A pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate and a preparation method thereof

Abstract

This invention discloses a pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate and its preparation method, belonging to the field of agricultural fertilizer technology. Each liter of the slow-release calcium fertilizer comprises the following components: 1000-1200 g of calcium nitrate tetrahydrate; 50-100 g of small peptide amino acid solution, wherein the free amino acid content in the small peptide amino acid solution is not less than 100 g / kg, and the small peptide amino acid content is not less than 330 g / kg; 60-100 g of erythritol; 3-10 g of sodium alginate; 10-50 g of citric acid; 10-40 g of mannitol; appropriate amount of triethanolamine for adjusting the pH value to 4.5-5.8; and water to a final volume of 1 L. This invention also provides a method for preparing the calcium fertilizer. This calcium fertilizer, through a unique synergistic stabilizing system of erythritol-small peptide-weak acid, not only can be mixed with potassium dihydrogen phosphate without precipitation, solving the problem of calcium-phosphorus antagonism, but also possesses pH-responsive release characteristics, intelligently releasing calcium ions in the acidic environment of plant rhizosphere, significantly improving calcium absorption and utilization.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer technology, and in particular to a pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate and its preparation method. Background Technology

[0002] Calcium is an essential micronutrient for plant growth and development, participating in various physiological processes such as cell wall formation, enzyme activity regulation, and signal transduction. However, in agricultural production, the application of calcium fertilizers often faces the following technical challenges: when conventional water-soluble calcium fertilizers (such as calcium nitrate and calcium chloride) are mixed with phosphate fertilizers (such as potassium dihydrogen phosphate), calcium ions (Ca)... 2+ It will react with phosphate ions (PO4). 3- The rapid reaction produces insoluble calcium phosphate precipitate. This precipitate not only leads to the double loss of calcium and phosphorus, reducing fertilizer efficiency, but also easily clogs the filters and nozzles of integrated water and fertilizer systems such as drip irrigation and sprinkler irrigation, severely limiting the synergistic application of calcium and phosphorus.

[0003] To address the aforementioned compatibility issues, existing technologies often employ chelation techniques, such as using EDTA (ethylenediaminetetraacetic acid) as a chelating agent to enhance the stability of calcium ions. However, such strong chelating agents are expensive, and the resulting chelates are too stable in soil, potentially leading to slow calcium ion release and hindering effective plant absorption, thus lacking a slow-release function. Some technologies also enhance calcium solubility by adding alcohols and organic acids, but these similarly lack intelligent regulatory mechanisms for calcium ion release behavior.

[0004] Therefore, existing technologies lack a calcium fertilizer solution that integrates high stability, intelligent slow-release performance, compatibility with liquid phosphate, and suitability for modern irrigation systems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate and its preparation method. This calcium fertilizer not only does not precipitate when mixed with potassium dihydrogen phosphate, but also intelligently releases calcium in the acidic environment of plant rhizosphere, thereby fundamentally solving the problem of calcium-phosphorus antagonism and significantly improving calcium absorption efficiency.

[0006] The technical solution adopted by this invention to solve its technical problem is as follows: A pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate is provided, wherein each liter of the slow-release calcium fertilizer comprises the following components: Calcium nitrate tetrahydrate 1000-1200 g; 50-100 g of small peptide amino acid solution, wherein the content of free amino acids in the small peptide amino acid solution is not less than 100 g / kg and the content of small peptide amino acids is not less than 330 g / kg; Erythritol 60–100 g; 3-10 g of sodium alginate; Citric acid 10-50 g; Mannitol 10–40 g; Triethanolamine is used to adjust the pH value to 4.5–5.8; Add water to bring the volume up to 1 L.

[0007] Furthermore, it also contains sodium salt of maleic acid-acrylic acid copolymer with an average molecular weight of 10-30 kDa, at an addition amount of 2-5 g / L.

[0008] Specifically, the sodium salt of maleic acid-acrylic acid copolymer simultaneously uses multiple carboxyl groups to capture the same calcium ion (Ca). 2+ This forms a cyclic chelate. In particular, the maleic acid unit provides an ortho-dicarboxyl group, which has a stronger chelating ability, thus preventing calcium ions (Ca) from forming. 2+ It will react with phosphate ions (PO4). 3- It reacts rapidly to form an insoluble calcium phosphate precipitate.

