Dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer

Abstract

The invention discloses a dynamic leaching-spectrophotometric detection method for the release rate of nutrients in a slow-release fertilizer, and relates to the field of agrochemical analys.The detection method comprises the following steps that S1, a slow-release fertilizer sample is placed in a leaching column to be leached, and leachate is collected; s2, sequentially adding a masking agent solution and a chromogenic reagent into the leachate, and carrying out chromogenic reaction; s3, pumping the solution into a double-optical-path flow cell, and measuring absorbance values under a target nutrient characteristic absorption wavelength and a background interference characteristic wavelength; s4, calculating the corrected net absorbance; and S5, calculating the nutrient concentration, and drawing a nutrient release kinetic curve. By adopting a dual-wavelength synchronous detection and real-time dynamic subtraction correction algorithm, the method can eliminate system errors of time-varying background chromaticity, so that accurate and reliable absorbance readings can be obtained at the initial stage of nutrient release even if the nutrient concentration in the leachate is very low, thereby ensuring the authenticity of the initial stage of a release curve and improving the accuracy of nutrient release. And initial release kinetic parameters are accurately captured.

Description

Technical Field

[0001] This invention relates to the field of agricultural chemical analysis technology, and more particularly to trace element analysis, specifically a dynamic leaching-spectrophotometric detection method for the nutrient release rate in slow-release fertilizers. Background Technology

[0002] Slow-release fertilizers, as a key carrier in modern agricultural precision fertilization systems, have been widely used in field crops, horticulture, and ecological restoration due to their ability to regulate nutrient release rates, reduce nutrient loss, and improve utilization efficiency. In recent years, to synergistically enhance both soil improvement and nutrient supply, many slow-release fertilizer formulations have incorporated natural organic active substances such as humic acid, fulvic acid, seaweed extracts, or specific amino acids. These additives not only improve soil aggregate structure and enhance microbial activity but also promote root development through physiological stimulation, thereby significantly improving crop nutrient absorption efficiency. Accurately measuring the nutrient release kinetics curves in simulated soil environments is crucial for product development, quality control, and agronomic guidance.

[0003] Traditional evaluation methods mainly include soil culture and laboratory leaching. Dynamic leaching is widely used due to its relatively simple operation, controllable conditions, and ability to obtain continuous release data. This method typically involves placing fertilizer in a leaching column, leaching it intermittently or continuously with a specific solution, and collecting the leachate periodically. The concentration of nutrients is then determined using chemical analysis methods. For the determination of inorganic nutrients such as nitrogen and phosphorus, spectrophotometry has become the mainstream choice due to its high sensitivity and ease of operation. For example, the indophenol blue method is used to determine ammonium nitrogen, and the vanadium molybdenum yellow method or molybdenum blue method is used to determine phosphate.

[0004] However, when slow-release fertilizers contain humic acids or dark-colored organic components derived from seaweed, they pose a significant challenge to traditional colorimetric nutrient detection methods. These water-soluble organic substances are not released all at once during leaching, but rather dissolve continuously and slowly over time, causing the color of the leachate to gradually change from initially colorless to light yellow, yellowish-brown, and even brownish-red. This color originates from the rich aromatic rings, quinone groups, and conjugated double bonds in the molecular structure, which exhibit broad absorption in the 400-500 nm visible light region. This absorption band highly overlaps with the main absorption peaks or secondary absorption regions of colorimetric products such as ammonium nitrogen and phosphate. This renders the conventional difference method using a pure solvent blank completely ineffective, as the sample's background absorption is not subtracted, leading to a systematically high absorbance value and a positive error. Especially in the early stages of nutrient release, when the concentration of the analyte is extremely low, organic matter dissolution may have already begun, resulting in a very low signal-to-noise ratio, severely distorted measurement data, and an inability to accurately obtain key parameters such as the initial release rate. Summary of the Invention

[0005] This invention overcomes the shortcomings of the prior art and provides a dynamic leaching-spectrophotometric detection method for the nutrient release rate in slow-release fertilizers. It combines dynamic leaching with dual-wavelength synchronous detection, introduces a masking agent to suppress metal ion interference, and performs real-time dynamic differential correction of the absorbance at the target wavelength based on a pre-calibrated correction factor, thereby obtaining pure and accurate nutrient concentration data, especially ensuring the measurement reliability in the low concentration range at the initial stage of release.

