Preparation method of nano-suspension slow-release liquid fertilizer

Abstract

The application belongs to the field of liquid fertilizer, and particularly relates to a preparation method of a nano-suspension slow-release liquid fertilizer, which comprises the following steps: mixing ammonium polyphosphate, methylene urea nitrogen, hyperbranched aldehyde urea polymer, phosphate, potassium dihydrogen phosphate and water, then adding maleic acid, ethylenediamine tetramethylene phosphonic acid and humic acid, uniformly mixing stabilizers, preparing into a mixed fertilizer, and dispersing the mixed fertilizer and kaolin nano-suspension to obtain the nano-suspension slow-release liquid fertilizer. The hyperbranched aldehyde urea polymer is combined with nitrogen fertilizer to form a macromolecular nitrogen chain, a nitrogen nutrient storage is established in a plant body, the nano-suspension can wrap the mixed fertilizer, nutrients can be continuously absorbed by crops, and the hyperbranched aldehyde urea polymer is combined to achieve long-acting slow release.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of liquid fertilizer, in particular to a preparation method of nano-suspension slow-release liquid fertilizer. BACKGROUND

[0002] In the modern agricultural production system, fertilizers, as the indispensable source of nutrients for plant growth, directly affect the growth and development, yield potential and final product quality of crops. However, for a long time, traditional fertilizers have exposed a series of problems to be solved in the process of use. Among them, the most notable is the phenomenon of rapid release of nutrients. This leads to the rapid release of a large amount of nutrients in a short time, which cannot be completely absorbed by plants in time, resulting in waste of nutrients, and even harm to plants due to excess nutrients. In addition, traditional fertilizers are also easy to be adsorbed and fixed by colloidal particles in the soil, or lost with rainwater runoff and infiltration, further reducing the actual utilization rate of fertilizers.

[0003] More complex is that there are many ions such as calcium, magnesium, iron and aluminum in the soil, which can often react with the effective components in the fertilizer to form insoluble compounds, thereby losing the original fertilizer effect of the fertilizer. However, ordinary liquid fertilizers are easy to cause loss of nutrients and water due to the flushing of water. SUMMARY

[0004] The purpose of the present application is to solve the problems of poor slow-release effect of liquid fertilizer and inability to provide nutrients for plants for a long time in the prior art, and to provide a preparation method of nano-suspension slow-release liquid fertilizer.

[0005] The preparation method of the nano-suspension slow-release liquid fertilizer provided by the present application comprises:

[0006] S1, adding anhydrous acetic acid and acetic anhydride with a volume ratio of (1.8-2.2):1, and adding benzoic acid and hexamethylenetetramine with a mass ratio of 1:(3-4) into a reaction container, stirring and heating, adding polyformaldehyde, and condensing and refluxing under the condition of heating to 120-130℃ to obtain an intermediate;

[0007] S2, adding the intermediate, concentrated sulfuric acid and water with a volume ratio of 1:(4-5) into the reaction container, heating to 90℃ and reacting for 1-5h, washing with ice water for 3-4 times after reaction, filtering, and drying to obtain 5-carboxyphthaldehyde;

[0008] S3, adding urea and water into the reaction container, stirring, heating to 30-40℃ until the urea is completely dissolved, adjusting the pH to be acidic, then adding 5-carboxyphthaldehyde, heating to 50-60℃, and reacting for 5-6h, after the reaction is completed, heating and concentrating, washing, and drying to obtain hyperbranched aldehyde urea polymer.

[0009] S4, ammonium polyphosphate, methylene urea nitrogen, hyperbranched aldehyde urea polymer, phosphate, potassium dihydrogen phosphate and water are mixed, then maleic acid, ethylenediamine tetramethylene phosphonic acid and humic acid are added, and a stabilizer is uniformly mixed to obtain a mixture, thereby obtaining a mixed fertilizer;

[0010] S5, the kaolin nanosuspension is diluted, and the diluted kaolin nanosuspension and the mixed fertilizer are added to a high-speed emulsifying disperser for dispersion, and after standing for 5-10 h, a nanosuspension slow-release liquid fertilizer is obtained.