[0009] A method for preparing a pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate includes the following steps: (1) Add 15% of the total volume of water to the reaction vessel, then add small peptide amino acid solution, erythritol, mannitol and citric acid, heat to 50 °C and stir until completely dissolved; (2) Add sodium alginate to the solution obtained in step (1) and stir until homogeneous; (3) Add calcium nitrate tetrahydrate slowly in batches, and control the temperature at 40-50 ℃ during the addition process; (4) Adjust the pH of the mixture to 4.5–5.8 using triethanolamine; (5) Add water to the total volume of 1 L, filter to remove impurities, and obtain clear liquid calcium fertilizer.

[0010] Specifically, in step (5), a 200-400 mesh filter cloth is used for filtration.

[0011] Furthermore, after step (2) and before step (3), the process also includes adding sodium salt of maleic acid-acrylic acid copolymer with a molecular weight of 10 to 30 kDa.

[0012] Furthermore, in step (3), calcium nitrate tetrahydrate is added in 3 to 5 batches, and each batch is stirred thoroughly until completely dissolved.

[0013] A fertilizer composition comprising slow-release calcium fertilizer and potassium dihydrogen phosphate, wherein the weight ratio of the slow-release calcium fertilizer to potassium dihydrogen phosphate is 1:1.

[0014] The application of the slow-release calcium fertilizer in foliar fertilization or fertigation systems.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention effectively complexes calcium ions through a unique sugar alcohol-small peptide-weak acid synergistic stabilization system, keeping them stable in a liquid environment, thus solving the long-standing technical problem of precipitation caused by the mixing of traditional calcium fertilizer and phosphate fertilizer. 2. The system constructed in this invention has excellent pH-responsive release function. Calcium is rapidly released upon reaching the acidic microzone of the root system, which greatly reduces the fixation and leaching of calcium in the soil and significantly improves the absorption efficiency of calcium. 3. The sodium salt of maleic acid-acrylic acid copolymer, small peptide amino acid solution, erythritol, mannitol, etc., described in this invention can form stable soluble complexes with calcium ions, constituting the first stabilizing barrier. Sodium alginate and calcium ions can form a weak gel network under specific pH conditions, which physically encapsulates and slows down the release of calcium ions, constituting the second controlled release barrier. The entire system is sensitive to pH changes, stable under neutral conditions, and the gel network swells under acidic conditions, weakening the complexation effect, thereby achieving rapid release of calcium ions. This multi-component, multi-level synergistic mechanism gives the calcium fertilizer excellent compatibility with potassium dihydrogen phosphate, storage stability, and pH-responsive intelligent release characteristics. 4. This invention is a clear liquid formulation with good stability. It can be easily dissolved and mixed without special stirring equipment, and is suitable for a variety of modern and precise fertilization methods. 5. This invention mainly uses natural or environmentally friendly raw materials such as small peptide amino acid liquid, sugar alcohol, and citric acid. Compared with expensive synthetic chelating agents such as EDTA, the cost is significantly reduced, making it easier for the market to accept and for large-scale production. Attached Figure Description

[0016] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 A comparison diagram showing the state of calcium fertilizers prepared in Example 1 (right) and Comparative Example 1 (left); Figure 2 The images show the state of calcium fertilizer and potassium dihydrogen phosphate after 24 hours of mixing in Example 1 (right) and Comparative Example 1 (left). Detailed Implementation

[0017] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0018] Preparation of slow-release calcium fertilizer Example 1

[0019] The liquid calcium fertilizer contains, per liter: 1000 g of calcium nitrate tetrahydrate, 100 g of small peptide amino acid solution (free amino acid content 120 g / kg, small peptide amino acid content 350 g / kg), 80 g of erythritol, 6 g of sodium alginate, 20 g of citric acid, 40 g of mannitol, 2 g of sodium salt of maleic acid-acrylic acid copolymer with an average molecular weight of 10 kDa, and triethanolamine to adjust the pH to 5.0, with water added to make up to 1 L.

