cm based on the soil electrical conductivity.

[0021] As one of the preferred options, when the mass ratio of Spartina alterniflora hydrocharcoal to the surface saline soil in the coastal area is 0.5:100, it can not only reduce ammonia volatilization from rice fields, but also increase rice yield, soil nitrogen content and soil organic matter content, and has a good effect in improving saline soil and preventing ammonia volatilization.

[0022] In the implementation case of the present invention, after rice is transplanted, basal fertilizer, tillering fertilizer and ear fertilizer are applied normally, and after the basal fertilizer is applied, the water content of the saline soil in the paddy field is managed so that the concentration of soluble salt in the saline soil is about 2000 μS / cm. Since a higher salt concentration promotes ammonia volatilization, the saline soil in the paddy field is drained after the basal fertilizer is applied, and the improvement of the saline soil by Spartina alterniflora is combined to further reduce the ammonia volatilization of the paddy field during the tillering fertilizer period and the ear fertilizer period.

[0023] Another object of the present invention is to provide the Spartina alterniflora hydrothermal charcoal prepared by the method of controlling soil ammonia volatilization and improving soil quality in coastal saline areas using the aforementioned Spartina alterniflora hydrothermal charcoal.

[0024] The last object of the present invention is to disclose the use of the aforementioned Spartina alterniflora hydrochar, the aforementioned method or application in preventing and controlling ammonia volatilization of coastal saline soil, and the use of the aforementioned Spartina alterniflora hydrochar, the aforementioned method or application in improving rice yield, soil nitrogen fertilizer utilization efficiency, soil nitrogen content and soil organic matter content.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The preparation process of the present invention is simple. The hydrothermal charcoal of Spartina alterniflora is synthesized by bimetallic / mineral two-phase catalysis. After optimization experiments, 5% aluminum sulfate and ferric sulfate solution are obtained, and the mineral is 0.5% kaolinite. The specific surface area of ​​the synthesized hydrothermal charcoal is increased by 5 times, and the ash content and nutrient element content (C, O, Mg, K, Ca) of the hydrothermal charcoal are greatly increased, which is more suitable for soil improvement.

[0027] (2) The hydrothermal charcoal prepared by the present invention has an obvious effect on preventing and controlling ammonia volatilization in saline soil. The hydrothermal charcoal absorbs NH4 + , affecting the microbial activity in the process of ammonium nitrate conversion, thereby reducing the ammonia volatilization of saline soil in coastal areas by more than 59.0%, increasing the total nitrogen content of the soil by 57.6%-60.4%, and greatly improving the soil fertility. Hydrochar is an effective soil conditioner for reducing ammonia volatilization in saline soil, but the appropriate application amount should be selected according to the specific situation. The present invention recommends a 0.5% hydrochar application amount.

[0028] (3) The hydrochar prepared by the present invention can effectively increase the soil organic matter content by 145.7%-204.6%, and also has a certain promoting effect on yield. The application amount of 0.5% and 1.5% of hydrochar can increase the rice yield by 12.0% and 10.6%, respectively. The relevant products are suitable for agricultural land in saline soil areas with the need to control non-point source pollution and improve soil quality.

[0029] (4) The hydrothermal charcoal prepared by the present invention does not inhibit the growth of rice. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0031] Figure 1 Scanning electron microscope image of the hydrothermal charcoal of Spartina alterniflora in Example 1 of the present invention;

[0032] Figure 2 Effect of hydrothermal charcoal addition of Spartina alterniflora on NH3 emission flux from saline soil paddy fields in coastal areas in Examples 1 and 2 of the present invention;

[0033] Figure 3 Effects of the addition of hydrothermal charcoal of Spartina alterniflora on the cumulative NH3 emissions during the monitoring period of saline soil paddy fields in coastal areas in Examples 1 and 2 of the present invention;

[0034] Figure 4 The effect of adding hydrothermal charcoal of Spartina alterniflora on the pH of surface water in saline soil paddy fields in coastal areas in Examples 1 and 2 of the present invention;

[0035] Figure 5 The hydrothermal carbon addition of Spartina alterniflora in Examples 1 and 2 of the present invention is used to treat NH4 + -The influence of N;

[0036] Figure 6 The effect of adding hydrothermal charcoal of Spartina alterniflora in Examples 1 and 2 of the present invention on total nitrogen and total organic matter in saline paddy soil in coastal areas;

[0037] Figure 7 This is the effect of the addition of hydrothermal charcoal of Spartina alterniflora in Examples 1 and 2 of the present invention on the metabolic activity of soil microorganisms in saline paddy fields in coastal areas. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0039] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, instruments, etc. used in the following examples are all commercially available unless otherwise specified.

