A foliar fertilizer for reducing citrus fruit cracking and improving fruit quality and application thereof

Abstract

The application provides a foliar fertilizer for reducing citrus fruit cracking and improving fruit quality and application thereof, and belongs to the technical field of fertilizers. The foliar fertilizer comprises, by weight fraction, 10-20 parts of methylphosphonium microspheres, 8-16 parts of chelated copper, 5-10 parts of chelated iron, and 8-15 parts of complexed calcium. The methylphosphonium microspheres are prepared by cross-linking methylphosphonium with carboxymethyl cellulose, sodium phytate and ferric iron, and then coating with rhamnose galacturonic acid polysaccharide. The foliar fertilizer can reduce the contact angle of the foliar fertilizer on citrus leaves, significantly improve the adhesion, reduce the loss of methylphosphonium, and improve the effective utilization rate. By spraying the foliar fertilizer at two key periods of fruit development, i.e. the end of fruit peel cell division and the end of physiological fruit drop, the citrus fruit cracking rate can be significantly reduced, and the quality of citrus fruits can be significantly improved, so that the output rate of high-quality citrus fruits is improved.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a foliar fertilizer that reduces citrus fruit cracking and improves fruit quality, and its application. Background Technology

[0002] Citrus, the most widely planted fruit in my country and even the world, often suffers from peel cracking, or fruit splitting, during its rapid expansion and even color-changing stages. Fruit splitting is a serious physiological disorder affecting citrus production efficiency. The splitting rate in navel oranges can reach 15%, the natural splitting rate in Wenzhou mandarins is around 10%, while in hybrid citrus varieties like Ganping, the splitting rate is as high as 70%. In recent years, with the frequent occurrence of abnormal weather and the intensified ecological changes caused by extensive orchard management, citrus fruit splitting has become increasingly severe.

[0003] Fruit cracking is a physiological disorder during fruit development, a physical process of mechanical fracture of the peel. The internal cause of cracking lies primarily in the disharmony between the growth of the pulp and the peel. Increased internal stress in the pulp, which the peel cannot withstand, ultimately leads to cracking. Citrus fruit cracking is a gradual rather than explosive process. Around late May to early June, peel cell division stops earlier than in the pulp, with significant differences in timing depending on the variety and growing environment. Subsequently, during the fruit enlargement stage, the pulp continuously compresses the mesocarp (white outer layer of the peel), causing cracks to gradually appear between the cells. As the fruit develops, these cracks widen and increase in number, forming cavities, resulting in a continuous decrease in the thickness and toughness of the peel. In July and August, the cuticle of the exocarp develops numerous microcracks due to the combined effects of strong sunlight and internal turgor pressure. Rain exacerbates these cracks, and many citrus fruit cracks begin with the rupture of these cracks. In addition, if a sudden downpour occurs after a prolonged drought, the pulp will swell rapidly, while the peel cannot grow accordingly and is not strong enough to resist the sudden change in internal stress, eventually causing the peel to crack. This not only causes a significant reduction in citrus production, but the cracked fruit also becomes an important vector for other diseases and pests in the orchard.

[0004] Citrus fruit cracking is the result of a combination of factors. Besides rainfall, varietal characteristics, fruit development processes, and hormonal and nutrient imbalances all contribute to its occurrence, particularly in traditional citrus-producing areas where long-term lack of scientific management has led to severe nutrient imbalances, with widespread deficiencies in copper and boron, as well as excessive levels of manganese and potassium. Therefore, addressing citrus fruit cracking from a nutrient management perspective is a crucial area for development. While current research on citrus fruit cracking control is broad, there is a significant disconnect between theory and practice, and a universally accepted, unified, efficient, and sustainable technical system has yet to be established. The existing technologies mainly suffer from the following systemic defects: (1) Fruit cracking has obvious regional and citrus variety characteristics. After a certain control method achieves certain results in a local area, it is difficult to achieve similar results in repeated trials in another region or even another year; (2) Fruit cracking is significantly correlated with the meteorological environment, especially the drastic fluctuations in water. However, water management is difficult to promote and apply in practice due to the lack of theoretical parameters, facilities and equipment; (3) Current management measures to reduce citrus fruit cracking will basically cause problems such as thickening of the peel, decrease in total acid and soluble solids, and delayed fading of green when the fruit matures, which seriously affects the marketability of the fruit; (4) High concentration, high frequency The blind application of secondary growth regulators may lead to abnormal fruit growth or even food safety issues; (5) The management method for preventing and controlling fruit cracking is complicated and incompatible with conventional management measures. It requires a large amount of materials and labor, and its popularization and promotion value is limited; (6) The measures for preventing and controlling fruit cracking are independent of other nutrient or pest and disease management measures in the orchard, which means that such measures are only experimental and not widely applicable; (7) The large-scale use of multi-element compound fertilizers and foliar fertilizers has an extremely unstable effect on the prevention and control of citrus fruit cracking, and instead exacerbates the nutrient imbalance in the orchard; (8) The key time point for preventing and controlling fruit cracking during the fruit enlargement period is often when there is more rain or high temperature and drought, which leads to a decrease in the effectiveness and persistence of the control agents. Summary of the Invention