[0020] Preparation method: (1) Add about 150 mL (15% of the total volume) of distilled water to the reaction vessel, and then add small peptide amino acid solution, erythritol, mannitol and citric acid in sequence; (2) Heat to 50 °C and stir until completely dissolved; (3) Add sodium alginate slowly while stirring continuously, and stir for 30 minutes to allow it to fully swell and disperse evenly; (4) Add sodium salt of maleic acid-acrylic acid copolymer while stirring continuously; (5) Control the temperature at 45 ℃ and slowly add calcium nitrate tetrahydrate to the above system in three batches. Add the next batch only after each batch has completely dissolved to avoid excessive local concentration. (6) Stop heating and wait for the system to cool to room temperature, then slowly adjust the pH of the mixture to 5.0 with triethanolamine; (7) Add distilled water to a total volume of 1 L, then filter through a 400-mesh filter cloth to obtain a clear, slightly viscous liquid calcium fertilizer. The resulting solution is as follows: Figure 1 As shown on the right. Example 2

[0021] The liquid calcium fertilizer contains, per liter: 1000 g of calcium nitrate tetrahydrate, 50 g of small peptide amino acid solution (free amino acid content 100 g / kg, small peptide amino acid content 330 g / kg), 60 g of erythritol, 3 g of sodium alginate, 30 g of citric acid, 10 g of mannitol, 5 g of sodium salt of maleic acid-acrylic acid copolymer with an average molecular weight of 30 kDa, and triethanolamine to adjust the pH to 4.5, with water added to make up to 1 L.

[0022] The preparation method is the same as in Example 1. Example 3

[0023] The liquid calcium fertilizer contains, per liter: 1100 g of calcium nitrate tetrahydrate, 100 g of small peptide amino acid solution (free amino acid content 100 g / kg, small peptide amino acid content 350 g / kg), 100 g of erythritol, 10 g of sodium alginate, 50 g of citric acid, 40 g of mannitol, 5 g of sodium maleic acid-acrylic acid copolymer with an average molecular weight of 15 kDa, and triethanolamine to adjust the pH to 5.8, with water added to make up to 1 L.

[0024] The preparation method is the same as in Example 1.

[0025] Comparative Example 1: The liquid calcium fertilizer contains, per liter: 1000 g calcium nitrate tetrahydrate, 80 g erythritol, 6 g sodium alginate, 20 g citric acid, 40 g mannitol, 2 g sodium salt of maleic acid-acrylic acid copolymer with an average molecular weight of 10 kDa, triethanolamine to adjust the pH to 5.0, and water to make up to 1 L.

[0026] Preparation method: (1) Add about 150 mL (15% of the total volume) of distilled water to the reaction vessel, and then add erythritol, mannitol and citric acid in sequence; (2) Heat to 50 °C and stir until completely dissolved; (3) Add sodium alginate slowly while stirring continuously, and stir for 30 minutes to allow it to fully swell and disperse evenly; (4) Add sodium salt of maleic acid-acrylic acid copolymer while stirring continuously; (5) Control the temperature at 45 ℃ and slowly add calcium nitrate tetrahydrate to the above system in three batches. Add the next batch only after each batch has completely dissolved to avoid excessive local concentration. (6) Stop heating and wait for the system to cool to room temperature, then slowly adjust the pH of the mixture to 5.0 with triethanolamine; (7) Add distilled water to a total volume of 1 L, then filter through a 400-mesh filter cloth to obtain a clear, slightly viscous liquid calcium fertilizer. The resulting solution is as follows: Figure 1 As shown on the left.

[0027] Comparative Example 2: The liquid calcium fertilizer contains, per liter: 1000 g of calcium nitrate tetrahydrate, 100 g of small peptide amino acid solution (free amino acid content 120 g / kg, small peptide amino acid content 350 g / kg), 6 g of sodium alginate, 20 g of citric acid, 2 g of sodium salt of maleic acid-acrylic acid copolymer with an average molecular weight of 10 kDa, and triethanolamine to adjust the pH to 5.0, with water added to make up to 1 L.

