Preparation method of modified biochar for preventing and controlling soil nitrogen loss

Abstract

The invention discloses modified biochar for preventing and controlling soil nitrogen loss and a preparation method thereof, and the preparation method comprises the following steps: 1) adding a FeSO4 solution into biochar; 2) adding dilute sulphuric acid into the mixed solution obtained in the step 1), and uniformly mixing; (3) oscillating and heating the mixed solution treated in the step (2); 4) centrifuging the mixed solution treated in the step 3), and repeatedly washing the precipitate with deionized water; and (5) putting the centrifuged precipitate obtained in the step (4) into an electrothermal blowing drying box, and drying at 105 DEG C until the weight is constant. According to the invention, after the ferrous modified biochar is applied to soil, the pH value, EC value and CEC value of the soil are increased, the volume weight (VW) of the soil is reduced, and the contents of carbon, nitrogen and phosphorus nutrients in the soil are increased. According to the method disclosed by the invention, the leaching loss of nitrate nitrogen and ammonium nitrogen in the soil is remarkably inhibited by adding the modified biochar. The method has the advantages of easily available raw materials, no pollution, low treatment cost, convenient operation, large-scale application, high economy, and suitableness for popularization and application in the industry.

Description

Technical Field

[0001] This application relates to the technical field of soil nitrogen loss, and particularly to a preparation method of modified biochar for controlling soil nitrogen loss. Background Art

[0002] Nitrogen fertilizers can promote the growth and development of crops and play a crucial role in China's agricultural production. As an essential nutrient element for plant growth, excessive application of nitrogen will cause relatively serious agricultural non-point source pollution problems. This process is relatively slow. Once polluted, the impact is extremely large, and the difficulty of soil remediation is also unexpected. Currently, measures to control the accumulation and leaching of soil nitrate nitrogen include reasonable fertilization, application of nitrification inhibitors, fine agricultural management, intercropping and rotation, biological control, and reasonable soil and water conservation measures (afforestation, scientific irrigation and drainage), etc. Although the above measures have achieved relatively ideal results, they have the disadvantages of complex technical requirements, high costs, and slow effectiveness. This will lead to the difficulty that the released nutrients can hardly meet the growth and development needs of multiple crops in a short time, and the effects produced are also difficult to continuously affect the soil and crops in a long time.

[0003] Therefore, there is an urgent need in the industry for a method of using modified biochar with a higher degree of nitrogen loss control and lower cost to control soil nitrogen loss. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of modified biochar for controlling soil nitrogen loss.

[0005] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions: A preparation method of modified biochar for controlling soil nitrogen loss, comprising the following steps: 1) Add FeSO 4 solution to the biomass; 2) Add an appropriate amount of dilute sulfuric acid to the mixed solution treated in step 1) and mix evenly; 3) Oscillate and heat the mixed solution treated in step 2); 4) Centrifuge the mixed solution treated in step 3), take the precipitate, and rinse it repeatedly with deionized water until no Fe 2+ is detected; 5) Dry the precipitate treated in step 4) to a constant weight to obtain modified biochar.

[0006] Further, the biomass is soaked in 0.2 mol / L FeSO4 solution.

[0007] Further, the biomass is biochar from crop straw and pig manure sources.

[0008] Further, step 1) also includes: drying, pulverizing, and sieving the biomass.

[0009] Further, the mesh number in the sieving process is 60 to 80.

[0010] Further, the solid-liquid ratio of the biomass to the FeSO 4 solution is (8 - 10%):(90 - 92%).

[0011] Further, in step 3), the heating temperature is 25°C and the oscillation time is set to 6 h.

[0012] Further, the drying temperature in step 5) is 105°C.

[0013] As can be seen from the above technical solutions, the advantages and positive effects of the preparation method of the modified biochar for controlling soil nitrogen loss of the present invention are as follows: In the present invention, FeSO 4 solution is added to the biochar, and an appropriate amount of dilute sulfuric acid is added. After mixing evenly, the precipitate is taken by centrifugation, and the free Fe is washed away. 2+ After that, it is dried to a constant weight to obtain ferrous-modified biochar. Moreover, the raw materials of this method are easily available and pollution-free, the treatment cost is low, the operation is convenient, it can be applied on a large scale, has high economic efficiency, and is extremely suitable for popularization and use in the industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a leaching soil column device diagram.

[0015] Figure 2 It is the influence of different modified biochar treatments on the leaching amount of soil nitrate nitrogen.

[0016] Figure 3 It is the influence of different modified biochar treatments on the leaching amount of soil ammonium nitrogen. DETAILED DESCRIPTION OF THE INVENTION

[0017] Now, the exemplary embodiments will be described more fully with reference to the accompanying drawings. However, the exemplary embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this invention will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. Like reference numerals in the figures denote the same or similar structures, and thus their detailed descriptions will be omitted.

