Method for determining bio-available phosphorus in rice field soil

Abstract

The invention belongs to the technical field of agricultural soil nutrition determination, and particularly discloses a method for determining paddy field soil bio-available phosphorus, which comprises the following steps: S1, placing a phosphorus extraction device with holes in the surface in a paddy field, and adding magnetic lanthanum particles; s2, taking out the device after a certain period of time, separating the magnetic lanthanum particles from the mud-water mixture by using a magnet, and then adding the magnetic lanthanum particles into an HCl solution for desorption; and S3, determining the phosphorus concentration by adopting an ICP method, and converting the phosphorus concentration into the amount of phosphorus adsorbed by the magnetic lanthanum particles in unit rice field soil. The method is rapid, accurate and easy to operate, the bio-available phosphorus provided by the rice field soil can be effectively determined, and farmland phosphate fertilizer application is guided.

Description

Technical Field

[0001] This invention relates to the field of agricultural soil nutrient determination technology, specifically to a method for determining bioavailable phosphorus in paddy field soil. Background Technology

[0002] Phosphorus is an essential nutrient for crops such as rice, and the main source of phosphorus for rice is the soil. Only a small portion of the phosphorus in the soil can be absorbed and utilized by plants; this portion is called bioavailable phosphorus (BaP) or available phosphorus in the soil. Rational fertilization based on the content of bioavailable phosphorus in the soil is not only a necessary prerequisite for ensuring high rice yields but also an important measure to prevent eutrophication of water bodies. Therefore, over the past century, many methods, tools, and equipment for measuring bioavailable phosphorus in the soil have been developed. Currently, the more mature methods include:

[0003] (1) Chemical method: Phosphorus in soil is extracted using chemical solutions, and then the phosphorus content in the extract is measured. Commonly used methods for determining bioavailable phosphorus in soil, such as the Bray-1 method, Olsen method, and Mehlich-3 method, were gradually developed from the 1940s to the 1980s. The chemical method remains the most important method for determining bioavailable phosphorus in soil, but its shortcomings are also obvious. First, the chemical method is destructive to soil components, resulting in different available phosphorus contents obtained from the same soil using different chemical extractants, requiring different measurement methods for different soil types. Therefore, the chemical method cannot reflect the true BaP content. Determining which extractant is suitable for a particular soil type requires correlation analysis with plant response, and when encountering new soil samples, the chemical extractant needs to be re-determined, leading to low work efficiency.

[0004] (2) Plant seedling method: This method involves cultivating single or multiple plants such as corn, wheat, and peanuts. After harvesting, drying, crushing, nitrifying, and extracting the phosphorus, the amount of phosphorus absorbed by the plants during their growth cycle is measured. This method can accurately reflect the amount of BaP provided by the soil to the cultivated plants. However, the measurement time is too long for the experimenters, while the time available for plants to absorb BaP is too short, especially when the amount of BaP in the soil exceeds the plant's adsorption capacity.

[0005] (3) Resin Method: This method utilizes anion exchange resins to adsorb phosphorus from the soil solution, promoting the release of readily available phosphorus from the soil solid phase. The phosphorus enriched in the resin is then measured and used as the soil's bioavailable phosphorus content. The resin method is similar to the process of phosphorus absorption from the soil by plant roots, thus providing a more accurate reflection of soil BaP. Resin adsorption of phosphorus is a rapid physicochemical process, overcoming the drawback of the long measurement time in the seedling method. In recent years, the resin method has been increasingly used due to its excellent extraction rate. However, the adsorption capacity of anion exchange resins for phosphorus is limited (even after resin modification, the phosphorus adsorption capacity only increases to 14.1 mg / g). -1 The resin exhibits poor selectivity, requiring increased resin consumption to achieve satisfactory phosphorus enrichment, especially in high-salinity soils in northern and coastal regions. Furthermore, to better separate the resin from the soil, soil particles smaller than 80 mesh (0.178 mm) are needed for testing, thus artificially excluding the contribution of larger soil particles to available phosphorus. Additionally, the resin tends to adhere to the soil and container, making separation and elution processes inconvenient.