[0028] Preparation method: (1) Add about 150 mL (15% of the total volume) of distilled water to the reaction vessel, and then add small peptide amino acid solution and citric acid in sequence; (2) Heat to 50 °C and stir until completely dissolved; (3) Add sodium alginate slowly while stirring continuously, and stir for 30 minutes to allow it to fully swell and disperse evenly; (4) Add sodium salt of maleic acid-acrylic acid copolymer while stirring continuously; (5) Control the temperature at 45 ℃ and slowly add calcium nitrate tetrahydrate to the above system in three batches. Add the next batch only after each batch has completely dissolved to avoid excessive local concentration. (6) Stop heating and wait for the system to cool to room temperature, then slowly adjust the pH of the mixture to 5.0 with triethanolamine; (7) Add distilled water to a total volume of 1 L, then filter with a 400-mesh filter cloth to obtain a clear, slightly viscous liquid calcium fertilizer.

[0029] Comparative Example 3: Liquid calcium fertilizer per liter contains: 1000 g calcium nitrate tetrahydrate, 100 g small peptide amino acid solution, 80 g erythritol, 20 g citric acid, 2 g sodium salt of maleic acid-acrylic acid copolymer with a molecular weight of 10-30 kDa, 40 g mannitol, triethanolamine to adjust the pH to 5.0, and water to make up to 1 L.

[0030] Preparation method: (1) Add about 150 mL (15% of the total volume) of distilled water to the reaction vessel, and then add erythritol, mannitol and citric acid in sequence; (2) Heat to 50 °C and stir until completely dissolved; (3) Add sodium salt of maleic acid-acrylic acid copolymer while stirring continuously; (4) Control the temperature at 45 ℃ and slowly add calcium nitrate tetrahydrate to the above system in three batches. Add the next batch only after each batch has completely dissolved to avoid excessive local concentration. (5) Stop heating and wait for the system to cool to room temperature, then slowly adjust the pH of the mixture to 5.0 with triethanolamine; (6) Add distilled water to a total volume of 1 L, then filter with a 400-mesh filter cloth to obtain a clear, slightly viscous liquid calcium fertilizer.

[0031] Comparative Example 4 Liquid calcium fertilizer contains, per liter: 1000 g calcium nitrate tetrahydrate, 100 g small peptide amino acid solution, 80 g erythritol, 20 g citric acid, 6 g sodium alginate, 40 g mannitol, triethanolamine to adjust pH to 5.0, and water to make up to 1 L.

[0032] Preparation method: (1) Add about 150 mL (15% of the total volume) of distilled water to the reaction vessel, and then add small peptide amino acid solution, erythritol, citric acid and mannitol in sequence; (2) Heat to 50 °C and stir until completely dissolved; (3) Add sodium alginate slowly while stirring continuously, and stir for 30 minutes to allow it to fully swell and disperse evenly; (4) Control the temperature at 45 ℃ and slowly add calcium nitrate tetrahydrate to the above system in three batches. Add the next batch only after each batch has completely dissolved to avoid excessive local concentration. (5) Stop heating and wait for the system to cool to room temperature, then slowly adjust the pH of the mixture to 5.0 with triethanolamine; (6) Add distilled water to a total volume of 1 L, then filter with a 400-mesh filter cloth to obtain a clear, slightly viscous liquid calcium fertilizer.

[0033] II. Compatibility test with potassium dihydrogen phosphate 1. Samples: Calcium fertilizers prepared in Examples 1-3 and Comparative Examples 1-4.

[0034] 2. Test methods: (1) Experimental group: Take three beakers, accurately weigh 1.00 g of potassium dihydrogen phosphate into each beaker and add 300 g of distilled water. Stir until completely dissolved. Add 1.00 g of calcium fertilizer samples from Examples 1-3 to each of the three beakers and stir until a homogeneous liquid is formed.

[0035] (2) Control group: Accurately weigh 1.00 g of potassium dihydrogen phosphate and place it in a beaker. Add 300 g of distilled water and stir until completely dissolved. Add 1.00 g of calcium fertilizer sample from Comparative Example 1-4 and stir until a homogeneous liquid is formed.

[0036] 3. Observation and testing: After standing for 24 hours, the solutions in the test group remained clear and transparent, with no visible precipitate or turbidity. Figure 2 The diagram shows the state of the calcium fertilizer and potassium dihydrogen phosphate of Example 1 and Comparative Example 1 after 24 hours of mixing.

