Slow-release oxygen fertilizer as well as preparation method and application thereof

Abstract

The invention discloses a slow-release oxygen fertilizer as well as a preparation method and application thereof, and belongs to the technical field of slow-release fertilizers. The slow-release oxygen fertilizer comprises a buffer layer, an oxygen source layer and a coating layer from inside to outside, and all the layers are isolated by filling layers. Wherein the buffer layer comprises a compound fertilizer composed of urea phosphate and a potash fertilizer; the oxygen source layer comprises a chemical oxygen producer calcium peroxide; the coating layer comprises polymer resin polyacrylate; the filling layer comprises a filling agent. The slow-release oxygen fertilizer developed by the invention has multiple functions of slow-release oxygen, acid-base buffering, nutrient supply and the like. The fertilizer is also suitable for being applied to acid-base sensitive crops, can promote the growth of various crops, and is not easy to cause soil hardening and salinization after being applied for a long time. In addition, when the slow-release oxygen fertilizer is applied to the mercury-polluted soil, the slow-release oxygen fertilizer has a remarkable inhibition effect on dissolution of mercury and formation of methyl mercury in the soil, and has important significance in promoting safe production of food crops.

Description

Technical Field

[0001] This invention belongs to the field of slow-release fertilizer technology, specifically relating to a slow-release oxygen fertilizer, its preparation method, and its application. Background Technology

[0002] Oxygen in the soil plays a crucial role in plant growth and the soil ecosystem. Low oxygen levels inhibit root growth, and poor root development affects the absorption of water and nutrients, leading to reduced crop yields. Simultaneously, many soil pathogens are anaerobic, and low oxygen levels cause these pathogens to proliferate, disrupting the soil ecosystem and increasing the risk of crop diseases. Of particular concern is that anaerobic environments in the soil increase mercury reactivity. Under the mediation of anaerobic microorganisms (such as sulfate-reducing bacteria, iron-reducing bacteria, and methanogens), mercury is converted into the more toxic methylmercury. Methylmercury exhibits a biomagnification effect, accumulating up to 10 times its original value in the food chain. 6 ~10 7 The anaerobic environment of flooded paddy soil provides an anaerobic environment for mercury-methylating bacteria, increasing the soil's capacity for mercury methylation. Furthermore, the anaerobic environment of paddy fields may promote the reducing dissolution of iron and manganese oxides, leading to enhanced mercury release and activation associated with this geochemical process. This increases the bioavailability of mercury and methylmercury to rice plants, exacerbating the risk of mercury contamination in rice and ultimately threatening human food safety.

[0003] Slow-release oxygen fertilizers are applied to the soil by coating an oxygenating agent. When the oxygenating agent comes into contact with water, it releases oxygen continuously and stably. Calcium peroxide (CaO2) is currently the most commonly used oxygenating agent and is widely used in agriculture. For example, Chinese invention patent application CN106747948A discloses a seedling oxygen-enhancing fertilizer comprising an immediate-release layer, a slow-release layer, and a coating layer. The immediate-release layer consists of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer, micronutrient fertilizer, chemical oxygenating agent, composite gel carrier, modified calcium oxide, and binder. The slow-release layer consists of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer, micronutrient fertilizer, chemical oxygenating agent, cyclodextrin, and binder. The coating layer is an alcohol-soluble polymer resin. The chemical oxygenating agent is CaO2, which is coated with an alcohol-soluble polymer resin to achieve slow oxygen release. Simultaneously, it coats nitrogen, phosphorus, and potassium fertilizers with an oxygenating agent, resulting in a fertilizer that combines slow-release nutrients and oxygen, thus promoting seedling growth. However, this patent fails to consider the problem of CaO2 oxygenating agent reacting with water to produce Ca(OH)2, leading to an increase in soil pH (to 12-13). Long-term application of this oxygenating fertilizer could cause soil compaction and salinization. Furthermore, this oxygenating fertilizer is no longer suitable for acid- and alkaline-sensitive crops.

