CN113880658A - Preparation method of magnesium modified biochar coated urea fertilizer - Google Patents
Preparation method of magnesium modified biochar coated urea fertilizer Download PDFInfo
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- C—CHEMISTRY; METALLURGY
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- C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
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- C05G3/00—Mixtures of one or more fertilisers with additives not having a specially fertilising activity
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- C05G5/00—Fertilisers characterised by their form
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Abstract
The invention provides a preparation method of a magnesium modified biochar coated urea fertilizer, belonging to the technical field of agricultural fertilizers. The preparation method of the magnesium modified charcoal coated urea fertilizer comprises the following steps: preparing biochar; preparing magnesium modified biochar; preparing a magnesium modified charcoal coating material; preparing the magnesium modified charcoal coated urea fertilizer. According to the invention, the magnesium chloride solution is used for modifying the biochar, the polyvinyl alcohol is added to prepare the coating material, and finally the coated urea is prepared, so that the problems of poor physical properties, low slow release performance and the like of the existing coated fertilizer are solved, the slow release period of the fertilizer is prolonged, the utilization efficiency of the fertilizer is improved, the environmental pollution is reduced, and the sustainable and healthy development of agriculture is ensured.
Description
Technical Field
The invention relates to the technical field of agricultural fertilizers, in particular to a preparation method of a magnesium modified biochar coated urea fertilizer.
Background
A major challenge in current agricultural practice is the need to increase productivity in a more sustainable and environmentally friendly way. Agricultural practices at the late green revolution have continued to increase the reliance on fertilizers to ensure higher production rates. Chemical fertilizers do improve soil productivity, but at the same time, they also cause significant ecological imbalance, such as loss of biodiversity, global warming, residues of heavy metals in organisms, etc., which jeopardize the sustainability of the environment. Firstly, the global climate rapid change, rapid urbanization and the use of a large amount of agricultural chemicals jointly affect the crop production in the world and cause crisis for the grain safety; secondly, the reduction of fertile land further endangers global grain safety; in addition, the production of large quantities of agricultural waste imposes additional burdens on agricultural practices. Thus, one of the possible solutions to the multifaceted challenges faced by agricultural practice is to increase agricultural productivity without compromising environmental sustainability.
The effect of increasing the yield per unit of crops on increasing the yield of grains is not negligible, and chemical fertilizers are widely used in the production process of various crops and play a key role in increasing the yield per unit of crops. However, the utilization rate of the fertilizer in China is not high, the utilization rate of the nitrogen fertilizer and the potassium fertilizer is only 30% -40%, and the utilization rate of the nitrogen fertilizer and the potassium fertilizer in developed agricultural countries is 50% -60%. The unreasonable application of the fertilizer causes the problems of the decrease of the soil quality of cultivated land, the eutrophication of water body and the like, and the lost nitrogen generates greenhouse gas under the action of nitrification and denitrification. The advent of slow/controlled release coated fertilizers has effectively alleviated these environmental problems and is an environmentally friendly fertilizer in agricultural production. Therefore, the slow/controlled release coated fertilizer which has the characteristics of high fertilizer efficiency utilization rate, low fertilizer application amount, environmental friendliness and the like becomes the main development direction of the fertilizer industry in China.
The surface property of the biochar can be improved by modifying the biochar, particularly by using a chemical modification (acid or alkali) method. Acid modification of the biochar can generate a large amount of oxygen-containing functional groups on the surface of the biochar, and alkali modification can generate higher aromatic functional groups and C/N on the surface. The adsorption capacity of the biological carbon obtained by the biological carbon impregnated by the nano material to organic and inorganic pollutants is enhanced, but the pore volume of the modified biological carbon is reduced. Therefore, the coated fertilizer prepared by using the modified biochar has the advantage of environmental friendliness compared with an organic high-molecular polymer coated fertilizer, and compared with unmodified biochar, the modified biochar is neutral and has better adaptability to acid-base soil.
Disclosure of Invention
The invention aims to provide a preparation method of a magnesium modified charcoal coated urea fertilizer. According to the invention, the magnesium chloride solution is used for modifying the biochar, the polyvinyl alcohol is added to prepare the coating material, and finally the coated urea is prepared, so that the problems of poor physical properties, low slow release performance and the like of the existing coated fertilizer are solved, the slow release period of the fertilizer is prolonged, the utilization efficiency of the fertilizer is improved, the environmental pollution is reduced, and the sustainable and healthy development of agriculture is ensured. .