[0037] The control group showed a large amount of white flocculent precipitate within 1 hour of standing, while the experimental group solution was clear, indicating that the calcium fertilizer prepared in Example 1 has good compatibility with potassium dihydrogen phosphate.

[0038] III. pH Response Release Characteristics Test of Calcium Fertilizer 1. Materials and Instruments Samples: Calcium fertilizer samples prepared in Examples 1-3 and Comparative Examples 1-4.

[0039] Buffer solutions: Prepare phosphate buffer systems with pH values ​​of 7.0, 6.0, 5.5, 5.0, and 4.5.

[0040] Instruments: constant temperature shaking incubator, 0.45 μm microporous filter membrane, EDTA titration device.

[0041] 2. Test methods: (1) Take a polyethylene bottle and add 49 mL of the above buffer solutions with different pH values ​​respectively.

[0042] (2) Add 1 mL of calcium fertilizer from Examples 1-3 and Comparative Examples 1-4 to each bottle.

[0043] (3) Place the bottle in a constant temperature shaking incubator (37 ℃, 100 rpm) for release experiment.

[0044] (4) After 48 hours, take 5 mL of sample from each bottle and filter it immediately through a 0.45 μm filter membrane.

[0045] Determination of Ca released from filtrate using EDTA titration 2+ ⁺ Concentration C t C0 represents the theoretical total calcium concentration in the calcium fertilizer samples of Examples 1-3 and Comparative Examples 1-4, with a value of 3.38 g / L. The cumulative calcium release rate (%) is calculated using the following formula: Calcium cumulative release rate (%) = [C t / C0]×100%.

[0046] 3. Test Results: Table 1 shows the cumulative calcium release rate over 48 hours under different pH conditions.

[0047] Table 1. Cumulative calcium release rate (%) over 48 h under different pH conditions pH 7 6 5.5 5 4.5 Example 1 12.3 15.5 41.9 67.9 68.2 Example 2 13.5 16.8 45.0 62.6 70.5 Example 3 10.3 13.8 39.6 60.9 72.1 Comparative Example 1 20.3 35.6 53.3 78.3 88.5 Comparative Example 2 35.4 49.8 58.2 79.5 88.6 Comparative Example 3 28.3 40.6 54.3 70.4 80.5 Comparative Example 4 40.5 55.8 70.2 89.6 94.4 The results showed that the calcium fertilizers prepared in Examples 1-3 of this invention exhibited significant release differences under different pH conditions: under neutral conditions of pH 7.0, the cumulative calcium release rate after 48 h was only 10.3%–13.5%, with a slow release; as the pH value decreased, the release rate gradually increased, and under acidic conditions of pH 4.5, the cumulative calcium release rate after 48 h increased to 68.2%–72.1%. Comparing Example 1 with Comparative Example 1 (both had essentially the same formulation, except Comparative Example 1 lacked the small peptide amino acid solution), it can be seen that the release rate of Comparative Example 1 was significantly higher than that of Example 1 under all pH conditions. This indicates that the small peptide amino acid solution can achieve the slow-release performance of calcium ions, forming a soluble complex with calcium ions to constitute the first stabilizing barrier. Comparative Example 4 (without the addition of maleic acid-acrylic acid copolymer sodium salt) had the highest release rate, indicating that the addition of maleic acid-acrylic acid copolymer sodium salt further enhanced the slow-release effect.

[0048] The above results indicate that the calcium fertilizer system described in this invention achieves good pH-responsive release performance through the synergistic effect of multiple components, including small peptide amino acid liquid, sugar alcohol, sodium alginate, and sodium maleic acid-acrylic acid copolymer: it maintains stable and slow release under neutral conditions, which is beneficial for the transport of calcium fertilizer in the soil; while under acidic conditions (such as plant rhizosphere or acidic soil), it can rapidly release calcium elements to achieve precise supply.

[0049] IV. Pot Experiment – ​​Effects of Spraying Slow-Release Calcium Fertilizer on Yield and Leaf Calcium Content of Sand-Cultivated Tomatoes 1. Experimental Materials and Methods: Five-leaf, one-heart tomato plants were transplanted and cultured in sand. They were then irrigated with calcium-free Hoagland and Arnon nutrient solutions. The nutrient solutions were prepared with distilled water. The experimental treatment was conducted after the tomatoes grew to eight leaves and one heart.

