Fertilizer-retaining zinc-rich foliar fertilizer and preparation method thereof

Abstract

The invention relates to the technical field of foliar fertilizers, and discloses a fertilizer-retaining zinc-rich foliar fertilizer and a preparation method thereof.The preparation method comprises the steps that hydroxymethyl urea, nano-zinc oxide and citric acid react to obtain citric acid modified urea formaldehyde and citric acid modified zinc oxide; a reversed-phase microemulsion method is adopted, citric acid modified urea formaldehyde, citric acid modified zinc oxide, chitosan and the like are used as raw materials, the surfaces of the citric acid modified urea formaldehyde and the citric acid modified zinc oxide are coated with the chitosan, and the modified chitosan composite nanoparticles are obtained. The modified polyvinyl alcohol resin is prepared by taking urea, acrylic acid and polyvinyl alcohol as raw materials through an aqueous solution polymerization method. Finally, the modified polyvinyl alcohol resin and the modified chitosan composite nanoparticles are added into monopotassium phosphate to be stirred and mixed to be uniform, drying is conducted, the leaf fertilizer is obtained, and the fertilizer retention and slow release effects of the leaf fertilizer are improved through carboxyl, hydroxyl and other groups contained on the surfaces of the modified polyvinyl alcohol resin and the modified chitosan composite nanoparticles.

Description

Technical Field

[0001] The invention relates to the technical field of foliar fertilizers, in particular to a fertilizer-retaining zinc-rich foliar fertilizer and a preparation method thereof. Background Art

[0002] Most terrestrial plants rely on their roots to absorb nutrients, but the leaves of plants can also absorb exogenous substances, such as gases, nutrients, pesticides, etc. While absorbing water, the leaves can also absorb nutrients into the plant body like roots. Therefore, foliar fertilizer was born.

[0003] Foliar fertilizer can improve nutrient deficiency, increase crop yield and product quality, and avoid the adverse effects of soil fertilizers, such as plant toxicity and soil loss. However, foliar fertilizer still has problems such as poor slow-release fertilizer retention and poor moisture retention. In actual agricultural applications, foliar fertilizer needs to be sprayed multiple times to achieve the desired effect. Therefore, in order to increase crop yield and fertilizer utilization, it is necessary to improve the fertilizer retention and slow-release effect of foliar fertilizer.

[0004] Zinc is an essential trace nutrient for maintaining human health and plays a vital role in human health. Currently, many experts and scholars are committed to studying the mechanism of zinc enrichment in crops to improve the current situation of zinc deficiency in people. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the deficiencies in the prior art, the present invention provides a fertilizer-retaining zinc-rich foliar fertilizer and a preparation method thereof. The prepared fertilizer-retaining zinc-rich foliar fertilizer has good fertilizer-retaining and slow-release effect.

[0007] (II) Technical solution

[0008] A fertilizer-retaining zinc-rich foliar fertilizer comprises the following raw materials, measured by weight: the fertilizer-retaining zinc-rich foliar fertilizer comprises 1 part of potassium dihydrogen phosphate, 50-70 parts of modified polyvinyl alcohol resin, and 5-15 parts of modified chitosan composite nanoparticles;

[0009] The preparation method of the fertilizer-retaining zinc-rich foliar fertilizer is:

[0010] Potassium dihydrogen phosphate is added into deionized water, stirred to dissolve, and then modified polyvinyl alcohol resin and modified chitosan composite nanoparticles are added thereto, stirred and mixed evenly, and dried to obtain foliar fertilizer.

[0011] Preferably, the preparation method of the modified polyvinyl alcohol resin is as follows: adding a 5% by mass potassium hydroxide aqueous solution to acrylic acid, stirring and dispersing, and controlling the neutralization degree to 70% to obtain a solution A; adding polyvinyl alcohol to deionized water under a nitrogen atmosphere, heating to 85-90° C., stirring and dissolving to obtain a solution B, then adding the solution A and potassium persulfate to the solution B, stirring and reacting at 65-75° C. for 3-5 hours, then cooling to 45-55° C., adding urea and N,N-methylenebisacrylamide crosslinking agent thereto, stirring and reacting for 1-3 hours, cooling after the reaction, filtering with suction, and drying to obtain a modified polyvinyl alcohol resin.

