A method for extracting exchangeable nutrients from soil interface

Abstract

A soil interface exchangeable nutrient extraction method comprises the following steps: step S01, collecting original soil samples; step S02, saturating the soil samples; step S03, heating the soil samples; step S04, extracting soil sample solutions; step S05, filtering the soil sample solutions: filtering the collected solutions and retaining them; step S06, testing the soil sample solutions on a machine: testing the solutions on a machine according to the measured indicators. The present invention collects original soil samples, supersaturates the soil samples with distilled water, and collects soil solutions at a suitable temperature. The present invention has a high degree of reduction to the actual state of the substance.

Description

Technical Field

[0001] The invention relates to the technical field of soil detection, and in particular to a method for extracting exchangeable nutrients from a soil interface. Background Art

[0002] For the solid phase of soil, the current extraction of interfacial exchangeable nutrients usually uses extractants based on the type of nutrients, and the sources of extractants are mostly simulated rhizosphere environments (slightly acidic) and based on soil properties. For example, KCl solution is used to measure the nitrate nitrogen content in the soil.

[0003] However, this approach has several drawbacks:

[0004] (1) Extraction tests are generally conducted at room temperature in the laboratory, usually 20-25°C, which is not the optimal temperature for soil ion leaching;

[0005] (2) In most extraction methods, the water-soil ratio exceeds the normal ratio, far exceeding saturation. At this time, the amount of exchangeable nutrients extracted is already within the range that can be absorbed by plant roots under unnatural conditions;

[0006] (3) The soil is sieved before the extraction test. Fresh soil or air-dried soil is often used in the extraction method, and impurities are removed. However, this process has destroyed the original state of the soil and lost its original structure. The test results cannot represent the real environment of the soil.

[0007] Although chemical reagents try their best to avoid mutual influence with the target elements in the extraction method, from a theoretical point of view, the above defects are unavoidable, resulting in a large deviation between the experimental method and actual conditions. Summary of the invention

[0008] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for extracting exchangeable nutrients from the soil interface, by collecting original soil samples, using distilled water to supersaturate the soil samples, and using a suitable temperature to collect soil solutions. The present invention has a high degree of reduction of the actual state of the substance.

[0009] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0010] A method for extracting exchangeable nutrients from soil interface comprises the following steps:

[0011] Step S01, collecting undisturbed soil samples;

[0012] Step S02, saturating the soil samples: soaking all the original soil samples in distilled water until the soil is saturated;

[0013] Step S03, heating the soil sample: wipe the saturated soil sample dry, seal it, put it in an oven, and heat it at 60-70°C for 1-1.5 hours until the soil sample reaches 55°C±5°C;

[0014] Step S04, extracting soil sample solution: compacting the soil sample after the heating treatment in step S03, and collecting the solution flowing out of the soil sample;

[0015] Step S05, filtering the soil sample solution: filtering the collected solution and retaining it;

[0016] Step S06, testing the soil sample solution on a machine: testing the solution on a machine according to the measured indicators.

[0017] Furthermore, in step S01, an in-situ soil sampling calibrator is used to collect soil samples in an in-situ state, and the sampling is repeated three times.

[0018] Furthermore, in step S02, the sandy soil is soaked for at least 24 hours, the loamy soil is soaked for at least 36 hours, and the clay soil is soaked for at least 48 hours.

[0019] Furthermore, in the step S03, the sealing is to put the soil sample into a ziplock bag and heat it in an oven at 70° C. for 1 hour.

[0020] Furthermore, in the step S04, the soil sample after the heating treatment is taken out and quickly squeezed by a compacting device to make the solution in the soil sample flow out, and the solution is collected.

[0021] Furthermore, the retention in step S05 is refrigerated if the test is to be carried out on the machine within 7 days, and is directly frozen and stored below -18°C after filtration if the test is to be carried out on the machine beyond 7 days.

