Organic-inorganic composite nutritional agent for saline-alkali soil and preparation method of organic-inorganic composite nutritional agent

Abstract

The invention relates to the technical field of saline-alkali soil improvement, and discloses an organic-inorganic composite nutritional agent for saline-alkali soil and a preparation method of the organic-inorganic composite nutritional agent. According to the organic-inorganic composite nutritional agent for the saline-alkali soil, biochar is adopted for modification to increase internal groups, and the organic-inorganic composite nutritional agent is mixed with coconut shell activated carbon and embedded with calcium silicate to prevent loss of the groups; humic acid and calcium silicate are compounded, so that the humic acid is attached more firmly; and finally, mixing the embedded activated carbon with gypsum, KH2PO4 and potassium silicate to prepare the organic-inorganic composite nutrient for the saline-alkali soil. The nutritional agent obtained by the method can effectively reduce the content of salt ions in soil and improve the survival rate and yield of crops, and is a good saline-alkali soil modifier.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of saline-alkali soil improvement, and particularly relates to an organic-inorganic compound nutrient agent for saline-alkali soil and a preparation method thereof. BACKGROUND

[0002] The saline-alkali soil in China is large in area and widely distributed, mainly in the northwest, north China, northeast and coastal areas. According to relevant statistics, the area of saline-alkali soil in China is about 520 million mu (1 mu = 667 m 2 ), of which only 16.53% is cultivated and used as farmland. In agricultural production, soil salinization reduces soil nutrient utilization rate, organic matter content and soil fertility, inhibits the normal growth and reproduction of crops, and ultimately affects the yield and quality of crops. At present, how to effectively improve soil salinization and improve crop yield and quality is a key problem. Among the many improvement measures, chemical improvement measures are to apply gypsum, sulfuric acid and acidic salt, weathered coal or organic matter such as peat to the soil. A large number of scholars have shown that gypsum, aluminum sulfate, sulfur, fly ash, citric acid residue, etc. can effectively reduce the pH value and alkalization degree of soil, increase the content of Ca 2+ , Mg 2+ in soil, and alleviate the alkalization of soil. The application of organic fertilizer can provide necessary nutrients for crops and microorganisms, change the microbial population and activity, reduce the soil bulk density, increase the total porosity and capillary porosity of soil, improve the soil infiltration rate, which is beneficial to the leaching of salt in saline soil, reduces the sodium alkalization degree and electrical conductivity of soil, increases the soil micro-aggregate content, changes the soil hardening and poor permeability, and thus improves the crop yield. The existing formula is mostly general type, lacking of precise adaptation to different types of saline-alkali soil (such as soda saline-alkali soil, chloride type saline-alkali soil).

[0003] The soil affected by salinization in Gansu Province has reached nearly 30,000 square kilometers, especially in the Hexi and Yellow River irrigation areas, due to unreasonable irrigation, the area of soil salinization has increased year by year, which is the main distribution area of saline-alkali soil in Gansu Province. Zhangye City is located in the middle of the Hexi Corridor and the middle reaches of the Heihe River, with sufficient water, soil, light and heat resources, superior cultivation conditions and developed irrigation agriculture. Zhangye is a typical inland basin, the closed topography makes water and salt cannot be normally discharged, combined with drought, low rainfall, high annual evaporation and upward accumulation of original salt in underground water, which is the main reason for the salinization of cultivated land. Soil salinization is one of the limiting factors restricting the development of local agricultural economy, and the governance of saline-alkali soil is a systematic and complex project. For a long time, the governance of saline-alkali soil in the city has the problems of single governance measure, non-standard technology and secondary salinization. The current mainstream technologies such as dark pipe salt drainage, chemical improvement agent (such as gypsum, microbial agent) and intelligent irrigation system can reduce salt in the short term, but the cost is high and the maintenance is complex, which is difficult to popularize in economically underdeveloped areas. Cl - and Na +Accumulation of increased soil osmotic pressure, leading to plant root water absorption difficult.