[0040] Example 1

[0041] First, the Spartina alterniflora biomass is dried, crushed and sieved, and then mixed with a bimetallic salt solution, and then clay minerals are added, and ultrasonication is performed for 30 minutes to ensure uniform mixing; the mixture is placed in a sealed reactor, and the temperature is 220° C. and the pressure is 10 MPa for hydrothermal carbonization reaction for 1 hour, and after cooling to room temperature, the product is taken out from the reactor; the reactant is filtered to obtain a solid product, and the solid product is placed in an oven and dried at 80° C. to obtain Spartina alterniflora hydrothermal carbon (HBC), which can be used without aging;

[0042] The particle size of Spartina alterniflora after crushing is 0.6-1 cm, and the ratio of Spartina alterniflora to the bimetallic catalytic solution after crushing is 1 g:10 mL; the bimetallic salt solution contains 5% aluminum sulfate and 5% iron sulfate (the percentage is mass concentration); the clay mineral is kaolin, and the addition ratio is 0.5% (mass fraction), and 0.5% refers to the mass ratio of kaolin to the total mass of Spartina alterniflora and the bimetallic catalytic solution.

[0043] Example 2

[0044] The Spartina alterniflora biomass was first dried, crushed and sieved, and then mixed with pure water, and ultrasonicated for 30 minutes to ensure uniform mixing; the mixture was placed in a sealed reactor, and the temperature was 220°C and the pressure was 10MPa for hydrothermal carbonization reaction for 1 hour. After cooling to room temperature, the product was taken out from the reactor; the reactants were filtered to obtain a solid product, which was placed in an oven and dried at 80°C to obtain Spartina alterniflora hydrothermal charcoal (HC) without aging; the particle size of the Spartina alterniflora after crushing was 0.6-1cm, and the ratio of the Spartina alterniflora to pure water after crushing was 1g:10mL.

[0045] Example 3

[0046] A soil column simulation experiment was conducted using saline soil in Dongtai, Jiangsu as the test soil and rice (Nan 9108) as the test crop: the soil column diameter was 30 cm; the height was 50 cm, and each soil column was filled with 35 kg of test soil. The simulation experiment was carried out from June 15, 2021 to October 23, 2021 at the Jiangsu Academy of Agricultural Sciences (118.87°N, 32.03°E). Among them, the basic properties of the test soil are as follows: pH is 8.51, EC is 4998μS / cm, total nitrogen is 0.703g / kg, and organic matter is 4.843g / kg.

[0047] In order to clarify the effect of hydrocharcoal of Spartina alterniflora on controlling ammonia volatilization of rice in saline soil, a total of 5 treatments were set up in this experiment, namely: conventional fertilization control (CKU), hydrocharcoal prepared by adding 0.5% (0.5HC) and 1.5% (1.5HC) pure water, and bimetallic / mineral catalytic hydrocharcoal treatments with 0.5% (0.5HBC) and 1.5% (1.5HBC), where the percentage represents the mass ratio of hydrocharcoal to the saline soil on the surface of the soil column. Three replicates were set for each treatment. Before transplanting rice, 25kg of saline soil was first filled into the column, and then different amounts of hydrocharcoal were mixed with saline soil (10kg), stirred evenly, and filled into the column to form the surface soil. The CKU treatment was also disturbed in the same way.

[0048] Flooding irrigation was used during the rice growing period, and the fertilization measures were shown in Table 1. In order to ensure that the salinity of saline soil was reduced, all treatments were treated with soil salt removal after basal fertilizer: a drainage outlet was set at the bottom of the soil column, the soil leachate was continuously discharged, and fresh water was added to the top of the soil column to keep the water level 3 to 5 cm above the soil surface.

[0049] Table 1 Fertilizer application plan during rice growth period

[0050]

[0051] Performance Analysis of Hydrothermal Charcoal from Spartina alterniflora

[0052] The performance of hydrothermal carbon of Spartina alterniflora prepared by pure water and bimetallic / mineral catalyst was analyzed. As shown in Table 2, the hydrothermal carbon (HBC) prepared by bimetallic / mineral catalysis has a higher pH and specific surface area. From the perspective of element content, the material retains more elements such as C, O, S, Ca, Mg and K, which is suitable for soil improvement. From the scanning electron microscopy image of HBC ( Figure 1 ) It can be seen that the hydrothermal charcoal has a good layered structure and a brighter mineral layer is attached to the surface.