The invention provides a preparation method of a magnesium modified biochar coated urea fertilizer, which comprises the following steps:
(1) sequentially crushing, sieving, carbonizing and cracking agricultural wastes to obtain biochar;
(2) grinding the biochar to obtain biochar powder, then mixing the biochar powder with a magnesium chloride solution, stirring, filtering, washing and drying to obtain magnesium modified biochar;
(3) grinding the magnesium modified charcoal to obtain magnesium modified charcoal powder, and then uniformly mixing the magnesium modified charcoal powder with a polyvinyl alcohol solution, a plasticizer and a catalyst to obtain a magnesium modified charcoal coating material;
(4) and carrying out coating treatment on the magnesium modified charcoal coating material and urea to obtain the magnesium modified charcoal coated urea fertilizer.
Preferably, the agricultural waste comprises one or more of crop straw, hulls and shoots.
Preferably, the temperature of the carbonization and cracking is 300-700 ℃, and the time is 1-3 h.
Preferably, the mixing ratio of the charcoal powder and the magnesium chloride solution is 1 g: 50 mL.
Preferably, the concentration of the magnesium chloride solution is 0.01 mol/L.
Preferably, the weight ratio of the magnesium modified biochar to the polyvinyl alcohol is 3-9: 100.
Preferably, the volume ratio of the polyvinyl alcohol solution to the plasticizer to the catalyst is 100: 1-2: 5-6.
Preferably, the plasticizer comprises glutaraldehyde, the catalyst comprises acetic acid, and the defoamer comprises 1-octanol.
Preferably, the weight ratio of the magnesium modified charcoal coating material to urea is 1-5: 100.
Preferably, the liquid spraying amount of the magnesium modified charcoal coating material in the coating treatment is 50-90 mL, and the coating temperature is 30-50 ℃.
The invention has the beneficial technical effects that:
(1) the invention overcomes the defects that the original biochar coated fertilizer is too coarse to grind and the membrane liquid is not uniform after coating the surface of the fertilizer, and improves the slow release effect of nitrogen;
(2) the invention improves the physical properties of the coating material, particularly obviously improves the performance on tensile strength and elongation at break, is beneficial to the transportation and storage of fertilizer, and overcomes the defect that the slow release performance of the conventional coating nitrogen is reduced due to the membrane breakage;
(3) the leaching test in soil proves that the slow release effect of the nitrogen is superior to that of common biochar coated urea and common coated nitrogen fertilizers on the market, the utilization rate of the nitrogen fertilizer is improved, the quantity of the nitrogen flowing into the atmosphere and water is reduced, and the environment-friendly performance is better.
Drawings
FIG. 1 is an electron microscope image of biochar and magnesium-modified biochar; wherein a and c are biochar electron micrographs respectively 200 times and 3000 times; b. d is respectively an electron microscope image of the magnesium modified biochar under 200 times and 3000 times;
FIG. 2 is a graph of Fourier transform infrared spectroscopy (FT-IR) analysis of magnesium modified biochar;
FIG. 3 is a graph of the tensile strength of the coating material;
FIG. 4 is a graph of elongation at break of the coated fertilizer;
FIG. 5 is a graph of ammonium ion permeability for coating materials of different formulations;
fig. 6 is a graph of cumulative release rate.
Detailed Description
The invention provides a preparation method of a magnesium modified biochar coated urea fertilizer, which comprises the following steps:
(1) sequentially crushing, sieving, carbonizing and cracking agricultural wastes to obtain biochar;
(2) grinding the biochar to obtain biochar powder, then mixing the biochar powder with a magnesium chloride solution, stirring, filtering, washing and drying to obtain magnesium modified biochar;
(3) grinding the magnesium modified charcoal to obtain magnesium modified charcoal powder, and then uniformly mixing the magnesium modified charcoal powder with a polyvinyl alcohol solution, a plasticizer and a catalyst to obtain a magnesium modified charcoal coating material;
(4) and carrying out coating treatment on the magnesium modified charcoal coating material and urea to obtain the magnesium modified charcoal coated urea fertilizer.
The invention sequentially crushes, screens, carbonizes and cracks agricultural wastes to obtain the biochar.