[0005] Technical Problems to be Solved: Addressing the issues of frequent fruit cracking, severe quality loss, poor adhesion and low utilization of traditional foliar fertilizers, and nutrient imbalance exacerbated by indiscriminate fertilization in the citrus industry, this invention provides a foliar fertilizer and its application to reduce citrus fruit cracking and improve fruit quality. The foliar fertilizer is a core-shell structured microsphere, consisting of a core loaded with functional components and an adhesive outer shell. It aims to systematically solve problems such as poor adhesion of traditional foliar fertilizers, uncontrollable release of active ingredients, and frequent fruit cracking under adverse stress, providing an innovative solution for green and high-quality citrus cultivation.

[0006] Technical solution: This invention provides a foliar fertilizer that reduces citrus fruit cracking and improves fruit quality. By weight, it comprises the following components: 10-20 parts of mepiquat microspheres, 8-16 parts of chelated copper, 5-10 parts of chelated iron, and 8-15 parts of chelated calcium.

[0007] Preferably, the chelated copper is EDTA chelated copper and / or amino acid chelated copper; the chelated iron is EDTA chelated iron and / or EDDHA chelated iron; and the complexed calcium is any one or more of amino acid complexed calcium, sucrose complexed calcium, and humic acid complexed calcium.

[0008] The present invention also provides a method for preparing the above-mentioned mepiquat chloride microspheres, comprising the following steps:

[0009] S1. Carboxymethyl cellulose is added to water and stirred at 50-70℃ until completely dissolved. After cooling, it is allowed to stand for 2-8 hours to obtain a carboxymethyl cellulose solution. Mepiquat chloride is dissolved in a small amount of water and added to the carboxymethyl cellulose solution. The mixture is stirred at 300-600 rpm for 40-80 minutes to obtain a CMC-mepiquat chloride mixture. Sodium phytate is dissolved in a small amount of water and added to the above mixture. The mixture is stirred for 1-3 hours to obtain a premix.

[0010] S2. The ferric salt was dissolved in an acetate-sodium acetate buffer solution. The premixed solution was added dropwise to the above solution while stirring. After the addition was complete, stirring was continued for 30-60 min. The microspheres were collected by filtration, washed with ethanol, and dried to obtain the mepiquat core.

[0011] S3. Rhamnose galacturonic acid polysaccharide was dissolved in an aqueous solution containing H3BO3 and NaCl, the pH was adjusted to 4.0-4.5, and the solution was stirred until dissolved to obtain a coating solution; a small amount of the coating solution was added to the mepiquat kernel, stirred until uniformly dispersed, and then added dropwise to the remaining coating solution. After the addition was completed, stirring was continued for 2-4 hours, and the microspheres were collected by filtration.

[0012] S4. The microspheres were transferred to an aqueous solution containing H3BO3 and NaCl, stirred at 100-300 rpm for 1-4 h, filtered to collect the microspheres, washed with water at 0-4℃, and dried to obtain mepiquat chloride microspheres.

[0013] Preferably, in step S1, the mass fraction of the carboxymethyl cellulose solution is 0.5-3%; the mass ratio of carboxymethyl cellulose, mepiquat chloride, and sodium phytate is 1-5:1-1.5:1-3.

[0014] Preferably, in step S2, the ferric salt is any one or more of ferric chloride, ferric sulfate, and ferric nitrate; the amount of ferric salt added is 40-55% of the total mass of carboxymethyl cellulose and sodium phytate.

[0015] Preferably, in step S3, the mass ratio of rhamnose galacturonic acid polysaccharide to mepiquat kernel is 1~1.2:0.6~1.

