Anti-leaching nutrient slow-release synergistic compound fertilizer and preparation method thereof

Abstract

The invention discloses an anti-leaching nutrient slow-release synergistic compound fertilizer, and particularly discloses an anti-leaching nutrient slow-release synergistic compound fertilizer and a preparation method thereof. The compound fertilizer comprises the following components in parts by weight: 30-50 parts of urea particles, 15-25 parts of monoammonium phosphate, 20-30 parts of potassium sulfate, 2-5 parts of a slow-release synergistic coating agent, 1-3 parts of a bonding wrapping layer and 10-20 parts of a filling material. The slow-release synergistic coating agent comprises polyaspartic acid (PASP) and a composite inhibitor (a urease inhibitor and a nitrification inhibitor), and the bonding wrapping layer is made of a polyvinyl alcohol / sodium polyethylene acid-based cementing material. The preparation method comprises the following steps: mixing and granulating raw materials, carrying out primary coating (slow-release synergist), carrying out secondary coating (bonding a coating layer), and drying and screening. Through the synergistic effect of the double coating technology and the compound inhibitor, the nitrogen conversion and release are obviously delayed, the nutrient leaching loss is reduced by 20-40%, the fertilizer utilization rate is improved by 25-30%, and the compound fertilizer is suitable for high-temperature and rainy areas.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural fertilizers, and in particular to an anti-leaching nutrient slow-release synergistic compound fertilizer and a preparation method thereof. Background Art

[0002] In tropical and subtropical regions, high temperatures and high rainfall lead to nitrogen losses from traditional fertilizer applications through ammonia volatilization and nitrification leaching. Phosphorus is fixed in the soil, resulting in a utilization rate of only 30%-35%. Existing slow-release fertilizers often use sulfur coatings or resin coatings, which are costly and difficult to degrade. Single inhibitors, such as NBPT, have limited effectiveness in inhibiting nitrification. Existing technologies combine polyaspartic acid (PASP) with urease inhibitors, but this lacks protection for phosphorus and potassium. Encapsulated compound inhibitor fertilizers have been developed, but these do not address the issue of stable PASP loading. Therefore, a low-cost, highly effective slow-release technology that prevents leaching is urgently needed. Summary of the Invention

[0003] The present invention relates to a leaching-proof nutrient slow-release synergistic compound fertilizer and a preparation method thereof. Aiming at the technical pain points of severe fertilizer leaching loss and low utilization rate in hot and rainy areas, the invention realizes a triple leaching-proof mechanism through an innovative formula structure and preparation process: 1. Design of synergistic sustained-release system Biochemical inhibition layer: The first polyaspartic acid (PASP) + ternary compound inhibitor combination: NBPT (urease inhibitor): Delays urea hydrolysis by 48-72 hours (twice as long as a single inhibitor) DCD+DMPP (dual-channel nitrification inhibitor): extends the retention time of ammonium nitrogen to more than 30 days.

[0004] Physical barrier layer: Double-layer membrane structure: Inner layer: PASP / inhibitor ethanol solution is sprayed in a fluidized bed (70℃ atomization) to form a microporous sustained-release layer Outer layer: polyvinyl alcohol (PVA) / sodium polyacrylate (PAAS) adhesive film (viscosity 3000 mPa·s) 2. Prevent phosphorus fixation breakthrough Calcium hydroxide synergistic mechanism: By adding 10-20% calcium hydroxide to the coating layer and maintaining a pH microenvironment of 7.5-8.0 on the particle surface, the effective utilization rate of phosphorus in monoammonium phosphate was increased by 28% (compared to the group without addition). Compared with the prior art, the present invention has the following beneficial effects: 1. Nutrient anti-leaching performance Nitrogen leaching rate decreased by 56%:

[0005] N2O emissions reduced by 62.5% 2. Fertilizer utilization rate jumps, nitrogen utilization rate reaches 58.2% (84% higher than conventional fertilizer): PASP promotes root absorption: potassium ion transport speed increased by 3 times Triple inhibitors extend the effective period of fertilizer to 120 days (meeting the needs of the entire growth period of single-season crops) The effective utilization rate of phosphorus increased by 40.7%: Calcium hydroxide reduced the phosphorus fixation rate from 62% to 22%. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings: Figure 1 Flowchart of the present invention DETAILED DESCRIPTION 1. Core raw materials and equipment Basic fertilizer raw materials Urea: nitrogen content ≥46%, particle size ≤3 mm (commercially available granular urea needs to be crushed and screened); Monoammonium phosphate: Implementation standard GB 10205-2001, N ≥ 11%, P2O5 ≥ 44%; Potassium sulfate: Implementation standard GB / T 20406-2017, K2O ≥ 50%, chloride ion ≤ 1.5%.

