Monodisperse nanocalcium carbonate-based foliar calcium fertilizer, preparation method therefor, and use thereof

Abstract

Disclosed in the present invention is a monodisperse nanocalcium carbonate-based foliar calcium fertilizer, comprising the following raw materials in parts by mass: 1-20 parts of a monodisperse nanocalcium carbonate filter cake, 0.05-0.9 parts of ethoxy-modified polytrisiloxane, 0.01-0.8 parts of modified casein, 0.01-0.8 parts of an enzyme, 0.05-0.9 parts of a sugar alcohol, and 10-180 parts of water. After being diluted by means of water such that the solid content of calcium carbonate is 0.5-2%, the foliar calcium fertilizer is used for foliar calcium supplementation of various crops and fruit and vegetable crops. The novel foliar calcium fertilizer is safe and non-toxic, can be directly sprayed onto foliar and fruit surfaces of crops and fruits and vegetables, effectively ensures calcium absorption and utilization in crops, achieves the effect of increasing yield and increasing income, and can also improve the yield of fruits and vegetables.

Description

A monodisperse nano-calcium carbonate-based foliar calcium fertilizer, its preparation method and application

[0001] Cross-reference to related applications This application is based on Chinese Patent Application No. 202411923246.6, filed on December 25, 2024, and claims priority to that Chinese Patent Application, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention belongs to the field of crop foliar fertilizers, specifically relating to a novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer, its preparation method, and its application. Background Technology

[0003] Fruits, vegetables, sugarcane, and other non-grain crops, as well as grain crops, have a high demand for calcium. Calcium deficiency has a significant negative impact on crops, leading to a series of problems such as fruit cracking, disease, fruit drop, and reduced yield. How to conveniently supplement calcium is an urgent problem that modern agriculture needs to solve. On the other hand, the absorption and utilization of calcium in the soil by plants requires stringent conditions. Crops cannot absorb traditional solid calcium salts. Calcium fertilizers in the soil often need to form water-soluble calcium ions through ion exchange before they can be absorbed and utilized by crop roots. Since the calcium salts corresponding to most anions present in the soil have low solubility, even soluble calcium fertilizers are easily fixed and ineffective by other anions in the soil after root application. Moreover, the type and state of calcium fertilizer, the content of other elements such as nitrogen, phosphorus, and potassium, and soil pH all affect the absorption and utilization of calcium ions by crops. For example, in areas with high pH, ​​the calcium ion exchange capacity is weaker, resulting in poor calcium ion absorption by crops; while areas with high levels of macroelements such as nitrogen, phosphorus, and potassium in the soil can also inhibit the absorption of calcium ions by crops. Furthermore, studies have shown that calcium ions are much more difficult to transport within plants than other nutrients. This, combined with the long transport distance from the root absorption system to the leaves and fruits, makes calcium deficiency at the plant apex a common occurrence. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer. This foliar calcium fertilizer is non-toxic, safe, and environmentally friendly. It can be directly sprayed onto the leaves or fruit surfaces of fruits, vegetables, and crops to meet their calcium requirements during growth. When used in fruit cultivation, it effectively inhibits fruit cracking and drop, increases fruit plumpness, improves calcium content and yield, and significantly enhances fruit taste and quality. When used in the cultivation of vegetables, sugarcane, rice, and other crops, it can significantly improve crop quality and yield.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows:

[0006] A novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer comprises, by weight, 1-20 parts monodisperse nano-calcium carbonate filter cake, 0.05-0.9 parts ethoxylated modified polytrisiloxane, 0.01-0.8 parts modified casein, 0.01-0.8 parts enzyme, 0.05-0.9 parts sugar alcohol, and 10-180 parts water.

[0007] According to the above scheme, the monodisperse nano-calcium carbonate filter cake has the following characteristics: the filter cake has a moisture content of 35%~40%; the calcium carbonate particles are cubic or nearly spherical in shape, with an average particle size between 20 and 100 nm, and particles with a diameter greater than 100 nm are less than 5%; the particle surface is clean, in a monodisperse state, and has a small surface energy, with a specific surface area of ​​less than 25 m². 2 / g, with a preferred specific surface area of ​​20~23 m² 2 / g; the content of harmful metal elements such as cadmium in calcium carbonate is less than 200 ppm; the monodisperse nano calcium carbonate filter cake can be stirred and dispersed in aqueous solution without the addition of any chemical dispersant and remain in stable suspension.

[0008] According to the above scheme, the method for preparing the monodisperse nano-calcium carbonate filter cake includes the following steps:

[0009] S1. Calcium carbonate slurry was prepared using calcination, digestion, and carbonation processes. The calcination process involved selecting limestone with uniform grain size and a content of harmful heavy metals such as cadmium, lead, and chromium less than 400 ppm as raw material. A calcination temperature matching the grain size was used to obtain quicklime with ideal activity. The activity of the quicklime was between 250 and 300 mL (4 mol / L HCl, 40±1℃, 10 min), exhibiting good uniformity and consistency. The digestion process involved digesting the calcined quicklime in hot water at 50–90℃ to obtain lime slurry. The aging and impurity removal process involved aging the digested lime slurry for 24–48 hours. h, and after filtration to remove impurities, refined raw pulp is obtained; the carbonation process is as follows: water is added to the refined raw pulp to adjust the solid content to 5% to 8%, and then carbonation is carried out. The initial carbonation temperature is 10 to 20℃, and the CO2 content is 20% to 40% (here, CO2 content refers to the content of carbon dioxide in the carbonation atmosphere during the carbonation process. For the carbonation process, carbonation is carried out by introducing carbon dioxide. A carbonation atmosphere with a certain CO2 content is sufficient. Pure carbon dioxide atmosphere is rarely used directly, as this is conducive to controlling the reaction progress of the carbonation process). Carbonation is carried out until the pH of the pulp reaches 7.5 to 9.0, and then carbonation is ended to obtain calcium carbonate cooked pulp;

[0010] The calcium carbonate particles in the calcium carbonate slurry are nearly spherical or chain-like in shape. The average particle size of the nearly spherical particles is 10-60 nm, and the average width of the chain-like particles is 10-60 nm.