In the present invention, the agricultural waste preferably comprises one or more of crop straw, preferably one or more of corn stover, rice straw, wheat straw and soybean stover, husk preferably comprises peanut husk, and shoots preferably comprise fruit tree shoots.
The invention preferably pulverizes the agricultural waste into powder and then passes through a 5-mesh sieve.
In the invention, the carbonization and cracking are preferably carried out under an anaerobic condition, the carbonization and cracking temperature is preferably 300-700 ℃, the carbonization and cracking time is preferably 1-3 h, and after the carbonization and cracking are carried out to obtain the biochar, the carbon content in the biochar is preferably higher than 30%, and more preferably 30-60%.
After the biochar is obtained, the biochar is ground to obtain biochar powder, and then the biochar powder is mixed with a magnesium chloride solution, stirred, filtered, washed and dried to obtain the magnesium modified biochar.
In the present invention, it is preferable that the charcoal powder is obtained by sieving the ground charcoal with a 200-mesh sieve.
In the present invention, the mixing ratio of the charcoal powder and the magnesium chloride solution is preferably 1 g: 50mL, the concentration of the magnesium chloride solution is preferably 0.01mol/L, and the magnesium chloride is preferably MgCl2·6H2And O, the molecular weight of the magnesium chloride is preferably 95.21, the mixing is preferably carried out in a magnetic stirrer, the stirring speed is preferably 1500-2000 r/min, and the stirring time is preferably 2-4 h, and more preferably 3 h.
The invention has no special requirements on the steps of filtering, washing and drying, and can be carried out by adopting a scheme well known by the technical personnel in the field.
In the invention, the specific drying step is preferably that after the biochar is modified by a magnesium chloride solution, the solution is filtered by a suction filter, the modified biochar solution passes through a Buchner funnel with 9cm qualitative filter paper for a few times, after the filtration is finished, a small amount of ultrapure water is added into the funnel, after water is filtered out, the washing is finished by repeating for 1 to 2 times, the filter paper attached with the biochar is put into an oven and dried for 24 hours at 50 ℃, and then the magnesium modified biochar solid is obtained.
After the magnesium modified charcoal is obtained, the magnesium modified charcoal is ground to obtain magnesium modified charcoal powder, and then the magnesium modified charcoal powder is uniformly mixed with polyvinyl alcohol solution, plasticizer and catalyst to obtain the magnesium modified charcoal coating material.
The invention preferably passes the ground magnesium modified charcoal through a 200-mesh sieve to obtain the magnesium modified charcoal powder.
In the invention, the weight ratio of the magnesium modified biochar to the plasticizer is preferably 3-9: 100, respectively; the polyvinyl alcohol is preferably selected according to the polymerization degree and the alcoholysis degree of the polyvinyl alcohol, and the polyvinyl alcohol is particularly preferably one or more of polyvinyl alcohol 1750 (polymerization degree 1750, alcoholysis degree 50%, content not less than 90%) and polyvinyl alcohol 1788 (polymerization degree 1788, alcoholysis degree 88%, content not less than 90%), and polyvinyl alcohol 2488 (polymerization degree 2488, alcoholysis degree 88%, content not less than 90%). In the present invention, the source of the polyvinyl alcohol is not particularly limited, and a commercially available product may be used.
The polyvinyl alcohol is preferably a polyvinyl alcohol solution, and the concentration of the polyvinyl alcohol solution is preferably 0.05-0.1 g/mL.
In the invention, the plasticizer preferably comprises glutaraldehyde, the catalyst preferably comprises acetic acid, and the volume ratio of the polyvinyl alcohol to the plasticizer to the catalyst is preferably 100: 1-2: 5-6.
In the invention, the defoaming agent is preferably 1-octanol, and the addition amount of the defoaming agent is preferably 0.05-0.1% of polyvinyl alcohol solution.
The sources of the plasticizer, the catalyst and the defoaming agent are not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.
In the present invention, one alternative scheme for the specific dissolution process of the polyvinyl alcohol is as follows: respectively adding 20g of polyvinyl alcohol solid (the polymerization degree is 1750-.
In the invention, the concrete process of uniformly mixing the magnesium modified charcoal powder, the polyvinyl alcohol, the plasticizer, the catalyst and the defoaming agent is preferably as follows: and plasticizing the polyvinyl alcohol solid solution after obtaining the polyvinyl alcohol solid solution, adding a plasticizer and a catalyst into a beaker, continuously heating for 40min at 90-100 ℃, reducing the temperature to 60-70 ℃ after the reaction is finished, adding a defoaming agent, and then uniformly mixing with the magnesium modified charcoal powder to obtain the magnesium modified charcoal coating material.