[0006] Therefore, there is an urgent need to establish a new, simple, and accurate testing method that can better reflect the BaP status of soil. Summary of the Invention

[0007] The purpose of this invention is to provide a rapid, accurate, and easy-to-operate method for determining bioavailable phosphorus in paddy soil.

[0008] To achieve the above objectives, the specific technical solution adopted by the present invention is as follows:

[0009] A method for determining bioavailable phosphorus in paddy field soil includes the following steps:

[0010] S1. A phosphorus extraction device with perforated surface is placed in a paddy field, and magnetic lanthanum particles are added. The magnetic lanthanum particles, which act as a phosphorus reservoir, fix available phosphorus in the water and promote the release of phosphorus in the soil. This process simulates the process of rice absorbing phosphorus from the soil.

[0011] S2. After a certain period of time, remove the device and use a magnet to separate the lanthanum magnetic particles from the mud-water mixture. Then, add the lanthanum magnetic particles to an HCl solution for desorption.

[0012] S3. The phosphorus concentration was determined by ICP method and converted into the amount of phosphorus adsorbed by magnetic lanthanum particles per unit of paddy soil.

[0013] Preferably, in step S1, the phosphorus extraction device is divided into zone A and zone B from top to bottom, with a dividing line between the two zones; zone A is a hollow cylindrical tube with a top cover, and its bottom is connected to zone B; zone B is a hollow cone with its tip pointing downwards; small holes are evenly distributed on the surfaces of zones A and B; the device is placed in a paddy field, with zone B vertically embedded in the paddy soil; the dividing line at the boundary between zones A and B is at the same height as the water interface of the paddy field mud.

[0014] Furthermore, the phosphorus extraction device is made of stainless steel or plastic. Section A is a hollow cylindrical tube with a diameter of 2.9 cm and a length of 15 cm. Section B is a hollow cone with a height of 10 cm. The bottom of Section A and the top of Section B are threaded together. Both Section A and Section B have 20 evenly distributed holes with a diameter of 1 mm on their surfaces.

[0015] Preferably, in step S1, the magnetic lanthanum particles are magnetite, composed of lanthanum and cross-linking polysaccharides (such as chitosan or sodium alginate), with a particle size of 1.2–2.0 mm, a magnetic saturation strength of 10–20 emu / g, and a phosphorus saturation adsorption capacity of 20–40 mg / g. Specifically, Phosfixer-101 from Zhanyuan (Shandong) Ecological Environment Technology Co., Ltd. can be selected. The magnetic lanthanum particles of this invention can generally adsorb more than 90% of the phosphorus in water within minutes, and their adsorption performance (maximum adsorption capacity) is twice that of the most widely used phosphorus-locking agents currently available, enabling rapid and sufficient adsorption of phosphorus.

[0016] Furthermore, the amount of magnetic lanthanum particles added to the phosphorus extraction device is 0.3 to 1.2 g, and the amount of material added is calculated based on 3 times the conventional phosphorus content inside the device.

[0017] Preferably, in step S2, the specified time period is 1 to 7 days, so that phosphorus in the soil can be fully released.

[0018] Preferably, in step S2, 0.5–1.5 mol / L HCl is used for desorption, and the liquid-to-solid ratio (the ratio of HCl volume to the mass of the magnetic lanthanum particles) is 500–1000 ml / g.

[0019] Preferably, in step S3, the formula for calculating the P content in the paddy field is:

[0020] P = P icp *n*V 洗 / V B β

[0021] In the formula: P is the bioavailable phosphorus content in paddy fields (mg / Kg); P icp The phosphorus concentration (mg / L) was determined by ICP; n is the dilution factor; V 洗 V represents the volume of the elution buffer (L). B β: Volume of zone B in the extractor (L); β: Soil bulk density (Kg / L).