[0004] Soil conditioner can significantly change the soil physical properties, such as changing the soil aggregate structure, increasing the soil capillary porosity, non-capillary porosity, reducing the soil bulk density, increasing the soil aeration and saturated hydraulic conductivity, storing water, reducing evaporation, and effectively improving the utilization efficiency of precipitation. At the same time, the soil conditioner can also improve the soil chemical properties, increase the soil organic matter content, adjust the soil pH, enhance the soil buffering capacity and water erosion resistance, improve the saline-alkali soil, and adsorb heavy metals. Biochar, as a multifunctional carbon material, is prepared by pyrolysis of biomass materials (such as wood, crop residues, livestock and poultry manure, etc.) under anaerobic or low oxygen conditions. This process not only preserves the carbon structure of the original biomass, but also endows biochar with a series of unique physical and chemical properties. However, single carbon pore size is fixed, and the adsorption effect is limited in the face of different ions. Conventional carbon pore size is directly exposed, and the internal groups are easily attacked and destroyed in the soil. At present, the method for improving saline-alkali soil relies on microbial agents or high molecular materials. The microbial agent has the risk of agent inactivation, which is not conducive to storage. The high molecular material is prone to cause microplastic pollution and other problems. SUMMARY

[0005] In view of the above problems, the present application aims to provide an organic-inorganic composite nutrient agent for saline-alkali soil, which is based on modified biochar and wrapped with a calcium silicate inorganic film layer to prevent the loss of internal groups of activated carbon. Biochar, inorganic minerals and natural organic matter are used to avoid the problems of microbial activity fluctuation and high molecular residue. The salt content in the soil is greatly reduced, the degree of soil salinization is improved, and the pollution is reduced while the crop yield is increased.

[0006] To achieve the above purpose, the present application provides a preparation method of an organic-inorganic composite nutrient agent for saline-alkali soil, comprising the following steps:

[0007] S1. Corn cob and rice husk are mixed, dried and then put into a tubular carbonization furnace, nitrogen is introduced, and pyrolysis is carried out by heating, and then cooled to obtain biochar;

[0008] S2. The biochar is immersed in an H2SO4 solution, stirred at room temperature, washed with water, filtered to remove water, and an acid-modified biochar is obtained; the acid-modified biochar is added to a KMnO4 solution, stirred, washed with water until colorless, filtered, and an oxidized biochar is obtained; the oxidized biochar is added to a CaCl2 solution, stirred, filtered and dried, and a double-modified biochar is obtained; the double-modified biochar is mixed with coconut activated carbon in a certain proportion to obtain a mixed carbon;

[0009] S3. Humic acid is crushed, sodium silicate solution and tetrabutyl titanate are added, and ultrasonic dispersion is performed to form a uniform humic acid-sodium silicate composite liquid; the mixed carbon is added to a fluidized bed, and nitrogen is introduced to prevent oxidation; the humic acid-sodium silicate composite liquid and CaCl2 solution are sprayed synchronously until a uniform film layer is formed on the surface of the particles, and nitrogen is continuously introduced to dry the calcium silicate-coated carbon;

[0010] S4. Gypsum, magnesium sulfate, and potassium silicate are respectively crushed; humic acid is mixed with gypsum, and the calcium silicate-coated carbon, KH2PO4, and potassium silicate are added, stirred, and sieved to remove agglomerated particles to obtain an organic-inorganic composite nutrient agent.

[0011] Preferably, in S1, the mass ratio of the corn cob and rice husk is 6:(3-5); the pyrolysis temperature is 500-600℃, and the time is 1.5-2.5h.

[0012] Preferably, in S2, the ratio of the biochar and H2SO4 solution is 5kg:(8-12L), the molar concentration of the H2SO4 solution is 0.4-0.6mol / L; the stirring speed at room temperature is 150-250rpm, and the time is 1.5-2.5h.

[0013] Preferably, in S2, the ratio of the acid-modified biochar and KMnO4 solution is 5kg:(8-12L), the molar concentration of the KMnO4 solution is 0.2-0.4mol / L; the stirring speed at room temperature is 150-250rpm, and the time is 0.5-1.5h.

[0014] Preferably, in S2, the ratio of the oxidized biochar and CaCl2 solution is 5kg:(8-12L), the molar concentration of the CaCl2 solution is 0.1-0.3mol / L; the stirring speed at room temperature is 150-250rpm, and the time is 10-14h; the drying temperature is 50-70℃, and the time is 10-14h.

[0015] Preferably, in S2, the mass ratio of the double-modified biochar and coconut shell activated carbon is (3-9):1.

[0016] Preferably, in S3, the ratio of the humic acid, sodium silicate solution, and tetrabutyl titanate is 1kg:(5-7L):(40-60g); the ultrasonic dispersion time is 20-40min; the molar concentration of the CaCl2 solution is 0.8-1.2mol / L, the ratio of the CaCl2 solution and humic acid is (4-6L):1kg; the drying temperature is 50-70℃, and the time is 10-14h.

[0017] Preferably, in the S4, the mass ratio of humic acid to gypsum is (0.3-0.4):1; the mass ratio of calcium silicate wrapped carbon, KH2PO4 and potassium silicate is 1:(0.08-0.1):(0.05-0.07).