[0004] In summary, developing a compound fertilizer that has slow-release oxygen, moderate pH, and fertilizing effect is of great significance for promoting the growth of different plants and the health of soil ecology. Summary of the Invention

[0005] 1. The problem to be solved

[0006] To address the problem that existing CaO2-containing oxygen-enhancing fertilizers cause an increase in soil pH during use and are unsuitable for acid- and alkaline-sensitive crops, this invention provides a multifunctional slow-release oxygen fertilizer with buffering capabilities. It is designed from the inside out as a buffer layer, an oxygen source layer, and a coating layer, with each layer isolated by a filling layer. This design effectively isolates the acidic buffer in the buffer layer from the alkaline CaO2 oxygenator in the oxygen source layer, preventing premature contact and reaction between the acidic buffer and CaO2, which could lead to fertilizer failure. Simultaneously, by placing the CaO2 oxygenator in the middle layer of the slow-release fertilizer, it is not affected by the acidic environment of the inner acidic buffer layer when soil moisture penetrates from the outside in, thus preventing rapid oxygen release. Both layers can still independently perform their functions of slow oxygen release and soil pH buffering.

[0007] 2. Technical Solution

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] This invention provides a slow-release oxygen fertilizer, which comprises, from the inside out, a buffer layer, an oxygen source layer, and a coating layer, with each layer separated by a filling layer. The buffer layer comprises a buffer compound fertilizer and an adhesive, and the compound fertilizer comprises at least urea phosphate. The oxygen source layer comprises a chemical oxygenating agent and an adhesive. The coating layer comprises a polymer resin. The filling layer comprises a filler and an adhesive.

[0010] Furthermore, the aforementioned buffer compound fertilizer includes urea phosphate and potassium fertilizer.

[0011] Furthermore, the aforementioned potassium fertilizer includes potassium chloride.

[0012] Furthermore, the mass ratio of urea phosphate to potassium chloride is (6.0–7.0):1.

[0013] Furthermore, the mass ratio of urea phosphate to potassium chloride is 6.6:1.

[0014] Furthermore, the aforementioned chemical oxygenating agents include calcium peroxide.

[0015] Furthermore, the aforementioned polymeric resin includes polyacrylate.

[0016] Furthermore, the mass ratio of the above-mentioned buffer compound fertilizer, chemical oxygenating agent and polymer resin is (0.9-1):1:(0.2-0.4).

[0017] Furthermore, the mass ratio of the aforementioned buffer compound fertilizer, chemical oxygenator, and polymer resin is 0.92:1:0.3.

[0018] Furthermore, the aforementioned filler includes attapulgite.

[0019] Furthermore, the aforementioned adhesive includes sodium alginate.

[0020] Furthermore, the above-mentioned adhesive is a sodium alginate solution, which is prepared by weighing sodium alginate and mixing it evenly in ultrapure water, then adding an acidic solution, stirring evenly, and then heating to dissolve it to obtain a sodium alginate solution.

[0021] Furthermore, the concentration of sodium alginate mentioned above is 20–30 g / L.

[0022] Furthermore, the concentration of sodium alginate mentioned above is 26 g / L.

[0023] Furthermore, the acidic solution mentioned above is hydrochloric acid, and the amount added is 0.5% to 0.7% (v / v).

[0024] Furthermore, the acidic solution mentioned above is hydrochloric acid, and the amount added is 0.67% (v / v).

[0025] Furthermore, the above stirring is carried out on a magnetic stirrer at 80-120 rpm for 10-20 minutes.

[0026] Furthermore, the above stirring was carried out on a magnetic stirrer at 100 rpm for 20 minutes.

[0027] Furthermore, the heating device is a water bath, with a heating temperature of 70–90°C and a heating time of 50–70 minutes.

[0028] Furthermore, the heating device is a water bath with a heating temperature of 80°C and a heating time of 60 minutes.

[0029] This invention also provides a method for preparing the above-mentioned slow-release oxygen fertilizer, the method comprising the following steps:

[0030] S1. Preparation of buffer layer particles

[0031] The uniformly mixed buffer compound fertilizer is fed into a granulator, moistened with an adhesive, granulated and screened to obtain buffer layer particles with a particle size of 2.0 to 2.2 mm.