[0022] The present invention has the following beneficial effects:

[0023] This invention designs a unique and simple split-type device to simulate the process of phosphorus absorption by rice; it uses magnetic adsorption materials to rapidly recover available phosphorus from the soil; and by combining magnetic separation and ICP, it simplifies the operation process and enables rapid and accurate determination of bioavailable phosphorus in paddy soil. This method avoids the steps of soil sampling, drying, and screening in chemical methods, avoids the problems of resin adhesion and separation difficulties in resin methods, and overcomes the time-consuming problem of plant seedling methods (biological methods).

[0024] This invention provides a rapid, accurate, and easy-to-operate detection method that can effectively determine the bioavailable phosphorus provided by paddy field soil, guiding the application of phosphate fertilizers in farmland. It is expected to be widely used in rice production in my country. Furthermore, this method not only provides guidance for timely and rational replenishment of soil phosphorus, but also helps control agricultural non-point source pollution by promptly stopping fertilization when soil phosphorus levels are excessive and maintaining proper control of soil phosphorus content. Attached Figure Description

[0025] Figure 1 : A schematic diagram of the phosphorus extraction device in the specific implementation method.

[0026] Figure 2 : A schematic diagram of the phosphorus extraction device being inserted into a paddy field in a specific implementation method.

[0027] Figure 3 : Illustration of MLAB particles in a specific implementation method.

[0028] Figure 4 The illustration shows the separation and cleaning of lanthanum particles using a magnet in a specific implementation method. Detailed Implementation

[0029] Through long-term and in-depth research, the inventors, addressing the shortcomings of existing methods for determining bioavailable phosphorus in farmland, have provided a method for determining bioavailable phosphorus in paddy fields. This method replaces the extraction material for bioavailable phosphorus in paddy fields and optimizes the extraction method, facilitating rapid and accurate determination of bioavailable phosphorus in paddy fields. Based on the use of magnetic lanthanum particles with excellent adsorption capacity, combined with a simple device and optimized relevant parameters (including device size, number of openings, amount of magnetic lanthanum particles used, type and concentration of eluent, liquid-solid ratio, etc.), this invention develops an effective method for determining soil fertility beyond traditional methods. Furthermore, magnetic adsorption materials are currently widely used for phosphorus removal in water bodies; this invention successfully applies magnetic adsorption materials to the determination of available phosphorus in soil, filling a technological gap in soil-related applications. Specifically, the method includes the following steps:

[0030] (1) Select the measurement location. Select the area to be measured as needed. The water depth in the paddy field in the area should be 0-20cm. Conduct a preliminary inspection within the measurement area to ensure that there are no large stones that may affect the next step of the operation.

[0031] (2) The phosphorus extraction device is placed in the paddy field, and the phosphorus extraction device is as follows: Figure 1-2 As shown, the device is made of stainless steel or plastic and is divided into two sections, A and B. Section A is the upper part and section B is the lower part. Sections A and B are connected by a threaded rotation. Section A is a hollow round tube with a diameter of 2.9 cm and a length of 10 cm. Section B is a hollow cone with a height of 10 cm and a downward-pointing tip. There are 20 evenly distributed round holes with a diameter of 1 mm on the surface of sections A and B respectively. The phosphorus extraction device is placed in a paddy field. The device is placed in the paddy field and section B is vertically embedded in the paddy soil. The boundary between sections A and B is at the same height as the water interface of the paddy field mud.

[0032] (3) Add 0.3–1.2 g of magnetic lanthanum particles (MLAB) to the phosphorus extraction device and mix thoroughly with paddy soil in zone B. The magnetic lanthanum particles are as follows: Figure 3 As shown, the product is Phosfixer-101 (abbreviated as P-101), which is a phosphorus removal granule (i.e., phosphorus beads) purchased from Zhanyuan (Shandong) Ecological Environment Technology Co., Ltd.