[0012] Preferably, the mass ratio of acrylic acid to polyvinyl alcohol is 2-5:1.

[0013] Preferably, the mass of the urea is 0.5-1.5% of the total mass of acrylic acid and polyvinyl alcohol; the mass of potassium persulfate is 0.5-1% of the total mass of acrylic acid and polyvinyl alcohol; and the mass of the cross-linking agent is 0.03-0.06% of the total mass of acrylic acid and polyvinyl alcohol.

[0014] Preferably, the preparation method of the modified chitosan composite nanoparticles is:

[0015] (1) adding formaldehyde to deionized water, adjusting the pH to 8 with a 5% by mass potassium hydroxide aqueous solution, adding urea thereto, stirring and dispersing, reacting at 45-55° C. for 2-5 hours, adding citric acid thereto after the reaction is completed, mixing evenly, and continuing the reaction for 10-20 minutes, and drying after the reaction is completed to obtain citric acid-modified urea formaldehyde;

[0016] (2) adding citric acid to deionized water, stirring and dispersing, adjusting the pH to 6 with a 5% by mass potassium hydroxide aqueous solution, adding nano zinc oxide thereto, stirring and reacting at 55-65° C. for 3-6 hours, centrifuging after the reaction, washing with deionized water, and drying to obtain citric acid-modified zinc oxide;

[0017] (3) Add citric acid-modified urea formaldehyde and citric acid-modified zinc oxide to the chitosan aqueous solution, stir and disperse to form an aqueous phase solution, use 3% by mass of Span-80 paraffin solution as the oil phase, mix the aqueous phase solution and the oil phase solution, stir evenly, stir at 50-60° C. for 1-2 h, wash with ether and ethanol in turn, and dry to obtain modified chitosan composite nanoparticles.

[0018] Preferably, in (1), the mass ratio of formaldehyde to urea is 1:2.4-3.

[0019] Preferably, in (2), the mass ratio of citric acid to nano zinc oxide is 0.01-0.05:1.

[0020] Preferably, in (3), the mass ratio of citric acid-modified urea formaldehyde, citric acid-modified zinc oxide and chitosan is 0.5-1:0.5-1:1.

[0021] (III) Beneficial technical effects

[0022] The invention utilizes formaldehyde to react with urea to generate hydroxymethyl urea, which is then reacted with citric acid to obtain citric acid modified urea formaldehyde. The carboxyl group in citric acid is used to carry out esterification reaction with the hydroxyl group on the surface of nano zinc oxide to obtain citric acid modified zinc oxide. The reverse microemulsion method is adopted, and citric acid modified urea formaldehyde, citric acid modified zinc oxide, chitosan and the like are used as raw materials, and chitosan is coated on the surfaces of citric acid modified urea formaldehyde and citric acid modified zinc oxide to obtain modified chitosan composite nanoparticles. The aqueous solution polymerization method is adopted, and urea, acrylic acid and polyvinyl alcohol are used as raw materials, potassium persulfate is used as an initiator, and N,N-methylenebisacrylamide is used as a crosslinking agent to prepare a modified polyvinyl alcohol resin. Finally, the modified polyvinyl alcohol resin and the modified chitosan composite nanoparticles are added to potassium dihydrogen phosphate, stirred and mixed evenly, and dried to obtain foliar fertilizer.

[0023] When foliar fertilizer is applied on the leaf surface, the foliar fertilizer contains a large amount of hydrophilic groups such as carboxyl and hydroxyl, which can improve the wetting performance of the foliar fertilizer, increase the contact area between the foliar fertilizer and the leaf surface, and reduce the possibility of fertilizer droplets sliding on the leaf surface, thereby improving the adhesion performance of the foliar fertilizer on the leaf surface and increasing the utilization rate of the foliar fertilizer. The modified polyvinyl alcohol resin and the modified chitosan composite nanoparticles contained in the fertilizer can both absorb water, and when the external nutrient element content is low, the nutrient elements can be slowly released by the dynamic exchange of water, but due to the presence of hydrogen bonding in the urea in the modified polyvinyl alcohol resin, the modified chitosan composite nanoparticles are a structure that encapsulates the nutrient elements, so they are not easy to lose, and the nutrient elements can be slowly released. The foliar fertilizer prepared by the present invention has a good fertilizer retention and slow release effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the SEM image of the modified chitosan composite nanoparticles of Example 1. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] (1) 10 g of formaldehyde was added to deionized water, and the pH value was adjusted to 8 using a 5% by mass potassium hydroxide aqueous solution. 30 g of urea was added thereto, and the mixture was stirred and dispersed. The mixture was reacted at 50° C. for 4 h. After the reaction, 10 g of citric acid was added thereto, and the mixture was mixed evenly. The mixture was reacted for 15 min. After the reaction was completed, the mixture was dried to obtain citric acid-modified urea formaldehyde.