After the magnesium modified charcoal coated material is obtained, the magnesium modified charcoal coated material and urea are subjected to coating treatment to obtain the magnesium modified charcoal coated urea fertilizer.
In the invention, the weight ratio of the magnesium modified charcoal coating material to urea is 1-5: 100.
According to the method, preferably, a magnesium modified charcoal coating material is poured into a sample inlet of a peristaltic pump, urea is put into a rotary drum of a coating machine, the position of an air outlet and the coating temperature are adjusted, the coating of the fertilizer is started after the coating machine is preheated, and the preheating temperature is preferably 35-45 ℃ and more preferably 40 ℃.
In the invention, the liquid spraying amount of the magnesium modified charcoal coating material in the coating treatment is preferably 50 mL-90 mL, the specific liquid spraying amount is preferably 5 gradients which are respectively 50mL, 60mL, 70mL, 80mL and 90mL, the coating temperature is preferably 30-50 ℃, the specific coating temperature is preferably 5 gradients which are respectively 30 ℃, 35 ℃, 40 ℃, 45 ℃ and 50 ℃, the drying temperature is preferably 40-60 ℃, the specific drying temperature is preferably 5 gradients which are respectively 40 ℃, 45 ℃, 50 ℃, 55 ℃ and 60 ℃.
In the invention, various spraying liquid volume gradients, coating temperature gradients and drying temperature gradients are set to obtain various fertilizer combinations.
In the invention, the rotating speed of the rotary drum is preferably 40r/min, and the particle size of the urea is preferably 3-5 mm.
In the invention, the liquid spraying time is controlled in the preferable fertilizer preparation process, the principle of 'a small amount of liquid spraying for multiple times' is adopted to ensure that the coating liquid is uniformly sprayed on the surfaces of urea particles, and a scraper is adopted to scrape off the fertilizer attached to the inner wall of the rotary drum; the thickness of the coating is adjusted to be within the range of 1-5% by controlling the amount of the liquid spraying amount.
After the coating treatment is finished, the prepared magnesium modified biochar coated urea fertilizer is preferably placed in an oven and dried at 50-60 ℃.
In order to further illustrate the present invention, the following examples are provided to describe the preparation method of the magnesium modified biochar coated urea fertilizer provided by the present invention in detail, but they should not be construed as limiting the scope of the present invention.
Example 1
The preparation method of the magnesium modified charcoal coated urea fertilizer comprises the following steps:
(1) preparation of biochar
Sequentially crushing crop straws, sieving with a 5-mesh sieve, and performing carbonization and pyrolysis for 2h at 500 deg.C under anaerobic condition to obtain biochar (P for short)1B1)；
(2) Preparation of magnesium modified biochar
Grinding the biochar and sieving the biochar by a 200-mesh sieve to obtain biochar powder, and mixing the biochar powder with prepared 0.01 mol.L-1Magnesium chloride (MgCl)2·6H2O) solution is mixed according to the ratio of 1: 50 (m: V), the bottle mouth is sealed by a preservative film, a magnetic stirrer is adopted to stir strongly (1800r/min) for 3 hours, and then filtration, washing and drying are carried out to obtain magnesium modified biochar;
(3) preparation of magnesium modified charcoal coating material
Grinding the magnesium modified charcoal and sieving the ground magnesium modified charcoal with a 200-mesh sieve to obtain magnesium modified charcoal powder;
respectively adding 20g of polyvinyl alcohol solid (the polymerization degree is 1750-2488 and the alcoholysis degree is 50% -88%) and 250mL of distilled water into a 500mL beaker, sealing the opening of the beaker by using a sealing film, heating to 90 ℃ by using a constant-temperature heating magnetic stirrer, and continuously stirring until the polyvinyl alcohol solid is completely dissolved;
plasticizing polyvinyl alcohol, adding 3.3mL of plasticizer (glutaraldehyde) and 13.3mL of catalyst (acetic acid) into a beaker, continuously heating for 40min, reducing the temperature to 60-70 ℃ after the reaction is finished, adding 0.2mL of defoaming agent (1-octanol) and 1.2g of magnesium modified charcoal powder, and preparing a magnesium modified charcoal coating material after the magnesium modified charcoal is completely mixed with polyvinyl alcohol solution;
(4) preparation of magnesium modified biochar coated urea fertilizer
Pouring the magnesium modified charcoal coating material prepared in the step 3 into a sample inlet of a peristaltic pump, weighing 100g of large-particle urea by using a balance, putting the large-particle urea into a rotary drum of a coating machine, adjusting the position of an air outlet and the coating temperature, and beginning to coat the fertilizer after the coating machine is preheated; wherein the liquid spraying amount is 70mL, the coating temperature is set to be 40 ℃, and the drying temperature is 50 ℃; controlling the liquid spraying time in the fertilizer preparation, adopting the principle of 'a small amount of liquid spraying for multiple times' to ensure that the coating liquid is uniformly sprayed on the surfaces of urea particles, and scraping off the fertilizer attached to the inner wall of the rotary drum by using a scraper; the thickness of the coating is adjusted to be within the range of 1-5% by controlling the amount of the liquid spraying amount. And after coating, putting the prepared fertilizer in an oven, and drying the fertilizer at 60 ℃ to obtain the magnesium modified biochar coated urea fertilizer.