[0032] S2, Encapsulation Filler Layer

[0033] The buffer layer particles in S1 are fed into a granulator, wetted with an adhesive, and then filled with a filler. After granulation and screening, particles with a surface coating and filling layer with a particle size of 2.4 to 2.6 mm are obtained.

[0034] S3, Encapsulated oxygen source layer

[0035] The particles with the surface coating filling layer in S2 are fed into a granulator, wetted with an adhesive, and a chemical oxygenating agent is added. After granulation and screening, particles with a surface coating oxygen source layer with a particle size of 3.6 to 3.8 mm are obtained.

[0036] S4, Encapsulation Filler Layer

[0037] The particles with the surface-coated oxygen source layer in S3 are fed into a granulator, wetted with an adhesive, and then filled with a filler. After granulation and screening, particles with a surface-coated filling layer with a particle size of 3.8 to 4.0 mm are obtained.

[0038] S5, Encapsulation / Encapsulation Layer

[0039] The particles with the surface coating filling layer in S4 are fed into a granulator, and the coating agent is applied to the surface of the particles. After drying, a slow-release oxygen fertilizer is obtained.

[0040] Furthermore, the operating speed of the granulator in S1 to S5 above is 20 to 40 r / min.

[0041] Furthermore, the operating speed of the granulator in S1 to S5 above is 30 r / min.

[0042] Furthermore, the operating temperature of the granulator in S1 is 40–60°C.

[0043] Furthermore, the operating temperature of the granulator in S1 above is 50°C.

[0044] Furthermore, the operating temperature of the granulator in S2 to S4 is 30 to 50°C.

[0045] Furthermore, the operating temperature of the granulator in S2 to S4 above is 40°C.

[0046] Furthermore, the operating temperature of the granulator in S5 is 50–70°C.

[0047] Furthermore, the operating temperature of the granulator in S5 is 60°C.

[0048] Furthermore, in the adhesive wetting process described in S1 to S5 above, the adhesive is pressurized by placing it in an air compressor and spraying it out as a water mist through a flow spray device to achieve wetting.

[0049] Furthermore, in the above-mentioned S5, the coating process is achieved by spraying a water mist of coating agent through a flow spray device.

[0050] The present invention also provides the application of the above-mentioned slow-release oxygen fertilizer in inhibiting mercury activation and / or mercury methylation in soil.

[0051] 3. Beneficial effects

[0052] Compared with the prior art, the advantages of this invention are as follows:

[0053] (1) The present invention provides a slow-release oxygen fertilizer, its preparation method, and its application. A buffer layer is added to the traditional slow-release oxygen fertilizer. This buffer layer is fully isolated from the CaO2-containing oxygen source layer, and the oxygen source layer is coated outside the buffer layer. This not only does not affect the slow-release oxygen effect of CaO2, but also effectively buffers the alkaline soil environment caused by the CaO2 reaction, maintaining the soil pH value within a neutral to slightly alkaline range. Because the slow-release oxygen fertilizer of the present invention has acid-base buffering function, long-term application will not cause soil compaction or salinization, and it is also suitable for acid- and alkali-sensitive crops.

[0054] (2) The present invention provides a slow-release oxygen fertilizer and its preparation method and application. The buffer layer in the slow-release oxygen fertilizer is a compound fertilizer of urea phosphate and potassium chloride. The present invention scientifically proportions urea phosphate and KCl, which can provide nutrients for crops while playing a buffering role. This realizes the integration of soil remediation into crop production management.

[0055] (3) The present invention provides a slow-release oxygen fertilizer and its preparation method and application. The slow-release oxygen fertilizer has been verified to achieve stable slow release of oxygen and acid-base buffering of the application environment. More importantly, when applied to mercury-contaminated soil, it can significantly inhibit the formation of active mercury and methylmercury, which may improve the redox state of the soil. This is of great significance for the safe production of aquatic food crops such as rice. Attached Figure Description

[0056] Figure 1 This is a flowchart of the slow-release oxygen fertilizer preparation process of the present invention.

[0057] Figure 2 Figure A shows the morphology (Figure A) and cross-sectional schematic diagram (Figure B) of the slow-release oxygen fertilizer particles prepared by this invention.