[0011] S2. Add an inorganic salt grain surface reconstructing agent and an organic grain surface reconstructing agent to the calcium carbonate slurry obtained in S1, and then keep it at 120~140℃ for 1~4 h to obtain a calcium carbonate suspension. The inorganic grain surface reconstructing agent is one or more inorganic salts such as sodium silicate, sodium chloride, aluminum chloride, and zinc sulfate, and is used in an amount of 0.5%~3% of the dry weight of calcium carbonate. The organic grain surface reconstructing agent is one or more organic compounds such as ethanol, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and disodium ethylenediaminetetraacetate, and is used in an amount of 1%~5% of the dry weight of calcium carbonate.

[0012] S3. The calcium carbonate suspension obtained in S2 is dehydrated by hydraulic filtration to obtain a calcium carbonate filter cake. The moisture content of the filter cake is controlled between 35% and 40%, which is a monodisperse nano-calcium carbonate filter cake. At this point, it meets the following requirements: "The morphology of calcium carbonate particles is cubic or nearly spherical, with an average particle size between 20 and 100 nm, and particles with a diameter greater than 100 nm are less than 5%; the particle surface is clean, in a monodisperse state, with low surface energy, and its specific surface area is less than 25 m²". 2 The product exhibits the following characteristics: ⁶g; ⁷ ppm of harmful metals such as cadmium in calcium carbonate; ⁷ ppm of precipitate ...

[0013] The preparation method of the above-mentioned novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer includes the following steps:

[0014] (1) Prepare 1-20 parts of monodisperse nano calcium carbonate filter cake, 0.05-0.9 parts of ethoxylated modified polytrisiloxane, 0.01-0.8 parts of modified casein, 0.01-0.8 parts of enzyme, 0.05-0.9 parts of sugar alcohol, and 10-180 parts of water according to the proportions of each raw material and mass of the foliar calcium fertilizer described in this invention;

[0015] (2) Place the monodisperse nano calcium carbonate filter cake in a small amount of water at a temperature of 5~30℃ (the weight of the “small amount of water” is 1~2 times the weight of the monodisperse nano calcium carbonate filter cake in the formula), and disperse it in a high-speed disperser at a linear velocity of 80~120 m / min at room temperature for 15~40 min.

[0016] (3) After the stirring in step (2) is completed, add the remaining raw materials and the remaining water, and continue to disperse in a high-speed disperser at a linear speed of 80~120 m / min for 15~30 min to obtain the novel monodisperse nano calcium carbonate-based foliar calcium fertilizer of the present invention.

[0017] When using this novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer, it can be further diluted according to the different application targets. It is recommended to dilute it with water until the solid content of calcium carbonate is 0.5%~2% before spraying.

[0018] According to the above scheme, the grain crops mentioned in this invention include rice, wheat, sorghum, etc.; the non-grain crops include fruits such as apples, citrus, pears, plums, mangoes, cherry tomatoes, grapes, dragon fruit, oranges, loquats, apricots, kiwifruit, pomelos, pomegranates, jujubes, guavas, peaches, etc.; vegetables such as baby bok choy, cabbage, loofah, bitter melon, pumpkin, lettuce, etc.; and cassava, sugarcane, etc.

[0019] The novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer of the present invention can be used for crop planting. The application method is as follows: In dry weather without rain, dilute the foliar calcium fertilizer of the present invention and spray it on the leaves of grain crops or non-grain crops. There is no need to avoid the fruit. It needs to be sprayed 2 to 4 times during the crop growth process, with an interval of 15 to 20 days between adjacent sprays.

[0020] This invention uses limestone with uniform grain size and a content of harmful heavy metals such as cadmium, lead, and chromium of less than 400 ppm as raw material for preparing monodisperse nano-calcium carbonate filter cake. Then, a calcination temperature matching the grain size is used to obtain quicklime with moderate and uniform activity. This quicklime is then digested and carbonized to obtain a slurry of calcium carbonate. The uniform grain size of the limestone is used to adjust the lime activity through a limestone calcination process, avoiding partial under-burning and over-burning caused by mottled grains. The good uniformity and moderate activity of the lime facilitate the control of the digestion reaction, obtaining a homogeneous lime slurry with controllable properties, thereby enabling control of the subsequent carbonation process and obtaining a slurry of calcium carbonate with the desired particle size and grain morphology. The content of harmful heavy metals such as cadmium, lead, and chromium in the limestone is less than 400 ppm, ensuring that the content of harmful heavy metals in the prepared monodisperse nano-calcium carbonate filter cake is less than 200 ppm.

[0021] After carbonization, a grain surface reconstruction process is performed by adding inorganic and organic surface reconstruction agents and maintaining the temperature at a certain level. This promotes grain surface reconstruction, resulting in more complete crystals, smoother particle surfaces, and reduced surface energy, thus facilitating dispersion. The inorganic surface reconstruction agent promotes crystal development, repairs defects, and makes the crystals more complete; the organic surface reconstruction agent regulates the surface potential of the particles, controls the mutual repulsion of the grains in water, and prevents adhesion during the crystal repair process. This invention controls the average particle size of calcium carbonate particles to 20-100 nm and achieves a highly monodisperse state by controlling the temperature and time of grain surface reconstruction. This morphology of calcium carbonate particles ensures visible light diffraction transmission, thus not affecting the photosynthesis and surface coloring of crop leaves and fruits. Simultaneously, it effectively absorbs harmful ultraviolet light (for example, when the foliar calcium fertilizer described in this invention is diluted to a calcium carbonate solid content of 1% and sprayed to form a film, the absorption of ultraviolet light can reach over 80%, while the absorption of visible light is less than 15%). The monodisperse nano-calcium carbonate slurry obtained by reconstructing the crystal surface is then subjected to pressure filtration or centrifugation to obtain monodisperse calcium carbonate filter cakes of the desired particle size. Pressure filtration and centrifugation remove excess water, facilitating the processing and transportation of calcium carbonate, while also rapidly reducing other soluble ions present in the solution during production, thus achieving the goal of not affecting or interfering with the use and effectiveness of the foliar calcium fertilizer of this invention.

[0022] Based on the above, this invention uses the monodisperse nano-calcium carbonate filter cake as the main raw material, and mixes it with other raw materials to disperse in water, thereby obtaining the foliar calcium fertilizer described in this invention. The monodisperse nano-calcium carbonate filter cake maintains 35%–40% moisture content, preserving a water film and electric double layer structure between the calcium carbonate solid particles. This maximizes the preservation of the surface state and repulsive forces of the calcium carbonate particles, preventing agglomeration. Therefore, it can be rapidly redispersed in the aqueous solution during assisted stirring in a disperser and maintain stable suspension.