FIG. 1 is an electron microscope image of biochar before and after modification in step (1) and step (2) of the present invention; wherein a and b are biochar electron micrographs respectively 200 times and 3000 times; c. d is electron microscope images of magnesium modified biochar at 200 times and 3000 times respectively. As can be seen from the figure, after modification, the pores on the surface of the biochar are obviously collapsed and broken, the diameter of the pores on the surface of the magnesium-modified biochar is reduced compared with that of the pores on the surface of the biochar which is not modified by magnesium, and fewer pores serving as coating materials are more beneficial to prolonging the period of nutrient release of the coated fertilizer.
The biochar before and after modification was subjected to elemental determination using an energy dispersive X-ray spectrometer, EDX for short, and the results are shown in table 1.
TABLE 1
| Magnesium ion (Unit%) | Calcium ion (%) | Potassium ion (%) | Phosphorus ion (%) | |
| Pre-modified biochar | 1 | 1 | 1 | 2 |
| Modified biochar | 4 | 6 | 2 | 4 |
It can be obtained from table 1 that the modified biochar completes the enrichment of magnesium, and compared with the biochar before modification, the content of magnesium is increased by 4 times, and the content of calcium ions, potassium ions and phosphorus ions is increased by 6 times, 2 times and 2 times.
FIG. 2 is a Fourier transform infrared spectroscopy (FT-IR) chart of the magnesium modified biochar prepared in step (2) of the present invention, and it can be seen that the absorption peak of the Fourier transform infrared spectroscopy (FT-IR) of the biochar is increased, and the number of-OH groups and carboxylate functional groups is significantly increased.
Example 2
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 11B2): preparing a magnesium modified biochar coated material according to the step (3) by using 1.2g of biochar, 20g of polyvinyl alcohol (the polymerization degree is 1750 and the alcoholysis degree is 50%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanol, and preparing the magnesium modified biochar coated urea fertilizer according to the step (4).
Example 3
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 11B3): preparing a magnesium modified biochar coated material according to the step (3) by using 1.8g of biochar, 20g of polyvinyl alcohol (the polymerization degree is 1750 and the alcoholysis degree is 50%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanol, and preparing the magnesium modified biochar coated urea fertilizer according to the step (4).
Example 4
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 12B1): preparing magnesium modification according to the step (3) by adopting 0.6g of biochar, 20g of polyvinyl alcohol (polymerization degree 1788 and alcoholysis degree 88%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanolAnd (4) preparing a biochar coated material, namely preparing the magnesium modified biochar coated urea fertilizer according to the step (4).
Example 5
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 12B2): preparing a magnesium modified biochar coated material according to the step (3) by using 1.2g of biochar, 20g of polyvinyl alcohol (polymerization degree 1788 and alcoholysis degree 88%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanol according to the step (4) to prepare the magnesium modified biochar coated urea fertilizer.
Example 6
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 12B3): preparing a magnesium modified biochar coated material according to the step (3) by using 1.8g of biochar, 20g of polyvinyl alcohol (polymerization degree 1788 and alcoholysis degree 88%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanol according to the step (4) to prepare the magnesium modified biochar coated urea fertilizer.