[0022] The soil interface exchangeable nutrient extraction method of the present invention is more scientific than the chemical separation method and has a higher degree of reduction to the actual state of the substance. The advantages and beneficial effects of the present invention are as follows:

[0023] (1) Distilled water is used as the extractant instead of chemical reagents. The chemical adsorption caused by chemical reagents is irreversible, while the physical adsorption under distilled water is reversible. Chemical reagents have a transition release when they are exchanged at the solid phase interface, while distilled water does not have a transition release when extracting exchangeable substances at the solid phase interface, and there is no interference from any chemical components.

[0024] (2) In-situ samples are used for soil samples, without destroying the original structure of the soil (including texture, bulk density, porosity, specific surface area, etc.), so that the content of the exchangeable substances extracted is within the range of the content that can be obtained when the soil is in its natural state. The real state of the solid phase interface is highly restored, which is better than the bulk soil samples used in chemical extraction. The bulk soil samples destroy the original structure of the soil, change the actual bulk density, porosity, specific surface area, etc., and make the final extraction results inconsistent with the actual situation.

[0025] Considering the double layer structure of soil clay (including IHP, OHP, diffusion layer, and bulk liquid), chemical extraction releases a large number of inner layer ions that cannot be released in the original state of the soil. The deeper the layer, the more ions cannot be released in the actual state, and the content of these ions (in IHP, OHP, and diffusion layer) is huge. For example, in the diffusion layer of soil clay, the proportion of exchangeable nutrient ions available in sandy soil, loamy soil, and clay soil under distilled water extraction is approximately 70%, 50%, and 30%, respectively, because the clay double layer of clay soil is thicker, and the clay double layer of sandy soil is relatively thinner.

[0026] (3) The amount of physical extractant used is to reach the saturation state of the soil sample, and the placement time for sand, loam, and clay is 24, 36, and 48 hours, respectively. In comparison, the use of chemical extractants is to make the soil sample supersaturated, and the exchangeable substances extracted are higher than the amount obtained in the actual state of the soil, and the maximum amount of the solution in the actual state of the soil is saturated.

[0027] (4) Physical separation is carried out at 55℃±5℃. The conclusion is drawn from experiments that 55℃ is the optimal energy state for the migration of exchangeable substances in the soil.

[0028] (5) Heating setting: oven at 70°C for 1 hour. This result is the conclusion of the experiment and is a key step in energy treatment before separation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a data diagram of correlation analysis of nitrate nitrogen content under distilled water extraction and KCl extraction in a specific embodiment of the present invention;

[0030] Figure 2 It is a correlation analysis diagram of ammonium nitrogen content under two extraction methods in the comparative example of the present invention;

[0031] Figure 3 It is a correlation analysis diagram of nitrate nitrogen content under two extraction methods in the comparative example of the present invention. DETAILED DESCRIPTION

[0032] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0033] There are several kinds of nutrients in the soil, among which effective nutrients can be divided into two types: water-soluble and exchangeable. The extraction of exchangeable nutrients is one of the cases of solid interface exchangeable substance extraction. There are several kinds of exchangeable nutrients in the soil, for example, exchangeable ammonium nitrogen, exchangeable nitrate nitrogen, exchangeable acid, exchangeable potassium ion, etc. The present invention provides a soil interface exchangeable nutrient extraction method, comprising the following steps:

[0034] Step S01, collecting original soil samples: using an in-situ soil sampling calibrator to collect soil samples in the in-situ state, the number of soil samples collected, the location of the soil samples, and the depth of the soil samples need to be determined based on the needs of the user, and the sampling is generally repeated three times.

[0035] The present invention adopts undisturbed soil samples because the undisturbed soil samples retain the actual state of the solid phase of soil in the field, do not destroy the original structure, and can improve the accuracy of measurement.

[0036] Step S02, saturating the soil samples: soak all the original soil samples in distilled water until the soil is saturated. The soaking time depends on the soil texture, sandy soil is soaked for at least 24 hours, loamy soil is soaked for at least 36 hours, and clay soil is soaked for at least 48 hours.