[0023] This invention processes calcium carbonate into monodisperse cubic and near-spherical nanoparticles. Utilizing the hydroxyl and carboxyl groups in the long-chain fatty acid polymers—the main components of the leaf's outermost cuticle—it bonds with calcium ions on the surface of the nano-calcium carbonate, allowing calcium ions to effectively penetrate the cuticle and enter the leaf. Furthermore, it leverages the small size of the calcium carbonate nanoparticles and submicron particles to establish rapid calcium ion channels through stomata (approximately 10–20 µm in diameter) on the leaf surface. This allows plants to directly absorb solid calcium carbonate as a calcium fertilizer through the leaves, forming a key technology for direct and rapid calcium supplementation via foliar application. In addition, the abundant sugar alcohols on the fruit surface can bind with free calcium ions on the nano-calcium carbonate surface and directly transport them into the fruit to form calcium gluconate, increasing the calcium content in the fruit pulp. Simultaneously, the sugar alcohols in this foliar calcium fertilizer formulation have penetrating and wetting functions, further enhancing the calcium ion transport effect on the leaves.

[0024] This invention provides a novel foliar calcium fertilizer that rapidly forms a light-colored protective film on crop leaves. Utilizing nano-calcium carbonate particles, it induces "systemically acquired resistance" and "systemically acquired adaptation" responses in plants by triggering reactive oxygen species outside the plant cell membrane. This achieves a mechanism that coordinates plant growth and resistance, resulting in crops treated with this novel foliar calcium fertilizer exhibiting excellent stress resistance and effectively resisting pests and diseases. Due to the special particle size and dispersibility design of calcium carbonate, the protective film does not affect the transmission of visible light, thus not affecting fruit photosynthesis. Furthermore, by utilizing the ultraviolet absorption and infrared radiation properties of calcium carbonate, combined with the particle size design of this invention, it can effectively reduce ultraviolet scorching of crops and fruits, lower the temperature of crops and fruits, and form effective physical and optical protection.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer of this invention is safe, environmentally friendly, and non-toxic. It can be used in the production of grain crops such as rice, wheat, and sorghum, as well as non-grain crops such as cassava, sugarcane, fruits, and vegetables. It effectively ensures the absorption and utilization of calcium by crops, meets the calcium requirements of crops during growth, and achieves the effect of increasing yield and income. It effectively inhibits fruit cracking and fruit drop, increases fruit fullness, improves the calcium content and yield of fruits, and significantly improves the taste and quality of fruits.

[0027] 2. The novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer of the present invention can be used, especially for fruit (such as apples, pears, plums, citrus, dragon fruit, mangoes, etc.) cultivation. When used, it can be sprayed directly onto the leaves of the crop without having to avoid the fruit. It can increase yield while having good physical insect control and repellency effects, and can significantly improve the disease and insect resistance of fruits, and reduce diseased and insect-infested fruits.

[0028] 3. The novel foliar calcium fertilizer described in this invention can effectively absorb ultraviolet rays and radiate infrared rays, reducing crop temperature. It does not affect the transmission of visible light and does not interfere with the normal photosynthesis of fruit and vegetable crops, making it suitable for fruit and vegetable cultivation. Attached Figure Description

[0029] Figure 1 is a scanning electron microscope image of calcium carbonate particles in the calcium carbonate slurry prepared in Example 1.

[0030] Figure 2 is a scanning electron microscope image of the monodisperse nano-calcium carbonate prepared in Example 1;

[0031] Figure 3 shows the effect of the novel foliar calcium fertilizer prepared in Example 1 on baby bok choy and the effect of spraying with water as a control.

[0032] Figure 4 is a scanning electron microscope image of calcium carbonate particles in the calcium carbonate slurry prepared in Example 2.

[0033] Figure 5 is a scanning electron microscope image of the monodisperse nano-calcium carbonate prepared in Example 2;

[0034] Figure 6 shows the effect of the novel foliar calcium fertilizer prepared in Example 2 on rice and the effect of spraying with water as a control.

[0035] Figure 7 is a scanning electron microscope image of calcium carbonate particles in the calcium carbonate slurry prepared in Example 3.

[0036] Figure 8 is a scanning electron microscope image of the monodisperse nano-calcium carbonate prepared in Example 3;

[0037] Figure 9 shows the effect of the novel foliar calcium fertilizer prepared in Example 3 on sugarcane.

[0038] Figure 10 is a scanning electron microscope image of calcium carbonate particles in the calcium carbonate slurry prepared in Example 4.

[0039] Figure 11 is a scanning electron microscope image of the monodisperse nano-calcium carbonate prepared in Example 4;

[0040] Figure 12 shows the effect of the novel foliar calcium fertilizer prepared in Example 4 on pears;

[0041] Figure 13 is a scanning electron microscope image of calcium carbonate particles in the calcium carbonate slurry prepared in Example 5.

[0042] Figure 14 is a scanning electron microscope image of the monodisperse nano-calcium carbonate prepared in Example 5.

[0043] Figure 15 shows the effect of the novel foliar calcium fertilizer prepared in Example 5 on apples.

[0044] Figure 16 is a scanning electron microscope image of the calcium carbonate prepared in Comparative Example 1.

[0045] Figure 17 shows the effect of the foliar calcium fertilizer prepared using Comparative Example 1 on baby bok choy.

[0046] Figure 18 shows the effect of the foliar calcium fertilizer prepared using Comparative Example 2 on rice.

[0047] Figure 19 is a scanning electron microscope image of the calcium carbonate prepared in Comparative Example 3.

[0048] Figure 20 is a comparison diagram of the effects of calcium carbonate dispersion in water in the examples and comparative examples;

[0049] Figure 21 shows the effect of foliar calcium fertilizer made from calcium carbonate (Comparative Example 3) on pears.

[0050] Figure 22 shows the effect of foliar calcium fertilizer made from calcium carbonate (Comparative Example 4) on pears.

[0051] Figure 23 shows the effect of foliar calcium fertilizer made from calcium carbonate (Comparative Example 5) on apples.