[0033] (4) Cover the phosphorus extraction device to prevent external interference caused by water splashing, mosquitoes falling in, etc. Let the magnetic lanthanum particles stand in the device for 1 to 7 days for phosphorus adsorption.

[0034] (5) Remove the device, pour the mud and lanthanum particles into a plastic or glass container, use a magnet to remove the lanthanum particles, and clean the MLAB surface with distilled water (e.g., Figure 4 (As shown).

[0035] (6) When adding lanthanum magnetic particles, use 0.5-1.5 mol / L HCl for desorption, and the liquid-to-solid ratio is 500-1000 ml / g.

[0036] (7) Take 1 ml of the desorption solution, dilute it 10-100 times, and determine the phosphorus concentration using the ICP method after dilution. Then, convert the phosphorus concentration to the amount adsorbed by the magnetic lanthanum particles per unit of paddy soil. The calculation formula is:

[0037] P = P icp *n*V 洗 / V B β

[0038] P represents the bioavailable phosphorus content in paddy fields (mg / Kg);

[0039] P icp The phosphorus concentration (mg / L) was determined by ICP method.

[0040] n is the dilution factor of the desorption solution;

[0041] V 洗 The volume of the elution buffer is in L.

[0042] V B V represents the volume (L) of region B in the extractor. B =π*(2.9 / 2)2*10 / 3 / 1000=0.022(L);

[0043] β: Soil bulk density (Kg / L).

[0044] In a preferred embodiment, the amount of magnetic lanthanum particles added is 1.2 g; the magnetic lanthanum particles are desorbed using a liquid-to-solid ratio of 500 mL / g and 0.5 mol / L HCl; 1 ml of the desorption solution is taken, diluted 20-100 times, and the phosphorus content is determined by ICP method after dilution.

[0045] In another preferred embodiment, the amount of magnetic lanthanum particles added is 0.6g; the magnetic lanthanum particles are desorbed using 1.5mol / L HCl with a liquid-to-solid ratio of 800mL / g; 1ml of the desorption solution is taken, diluted 10-30 times, and the phosphorus content is determined by ICP method after dilution.

[0046] Extensive experiments have shown that a dosage of 0.3g of lanthanum magnetic particles is suitable for determining soil BAP in typical rice-growing regions of my country, including Heilongjiang, Jiangsu, Hunan, Hainan, and Sichuan. However, it should be understood that the dosage of lanthanum magnetic particles and the dilution ratio of the desorption solution can be adjusted according to actual conditions to ensure that the diluted desorption solution meets the ICP measurement range (generally 0.001-0.1 mg / L, depending on the instrument used), thereby improving data accuracy and reliability and thus forming a new or preferred technical solution.

[0047] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0048] Example 1: Experiment on the determination of bioavailable phosphorus in paddy field soil in Fengxian District, Shanghai

[0049] (1) Selecting the measurement area. The selected experimental area has a water depth of 5 cm in the paddy field, and there are no stones in the experimental area after inspection;

[0050] (2) Place the phosphorus extraction device in the paddy field. The dividing line at the boundary between A and B on the phosphorus extraction device is at the same height as the water interface of the paddy field mud. Add 1g MLAB to the device.

[0051] (3) Cover the phosphorus extraction device and remove it from the paddy field after 1 day. Use a magnet to separate the magnetic lanthanum particles from the device, wash it 3 times with distilled water, and desorb it with 0.5L 1mol / L HCl.

[0052] (4) Take 1 ml of the desorption solution, dilute it 100 times, and determine the phosphorus content by ICP method after dilution. In this example, the phosphorus content was measured to be 0.0209 mg / L by ICP-MS (inductively coupled plasma mass spectrometer) of Thermo Scientific Corporation of the United States. The phosphorus content was converted into the amount of phosphorus adsorbed by magnetic lanthanum particles per unit paddy soil according to the calculation formula: P = 0.0209 mg / L × 100 × 0.5 L / (0.022 L × 1.3 Kg / L) = 36.5 mg / Kg.