[0037] The reason for saturating the soil sample in step S02 of the present invention is as follows:

[0038] (1) Use distilled water instead of tap water or other water: This is to control variables. The water quality in different regions of the country is different, and the minerals and other components contained in different water quality are different. In order to avoid interference with nutrients (the content of some nutrients is inherently low), distilled water is used uniformly.

[0039] In addition, the soil microscopic state and the diffusion layer in the double electrical layer structure of soil clay particles are also taken into account, in which the ion adsorption occurring includes physical adsorption and chemical adsorption.

[0040] Among them, chemical adsorption: forms a coordination bond or specific bond centered on Pauli force. The energy is about 10 times that of physical adsorption, about 400kJ / mol, 100kcal / J.

[0041] Physical adsorption: mainly based on Coulomb force, which is the interaction force between two charges. The closer the distance, the greater the Coulomb force. In addition, it is also related to the electric dipole moment of water, which is a physical quantity that measures the asymmetry of charge distribution. For water molecules, the size of its electric dipole moment is 6.20×10 -30C·m, this value reflects the degree of separation between the positive and negative charge centers of water molecules. Water molecules have a large electric dipole moment, which enables them to exhibit certain polarization behaviors in an electric field. From an energy perspective, physical adsorption is ≤40kJ / mol, or 10 kcal / J. The state of water corresponding to this energy is the heat of vaporization, which is the energy when water reaches the boiling point of 100°C.

[0042] Physical adsorption is reversible, while chemical adsorption is irreversible.

[0043] The diffusion process of adsorbed ions to the adsorbent (soil) is divided into membrane diffusion and particle diffusion. Membrane diffusion is the diffusion of ions from the solution to the outer surface of the adsorbent through the water film, and particle diffusion is the diffusion of ions from the adsorbent surface to the inside of the particle (inner surface). 0.1mol / L is the critical concentration, and compared with traditional extraction methods, such as the M3 method, it can be found that all its extractant concentrations are too high than 0.1mol / L. A large number of internal surface ions will be exchanged, and many of these ions are ineffective for crops in the actual soil environment. The physical analysis using distilled water is different, and the replaced part is the part that can be used by plants.

[0044] (2) Application of saturated soil samples:

[0045] The medium and state of water in soil are very important. According to the classification of potential energy indicators, the state of soil water can be divided into hygroscopic water (matrix potential is -31 bar, absorbing liquid water molecules), film water (matrix potential is -15 bar, cannot absorb liquid water molecules, which is determined by the interface, and the interface is determined by the structure and components), free water (matrix potential -15 bar~0 bar, capillary adsorbed water, pure liquid water, 0 bar is the state where water fills all pores, that is, saturation), and other water.

[0046] The other water includes two media, -0.1FC~-0.3bar and -1bar~-10bar. The former is the water obtained by capillary force (there is no water in large pores, only small pores), and the influence of the latter depends on the soil quality. The sandier the soil texture, the weaker the double layer effect, and the change of matrix potential has little impact on the actual effect, -1bar~-10bar may not make much difference, but the stickier the soil, the stronger the double layer effect of clay particles, the greater the impact of changes in matrix potential, and the change from -1bar to -10bar is large.

[0047] Therefore, when the matrix potential is between FC and 0 bar, all nutrients cannot be measured due to interference from water, but when saturated, it is the state where the maximum nutrient content can be leached, that is, the maximum nutrient content that can be leached from the soil under actual field conditions.

[0048] (3) Reasons for considering soil texture (sand, loam, clay):

[0049] Soil is a multi-component mixture composed of different particle sizes. Different particle sizes have different adsorption characteristics and have mutual influence on ion adsorption. The total adsorption of the mixed sample is not a simple sum of the adsorption of each particle size component. Different particle sizes have interactive effects on the adsorption of the same ion. For example, in a certain soil sample, the clay particles are closely arranged in the in-situ state, and the ability to adsorb ions is 5. When the in-situ structure of this soil sample is destroyed, the close relationship between the clay particles is destroyed, and the total surface area of ​​clay particles in contact with ions increases, then the ability to adsorb ions at this time will become 20.