[0016] Preferably, in steps S3 and S4, the concentration of H3BO3 in the aqueous solution containing H3BO3 and NaCl is 0.05~0.3 mol / L, and the concentration of NaCl is 0.02~0.1 mol / L.

[0017] This invention also provides the application of the above-mentioned foliar fertilizer in reducing citrus fruit cracking and improving citrus fruit quality.

[0018] This invention also provides a method for reducing citrus fruit cracking and improving citrus fruit quality, comprising the following steps:

[0019] (1) Mepiquat microspheres were dispersed in water, and chelated copper, chelated iron and complexed calcium were dissolved in water respectively. Complexed calcium, chelated iron, chelated copper and mepiquat microspheres were added to water in sequence and mixed evenly to obtain foliar fertilizer.

[0020] (2) Spray foliar fertilizer on the canopy of citrus trees at the end of the fruit peel cell division stage and the end of the physiological fruit drop stage. Spray evenly on the leaves and fruit surface, focusing on the fruit, and ensure that the inner canopy of the tree is sprayed evenly to avoid repeated spraying.

[0021] Preferably, the foliar fertilizer sprayed at the end of the fruit peel cell division stage comprises the following components by weight: 16-18 parts of mepiquat chloride microspheres, 9-14 parts of chelated copper, 6-8 parts of chelated iron, and 10-12 parts of chelated calcium.

[0022] Preferably, the foliar fertilizer sprayed at the end of the physiological fruit drop period comprises the following components by weight: 10-15 parts of mepiquat chloride microspheres, 8-12 parts of chelated copper, 6-8 parts of chelated iron, and 8-12 parts of chelated calcium.

[0023] Beneficial effects:

[0024] 1. This invention's foliar fertilizer is composed of mepiquat chloride microspheres and a compound of copper, iron, and calcium. The mepiquat chloride microspheres are made by cross-linking mepiquat chloride with carboxymethyl cellulose, sodium phytate, and ferric iron, followed by coating with rhamnose-galacturonic acid polysaccharide. This achieves highly efficient encapsulation and protection of mepiquat chloride, preventing premature release or inactivation during storage and application. When citrus fruits are subjected to adverse stresses such as high temperature, strong light, or prolonged drought followed by sudden rain, the risk of fruit cracking increases, and the ROS level in the peel cells rises, causing the Fe in the carrier to be released. 3+ Reduced to Fe 2+The carrier structure dissociates, releasing mepiquat chloride. Mepiquat chloride regulates the excessive growth of pericarp cells, preventing fruit cracking caused by severe fissures in the pericarp cell arrangement during the fruit enlargement period, effectively reducing fruit cracking. Copper, iron, and calcium elements in the foliar fertilizer stabilize cell walls, promote chlorophyll synthesis, and regulate nutrient transport, working together with mepiquat chloride to reduce fruit cracking and promote nutrient accumulation in the fruit. This invention can significantly improve fruit cracking in citrus fruits, enhance fruit quality, thereby increasing the yield of premium citrus fruits and improving the production benefits for fruit farmers.

[0025] 2. This invention addresses the industry problem of poor adhesion of foliar fertilizers. It abandons the traditional approach of relying on surfactants to reduce surface tension or physical thickening, and instead uses RG-II to reduce the static contact angle of foliar fertilizers on leaves, thereby achieving effective adhesion and spreading of foliar fertilizers on the leaf surface. This prolongs the fertilizer retention time and improves the nutrient utilization rate of leaves, fundamentally solving the problem of poor adhesion and retention.

[0026] 3. This invention achieves excellent leaf adhesion and controlled release of active ingredients while significantly reducing the amount of non-nutritive and non-functional excipients added to the formulation. These microspheres can be directly formulated as a suspension, significantly reducing the reliance on various flow aids, anti-adhesion agents, or chemical stabilizers in traditional foliar fertilizer formulations, and decreasing the types and amounts of excipients used. On the one hand, this avoids the risk of stomata clogging by large amounts of excipients; on the other hand, it reduces the nutrient imbalance in orchards exacerbated by the indiscriminate addition of multi-element compound fertilizers and excipients, making the application of foliar fertilizers more precise and environmentally friendly.