[0018] In the following description of different examples of the present invention, reference is made to the accompanying drawings, which form a part of the present invention, and in which different exemplary structures, systems, and steps are shown by way of example in which various aspects of the present invention can be implemented. It should be understood that other specific solutions of components, structures, exemplary devices, systems, and steps can be used, and structural and functional modifications can be made without departing from the scope of the present invention. Moreover, although terms such as "top", "bottom", "front", "rear", "side", etc. may be used in this specification to describe different exemplary features and elements of the present invention, these terms are used herein only for convenience, for example, the orientation of the examples described in the drawings. Nothing in this specification should be construed as requiring a specific three-dimensional orientation of the structure to fall within the scope of the present invention.

[0019] The method for controlling soil nitrogen loss by modified biochar in this embodiment includes the following steps: 1) adding FeSO 4 solution to biomass; 2) adding an appropriate amount of dilute sulfuric acid to the mixed solution treated in step 1), and mixing evenly to make the pH of the solution lower than 6.5; 3) transferring the mixed solution treated in step 2) into a centrifuge tube with a lid, tightening the lid, and putting it into a speed regulating oscillator to oscillate and heat; 4) centrifuging the mixed solution treated in step 3), and taking the precipitate and rinsing it repeatedly with deionized water until no free Fe 2+ is detected; 5) drying the precipitate treated in step 4) in an electrothermal constant temperature drying oven until constant weight, and setting the temperature of the electrothermal constant temperature drying oven to 105°C.

[0020] In this embodiment, biochar, as a commonly used adsorption material, has a large specific surface area and developed porosity, and the adsorption sites on its surface have a certain adsorption effect on nitrate nitrogen. Due to its own developed pore structure, biochar can play the performance of holding water and retaining fertilizer in the soil, and has a certain effect on retaining nitrogen in the soil. Through metal modification, the specific surface area and porosity of biochar can be increased, and its surface structure can be optimized, so that its physical adsorption effect can be significantly improved. In addition, the metal oxides and metal cations on the surface of metal-modified biochar can adsorb nitrate nitrogen through electrostatic interaction, significantly improving the chemical adsorption effect of biochar.

[0021] In this embodiment, in step 1), the concentration of metal salt ions in the FeSO 4 solution is 0.2 mol / L. Ferrous sulfate is used to perform surface modification on corn straw biochar and pig manure biochar to explore whether ferrous-modified biochar can effectively slow down the loss of nitrate nitrogen in the soil while increasing the ammonium nitrogen in the soil, so as to provide a theoretical basis for the preparation of a new type of carbon-based material for controlling nitrogen loss.

[0022] In this embodiment, the biomass in step 1) can be crop straw sources, such as corn straw, wheat straw, rice straw, etc., or other suitable organic substances; the crop straw can be first dried by a dryer, and then the dried crop straw is pulverized, and then the pulverized crop straw is sieved, and the sieve mesh number for sieving is 60 to 80 meshes: the sieved crop straw is added to FeSO 4 solution, and the solid-liquid ratio of the biomass to the FeSO 4 solution is (8~10%):(90~92%), so that the sieved crop straw is mixed evenly with the FeSO 4 solution after the treatment in step 1).

[0023] In this embodiment, in step 2), the biochar solution added with FeSO 4 solution is put into a variable-speed multi-purpose oscillator for oscillation and heating, and the temperature of the oscillator is adjusted to 25°C and the oscillation time is set to 6 h.

[0024] The following is the process and results of a specific experiment to illustrate the technical effects that the present invention can have. However, it should be noted that the experimental data is only for explaining the present invention, and the specific content details of the experiment do not limit the claims of the present invention: The straw biochar was pyrolyzed under anaerobic conditions at 500°C. This method is a soil column leaching experiment. A total of 9 treatments were set in the experiment, including a blank control group (CK), adding 2% unmodified straw biochar (2YBC-500), adding 5% unmodified straw biochar (5YBC-500), adding 2% unmodified pig manure biochar (2ZBC-500), adding 5% unmodified pig manure biochar (5ZBC-500), adding 2% ferrous-modified straw biochar (2FYBC-500), adding 5% ferrous-modified straw biochar (5FYBC-500), adding 2% ferrous-modified pig manure biochar (2FZBC-500), adding 5% ferrous-modified pig manure biochar (SFZBC-500). The same amount of nitrogen fertilizer (200 mg / kg, KNO 3 and NH 4 Cl were added in a 1:1 ratio).