[0058] Figure 3 This is a graph showing the pH change over time in pure water treated with the slow-release oxygen fertilizer and CaO2 of this invention.

[0059] Figure 4 This is a graph showing the change in dissolved oxygen (DO) in pure water over time when treated with slow-release oxygen fertilizer and CaO2 according to the present invention.

[0060] Figure 5 This invention describes the variation characteristics of THg content in soil solution over time.

[0061] Figure 6 This invention describes the variation characteristics of MeHg content in soil solution over time. Detailed Implementation

[0062] The present invention will be further described below with reference to specific embodiments.

[0063] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0064] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0065] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular variable.

[0066] As used herein, the term “at least one of…” is intended to be synonymous with “one or more of…”. For example, “at least one of A, B, and C” explicitly includes only A, only B, only C, and combinations thereof.

[0067] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as “less than about 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0068] The reagents used in the embodiments of this invention are as follows:

[0069] CaO2 (Shanghai E. En Chemical Technology Co., Ltd., analytical grade)

[0070] Urea phosphate (Guangdong Xingfu Chemical Reagent Co., Ltd., analytical grade),

[0071] Attapulgite (Xincheng Mineral Products, High Purity)

[0072] Polyacrylate emulsion (Beijing Hongya Jianye Building Materials Co., Ltd.)

[0073] Sodium alginate (Tianjin Dengfeng Chemical Reagent Factory, analytical grade).

[0074] The instruments used in the embodiments of this invention are as follows:

[0075] Round pot granulator (Jinxing Machinery, Type 40).

[0076] Example 1

[0077] This embodiment provides a slow-release oxygen fertilizer and its preparation method.

[0078] The materials prepared are as follows:

[0079] Buffered compound fertilizer: 80g urea phosphate (buffer); Potassium fertilizer: 12g KCl;

[0080] Oxygenating agent: CaO2 100g;

[0081] Filler: 80g of attapulgite soil;

[0082] Adhesive: 4g sodium alginate; In this embodiment, when using sodium alginate solution as an adhesive, it is prepared as a water mist as follows: 4g of sodium alginate (analytical grade) is placed in a clean glass beaker, 150ml of ultrapure water and 1ml of hydrochloric acid are added, and then the mixture is stirred at 100rpm for 20min on a magnetic stirrer to ensure uniform dispersion; then it is placed in a water bath preheated to 80℃ and heated for 60min to dissolve it. The obtained sodium alginate solution is pressurized using an air compressor and then sprayed out as a water mist through an adjustable flow spray device.

[0083] Coating layer (polymer resin): 30g of polyacrylate emulsion; In this embodiment, a water mist polyacrylate emulsion is used, which is achieved as follows: the emulsion is pressurized by an air compressor and then sprayed out as a water mist through an adjustable flow spraying device.

[0084] Specifically, in this embodiment, the slow-release oxygen fertilizer is formed by granulation using a circular pot granulator, and the process flow is as follows: Figure 1 As shown, the specific process is as follows:

[0085] S1. Preparation of buffer layer particles

[0086] Adjust the speed of the round pot granulator to 30 r / min and the heating device to 50℃; add the well-mixed urea phosphate and KCl compound fertilizer (urea phosphate: KCl fertilizer = 20:3, the fertilizer is pre-ground into powder), quickly wet it with water mist (2 ml / min) sodium alginate binder, and after granulation and screening, obtain buffer layer particles with a particle size of 2.0-2.2 mm for later use;

[0087] S2, Encapsulation Filler Layer

[0088] Adjust the speed of the round pot granulator to 30 r / min and the heating device to 40℃. Put all the buffer layer particles in S1 into the round pot granulator and wet the particles in the same way. Then slowly and evenly add attapulgite clay (40g in total) to coat the particles (to isolate the buffer layer and the oxygen source layer). During granulation, continuously take out the particles for sieving. When the particle size of 2.4 to 2.6 mm is obtained, the coating operation is ended and the particles are collected for later use.