[0007] Functional additives Polyaspartic acid (PASP): Molecular weight range: 2000-100,000 (preferably 6000-40,000); Structural formula selection: Formula 1 (linear hydrolyzed polysuccinimide) or Formula 2 (α / β mixed polyaspartic acid); Combined inhibitors: Example of component purity requirements for suppliers NBPT ≥ 98% DCD≥99% DMPP ≥ 95% Bonding wrap material: Polyvinyl alcohol (PVA): degree of polymerization 1700, alcoholysis degree 88% (brand PVA-1788); Sodium polyacrylate (PAAS): molecular weight 3000-5000, solid content ≥40%; Calcium hydroxide: industrial grade, Ca(OH)2≥90%, particle size≤0.15 mm.

[0008] Filling materials and solvents: Bentonite: sodium bentonite, cation exchange capacity ≥80 mmol / 100g (produced in Jianping, Liaoning); Humic acid: fulvic acid content ≥50% (extracted from Shanxi weathered coal); Organic solvent: anhydrous ethanol (purity ≥99.7%) or ether (AR grade).

[0009] Production equipment list:

[0010] 2. Specific Preparation Examples Example 1 (standard ratio) (1) Raw material formula (by weight)

[0011] (2) Detailed explanation of the process flow Step 1: Raw material pretreatment Urea, monoammonium phosphate and potassium sulfate were put into the toothed disc crusher respectively, and then passed through a 2 mm vibrating screen after crushing; Bentonite and humic acid were premixed in a V-type mixer for 10 min (speed 25 rpm); The crushed fertilizer granules and filler materials were put into a twin-screw granulator, sprayed with an appropriate amount of water (5% of the total weight), and extruded to prepare a cylindrical core with a diameter of 2 mm.

[0012] Step 2: Fluidized bed primary coating (key technology) Dissolve PASP (0.5 parts), NBPT (0.2 parts), and DCD (0.2 parts) in 400 ml of anhydrous ethanol; The core particles are put into the fluidized bed and the parameters are set: Inlet air temperature: 70±2℃ Atomization pressure: 0.1 Pa Spray rate: 15 ml / min Fluidizing gas velocity: 1.2 m / s After the spraying is completed, the fluidization is maintained for 5 min to allow the solvent to evaporate.

[0013] Step 3: Secondary bonding layer wrapping Add PVA (1 part), PAAS (0.8 part), and calcium hydroxide (0.2 part) to boiling water, stir and simmer at 90°C until the viscosity reaches 3000 mPa·s (the adhesive solution is in a transparent gel-like state); A high-pressure airless spraying system was used to evenly spray the glue onto the surface of the particles at a pressure of 0.3 MPa, and the spraying amount was controlled to be 2% of the particle weight.

[0014] Step 4: Post-processing After wrapping, the pellets were transferred to a fluidized bed dryer and dried at 130°C for 25 min (material temperature ≤ 80°C). After cooling to 25°C, the mixture was sieved through a double-layer vibrating sieve (upper layer 4 mm / lower layer 2 mm); Qualified particles (2-4 mm) are sealed and packaged in aluminum-plastic composite bags.

[0015] Example 2 (Highly Inhibited Ratio) Recipe adjustment points: Combined inhibitor: NBPT 0.15 parts + DCD 0.15 parts + DMPP 0.1 parts (total 0.4 parts); The molecular weight of PASP increased to 40,000; Increase the amount of calcium hydroxide in the bonding layer to 15 parts (to improve the ability to prevent phosphorus from fixing).

[0016] Process improvements: The primary coating solvent was changed to ether (low boiling point, faster evaporation); The air inlet temperature of the fluidized bed was reduced to 65°C to prevent thermal decomposition of DMPP.

[0017] 3. Comparative Examples and Comparative Examples Comparative Example 1 (without composite inhibitor) Only 0.9 parts of PASP are used, and NBPT / DCD / DMPP are eliminated; The rest is the same as in Example 1.

[0018] Comparative Example 2 (single-layer coating) Eliminate the adhesive wrapping layer (i.e. no PVA / PAAS / calcium hydroxide coating); The slow-release synergist is directly mixed with the fertilizer and granulated.

[0019] Comparative Example 3 (commercially available resin-coated fertilizer) Commercially available sulfur + resin coated urea (nitrogen content 42%, coating rate 8%) was selected.