[0011] Preferably, in step S3, the volume ratio of 5-carboxyisophthalaldehyde to urea is 1:(3-4).

[0012] Preferably, in step S4, the stabilizer is one or more of sorbitol and mannitol.

[0013] Preferably, in step S5, the kaolin nanosuspension is added to water, and the mass ratio of the kaolin nanosuspension to water is (0.1-0.5):100.

[0014] Preferably, the preparation process of the kaolin nanosuspension is as follows: kaolin mud slurry is ground, then added to water, and a suspension with a mass ratio of 1:(1.5-1.7) of kaolin to water is prepared, an alkaline solution is added dropwise to the suspension until it is alkaline, and then placed into a high-speed emulsifying disperser for stirring at 3x10 4 -5x10 4 r / min for 1-3 h, standing for 24-36 h, adding dilute hydrochloric acid to adjust the pH of the suspension to 6.8-7.2, and then placing into a high-speed emulsifying disperser for stirring at 3x10 4 -5x10 4 r / min for 10-20 min, to obtain the kaolin nanosuspension.

[0015] Preferably, the alkaline solution is a potassium hydroxide solution or a sodium hydroxide solution.

[0016] The present application has the following beneficial effects: the present application prepares a kaolin nanosuspension by emulsifying and dispersing kaolin and water, an intermediate is prepared by reacting benzoic acid and hexamethylenetetramine in the presence of anhydrous acetic acid, acetic anhydride and paraformaldehyde, the intermediate is hydrolyzed to obtain 5-carboxyisophthalaldehyde, the 5-carboxyisophthalaldehyde is reacted with urea to obtain a hyperbranched aldehyde urea polymer, then ammonium polyphosphate, methylene urea nitrogen, the hyperbranched aldehyde urea polymer, phosphate, potassium dihydrogen phosphate and water are mixed, then maleic acid, ethylenediamine tetramethylene phosphonic acid and humic acid are added, and a stabilizer is uniformly mixed to obtain a mixture, thereby obtaining a mixed fertilizer, and then the mixed fertilizer is dispersed with the kaolin nanosuspension to obtain a nanosuspension slow-release liquid fertilizer.

[0017] The intermediate is prepared by reacting benzoic acid and hexamethylenetetramine in the presence of anhydrous acetic acid, acetic anhydride and polyformaldehyde, the intermediate is obtained by hydrolysis reaction to obtain 5-carboxybenzene-1,3-dial, the carboxyl and aldehyde group on the 5-carboxybenzene-1,3-dial react with the amino group on the urea, the hyperbranched aldehyde urea resin has a low curing temperature and a good thermal stability, can maintain stable performance, can provide slow and stable nitrogen nutrition, the free formaldehyde content in the hyperbranched aldehyde urea resin is significantly reduced, and the hyperbranched aldehyde urea resin is more environmentally friendly; the hyperbranched aldehyde urea polymer contains multiple urethane groups in the structure, can be combined with nitrogen fertilizer to form a macromolecular nitrogen chain, the carboxyl on the 5-carboxybenzene-1,3-dial can react with the amino group on the urea to form a peptide bond, can adsorb metals in the soil and improve heavy metal pollution in the soil; the polymer has a high molecular weight and a complex network structure, can effectively control the release time of nitrogen nutrients, and makes the nitrogen retention period of the nitrogen fertilizer reach 50-60 days; the kaolin nano suspension can wrap the mixed fertilizer, and can make the nutrients be continuously absorbed by crops, achieving long-acting slow release. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is the reaction equation for preparing the intermediate of the application.

[0019] Figure 2 is the reaction equation for preparing 5-carboxybenzene-1,3-dial of the application. DETAILED DESCRIPTION

[0020] The application will be further described below in combination with specific examples.

[0021] Example 1:

[0022] The kaolin mud is ground, and then added into water to prepare a mixed suspension of 30 g of kaolin and 45 g of water, and the suspension is added dropwise with potassium hydroxide solution until alkaline, and then placed into a high-speed emulsification disperser to stir at 5x10 4 r / min for 3 h, and then placed for 36 h, and then added with dilute hydrochloric acid to adjust the pH of the suspension to 6.8, and then placed into the high-speed emulsification disperser to stir at 5x10 4 r / min for 20 min to obtain a kaolin nano suspension.