[0018] Compared with the prior art, the beneficial effects of the present application are embodied in:

[0019] (1) After corn cob and rice husk are mixed and pyrolyzed, a porous structure mainly with mesopores is formed, the mesopores act as a salt transport channel to quickly capture Cl - and SO4 2- in the solution, microporous coconut activated carbon adsorbs Na + , and the adsorption capacity remains stable under high salt concentration; the mesoporous network of agricultural waste biochar increases soil porosity, and the microporous filling of coconut activated carbon enhances the stability of aggregates, and the combination of the two effectively reduces the content of salt in the soil through pore size complementarity and adsorption synergy. By acid pickling to remove impurities, active sites are exposed, and potassium permanganate oxidation introduces carboxyl groups, which increases the total acidic functional groups and forms a coordination structure of Ca 2+ -carboxyl, which increases the adsorption of Cl - and SO4 2- .

[0020] (2) Humic acid is introduced into sodium silicate solution, and humic acid is embedded into the film layer by ultrasonic dispersion to form a humic acid-calcium silicate composite interface, which improves the adsorption efficiency. Simultaneous spraying of humic acid-sodium silicate composite solution and calcium chloride solution generates a uniform calcium silicate film on the surface of the mixed carbon, and the film layer is stable in a pH 8-10 environment, which helps to protect the internal groups of biochar from being destroyed. Calcium silicate can be slowly degraded in the soil and will not cause damage to the environment. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a preparation flow chart of an organic-inorganic composite nutrient agent for saline-alkali soil. DETAILED DESCRIPTION

[0022] The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0023] The compounds used in the examples and comparative examples are all commercially available and are not further purified.

[0024] Example 1

[0025] A preparation method of an organic-inorganic composite nutrient agent for saline-alkali soil, comprising the following steps:

[0026] S1. 6 kg of corncob was mixed with 4 kg of rice husk, dried at 105℃ for 12 h, and then put into a tube-type carbonization furnace, nitrogen was introduced, and the temperature was raised to 550℃ for pyrolysis for 2 h. After cooling, biochar was obtained;

[0027] S2. 5 kg of biochar was immersed in 10 L of 0.5 mol / L H2SO4 solution, stirred at 200 rpm at room temperature for 2 h, washed with water until pH = 6-7, and then filtered to remove water to obtain acid-modified biochar. The acid-modified biochar was added to 10 L of 0.3 mol / L KMnO4 solution, stirred at 200 rpm for 1 h, washed with water until colorless, and then filtered to obtain oxidized biochar. The oxidized biochar was added to 10 L of 0.2 mol / L CaCl2 solution, stirred at 200 rpm for 12 h, and then filtered to obtain the filter residue. The filter residue was dried at 60℃ for 12 h to obtain double-modified biochar. 4.5 kg of double-modified biochar was mixed with 1 kg of coconut shell activated carbon to obtain mixed carbon;

[0028] S3. 0.5 kg of humic acid was ground to 200 mesh, 3 L of 1.5 mol / L sodium silicate solution and 25 g of tetrabutyl titanate were added, and ultrasonic dispersion was performed for 30 min to form a uniform humic acid-sodium silicate composite liquid. 5.5 kg of mixed carbon was added to a fluidized bed, and nitrogen was introduced to prevent oxidation. Simultaneously, the humic acid-sodium silicate composite liquid and 2.4 L of 1.0 mol / L CaCl2 solution were sprayed, and a uniform film layer was formed on the surface of the particles. Nitrogen was continuously introduced, and the mixture was dried at 60℃ for 12 h to obtain calcium silicate-coated carbon;

[0029] S4. Gypsum, KH2PO4, and K2SiO3 were ground to 200 mesh, respectively. 0.7 kg of humic acid was mixed with 2 kg of gypsum, and 6.8 kg of calcium silicate-coated carbon, 0.6 kg of KH2PO4, and 0.4 kg of K2SiO3 were added. After stirring, the lumpy particles were removed by sieving to obtain an organic-inorganic composite nutrient agent.