[0089] S3, Encapsulated oxygen source layer

[0090] Adjust the speed of the round pot granulator to 30 r / min and the heating device to 40℃. Put all the particles in S2 into the round pot granulator and wet the particles in the same way. Then slowly and evenly add CaO2 (pre-ground into powder) to coat the surface of the particles in S2. During the granulation process, continuously take out the particles for sieving. When particles with a particle size of 3.6 to 3.8 mm are obtained, the CaO2 coating operation is ended and the particles are collected for later use.

[0091] S4, Encapsulation Filler Layer

[0092] Adjust the speed of the round pot granulator to 30 r / min and the heating device to 40℃. Put all the particles in S3 into the round pot granulator and wet the particles in the same way. Then slowly and evenly add attapulgite clay (40g in total) to coat the particles in S3 (to isolate the oxygen source layer and the coating layer). During granulation, continuously take out the particles for sieving. When the particle size is 3.8 to 4.0 mm, the coating operation is completed and the particles are collected for later use.

[0093] S5, Encapsulation / Encapsulation Layer

[0094] Adjust the speed of the round pot granulator to 30 r / min and the heating device to 60℃. Put all the granules from S4 into the round pot granulator. Pour the coating agent polyacrylate emulsion into the spraying device and slowly spray it onto the surface of the granules in a water mist manner (2 ml / min) until all 30 g of polyacrylate emulsion has been sprayed. Take out the formed slow-release oxygen fertilizer granules and place them in an oven at 60℃ until the granules are completely dried. Take them out and cool them to 20-30℃ to obtain the slow-release oxygen fertilizer. Seal and store them in a dark environment.

[0095] The morphology and cross-sectional diagram of the slow-release oxygen fertilizer product obtained in this embodiment are shown below. Figure 2 As shown, from the inside out, it consists of a buffer layer, an oxygen source layer, and a coating layer, with each layer separated by a filling layer.

[0096] Example 2

[0097] This embodiment provides a test of the pH regulation performance of slow-release oxygen fertilizer in water.

[0098] To investigate the effect of the slow-release oxygen fertilizer prepared in Example 1 on the pH of the aqueous solution, the following experiment was conducted:

[0099] Accurately weigh 2g of slow-release oxygen fertilizer into a clean 50ml centrifuge tube, add 40ml of ultrapure water, and designate this as the slow-release oxygen fertilizer group. Simultaneously weigh 0.66g of CaO2 powder (the amount weighed here is based on the CaO2 contained in 2g of slow-release oxygen fertilizer) into a clean 50ml centrifuge tube, add 40ml of ultrapure water, and designate this as the CaO2 group. Each treatment group has three replicates. The pH value of the aqueous solution was measured on days 0, 5, 10, 15, 30, 60, and 90.

[0100] Results Analysis: The pH changes of the aqueous solutions in the slow-release oxygen fertilizer group and the CaO2 group are as follows: Figure 3 As shown, the pH value of the CaO2 group aqueous solution ranged from 9.01 to 13.23. The pH value increased sharply in the first 5 days, then stabilized at around 13.1 until the end of the experiment, indicating a strongly alkaline solution. The pH value of the slow-release oxygen fertilizer group aqueous solution fluctuated between 6.52 and 8.97, showing a slow increasing trend in the first 30 days, stabilizing at around 8.8 after the 30th day. Compared with the CaO2 group, the pH value of the slow-release oxygen fertilizer group aqueous solution was significantly lower (P<0.05). This is related to the hydrolysis of urea phosphate in the slow-release oxygen fertilizer; the phosphoric acid produced by the hydrolysis of urea phosphate reacts with the OH- produced by the hydrolysis of CaO2. - A neutralization reaction occurs, which acts as a buffer and lowers the pH value of the aqueous solution to a certain extent.

[0101] In summary, slow-release oxygen fertilizer, acting as a buffer, effectively buffers the highly alkaline CaO2, maintaining the pH of the application environment within a slightly alkaline to neutral range. When applied to the soil, it does not significantly impact soil acidity or alkalinity. Combined with the soil's own buffering capacity, long-term application will not lead to soil compaction or salinization. Simultaneously, the N, P, and K nutrients contained in the buffering compound fertilizers urea phosphate and potassium fertilizer provide nourishment for crops, thus integrating soil remediation into crop production management.

