Double-source humic acid biological slow-release compound fertilizer complexed with nitrogen, phosphorus, potassium and medium trace elements and preparation method of double-source humic acid biological slow-release compound fertilizer

Abstract

The double-source humic acid biological slow-release compound fertilizer comprises the following components in percentage by mass: 15%-45% of nitrogen, phosphorus and potassium (NPK) in total, 5%-15% of medium trace elements in total, 10%-30% of mineral source nitro humic acid, 10%-50% of high-carbon biological organic fertilizer (organic matter is more than or equal to 30%), 5%-10% of potassium nitrate, 5%-10% of potassium nitrate, 5%-10% of potassium nitrate, 5%-10% of potassium nitrate, 5%-10% of potassium nitrate, 5%-10% of potassium nitrate the medium trace elements comprise at least three of calcium, magnesium, sulfur, iron, zinc, boron and molybdenum; according to the compound fertilizer, mineral source nitro humic acid is combined with NPK and medium trace elements through a step-by-step complexing process, a high-carbon bio-organic fertilizer is mixed, and a coated controlled release technology is adopted; through a step-by-step complexing process (nitrogen phosphorus first and then potassium and medium trace elements), stable combination of double-source humic acid, NPK and chelated trace elements is realized, ion antagonism is avoided, the nutrient utilization rate is improved, quick-acting and long-acting fertility is achieved, full-effect disease prevention is achieved, soil fertility is improved, soil is improved, and reduction and synergism of chemical fertilizers and pesticides are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of ore-source nitro humic acid compound fertilizers, in particular to a double-source humic acid biological slow-release compound fertilizer complexing nitrogen, phosphorus, potassium and medium and trace elements and a preparation method thereof. Background Art

[0002] In recent years, due to the extensive use of chemical fertilizers and pesticides, phenomena such as salinization, soil acidification, hardening, degradation, aggravated heavy metal pollution, and nutrient loss have occurred, the water and fertilizer retention capacity has decreased, and the growth environment of crops has been continuously deteriorating. The extensive application of chemical fertilizers has doubled the per-acre cost of crops, the fertilizer efficiency utilization rate has decreased year by year, and the nutrient loss and fixed fertilizers have also had a certain impact on the environment. Ore-source nitro humic acid is a kind of humic acid, containing a certain amount of active carbon, and has higher activity than other types of humic acids. It has remarkable effects in improving the physical and chemical properties of soil, increasing soil fertility, enhancing soil water retention capacity, promoting crop photosynthesis, improving crop quality, reducing the harm of various crop diseases and pests, and the heavy metal content in crop products.

[0003] Traditional compound fertilizers are mainly composed of nitrogen, phosphorus, and potassium (NPK), but the addition of medium and trace elements (such as calcium, magnesium, sulfur, iron, zinc, etc.) is insufficient or the form is unstable, resulting in crop nutrient imbalance and frequent occurrence of physiological diseases; at the same time, traditional compound fertilizers mainly composed of nitrogen, phosphorus, and potassium (NPK) lack a good soil cycle, that is, the soil maintains a dynamic balance in physical, chemical, and biological properties, and the C necessary to support plant growth and the multifunctionality of the ecosystem. It has no obvious effect on the treatment of saline-alkali soil and heavy metal-polluted soil, and the repair of acidified, hardened, and degraded soil, and there is an aggravating trend; in addition. In the conventional process, the simple mixing of humic acid and inorganic nutrients is prone to complexation failure due to pH value fluctuations or ion competition, reducing nutrient utilization rate; when ore-source nitro humic acid is directly compounded with high-concentration NPK, its active functional groups are easily saturated by excessive metal ions and are difficult to stably combine. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of low nutrient utilization rate caused by complexation failure and difficult stable combination existing in the existing ore-source nitro humic acid compound fertilizers, and to provide a double-source humic acid biological slow-release compound fertilizer complexing nitrogen, phosphorus, potassium and medium and trace elements and a preparation method thereof.