[0030] Example 2

[0031] A preparation method of an organic-inorganic composite nutrient agent for saline-alkali soil, comprising the following steps:

[0032] S1. 8 kg of corncob was mixed with 4 kg of rice husk, dried at 105℃ for 12 h, and then put into a tube-type carbonization furnace, nitrogen was introduced, and the temperature was raised to 500℃ for pyrolysis for 2.5 h. After cooling, biochar was obtained;

[0033] S2. 5 kg of biochar was immersed in 8 L of 0.6 mol / L H2SO4 solution, stirred at 150 rpm at room temperature for 2.5 h, washed with water until pH = 6-7, and filtered to remove water to obtain acid-modified biochar; the acid-modified biochar was added to 8 L of 0.2 mol / L KMnO4 solution, stirred at 150 rpm for 1.5 h, washed with water until colorless, and filtered to obtain oxidized biochar; the oxidized biochar was added to 8 L of 0.1 mol / L CaCl2 solution, stirred for 14 h, and filtered to obtain the filter residue, which was dried at 50℃ for 14 h to obtain double-modified biochar; 5.4 kg of double-modified biochar was mixed with 0.6 kg of coconut shell activated carbon to obtain a mixed carbon;

[0034] S3. 0.5 kg of humic acid was ground to 200 mesh, 2.5 L of 1.5 mol / L sodium silicate solution and 30 g of tetrabutyl titanate were added, and ultrasonic dispersion was performed for 30 min to form a uniform humic acid-sodium silicate composite liquid; 5.5 kg of mixed carbon was added to a fluidized bed, and nitrogen was introduced to prevent oxidation. Simultaneously, the humic acid-sodium silicate composite liquid and 2.4 L of 1.0 mol / L CaCl2 solution were sprayed, until a uniform film layer was formed on the surface of the particles, nitrogen was continuously introduced, and drying was performed at 50℃ for 14 h to obtain calcium silicate-coated carbon;

[0035] S4. Gypsum, KH2PO4, and K2SiO3 were ground to 200 mesh, respectively. 0.6 kg of humic acid was mixed with 2 kg of gypsum, 6.8 kg of calcium silicate-coated carbon, 0.68 kg of KH2PO4, and 0.476 kg of K2SiO3 were added, stirred, and sieved to remove caked particles to obtain an organic-inorganic composite nutrient agent.

[0036] Example 3

[0037] A preparation method of an organic-inorganic composite nutrient agent for saline-alkali soil, comprising the following steps:

[0038] S1. 6 kg of corn cob was mixed with 5 kg of rice husk, dried at 105℃ for 12 h, and then placed in a tubular carbonization furnace, nitrogen was introduced, the temperature was raised to 600℃, and pyrolysis was performed for 1.5 h, and then cooled to obtain biochar;

[0039] S2. 5 kg of the biochar was immersed in 12 L of 0.4 mol / L H2SO4 solution, stirred at 250 rpm at room temperature for 1.5 h, washed with water until pH = 6-7, and filtered to remove water to obtain acid-modified biochar; the acid-modified biochar was added to 12 L of 0.4 mol / L KMnO4 solution, stirred at 250 rpm for 0.5 h, washed with water until colorless, and filtered to obtain oxidized biochar; the oxidized biochar was added to 12 L of 0.3 mol / L CaCl2 solution, stirred at 250 rpm for 10 h, and filtered to obtain the filter residue, which was dried at 70°C for 10 h to obtain double-modified biochar; 4.5 kg of the double-modified biochar was mixed with 1.5 kg of coconut shell activated carbon to obtain mixed carbon;

[0040] S3. 0.5 kg of humic acid was ground to 200 mesh, 3.5 L of 1.5 mol / L sodium silicate solution and 20 g of tetrabutyl titanate were added, and ultrasonic dispersion was performed for 30 min to form a uniform humic acid-sodium silicate composite liquid; 5.5 kg of the mixed carbon was added to a fluidized bed, and nitrogen was introduced to prevent oxidation. Simultaneously, the humic acid-sodium silicate composite liquid and 2.4 L of 1.0 mol / L CaCl2 solution were sprayed, until a uniform film layer was formed on the surface of the particles, nitrogen was continuously introduced, and drying was performed at 70°C for 10 h to obtain calcium silicate-coated carbon.

[0041] S4. Gypsum, KH2PO4 and K2SiO3 were ground to 200 mesh, respectively. 0.8 kg of humic acid was mixed with 2 kg of gypsum, 6.8 kg of calcium silicate-coated carbon, 0.544 kg of KH2PO4 and 0.34 kg of K2SiO3 were added, stirred, and sieved to remove caked particles to obtain an organic-inorganic composite nutrient agent.