[0053] Table 2 Physicochemical properties and pore characteristics of hydrothermal charcoal of Spartina alterniflora in Example 1 and Example 2

[0054]

[0055] Effect of hydrothermal carbon improvement + water management on ammonia volatilization control in saline soil

[0056] Ammonia volatilization was collected by intermittent ventilation in a closed chamber, and the ammonia volatilization flux was obtained by absorption titration with 2% boric acid solution + 0.01% sulfuric acid solution. Figure 2 , 3 This is the effect of the addition of hydrocharcoal from Spartina alterniflora on NH3 volatilization from saline soil paddy fields in coastal areas in Example 3 of the present invention; it can be seen that compared with the hydrocharcoal (HC) prepared with pure water, the hydrocharcoal (HBC) from Spartina alterniflora prepared with bimetallic / mineral catalysis has a more significant ammonia volatilization blocking effect. During the basal fertilizer period, 0.5% hydrocharcoal (0.5HC and 0.5HBC) significantly reduced the soil NH3 emission flux, but the effect of 1.5% hydrocharcoal addition (1.5HC and 1.5HBC) began to slow down on the 5th day after the basal fertilizer. This may be attributed to the effect of high concentrations of hydrocharcoal on microbial metabolism, resulting in a decrease in the activity of microorganisms related to nitrogen conversion. After the basal fertilizer period, water management was used, that is, fresh water replenishment combined with bottom drainage to maintain the water depth above the rice not less than 5 cm, and the EC after salt drainage was about 2000μS / cm (the measured values ​​of each treatment were about 2011-2018μS / cm). Figure 2 It can be seen that during tillering fertilizer, the effect of hydrochar (1.5HC) prepared with pure water on controlling soil NH3 emission showed significant changes, while HBC addition at 0.5% and 1.5% significantly reduced soil ammonia volatilization. During ear fertilizer, hydrochar prepared with pure water had no obvious ammonia control effect, and the control ability of 1.5% HBC also decreased in the late ear fertilizer period. Only 0.5% HB addition significantly reduced NH3 emission from saline soil.

[0057] Overall ( Figure 3 ), HBC has an inhibitory effect on NH3 emission from saline soil paddy fields, and the cumulative inhibitory effect reaches 59.02% at an application rate of 0.5%; while HC has a weaker inhibitory effect on NH3 emission from paddy fields. In addition, from the application amount of hydrochar, the 0.5% ammonia volatilization inhibition effect is better than the 1.5% treatment, so special attention should be paid to the application amount of hydrochar.

[0058] Effects of hydrothermal carbon improvement and water management on pH and NH4 in surface water of saline soil + Determination of -N

[0059] Starting from the first day of each fertilization period, samples were collected every other day to measure the pH and NH4 +-N, soil pH was tested using a pH meter (Leici, PHS-3C, Shanghai); NH4 in field water was measured using a continuous flow analyzer (SKALAR, San++System, Holland) + -N concentration, the results are as follows Figure 4 and Figure 5 shown.

[0060] Figure 4 This is the effect of adding hydrothermal charcoal of Spartina alterniflora on the pH of surface water in saline soil paddy fields in coastal areas in Example 3 of the present invention; during the basal fertilizer period, the pH values ​​of the surface water of 0.5HC, 1.5HC, 0.5HBC and 1.5HBC were all lower than those of CKU, and the reducing effect of HC was greater than that of HBC. This may be because the addition of minerals neutralized some of the acidic substances in the carbonization process, and the pH of HBC itself was higher. During the tillering fertilizer period, the pH of all treatments increased, and compared with CKU, each treatment reduced the pH of the field water, and the effect of HC was greater than that of HBC. During the ear fertilizer period, the pH difference between the treatments was further reduced. In the late stage of ear fertilizer, HBC significantly reduced the pH of field water compared with HC. From the perspective of the reducing effect of the application amount on the pH of field water, the effect of 0.5% was significantly weaker than that of 1.5%.

[0061] Figure 5 Example 3 of the present invention is the addition of hydrothermal carbon from Spartina alterniflora to NH4 + -N. During the basal fertilizer period, 1.5HBC significantly increased the NH4 + -N concentration, the peak value can reach 12.32mg L -1 , and the surface water NH4 + The changes in -N concentrations tended to be consistent, first increasing and then decreasing, and finally tended to 1.02-7.54 mg L -1 During tillering fertilizer, all treatments reached their peak on the 3rd day, and the peaks of the hydrocharcoal treatment were higher than those of the CKU treatment, with a relatively consistent trend. During the ear fertilizer period, the ammonium nitrogen content in the field water of the HC treatment was consistent with that of the CKU treatment, while the ammonium nitrogen content in the HBC treatment was lower and remained relatively stable. This is consistent with the results of soil NH3 volatilization, and the field water NH4 + -N concentration is the main factor affecting soil NH3 emission.