[0006] To achieve the above objectives, the technical solution adopted by this invention is as follows: This invention provides a dynamic leaching-spectrophotometric detection method for the nutrient release rate in slow-release fertilizers, comprising the following steps:

[0007] S1. Place the slow-release fertilizer sample in a leaching column and use a leaching solution for intermittent dynamic leaching, collecting the leaching liquid at different time points;

[0008] S2. Add masking agent solution and colorimetric reagent to the leachate in sequence, and carry out the colorimetric reaction under constant temperature conditions;

[0009] S3. Pump the colorimetric solution into a double-path flow cell and simultaneously measure its absorption at the characteristic wavelength of the target nutrient. and background interference characteristic wavelength The absorbance value at the specified value;

[0010] S4. According to the formula Calculate the corrected net absorbance; where, This represents the absorbance value measured at the characteristic absorption wavelength of the target nutrient; This represents the absorbance value measured at the characteristic wavelength of background interference. This represents the pre-calibrated correction factor;

[0011] S5. Calculate the nutrient concentration based on the net absorbance and plot the nutrient release kinetic curve.

[0012] In a preferred embodiment of the present invention, in step S1, the leaching column has an inner diameter of 2-3 cm and a height of 25-35 cm, and the bottom of the column is lined with quartz wool and acid-washed quartz sand; the slow-release fertilizer sample has a particle size of 30-70 mesh and a sample weight of 0.50-2 g.

[0013] In a preferred embodiment of the present invention, in step S1, the leaching solution is one of calcium chloride solution, potassium chloride solution or calcium nitrate solution, and its concentration is 0.005-0.05 mol / L.

[0014] In a preferred embodiment of the present invention, in step S1, the intermittent leaching mode is as follows: 30-100 mL of leaching solution is injected every 0.5-2 h, soaked for 20-40 min, and then discharged and collected at a flow rate of 3-10 mL / min.

[0015] In a preferred embodiment of the present invention, in step S2, the masking agent comprises one of disodium EDTA, citrate, tartrate, or oxalate, with a concentration of 1-10 wt%; the colorimetric reagent is a reagent system suitable for colorimetric development of the target nutrient, including indophenol blue reagent, vanadium molybdenum yellow reagent, or molybdenum blue reagent.

[0016] In a preferred embodiment of the present invention, the colorimetric reagent is an indophenol blue reagent, which comprises:

[0017] Reagent A: An alkaline solution containing 0.5-2 M phenol and 0.5-1 mM sodium nitroprusside, with a pH of 11.5-13;

[0018] Reagent B: 0.1-1 wt% sodium hypochlorite solution;

[0019] Mix reagent A and reagent B at a volume ratio of 4-6:1 before use.

[0020] In a preferred embodiment of the present invention, in step S2, the temperature of the isothermal reaction is 30-40 °C and the reaction time is 10-20 min.

[0021] In a preferred embodiment of the present invention, in step S3, the target nutrient characteristic absorption wavelength The wavelength is determined based on the type of nutrient being measured, and is selected from 620-640 nm, 870-890 nm, or 215-225 nm; the background interference characteristic wavelength is described. Selected from 490-510 nm, 690-710 nm, 640-660 nm or 270-280 nm.

[0022] In a preferred embodiment of the present invention, in step S4, the correction factor The following method was used to determine the background: a series of background simulated standard solutions of different concentrations were prepared, and their values ​​were measured without the addition of a colorimetric reagent. and The absorbance at that point, in order to right Performing linear regression yields the slope. value.

