Preparation method and application of slow-release phosphorus fertilizer based on buckwheat hull

Abstract

The application discloses a preparation method of slow-release phosphorus fertilizer based on buckwheat hull as raw material, and specifically implements the following steps: step 1, washing buckwheat hull with deionized water, drying and then crushing and sieving; step 2, extracting pigment from the sieved buckwheat hull; step 3, mixing and oscillating the treated buckwheat hull in step 2 with anhydrous calcium chloride; step 4, pyrolyzing and sieving the mixture in step 3 to obtain CaCl2 modified buckwheat hull biochar; and step 5, placing the biochar in a conical flask containing a phosphorus-rich solution, sealing and oscillating, then filtering the solid and drying to obtain slow-release phosphorus fertilizer. The application is simple in preparation, saves resources and protects environment, and solves the problems of excessive phosphorus in water and phosphorus deficiency in soil. On the other hand, slow-release phosphorus fertilizer is added into soil to slowly release phosphorus, avoids the problem of phosphorus loss caused by traditional chemical phosphorus fertilizer, and can also improve the physicochemical properties of soil, reduce the soil bulk density and increase the soil organic matter content.

Description

Technical Field

[0001] This invention belongs to the technical field of novel agricultural fertilizer preparation methods, specifically relating to a method for preparing slow-release phosphate fertilizer based on buckwheat hulls as raw material, and also relating to the application of this slow-release phosphate fertilizer. Background Technology

[0002] Phosphorus, an essential element for plant growth, plays a vital role in plant development. However, phosphorus deficiency in soil has been a persistent problem. 70-80% of phosphate fertilizers applied to farmland seep into groundwater and surface water, leading to continuous phosphorus deficiency in the soil. Simultaneously, with the rapid development of my country's industrial and agricultural economies and the continuous advancement of urbanization, the degree of eutrophication in water bodies has worsened, seriously endangering the natural environment and human water safety. Effective phosphorus recovery is key to solving the problem of eutrophication.

[0003] Biomass is an important component of the dual carbon field. Porous biochar can be prepared using agricultural and forestry waste such as fruit and vegetable shells and peels. This method is low-cost and can effectively recover phosphorus. At the same time, the biochar after phosphorus recovery can be applied to the soil as a slow-release phosphate fertilizer, achieving the dual purpose of improving soil properties and increasing crop yield. It also realizes the natural cycle of "carbon" and "phosphorus" and effectively solves the problem of eutrophication of water bodies. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing slow-release phosphate fertilizer based on buckwheat hulls, which can effectively solve the problem of phosphorus pollution in water bodies.

[0005] Another objective of this invention is to provide the application of the aforementioned slow-release phosphate fertilizer in farmland cultivation.

[0006] The technical solution adopted in this invention is a method for preparing slow-release phosphate fertilizer based on buckwheat hulls as raw material, which is implemented according to the following steps:

[0007] Step 1: Wash the buckwheat hulls with deionized water, dry them, and then grind and sieve them.

[0008] Step 2: Extract pigments from the sieved buckwheat hulls;

[0009] Step 3: Mix the buckwheat hulls processed in Step 2 with anhydrous calcium chloride and shake.

[0010] Step 4: Pyrolyze the mixture from Step 3 and sieve it to obtain CaCl2 modified buckwheat hull biochar;

[0011] Step 5: Place the CaCl2-modified buckwheat hull biochar in a conical flask containing a phosphorus-rich solution, seal and shake, then filter the solid and dry it to obtain a slow-release phosphate fertilizer.

[0012] The invention is further characterized in that,

[0013] The buckwheat hulls washed with deionized water in step 1 are dried in an oven at 105°C, pulverized, and passed through a 30-mesh sieve.

[0014] In step 2, the sieved buckwheat hulls were extracted with pigment using 60% anhydrous ethanol, and the process was repeated three times, with each operation lasting 30 to 60 minutes. The hulls were then washed with deionized water and dried in an oven at 105°C for 12 to 24 hours.

[0015] Step 3 specifically involves drying anhydrous calcium chloride at 105℃ until constant weight. Then, the buckwheat hulls treated in step 2 are mixed with anhydrous calcium chloride at a 1:1 mass ratio, water is added and stirred, and the mixture is placed in a constant temperature shaker at 25℃ and 150 rpm. -1 Shake for 12 hours under the specified conditions to fully soak the buckwheat hulls, then dry at 105℃.