Example 7
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 13B1): preparing a magnesium modified biochar coated material according to the step (3) by adopting 0.6g of biochar, 20g of polyvinyl alcohol (the polymerization degree is 2488 and the alcoholysis degree is 88%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanol, and preparing the magnesium modified biochar coated urea fertilizer according to the step (4).
Example 8
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 13B2): preparing a magnesium modified biochar coated material according to the step (3) by using 1.2g of biochar, 20g of polyvinyl alcohol (the polymerization degree is 2488 and the alcoholysis degree is 88%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanol, and preparing the magnesium modified biochar coated urea fertilizer according to the step (4).
Example 9
The magnesium modified biochar material 1 (P for short) is prepared according to the step (1) of the example 13B3): preparing a magnesium modified biochar coating material according to the step (3) by 1.8g of biochar, 20g of polyvinyl alcohol (polymerization degree 2488 and alcoholysis degree 88%), 3.3mL of glutaraldehyde, 13.3mL of acetic acid and 0.2mL of 1-octanol according to the stepsAnd (4) preparing the magnesium modified biochar coated urea fertilizer.
Physical resistance measurement of coating materials of different formulations
The coating material was cut into a rectangle of 5X 10cm size, and the coating material was fixed in an electronic universal tester with a jig at an original distance of 8cm and an elongation rate of 200mm/min, and each treatment was repeated 5 times. And after the measurement is finished, the tensile strength is derived from the instrument, and the elongation at break of the coating material is calculated.
Fig. 3 and 4 are graphs of tensile strength and elongation at break of the coating material, respectively. Comprehensive analysis of tensile strength and elongation at break of coating material, 9 formula combinations, coating material formula P2B1And P2B2Most preferably, followed by coating formulation P1B2、P1B3And P3B1。
Ammonium ion permeability of coating materials of different formulations
Cutting the preservative film into squares with side length of about 5cm, cutting a circular hole with the diameter of 2cm in the middle, cutting the film material into a proper size for later use, selecting a transparent plastic bottle with the capacity of 50mL for weighing and recording, and then adding about 10g of ammonium sulfate solution (50mL, NH) into the bottle4 +Concentration 7500 mg/L). Then pressing the cut coating material on the bottle mouth, covering the coating material with a preservative film, sealing, finally putting the sealed small bottle into a 100ml beaker filled with 50ml of water, sealing the beaker, standing for 24h at 25 ℃, and measuring the ammonium ion concentration in the beaker by using a Kjeldahl apparatus, as shown in figure 5.
Therefore, the addition amount of the magnesium modified biochar has little influence on the water permeability and the ammonium ion permeability of the biochar, and no statistically significant difference exists.
Comparative test
And (4) selecting three magnesium modified coating materials to prepare coated urea according to the step (4) for a slow release effect comparison test. The experiment set up 7 treatments: blank control group (CK), sulfur coated urea (S), large granular urea (N), common biochar coated urea (N + C), magnesium modified biochar coated urea (45), magnesium modified biochar coated urea (50) and magnesium modified biochar coated urea (1788), and the test is repeated for 5 times. Specific conditions for preparing the magnesium-modified biochar are shown in table 2.
TABLE 2 magnesium modified charcoal preparation Condition parameters
Cleaning and drying a mineral water bottle with the capacity of 500ml, then subtracting the bottom, fixing the bottle mouth with absorbent gauze, preventing soil loss in a soil column in the leaching process, adding 250g of aeolian sandy soil into the bottle, then accurately weighing 0.224g of coated fertilizer according to the nitrogen application amount of 0.222g/kg, uniformly mixing the fertilizer and the soil, then adding 250g of soil into the soil column, placing gauze above the soil layer, and preventing water flow from disturbing the upper soil layer in leaching. A100 ml beaker is placed below the soil column to receive the leaching solution, a preservative film is used for sealing above the soil column to prevent the volatilization of fertilizer nutrients, and a certain amount of water is added into the soil column to reach the saturated water content of the soil after the soil column is manufactured. And (3) filling 50ml of distilled water above the earth column during each leaching, slowly adding the distilled water into the earth column, stopping leaching until no liquid drips in a beaker below the earth column, filtering the filtrate in the beaker, filling the filtrate into a PET (polyethylene terephthalate) plastic bottle for storage, measuring the total nitrogen content in the filtrate by using a Kjeldahl apparatus, and calculating the nutrient release rate to prepare a nutrient accumulated release rate curve. Sampling was performed at 1d, 2d, 3d, 4d, 5d, 6d, 7d, 15d, 30d, 60d, respectively. The nutrient release rate is calculated by the formula V _ t ═ omega _ t/omega. In the formula: vt is the nutrient release rate of the coated fertilizer in unit percent; t is the nutrient release period, unit d; omega _ t is the nutrient release mass fraction of the leaching solution at 25 ℃, unit%; omega is the mass fraction of total nutrients in the coated fertilizer, and the unit percent is.