[0005] A double-source humic acid biological slow-release compound fertilizer complexing nitrogen, phosphorus, potassium and medium and trace elements contains the following components and mass percentages: the total amount of nitrogen, phosphorus, and potassium (NPK) is 15% - 45%, the total amount of medium and trace elements is 5% - 15%, the ore-source nitro humic acid is 10% - 30%, and the high-carbon biological organic fertilizer (organic matter ≥ 30%) is 10% - 50%. The medium and trace elements include at least three of calcium, magnesium, sulfur, iron, zinc, boron, and molybdenum;

[0006] The compound fertilizer combines mineral-source nitrohumic acid with NPK and medium and trace elements through a step-by-step complexation process, mixes high-carbon biological organic fertilizer, and adopts a coating-controlled release technology;

[0007] The mineral-source nitrohumic acid is prepared through the following steps:

[0008] S1.1: Using lignite or weathered coal as raw materials, after crushing, washing, and drying, grind to more than 80 meshes;

[0009] S1.2: Mix the ground material in S1.1 with nitric acid with a mass concentration of 10% - 25% at a mass ratio of 1:3, react at 60°C for 2 hours, and neutralize to pH 6.0 to obtain a mineral-source nitrohumic acid solution;

[0010] The step-by-step complexation process includes:

[0011] S2.1: First-stage nitrogen and phosphorus complexation: Mix the mineral-source nitrohumic acid solution and monoammonium phosphate at a mass ratio of 2:1, adjust the pH to 4.5 - 5.5, and stir and react at 60°C for 1 hour;

[0012] S2.2: Second-stage potassium and medium and trace element integration: Sequentially add potassium sulfate, magnesium sulfate, calcium nitrate, sodium molybdate, borax, and chelated trace elements to the product of step S2.1, control the temperature at 50°C and the pH at 5.0 - 6.0, and react for 2 hours.

[0013] Furthermore, the chelated trace elements are at least one of Fe-EDTA and Zn-EDTA, and the addition amount is 0.5% - 2% of the total mass of the compound fertilizer.

[0014] Furthermore, the coating-controlled release technology is: Spray a polyacrylate coating on the surface of the granules formed by granulation, and add sulfur powder accounting for 5% of the mass of the coating layer; The particle size of the fertilizer granules is 2 - 4 mm, and the moisture content ≤ 3%.

[0015] A preparation method of a complexed nitrogen, phosphorus, potassium and medium and trace element dual-source humic acid biological slow-release compound fertilizer includes the following steps:

[0016] S1: Preparation of mineral-source nitrohumic acid;

[0017] S2: Complex nitrogen, phosphorus, potassium and medium and trace elements in stages;

[0018] S3: Add high-carbon biological organic fertilizer to the product of step S2, and stir and mix;

[0019] S4: Spray drying, granulation and coating treatment.

[0020] Furthermore, the granulation treatment is: Spray dry the complexed slurry and mix it with a sodium lignosulfonate binder, and extrude and granulate to form granules with a particle size of 2 - 4 mm.

[0021] Further, in the coating treatment, the thickness of the polyacrylate coating is 50-100 μm, and the nitrogen release period of the fertilizer in water at 25°C after coating is 60-90 days.

[0022] The beneficial effects of the present invention are as follows:

[0023] (1) Through the dual-source combination of mineral-source nitrohumic acid and high-carbon bio-organic fertilizer, an organic-inorganic composite slow-release system is formed: Mineral-source nitrohumic acid contains active functional groups (carboxyl group, phenolic hydroxyl group) that can complex NPK and medium and trace elements, reducing nutrient loss; High-carbon bio-organic fertilizer provides a carbon source and a rich high-activity microbial flora, synergistically with humic acid to improve the soil aggregate structure and enhance the water and fertilizer retention capacity.

[0024] (2) Through the stepwise complexation process (nitrogen and phosphorus first, then potassium and medium and trace elements), the stable combination of mineral-source nitrohumic acid with NPK and chelated trace elements is achieved, avoiding ion antagonism, improving nutrient utilization efficiency, and having both quick-acting and long-acting fertility.

[0025] (3) Through the polyacrylate / sulfur composite coating, through the synergistic action of hydrophobicity and microporous diffusion, the nitrogen is slowly released within 60-90 days, reducing volatilization and leaching. Even with a 20% reduction in the application rate compared to ordinary compound fertilizers, the same yield increase effect can still be maintained.

[0026] (4) In this scheme, the highly active carboxyl and phenolic hydroxyl functional groups of mineral-source nitrohumic acid can passivate heavy metals and enhance the soil aggregate structure. Combined with chelated Fe / Zn, it promotes crop photosynthesis and the expression of stress-resistant genes, increasing the yield of crops in saline-alkali land.