[0050] Experimental Design: Blank control group: sprayed with water.

[0051] Slow-release calcium fertilizer group: Spray calcium fertilizer diluted 600 times in Examples 1-3.

[0052] Ordinary calcium fertilizer group: Spray with comparative ratio 1-4 calcium fertilizer diluted 600 times.

[0053] Four tomato plants were used in each treatment, for a total of 32 plants. The tomato plants were arranged in a randomized block design.

[0054] Treatment method: Spray evenly with a sprayer until both sides of the leaves are moistened. The amount of spray per plant is (20±2) mL each time, and spray once every 7 days for a total of 3 times. Five days after the third spray, take samples, separate the veins and leaves of the top leaves, dry them, and measure the calcium content separately. After harvest, measure the fruit weight and calcium content.

[0055] 2. Experimental Results and Analysis Table 2 shows the effects of spraying different calcium fertilizers on the calcium content and yield of tomato leaves and veins in each treatment.

[0056] Table 2. Effects of different calcium fertilizers on calcium content and yield in tomato leaves and veins under each treatment. deal with Leaf vein calcium content / ‰ Leaf calcium content / ‰ Fruit calcium content / ‰ Yield / g Blank control group 1.14 - - 242.34 Example 1 4.03 1.02 1.13 352.55 Example 2 5.56 1.38 1.36 375.89 Example 3 4.43 1.32 1.45 369.31 Comparative Example 1 2.31 0.83 0.95 306.94 Comparative Example 2 2.01 0.73 0.96 280.74 Comparative Example 3 3.31 1.12 0.96 330.41 Comparative Example 4 1.21 0.74 0.79 289.31 The results showed that the calcium content and yield of leaf veins, leaves, and fruits in all treatments of the slow-release calcium fertilizer groups (Examples 1-3) were higher than those in the blank control group and the ordinary calcium fertilizer groups (Comparative Examples 1-4). Foliar application of both ordinary calcium fertilizer and slow-release calcium fertilizer increased the calcium content and yield of fruits and leaves, but the effect of slow-release calcium fertilizer was better, achieving a better yield increase.

[0057] V. Field Application Trial – Effects of Drip Irrigation Application of Slow-Release Calcium Fertilizer on the Yield and Quality of Nectarines in the Field 1. Experimental Materials and Methods: Experimental location: Orchard in Xiaotianzhuang Village, Mengyin Street, Mengyin County, Shandong Province. Drip irrigation fertilization was carried out 20 days after the peach blossoms.

[0058] Experimental materials: The test crop was a 3-year-old 'Zhongyou 13' nectarine, pollinated by the 'Shuguang' variety. The plant spacing was 1.5 m × 2.5 m, with 178 plants per mu (approximately 0.067 hectares). The experimental site was hilly with sandy loam soil, and its basic fertility is shown in the table below.

[0059] Table 3 Basic Soil Properties Organic matter / % Alkaline nitrogen / mg / kg Available phosphorus / mg / kg Available potassium / mg / kg pH 1.03 46.35 52.76 177.62 6.69 Experimental Design: Blank control group: water.

[0060] Ordinary calcium fertilizer group: Comparative ratio 1-4 calcium fertilizer diluted 600 times for drip irrigation.

[0061] Slow-release calcium fertilizer group: Calcium fertilizer of Examples 1-3 diluted 600 times for drip irrigation.

[0062] Five trees were used in each treatment, for a total of 40 trees in the experiment, which were arranged in a randomized block design.

[0063] Sampling and measurement: During the fruit ripening period, 30 fruits were randomly selected from each treatment for measurement.

[0064] Yield indicators: Count the number of fruits per plant, calculate the yield per plant and convert it to yield per acre.

[0065] Quality indicators: The weight of a single fruit was measured using an electronic balance; the soluble solids content was determined using a TD-45 fruit saccharimeter; the total soluble sugar content was determined using the Fehling's reagent method; the total soluble acid content was determined using the NaOH titration method; and the vitamin C (Vc) content was determined using the 2,6-dichlorophenolindophenol titration method.

[0066] 2. Experimental Results and Analysis: Table 4 shows the effect of different calcium fertilizers applied by drip irrigation on peach yield.