[0027] 4. This invention is highly compatible with existing conventional fertilization and plant protection management practices in citrus orchards, requiring no additional equipment or complex processes. All components are conventional reagents, resulting in low cost and high operability. By performing only two canopy sprays, without special equipment or complex operations, the effects of crack prevention and quality improvement can be achieved, making it easy to directly promote and apply in production. Attached Figure Description

[0028] Figure 1 This is a comparison of the microstructure morphology of citrus fruit epidermal cells in Example 2 and the control group. Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments:

[0030] Brewing yeast: Produced by Angel Yeast Co., Ltd.

[0031] Mepiquat chloride: a white soluble powder with an active ingredient content of ≥98%, produced by Sichuan Guoguang Agrochemical Co., Ltd.

[0032] Chelated copper (EDTA-Cu): Blue soluble powder, Cu≥14.5%, produced by Shandong Shimeite Agricultural Technology Co., Ltd.

[0033] Chelated iron (EDDHA-Fe): Red soluble powder, Fe≥6%, produced by Qingdao Vialite Biotechnology Co., Ltd.

[0034] Complexed calcium (amino acid complexed calcium): brown aqueous solution, Ca≥10%, produced by Italian company, Qiteng S.A.

[0035] Example 1

[0036] This embodiment describes a method for preparing rhamnose galacturonic acid polysaccharide (RG-II), which includes the following steps:

[0037] S1. After destemming the grapes, wash and crush them, add 1.5% of the grape weight of wine yeast, seal and ferment at 28℃ for 5 days, filter and concentrate the filtrate to 1 / 3 volume, add 2 times the volume of ethanol, place at 4℃ for 12 h, collect the precipitate, add 1 times the volume of ethanol again, place at 4℃ for 12 h, collect the precipitate.

[0038] S2. The precipitate was dialyzed through a dialysis bag (molecular weight cutoff 3500D), and then freeze-dried to obtain total polysaccharides. The total polysaccharides were dissolved in NaOAc solution (50 mmol / L, pH 5.0), filtered through a 0.45 μm filter membrane, and eluted with NaOAc solution (50 mmol / L, pH 5.0) at 1 mL / min using a Sephadex G-75 column. The RG-II eluent was collected, dialyzed through a dialysis bag (molecular weight cutoff 3500D), and then freeze-dried to obtain RG-II.

[0039] Example 2

[0040] This embodiment describes a method for preparing mepiquat chloride microspheres, including the following steps:

[0041] S1. Weigh 5 g of carboxymethyl cellulose (CMC), add 495 mL of deionized water, stir at 60℃ and 350 rpm until completely dissolved, prepare a 1% (w / v) CMC solution, cool naturally, and let stand for 4 h; weigh 1.5 g of mepiquat chloride, dissolve in a small amount of deionized water, and slowly add to the CMC solution, stirring at 300 rpm for 40 min; weigh 2 g of sodium phytate, dissolve in a small amount of deionized water, and slowly add dropwise to the CMC-mepiquat chloride mixture at 500 rpm, and continue stirring for 1.5 h after the addition is complete to obtain a premixed solution;

[0042] S2. Weigh 3.2 g FeCl3·6H2O and dissolve it in 1200 mL of acetate-sodium acetate buffer (0.2 mol / L acetic acid solution and 0.2 mol / L sodium acetate solution are mixed in a volume ratio of 8:2, pH 4.0). After stirring to dissolve, add acetate-sodium acetate buffer to make up to 1500 mL. Add the premixed solution dropwise to the above solution at 200 rpm using a syringe pump. After the addition is complete, continue stirring for 40 min. Filter to collect the microspheres, wash 3 times with anhydrous ethanol, and dry at 35℃ under normal pressure for 4 h to obtain mepiquat chloride core.

[0043] S3. Dissolve 1 g of RG-II in 100 mL of an aqueous solution containing 0.1 mol / L H3BO3 and 0.05 mol / L NaCl, adjust the pH to 4.0 with 1 mol / L NaOH, and stir at 200 rpm until completely dissolved to obtain a coating solution; add 0.8 g of mepiquat chloride kernel to a small amount of the coating solution, stir until uniformly dispersed, and slowly add it dropwise to the remaining coating solution at 300 rpm. After the addition is complete, stir for 3.5 h, filter and collect the microspheres;

[0044] S4. Prepare a 500 mL mixed solution containing 0.1 mol / L H3BO3 and 0.05 mol / L NaCl, adjust the pH to 4.0 with 1 mol / L NaOH, transfer the microspheres to the mixed solution, stir at 150 rpm for 2 h, filter to collect the microspheres, wash twice with deionized water at 4℃, and vacuum dry at 35℃ for 6 h to obtain mepiquat chloride microspheres.