[0027] (5) By using extrusion granulation (particle size 2-4 mm) and sodium lignosulfonate binder, the granules have relatively high compressive strength, and the drying energy consumption is reduced; The sulfur powder accounts for 5% in the coating material, providing sulfur elements while controlling release, and realizing the efficient utilization of functional fillers.

[0028] (6) By increasing the high-carbon bio-organic fertilizer by 10%-50%, it replenishes active carbon in the soil, increases the content of active carbon in the soil, maintains the soil's benign cycle, keeps the soil in a dynamic balance in terms of physical, chemical, and biological properties, supports the healthy growth of plants, and the ecosystem contributes to the multi-functionality of full nutrition. It has a significant effect in the treatment of saline-alkali soil and heavy metal-polluted soil, and the restoration of acidified and degraded soil, low-yield farmland, and degraded grassland.

[0029] (7) The use of this compound fertilizer is of great significance for achieving "no repeated salt and alkali return in saline-alkali soil, no acidification in southern soil, no degradation in grasslands, and no excessive heavy metal content in agricultural products", and has a boosting effect on achieving the vision of "enhancing soil fertility, increasing grain yield, reducing the use of chemical fertilizers and pesticides, and building a modern intelligent agricultural ecological chain". Detailed implementation mode

[0030] The following uses specific specific examples to illustrate the implementation mode of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation modes. The details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0031] Example 1

[0032] A preparation method of a complex nitrogen, phosphorus, potassium and medium and trace element dual-source humic acid biological slow-release compound fertilizer includes the following steps:

[0033] S1: Preparation of mineral source nitrohumic acid, and the mineral source nitrohumic acid is prepared through the following steps:

[0034] S1.1: Take lignite (humic acid content ≥ 60%) and crush it to a particle size ≤ 5 mm, wash it 3 times with deionized water to remove ash, and grind it to 100 meshes after drying;

[0035] S1.2: Mix the ground lignite with 20% nitric acid according to a mass ratio of 1:3, react at 60 °C for 2 hours, and neutralize with potassium hydroxide to pH 6 to obtain a mineral source nitrohumic acid solution (carboxyl content 4.2 mmol / g, solid content 30%).

[0036] S2: Complex nitrogen, phosphorus, potassium and medium and trace elements in stages, and the step-by-step complexing process includes:

[0037] S2.1: First-stage nitrogen and phosphorus complexing: Mix the mineral source nitrohumic acid solution and monoammonium phosphate according to a mass ratio of 2:1, adjust the pH to 5 with citric acid, and stir and react at 60 °C for 1 hour to form a nitrogen-phosphorus-humic acid complex;

[0038] S2.2: Second-stage potassium and medium and trace element integration: Add potassium sulfate, magnesium sulfate, calcium nitrate, sodium molybdate, borax and Fe-EDTA to step S2.1, control the temperature at 50 °C and pH 5.5, and react for 2 hours to obtain a complex slurry;

[0039] S3: Add high-carbon biological organic fertilizer to the complex slurry and stir and mix;

[0040] S4: Spray drying, granulation and coating treatment; Spray drying granulation: Spray dry the complex slurry (inlet air temperature 180 °C, outlet air temperature 80 °C), mix it with sodium lignosulfonate (addition amount 5%) and then extrude and granulate to obtain particles with a particle size of 3 mm;

[0041] Coated controlled release treatment: Using a fluidized bed coater, polyacrylate (containing 5% sulfur powder) is sprayed on the surface of the granules to form a coating layer with a thickness of 80 μm, and the final moisture content ≤ 2%.

[0042] In this solution, the raw material ratio (mass percentage): total NPK: 30% (nitrogen 12%, phosphorus 8%, potassium 10%); medium and trace elements: 10% (magnesium sulfate 3%, calcium nitrate 4%, borax 2%, sodium molybdate 1%); mineral source nitrohumic acid: 20% (lignite raw material, nitric acid concentration 20%), high-carbon bio-organic fertilizer (organic matter 45%): 40%, chelated trace element Zn-EDTA 1.5% (accounting for the total mass of the compound fertilizer); coating material: polyacrylate (coating layer thickness 80 μm, containing 5% sulfur powder).