[0023] In a preferred embodiment of the present invention, the target nutrient is one of ammonium nitrogen, nitrate nitrogen, or phosphate; the dual-wavelength synchronous detection in step S3 and the correction method in step S4 are applicable to the colorimetric system of the corresponding nutrient.

[0024] This invention addresses the shortcomings of the prior art and has the following beneficial effects:

[0025] (1) This invention provides a dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizers. It adopts dual-wavelength synchronous detection and real-time dynamic differential correction algorithm. It utilizes the fact that organic substances such as humic acid dissolved in fertilizer contain aromatic rings and conjugated double bond structures, which produce broad-spectrum absorption in the visible light region, overlapping with the absorption band of the colorimetric products of nutrients such as ammonium nitrogen. By synchronously measuring the absorbance of the target characteristic wavelength and the background characteristic wavelength, and using a pre-calibrated correction factor for real-time differential correction, the absorbance value contributed by the organic background color can be directly deducted. Compared with the existing technology that uses a single wavelength measurement or a pure solvent blank, this method can eliminate the systematic error of time-varying background color, so that even if the nutrient concentration in the leaching liquid is very low in the early stage of nutrient release, an accurate and reliable absorbance reading can be obtained, thereby ensuring the authenticity of the initial segment of the release curve and accurately capturing the initial release kinetic parameters.

[0026] (2) In this invention, by adding a masking agent solution in the sample processing step and combining it with dual-wavelength correction, the components such as disodium EDTA in the masking agent can form stable water-soluble complexes with metal ions such as iron and copper ions dissolved in the leachate, preventing these metal ions from catalyzing the oxidation of organic matter or reacting with the colorimetric agent. Dual-wavelength correction specifically eliminates the absorption interference of organic color, thereby making the colorimetric reaction respond only to the target nutrient, and the detection signal has high specificity, so that the nutrient release rate data obtained more purely reflects the dissolution behavior of the nutrient molecules themselves, thus providing a more accurate basis for evaluating fertilizer performance.

[0027] (3) In this invention, the dual-wavelength synchronous correction principle has good universality. Different nutrients, such as nitrate nitrogen or phosphate, have different characteristic absorption wavelengths for their colorimetric products. The absorption spectra of common colored organic additives are relatively flat in a specific region. Appropriate background characteristic wavelengths can be selected for monitoring. Then, by changing the detection wavelength and recalibrating the correction factor, the same method can be adapted to multiple nutrient release detection systems. Compared with the prior art, each nutrient detection often requires the independent development of complex background subtraction schemes. This invention can effectively reduce the method development cost, thereby expanding the application scope of this method in the evaluation of multifunctional slow-release fertilizers. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a flowchart of a dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to a preferred embodiment of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0032] It should be noted that the raw materials, equipment and reagents used in this invention can all be purchased from the market or obtained through existing preparation methods.

[0033] Example 1:

[0034] A dynamic leaching-spectrophotometric method for detecting nutrient release rate in slow-release fertilizers, referring to... Figure 1 As shown, it includes the following steps:

[0035] S1. Construction of a dynamic leaching system: The leaching column is made of transparent and corrosion-resistant material, specifically polytetrafluoroethylene or high borosilicate glass, with an inner diameter of 2.5 cm and a height of 30 cm. From bottom to top, a 0.5 cm thick layer of quartz wool and a 1 cm thick layer of acid-washed quartz sand are laid. The quartz sand has a particle size of 0.3-0.6 mm. After boiling in 1.0 mol / L hydrochloric acid for 30 min, it is repeatedly rinsed with water until neutral to eliminate the interference of its own ion exchange capacity on the components of the leachate. The slow-release fertilizer sample is subjected to standard sieving to control the particle size to 60 mesh. 1 g is weighed and evenly packed into the leaching column, avoiding compaction to maintain the natural pore structure. The leaching solution is a 0.01 mol / L calcium chloride solution. This concentration can effectively simulate the ionic strength of typical farmland soil solution and inhibit colloidal dispersion, while maintaining cation exchange balance and preventing abnormal nutrient desorption due to charge imbalance.