[0045] Example 3

[0046] The difference between this embodiment and Embodiment 2 is that the mass ratio of CMC, mepiquat chloride, and sodium phytate in this embodiment is 2:1:2.5, while the remaining steps are the same as in Embodiment 2.

[0047] Example 4

[0048] The difference between this embodiment and embodiment 2 is that in this embodiment, the mass ratio of RG-II to the core is 1.2:0.8, and the remaining steps are the same as in embodiment 2.

[0049] Example 5

[0050] The difference between this embodiment and Embodiment 2 is that in this embodiment, FeCl3·6H2O is replaced with Fe2(SO4)3·9H2O, while the other steps are the same as in Embodiment 2.

[0051] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows:

[0052] Comparative Example 1

[0053] The difference between this comparative example and Example 2 is that sodium phytate is not added in this comparative example, while the other steps are the same as in Example 2.

[0054] Comparative Example 2

[0055] The difference between this comparative example and Example 2 is that CMC is not added in this comparative example, while the other steps are the same as in Example 2.

[0056] Comparative Example 3

[0057] The difference between this comparative example and Example 2 is that sodium phytate is replaced with sodium tripolyphosphate in this comparative example, while the other steps are the same as in Example 2.

[0058] Comparative Example 4

[0059] The difference between this comparative example and Example 2 is that FeCl3·6H2O is replaced with AlCl3·6H2O in this comparative example, while the other steps are the same as in Example 2.

[0060] Comparative Example 5

[0061] The difference between this comparative example and Example 2 is that RG-II is not added in this comparative example, while the other steps are the same as in Example 2.

[0062] Comparative Example 6

[0063] The difference between this comparative example and Example 2 is that RG-II is replaced with sodium alginate in this comparative example, while the other steps are the same as in Example 2.

[0064] Indicator Test:

[0065] (1) Encapsulation rate determination:

[0066] 0.1 g of mepiquatium microspheres were added to 100 mL of sodium citrate solution (0.2 M), shaken at 30 °C for 24 h, and then an appropriate amount of hexanitrodiphenylamine was added. The mepiquatium content was determined using a Cary 100Bio UV-Vis spectrophotometer at a wavelength of 200 nm, and the encapsulation efficiency was calculated. Encapsulation efficiency = mepiquatium content in microspheres / amount added × 100%.

[0067] (2) Contact angle measurement:

[0068] Collect several fresh citrus leaves of similar size, randomly group them into two groups, one with the upper surface facing up and the other with the lower surface facing up, and repeat each group three times; add 0.1 g of mepiquat chloride microspheres to 100 mL of distilled water, dissolve them, and then drop 3 μL of the solution onto the leaves, and use a contact angle meter to measure the contact angle of the solution on the leaves.

[0069] (3) Suspension stability determination:

[0070] Add 0.1 g of mepimunium microspheres to 100 mL of distilled water and observe whether crystals precipitate or separate into layers in the sample over 30 days.

[0071] Table 1. Encapsulation efficiency of mepiquat chloride microspheres

[0072]

[0073] Note: Compared with Example 2, *P<0.05; **P<0.01.

[0074] As shown in Table 1, the encapsulation efficiency of the mepiquat chloride microspheres prepared in Examples 2-5 was significantly higher than that of the comparative example. Comparative Example 1 (without sodium phytate) relied solely on Fe... 3+ Coordination crosslinking with the carboxyl groups of CMC significantly reduced the network crosslinking density, resulting in a loose structure and substantial loss of mepiquat chloride. Comparative Example 2 (without carboxymethyl cellulose) lacked the polymer backbone provided by CMC, exhibiting poor structural formability and failing to form a stable crosslinking network, thus failing to effectively encapsulate mepiquat chloride. In Comparative Example 3 (sodium phytate replaced with sodium tripolyphosphate), the crosslinking efficiency of sodium tripolyphosphate was low, the crosslinking network integrity was insufficient, and the encapsulation capacity was reduced. Comparative Example 4 (FeCl3 replaced with AlCl3)... 3+ Replace with Al of the same valence state 3+ Although it can form a cross-linked network, its smaller ionic radius prevents sufficient coordination, resulting in insufficient cross-linked network strength and a decreased encapsulation rate. Comparative Example 5 (without RG-II) only has a core cross-linked network, lacking the protection of the RG-II outer layer, making mepiquat chloride more prone to leakage. Comparative Example 6 (RG-II replaced with sodium alginate) shows a slightly higher encapsulation rate after sodium alginate coating compared to Comparative Example 5, but it is still lower than Examples 2-5, indicating that the density of the outer shell structure formed by sodium alginate is lower than that of the RG-II shell.