[0028] (2) 0.15 g of citric acid was added to deionized water, stirred and dispersed, and a 5% by mass potassium hydroxide aqueous solution was used to adjust the pH to 6. Then 4 g of nano zinc oxide was added thereto, and the mixture was stirred and reacted at 65° C. for 5 h. After the reaction was completed, the mixture was centrifuged, washed with deionized water, and dried to obtain citric acid-modified zinc oxide.

[0029] (3) Add 6 g of citric acid-modified urea formaldehyde and 6 g of citric acid-modified zinc oxide to an aqueous solution containing 12 g of chitosan, stir and disperse to form an aqueous phase solution, use 3% by mass of Span-80 paraffin solution as the oil phase, mix the aqueous phase solution and the oil phase solution, stir evenly, stir at 55°C for 1.5 h, wash with ether and ethanol in turn, and dry to obtain modified chitosan composite nanoparticles.

[0030] (4) Add 5% by mass potassium hydroxide aqueous solution to 20g of acrylic acid, stir and disperse, and control the neutralization degree to 70% to obtain solution A; under a nitrogen atmosphere, add 10g of polyvinyl alcohol to deionized water, heat to 90°C, stir and dissolve to obtain solution B, then add solution A and 0.15g of potassium persulfate to solution B, stir and react at 70°C for 4h, then cool to 50°C, add 0.15g of urea and 0.009g of N,N-methylenebisacrylamide crosslinking agent, stir and react for 2h, after the reaction is completed, cool, filter and dry to obtain modified polyvinyl alcohol resin.

[0031] (5) 0.1 g of potassium dihydrogen phosphate was added to deionized water, stirred to dissolve, and then 5 g of modified polyvinyl alcohol resin and 0.5 g of modified chitosan composite nanoparticles were added thereto, stirred and mixed evenly, and dried to obtain foliar fertilizer.

[0032] Example 2

[0033] (1) 10 g of formaldehyde was added to deionized water, and the pH value was adjusted to 8 using a 5% by mass potassium hydroxide aqueous solution. 25 g of urea was added thereto, and the mixture was stirred and dispersed. The mixture was reacted at 55° C. for 5 h. After the reaction, 15 g of citric acid was added thereto. The mixture was mixed evenly and the reaction was continued for 20 min. After the reaction was completed, the mixture was dried to obtain citric acid-modified urea formaldehyde.

[0034] (2) 0.1 g of citric acid was added to deionized water, stirred and dispersed, and a 5% by mass potassium hydroxide aqueous solution was used to adjust the pH to 6. Then 4 g of nano zinc oxide was added thereto, and the mixture was stirred and reacted at 60° C. for 5 h. After the reaction was completed, the mixture was centrifuged, washed with deionized water, and dried to obtain citric acid-modified zinc oxide.

[0035] (3) Add 8 g of citric acid-modified urea formaldehyde and 7 g of citric acid-modified zinc oxide to an aqueous solution containing 12 g of chitosan, stir and disperse to form an aqueous phase solution, use 3% by mass of Span-80 paraffin solution as the oil phase, mix the aqueous phase solution and the oil phase solution, stir evenly, stir at 55°C for 2 h, wash with ether and ethanol in turn, and dry to obtain modified chitosan composite nanoparticles.