[0062] Determination of the effect of hydrothermal charcoal amendment + water management on rice yield

[0063] After the rice in Example 3 of the present invention matures, its yield is measured, its aboveground biological part is taken, its grains are separated from the straw, and the number of effective ears of rice is measured; the grains are air-dried under natural conditions, and the total grain weight and thousand-grain weight of the grains actually obtained are weighed. The results are shown in Table 3. The rice yield under 0.5HBC and 1.5HBC treatments increased by 12.0% and 10.6%, respectively, while the HC treatment under the corresponding addition amount caused the rice yield to decrease by 3.8% and 10.7%, respectively. This shows that the hydrothermal carbon catalyzed by bimetallic / mineral promotes the increase of rice yield in saline soil in coastal areas, and has good application prospects.

[0064] Table 3 Effects of hydrocharcoal application on rice yield in Spartina alterniflora

[0065]

[0066] Effects of hydrothermal charcoal amendment + water management on soil total nitrogen and total organic matter

[0067] Figure 6 It is the effect of adding hydrocharcoal of Spartina alterniflora on total nitrogen and soil organic matter in paddy fields of saline soil in coastal areas of the present invention in embodiment 3; Compared with CKU, adding hydrocharcoal of Spartina alterniflora significantly increases soil total nitrogen and organic matter content, and the total nitrogen in the soil increases by 57.6% and 60.4% respectively under 0.5HBC and 1.5HBC treatment, and the total organic matter in the soil increases by 145.7% to 204.6% respectively, and the lifting effect of HC on total nitrogen and total organic matter is weaker than that of HBC, at 2.4% to 45.87%. In addition, 1.5% hydrocharcoal of Spartina alterniflora increases soil total nitrogen and organic matter content more significantly. Therefore, adding hydrocharcoal of Spartina alterniflora can improve the soil fertility of saline-alkali land to a certain extent.

[0068] Effects of hydrochar amendment + water management on soil microbial metabolic activity

[0069] The Biolog plate method was used to determine the metabolic activity of microorganisms in paddy soils with different treatments, and the average absorbance (Average well color development, AWCD) was used to characterize the metabolic activity of soil microorganisms. Figure 7 As shown in the figure, both 0.5HBC and 1.5HBC treatments significantly increased the AWCD value of soil microorganisms, indicating that hydrochar prepared by bimetallic / mineral catalysis can effectively enhance the metabolic activity of soil microorganisms, strengthen the ammonium nitrate conversion process, and thus control ammonia volatilization. For hydrochar prepared by pure water, 0.5HC treatment had little effect on the metabolic activity of microorganisms, and the addition of 1.5% HC reduced the AWCD value of soil microorganisms. This result shows that high addition of hydrochar will inhibit the metabolic activity of soil microorganisms. Hydrochar prepared by bimetallic / mineral catalysis can enhance the metabolic activity of soil microorganisms, help crop growth and control ammonia volatilization.

[0070] The hydrothermal charcoal of Spartina alterniflora in the present invention is a product that utilizes the in-situ invasive species - Spartina alterniflora as a resource. It is not only economical and environmentally friendly, but also has a positive impact on the ecology of coastal areas. Compared with the preparation + modification method, the bimetallic / mineral catalytic preparation method has a simple process; compared with the pure water preparation, the hydrothermal charcoal generated by this preparation method has a large relative area, weak pH acidity, contains more organic matter and nutrients, and is more suitable for soil improvement.

[0071] The present invention applies the hydrochar prepared by bimetallic / mineral catalysis to the saline soil in the coastal area, effectively blocks the volatilization of soil ammonia and improves the soil fertility. The main mechanism is: (1) the hydrochar prepared by bimetallic / mineral catalysis has a larger specific surface area and more oxygen-containing groups, and has a stronger adsorption capacity, and can fix ammonium ions and release them slowly, thereby reducing the volatilization of ammonia in the saline soil in the coastal area; (2) the hydrochar prepared by bimetallic / mineral catalysis contains more nutrients and organic matter, and is used for soil improvement, which can increase soil organic matter and nitrogen, promote crop growth and microbial metabolic activity, accelerate soil ammonium nitrate conversion reaction, and achieve ammonia emission reduction; (3) applying the hydrochar in an appropriate amount is more effective in blocking the volatilization of ammonia in the saline soil in the coastal area, and in this case, the effect of 0.5% application amount is more obvious; however, compared with the hydrochar prepared by pure water, the hydrochar generated by bimetallic / mineral catalysis has a wider application amount, and there is no phenomenon of plant toxicity and inhibition of soil microbial metabolism. The invention is applicable to agricultural land in saline soil areas where there is a need to control surface source pollution and improve soil quality.