[0042] Comparative Example 1

[0043] The preparation method of the organic-inorganic composite nutrient agent (single biochar) comprises the following steps:

[0044] S1. 12 kg of corncob was dried at 105°C for 12 h, then was put into a tubular carbonization furnace, nitrogen was introduced, and the temperature was raised to 550°C for pyrolysis for 2 h, and then was cooled to obtain biochar;

[0045] S2. 5 kg of the biochar was immersed in 10 L of 0.5 mol / L H2SO4 solution, stirred at 200 rpm at room temperature for 2 h, washed with water until pH = 6-7, and filtered to remove water to obtain acid-modified biochar; the acid-modified biochar was added to 10 L of 0.3 mol / L KMnO4 solution, stirred at 200 rpm for 1 h, washed with water until colorless, and filtered to obtain oxidized biochar; the oxidized biochar was added to 10 L of 0.2 mol / L CaCl2 solution, stirred at 200 rpm for 12 h, and filtered to obtain the filter residue, which was dried at 60°C for 12 h to obtain double-modified biochar.

[0046] S3. 0.5 kg humic acid was ground to 200 mesh, 3 L of sodium silicate solution with a molar concentration of 1.5 mol / L and tetrabutyl titanate 25 g were added, and ultrasonic dispersion was performed for 30 min to form a uniform humic acid-sodium silicate composite solution; 5.5 kg of double modified biochar was added to a fluidized bed, and nitrogen was introduced to prevent oxidation. Simultaneously, the humic acid-sodium silicate composite solution and 2.4 L of CaCl2 solution with a molar concentration of 1.0 mol / L were sprayed, until a uniform film layer was formed on the surface of the particles, nitrogen was continuously introduced, and the calcium silicate coated carbon was obtained by drying at 60°C for 12 h;

[0047] S4. Gypsum, KH2PO4, and K2SiO3 were ground to 200 mesh, respectively. 0.7 kg of humic acid was mixed with 2 kg of gypsum, 6.8 kg of calcium silicate coated carbon, 0.6 kg of KH2PO4, and 0.4 kg of K2SiO3 were added, stirred, and sieved to remove clumped particles to obtain an organic-inorganic composite nutrient agent.

[0048] Comparative Example 2

[0049] The preparation method of the organic-inorganic composite nutrient agent (without acid treatment and KMnO4 oxidation of biochar) comprises the following steps:

[0050] S1. 6 kg of corn cob was mixed with 4 kg of rice husk, dried at 105°C for 12 h, and then put into a tubular carbonization furnace, nitrogen was introduced, and the temperature was raised to 550°C for pyrolysis for 2 h, and then cooled to obtain biochar;

[0051] S2. 5 kg of biochar was added to 10 L of CaCl2 solution with a molar concentration of 0.2 mol / L, stirred at 200 rpm for 12 h, filtered, and the filter residue was dried at 60°C for 12 h; 4.5 kg of biochar was mixed with 1 kg of activated carbon from coconut shell to obtain mixed carbon;

[0052] S3. 0.5 kg humic acid was ground to 200 mesh, 3 L of sodium silicate solution with a molar concentration of 1.5 mol / L and tetrabutyl titanate 25 g were added, and ultrasonic dispersion was performed for 30 min to form a uniform humic acid-sodium silicate composite solution; 5.5 kg of double modified biochar was added to a fluidized bed, and nitrogen was introduced to prevent oxidation. Simultaneously, the humic acid-sodium silicate composite solution and 2.4 L of CaCl2 solution with a molar concentration of 1.0 mol / L were sprayed, until a uniform film layer was formed on the surface of the particles, nitrogen was continuously introduced, and the calcium silicate coated carbon was obtained by drying at 60°C for 12 h;

[0053] S4. Gypsum, KH2PO4, and K2SiO3 were ground to 200 mesh, respectively. 0.7 kg of humic acid was mixed with 2 kg of gypsum, 6.8 kg of calcium silicate coated carbon, 0.6 kg of KH2PO4, and 0.4 kg of K2SiO3 were added, stirred, and sieved to remove clumped particles to obtain an organic-inorganic composite nutrient agent.

[0054] Comparative Example 3

[0055] The preparation method of the organic-inorganic compound nutrient agent (biochar is not embedded with sodium silicate) comprises the following steps:

[0056] S1. 6 kg of corn cobs are mixed with 4 kg of rice husks, dried at 105°C for 12 h, and then put into a tubular carbonization furnace, nitrogen is introduced, and the temperature is raised to 550°C for pyrolysis for 2 h, and then cooled to obtain biochar;

[0057] S2. 5 kg of biochar is immersed in 10 L of a 0.5 mol / L H2SO4 solution, stirred at 200 rpm at room temperature for 2 h, washed with water until the pH is 6-7, filtered to remove water to obtain acid-modified biochar; the acid-modified biochar is added to 10 L of a 0.3 mol / L KMnO4 solution, stirred at 200 rpm for 1 h, washed with water until colorless, and filtered to obtain oxidized biochar; the oxidized biochar is added to 10 L of a 0.2 mol / L CaCl2 solution, stirred at 200 rpm for 12 h, the filter residue is taken, and dried at 60°C for 12 h to obtain double-modified biochar; 4.5 kg of the double-modified biochar is mixed with 1 kg of coconut shell activated carbon to obtain mixed carbon;