[0036] (4) A 5% by mass potassium hydroxide aqueous solution was added to 40 g of acrylic acid, stirred and dispersed, and the degree of neutralization was controlled to be 70% to obtain a solution A; under a nitrogen atmosphere, 10 g of polyvinyl alcohol was added to deionized water, heated to 85° C., stirred and dissolved to obtain a solution B, and then the solution A and 0.2 g of potassium persulfate were added to the solution B, stirred and reacted at 70° C. for 4 h, then cooled to 55° C., 0.6 g of urea and 0.02 g of N,N-methylenebisacrylamide crosslinking agent were added thereto, stirred and reacted for 1 h, and after the reaction was completed, cooled, filtered, and dried to obtain a modified polyvinyl alcohol resin.

[0037] (5) 0.1 g of potassium dihydrogen phosphate was added to deionized water, stirred to dissolve, and then 5.5 g of modified polyvinyl alcohol resin and 0.8 g of modified chitosan composite nanoparticles were added thereto, stirred and mixed evenly, and dried to obtain foliar fertilizer.

[0038] Example 3

[0039] (1) 10 g of formaldehyde was added to deionized water, and the pH value was adjusted to 8 using a 5% potassium hydroxide aqueous solution. 24 g of urea was added thereto, and the mixture was stirred and dispersed. The mixture was reacted at 45° C. for 2 h. After the reaction, 20 g of citric acid was added thereto. The mixture was mixed evenly and the reaction was continued for 10 min. After the reaction was completed, the mixture was dried to obtain citric acid-modified urea formaldehyde.

[0040] (2) 0.04 g of citric acid was added to deionized water, stirred and dispersed, and a 5% by mass potassium hydroxide aqueous solution was used to adjust the pH to 6. Then 4 g of nano zinc oxide was added thereto, and the mixture was stirred and reacted at 65° C. for 5 h. After the reaction was completed, the mixture was centrifuged, washed with deionized water, and dried to obtain citric acid-modified zinc oxide.

[0041] (3) Add 9 g of citric acid-modified urea formaldehyde and 10 g of citric acid-modified zinc oxide to an aqueous solution containing 12 g of chitosan, stir and disperse to form an aqueous phase solution, use 3% by mass of Span-80 paraffin solution as the oil phase, mix the aqueous phase solution and the oil phase solution, stir evenly, stir at 50°C for 2 h, wash with ether and ethanol in turn, and dry to obtain modified chitosan composite nanoparticles.

[0042] (4) Add 5% by mass potassium hydroxide aqueous solution to 40g of acrylic acid, stir and disperse, and control the neutralization degree to 70% to obtain solution A; under a nitrogen atmosphere, add 10g of polyvinyl alcohol to deionized water, heat to 90°C, stir and dissolve to obtain solution B, then add solution A and 0.2g of potassium persulfate to solution B, stir and react at 65-75°C for 4h, then cool to 55°C, add 0.6g of urea and 0.01g of N,N-methylenebisacrylamide crosslinking agent, stir and react for 2h, after the reaction is completed, cool, filter and dry to obtain modified polyvinyl alcohol resin.

[0043] (5) 0.1 g of potassium dihydrogen phosphate was added to deionized water and stirred to dissolve, and then 6 g of modified polyvinyl alcohol resin and 1 g of modified chitosan composite nanoparticles were added thereto and stirred to mix evenly, and dried to obtain foliar fertilizer.

[0044] Example 4

[0045] (1) 10 g of formaldehyde was added to deionized water, and the pH value was adjusted to 8 using a 5% by mass potassium hydroxide aqueous solution. 29 g of urea was added thereto, and the mixture was stirred and dispersed. The mixture was reacted at 50° C. for 5 h. After the reaction, 10 g of citric acid was added thereto, and the mixture was mixed evenly. The mixture was reacted for 15 min. After the reaction was completed, the mixture was dried to obtain citric acid-modified urea formaldehyde.

[0046] (2) 0.1 g of citric acid was added to deionized water, stirred and dispersed, and a 5% by mass potassium hydroxide aqueous solution was used to adjust the pH to 6, and then 4 g of nano zinc oxide was added thereto. The mixture was stirred and reacted at 55° C. for 6 h. After the reaction was completed, the mixture was centrifuged, washed with deionized water, and dried to obtain citric acid-modified zinc oxide.