[0075] Table 2. Contact angle of mepiquat chloride microspheres diluted 1000 times on citrus leaves.

[0076]

[0077] Note: Compared with Example 2, *P<0.05; **P<0.01.

[0078] As shown in Table 2, when mepiquat chloride microspheres were diluted 1000 times and left on the front and back of leaves for 20 minutes, the contact angles were significantly smaller than those of the comparative examples. This indicates that mepiquat chloride microspheres are more conducive to adhesion and spread on citrus leaves, reducing pesticide loss and improving utilization. It is noteworthy that the contact angles of microspheres coated with RG-II (Examples 2-5, Comparative Examples 1-4) were generally smaller than those of microspheres not coated with RG-II (Comparative Example 5), indicating that the RG-II shell plays a crucial role in improving the adhesion of the pesticide to the leaf surface. Comparative Example 6 used sodium alginate instead of RG-II for shell coating. Although the contact angle was lower than that of Comparative Example 5, it was still higher than in the other examples, indicating that sodium alginate provides some wettability and facilitates spread, but its effect is not as good as that of RG-II.

[0079] Table 3. Stability of mepiquat chloride microsphere suspension over 30 days

[0080]

[0081] As shown in Table 3, no stratification occurred in Examples 2 to 5 within 30 days, and they were able to maintain long-term stable dispersion, making them suitable for use as liquid fertilizer.

[0082] Example 6

[0083] This embodiment describes a method for preparing foliar fertilizer, including the following steps:

[0084] S1. Preparation of the first application of foliar fertilizer: Take 180 mg of mepiquat chloride microspheres (Example 2 or Comparative Examples 1-6), 100 mg of chelated copper (EDTA-Cu), 60 mg of chelated iron (EDDHA-Fe), and 120 mg of complexed calcium (amino acid complexed calcium) and dissolve / disperse the above components independently with a small amount of water as a solvent. Add the complexed calcium, EDDHA-Fe, EDTA-Cu, and mepiquat chloride to 800 mL of water in that order, mix well, and add water to make up to a total volume of 1 L to prepare the first application of foliar fertilizer.

[0085] S2. Preparation of the second foliar fertilizer: Take 120 mg of mepiquat chloride microspheres (Example 2 or Comparative Examples 1-6), 90 mg of EDTA-Cu, 60 mg of EDDHA-Fe and 100 mg of calcium complex, respectively, and prepare them in the same way as in S1 to obtain the second foliar fertilizer.

[0086] Example 7

[0087] This example illustrates the effects of foliar fertilizer on citrus fruit. The experiment was conducted in 2025 at the Wenzhou mandarin orange production base in Yanjiang Town, Linhai City, Zhejiang Province. The subject was 20-year-old Miyagawa Wenzhou mandarin oranges grafted onto trifoliate orange rootstock. The specific method included the following steps:

[0088] S1. Set up experimental and control groups, with 5 trees in each group. There are 7 experimental groups, which are foliar fertilizers prepared in Example 6 (prepared from mepiquat chloride microspheres prepared in Example 2 and Comparative Examples 1-6, respectively). The control group is water. Protective rows are set up between treatment rooms, and conventional agricultural management is the same.

[0089] S2. Spray the foliar fertilizer prepared in S1 of Example 6 at the end of the pericarp cell division stage (May 27);

[0090] S3. Spray the foliar fertilizer prepared in S2 of Example 6 at the end of the physiological fruit drop period (June 15);

[0091] S4. In late July, count the number of fruits set; in mid-October, count the number of remaining fruits and calculate the fruit cracking rate; at the early stage of fruit ripening (November 5), collect fruits from the control and experimental areas for fruit quality testing.

[0092] Indicator Test:

[0093] (1) Calculation of fruit cracking rate: The total number of fruits (M) on each tree before fruit cracking after fruit setting (late July) and the total number of fruits (N) at the end of fruit cracking (mid-October) are counted separately. The difference between the two is the total number of cracked fruits. The fruit cracking rate is calculated according to the following formula: Fruit cracking rate = (MN) / M × 100%.