[0023] S2, 18 mL of anhydrous acetic acid and 10 mL of acetic anhydride are added into a reaction container, 8 g of benzoic acid and 32 g of hexamethylenetetramine are added, and then stirred and heated, and then polyformaldehyde is added, and then condensed and refluxed under the condition of heating to 120℃ to obtain an intermediate.

[0024] S3, add 3g of the intermediate, 5g of concentrated sulfuric acid and 20g of water into the reaction container, heat to 90℃ for 5h, after the reaction, cool, wash with ice water 4 times, filter, dry, to obtain 5-carboxyisophthalaldehyde.

[0025] S4, add 40g of urea and 200mL of water into the reaction container, stir, heat to 30℃ until the urea is completely dissolved, adjust the pH to be acidic, then add 10g of 5-carboxyisophthalaldehyde, heat to 60℃, react for 5h, after the reaction is complete, perform heating concentration, washing, drying, to obtain hyperbranched aldehyde urea polymer.

[0026] S5, mix 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched aldehyde urea polymer, 10 parts by weight of phosphate, 5 parts by weight of potassium dihydrogen phosphate with water, then add 2 parts by weight of maleic acid, 2 parts by weight of ethylenediaminetetramethylene phosphonic acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol to mix uniformly, obtain a mixture, and obtain a mixed fertilizer.

[0027] S6, dilute the kaolin nano suspension to 0.1% of the mass of kaolin, then add the diluted kaolin nano suspension and the mixed fertilizer into a high-speed emulsifying disperser for dispersion, after dispersion, stand for 5h, to obtain a nano-suspension slow-release liquid fertilizer.

[0028] Example two:

[0029] Grind the kaolin slurry, after grinding, add water to make a mixed suspension of 30g of kaolin and 51g of water, add potassium hydroxide solution dropwise to the suspension to be alkaline, place into a high-speed emulsifying disperser, stir at 3x10 4 r / min for 1h, stand for 24h, add dilute hydrochloric acid to adjust the pH of the suspension to 7.2, then place into a high-speed emulsifying disperser, stir at 3x10 4 r / min for 10min, to obtain a kaolin nano suspension.

[0030] S2, add 22mL of anhydrous acetic acid and 10mL of acetic anhydride to the reaction container, add 8g of benzoic acid and 24g of hexamethylenetetramine, stir and heat, add polyformaldehyde, heat to 130℃, condense and reflux, to obtain the intermediate.

[0031] S3, add 3g of the intermediate, 5g of concentrated sulfuric acid and 25g of water into the reaction container, heat to 90℃ for 4h, after the reaction, cool, wash with ice water 3 times, filter, dry, to obtain 5-carboxyisophthalaldehyde.

[0032] S4, to the reaction vessel, 30 g of urea and 200 mL of water are added, stirring, heating to 40℃, until the urea is completely dissolved, adjust the pH to acidic, then add 10 g of 5-carboxy isophthalaldehyde, heating to 50℃, reaction 6h, after the reaction, heating concentration, washing, drying, to obtain hyperbranched aldehyde urea polymer.

[0033] S5, 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched aldehyde urea polymer, 10 parts by weight of phosphate, 5 parts by weight of potassium dihydrogen phosphate are mixed with water, then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediamine tetramethylene phosphonic acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are mixed uniformly to obtain a mixture, and a mixed fertilizer is obtained.

[0034] S6, the kaolin nano suspension is diluted to 0.5% of the mass of kaolin, and the diluted kaolin nano suspension and the mixed fertilizer are added to a high-speed emulsifying disperser for dispersion. After dispersion, stand for 10h to obtain a nano-suspension slow-release liquid fertilizer.

[0035] Example three:

[0036] The kaolin slurry is ground, then added to water to prepare a mixed suspension of 30 g of kaolin and 47 g of water. The suspension is added dropwise with potassium hydroxide solution to alkaline, placed into a high-speed emulsifying disperser, stirred at 5x10 4 r / min for 2h, stand for 36h, add dilute hydrochloric acid to adjust the pH of the suspension to 7, then place into a high-speed emulsifying disperser, stir at 5x10 4 r / min for 15min to obtain a kaolin nano suspension.