[0043] Example 2

[0044] A preparation method of a complex nitrogen, phosphorus, potassium and medium and trace element dual-source humic acid bio-sustained release compound fertilizer, comprising the following steps:

[0045] S1: Preparation of mineral source nitrohumic acid, and the mineral source nitrohumic acid is prepared by the following steps:

[0046] S1.1: Take weathered coal (humic acid content ≥ 60%) and crush it to a particle size ≤ 5 mm, wash it 3 times with deionized water to remove ash, and grind it to 100 mesh after drying;

[0047] S1.2: Mix the ground weathered coal with 15% nitric acid at a mass ratio of 1:3, react at 60 °C for 2 hours, and neutralize with potassium hydroxide to pH 6 to obtain a mineral source nitrohumic acid solution (carboxyl content 4.2 mmol / g, solid content 30%).

[0048] S2: Complex nitrogen, phosphorus, potassium and medium and trace elements in stages, and the step-by-step complexation process includes:

[0049] S2.1: First-stage nitrogen and phosphorus complexation: Mix the mineral source nitrohumic acid solution and monoammonium phosphate at a mass ratio of 2:1, adjust the pH to 4.8 with citric acid, and stir and react at 60 °C for 1 hour to form a nitrogen and phosphorus-humic acid complex;

[0050] S2.2: Second-stage potassium and medium and trace element integration: Add 2.5% magnesium sulfate, 3% calcium nitrate and Fe-EDTA to step S2.1, control the temperature at 50 °C and pH 5.8, and react for 2 hours to obtain a complex slurry;

[0051] S3: Add high-carbon bio-organic fertilizer to the complex slurry and stir and mix;

[0052] S4: Spray drying, granulation and coating treatment; Spray drying granulation: Spray dry the complex slurry (inlet air temperature 180°C, outlet air temperature 80°C), mix it with sodium lignosulfonate (addition amount 5%), and then extrude and granulate to obtain particles with a particle size of 2.5 mm;

[0053] Coating controlled release treatment: Using a fluidized bed coater, spray polyacrylate (containing 5% sulfur powder) on the surface of the particles to form a coating layer with a thickness of 60 μm, and the final moisture content ≤ 2%.

[0054] In this solution, the raw material ratio (mass percentage): Total amount of NPK: 40% (nitrogen 10%, phosphorus 5%, potassium 25%); Medium and trace elements: 8% (magnesium sulfate 5%, calcium nitrate 3%); Mineral source nitrohumic acid: 25% (weathered coal raw material, nitric acid concentration 15%), high-carbon biological organic fertilizer (organic matter 45%): 27%, chelated trace element Zn-EDTA 0.8% (accounting for the total mass of the compound fertilizer); Coating material: polyacrylate (coating layer thickness 60 μm, containing 5% sulfur powder).

[0055] Example 3

[0056] A preparation method of a complex nitrogen, phosphorus, potassium and medium and trace element dual-source humic acid biological slow-release compound fertilizer, comprising the following steps:

[0057] S1: Preparation of mineral source nitrohumic acid, and the mineral source nitrohumic acid is prepared by the following steps:

[0058] S1.1: Take weathered coal (humic acid content ≥ 60%) and crush it to a particle size ≤ 5 mm, wash it 3 times with deionized water to remove ash, and grind it to 100 mesh after drying;

[0059] S1.2: Mix the ground weathered coal with 25% nitric acid according to a mass ratio of 1:3, react at 60°C for 2 hours, and neutralize it with potassium hydroxide to pH 6 to obtain a mineral source nitrohumic acid solution (carboxyl content 4.2 mmol / g, solid content 30%).

[0060] S2: Complex nitrogen, phosphorus, potassium and medium and trace elements in stages, and the step-by-step complex process includes:

[0061] S2.1: First-stage nitrogen and phosphorus complexation: Mix the mineral source nitrohumic acid solution and monoammonium phosphate according to a mass ratio of 2:1, adjust the pH to 4.8 with citric acid, and stir and react at 60°C for 1 hour to form a nitrogen and phosphorus-humic acid complex;

[0062] S2.2: Second-stage potassium and medium and trace element integration: Add magnesium sulfate, calcium nitrate, borax, Fe-EDTA, and Zn-EDTA to step S2.1, control the temperature at 50°C and pH 5.8, and react for 2 hours to obtain a complex slurry;

[0063] S3: Add high-carbon biological organic fertilizer to the complex slurry and stir to mix.

[0064] S4: Spray drying, granulation and coating treatment; Spray drying and granulation: Spray dry the complex slurry (inlet air temperature 180°C, outlet air temperature 80°C), mix it with sodium lignosulfonate (addition amount 5%) and then extrude granulation to obtain particles with a particle size of 2.5 mm.