[0036] It should be noted that the intermittent dynamic leaching operation was performed according to the following parameters: In the initial stage, 50 mL of leaching solution was injected into the leaching column and allowed to stand for 30 min to fully wet the fertilizer particles and initiate the diffusion process; then, all the leaching solution was discharged into a clean collection container at a constant flow rate of 5 mL / min, and the end time of this leaching was recorded as the zero point of time; thereafter, 50 mL of fresh leaching solution was injected every 1 h, and each time it was allowed to stand for 30 min before being discharged at the same flow rate and the leaching solution was collected quantitatively. The operation was carried out continuously for 168 h, and a total of 169 leaching samples were obtained at different time points. All leaching solutions were temporarily stored in a light-protected environment at 4 ℃ to ensure that subsequent color development and detection were completed within 24 h, preventing changes in nutrient form due to microbial degradation or chemical oxidation.

[0037] S2. Pretreatment stage for color development: For cases where the target nutrient is ammonium nitrogen, add 1 mL of masking agent solution and 2 mL of colorimetric reagent mixture to each 10 mL eluent. The masking agent solution is a 5 wt% EDTA disodium aqueous solution with a pH of 7.0, used to complex any Fe that may be present in the eluent. 3+ Cu 2+ Mn 2+ Transition metal ions are used to block the catalytic side reaction pathways of the indophenol blue colorimetric reaction. The colorimetric reagent adopts the indophenol blue method system, which is prepared by mixing reagent A and reagent B before use: reagent A is an aqueous solution of sodium hydroxide containing 1 M phenol and 0.8 mM sodium nitroprusside, with a pH of 12.5; reagent B is a 0.5 wt% sodium hypochlorite solution. When using, reagent A and reagent B are mixed at a volume ratio of 5:1 to form a stable colorimetric working solution. The order of addition follows the principle of masking agent first and then colorimetric reagent to avoid irreversible side reactions initiated by metal ions in the early stage of color development.

[0038] It should be noted that the colorimetric reaction was carried out in a constant temperature water bath at 35 ℃, and the reaction lasted for 15 minutes.

[0039] S3. After the colorimetric reaction is complete, immediately transfer the colorimetric solution to a dual-path flow cell for absorbance measurement. The dual-path flow cell is integrally manufactured from fused silica, with two channels each having a path length of 10 mm and an internal volume of 80 μL. The inlet and outlet are connected to a peristaltic pump via polyetheretherketone tubing to ensure a stable, bubble-free flow of the solution through the detection area. The detection system is equipped with a deuterium lamp and a tungsten halide composite light source, which outputs the characteristic absorption wavelengths of the target nutrients via a dual monochromator. Characteristic wavelengths of background interference Monochromatic light; for the detection of ammonium nitrogen, Set to 630 nm The reference wavelength was set to 500 nm. The reason for choosing 500 nm as the reference wavelength is that dark organic compounds such as humic acid and fulvic acid have significant and stable absorption at this wavelength, while the molar absorptivity of the indophenol blue color product at 500 nm is less than 5% of that at 630 nm, and can be regarded as having no absorption, thus satisfying the principle of selecting the reference wavelength.

[0040] In a preferred embodiment of the present invention, dual-wavelength synchronous detection is achieved through an integrated spectrophotometric detection system; this system comprises two independent but synchronously triggered photodetectors, which respectively receive wavelengths passing through the same solution sample. and The light beam was sampled at a frequency of 1 Hz to ensure sufficient data points were acquired during the brief window period of solution flow through the flow cell to calculate the average absorbance; the absorbance reading of each eluent sample was taken as the average value over a continuous 10 s period during the stable plateau phase, denoted as . and .