[0037] S2, to the reaction vessel, 20 mL of anhydrous acetic acid and 10 mL of acetic anhydride are added in a volume ratio, 8 g of benzoic acid and 28 g of hexamethylenetetramine are added, stirring and heating, adding polyformaldehyde, under the condition of heating to 120℃, condensation reflux, to obtain an intermediate.

[0038] S3, to the reaction vessel, 3 g of the intermediate, 5 g of concentrated sulfuric acid and 25 g of water are added, heated to 90℃ for 1h, after the reaction, cooling, washing with ice water for 3 times, filtering, drying, to obtain 5-carboxy isophthalaldehyde.

[0039] S4, to the reaction vessel, 35 g of urea and 200 mL of water are added, stirring, heating to 35℃, until the urea is completely dissolved, adjust the pH to acidic, then add 10 g of 5-carboxy isophthalaldehyde, heating to 55℃, reaction 6h, after the reaction, heating concentration, washing, drying, to obtain hyperbranched aldehyde urea polymer.

[0040] S5, 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched aldehyde urea polymer, 10 parts by weight of phosphate, 5 parts by weight of potassium dihydrogen phosphate, 2 parts by weight of maleic acid, 2 parts by weight of ethylenediamine tetramethylene phosphonic acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are mixed with water to obtain a mixture, and a mixed fertilizer is obtained.

[0041] S6, the kaolin nano suspension is diluted to 0.3% of the mass of kaolin, and the diluted kaolin nano suspension and the mixed fertilizer are added to a high-speed emulsifying disperser for dispersion. After dispersion, stand for 8h to obtain a nano-suspension slow-release liquid fertilizer.

[0042] Example Four:

[0043] The kaolin slurry is ground, then added to water to prepare a mixed suspension of 30g of kaolin and 49g of water. The suspension is added dropwise with potassium hydroxide solution to alkaline, placed into a high-speed emulsifying disperser, stirred at 5x10 4 r / min for 1h, and stood for 24h. Dilute hydrochloric acid is added to adjust the pH of the suspension to 6.8, and then placed into a high-speed emulsifying disperser, stirred at 5x10 4 r / min for 10min to obtain a kaolin nano suspension.

[0044] S2, add 22mL of anhydrous acetic acid and 10mL of acetic anhydride to the reaction container, add 8g of benzoic acid and 28g of hexamethylenetetramine, stir and heat, add polyformaldehyde, heat to 125℃, condense and reflux to obtain an intermediate.

[0045] S3, add 3g of the intermediate, 5g of concentrated sulfuric acid and 23g of water to the reaction container, heat to 90℃ and react for 3h. After the reaction, cool, wash with ice water 4 times, filter and dry to obtain 5-carboxyisophthalaldehyde.

[0046] S4, add 40g of urea and 200mL of water to the reaction container, stir, heat to 30℃ until the urea is completely dissolved, adjust the pH to be acidic, then add 10g of 5-carboxyisophthalaldehyde, heat to 60℃ and react for 5h. After the reaction is completed, heat and concentrate, wash and dry to obtain a hyperbranched aldehyde urea polymer.

[0047] S5, 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched aldehyde urea polymer, 10 parts by weight of phosphate, 5 parts by weight of potassium dihydrogen phosphate are mixed with water, then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediamine tetramethylene phosphonic acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are mixed uniformly to obtain a mixture, and a mixed fertilizer is obtained.

[0048] S6, the kaolin nanosuspension is diluted to 0.4% of the mass of kaolin, and the diluted kaolin nanosuspension and the mixed fertilizer are added to a high-speed emulsifying disperser for dispersion. After dispersion, stand for 9h to obtain a nanosuspension slow-release liquid fertilizer.

[0049] Comparative Example 1:

[0050] S1, 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 10 parts by weight of phosphate, 5 parts by weight of potassium dihydrogen phosphate are mixed with water, then 2 parts by weight of maleic acid, 2 parts by weight of ethylenediamine tetramethylene phosphonic acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are mixed uniformly to obtain a mixture, and a mixed fertilizer is obtained. The mixed fertilizer is added to a high-speed emulsifying disperser for dispersion. After dispersion, stand for 5h to obtain a nanosuspension slow-release liquid fertilizer.