[0058] S3. 1 kg of humic acid is ground to 200 mesh, 3 L of water and 25 g of tetrabutyl titanate are added, and ultrasonic dispersion is performed for 30 min to form a uniform humic acid composite liquid; 5.5 kg of mixed carbon is added to a fluidized bed, nitrogen is introduced to prevent oxidation. Spray the humic acid composite liquid and 2.4 L of a 1.0 mol / L CaCl2 solution at the same time, continue to introduce nitrogen, and dry at 60°C for 12 h to obtain humic acid combined carbon;

[0059] S4. Gypsum, KH2PO4, and K2SiO3 are ground to 200 mesh, respectively. 0.7 kg of humic acid is mixed with 2 kg of gypsum, 6.8 kg of humic acid combined carbon, 0.6 kg of KH2PO4, and 0.4 kg of K2SiO3 are added, stirred, and sieved to remove agglomerated particles to obtain an organic-inorganic compound nutrient agent.

[0060] Comparative Example 4

[0061] The preparation method of the organic-inorganic compound nutrient agent (humic acid is not compounded with sodium silicate) comprises the following steps:

[0062] S1. 6 kg of corn cobs are mixed with 4 kg of rice husks, dried at 105°C for 12 h, and then put into a tubular carbonization furnace, nitrogen is introduced, and the temperature is raised to 550°C for pyrolysis for 2 h, and then cooled to obtain biochar;

[0063] S2. 5 kg of biochar was immersed in 10 L of 0.5 mol / L H2SO4 solution, stirred at 200 rpm at room temperature for 2 h, washed with water until pH = 6-7, and filtered to remove water to obtain acid-modified biochar; the acid-modified biochar was added to 10 L of 0.3 mol / L KMnO4 solution, stirred at 200 rpm for 1 h, washed with water until colorless, and filtered to obtain oxidized biochar; the oxidized biochar was added to 10 L of 0.2 mol / L CaCl2 solution, stirred at 200 rpm for 12 h, and filtered to obtain the filter residue, which was dried at 60°C for 12 h to obtain double-modified biochar; 4.5 kg of double-modified biochar was mixed with 1 kg of coconut shell activated carbon to obtain mixed carbon;

[0064] S3. 3 L of 1.5 mol / L sodium silicate solution and 25 g of tetrabutyl titanate were ultrasonically dispersed for 30 min to form a uniform sodium silicate composite liquid; 5.5 kg of mixed carbon was added to a fluidized bed, and nitrogen was introduced to prevent oxidation. Simultaneously, the sodium silicate composite liquid and 2.4 L of 1.0 mol / L CaCl2 solution were sprayed, until a uniform film layer was formed on the surface of the particles, and nitrogen was continuously introduced, and the mixture was dried at 60°C for 12 h to obtain calcium silicate-coated carbon.

[0065] S4. Gypsum, KH2PO4, and K2SiO3 were ground to 200 mesh, respectively. 1.2 kg of humic acid was mixed with 2 kg of gypsum, and 6.3 kg of calcium silicate-coated carbon, 0.6 kg of KH2PO4, and 0.4 kg of K2SiO3 were added, stirred, and sieved to remove caked particles to obtain an organic-inorganic composite nutrient agent.

[0066] Experimental Example 1

[0067] Chloride and sulfate adsorption kinetics experiment

[0068] 5 g of the nutrient agent was weighed into a 250 mL conical flask, 100 mL of a salt solution containing 0.1 mol / L NaCl and 0.05 mol / L Na2SO4 was added, oscillation was carried out at 25°C and 150 rpm, and sampling was carried out after 24 h, 0.45 μm filter membrane filtration was carried out, ion chromatography was used to determine the concentrations of Na+, Cl-, and SO42-, and the adsorption amounts of the nutrient agent for Na+, Cl-, and SO42- were calculated (as shown in Table 1). + - 2- + - 2-

[0069] Table 1: Adsorption amounts of the nutrient agent for Na+, Cl-, and SO42- + - 2-

[0070] ​​​​​​​​​

[0071]

[0072] As can be seen from the data in Table 1, the nutrient agent prepared in Examples 1-3 has a higher absorption rate of Na + , Cl - , SO4 2- than Comparative Examples 1-4, indicating that the absorption efficiency of salt ions of the nutrient agent prepared by using mixed carbon and calcium silicate coating is significantly higher than that of the nutrient agent without mixed carbon and without calcium silicate coating. The absorption efficiency of Na + , Cl - of the nutrient agent is higher than that of SO4 2- , and Cl - is a monovalent ion, and SO4 2- is a divalent ion, and the electrostatic repulsion of the negative charge on the surface of the biochar to Cl - is weaker, and adsorption is more favorable.