[0052] Specific implementation methods

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0054] This invention provides a novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer, the raw materials of which, by mass parts, include: 1-20 parts monodisperse nano-calcium carbonate filter cake, 0.05-0.9 parts ethoxylated modified polytrisiloxane, 0.01-0.8 parts modified casein, 0.01-0.8 parts enzyme, 0.05-0.9 parts sugar alcohol, and 10-180 parts water.

[0055] In some specific embodiments, the mass of the monodisperse nano-calcium carbonate filter cake is 15 to 75 times that of the ethoxylated modified polytrisiloxane, preferably 15 to 25 times.

[0056] In some specific embodiments, the mass of water is 2 to 60 times that of the monodisperse nano-calcium carbonate filter cake, preferably 2 to 11 times.

[0057] In some specific embodiments, the mass of the monodisperse nano-calcium carbonate filter cake is 18.75 to 50 times that of the modified casein, preferably 25 to 50 times.

[0058] In some specific embodiments, the mass of the monodisperse nano-calcium carbonate filter cake is 25 to 100 times that of the enzyme, preferably 75 to 100 times.

[0059] In some specific embodiments, the mass of the monodisperse nano-calcium carbonate filter cake is 20 to 50 times that of the sugar alcohol, preferably 20 to 30 times.

[0060] In some specific embodiments, the sugar alcohol includes one or more of xylitol, ribitol, mannitol, sorbitol, maltitol, erythritol, and lactitol. All sugar alcohols are commercially available products with an active ingredient content greater than 70%.

[0061] In some specific embodiments, the modified casein is a milky white viscous liquid with a solid content of 15%–25%, a viscosity (at 20°C) greater than 100 mPa·s, and a pH value (10% aqueous solution) of 7–8. Specifically, the modified casein is an emulsion obtained by dissolving commercially available casein in weak alkaline water at 50–65°C. It appears as a milky white viscous liquid with a solid content of 20.0 ± 2.0%, a viscosity (at 20°C) greater than 100 mPa·s, and a pH value (10% aqueous solution) of 7–8. The casein is purchased from Gansu Hualing Dairy Co., Ltd., and its product type is edible casein.

[0062] In some specific embodiments, the enzyme is a commercially available agricultural enzyme containing agricultural biological agents, polysaccharides, amino acids, and other components. It is purchased from Jining Alida Bioengineering Co., Ltd., and the model number is MLQ-Plant Enzyme.

[0063] In some specific embodiments, the ethoxylated modified polytrisiloxane is a commercially available product purchased from GE Silicones USA, model number Silwet, with an active ingredient content greater than 98%.

[0064] Example 1

[0065] This embodiment provides a novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer, which is formulated from the following raw materials in parts by weight: 1 part monodisperse nano-calcium carbonate filter cake, 0.05 parts ethoxylated modified polytrisiloxane, 0.02 parts modified casein, 0.01 parts enzyme, 0.05 parts mannitol, and 60 parts water.

[0066] The preparation method of the novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer described in this embodiment is as follows: According to the above raw materials and mass proportions, 1 part of monodisperse nano-calcium carbonate filter cake is placed in 2 parts of water, and stirred for 40 min at a stirring speed of 80 m / min using a high-speed disperser. Then, according to the above formula, 0.05 parts of ethoxylated modified polytrisiloxane, 0.02 parts of modified casein, 0.01 parts of enzyme, 0.05 parts of mannitol, and the remaining 58 parts of water are added, and stirring is continued at a stirring speed of 80 m / min for 20 min to obtain the foliar calcium fertilizer described in this embodiment, with a calcium carbonate solid content of approximately 1%.

[0067] In this embodiment, the preparation steps of the monodisperse nano-calcium carbonate filter cake are as follows:

[0068] S1. Calcium carbonate slurry is prepared using calcination, digestion, and carbonation processes. The calcination process involves selecting limestone with a grain size of 0.2–0.5 mm and a content of harmful heavy metals such as cadmium, lead, and chromium of less than 400 ppm as raw material. Calcination is carried out at 900℃ for 2 hours to obtain ideally active quicklime. The digestion process involves digesting the calcined quicklime with water at 50℃ to obtain lime milk, which is then aged for 48 hours before impurity removal to obtain refined raw slurry. The carbonation process involves adding water to the refined raw slurry obtained from digestion to adjust the solid content to 5%, followed by carbonation at an initial temperature of 10℃ and a CO2 content of 40%. Carbonation continues until the slurry pH reaches 7.5–8.0, at which point carbonation is terminated to obtain calcium carbonate slurry.

[0069] As can be observed from the scanning electron microscope image (see Figure 1), the calcium carbonate particles in the obtained slurry are nearly spherical and short rod-shaped particles with an average particle size of about 15 nm.

[0070] S2. Add 0.5% aluminum chloride, 2% polyvinyl alcohol, 2% polyvinylpyrrolidone and 1% sodium dodecylbenzenesulfonate by dry weight of calcium carbonate to the calcium carbonate slurry obtained in S1, and keep it at 140℃ for 1.0 h to obtain calcium carbonate suspension.

[0071] S3. The calcium carbonate suspension obtained in S2 was dehydrated by hydraulic filtration to obtain a calcium carbonate filter cake. The moisture content of the filter cake was controlled between 35% and 40%, i.e., monodisperse nano-calcium carbonate. An appropriate amount of the filter cake was then dried at 105℃ and subjected to composition, specific surface area, microstructure, and particle size analysis. The composition and specific surface area tests were conducted according to the "Analytical Methods for Calcium Carbonate" (GB / T 19281-2014) standard, and the microstructure and particle size tests were conducted according to the "Nano-calcium Carbonate" (GB / T 19590-2023) standard. The obtained monodisperse nano-calcium carbonate contained less than 0.0002% of harmful impurities such as cadmium, lead, barium, mercury, and arsenic, and the total content of harmful impurities was less than 200 ppm; the specific surface area was approximately 24.66 m². 2 / g; Scanning electron microscopy images (see Figure 2) clearly show that the average particle size of the obtained monodisperse nano-calcium carbonate particles is about 30 nm, and the particles are nearly spherical and cubic with smooth and clean surfaces. The obtained monodisperse nano-calcium carbonate filter cake was dispersed in water to obtain a suspension with a solid content of 2%, and then the suspension effect was observed after standing for 4 hours. It was still stably suspended (see Figure 20).