[0051] Comparative Example 2:

[0052] S1, add 18mL of anhydrous acetic acid and 10mL of acetic anhydride to the reaction container in a volume ratio, add 8g of benzoic acid and 32g of hexamethylenetetramine, stir and heat, add polyformaldehyde, and condense and reflux under the condition of heating to 120℃ to obtain an intermediate.

[0053] S2, add 3g of the intermediate, 5g of concentrated sulfuric acid and 20g of water to the reaction container, heat to 90℃ and react for 5h, then cool, wash with ice water 4 times, filter and dry to obtain 5-carboxyisophthalaldehyde.

[0054] S3, add 40g of urea and 200mL of water to the reaction container, stir, heat to 30℃ until the urea is completely dissolved, adjust the pH to be acidic, then add 10g of 5-carboxyisophthalaldehyde, heat to 60℃ and react for 5h. After the reaction is completed, heat and concentrate, wash and dry to obtain a hyperbranched aldehyde urea polymer.

[0055] S4, 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of hyperbranched aldehyde urea polymer, 10 parts by weight of phosphate, 5 parts by weight of potassium dihydrogen phosphate, 2 parts by weight of maleic acid, 2 parts by weight of ethylenediamine tetramethylene phosphonic acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are mixed with water, and then uniformly mixed to obtain a mixture, a mixed fertilizer is obtained, the mixed fertilizer is added to a high-speed emulsifying disperser for dispersion, and after dispersion, the mixture is placed for 5 h to obtain a nano-suspension slow-release liquid fertilizer.

[0056] Comparative Example Three

[0057] S1, the kaolin mud is ground, and after grinding, water is added to prepare a mixed suspension of 30 g of kaolin and 45 g of water. The suspension is added dropwise with potassium hydroxide solution to alkaline, and placed in a high-speed emulsifying disperser for stirring at 5 x 10 4 r / min for 3 h, and placed for 36 h. Dilute hydrochloric acid is added to adjust the pH of the suspension to 6.8, and then placed in a high-speed emulsifying disperser for stirring at 5 x 10 4 r / min for 20 min to obtain a kaolin nano-suspension.

[0058] S2, 20 parts by weight of ammonium polyphosphate, 10 parts by weight of methylene urea nitrogen, 5 parts by weight of diurea triacetal polymer, 10 parts by weight of phosphate, 5 parts by weight of potassium dihydrogen phosphate, 2 parts by weight of maleic acid, 2 parts by weight of ethylenediamine tetramethylene phosphonic acid, 1 part by weight of humic acid, 2 parts by weight of sorbitol and 1 part by weight of mannitol are mixed with water, and then uniformly mixed to obtain a mixture, a mixed fertilizer is obtained.

[0059] S3, the kaolin nano-suspension is diluted to 0.1% of the mass of kaolin, and then the diluted kaolin nano-suspension and the mixed fertilizer are added to a high-speed emulsifying disperser for dispersion. After dispersion, the mixture is placed for 5 h to obtain a nano-suspension slow-release liquid fertilizer.

[0060] 10 mL of the nano-suspension slow-release liquid fertilizer is weighed and placed in a jar containing 100 mL of distilled water, and then placed in a 25℃ incubator. Samples are taken every 48 h until the 20th day of nutrient release. After each sampling, all the leachate in the jar is poured out, 100 mL of distilled water is added to the jar, and the mixture is incubated at 25℃. The cumulative release rate of urea is measured three times, and the average value is taken as the nutrient release rate.

[0061] Each urea-formaldehyde liquid slow-release fertilizer sample was tested 3 times, and the total nitrogen content of the urea-formaldehyde liquid slow-release fertilizer was 28%. One of the synthesis raw materials of the urea-formaldehyde liquid slow-release fertilizer was an aqueous formaldehyde solution. Due to incomplete chemical conversion, the product contained different concentrations of free formaldehyde. The formaldehyde was tested 3 times using a formaldehyde testing machine, and the total nitrogen content was determined 3 times using an automatic nitrogen determination instrument. The average value was obtained to obtain the test results.