[0041] Understandably, the correction factor The calibration is crucial for achieving dynamic background subtraction. Specifically, five background simulation standard solutions were prepared, with the basic components being a mixture of humic acid and fulvic acid, and total organic carbon concentrations of 5 mg / L, 10 mg / L, 20 mg / L, 40 mg / L, and 80 mg / L, respectively, covering the color range that the actual leachate may exhibit throughout the entire release cycle. These standard solutions were injected directly into the detection system without any colorimetric reagents, and their absorbance values ​​at 630 nm and 500 nm were recorded simultaneously under the same instrument conditions. Linear regression analysis was performed with A(630 nm) as the ordinate and A(500 nm) as the abscissa, yielding the linear equation A(630) = 0.182 × A(500) + 0.0012, and a correlation coefficient R0. 2=0.9987. Since this is less than the instrument noise level, the intercept term is ignored, and the slope of 0.182 is taken as the correction factor. This value is used consistently in all subsequent sample tests.

[0042] S4, Net Absorbance According to the formula Calculations were performed; for example, the leachate at a certain time point was measured at 630 nm. =0.254, at 500 nm =0.820, then =0.254-0.182×0.820=0.105; This value only reflects the true light absorption contribution of the indophenol blue colorimetric product, completely eliminating the tailing absorption interference of background organic matter at 630 nm.

[0043] S5. Based on net absorbance, nutrient concentration was inverted using a pre-established standard curve. The standard curve was prepared using a series of standard solutions made with pure ammonium sulfate, with concentration gradients of 0.1 mg N / L, 0.5 mg N / L, 1.0 mg N / L, 2.0 mg N / L, 5.0 mg N / L, 10.0 mg N / L, 20.0 mg N / L, and 50.0 mg N / L. After undergoing the same masking, color development, and detection procedures as the samples, the correlation between net absorbance and concentration was obtained. A linear equation was fitted to obtain the correlation. R 2 =0.9995, with a linear range covering 0.1-50 mg / L, meeting the detection requirements for controlled-release fertilizers throughout the entire process from initial burst release to later slow release; accordingly, the above... =0.105 corresponds to an ammonium nitrogen concentration of 5.03 mg / L.

[0044] Furthermore, the nutrient concentrations calculated at each time point were arranged in chronological order to plot a concentration-time curve, and then integrated to obtain a cumulative release-time curve, i.e., a nutrient release kinetic curve. This curve exhibits typical three-stage characteristics: the initial 0-2 h is a rapid burst release period, with the release amount accounting for 12% of the total; 2-72 h is a linear diffusion-dominated period with a stable release rate; after 72 h, it enters a slow decay period, which conforms to the first-order kinetic model; key parameters such as lag time, initial burst release rate, and diffusion coefficient can all be accurately extracted from it.

[0045] In a preferred embodiment of the present invention, the entire detection process is integrated through an automated control system. This system comprises a Siemens S7-1200 PLC programmable controller, an eight-channel peristaltic pump (Cole-Parmer Masterflex L / S), a Peltier temperature-controlled reaction module, an Ocean Insight HDX dual-channel fiber optic spectrometer, and an industrial computer data processing unit. The programmable controller coordinates each execution unit according to preset timing instructions: 5 minutes before the start of each leaching cycle, the peristaltic pump is activated to draw 50 mL of leaching solution from the storage bottle and inject it into the leaching column; after the soaking timer expires, the tubing is switched to transfer the leaching solution to the reaction tube; subsequently, 1 mL of masking agent and 2 mL of colorimetric reagent are injected sequentially, mixed, and then incubated in a 35 ℃ constant-temperature reaction module for 15 minutes; after the reaction ends, the solution is pushed to a dual-path flow cell, and the spectrometer simultaneously collects absorbance at 630 nm and 500 nm; the data is transmitted to the industrial computer via USB, and a built-in Python script automatically executes the data. The system performs calculations, concentration inversion, and curve plotting. It supports continuous operation for over 168 hours without human intervention. Daytime and nighttime ambient temperature fluctuations have no significant impact on the results, and the relative standard deviation (RSD) is less than 2.5%.