[0025] Furthermore, referring to Figure 1, the soil column leaching experiment was completed using a leaching device, which was a cylindrical PVC pipe with an inner diameter of 9 cm and a height of 30 cm. A filter paper was laid at the bottom of the pipe and a valve was installed to facilitate the collection of leachate. Approximately 2 cm thick quartz sand was added above the filter paper, and then 1.2 kg of soil sample was mixed evenly with the corresponding proportion of biochar (YBC-500, ZBC-500, FYBC-500, and FZBC-500) to form a biochar-soil mixture. After filling the biochar-soil mixture, approximately 2 cm thick quartz sand was added on top of it, and the soil column was compacted. The soil column was saturated with water, and after saturation, it was left standing for 24 h. Then, 40 mL of nitrogen nutrient solution (a mixed solution of KNO 3 and NH 4 Cl) was added to the soil column. After 6 h, ultrapure water was evenly added to the soil column with a sprayer and the leachate was collected as the first leaching water sample (on the first day). After that, water was applied on the day of collecting the leachate. Leachate was collected on the 1st, 3rd, 5th, 7th, 10th, 18th, and 30th days, and the volume of the leachate was accurately measured with a measuring cylinder. When the volume reached 500 mL, the valve was closed to stop leaching, and the concentrations of nitrate nitrogen and ammonium nitrogen in the leachate were measured with an ultraviolet spectrophotometer.

[0026] Referring to Figure 2 , the application of biochar and ferrous-modified biochar significantly inhibited the leaching of soil nitrate nitrogen. Compared with CK, the cumulative leaching amounts of nitrate nitrogen in the soil columns treated with 2YBC-500, 5YBC-500, 2ZBC-500, 5ZBC-500, 2FYBC-500, 5FYBC-500, 2FZBC-500, and 5FZBC-500 decreased by 66.88%, 86.71%, 21.22%, 54.76%, 80.61%, 91.20%, 39.99%, and 73.59% respectively. Compared with 2YBC-500, the leaching amount of the 2FYBC-500 treatment decreased by 41.45%; compared with 5YBC-500, the leaching amount of the 5FYBC-500 treatment decreased by 33.75%; compared with 2ZBC-500, the leaching amount of the 2FZBC-500 treatment decreased by 23.83%; compared with 5ZBC-500, the leaching amount of the 5FZBC-500 treatment decreased by 41.63%. This indicates that ferrous ion modification can effectively control the leaching of soil nitrate nitrogen. With the increase in the application amounts of biochar and ferrous-modified biochar, the leaching amount of nitrate nitrogen in the soil decreased, and the fixation effect of corn straw biochar on soil nitrate nitrogen was significantly better than that of pig manure biochar.

[0027] Referring to Figure 3, The application of biochar and ferrous-modified biochar also significantly inhibited the loss of soil ammonium nitrogen. Compared with CK, the cumulative leaching losses of ammonium nitrogen in the soil columns treated with 2YBC-500, 5YBC-500, 2ZBC-500, 5ZBC-500, 2FYBC-500, 5FYBC-500, 2FZBC-500 and 5FZBC-500 decreased by 36.84%, 72.12%, 23.46%, 65.88%, 54.66%, 82.29%, 45.63% and 78.42% respectively. Compared with 2YBC-500, the leaching loss of 2FYBC-500 treatment decreased by 28.22%; compared with 5YBC-500, the leaching loss of SFYBC-500 treatment decreased by 36.48%; compared with 2ZBC-500, the leaching loss of 2FZBC-500 treatment decreased by 28.96%; compared with 5ZBC-500, the leaching loss of 5FZBC-500 treatment decreased by 36.76%. It can be seen that ferrous ion modification also effectively controlled the leaching of soil ammonium nitrogen. With the increase of the application amount of biochar and ferrous-modified biochar, the leaching loss of ammonium nitrogen in the soil decreased, and the retention effect of corn straw biochar on soil ammonium nitrogen was better than that of pig manure biochar, which was consistent with nitrate nitrogen. The cumulative leaching loss of ammonium nitrogen was 5.03-28.43 mg, much lower than the cumulative leaching loss of nitrate nitrogen (7.28-82.74 mg), indicating that nitrate nitrogen in the soil had stronger mobility and was more likely to be lost.

[0028] The addition of biochar, especially ferrous-modified biochar, can largely control the leaching of soil nitrate nitrogen and ammonium nitrogen. Compared with CK, the cumulative leaching loss of soil nitrate nitrogen in the biochar-added treatments decreased by 21.22%-86.71%, and the cumulative leaching loss of ammonium nitrogen decreased by 23.46%-72.12%; the cumulative leaching loss of soil nitrate nitrogen in the ferrous-modified biochar-added treatments decreased by 39.99%-91.20%, and the cumulative leaching loss of ammonium nitrogen decreased by 45.63%-82.29%. This shows that after the biochar is modified by ferrous ions, its inhibitory effect on the leaching of soil nitrate nitrogen and ammonium nitrogen is enhanced. The main reason is that the specific surface area and porosity of the biochar increase after ferrous modification, and the metal modification optimizes the surface structure of the biochar and improves the physical adsorption of the biochar. The specific surface area of the modified corn straw biochar increased by 44.18%, and the specific surface area of the modified pig manure biochar increased by 25.12%. Moreover, the biochar mainly has mesoporous structures, which will adsorb nitrate nitrogen and ammonium nitrogen in the soil through a large number of mesopores, thus controlling their loss. Since the specific surface area of corn straw biochar is much larger than that of pig manure biochar, its retention effect on soil nitrogen is better than that of pig manure biochar. The cumulative leaching loss of NH 4 *-N in the CK treatment was lower than that of NO 3--N. This is because soil colloids are negatively charged and have a better adsorption capacity for NH4-N with a positive charge, while having a lower adsorption capacity for NO 3 --N which also has a negative charge.