[0062] Effect of nano-suspension slow-release liquid fertilizer nutrients on vegetables and fruits, bok choy area 28.5 m 2 The random block arrangement was used, and 7.5 kg of chicken manure fertilizer was applied as a base fertilizer in each plot. The liquid fertilizer topdressing fertilizer application amount was consistent, and was used in 3 times: the first topdressing was 10 days after transplanting, and the fertilizer application amount was 30% of the total amount; the second topdressing was 17 days after transplanting, and the fertilizer application amount was 40% of the total amount; the third topdressing was 27 days after transplanting, and the fertilizer application amount was 30% of the total amount. The liquid fertilizer was diluted with water and then applied, and the same water amount was maintained for each group during each fertilization. The yield of each plot was counted at the harvest period of the bok choy, and 6 plants were collected. The vitamin C, soluble sugar, and nitrate content of the agricultural products were determined according to the principles and techniques of plant physiology and biochemistry.

[0063] Table 1 is the test results of the nano-suspension slow-release liquid fertilizer nutrient release

[0064]

[0065] Table 2 is the vitamin C, soluble sugar, and nitrate content of the agricultural products applied with the liquid fertilizer

[0066] VC (mg / 100 g) Soluble sugars (%) Nitrate (mg / kg) Example 1 25.66 1.76 2003 Example 2 25.85 1.69 1987 Example 3 24.11 1.68 1889 Example 4 24.06 1.57 1994 Comparative Example 1 21.14 1.41 1653 Comparative Example 2 22.23 1.49 1766 Comparative Example 3 22.97 1.50 1842

[0067] As shown in Table 1-Table 2, the nutrient cumulative release rate and free formaldehyde mass fraction in Examples 1-4 are lower than those in Comparative Examples 1-3, the total nitrogen content in Examples 1-4 is higher than that in Comparative Examples 1-3, and the vitamin C, soluble sugar and nitrate content of agricultural products in Examples 1-4 is higher than that in Comparative Examples 1-3; because the intermediate is prepared by reacting benzoic acid and hexamethylenetetramine in anhydrous acetic acid, acetic anhydride and paraformaldehyde, the carboxyl and aldehyde group on the 5-carboxybenzene dicarboxaldehyde obtained by hydrolysis of the intermediate react with the amino group on the urea, the hyperbranched aldehyde urea resin has a lower curing temperature and better thermal stability, can maintain stable performance, can provide slow and stable nitrogen nutrition, and the free formaldehyde content in the hyperbranched aldehyde urea resin is significantly reduced, which is more environmentally friendly than aldehyde urea resin; the hyperbranched aldehyde urea polymer contains multiple urethane groups in its structure, which can combine with nitrogen fertilizer to form a macromolecular nitrogen chain, the carboxyl group on the 5-carboxybenzene dicarboxaldehyde can react with the amino group on the urea to form a peptide bond, which can adsorb metals in the soil and improve heavy metal pollution in the soil; this polymer has a high molecular weight and a complex network structure, which can effectively control the release time of nitrogen nutrients, so that the nitrogen retention period of the fertilizer reaches 50-60 days; the kaolin nano suspension can wrap the mixed fertilizer, so that the nutrients can be continuously absorbed by crops, and the nutrients can be slowly and continuously provided, the total nitrogen content in Examples 1-4 is higher than that in Comparative Examples 1-3, and the vitamin C, soluble sugar and nitrate content of agricultural products in Examples 1-4 is higher than that in Comparative Examples 1-3.

[0068] Comparative Example 1 and Example 1 are compared, the nutrient cumulative release rate and free formaldehyde mass fraction in Example 1 are lower than those in Comparative Example 1, the total nitrogen content in Example 1 is higher than that in Comparative Example 1, and the vitamin C, soluble sugar and nitrate content of agricultural products in Example 1 is higher than that in Comparative Example 1, Comparative Example 1 does not add hyperbranched aldehyde urea resin and kaolin nano suspension, and cannot provide nutrients slowly and continuously, indicating that the nutrient slow-release effect of the comparative example is not good.