[0047] (3) Add 11 g of citric acid-modified urea formaldehyde and 12 g of citric acid-modified zinc oxide to an aqueous solution containing 12 g of chitosan, stir and disperse to form an aqueous phase solution, use 3% by mass of Span-80 paraffin solution as the oil phase, mix the aqueous phase solution and the oil phase solution, stir evenly, stir at 60°C for 2 h, wash with ether and ethanol in turn, and dry to obtain modified chitosan composite nanoparticles.

[0048] (4) Add 5% by mass potassium hydroxide aqueous solution to 50g of acrylic acid, stir and disperse, and control the neutralization degree to 70% to obtain solution A; under a nitrogen atmosphere, add 10g of polyvinyl alcohol to deionized water, heat to 85°C, stir and dissolve to obtain solution B, then add 0.3g of potassium persulfate from solution A to solution B, stir and react at 75°C for 3h, then cool to 55°C, add 0.9g of urea and 0.036g of N,N-methylenebisacrylamide crosslinking agent, stir and react for 1h, after the reaction is completed, cool, filter and dry to obtain modified polyvinyl alcohol resin.

[0049] (5) 0.1 g of potassium dihydrogen phosphate was added to deionized water, stirred to dissolve, and then 6.5 g of modified polyvinyl alcohol resin and 1.2 g of modified chitosan composite nanoparticles were added thereto, stirred and mixed evenly, and dried to obtain foliar fertilizer.

[0050] Example 5

[0051] (1) 10 g of formaldehyde was added to deionized water, and the pH value was adjusted to 8 using a 5% by mass potassium hydroxide aqueous solution. 28 g of urea was added thereto, and the mixture was stirred and dispersed. The mixture was reacted at 50° C. for 3 h. After the reaction, 12 g of citric acid was added thereto, and the mixture was mixed evenly. The mixture was reacted for 15 min. After the reaction was completed, the mixture was dried to obtain citric acid-modified urea formaldehyde.

[0052] (2) 0.2 g of citric acid was added to deionized water, stirred and dispersed, and the pH was adjusted to 6 using a 5% by mass potassium hydroxide aqueous solution. Then 4 g of nano zinc oxide was added thereto, and the mixture was stirred and reacted at 60° C. for 3 h. After the reaction was completed, the mixture was centrifuged, washed with deionized water, and dried to obtain citric acid-modified zinc oxide.

[0053] (3) Add 12 g of citric acid-modified urea formaldehyde and 12 g of citric acid-modified zinc oxide to an aqueous solution containing 12 g of chitosan, stir and disperse to form an aqueous phase solution, use 3% by mass of Span-80 paraffin solution as the oil phase, mix the aqueous phase solution and the oil phase solution, stir evenly, stir at 55°C for 1 h, wash with ether and ethanol in turn, and dry to obtain modified chitosan composite nanoparticles.

[0054] (4) A 5% by mass potassium hydroxide aqueous solution was added to 40 g of acrylic acid, stirred and dispersed, and the degree of neutralization was controlled to be 70% to obtain a solution A; under a nitrogen atmosphere, 10 g of polyvinyl alcohol was added to deionized water, heated to 85° C., stirred and dissolved to obtain a solution B, and then the solution A and 0.2 g of potassium persulfate were added to the solution B, stirred and reacted at 65° C. for 5 h, then cooled to 45° C., 0.5 g of urea and 0.02 g of N,N-methylenebisacrylamide crosslinking agent were added thereto, stirred and reacted for 3 h, and after the reaction was completed, cooled, filtered, and dried to obtain a modified polyvinyl alcohol resin.

[0055] (5) 0.1 g of potassium dihydrogen phosphate was added to deionized water and stirred to dissolve, and then 7 g of modified polyvinyl alcohol resin and 1.5 g of modified chitosan composite nanoparticles were added thereto and stirred to mix evenly, and dried to obtain foliar fertilizer.

[0056] Comparative Example 1

[0057] The difference between this comparative example and Example 1 is that step (5) does not contain modified chitosan composite nanoparticles.

[0058] Fertilizer retention and slow release performance test:

[0059] Place 0.5 g of foliar fertilizer in a 150 μm nylon mesh bag, then place it in a 300 mL plastic bottle, add 100 mL of deionized water, cover and seal, and culture at 25°C for 1 day, 7 days, and 14 days. Turn the bottle upside down three times, take 20 mL of liquid sample and transfer it to a 100 mL volumetric flask, and use a Case distiller to determine the nitrogen release.