[0029] Compared with unmodified biochar, the modified biochar with ferrous ions has a better adsorption effect on soil NO3--N. This is because through the modification with FeSO 4 solution, the number of metal oxides (ferrous and iron oxides) and metal cations (Fe(H), Fe(I)) on the biochar surface is increased. It can adsorb NO3--N in the soil through electrostatic interaction, significantly improving the chemisorption of biochar. Therefore, after adding the modified biochar with ferrous ions, the cumulative leaching loss of NO3--N in the soil decreases significantly and is basically equivalent to the cumulative leaching loss of NH4+-N. After being modified with FeSO 4 the corn straw biochar reduces the cumulative leaching loss of soil NO 3 --N and NH 4 +-N to a great extent compared with unmodified corn straw biochar.

[0030] In the present invention, as an efficient soil conditioner, biochar will affect the retention of soil nitrogen after application, and thus affect the nitrogen retention capacity of the soil. Biochar can enhance the water and fertilizer retention performance of the soil and effectively reduce the loss of nitrogen in the soil caused by its migration with water. The developed pore structure and specific surface area of biochar endow it with strong physical adsorption performance, which is also an important reason for biochar to slow down the loss of soil nitrogen. The addition of biochar increases the CEC value, pH value, etc. of the soil, thereby enhancing the chemisorption performance of the soil. Biochar interacts with soil microorganisms, thus affecting the recycling of nitrogen elements in the soil. In the present invention, by adding the modified biochar with ferrous ions to the soil, Fe(II) is coupled with the DNRA process, so that the more mobile NO3--N is converted into the less mobile NH4+-N, so that the nitrogen in the soil can be better retained and the nitrogen utilization rate is improved. Moreover, the raw materials of this method are easily available and pollution-free, the treatment cost is low, the operation is convenient, it can be applied on a large scale, has high economic efficiency, and is extremely suitable for popularization and use in the industry.

[0031] Those of ordinary skill in the art to which the present invention pertains should understand that the specific structures and process procedures shown in the above specific implementation part are only exemplary, not restrictive. Moreover, those of ordinary skill in the art to which the present invention pertains can combine the various technical features shown above in various possible ways to form new technical solutions, or make other modifications, and all belong to the scope of the present invention.

Claims

1. A method for preparing modified biochar for preventing and controlling soil nitrogen loss, characterized in that: The following steps are involved: 1) Adding FeSO4 solution to biomass; 2) adding dilute sulfuric acid to the mixed solution treated in step 1) and mixing evenly, and controlling the pH value of the solution between 3.55 and 3.8; 3) shaking and heating the mixed solution treated in step 2); 4) Centrifuge the mixed solution after step 3), take the precipitate, and repeatedly rinse with deionized water until there is no Fe 2+ Check out; 5) Drying the precipitate treated in step 4) to a constant weight to obtain modified biochar.

2. The method for preparing modified biochar for preventing soil nitrogen loss according to claim 1, characterized in that: The biomass was soaked in 0.2 mol / L FeSO4 solution.

3. The method for preparing modified biochar for preventing soil nitrogen loss according to claim 2, characterized in that: The biomass is crop straw-derived or pig manure-derived biochar.

4. The method for preparing modified biochar for preventing and controlling soil nitrogen loss according to claim 3, characterized in that: Step 1) also includes: drying, crushing and screening the biomass.

5. The method for preparing modified biochar for preventing and controlling soil nitrogen loss according to claim 4, characterized in that: The mesh number in the sieving process is 60 to 80.

6. The method for preparing modified biochar for preventing and controlling soil nitrogen loss according to claim 3, characterized in that: The solid-liquid ratio (W:V) of the biomass and the FeSO4 solution is (8-10%):(90-92%).

7. The method for preparing modified biochar for preventing soil nitrogen loss according to claim 1, characterized in that: In step 3), the heating temperature is 25° C. and the shaking time is set to 6 h.

8. The method for preparing modified biochar for preventing soil nitrogen loss according to claim 1, characterized in that , the drying temperature in step 5) is 105°C.

Images