[0094] (2) Observation of pericarp cell morphology: Pericarp cell morphology was observed using the pericarp anatomical structure observation method (paraffin section observation method). At the early stage of fruit cracking (August 5), fruits from the control and Example 2 were collected, one fruit from each of the four directions (east, south, west, and north), placed in a foam box with ice packs, and brought back to the laboratory for processing. The surface of the pericarp was washed with running water to remove dirt, dried, and then cut transversely at the equator to cut small pieces of pericarp of 0.5 cm × 2.0 cm. These pieces were placed in FAA fixative, vacuumed for 15 min, and then placed in a 4℃ refrigerator for 24 h before being transferred to room temperature for storage. Paraffin sections were prepared. The fixed pericarp pieces underwent a series of steps including trimming, rinsing, dehydration, clearing and waxing, embedding, trimming, sectioning, spreading and mounting, dewaxing and staining, dehydration and clearing, and mounting to finally obtain permanent slides. Safranin-Fix Green staining was used. The slides were observed and photographed using an OLYMPUS biological microscope.

[0095] (3) Fruit quality index determination: Eight fruits were collected from each tree, and a total of 40 fruits were collected for each treatment. The collected fruit samples were immediately transported back to the laboratory, and the fruit quality index was determined on the same day. The weight of a single fruit was determined using a 1 / 100 scale; the peel thickness, transverse diameter, and longitudinal diameter of the fruit were determined using vernier calipers. The fruit shape index was calculated using the following formula: Fruit shape index = longitudinal diameter of fruit / transverse diameter of fruit.

[0096] (4) The content of soluble solids and citric acid in the fruit was determined using a Japanese ATAGO portable sugar and acid rapid tester (PAL-BX / ACID F5). The solid-acid ratio was calculated using the following formula: soluble solids content / total acid content.

[0097] Table 4. Fruit cracking rate of citrus fruits

[0098]

[0099] Note: Compared with the control group, *P<0.05; **P<0.01; compared with Example 2, #P<0.05; ##P<0.01.

[0100] As shown in Table 4, the effects of different treatments on the control of fruit cracking in Wenzhou mandarin oranges varied significantly. Example 2 showed the lowest cracking rate at 3.4%, a reduction of 77.2% compared to the control group (water treatment). This indicates that the foliar fertilizer prepared in this invention can effectively improve the cracking of Wenzhou mandarin oranges and significantly increase the yield of marketable fruit. Looking at the results of the comparative examples, Comparative Example 5 (without RG-II) had a cracking rate of 11.3%. Combined with the contact angle test results, this indicates that RG-II mainly enhances the anti-cracking effect by increasing the adhesion and deposition of microspheres on the peel surface and prolonging the duration of efficacy. Comparative Example 6 (RG-II replaced with sodium alginate) showed a cracking rate reduced to 8.8%, with a lower control effect than Example 2, indicating that although sodium alginate has certain adhesive properties, it cannot completely replace the function of RG-II. Furthermore, the integrity of the core cross-linking system also affects the anti-cracking effect. Although the cracking rates of Comparative Examples 1-4 were lower than the control group (water treatment), their anti-cracking effects were all inferior to Example 2.

[0101] like Figure 1 As shown, compared with the control group (water treatment), the foliar fertilizer prepared in Example 2 effectively improved the morphology of fruit peel cells. The cell morphology near the epidermal layer of the fruit peel was more regular, the cell arrangement layer was more obvious, and the overall structure was more compact. This helps to buffer the rapid development of intercellular fissures during fruit peel development, thereby reducing the risk of fruit peel cracking.

[0102] Table 5 Quality Indicators of Citrus Fruit

[0103]

[0104] Traditional fruit cracking control measures often result in increased peel thickness, fruit morphological variations, or reduced soluble solids content in citrus fruits, all of which are detrimental to the production of high-quality fruit. As shown in Table 5, the foliar fertilizer of this invention effectively improves fruit flavor. Without significantly affecting fruit shape, it significantly increases the single fruit weight, soluble solids content, total acid content, and solids-acid ratio of Wenzhou mandarins. The increase in soluble solids content is particularly significant, further enhancing the commercial value of the fruit.