[0102] Example 3

[0103] This embodiment provides a test of the oxygen release performance of slow-release oxygen fertilizer.

[0104] To investigate the oxygen release of the slow-release oxygen fertilizer prepared in Example 1 in aqueous solution, the following experiment was conducted:

[0105] Accurately weigh 2g of slow-release oxygen fertilizer into a clean 50ml centrifuge tube, add 40ml of ultrapure water, and record this as the slow-release oxygen fertilizer group; weigh 0.66g of CaO2 powder (as in Example 2, 2g of slow-release oxygen fertilizer contains 0.66g of CaO2) into a clean 50ml centrifuge tube, add 40ml of ultrapure water, and record this as the CaO2 group; simultaneously, add 40ml of ultrapure water to a clean 50ml centrifuge tube as the blank control group (no CaO2 or slow-release oxygen fertilizer added). Each treatment group has 3 replicates. The dissolved oxygen (DO) content of the aqueous solution is measured on days 0, 5, 10, 15, 30, 60, and 90, and the average dissolved oxygen value of the pure water blank control group is calculated. The dissolved oxygen values ​​of the CaO2 group and the slow-release oxygen fertilizer group are subtracted from the average value of the blank control group, and the net dissolved oxygen value is recorded.

[0106] Results Analysis: The changes in net dissolved oxygen content in the aqueous solutions of the CaO2 group and the slow-release oxygen fertilizer group are as follows: Figure 4 As shown in the figure, the net dissolved oxygen content in the CaO2 group ranged from 0.05 to 7.38 mg / L, reaching a peak of 7.38 mg / L within 15 to 20 days, and then rapidly decreasing between 20 and 30 days, exhibiting a trend of first rapidly rising and then rapidly falling. The net dissolved oxygen content in the slow-release oxygen fertilizer group ranged from 0.06 to 4.78 mg / L, reaching a peak of 4.78 mg / L on day 10, stabilizing at around 4.1 mg / L within 10 to 30 days, and then showing a slow decreasing trend. Compared with the CaO2 group, the dissolved oxygen change trend in the slow-release oxygen fertilizer group was more stable, without any explosive release or rapid decline of oxygen. Its high dissolved oxygen level persisted until day 60, achieving the effect of slowing down the oxygen release rate. These results indicate that the slow-release oxygen fertilizer of this invention achieves a stable and slow release of oxygen.

[0107] Example 4

[0108] This embodiment provides the effect of slow-release oxygen fertilizer on the behavior of total mercury (THg) in soil solution and methylmercury (MeHg) in soil.

[0109] Specifically, using typical mercury-contaminated farmland soil from Lanmuchang, Qiannan Prefecture, Guizhou Province as the test subject, 20g of air-dried soil (passed through a 4mm sieve) was weighed into 50mL centrifuge tubes. A control group (no additives) and a slow-release oxygen fertilizer treatment group (1% by mass, i.e., 0.2g of slow-release oxygen fertilizer added per tube) were set up, with three replicates for each treatment group. 40mL of oxygen-free ultrapure water (water-to-soil ratio 2:1) purged with nitrogen for 2 hours was added, and the mixture was placed in an anaerobic glove box for 3 days to establish an anaerobic reducing environment, followed by sealed in the dark for incubation. During this period, the mixture was manually shaken twice daily to ensure uniform reaction. Soil and supernatant samples were collected at 1, 7, 14, 30, 60, and 90 days to analyze the THg content in the soil solution and the MeHg content in the soil.

[0110] Results analysis:

[0111] The characteristics of THg content changes over time are as follows: Figure 5 As shown, the THg concentration in the soil solution of the control group ranged from 1.86 to 4.98 μg / L, showing a trend of first decreasing and then increasing; while the THg concentration in the slow-release oxygen fertilizer group was significantly reduced, ranging from only 0.18 to 0.37 μg / L, and remained at a low level. The average THg concentration was reduced by 93% compared with the control group, indicating that the slow-release oxygen fertilizer in this invention significantly inhibited the dissolution and activation process of mercury in the soil.