[0069] Comparative Example 2 and Example 1 are compared, the nutrient cumulative release rate and free formaldehyde mass fraction in Example 1 are lower than those in Comparative Example 2, the total nitrogen content in Example 1 is higher than that in Comparative Example 2, and the vitamin C, soluble sugar and nitrate content of agricultural products in Example 1 is higher than that in Comparative Example 2, Comparative Example 2 does not add kaolin nano suspension, which can wrap urea and make urea provide nutrients slowly and continuously, and does not add kaolin nano suspension, which has a poor nutrient slow-release effect.

[0070] Comparing the comparative example 3 and the example 1, the nutrient cumulative release rate and the free formaldehyde mass fraction in the example 1 are lower than those in the comparative example 3, the total nitrogen content in the example 1 is higher than that in the comparative example 3, the vitamin C, soluble sugar and nitrate contents of the agricultural products in the example 1 are higher than those in the comparative example 3, the hyperbranched aldehyde urea polymer in the comparative example 3 is replaced by the diurea tri-aldehyde polymer, the hyperbranched polymer has more stable properties, the formaldehyde release amount is lower, and it is more environmentally friendly. Although the diurea tri-aldehyde polymer also has a certain slow-release effect, the stability and slow-release property are not as good as those of the hyperbranched polymer, so the nutrient slow-release effect of the comparative example 3 is not good.

Claims

1. A method for preparing a nano-suspension slow release liquid fertilizer, characterized in that, The method comprises the following steps: S1, adding anhydrous acetic acid and acetic anhydride in a volume ratio of (1.8-2.2):1, adding benzoic acid and hexamethylenetetramine in a mass ratio of 1:(3-4) into a reaction container, stirring and heating, adding polyformaldehyde, and condensing and refluxing at 120-130℃ for 3-4h to obtain an intermediate; S2, adding the intermediate, concentrated sulfuric acid and water in a volume ratio of 1:(4-5) into a reaction container, heating to 90℃ for 1-5h, cooling after reaction, washing with ice water for 3-4 times, filtering, and drying to obtain 5-carboxyphthalaldehyde; S3, adding urea and water into a reaction container, stirring, heating to 30-40℃ until the urea is completely dissolved, adjusting the pH to be acidic, then adding 5-carboxyphthalaldehyde, wherein the mass ratio of 5-carboxyphthalaldehyde to urea is 1:(3-4), heating to 50-60℃, and reacting for 5-6h, after the reaction, heating and concentrating, washing, and drying to obtain hyperbranched aldehyde urea polymer; S4, mixing ammonium polyphosphate, methylene urea nitrogen, hyperbranched aldehyde urea polymer, phosphate, potassium dihydrogen phosphate, and water, then adding maleic acid, ethylenediaminetetramethylene phosphonic acid, humic acid, and a stabilizer to mix uniformly to obtain a mixed fertilizer; the stabilizer is one or more of sorbitol and mannitol; S5, adding kaolin nano suspension into water, the mass ratio of kaolin nano suspension to water is (0.1-0.5):100, then adding the diluted kaolin nano suspension and the mixed fertilizer into a high-speed emulsifying disperser to disperse, and after dispersion, standing for 5-10h to obtain a nano suspension slow-release liquid fertilizer; The preparation process of the kaolin nano-suspension is as follows: the kaolin mud slurry is ground, and then added into water, the mass ratio of the kaolin and water in the suspension is 1:(1.5-1.7), the suspension of the kaolin and water is prepared, the suspension is added dropwise into alkaline solution until alkaline, and then placed into a high-speed emulsifying disperser, stirred at 3x10 4 -5x10 4 r / min for 1-3h, and then placed for 24-36h, the pH of the suspension is adjusted to 6.8-7.2 by adding dilute hydrochloric acid, and then placed into the high-speed emulsifying disperser, stirred at 3x10 4 -5x10 4 r / min for 10-20min, so as to obtain the kaolin nano-suspension.

2. The nano-suspension slow-release liquid fertilizer according to claim 1, characterized in that, adding an alkaline solution dropwise to the suspension to make the pH alkaline, and the alkaline solution is potassium hydroxide solution or sodium hydroxide solution.

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