[0105] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the technical solutions of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A foliar fertilizer that reduces citrus fruit cracking and improves fruit quality, characterized in that, By weight, it comprises the following components: 10-20 parts of mepiquat chloride microspheres, 8-16 parts of chelated copper, 5-10 parts of chelated iron, and 8-15 parts of complexed calcium; The preparation method of the mepiquat chloride microspheres includes the following steps: S1. Carboxymethyl cellulose is added to water and stirred at 50-70℃ until completely dissolved. After cooling, it is allowed to stand for 2-8 hours to obtain a carboxymethyl cellulose solution. Mepiquat chloride is dissolved in a small amount of water and added to the carboxymethyl cellulose solution. The mixture is stirred at 300-600 rpm for 40-80 minutes to obtain a CMC-mepiquat chloride mixture. Sodium phytate is dissolved in a small amount of water and added to the above mixture. The mixture is stirred for 1-3 hours to obtain a premix. S2. The ferric salt was dissolved in an acetate-sodium acetate buffer solution. The premixed solution was added dropwise to the above solution while stirring. After the addition was complete, stirring was continued for 30-60 min. The microspheres were collected by filtration, washed with ethanol, and dried to obtain the mepiquat core. S3. Rhamnose galacturonic acid polysaccharide was dissolved in an aqueous solution containing H3BO3 and NaCl, the pH was adjusted to 4.0-4.5, and the solution was stirred until dissolved to obtain a coating solution; a small amount of the coating solution was added to the mepiquat kernel, stirred until uniformly dispersed, and then added dropwise to the remaining coating solution. After the addition was completed, stirring was continued for 2-4 hours, and the microspheres were collected by filtration. S4. The microspheres were transferred to an aqueous solution containing H3BO3 and NaCl, stirred at 100-300 rpm for 1-4 h, filtered to collect the microspheres, washed with water at 0-4℃, and dried to obtain mepiquat chloride microspheres.

2. The foliar fertilizer according to claim 1, characterized in that: The chelated copper is EDTA chelated copper and / or amino acid chelated copper; the chelated iron is EDTA chelated iron and / or EDDHA chelated iron; the complexed calcium is any one or more of amino acid complexed calcium, sucrose complexed calcium and humic acid complexed calcium.

3. The foliar fertilizer according to claim 1, characterized in that: In step S1, the mass fraction of the carboxymethyl cellulose solution is 0.5-3%; the mass ratio of carboxymethyl cellulose, mepiquat chloride, and sodium phytate is 1-5:1-1.5:1-3.

4. The foliar fertilizer according to claim 1, characterized in that: In step S2, the ferric salt is any one or more of ferric chloride, ferric sulfate, and ferric nitrate; the amount of ferric salt added is 40-55% of the total mass of carboxymethyl cellulose and sodium phytate.

5. The foliar fertilizer according to claim 1, characterized in that: In step S3, the mass ratio of rhamnose galacturonic acid polysaccharide to mepiquat kernel is 1~1.2:0.6~1.

6. The foliar fertilizer according to claim 1, characterized in that: In steps S3 and S4, the concentration of H3BO3 in the aqueous solution containing H3BO3 and NaCl is 0.05~0.3 mol / L, and the concentration of NaCl is 0.02~0.1 mol / L.

7. The application of the foliar fertilizer according to any one of claims 1 to 6 in reducing citrus fruit cracking and improving citrus fruit quality.

8. The application according to claim 7, characterized in that, The method for reducing citrus fruit cracking and improving citrus quality includes the following steps: (1) Mepiquat microspheres were dispersed in water, and chelated copper, chelated iron and complexed calcium were dissolved in water respectively. Complexed calcium, chelated iron, chelated copper and mepiquat microspheres were added to water in sequence and mixed evenly to obtain foliar fertilizer. (2) Spray foliar fertilizer on the canopy of citrus trees at the end of the fruit peel cell division stage and the end of the physiological fruit drop stage. Spray evenly on the leaves and fruit surface, focusing on the fruit, and ensure that the inner canopy of the tree is sprayed evenly to avoid repeated spraying.

9. The application according to claim 8, characterized in that, The foliar fertilizer sprayed at the end of the fruit peel cell division stage comprises the following components by weight: 16-18 parts of mepiquat chloride microspheres, 9-14 parts of chelated copper, 6-8 parts of chelated iron, and 10-12 parts of chelated calcium.

10. The application according to claim 8, characterized in that, The foliar fertilizer sprayed at the end of the physiological fruit drop period includes the following components by weight: 10-15 parts of mepiquat chloride microspheres, 8-12 parts of chelated copper, 6-8 parts of chelated iron, and 8-12 parts of chelated calcium.

Images