[0060] Table 1:

[0061]

[0062]

[0063] It can be seen from the table that the fertilizer-retaining zinc-rich fertilizer prepared by the present invention has good fertilizer-retaining and slow-release performance.

[0064] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A zinc-rich foliar fertilizer, characterized in that: The raw materials include, by weight: 1 part of potassium dihydrogen phosphate, 50-70 parts of modified polyvinyl alcohol resin, and 5-15 parts of modified chitosan composite nanoparticles; The preparation method of the fertilizer-retaining zinc-rich foliar fertilizer is: Potassium dihydrogen phosphate is added into deionized water, stirred to dissolve, and then modified polyvinyl alcohol resin and modified chitosan composite nanoparticles are added thereto, stirred and mixed evenly, and dried to obtain foliar fertilizer.

2. The fertilizer-retaining zinc-rich foliar fertilizer according to claim 1, characterized in that The preparation method of the modified polyvinyl alcohol resin comprises the following steps: adding a 5% by mass potassium hydroxide aqueous solution to acrylic acid, stirring and dispersing, and controlling the neutralization degree to be 70% to obtain a solution A; adding polyvinyl alcohol to deionized water under a nitrogen atmosphere, heating to 85-90° C., stirring and dissolving to obtain a solution B; then adding the solution A and potassium persulfate to the solution B, stirring and reacting at 65-75° C. for 3-5 hours, then cooling to 45-55° C., adding urea and N,N-methylenebisacrylamide crosslinking agent thereto, stirring and reacting for 1-3 hours, cooling after the reaction, filtering by suction, and drying to obtain the modified polyvinyl alcohol resin.

3. The fertilizer-retaining zinc-rich foliar fertilizer according to claim 2, characterized in that, The mass ratio of the acrylic acid to the polyvinyl alcohol is 2-5:

1.

4. The fertilizer-retaining zinc-rich foliar fertilizer according to claim 2, characterized in that The mass of the urea is 0.5-1.5% of the total mass of acrylic acid and polyvinyl alcohol; the mass of potassium persulfate is 0.5-1% of the total mass of acrylic acid and polyvinyl alcohol; and the crosslinking agent is 0.03-0.06% of the total mass of acrylic acid and polyvinyl alcohol.

5. The fertilizer-retaining zinc-rich foliar fertilizer according to claim 1, characterized in that The preparation method of the modified chitosan composite nanoparticles is: (1) adding formaldehyde to deionized water, adjusting the pH to 8 with a 5% by mass potassium hydroxide aqueous solution, adding urea thereto, stirring and dispersing, reacting at 45-55° C. for 2-5 hours, adding citric acid thereto after the reaction is completed, mixing evenly, and continuing the reaction for 10-20 minutes, and drying after the reaction is completed to obtain citric acid-modified urea formaldehyde; (2) adding citric acid to deionized water, stirring and dispersing, adjusting the pH to 6 with a 5% by mass potassium hydroxide aqueous solution, adding nano zinc oxide thereto, stirring and reacting at 55-65° C. for 3-6 hours, centrifuging after the reaction, washing with deionized water, and drying to obtain citric acid-modified zinc oxide; (3) Add citric acid-modified urea formaldehyde and citric acid-modified zinc oxide to the chitosan aqueous solution, stir and disperse to form an aqueous phase solution, use 3% by mass of Span-80 paraffin solution as the oil phase, mix the aqueous phase solution and the oil phase solution, stir evenly, stir at 50-60° C. for 1-2 h, wash with ether and ethanol in turn, and dry to obtain modified chitosan composite nanoparticles.

6. The fertilizer-retaining zinc-rich foliar fertilizer according to claim 5, characterized in that In the above (1), the mass ratio of formaldehyde to urea is 1:2.4-3.

7. The fertilizer-retaining zinc-rich foliar fertilizer according to claim 5, characterized in that In the above (2), the mass ratio of citric acid to nano zinc oxide is 0.01-0.05:

1.

8. The fertilizer-retaining zinc-rich foliar fertilizer according to claim 5, characterized in that In the above (3), the mass ratio of citric acid modified urea formaldehyde, citric acid modified zinc oxide and chitosan is 0.5-1:0.5-1:1.

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