[0067]

[0068] The results showed that, compared with the blank control group, the application of both ordinary calcium fertilizer and the slow-release calcium fertilizer of this invention could increase the yield of nectarines, and the yield-increasing effect of the slow-release calcium fertilizer was better than that of ordinary calcium fertilizer.

[0069] Table 5 shows the effects of different calcium fertilizers applied through drip irrigation on the single fruit weight and quality indicators of peaches.

[0070] Table 5. Effects of different calcium fertilizers applied via drip irrigation on single fruit weight and quality indicators of peaches. deal with Single fruit weight / g Soluble solids / % Total soluble sugars / % Total soluble acids / % Vitamin C / mg / 100g Blank control group 132.3 8.32 8.43 1.12 4.22 Example 1 165.3 11.47 9.36 0.93 6.49 Example 2 175.7 11.69 9.53 0.86 7.26 Example 3 170.4 11.21 10.21 0.65 7.07 Comparative Example 1 147.3 11.35 9.11 1.04 5.82 Comparative Example 2 138.2 10.21 8.31 0.78 5.21 Comparative Example 3 150.7 9.28 9.21 0.91 6.29 Comparative Example 4 158.2 10.87 9.47 1.12 7.57 The results showed that the slow-release calcium fertilizer group had significantly higher single fruit weight, soluble solids, and total soluble sugar content in nectarines than the control group, while having the lowest total soluble acid content. This indicates that the product of this invention can significantly improve the commercial quality and flavor of nectarines.

[0071] Field trials have shown that, compared with the conventional calcium fertilizer group and the blank control group, the pH-responsive slow-release calcium fertilizer of this invention can significantly improve the yield and overall quality of nectarines, demonstrating excellent field application effects.

[0072] Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-mentioned technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by substituting the above-mentioned features with technical features disclosed in this application (but not limited to) that have similar functions.

Claims

1. A pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate, characterized in that, Each liter of the slow-release calcium fertilizer comprises the following components: Calcium nitrate tetrahydrate 1000-1200 g; 50-100 g of small peptide amino acid solution, wherein the content of free amino acids in the small peptide amino acid solution is not less than 100 g / kg and the content of small peptide amino acids is not less than 330 g / kg; Erythritol 60–100 g; 3-10 g of sodium alginate; Citric acid 10-50 g; Mannitol 10–40 g; Triethanolamine is used to adjust the pH value to 4.5–5.8; Add water to bring the volume up to 1 L.

2. The slow-release calcium fertilizer according to claim 1, characterized in that, It also contains sodium salt of maleic acid-acrylic acid copolymer with an average molecular weight of 10-30 kDa, which is added at an amount of 2-5 g / L.

3. A method for preparing a pH-responsive slow-release calcium fertilizer compatible with potassium dihydrogen phosphate as described in claim 1 or 2, characterized in that, Includes the following steps: (1) Add 15% of the total volume of water to the reaction vessel, then add small peptide amino acid solution, erythritol, mannitol and citric acid, heat to 50 °C and stir until completely dissolved; (2) Add sodium alginate to the solution obtained in step (1) and stir until homogeneous; (3) Add calcium nitrate tetrahydrate slowly in batches, and control the temperature at 40-50 ℃ during the addition process; (4) Adjust the pH of the mixture to 4.5–5.8 using triethanolamine; (5) Add water to the total volume of 1 L, filter to remove impurities, and obtain clear liquid calcium fertilizer.

4. The method according to claim 3, characterized in that, After step (2) and before step (3), the process also includes adding sodium salt of maleic acid-acrylic acid copolymer with a molecular weight of 10 to 30 kDa.

5. The method according to claim 3, characterized in that, In step (3), calcium nitrate tetrahydrate is added in 3 to 5 batches, and each batch is stirred thoroughly until completely dissolved.

6. A fertilizer composition, characterized in that, The mixture comprises the slow-release calcium fertilizer as described in claim 1 or 2 and potassium dihydrogen phosphate, wherein the weight ratio of the slow-release calcium fertilizer to potassium dihydrogen phosphate is 1:

1.

7. The application of the slow-release calcium fertilizer according to claim 1 or 2 in foliar fertilization or fertigation systems.

Images