[0046] Furthermore, this method can be adapted to the detection needs of different target nutrients. When determining phosphate, the chromogenic reagent is replaced with the molybdenum blue method system: the masking agent remains 5% disodium EDTA solution; the chromogenic reagent is prepared by mixing 0.5% ammonium molybdate-0.1% potassium antimony tartrate mixed acid solution and 10% ascorbic acid solution at a volume ratio of 4:1; λ1 is set to 880 nm, and λ2 is selected as 700 nm; the background simulation standard solution is prepared using seaweed extract, with a concentration gradient of 10 to 100 mg / L; the correction factor k is obtained through the same calibration procedure, with a typical value of 0.215. When determining nitrate nitrogen, no chromogenic reagent or masking agent needs to be added; simply take 10.0 mL of eluent, filter it, and inject it into the flow cell. Set to 220 nm, The wavelength is set to 275 nm; because humic acid has strong aromatic absorption at 275 nm while nitrate nitrogen has no absorption at this wavelength, the two constitute an ideal reference pair; correction factor The values ​​were obtained by regression analysis of the absorbance of the humic acid standard solution at 220 and 275 nm, with a typical value of 0.380.

[0047] To verify the effectiveness of this method, comparative experiments were conducted between the proposed embodiments and the comparative examples.

[0048] Example 1 uses the complete process described in this invention to detect the ammonium nitrogen release behavior of a coated urea slow-release fertilizer containing humic acid (5% w / w).

[0049] Comparative Example 1 uses the traditional single-wavelength detection method, that is, the absorbance is measured only at 630 nm without background correction.

[0050] Comparative Example 2 uses a blank leaching solution as a reference for baseline subtraction, but does not consider the dynamic characteristics of background changes over time.

[0051] All three experiments used the same batch of fertilizer samples and were conducted in parallel under the same leaching conditions; the experimental results are shown in Table 1.

[0052] Table 1: Experimental results of Example 1 and Comparative Examples 1-2

[0053] Time point (h) <![CDATA[The NH4 concentration (mg / L) measured in Example 1 + > <![CDATA[Measured NH4 in Comparative Example 1 + Concentration (mg / L)]]> <![CDATA[The NH4 concentration (mg / L) measured in Comparative Example 2]]> + > 1 3.8 6.2 5.1 2 4.5 7.0 5.8 6 5.2 7.5 6.3 24 6.0 7.8 6.7 72 6.5 7.8 7.0 168 6.8 8.0 7.2

[0054] As shown in Table 1, during the initial 1-6 hours of release, the measured values ​​of Comparative Examples 1 and 2 were significantly higher than those of Example 1, with deviations of 38-63% and 25-35%, respectively. This indicates that the uncorrected background absorption severely overestimated the nutrient content in the low concentration range. As release progressed, the background color stabilized, and the deviation gradually decreased, but a systematic positive deviation still existed throughout the entire cycle. The release curve obtained in Example 1 was smooth and conformed to the laws of physical diffusion, while the comparative example curve showed a non-physical steep rise in the initial stage, affecting the accurate determination of lag time and burst release rate.

[0055] In addition, the precision and accuracy of the method were examined. The same eluent sample was measured six times repeatedly, and the relative standard deviation of the net absorbance was 1.8%. Spike recovery experiments were conducted at three concentration levels: 2.0 mg / L, 10.0 mg / L, and 30.0 mg / L, with average recoveries of 98.5%, 101.2%, and 99.3%, respectively, indicating that the method has good repeatability and accuracy.

[0056] Regarding long-term operational stability, the same 5.0 mg / L NH4 was measured daily for 7 consecutive days. + The concentration standard solution had a daily coefficient of variation of 2.1% for net absorbance, demonstrating that the correction factor remained stable throughout the experimental period and did not require frequent recalibration.