[0016] Step 4 specifically involves: taking an appropriate amount of the mixture from step 3, placing it in a crucible, and then placing it in a muffle furnace. The mixture is then heated at 5°C / min under a nitrogen atmosphere. -1 Heat to 700℃, hold for 2 hours, and remove from the muffle furnace after it has cooled to room temperature. Grind and pass through a 100-mesh sieve.

[0017] Step 5 specifically involves: weighing 5g of the CaCl2-modified buckwheat hull biochar obtained in step 4 and placing it into a 200ml container with a concentration of 1000mg·L⁻¹. -1 The phosphorus-rich solution was placed in an Erlenmeyer flask, sealed with a thin film, and incubated at 25°C and 150 rpm. -1 Shake for 24 hours under the specified conditions, filter the solid and dry at 105℃ for 12-24 hours.

[0018] The phosphorus-rich solution in step 5 is prepared with K2HPO4.

[0019] The beneficial effects of this invention are:

[0020] 1. This invention provides a method for preparing slow-release phosphate fertilizer based on buckwheat hulls. The preparation is simple, economical and environmentally friendly. It solves the problems of excessive phosphorus in water and phosphorus deficiency in soil. On the other hand, when slow-release phosphate fertilizer is added to the soil, it slowly releases phosphorus, avoiding the phosphorus loss problem that occurs with traditional chemical phosphate fertilizers. It can also improve the physical and chemical properties of soil, reduce soil bulk density, and increase soil organic matter content.

[0021] 2. The slow-release phosphate fertilizer prepared by the method of using buckwheat hulls as raw material in this invention has a rich porous structure and surface functional groups. Phosphorus is loaded on the surface of biochar in the form of CaHPO4, and the K of CaHPO4... SP =1×10 -7The size is moderate, avoiding the problems of phosphorus release being too fast or too slow. In addition, slow-release phosphate fertilizer is also rich in a large amount of nutrients essential for plants, such as C, N, H and Ca, creating a good growing environment for plants. Attached Figure Description

[0022] Figure 1 This is a flowchart of the present invention;

[0023] Figure 2 This is a scanning electron microscope image of the slow-release phosphate fertilizer of this invention;

[0024] Figure 3 This is a diagram showing the phosphorus release from slow-release phosphate fertilizer in water.

[0025] Figure 4 This is a diagram showing the phosphorus release from soil by slow-release phosphate fertilizers and chemical phosphate fertilizers;

[0026] Figure 5 This is a diagram showing the root and stem lengths of the potted experimental plants;

[0027] Figure 6 This is a graph showing the dry and wet weights of plants from a potted experiment.

[0028] Figure 7 This is a graph showing the chlorophyll a and chlorophyll b content of potted plants. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0030] This invention relates to a method for preparing slow-release phosphate fertilizer based on buckwheat hulls, such as... Figure 1 As shown, please follow these steps:

[0031] Step 1: Wash the buckwheat hulls with deionized water, then dry them in an oven at 105℃, pulverize them, and pass them through a 30-mesh sieve.

[0032] Step 2: The sieved buckwheat hulls are extracted with pigment using 60% anhydrous ethanol, and the process is repeated three times, each time for 30 to 60 minutes. Then, the hulls are washed with deionized water and dried in an oven at 105°C for 12 to 24 hours.

[0033] Step 3: Dry anhydrous calcium chloride at 105℃ until constant weight. Then mix it with the buckwheat hulls treated in Step 2 and the dried anhydrous calcium chloride at a mass ratio of 1:1. Add water and stir. Place the mixture in a constant temperature shaker at 25℃ and 150 rpm. -1 Shake for 12 hours under the specified conditions to fully soak the buckwheat hulls, then dry at 105℃.

[0034] Step 4: Take an appropriate amount of the mixture from Step 3 and place it in a crucible, then place it in a muffle furnace and heat it at 5°C / min under a nitrogen atmosphere. -1Heat to 700℃, hold for 2 hours, and after the muffle furnace cools down to room temperature, remove it, grind it, and pass it through a 100-mesh sieve to obtain CaCl2 modified buckwheat hull biochar at 700℃.

[0035] Step 5: Weigh 5g of the CaCl2-modified buckwheat hull biochar from Step 4 and place it into a 200ml container with a concentration of 1000mg·L⁻¹. -1 The phosphorus-rich solution was placed in an Erlenmeyer flask, sealed with a thin film, and incubated at 25°C and 150 rpm. -1 Shake for 24 hours under the condition, filter the solid and dry at 105℃ for 12-24 hours to obtain slow-release phosphate fertilizer;

[0036] The phosphorus-rich solution in step 5 is prepared with K2HPO4.