[0072] When used for foliar spraying of baby bok choy: During the rosette stage, directly and evenly spray the foliar calcium fertilizer prepared in this embodiment onto the leaves of the baby bok choy. After spraying, record the growth status of the entire baby bok choy plant by taking photos. Thereafter, observe regularly every week. Before the baby bok choy enters the heading stage, it needs to be sprayed 1-2 times. If there is more than 3 days of rainfall with a rainfall of 120mm or more, it is necessary to spray again after the rain.

[0073] Figure 3 shows the effect of using foliar calcium fertilizer in this embodiment on baby bok choy.

[0074] Table 1 shows the results of calcium content detection in the aboveground parts of baby bok choy after spraying with the foliar calcium fertilizer of this embodiment (set-1) and after spraying with water (ck-1). The calcium content in the aboveground parts of baby bok choy increased by 22.87% after spraying with the new foliar calcium fertilizer of this embodiment.

[0075] Example 2

[0076] This embodiment provides a novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer, which is formulated from the following raw materials in the indicated weight ratios: 20 parts monodisperse nano-calcium carbonate filter cake, 0.9 parts ethoxylated modified polytrisiloxane, 0.5 parts modified casein, 0.8 parts enzyme, 0.9 parts xylitol, and 40 parts water.

[0077] The preparation method of the novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer described in this embodiment is as follows: According to the above raw materials and mass proportions, 20 parts of monodisperse nano-calcium carbonate filter cake are placed in 28 parts of water. After stirring with a high-speed disperser at a stirring speed of 100 m / min for 40 min, 0.9 parts of ethoxylated modified polytrisiloxane, 0.5 parts of modified casein, 0.8 parts of enzyme, 0.9 parts of xylitol and the remaining 12 parts of water are added according to the above formula. Stirring is continued at a stirring speed of 120 m / min for 15 min to obtain the foliar calcium fertilizer described in this embodiment, with a calcium carbonate solid content of approximately 20%. The preparation steps of the monodisperse nano-calcium carbonate filter cake differ from those in Example 1 in that: the digestion temperature in step S1 is 90℃, the aging time is 24 h, the carbonation initiation temperature during the carbonation process is 20℃, the CO2 content is 33%, and carbonation ends when the pH reaches 7.5~8.5. After carbonation, the calcium carbonate particles in the resulting slurry are characterized by microscopic morphology, and it can be observed that the calcium carbonate particles are nearly spherical or short rod-shaped with an average particle size of about 31 nm (see Figure 4); in step S2, during the crystal surface reconstruction process, 1.5% sodium chloride, 0.5% zinc sulfate, 1% sodium silicate, 0.5% ethanol, and 0.5% disodium ethylenediaminetetraacetate by dry weight of calcium carbonate are added, and the mixture is kept at 130℃ for 3.0 h.

[0078] The monodisperse nano-calcium carbonate filter cake obtained in this example was analyzed for composition, specific surface area, microstructure, and particle size using the same testing methods as in Example 1. The contents of harmful impurities such as cadmium, lead, barium, mercury, and arsenic in the obtained monodisperse nano-calcium carbonate were all less than 0.0002%, and the total content of harmful impurities was less than 200 ppm; the specific surface area was approximately 19.82 m². 2 / g; From the SEM image (see Figure 5), it can be clearly seen that the average particle size of the obtained monodisperse nano-calcium carbonate particles is about 66 nm, the particles are cubic, and the surface is flat and clean. The obtained monodisperse nano-calcium carbonate filter cake was dispersed in water to obtain a suspension with a solid content of 2%, and then the suspension effect was observed after standing for 4 h. It could still be stably suspended (see Figure 20).

[0079] Application Testing: The novel foliar calcium fertilizer prepared in this embodiment was used in rice cultivation. Specifically, during the tillering and growth stages, from late March to early April and in June each year, in rainless weather, the novel foliar calcium fertilizer was diluted 10 times (with a calcium carbonate solid content of approximately 2%) and sprayed onto the rice leaves. After spraying, the growth status of the entire rice plant was recorded by taking photos, and then observed regularly once a month thereafter. If, within 24 hours after spraying, there is more than 3 days of rainfall with a precipitation of 120 mm or more, a second spraying is required after the rain.

[0080] Figure 6 shows the effect of using the foliar calcium fertilizer in this embodiment on rice.

[0081] Table 1 shows the results of the calcium content test of the edible parts of rice after spraying with the foliar calcium fertilizer of this embodiment (set-2) and after spraying with water (ck-2). The calcium content of the edible parts of rice increased by 15.53% after spraying with the new foliar calcium fertilizer of this embodiment.

[0082] Example 3

[0083] This embodiment provides a novel monodisperse nano-calcium carbonate-based foliar calcium fertilizer, which is formulated from the following raw materials in parts by weight: 15 parts monodisperse nano-calcium carbonate filter cake, 0.2 parts ethoxylated modified polytrisiloxane, 0.8 parts modified casein, 0.2 parts enzyme, 0.6 parts erythritol, and 45 parts water.

[0084] The preparation method of the novel foliar calcium fertilizer described in this embodiment is as follows: According to the above raw materials and mass proportions, 15 parts of monodisperse nano calcium carbonate filter cake are placed in 20 parts of water. After stirring with a high-speed disperser at a stirring speed of 90 m / min for 30 min, 0.2 parts of ethoxylated modified polytrisiloxane, 0.8 parts of modified casein, 0.2 parts of enzyme, 0.6 parts of erythritol and the remaining 25 parts of water are added according to the above formula. Stirring is continued at a stirring speed of 110 m / min for 25 min to obtain the foliar calcium fertilizer described in this embodiment, with a calcium carbonate solid content of approximately 15%. The preparation steps of the monodisperse nano-calcium carbonate filter cake differ from those in Example 1 in that the solid content of the refined raw pulp in step S1 is 6%, the carbonation initiation temperature is 15℃, the CO2 content is 35%, and carbonation ends when the pH reaches 8.0~9.0. After carbonation, the calcium carbonate particles in the resulting cooked pulp are characterized by microscopic morphology, and it can be observed that the calcium carbonate particles are short chains with an average width of about 21 nm (see Figure 7). In step S2, during the crystal surface reconstruction process, 0.2% zinc sulfate, 0.5% sodium silicate, 1.4% polyethylene glycol, and 0.6% hexadecyltrimethylammonium bromide by dry weight of calcium carbonate are added, and the mixture is kept at 120℃ for 6 h.