[0057] In summary, this invention establishes a method for detecting the nutrient release rate of slow-release fertilizers containing dark-colored organic additives by precisely controlling leaching conditions, introducing masking agents to eliminate metal interference, employing dual-wavelength synchronous acquisition, and combining dynamic subtraction with a fixed correction factor. This method is highly feasible in engineering implementation and ensures the accuracy of measurements throughout the entire release cycle, especially in the initial low-concentration range.

[0058] The above description is based on the preferred embodiments of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of the invention is defined by the appended claims rather than the foregoing description, and all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0059] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A dynamic leaching-spectrophotometric method for detecting the nutrient release rate in slow-release fertilizers, characterized in that, Includes the following steps: S1. Place the slow-release fertilizer sample in a leaching column, use leaching solution for intermittent dynamic leaching, and collect the leaching liquid at different time points; S2. Add masking agent solution and colorimetric reagent to the leachate in sequence, and carry out the colorimetric reaction under constant temperature conditions; S3. Pump the colorimetric solution into a double-path flow cell and simultaneously measure its absorption at the characteristic wavelength of the target nutrient. and background interference characteristic wavelength The absorbance value at the specified value; S4. According to the formula Calculate the corrected net absorbance; where, This represents the absorbance value measured at the characteristic absorption wavelength of the target nutrient; This represents the absorbance value measured at the characteristic wavelength of background interference. This represents the pre-calibrated correction factor; S5. Calculate the nutrient concentration based on the net absorbance and plot the nutrient release kinetic curve.

2. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: In step S1, the leaching column has an inner diameter of 2-3 cm and a height of 25-35 cm, and the bottom of the column is lined with quartz wool and acid-washed quartz sand; the slow-release fertilizer sample has a particle size of 30-70 mesh and a sample weight of 0.50-2 g.

3. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: In step S1, the leaching solution is one of calcium chloride solution, potassium chloride solution, or calcium nitrate solution, and its concentration is 0.005-0.05 mol / L.

4. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: In step S1, the intermittent leaching mode is as follows: 30-100 mL of leaching solution is injected every 0.5-2 h, soaked for 20-40 min, and then discharged and collected at a flow rate of 3-10 mL / min.

5. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: In step S2, the masking agent comprises one of disodium EDTA, citrate, tartrate, or oxalate, with a concentration of 1-10 wt%; the colorimetric reagent is a reagent system suitable for colorimetric development of the target nutrient, including indophenol blue reagent, vanadium molybdenum yellow reagent, or molybdenum blue reagent.

6. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 5, characterized in that: The colorimetric reagent is an indophenol blue reagent, which includes: Reagent A: An alkaline solution containing 0.5-2 M phenol and 0.5-1 mM sodium nitroprusside, with a pH of 11.5-13; Reagent B: 0.1-1 wt% sodium hypochlorite solution; Mix reagent A and reagent B at a volume ratio of 4-6:1 before use.

7. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: In step S2, the temperature of the isothermal reaction is 30-40 °C, and the reaction time is 10-20 min.

8. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: In step S3, the target nutrient characteristic absorption wavelength The wavelength is determined based on the type of nutrient being measured, and is selected from 620-640 nm, 870-890 nm, or 215-225 nm; the background interference characteristic wavelength is described. Selected from 490-510 nm, 690-710 nm, 640-660 nm or 270-280 nm.

9. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: In step S4, the correction factor The following method was used to determine the background: a series of background simulated standard solutions of different concentrations were prepared, and their values ​​were measured without the addition of a colorimetric reagent. and The absorbance at that point, in order to right Performing linear regression yields the slope. value.

10. The dynamic leaching-spectrophotometric detection method for nutrient release rate in slow-release fertilizer according to claim 1, characterized in that: The target nutrient is one of ammonium nitrogen, nitrate nitrogen, or phosphate; the dual-wavelength synchronous detection in step S3 and the correction method in step S4 are applicable to the colorimetric system of the corresponding nutrient.

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