[0020] 4. Effect Verification Experiment 1. Leaching simulation test (refer to GB / T 8572-2010) Methods: 50 g of fertilizer was loaded into a leaching column, deionized water was dripped into the column at a rate of 200 ml / h, and the leachate was collected for 72 hours. Detection indicators: nitrate nitrogen (UV method), ammonium nitrogen (indophenol blue method), potassium ion (flame photometry).

[0021] Test results:

[0022] Conclusion: The combined inhibitor + double-layer coating reduced nitrogen leaching rate by 53% compared with PASP alone and was 33% lower than commercial fertilizer.

[0023] 2. Field application test Plot conditions: sandy soil (pH 5.8), annual rainfall 1800 mm; Fertilization program: Base fertilizer 600 kg / ha, compared with ordinary compound fertilizer (15-15-15).

[0024]

[0025] 5. Analysis of the mechanism of action of key parameters Synergistic effect of combined inhibitors NBPT: inhibits soil urease activity and delays urea hydrolysis for 24-48 hours; DCD + DMPP: Dual-channel blocking of nitrification, extending the retention time of ammonium nitrogen to more than 30 days.

[0026] PASP molecular weight selection basis <2000: The molecular chain is too short and the chelating ability is weak; >100,000: Solubility decreases and coating uniformity decreases; 6000-40000: Optimal mobility (promotes K⁺ transport to the roots).

[0027] The core value of calcium hydroxide in bonding layer Maintaining the pH of the particle surface at 7.5-8.0 reduces the binding of phosphate to iron and aluminum; Experimental data: Fertilizer containing 10% calcium hydroxide increases the effective utilization rate of phosphorus by 28%.

[0028] Scientific considerations for solvent selection

[0029] VI. Key Points for Industrialization Implementation Primary coating process control chart Fluidized bed temperature curve: 0-10 min: 60℃ (preheating) → 10-30 min: 70℃ (spraying period) → 30-35 min: 75℃ (curing period) Quality inspection standards Slow-release performance: Nitrogen release rate in water at 25°C: ≤15% on the first day, ≥80% on the 28th day (refer to ISO 18644); Mechanical strength: Particle crushing resistance ≥ 35 N (testing instrument TA.XT Plus); Envelope integrity: electron microscope observation (no cracks in the membrane layer, coverage ≥95%).

[0030] Environmental protection and safety measures Ether recovery system: condensation recovery rate ≥ 85%; Dust control: Pulse bag dust collector is installed in the granulation workshop (emission concentration ≤ 20 mg / m³).

[0031] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A leaching-proof nutrient slow-release synergistic compound fertilizer, characterized in that: The following components are included in parts by weight: 30-50 parts of urea granules; 15-25 parts of monoammonium phosphate; 20-30 parts potassium sulfate; 2-5 parts of sustained-release synergistic coating agent, containing 0.1-1 part of polyaspartic acid (PASP) and 0.1-1 part of compound inhibitor; 1-3 parts of adhesive wrapping layer, composed of 40-60 parts of polyvinyl alcohol, 30-50 parts of sodium polyacrylate, and 10-20 parts of calcium hydroxide; The filling material is 10-20 parts, including 50-70 parts of bentonite and 30-50 parts of humic acid.

2. The compound fertilizer according to claim 1, characterized in that: The composite inhibitor is composed of the following components by weight: 20-40% of N-butylthiophosphoric triamide (NBPT), 20-40% of dicyandiamide (DCD), and 20-40% of 3,4-dimethylpyrazole phosphate (DMPP).

3. The compound fertilizer according to claim 1, characterized in that: The molecular weight of the polyaspartic acid (PASP) is 2000-100,000, and the structural formula is as shown in Formula 1 or Formula 2: Formula 1 (Linear polysuccinimide hydrolysis product) Formula 2 (α / β mixed polyaspartic acid).

4. A method for preparing the compound fertilizer according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) Raw material pretreatment: crush urea, monoammonium phosphate, and potassium sulfate to less than 2 mm and mix them evenly with the filler; (2) Primary granulation and coating: The mixed material is fed into a fluidized bed and sprayed with a slow-release synergistic coating agent (PASP + compound inhibitor) dissolved in an organic solvent. The inlet air temperature is controlled at 60-75°C and the atomization pressure is controlled at 0.05-0.15 Pa. (3) Secondary coating: dissolving the raw materials for the adhesive coating layer in boiling water to form a colloidal liquid, and spraying it onto the surface of the particles obtained in step (2); (4) Post-processing: The granules are dried at 110-150°C for 20-30 min, cooled to 20-25°C, and sieved to obtain finished products with a particle size of 2-4 mm.

5. The preparation method according to claim 4, characterized in that: The organic solvent in step (2) is ethanol or ether, and the amount used is 5-10 ml per 100 parts of raw materials.

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