[0085] The monodisperse nano-calcium carbonate filter cake obtained in this example was analyzed for composition, specific surface area, microstructure, and particle size using the same testing methods as in Example 1. The contents of harmful impurities such as cadmium, lead, barium, mercury, and arsenic in the obtained monodisperse nano-calcium carbonate were all less than 0.0002%, and the total content of harmful impurities was less than 200 ppm; the specific surface area was approximately 22.82 m². 2 / g; From the SEM image (see Figure 8), it can be clearly seen that the average particle size of the obtained monodisperse nano-calcium carbonate particles is about 45 nm, the particles are cubic, and the surface is flat and clean. The obtained monodisperse nano-calcium carbonate filter cake was dispersed in water to obtain a suspension with a solid content of 2%, and then the suspension effect was observed after standing for 4 h. It could still be stably suspended (see Figure 20).

[0086] Application Testing: The novel foliar calcium fertilizer prepared in this embodiment was applied to sugarcane cultivation. Specifically, during the tillering and growth stages, from late March to early April and in June each year, in rainless weather, the novel foliar calcium fertilizer was diluted 10 times (with a calcium carbonate solid content of approximately 1.5%) and sprayed onto the sugarcane leaves. After spraying, the growth status of the entire sugarcane plant was recorded by taking photos, and then observed regularly once a month thereafter. If, within 24 hours after spraying, there is more than 3 days of rainfall with a precipitation of 120 mm or more, a second spraying is required after the rain.

[0087] Figure 9 shows the effect of using foliar calcium fertilizer in this embodiment on sugarcane.

[0088] Table 1 shows the results of calcium content testing on the edible parts of sugarcane after spraying with the foliar calcium fertilizer of this embodiment (set-3) and after spraying with water (ck-3). The calcium content of the edible parts of sugarcane increased by 11.11% after spraying with the new foliar calcium fertilizer of this embodiment.

[0089] Example 4

[0090] This embodiment provides a novel foliar calcium fertilizer, which is formulated with the following mass ratio: 5 parts monodisperse nano calcium carbonate filter cake, 0.3 parts ethoxylated modified polytrisiloxane, 0.2 parts modified casein, 0.05 parts enzyme, 0.1 parts lactitol, and 55 parts water.

[0091] The preparation method of the novel foliar calcium fertilizer described in this embodiment is as follows: According to the above raw materials and mass proportions, 5 parts of monodisperse nano calcium carbonate filter cake are placed in 10 parts of water. After stirring with a high-speed disperser at a stirring speed of 120 m / min for 15 min, 0.3 parts of ethoxylated modified polytrisiloxane, 0.2 parts of modified casein, 0.05 parts of enzyme, 0.1 parts of lactitol and the remaining 45 parts of water are added according to the above formula. Stirring is continued at a stirring speed of 90 m / min for 30 min to obtain the foliar calcium fertilizer described in this embodiment, with a calcium carbonate solid content of about 5%. The preparation steps of the monodisperse nano-calcium carbonate filter cake differ from those in Example 1 in that: the digestion temperature in step S1 is 70℃, the aging time is 36 h, the solid content of the refined raw pulp during carbonation is 7%, the carbonation initiation temperature is 12℃, the CO2 content is 30%, and carbonation ends when the pH reaches 8.0~8.5. After carbonation, the calcium carbonate particles in the resulting mature pulp are characterized by microscopic morphology, and it can be observed that the calcium carbonate particles are chain-like with an average width of about 25 nm (see Figure 10); in step S2, during the crystal surface reconstruction process, 0.5% sodium silicate, 1.5% aluminum chloride, 0.5% sodium dodecylbenzenesulfonate, and 2% sodium dodecyl sulfate by dry weight of calcium carbonate are added, and the mixture is kept at 140℃ for 2 h.

[0092] The monodisperse nano-calcium carbonate filter cake obtained in this example was analyzed for composition, specific surface area, microstructure, and particle size using the same testing methods as in Example 1. The contents of harmful impurities such as cadmium, lead, barium, mercury, and arsenic in the obtained monodisperse nano-calcium carbonate were all less than 0.0002%, and the total content of harmful impurities was less than 200 ppm; the specific surface area was approximately 21.15 m². 2 / g; From the SEM image (see Figure 11), it can be clearly seen that the average particle size of the obtained monodisperse nano-calcium carbonate particles is about 56 nm, the particles are cubic, and the surface is flat and clean. The obtained monodisperse nano-calcium carbonate filter cake was dispersed in water to obtain a suspension with a solid content of 2%, and then the suspension effect was observed after standing for 4 h. It could still be stably suspended (see Figure 20).

[0093] When used for pear cultivation: Before the pear fruit enlargement stage, dilute the novel foliar calcium fertilizer prepared in this embodiment 10 times (calcium carbonate solid content is approximately 0.5%) and spray it on the pear tree leaves. After spraying, record the growth status of the entire pear tree by taking photos. Thereafter, observe regularly once a week. During the pear ripening process, spray 1-2 times. If there is rainfall of 120 mm or more over 3 days, it is necessary to spray again after the rain. Before re-spraying, ensure that there will be no rain for 24 hours.

[0094] Figure 12 shows the effect of the novel foliar calcium fertilizer prepared in this embodiment on pears. The novel foliar calcium fertilizer can quickly spread and adhere evenly to the pear leaves.

[0095] The results of the calcium content test of pear pulp after spraying with the novel foliar calcium fertilizer prepared in this embodiment (set-4) and spraying with water (ck-4) are shown in Table 1. After spraying with the novel foliar calcium fertilizer prepared in this embodiment, the calcium content in pear pulp increased by 173.17%.

[0096] Example 5

[0097] This embodiment provides a novel foliar calcium fertilizer, which is formulated with the following mass ratio: 20 parts monodisperse nano calcium carbonate filter cake, 0.8 parts ethoxylated modified polytrisiloxane, 0.8 parts modified casein, 0.2 parts enzyme, 0.7 parts maltitol, and 180 parts water.