[0053] In this embodiment, the available phosphorus in the soil of this area was measured to be 36.5 mg / kg. -1 Because the soil was acidic, the Bray-1 method, which is suitable for acidic soils, was used for measurement. The same sample measured 40.2 mg / kg using the Bray-1 method. -1 Additionally, a biological method capable of accurately reflecting soil BaP was used for determination, yielding a result of 32.8 mg / kg. -1 Therefore, this method is closer to the plant's requirements than the Bray-1 method (national standard).

[0054] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. Any changes made by those skilled in the art after reading the specification of the present invention, as long as they are within the scope of the claims of the present invention, will be protected by patent law.

Claims

1. A method for determining bioavailable phosphorus in paddy field soil, characterized in that, Includes the following steps: S1. Place the phosphorus extraction device with perforated surface in the paddy field and add magnetic lanthanum particles; S2. After a certain period of time, remove the device and use a magnet to separate the lanthanum magnetic particles from the mud-water mixture. Then, add the lanthanum magnetic particles to an HCl solution for desorption. S3. The phosphorus concentration was determined by ICP method and converted into the amount of phosphorus adsorbed by magnetic lanthanum particles per unit of paddy soil.

2. The method for determining bioavailable phosphorus in paddy field soil according to claim 1, characterized in that, In step S1, the phosphorus extraction device is divided into zone A and zone B from top to bottom, with a dividing line between the two zones. Zone A is a hollow cylindrical tube with a top cover, and its bottom is connected to zone B. Zone B is a hollow cone with its tip pointing downwards. Small holes are evenly distributed on the surfaces of zones A and B. The device is placed in a paddy field, with zone B vertically embedded in the paddy soil. The dividing line at the boundary between zones A and B is at the same height as the water interface of the paddy field mud.

3. The method for determining bioavailable phosphorus in paddy field soil according to claim 2, characterized in that, The phosphorus extraction device is made of stainless steel or plastic. Section A is a hollow cylindrical tube with a diameter of 2.9 cm and a length of 15 cm. Section B is a hollow cone with a height of 10 cm. The bottom of Section A and the top of Section B are threaded together. There are 20 holes with a diameter of 1 mm evenly distributed on the surfaces of Sections A and B respectively.

4. The method for determining bioavailable phosphorus in paddy field soil according to claim 1, characterized in that, In step S1, the magnetic lanthanum particles are magnetite, composed of lanthanum and a cross-linking polysaccharide, with a particle size of 1.2–2.0 mm, a magnetic saturation strength of 10–20 emu / g, and a phosphorus saturation adsorption capacity of 20–40 mg / g.

5. The method for determining bioavailable phosphorus in paddy field soil according to claim 4, characterized in that, In step S1, the magnetic lanthanum particles are Phosfixer-101 products purchased from Zhanyuan (Shandong) Ecological Environment Technology Co., Ltd.

6. The method for determining bioavailable phosphorus in paddy field soil according to claim 4, characterized in that, The amount of the magnetic lanthanum particles added to the phosphorus extraction device is 0.3–1.2 g.

7. The method for determining bioavailable phosphorus in paddy field soil according to claim 1, characterized in that, In step S2, the specified time period is 1 to 7 days.

8. The method for determining bioavailable phosphorus in paddy field soil according to claim 1, characterized in that, In step S2, desorption is performed using 0.5–1.5 mol / L HCl at a liquid-to-solid ratio of 500–1000 ml / g.

9. The method for determining bioavailable phosphorus in paddy field soil according to claim 1, characterized in that, In step S3, the formula for calculating the P content in paddy fields is: P=P icp *n*V 洗 / V B β P represents the bioavailable phosphorus content in paddy fields (mg / Kg); P icp The phosphorus concentration (mg / L) was determined by ICP method. n is the dilution factor; V 洗 The volume of the elution buffer is in L. V B The volume (L) of region B in the extractor; β: Soil bulk density (Kg / L).

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