[0037] The phosphorus release effect of the slow-release phosphate fertilizer obtained in step 5 in the water body was tested. 1g of slow-release phosphate fertilizer was put into a conical flask containing 200ml of deionized water, sealed with a sealing film, and shaken continuously for 15 days. The phosphorus concentration in the conical flask was measured at a fixed time every day.

[0038] The slow-release phosphate fertilizer obtained in step 5 was used in a pot experiment, with four groups: a control group, a biochar group, a slow-release phosphate fertilizer group, and a chemical phosphate fertilizer group (P2O5, 12%). Each group had three parallel experiments. Buckwheat was harvested 15 days after sowing, and its growth indicators were measured.

[0039] The application rate of slow-release phosphate fertilizer is 1% of the soil mass. Buckwheat plant growth indicators include stem and root length, wet and dry weight, and chlorophyll a and chlorophyll b content in leaves.

[0040] Example 1

[0041] The method for preparing slow-release phosphate fertilizer based on buckwheat hulls is as follows: Commercially purchased buckwheat hulls are washed with deionized water, dried in an oven at 105℃, pulverized, and passed through a 30-mesh sieve. Pigment extraction is performed using 60% anhydrous ethanol, repeated three times. The hulls are then washed with deionized water and dried at 105℃ until constant weight. An appropriate amount of anhydrous calcium chloride is then dried at 105℃ until constant weight. The dried buckwheat hulls and anhydrous calcium chloride are mixed at a 1:1 mass ratio and placed in a constant-temperature shaker at 25℃ and 150 rpm. -1 Shake for 12 hours under the above conditions to fully impregnate the buckwheat hulls, then dry at 105℃. Place the mixed sample obtained in the above steps into a crucible, put it into a muffle furnace, and dry at 5℃·min under a nitrogen atmosphere. -1The temperature was raised to 700℃ and held for 2 hours. After the muffle furnace cooled to room temperature, the material was removed, ground, and passed through a 100-mesh sieve to obtain CaCl2-modified buckwheat hull biochar obtained at 700℃. Additive-free CaCl2 biochar was prepared from buckwheat hulls at 700℃ using the same method.

[0042] The pore structure and physicochemical properties of biochar with and without added CaCl2 were tested, as shown in Tables 1 and 2:

[0043] Table 1 Pore structure parameters of biochar

[0044] 1 No additives 438.66 0.28 2.45 2 <![CDATA[CaCl2]]> 82.76 0.20 9.21

[0045] Note: S BET Specific surface area; V tot Total pore volume; D p Average aperture

[0046] Table 2 Physicochemical properties of biochar

[0047]

[0048] Biochar with added CaCl2 and phosphorus-rich solution were placed in an Erlenmeyer flask and shaken in a constant-temperature shaker. The mixture was then sealed with a thin film and kept at 25°C and 150 rpm. -1 The mixture was shaken for 24 hours under the specified conditions, the solid was filtered, and dried at 105℃ to obtain slow-release phosphate fertilizer. The morphological characteristics of the slow-release phosphate fertilizer could be observed using a scanning electron microscope, such as... Figure 2 As shown.

[0049] The phosphorus release effect of the obtained slow-release phosphate fertilizer in water was tested. 1g of slow-release phosphate fertilizer was placed in an Erlenmeyer flask containing 200ml of deionized water, sealed with a sealing film, and incubated at 25℃ and 150r·min. -1 Under these conditions, the mixture was continuously shaken for 15 days, and the phosphorus concentration in the conical flask was measured at a fixed time each day. Figure 3 As shown, the phosphorus release concentration on day 1 was 59.33 mg·L⁻¹. -1 The phosphorus release concentration on day 15 was 119.15 mg·L⁻¹. -1 This study verified the slow-release performance of slow-release phosphate fertilizer in water, laying the foundation for its subsequent practical application in soil.