[0073] Experimental Example 2

[0074] Sodium ion (Na + ) displacement experiment

[0075] In order to verify the displacement ability of Ca 2+ released from gypsum and calcium silicate film layer to soil colloidal Na + , 50 g of soil sample was mixed with 0.5 g of nutrient agent, 100 mL of deionized water was added, and oscillation was performed for 24 h; after centrifugation, the supernatant was taken, and the Na + concentration was determined by atomic absorption spectrometry, and the displacement rate was calculated by taking the soil without adding the nutrient agent as a control (as shown in Table 2).

[0076] Table 2: Na + displacement rate

[0077] Group Na + Replacement rate / %]] Example 1 71.5 Example 2 70.4 Example 3 70.8 Comparative Example 1 52.6 Comparative Example 2 48.9 Comparative Example 3 35.1 Comparative Example 4 42.4

[0078] As can be seen from the data in Table 2, the Na + displacement rate of the nutrient agent of Examples 1-3 is greater than 70%, which is significantly higher than that of Comparative Examples 1-4; and the displacement rate of Comparative Example 3 without calcium silicate embedding mixed carbon is only 35.1%, indicating that the embedding of calcium silicate plays a key role in the displacement of sodium ions in the soil. The nutrient agent obtained by the method of the examples has a good effect on the displacement of sodium ions in the soil, and can significantly reduce the content of sodium ions in the soil and reduce the damage of salt to plants.

[0079] Experimental Example 3

[0080] Soil column leaching experiment

[0081] Chromatographic column (diameter 5 cm, height 60 cm), 2 cm of quartz sand was laid at the bottom of the column, and 1 kg of saline-alkali soil was uniformly mixed with 10 g of nutrient agent. Deionized water was used to leach at a flow rate of 50 mL / h for 20 h, the leaching liquid was collected, and the Cl - / SO4 2- / Na + concentration was determined; the cumulative leaching amount and salt removal rate were calculated.

[0082] Table 3: Ion content and removal rate of leaching liquid

[0083]

[0084] As can be seen from the data in Table 3, the removal rates of Cl-, SO4 2- and Na + in the soil of the nutrient agents of Examples 1-3 are higher than those of Comparative Examples 1-4, which indicates that the use of modified mixed carbon and calcium silicate embedding has a better effect on the removal of ions in the soil, and is obviously higher than that of the nutrient agent prepared by using single carbon, unmodified carbon and carbon not embedded with calcium silicate, which indicates that the technical scheme of the present application can more effectively remove salt ions in saline-alkali soil.

[0085] Experimental Example 3

[0086] Saline-alkali land experiment

[0087] A saline-alkali land in Zhangye City, Gansu Province was selected, and different regions (2 m x 5 m) were divided according to 10 m 2 The regions were marked as Examples 1-3, Comparative Examples 1-4 and a control group, respectively, and 1 kg / m 2 of nutrient agent was uniformly applied, and the soil was mixed to a depth of 10 cm. The control group was a saline-alkali land without any nutrient agent. The first irrigation amount was 10 L / m 2 , and drip irrigation was performed to fully dissolve the nutrient agent. After irrigation, the land was dried for 3 days, and cotton seedlings were planted after the surface was dried, with 50 cotton seedlings planted per plot. The soil water content was maintained at no less than 60%. After the cotton was harvested, the cotton yield and the Cl - / Na + content in the soil were counted.

[0088] Table 4: Cotton survival rate and yield

[0089]

[0090]

[0091] As shown in Table 3, the nutrient agent of Examples 1-3 can significantly increase the survival rate of cotton. After the saline-alkali soil is improved by the nutrient agent of Examples 1-3, the survival rate of cotton is 98%, while the survival rate of cotton in the unimproved saline-alkali soil is only 45%. The nutrient agent of Examples 1-3 can also significantly increase the yield of cotton. Compared with Comparative Examples 1-4 and the control, the nutrient agent of Examples 1-3 effectively promotes the growth of cotton and improves the yield of cotton. Compared with the unimproved saline-alkali soil, the yield of cotton is increased by about 200%. Therefore, the nutrient agent prepared by the method of Examples 1-3 has a good saline-alkali soil improvement effect, can effectively adsorb salt ions in the soil, improve the soil environment, promote the growth of plants, and improve the yield.