[0112] The characteristics of MeHg content changes over time, such as... Figure 6 As shown, the concentration of methylmercury in the soil of the control group ranged from 1.95 to 24.86 μg / kg, showing a continuous upward trend; the concentration of MeHg in the slow-release oxygen fertilizer group remained between 0.71 and 1.96 μg / kg, and the MeHg concentration on day 90 was reduced by 95% compared with the control group, indicating that the slow-release oxygen fertilizer in this invention significantly inhibited the mercury methylation process under anaerobic conditions.

[0113] In summary, the slow-release oxygen fertilizer developed in this invention possesses multiple functions, including slow-release and controlled oxygen release, acid-base buffering, and nutrient supply. Therefore, it is suitable for acid- and alkaline-sensitive crops and can be applied to various crop soils to promote crop growth. Furthermore, when applied to mercury-contaminated soils, it significantly inhibits the formation of reactive mercury and methylmercury in the soil solution, achieving both mercury pollution control and agronomic production goals. This demonstrates significant technological innovation and potential for widespread application.

Claims

1. A slow-release oxygen fertilizer, characterized in that, The slow-release oxygen fertilizer comprises, from the inside out, a buffer layer, an oxygen source layer, and a coating layer, with each layer separated by a filler layer. The buffer layer includes a buffer compound fertilizer and an adhesive, and the compound fertilizer includes at least urea phosphate. The oxygen source layer includes a chemical oxygenating agent and an adhesive. The coating layer includes a polymer resin. The filler layer includes a filler and an adhesive.

2. The slow-release oxygen fertilizer according to claim 1, characterized in that, The buffer compound fertilizer includes urea phosphate and potassium fertilizer.

3. The slow-release oxygen fertilizer according to claim 2, characterized in that, The mass ratio of urea phosphate to potassium fertilizer is (6.0-7.0):

1.

4. The slow-release oxygen fertilizer according to any one of claims 1-3, characterized in that, The chemical oxygenating agent includes calcium peroxide.

5. The slow-release oxygen fertilizer according to claim 4, characterized in that, The polymeric resin includes polyacrylate.

6. The slow-release oxygen fertilizer according to claim 5, characterized in that, The mass ratio of the buffer compound fertilizer, chemical oxygenating agent and polymer resin is (0.9-1):1:(0.2-0.4).

7. The slow-release oxygen fertilizer according to claim 6, characterized in that, The filler includes attapulgite.

8. The slow-release oxygen fertilizer according to claim 7, characterized in that, The adhesive includes sodium alginate.

9. The method for preparing the slow-release oxygen fertilizer according to any one of claims 1-8, characterized in that, The method includes the following steps: S1. Preparation of buffer layer particles The uniformly mixed buffer compound fertilizer is fed into a granulator, moistened with an adhesive, granulated and screened to obtain buffer layer particles with a particle size of 2.0 to 2.2 mm. S2, Encapsulation Filler Layer The buffer layer particles in S1 are fed into a granulator, wetted with an adhesive, and then filled with a filler. After granulation and screening, particles with a surface coating and filling layer with a particle size of 2.4 to 2.6 mm are obtained. S3, Encapsulated oxygen source layer The particles with the surface coating filling layer in S2 are fed into a granulator, wetted with an adhesive, and a chemical oxygenating agent is added. After granulation and screening, particles with a surface coating oxygen source layer with a particle size of 3.6 to 3.8 mm are obtained. S4, Encapsulation Filler Layer The particles with the surface-coated oxygen source layer in S3 are fed into a granulator, wetted with an adhesive, and then filled with a filler. After granulation and screening, particles with a surface-coated filling layer with a particle size of 3.8 to 4.0 mm are obtained. S5, Encapsulation / Encapsulation Layer The particles with the surface coating and filling layer in S4 are fed into a granulator, and the coating agent is applied to the surface of the particles. After drying, a slow-release oxygen fertilizer is obtained.

10. The use of the slow-release oxygen fertilizer according to any one of claims 1-8 in inhibiting mercury activation and / or mercury methylation in soil.

Images