As shown in fig. 6, as the number of days for leaching the soil column increases, the difference of nutrient release rate between different treatments gradually increases, and the size sequence is 50>45>1788> sulfur-coated urea > common biochar-coated urea > large-particle urea; at 30 days of leaching, the cumulative release rate of the large-particle urea treatment is 90.33 percent, the cumulative release rate of the 45 treatment is 67.20 percent, the nitrogen release of the 50 treatment is the least, the nitrogen release is 60.43 percent, the nitrogen release is 21.90 percent lower than that of the sulfur-coated urea treatment, the nitrogen release is 23.93 percent lower than that of the common biochar coated urea treatment, and the slow release effect is obvious. Compared with common biochar coated urea, the magnesium modified biochar coated urea can effectively reduce the accumulated release rate of nutrients.
The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be construed as the protection scope of the present invention.
Claims (10)
1. A preparation method of a magnesium modified biochar coated urea fertilizer is characterized by comprising the following steps:
(1) sequentially crushing, sieving, carbonizing and cracking agricultural wastes to obtain biochar;
(2) grinding the biochar to obtain biochar powder, then mixing the biochar powder with a magnesium chloride solution, stirring, filtering, washing and drying to obtain magnesium modified biochar;
(3) grinding the magnesium modified charcoal to obtain magnesium modified charcoal powder, and then uniformly mixing the magnesium modified charcoal powder with a polyvinyl alcohol solution, a plasticizer and a catalyst to obtain a magnesium modified charcoal coating material;
(4) and carrying out coating treatment on the magnesium modified charcoal coating material and urea to obtain the magnesium modified charcoal coated urea fertilizer.
2. The method of claim 1, wherein the agricultural waste comprises one or more of crop straw, hulls, and shoots.
3. The preparation method of claim 1, wherein the carbonization cracking temperature is 300-700 ℃ and the carbonization cracking time is 1-3 h.
4. The preparation method according to claim 1, wherein the mixing ratio of the charcoal powder and the magnesium chloride solution is 1 g: 50 mL.
5. The method according to claim 1, wherein the concentration of the magnesium chloride solution is 0.01 mol/L.
6. The preparation method of claim 1, wherein the weight ratio of the magnesium-modified biochar to the polyvinyl alcohol solution is 3-9: 100.
7. The preparation method according to claim 1, wherein the volume ratio of the polyvinyl alcohol solution, the plasticizer, the catalyst and the defoaming agent is 100: 1-2: 5-6.
8. The method of claim 1 or 7, wherein the plasticizer comprises glutaraldehyde and the catalyst comprises acetic acid.
9. The preparation method according to claim 1, wherein the weight ratio of the magnesium-modified biochar coating material to urea is 1-5: 100.
10. The preparation method according to claim 1, wherein the liquid injection amount of the magnesium-modified biochar coating material in the coating treatment is 50-90 mL, and the coating temperature is 30-50 ℃.
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| CN109095955A (en) * | 2018-07-03 | 2018-12-28 | 西北农林科技大学 | A kind of preparation method and applications of magnesium salts modification biological charcoal |
| CN111848292A (en) * | 2020-07-13 | 2020-10-30 | 上海大学 | Urea slow-release compound fertilizer and preparation method thereof |
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| CN109095955A (en) * | 2018-07-03 | 2018-12-28 | 西北农林科技大学 | A kind of preparation method and applications of magnesium salts modification biological charcoal |
| CN111848292A (en) * | 2020-07-13 | 2020-10-30 | 上海大学 | Urea slow-release compound fertilizer and preparation method thereof |
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| HUANG ET AL.: "Adsorption of Pb(II) in Aqueous Solution by the Modified Biochar Derived from Corn Straw with Magnesium Chloride", 《NATURE ENVIRONMENT AND POLLUTION TECHNOLOGY》 * |
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