[0092] The above only describes the preferred embodiments of the present application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the technical principles of the present application. These improvements and modifications should also be considered as falling within the scope of the present application.

Claims

1. A method for preparing an organic-inorganic composite nutrient agent for saline-alkali land, characterized in that, Includes the following steps: S1. Corn cobs and rice husks are mixed, dried, and then placed in a tubular carbonization furnace. Nitrogen gas is introduced, the mixture is heated and pyrolyzed, and then cooled to obtain biochar. S2. The biochar was immersed in H2SO4 solution, stirred at room temperature, washed with water, and filtered to remove water to obtain acid-modified biochar; the acid-modified biochar was added to KMnO4 solution, stirred, washed with water until colorless, and filtered to obtain oxidized biochar; the oxidized biochar was added to CaCl2 solution, stirred, filtered and dried to obtain double-modified biochar. Double-modified biochar and coconut shell activated carbon are mixed in a certain proportion to obtain mixed char. S3. Humic acid is pulverized, sodium silicate solution and tetrabutyl titanate are added, and ultrasonic dispersion is performed to form a uniform humic acid-sodium silicate composite solution; the mixed carbon is added to a fluidized bed and nitrogen gas is introduced to prevent oxidation; the humic acid-sodium silicate composite solution and CaCl2 solution are sprayed simultaneously until a uniform film layer is formed on the particle surface, nitrogen gas is continued to be introduced, and the carbon is dried to obtain calcium silicate-coated carbon. S4. Gypsum, KH2PO4, and potassium silicate are crushed separately; humic acid is mixed with gypsum, calcium silicate-coated carbon, KH2PO4, and potassium silicate are added, stirred, and sieved to remove clumps, thus obtaining an organic-inorganic composite nutrient.

2. The method for preparing the organic-inorganic composite nutrient agent for saline-alkali land according to claim 1, characterized in that, In S1, the mass ratio of corn cob to rice husk is 6:(3-5); the pyrolysis temperature is 500-600℃, and the time is 1.5-2.5h.

3. The method for preparing the organic-inorganic composite nutrient agent for saline-alkali land according to claim 1, characterized in that, In S2, the ratio of biochar to H2SO4 solution is 5 kg:(8-12 L), and the molar concentration of H2SO4 solution is 0.4-0.6 mol / L; the stirring speed at room temperature is 150-250 rpm, and the time is 1.5-2.5 h.

4. The method for preparing the organic-inorganic composite nutrient agent for saline-alkali land according to claim 1, characterized in that, In S2, the ratio of acid-modified biochar to KMnO4 solution is 5 kg:(8-12 L), and the molar concentration of KMnO4 solution is 0.2-0.4 mol / L; the stirring speed at room temperature is 150-250 rpm, and the stirring time is 0.5-1.5 h.

5. The method for preparing the organic-inorganic composite nutrient agent for saline-alkali land according to claim 1, characterized in that, In S2, the ratio of oxidized biochar to CaCl2 solution is 5 kg:(8-12 L), and the molar concentration of CaCl2 solution is 0.1-0.3 mol / L; the stirring speed at room temperature is 150-250 rpm, and the time is 10-14 h; the drying temperature is 50-70℃, and the time is 10-14 h.

6. The method for preparing the organic-inorganic composite nutrient agent for saline-alkali land according to claim 1, characterized in that, In S2, the mass ratio of the dual-modified biochar to coconut shell activated carbon is (3-9):

1.

7. The method for preparing the organic-inorganic composite nutrient agent for saline-alkali land according to claim 1, characterized in that, In S3, the ratio of humic acid, sodium silicate solution, and tetrabutyl titanate is 1 kg:(5-7 L):(40-60 g); the ultrasonic dispersion time is 20-40 min; the molar concentration of CaCl2 solution is 0.8-1.2 mol / L, and the ratio of CaCl2 solution to humic acid is (4-6 L):1 kg; the drying temperature is 50-70℃, and the drying time is 10-14 h.

8. The method for preparing the organic-inorganic composite nutrient agent for saline-alkali land according to claim 1, characterized in that, In S4, the mass ratio of humic acid to gypsum is (0.3-0.4):1; the mass ratio of calcium silicate-coated carbon, KH2PO4 and potassium silicate is 1:(0.08-0.1):(0.05-0.07).

9. An organic-inorganic composite nutrient agent for saline-alkali land, characterized in that, It is obtained by the preparation method described in any one of claims 1-8.

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