[0050] Example 2

[0051] To verify the application of the obtained slow-release phosphate fertilizer in soil, a pot experiment was conducted with four groups: a control group, a biochar group, a slow-release phosphate fertilizer group (phosphorus content 65.44 mg·g⁻¹), and a control group. -1The experiment included two groups: a control group (no biochar) and a chemical phosphate fertilizer group (P2O5, 12%). Three parallel experiments were conducted in each group. The collected farmland soil was air-dried, ground to pass through a 100-mesh sieve, and 1.00 (±0.01) kg of soil was placed in each pot. The control group received no biochar, the biochar group received 10 g of untreated CaCl2 biochar, the slow-release phosphate fertilizer group received 10 g of slow-release phosphate fertilizer, and the chemical phosphate fertilizer group received 5.45 g (calculated from the phosphorus content of the slow-release phosphate fertilizer) of superphosphate (P2O5, 12%). After the biochar was evenly mixed with the soil, 10 buckwheat seeds treated with 10% H2O2 were sown in each pot, watered with deionized water, and placed on a sunny balcony for cultivation. Seed germination was recorded. The phosphorus content in the surface soil of the slow-release phosphate fertilizer group and the chemical phosphate fertilizer group was measured on days 0, 3, 6, 9, 12, and 15 after sowing. Fifteen days after sowing, buckwheat seedlings were harvested. The stem and root lengths of the buckwheat seedlings were measured using a ruler, and the wet and dry weights of the buckwheat seedlings were measured using an analytical balance. The chlorophyll a and chlorophyll b contents of the leaves of the buckwheat seedlings in the four experimental groups were measured using a grinding method, and the soil bulk density of the four experimental groups was measured using a ring cutter method.

[0052] Based on the pot experiment, the soil physicochemical properties and seed germination rate were measured, as shown in Table 3:

[0053] Table 3. Physicochemical properties and seed germination rates of soils treated with different methods

[0054]

[0055] Table 3 shows that compared with the control group, the buckwheat germination rate of the biochar group and the slow-release phosphate fertilizer group increased by 10% and 13%, respectively. The main reason is that the soil bulk density decreased after the addition of biochar; the bulk density of the biochar group and the slow-release phosphate fertilizer group decreased by 15% and 11.4%, respectively. The lower the bulk density, the looser and more porous the soil pore structure, which better retains soil moisture and provides a suitable growth environment for seed germination. Compared with the control group, the germination rate of the chemical phosphate fertilizer group decreased by 33.33%, which contradicts the generally accepted view that phosphate fertilizer is beneficial to crop growth. The main reason is that the application of phosphate fertilizer led to a decrease in soil pH (from 8.69 to 7.97) and an increase in soil bulk density (from 1.23 to 1.58 g·cm³). -3 In such cases, the soil structure becomes compacted and lacks granular structure, which is detrimental to seed germination. However, the application of slow-release phosphate fertilizer not only has little impact on soil pH, but also reduces soil bulk density, increases soil organic matter and phosphorus content, and enhances soil fertility without causing adverse effects on the soil, thus benefiting crop growth. In the long run, slow-release phosphate fertilizer will not have a negative impact on soil properties.

[0056] Example 3

[0057] Based on a buckwheat pot experiment, relevant data on changes in soil phosphorus content were measured, such as... Figure 4The figure shows the phosphorus release from soil under slow-release phosphate fertilizer and chemical phosphate fertilizer conditions. Phosphorus release tests were conducted on soil samples from both the slow-release phosphate fertilizer group and the chemical phosphate fertilizer group at fixed time points. Over 15 days, the phosphorus release from the slow-release phosphate fertilizer group increased from 0.021 mg / g. -1 Up to 0.107 mg·g -1 The phosphorus release rate increased slowly, while that of the chemical phosphate fertilizer group increased from 0.151 mg / g. -1 Reduced to 0.119 mg / g -1 The loss rate reached 21.2%. Long-term use of chemical phosphate fertilizers not only aggravates soil compaction but also leads to phosphorus loss, resulting in a huge waste of phosphorus resources and pollution of the water environment. Slow-release phosphate fertilizers can overcome these shortcomings of chemical phosphate fertilizers and are more conducive to crop growth. They are a new type of "phosphate fertilizer" that can perfectly replace traditional phosphate fertilizers.