[0065] Coating and controlled release treatment: Use a fluidized bed coater to spray polyacrylate (containing 5% sulfur powder) on the surface of the particles to form a coating layer with a thickness of 70 μm, and the final moisture content ≤ 2%.

[0066] In this solution, the raw material ratio (mass percentage): Total amount of NPK: 18% (nitrogen 6%, phosphorus 5%, potassium 7%); Medium and trace elements: 15% (magnesium sulfate 5%, calcium nitrate 6%, borax 4%); Mineral source nitrohumic acid: 30% (weathered coal raw material, nitric acid concentration 25%), high-carbon biological organic fertilizer (organic matter 45%): 37%, chelated trace elements 0.8% (Zn-EDTA and Fe-EDTA 1:1, accounting for the total mass of the compound fertilizer); Coating material: polyacrylate (coating layer thickness 70 μm, containing 5% sulfur powder).

[0067] Perform index detection on Examples 1 to 3, and conduct statistics from the aspects of nitrogen release period (days, 25°C), nutrient utilization rate (%), crop yield increase rate (%), soil organic matter increment (%), soil pH adjustment ability, controlled release membrane degradation rate (90 days), and trace element availability (%) to obtain the following Table 1:

[0068] Table 1 Detection data

[0069]

[0070]

[0071] Through the analysis of Examples 1 to 3 and the results in Table 1 as follows,

[0072] (1) Nutrient release and utilization efficiency

[0073] Example 1: The nitrogen release period is 75 days, and the nutrient utilization rate is 65%, which is significantly higher than that of the control group (45%). Thanks to the complex structure of humic acid and NPK and the coating controlled release technology, the nutrient release time is extended.

[0074] Example 2: Under the high-potassium ratio (potassium 25%), the nitrogen release period is extended to 85 days, and the nutrient utilization rate reaches 68%. It is suitable for crops with high potassium requirements such as fruit trees, and the yield increase is 18% (no increase in the control group).

[0075] Example 3: The double-layer coating (polyacrylate + starch film) enables a nitrogen release period of 90 days, and the outer starch film is completely degraded in 90 days, with better environmental protection; the availability of trace elements (such as 92% iron) is significantly improved, which is suitable for nutrient-deficient soils.

[0076] In Example 3, the combination of mineral-source nitrohumic acid (30%) and high-carbon bio-organic fertilizer (37%) increases the soil organic matter by +2.5% (only +0.3% in the control group), and the water retention rate is increased by 45%, verifying the "carbon supplement" and aggregate structure improvement ability of the dual-source combination. In Example 1, through the carboxyl complexation of humic acid, the nutrient utilization rate is increased from 45% of ordinary fertilizer to 65%, and the fertilizer retention effect is significant. The reason is that the active functional groups (carboxyl group, phenolic hydroxyl group) of mineral-source nitrohumic acid adsorb NPK ions and reduce leaching; the high-carbon bio-organic fertilizer provides a carbon source for microbial metabolism, promotes the formation of humic acid-mineral complexes, and enhances the soil water retention capacity. This solution can achieve "quick-acting - slow-acting - long-acting - all-round" four-level fertilizer supply and "yield increase - quality improvement - soil improvement" multi-functional synergy through component ratio regulation, meeting the needs of different agricultural scenarios.

[0077] (2) Soil improvement effect

[0078] Increase in organic matter: In Example 3, due to high humic acid (30%) + high-carbon organic fertilizer (37%), the soil organic matter is increased by 2.5%, far exceeding the control group (+0.3%). Through the buffering effect of humic acid and neutralization of nitric acid, all examples adjust acidic soil (pH 5.5 - 6.0) to near neutral (6.1 - 6.3).

[0079] In this solution, sulfur powder only exists in the coating layer and has no direct contact with sodium lignosulfonate in the particle core, and there is no chemical interference between the two.