[0098] The preparation method of the novel foliar calcium fertilizer described in this embodiment is as follows: According to the above raw materials and mass proportions, 20 parts of monodisperse nano calcium carbonate filter cake are placed in 20 parts of water. The mixture is stirred for 20 minutes at a stirring speed of 110 m / min using a high-speed disperser. Then, according to the above formula, 0.8 parts of ethoxylated modified polytrisiloxane, 0.8 parts of modified casein, 0.2 parts of enzyme, 0.7 parts of maltitol, and the remaining 160 parts of water are added. The mixture is stirred for another 20 minutes at a stirring speed of 100 m / min to obtain the foliar calcium fertilizer described in this embodiment, with a calcium carbonate solid content of approximately 6%. The preparation steps of the monodisperse nano-calcium carbonate filter cake differ from those in Example 1 in that: the digestion temperature in step S1 is 80℃, the aging time is 30 h, the solid content of the refined raw pulp during carbonation is 8%, the carbonation initiation temperature is 10℃, the CO2 content is 35%, and carbonation ends when the pH reaches 7.5~8.0. After carbonation, the calcium carbonate particles in the resulting mature pulp are characterized by microscopic morphology, and it can be observed that the calcium carbonate particles are chain-like with an average width of about 45 nm (see Figure 13); in step S2, during the crystal surface reconstruction process, 1.5% zinc sulfate and 2% disodium ethylenediaminetetraacetate by dry weight of calcium carbonate are added, and the mixture is kept at 135℃ for 5 h.

[0099] The monodisperse nano-calcium carbonate filter cake obtained in this example was analyzed for composition, specific surface area, microstructure, and particle size using the same testing methods as in Example 1. The contents of harmful impurities such as cadmium, lead, barium, mercury, and arsenic in the obtained monodisperse nano-calcium carbonate were all less than 0.0002%, and the total content of harmful impurities was less than 200 ppm; the specific surface area was approximately 19.31 m². 2 / g; From the SEM image (see Figure 14), it can be clearly seen that the average particle size of the obtained monodisperse nano-calcium carbonate particles is about 85 nm, the particles are cubic, and the surface is flat and clean. The obtained monodisperse nano-calcium carbonate filter cake was dispersed in water to obtain a suspension with a solid content of 2%, and then the suspension effect was observed after standing for 4 h. It could still be stably suspended (see Figure 20).

[0100] When used in apple cultivation: Before the apple fruit begins to swell, dilute the novel foliar calcium fertilizer prepared in this embodiment 6 times (calcium carbonate solid content is approximately 1.0%) and spray it on the leaves of the apple tree. After spraying, record the growth status of the entire apple tree by taking photos. Thereafter, observe the tree regularly once a week. During the apple ripening process, spray 1-2 times. If there is rainfall of 120 mm or more over 3 days, a second spray is required after the rain. Before the second spray, ensure that there will be no rain for 24 hours.

[0101] Figure 15 shows the effect of the novel foliar calcium fertilizer prepared in this embodiment on apple trees. The novel foliar calcium fertilizer can quickly spread and adhere evenly to the apple tree leaves.

[0102] The results of the calcium content test of apple pulp after spraying with the novel foliar calcium fertilizer prepared in this embodiment (set-5) and spraying with water (ck-5) are shown in Table 2. The calcium content of apple pulp increased by 58.80%.

[0103] Comparative Example 1

[0104] Comparative Example 1 has the same formulation as Example 1, except that no inorganic grain surface reconstruction agent was added in the preparation method of calcium carbonate. The microstructure of the obtained product is shown in Figure 16.

[0105] In Comparative Example 1, because no inorganic crystal surface remodeling agent was added, the calcium carbonate crystal surface was rough, resulting in relatively poor dispersion between particles. This led to the formation of bonds between particles, reducing dispersion stability in water. Furthermore, due to the hard agglomeration of particles, the sprayed product was unevenly dispersed on the leaves of the baby bok choy (as shown in Figure 17), with locally higher concentrations. This clogged the stomata on the leaf surface, weakening the baby bok choy's calcium absorption capacity.

[0106] Comparative Example 2

[0107] Comparative Example 2 uses the same method as Example 2 for preparing calcium carbonate, directly using the calcium carbonate filter cake prepared in Example 2 as a foliar calcium fertilizer without adding ethoxylated modified polytrisiloxane, modified casein, enzymes, mannitol and other excipients.

[0108] In Comparative Example 2, because no adjuvants were added, the foliar calcium fertilizer did not soak into the rice leaves during the spraying process, resulting in uneven application of the foliar calcium fertilizer, as shown in Figure 18, and poor calcium absorption.

[0109] Comparative Example 3

[0110] Comparative Example 3 and Example 4 have the same formulation, except that no organic grain surface remodeling agent was added in the preparation method of calcium carbonate. The microstructure of the obtained product is shown in Figure 19.

[0111] In Comparative Example 2, because no organic crystal surface remodeling agent was added, the calcium carbonate crystal surface was clean, but the dispersion between particles was still relatively poor, and the particles formed bonds, resulting in reduced dispersion stability in water, as shown in Figure 20. Furthermore, due to the hard agglomeration of particles, uniform adhesion could not be achieved when sprayed onto pear trees, as shown in Figure 21, resulting in numerous spots on the surface of the pear fruit and poor calcium absorption.

[0112] Comparative Example 4

[0113] Comparative Example 4 has the same formulation as Example 4, except that the preparation method of the foliar calcium fertilizer is not carried out in a two-step dispersion step. Instead, 5 parts of monodisperse nano calcium carbonate filter cake are directly added to 55 parts of water and stirred for 15 min at a stirring speed of 120 m / min using a high-speed disperser. After stirring evenly, ethoxylated modified polytrisiloxane, modified casein, enzyme and lactitol are added according to the ingredient ratio, and stirring is continued at a stirring speed of 100 m / min for 15 min.

[0114] Comparative Example 5, lacking a high-concentration stirring step, resulted in poor calcium carbonate dispersion. When used for calcium supplementation in pear cultivation, it could not adhere evenly, exhibiting localized differences in concentration, as shown in Figure 22. Furthermore, it tended to accumulate at the fruit stem, leading to numerous spots on the mature fruit surface and a higher fruit drop rate.

[0115] Comparative Example 5

[0116] Comparative Example 5 has the same formulation as Example 5, except that the calcium carbonate preparation method does not involve pressure filtration to obtain a monodisperse calcium carbonate filter cake with a special morphology. Instead, the slurry obtained after reconstructing the crystal surface is directly prepared according to the proportions described in Example 1.