[0058] Based on the pot experiment of planting buckwheat, the growth of buckwheat was measured after 15 days. Figure 5 The image shown depicts the root and stem lengths of buckwheat plants grown in pots. Figure 6 Figure 1 shows the dry and wet weights of buckwheat plants in a pot experiment. Figure 7 The image shows the chlorophyll a and chlorophyll b content of buckwheat plants in a pot experiment. Compared with the control group, the root length of the biochar group and the slow-release phosphate fertilizer group increased by 0.96 cm and 3.46 cm, respectively; the stem length increased by 3.20 cm and 6.10 cm, respectively; the wet weight increased by 0.07 g and 0.09 g, respectively; and the chlorophyll a content increased by 0.08 mg / g, respectively. -1 and 0.12 mg·g -1 The chlorophyll b content increased by 0.02 mg / g. -1 and 0.03 mg·g -1 The buckwheat plants in the biochar group and the slow-release phosphate fertilizer group grew better because the soil treated with biochar had a higher organic matter (SOM) content, increasing from 3.62 g·kg⁻¹ to 1.62 g·kg⁻¹. -1 Increased to 19.63 g·kg -1 and 15.83 g·kg -1 The plants in the slow-release phosphate fertilizer group grew better because the phosphorus in the slow-release phosphate fertilizer is slowly released into the soil, providing sufficient nutrients for plant growth. Meanwhile, relevant growth indicators of buckwheat plants in the control group and the chemical phosphate fertilizer group were compared. The stem length, root length, wet weight, and chlorophyll a and chlorophyll b content of the buckwheat plants in the chemical phosphate fertilizer group were reduced by 4.93 cm, 0.50 cm, 0.05 g, and 0.31 mg·g, respectively, compared to the control group. -1 and 0.06 mg·g -1 Pot experiments showed that the slow-release phosphate fertilizer group > biochar group > blank group > chemical phosphate fertilizer group, confirming that the slow-release phosphate fertilizer obtained by this invention is a new type of environmentally friendly fertilizer.

[0059] This invention relates to a method for preparing slow-release phosphate fertilizer using buckwheat hulls as raw material, and provides a solution for both phosphorus excess in water bodies and phosphorus deficiency in soil. Biochar recovered from phosphorus is used as a slow-release phosphate fertilizer for buckwheat replanting, simultaneously achieving phosphorus recovery from wastewater and effective utilization of phosphorus in the soil. The prepared slow-release phosphate fertilizer can reduce soil phosphorus loss, lower soil bulk density, increase soil organic matter and phosphorus content, and promote buckwheat growth. It is a promising phosphorus-containing slow-release fertilizer with significant implications for the resource utilization of agricultural waste.

Claims

1. A method for preparing slow-release phosphate fertilizer based on buckwheat hulls, characterized in that, The specific steps are as follows: Step 1: Wash the buckwheat hulls with deionized water, dry them, and then grind and sieve them. Step 2: Extract pigments from the sieved buckwheat hulls; Step 3: Mix the buckwheat hulls processed in Step 2 with anhydrous calcium chloride and shake. Step 4: Pyrolyze the mixture from Step 3 and sieve it to obtain CaCl2 modified buckwheat hull biochar; Step 5: Place the CaCl2-modified buckwheat hull biochar in a conical flask containing a phosphorus-rich solution, seal and shake, then filter the solid and dry it to obtain a slow-release phosphate fertilizer. The buckwheat hulls washed with deionized water in step 1 are dried in an oven at 105°C, pulverized, and passed through a 30-mesh sieve. In step 2, the sieved buckwheat hulls were extracted with pigment using 60% anhydrous ethanol, and the process was repeated three times, each time for 30 to 60 minutes. Then, the hulls were washed with deionized water and dried in an oven at 105°C for 12 to 24 hours. The step 3 is specifically: taking anhydrous calcium chloride to be dried at 105 ℃ until the constant weight, then mixing with buckwheat hulls treated in step 2 and anhydrous calcium chloride dried at 105 ℃ according to the mass ratio of 1:1, adding water to stir, and putting into a constant temperature shaker to oscillate at 25 ℃, 150 r·min -1 for 12 h, so that the buckwheat hulls are fully immersed, and then dried at 105 ℃; Step 4 specifically involves: taking an appropriate amount of the mixture from step 3 and placing it in a crucible, then placing it in a muffle furnace and heating it at 5°C·min under a nitrogen atmosphere. -1 Heat to 700℃, hold for 2 hours, and remove from the muffle furnace after it has cooled to room temperature. Grind and pass through a 100-mesh sieve. Step 5 specifically involves: weighing 5g of the biochar from step 4 and placing it into a 200ml container with a concentration of 1000mg·L⁻¹. -1 The phosphorus-rich solution was placed in an Erlenmeyer flask, sealed with a thin film, and incubated at 25°C and 150 r·min. -1 Shake for 24 hours under the specified conditions, filter the solid and dry at 105℃ for 12-24 hours; The phosphorus-rich solution in step 5 is prepared using K2HPO4.

2. The application of the slow-release phosphate fertilizer based on buckwheat hulls as described in claim 1 in farmland planting.

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