[0080] The comparison of the three examples shows that the combination of humic acid and high-carbon organic fertilizer synergistically improves the water and fertilizer retention capacity (+45% water retention rate in Example 3); the step-by-step complexation process avoids ion antagonism, and the nutrient utilization rate is increased by 20% - 30% (up to 72% in Example 3); coating-controlled release and reduced application: reducing application by 20% still maintains yield increase, and the sulfur element utilization rate > 85%; heavy metal passivation and stress resistance, the yield in saline-alkali land is increased by 25%, and the heavy metal exceeding standard rate < 5%; particle functional design: the compressive strength is increased by 80%, the drying energy consumption is reduced by 30%, and sulfur powder is efficiently utilized. The comprehensive results prove that this solution has achieved breakthroughs in multiple dimensions such as efficiency increase, environmental protection, and soil remediation, and is especially suitable for the sustainable development of agriculture under adverse conditions such as saline-alkali land and acidified soil.

[0081] Comparative Example 1

[0082] This Comparative Example 1 is the same as Example 1, except that for the dual-source, it uses mineral-source nitrohumic acid (20%) + ordinary organic fertilizer 40% (organic matter 15%).

[0083] Comparative Example 2

[0084] This Comparative Example 1 is the same as Example 1, except that: one-step mixing is adopted during complexation (all raw materials react synchronously, pH 6.0), and the chelated element is ferrous sulfate (1.5%).

[0085] Comparative Example 3

[0086] This Comparative Example 1 is the same as Example 1, except that: the coating process adopts ordinary resin coating (without sulfur powder, thickness 80μm); the granulation process adopts disk granulation (without binder, particle size 3mm).

[0087] Table 2: Comparison Table of Component / Process Differences between Comparative Examples and Example 1

[0088]

[0089] According to the above Comparative Examples 1 to 3, tests were respectively carried out in terms of nitrogen release period (days), nutrient utilization rate (%), soil organic matter increment (%), water retention rate improvement (%), particle compressive strength (MPa), sulfur element release rate (90 days), and trace element availability (iron %). The data in Table 3 were obtained:

[0090] Table 3: Performance Comparison between Comparative Examples and Example 1 (Key Indicators)

[0091]

[0092]

[0093] By comparing and analyzing Example 1 with Comparative Examples 1 to 4, the creative idea of this solution is further elaborated:

[0094] 1. Necessity of dual-source combination (Comparative Example 1)

[0095] After replacing the high-carbon bio-organic fertilizer (organic matter 45%) with ordinary organic fertilizer (organic matter 15%), the increment of soil organic matter is only +0.6% (it is +1.8% in Example 1), and the water retention rate drops to 10% (it is 30% in Example 1). It shows that the high organic matter content of the high-carbon bio-organic fertilizer is the key to improving the soil carbon pool and water holding capacity, and the ordinary organic fertilizer cannot achieve the "carbon supplement and fertilizer increase" synergistic effect.

[0096] 2. Superiority of the stepwise complexation process (Comparative Example 2)

[0097] After adopting a one-step mixing process (pH 6.0), iron precipitates due to the alkaline environment, and its effectiveness is only 45% (78% in Example 1), and the nutrient utilization rate drops to 52%. This shows that the step-by-step complexation stabilizes NPK and trace elements in stages by controlling pH, avoiding ion antagonism, and is the core process to improve nutrient effectiveness.

[0098] 3. Technical advantages of composite coating (Comparative Example 3)

[0099] After adopting ordinary resin coating (without sulfur powder), the nitrogen release period is shortened to 35 days (75 days in Example 1), and the sulfur element release rate is 0%. This shows that the polyacrylate / sulfur composite coating prolongs the release period through the synergism of the hydrophobic layer and micropores, and at the same time the sulfur powder provides sulfur nutrition, realizing the dual functions of "controlled release + nutrient supplement".

[0100] 4. Role of granulation process and binder (Comparative Example 3)

[0101] The compressive strength of the particles by disk granulation (without binder) is only 8 MPa (15 MPa in Example 1), and the transportation breakage rate increases by 30%. This shows that extrusion granulation + sodium lignosulfonate binder improves the particle density and strength, and reduces production energy consumption.

[0102] 5. Necessity of chelated trace elements (Comparative Example 2)

[0103] After using ferrous sulfate to replace Fe-EDTA, the iron effectiveness drops to 45% (lost due to precipitation), and the yellowing rate of crop leaves increases by 20%. This shows that chelated trace elements (such as Fe-EDTA) avoid precipitation by stabilizing the chemical state and significantly improve the absorption efficiency.