[0117] Comparative Example 5, because it did not undergo pressure filtration to remove soluble ions from the slurry, was used for apple cultivation and could not adhere evenly, resulting in more spots and cracks on the surface of the apples after ripening, as shown in Figure 23.

[0118] The calcium content of the edible parts of the fruits and vegetables in the above examples and comparative examples was determined in accordance with GB 5009.268-2016.

[0119] Table 1

[0120]

[0121] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer, the raw material composition by mass parts comprising: 1-20 parts of monodisperse nano-calcium carbonate filter cake, 0.05-0.9 parts of ethoxylated modified polytrisiloxane, 0.01-0.8 parts of modified casein, 0.01-0.8 parts of enzyme, 0.05-0.9 parts of sugar alcohol, and 10-180 parts of water; The monodisperse nano-calcium carbonate filter cake has a moisture content of 35%–40%, the average particle size of the calcium carbonate particles is between 20 and 100 nm, the particles with a diameter greater than 100 nm are less than 5%, and the specific surface area is less than 25 m². 2 / g; and the monodisperse nano-calcium carbonate filter cake is stirred and dispersed in aqueous solution without the addition of any chemical dispersant, and remains in stable suspension.

2. The monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The mass of monodisperse nano-calcium carbonate filter cake is 15 to 75 times that of ethoxylated modified polytrisiloxane.

3. The monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 2, wherein, The mass of monodisperse nano-calcium carbonate filter cake is 15 to 25 times that of ethoxylated modified polytrisiloxane.

4. The monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The mass of water is 2 to 60 times that of monodisperse nano-calcium carbonate filter cake.

5. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 4, wherein, The mass of water is 2 to 11 times that of monodisperse nano-calcium carbonate filter cake.

6. The monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The mass of monodisperse nano-calcium carbonate filter cake is 18.75 to 50 times that of modified casein.

7. The monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The mass of monodisperse nano-calcium carbonate filter cake is 25 to 100 times that of enzymes.

8. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 7, wherein, The mass of monodisperse nano-calcium carbonate filter cake is 75 to 100 times that of enzymes.

9. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The mass of monodisperse nano-calcium carbonate filter cake is 20 to 50 times that of sugar alcohol.

10. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The method for preparing the monodisperse nano-calcium carbonate filter cake includes the following steps: S1. Calcium carbonate slurry is prepared using a process that includes calcination, digestion, and carbonation. S2. Add inorganic salt grain surface remodeling agent and organic grain surface remodeling agent to the calcium carbonate slurry obtained in S1, and then keep it at 120~140℃ for 1.0~4.0 h to obtain calcium carbonate suspension; S3. The calcium carbonate suspension obtained in S2 is dehydrated by hydraulic filtration to obtain a calcium carbonate filter cake. The moisture content of the filter cake is controlled between 35% and 40%, which is a monodisperse nano calcium carbonate filter cake.

11. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 10, wherein, The calcination process is as follows: limestone with uniform grain size and a harmful heavy metal content of less than 400 ppm is selected as raw material and calcined to obtain quicklime. The activity of quicklime is in the range of 250-300 mL. The digestion process is as follows: the quicklime obtained from the above calcination is digested in hot water at 50-90℃ to obtain lime milk, then aged for 24-48 hours, and filtered to remove impurities to obtain refined raw pulp; The carbonation process is as follows: water is added to the refined raw pulp to adjust the solid content to 5% to 8%, and then carbonation is carried out. The initial carbonation temperature is 10 to 20℃, the CO2 content is 20% to 40%, and carbonation is carried out until the pH of the pulp reaches 7.5 to 9.

0. The carbonation is then stopped to obtain calcium carbonate cooked pulp.

12. The monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 10, wherein, The inorganic salt grain surface remodeling agent is one or more of the inorganic salts sodium silicate, sodium chloride, aluminum chloride, and zinc sulfate, and the amount used is 0.5% to 3% of the dry basis mass of calcium carbonate.

13. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 10, wherein, The organic grain surface remodeling agent is one or more of ethanol, polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, sodium dodecylbenzenesulfonate, hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, and disodium ethylenediaminetetraacetate, and the amount used is 1% to 5% of the dry weight of calcium carbonate.

14. The monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The monodisperse nano-calcium carbonate filter cake is dispersed in an aqueous solution by stirring to obtain a suspension. When the solid content of the suspension is 5% to 30%, it can be stably suspended for more than 14 hours.

15. A monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 1, wherein, The sugar alcohols include one or more of xylitol, ribitol, mannitol, sorbitol, maltitol, erythritol, and lactitol; the enzymes are commercially available agricultural enzymes.

16. A method for preparing the monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to any one of claims 1 to 15, comprising the following steps: (1) According to the raw materials and their mass fractions, prepare 1-20 parts of monodisperse nano calcium carbonate filter cake, 0.05-0.9 parts of ethoxy-modified polytrisiloxane, 0.01-0.8 parts of modified casein, 0.01-0.8 parts of enzyme, 0.05-0.9 parts of sugar alcohol, and 10-180 parts of water; (2) Place the monodisperse nano calcium carbonate filter cake in a portion of water at a temperature of 5~30℃ and disperse it in a high-speed disperser at a linear velocity of 80~120 m / min for 15~40 min. (3) After the stirring in step (2) is completed, add other raw materials and the remaining water, and continue to disperse in a high-speed disperser at a linear speed of 80~120 m / min for 15~30 min to obtain the monodisperse nano calcium carbonate-based foliar calcium fertilizer.

17. In the preparation method of monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 16, in step (2), the amount of water used to disperse the monodisperse nano-calcium carbonate filter cake is 1 to 2 times the weight of the monodisperse nano-calcium carbonate filter cake.

18. The method of applying the monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to any one of claims 1 to 15, wherein the foliar calcium fertilizer is diluted with water to a solid content of calcium carbonate of 0.5% to 2%, and then sprayed directly.

19. The application method of the monodisperse nano-calcium carbonate-based foliar calcium fertilizer according to claim 18, characterized in that, In dry, rainless weather, dilute the foliar calcium fertilizer and spray it on the leaves of grain or vegetable crops. There is no need to specifically avoid the fruit. Spray 2 to 4 times during the crop's growth process.

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