[0072] The present invention has been described in sufficient detail with certain particularity. It should be understood by those skilled in the art that the description in the embodiments is merely exemplary, and all changes made without departing from the true spirit and scope of the present invention should fall within the scope of protection of the present invention. The scope of protection claimed by the present invention is defined by the claims, rather than by the above description in the embodiments.

Claims

1. A method for preventing soil ammonia volatilization and improving soil quality in coastal saline areas using hydrothermal charcoal from Spartina alterniflora, characterized in that: The preparation of Spartina alterniflora hydrothermal charcoal comprises the following steps: First, the Spartina alterniflora is dried, crushed and sieved, and then mixed with a bimetallic salt solution, and then a certain amount of clay mineral is added and mixed evenly; the mixture is placed in a sealed reactor, and the temperature is 215-225° C. and the pressure is 9-11 MPa for hydrothermal carbonization reaction for 0.5-1.5 hours, and after cooling to room temperature, the product is taken out from the reactor; the reactant is filtered to obtain a solid product, and the solid product is placed in an oven and dried at 70-90° C. to obtain the Spartina alterniflora hydrothermal carbon; The particle size of the Spartina alterniflora after crushing is 0.6-1 cm, and the ratio of the Spartina alterniflora to the bimetallic catalyst solution after crushing is 1 g: (9-11) mL; The bimetallic salt solution contains 4-6% aluminum sulfate and 4-6% iron sulfate (mass concentration); The clay mineral is kaolin, and the addition ratio is 0.3-0.7% (mass fraction).

2. The method for controlling soil ammonia volatilization and improving soil quality in coastal saline areas by hydrothermal charcoal of Spartina alterniflora according to claim 1, characterized in that: The Spartina alterniflora hydrothermal charcoal is not aged before use.

3. The method for controlling soil ammonia volatilization and improving soil quality in coastal saline areas by hydrothermal charcoal of Spartina alterniflora according to claim 1, characterized in that: The mixture was placed in a sealed reactor, subjected to hydrothermal carbonization reaction at a temperature of 220°C and a pressure of 10 MPa for 1 h, and then cooled to room temperature.

4. The method for controlling soil ammonia volatilization and improving soil quality in coastal saline areas by hydrocharcoal from Spartina alterniflora according to claim 1, characterized in that: The ratio of the crushed Spartina alterniflora to the bimetallic catalytic solution is 1 g:10 mL.

5. The method for controlling soil ammonia volatilization and improving soil quality in coastal saline areas using hydrothermal charcoal of Spartina alterniflora according to claim 1, characterized in that: The bimetallic salt solution contains 5% aluminum sulfate and 5% iron sulfate (mass concentration); the clay mineral is kaolin, and the addition ratio is 0.5% (mass fraction).

6. An application of Spartina alterniflora hydrothermal charcoal in preventing soil ammonia volatilization and improving soil quality in coastal saline areas, characterized in that: Before planting rice, the hydrocharcoal of Spartina alterniflora is mixed with the surface layer of saline soil in a mass ratio of (0.5-1.5):100, where the surface layer refers to the soil layer with a thickness of 10 cm to 14 cm from the soil surface downwards; after transplanting rice, basal fertilizer, tillering fertilizer and ear fertilizer are applied normally; after the basal fertilizer period, soil salt is discharged in combination with water management.

7. The use of the hydrothermal charcoal of Spartina alterniflora in controlling soil ammonia volatilization and improving soil quality in coastal saline areas according to claim 6, characterized in that: The method of removing salt from the soil in combination with water management after the basal fertilizer period: Remove salt after the basal fertilizer period so that the soluble salt concentration is about 2000μS / cm based on the soil conductivity meter.

8. The Spartina alterniflora hydrothermal charcoal obtained by the method for controlling soil ammonia volatilization and improving soil quality in coastal saline areas using the Spartina alterniflora hydrothermal charcoal as described in claim 1.

9. Use of the Spartina alterniflora hydrocharcoal according to claim 8, the method according to any one of claims 1 to 5, or the application according to claim 6 or 7 in preventing and controlling ammonia volatilization from coastal saline soil.

10. Use of the Spartina alterniflora hydrocharcoal according to claim 8, the method according to any one of claims 1 to 5, or the application according to claim 6 or 7 in improving rice yield, soil nitrogen fertilizer utilization efficiency, soil nitrogen content, and soil organic matter content.

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