[0104] In summary, through comparative experimental data, it can be seen that the dual-source combination (humic acid + high-carbon organic fertilizer) is the core of soil improvement and water and fertilizer retention; the step-by-step complexation process is the key step to avoid ion antagonism and improve nutrient utilization rate; the composite coating technology (sulfur powder + polyacrylate) has both the value of controlled release and functional fillers; extrusion granulation + chelated trace elements ensure product stability and effectiveness from physical and chemical aspects respectively. The comparative example data reversely verifies the irreplaceability of the technical solutions in the claims, and the lack of any single innovation point will lead to a significant decline in performance.

[0105] Next, the technical idea of this solution will be further elaborated.

[0106] 1. Dynamic slow-release mechanism of dual-source humic acid system

[0107] Chemical slow release of mineral source nitrohumic acid (NHA): The nitro group (-NO2) introduced by nitrification reaction forms a multi-toothed coordination structure with carboxyl group (-COOH) and phenolic hydroxyl group (-OH), and preferentially complexes with high-valent metal ions (such as Ca 2+ 、Mg2+ ), forming humic acid-metal chelates. Such chelates dissociate in the soil through pH-dependent dissociation (stable at pH 5.0 - 7.0), gradually releasing NPK nutrients. Physical adsorption: The porous network structure of humic acid can adsorb NH4 + 、NO3 - and other ions, reducing their migration rate in the soil solution.

[0108] High-carbon bio-organic fertilizer (HBOF) Microbial-driven slow release: EM bacteria, Bacillus amyloliquefaciens, Trichoderma and other bacteria in the organic fertilizer secrete extracellular enzymes (such as urease, phosphatase), gradually decomposing the insoluble nutrients (such as calcium magnesium phytate) in the organic matter and releasing absorbable NPK. Carbon-nitrogen synergy: High carbon content (C / N ratio > 20) delays the mineralization rate of nitrogen by microorganisms, avoiding the concentrated release of nitrogen in the short term.

[0109] Synergistic effect: NHA and HBOF form a "chemical complexation - microbial decomposition" two-stage slow-release system. The humic acid complex is further degraded under the action of microorganisms, realizing the matching of the nutrient release period with the fertilizer requirement of crops.

[0110] 2. Chelation stabilization of medium and trace elements

[0111] Chelated trace elements (Fe-EDTA / Zn-EDTA), the six-tooth coordination structure of EDTA forms a stability constant with Fe 3+ 、Zn 2+ , avoiding their fixation as hydroxide or phosphate precipitates in the soil. In the stepwise complexation process, high-concentration phosphate (PO4 3- ) is first complexed with NH4 + to form (NH4)3PO4-HA complex, and then chelated micro-fertilizer is introduced to eliminate the competition of polyvalent ions, improving the effectiveness of micro-fertilizer.

[0112] This scheme adopts the ion selectivity of staged pH regulation. In the first stage (nitrogen and phosphorus complexation, pH 4.5 - 5.5), under acidic conditions, the degree of protonation of the carboxyl group of humic acid decreases (pKa≈4.5), preferentially binding to NH4 + through ionic bonds, and at the same time forming a hydrogen bond network with PO4 3- to generate a three-dimensional cross-linked humic acid-nitrogen and phosphorus complex. Controlling pH < 5.5 can inhibit the premature precipitation of divalent ions such as Ca 2+ 、Mg 2+ (the solubility product of their hydroxides drops sharply at pH > 6.0).

[0113] In the second stage (potassium and trace element integration, pH 5.0 - 6.0), the pH is slightly adjusted to near neutrality, deprotonating the phenolic hydroxyl group of humic acid, exposing more ligand sites, and binding to K +A weak coordination bond (bond energy about 50 - 100 kJ / mol) is formed to achieve the slow release of potassium. Fe-EDTA remains stable within this pH range (Fe-EDTA does not dissociate when pH > 4.0), avoiding the hydrolysis loss of free Fe 3+ .

[0114] (3) The mechanism of action of the multi-stage coating controlled release technology, the diffusion - erosion coupling controlled release of the polyacrylate coating, diffusion control: The coating layer (50 - 100 μm) acts as a semi-permeable membrane, and water penetrates into the interior of the particles through the micropores (diameter 1 - 10 nm) in the membrane, and the dissolved nutrients diffuse outwards along the concentration gradient. Erosion control: Soil microorganisms secrete esterase to degrade the ester bonds of polyacrylate, and the membrane layer gradually disintegrates, and the release rate accelerates in the later stage, forming a two-phase release mode of "slow release in the initial stage - rapid release in the later stage". Sulfur (S 0 ) is oxidized to SO4 2- in the soil by Thiobacillus, and the reaction formula is:

[0115] 2S 0 + 3O2 + 2H2O → 2H2SO4 (Thiobacillus)

[0116] The generated H2SO3 locally acidifies the membrane layer, corrodes to form micropores (pore diameter expands to 50 - 200 nm), and the release rate is increased by 2 - 3 times. By adjusting the sulfur addition amount (5% - 7%), the micropore density is controlled, and the release period can be adjusted within 60 - 90 days.

[0117] In summary, this compound fertilizer realizes the precise matching of nutrient release and crop requirements through the triple slow release mechanisms of "chemical complexation - microbial decomposition - physical barrier", combined with the ion selectivity control of stepwise complexation and the dynamic regulation technology of sulfur micropores. At the same time, the humic acid - bio-organic fertilizer is used to synergistically improve the soil micro-ecology to achieve the goal of "reducing fertilizer application and increasing efficiency".

[0118] The above-described embodiments merely represent the specific implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A biological slow-release compound fertilizer of complex nitrogen, phosphorus, potassium and medium and trace elements dual-source humic acid, characterized in that: The invention comprises the following components and mass percentages: 15% to 45% of the total amount of nitrogen, phosphorus and potassium (NPK), 5% to 15% of the total amount of medium and trace elements, 10% to 30% of mineral nitro humic acid, and 10% to 50% of high-carbon biological organic fertilizer (organic matter ≥ 30%), wherein the medium and trace elements include at least three of calcium, magnesium, sulfur, iron, zinc, boron and molybdenum; The compound fertilizer combines mineral nitrohumic acid with NPK and medium and trace elements through a step-by-step complexation process, mixes high-carbon biological organic fertilizer, and adopts coating controlled release technology; The mineral-source nitro humic acid is prepared by the following steps: S1.1: Use lignite or weathered coal as raw material, grind to 80 mesh or above after crushing, washing, drying; S1.2: The ground material in S1.1 is mixed with nitric acid having a mass concentration of 10% to 25% in a mass ratio of 1:3, reacted at 60°C for 2 hours, and neutralized to pH 6.0 to obtain a mineral-derived nitro humic acid solution; The step-by-step complexing process comprises: S2.1: The first stage of nitrogen-phosphorus complexation: Mix the mineral nitro humic acid solution and monoammonium phosphate in a mass ratio of 2:1, adjust the pH to 4.5-5.5, and stir the reaction at 60°C for 1 hour; S2.2: Second stage potassium and trace element integration: potassium sulfate, magnesium sulfate, calcium nitrate, sodium molybdate, borax and chelated trace elements are added to the product of step S2.1 in sequence, the temperature is controlled at 50°C, pH 5.0-6.0, and the reaction is carried out for 2 hours.

2. The biological slow-release compound fertilizer of complex nitrogen, phosphorus, potassium and medium and trace elements dual-source humic acid according to claim 1, characterized in that: The chelated trace element is at least one of Fe-EDTA and Zn-EDTA, and the added amount is 0.5% to 2% of the total mass of the compound fertilizer.

3. The biological slow-release compound fertilizer of complex nitrogen, phosphorus, potassium and medium and trace elements dual-source humic acid according to claim 1, characterized in that: The coating controlled release technology is as follows: spraying a polyacrylate coating on the surface of the granules formed by granulation, and adding sulphur powder accounting for 5% of the coating layer mass; the fertilizer granule diameter is 2-4mm, and the moisture content is ≤3%.

4. A method for preparing a biological slow-release compound fertilizer of complex nitrogen, phosphorus, potassium and medium and trace elements dual-source humic acid according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1: Preparation of mineral-derived nitrohumic acid; S2: complex nitrogen, phosphorus, potassium and trace elements in stages; S3: adding high carbon bio-organic fertilizer to the product of step S2, and stirring and mixing; S4: spray drying, granulation and coating treatment.

5. The preparation method according to claim 4, characterized in that: The granulation treatment comprises the following steps: spray-drying the complex slurry and mixing it with a sodium lignin sulfonate binder, and then extruding and granulating the slurry to form particles with a particle size of 2 to 4 mm.

6. The preparation method according to claim 4, characterized in that: In the coating treatment, the thickness of the polyacrylate coating is 50 to 100 μm, and the nitrogen release period of the coated fertilizer in 25° C. water is 60 to 90 days.

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