[0050] The clay content in different soil textures is different. Generally, clay soil has the highest content and sandy soil has the lowest content. Therefore, it is very necessary to consider different soil types separately.

[0051] Step S03, heating the soil sample: wipe the saturated soil sample dry, seal it, put it in an oven, and heat it at 60-70°C for 1-1.5 hours until the soil sample reaches 55°C±5°C;

[0052] Specifically, the sealing is to put the soil sample into a ziplock bag, put it into an oven and heat it at 70°C for 1 hour until the soil sample reaches 55°C±5°C.

[0053] The reasons for heating the soil sample in step S03 of the present invention are as follows:

[0054] (1) Heating time is 1 hour

[0055] Through experiments, it was found that the heating time should not exceed 2 hours. Too long a time will lead to excessive thermal power and destroy the clay structure of the soil. Therefore, three gradients were set, namely 0.5h, 1h, and 1.5h.

[0056] The test results show that 0.5h needs to be achieved at an initial temperature of 130℃, 1h corresponds to an initial temperature of 70℃, and 1.5h corresponds to an initial temperature of 60℃.

[0057] Analysis of test results: 130℃ is too high a temperature, exceeding the boiling point of water and will damage the soil structure, so it cannot be used; 60℃ and 70℃ are both within the acceptable temperature range for soil clay, but 1.5h is longer than 1h, so it is better to complete this step in a short time.

[0058] Test conclusion: The heating treatment was performed for 1 hour with the initial temperature being 70°C.

[0059] (2) Soil sample heated to 55°C:

[0060] Increasing temperature means increasing energy state. The energy of ion adsorption by crops is 4~7kcal / mol (average value, including most cations and a small number of anions). According to the linear relationship, the temperature range corresponding to this energy is between 40℃~70℃, 100℃ corresponds to 10kcal / J, and 0℃ corresponds to 0kcal / J.

[0061] For ion diffusion, the diffusion coefficient increases by 27-52% for every 10°C increase in temperature, which means that the diffusion energy decreases and the diffusion constraint decreases, but it does not decrease all at once, but slowly. That is, as the temperature rises, the diffusion layer gradually becomes thinner from the outside to the inside, causing the ion migration to gradually increase. In other words, the ions closer to the inner layer are more difficult to release because they are bound by Coulomb force, and the closer to the inside, the less water environment there is. The connection between ions is mainly chemical bonds, which is about 10 times the Coulomb force.

[0062] Therefore, the energy state closest to the "activation energy 4~7kcal / mol" was found through experiments, and this result was obtained by comparing with the traditional extraction method experiment. Under a variety of nutrient ions (ammonium nitrogen, nitrate nitrogen, potassium ions, etc.), three soil types (sand, loam, clay), and 3 temperature gradients (40, 55, and 70°C), they were compared with the extraction method. The comparison and analysis results of the loam soil extraction results at various temperatures are shown in Table 1. The results showed that only at a temperature of 55°C, the measurement results were closest to the extraction method, indicating that at this temperature, the solid-phase interface material exchange is maximized. The correlation analysis data of nitrate nitrogen content under distilled water extraction and KCl extraction are shown in the figure below. Figure 1 shown.

[0063] Table 1 is a comparison table of the extraction results of loam soil at various temperatures.

[0064]

[0065] Step S04, extracting the soil sample solution: compacting the soil sample after the heating treatment in step S03, and collecting the solution flowing out of the soil sample. Specifically, after taking out the heated soil sample, quickly squeeze the soil sample with a compacting device to make the solution in the soil sample flow out, and collect the solution.

[0066] Step S05, filtering the soil sample solution: the collected solution is filtered and retained. Specifically, if the machine test can be carried out within 7 days, it can be refrigerated. If it exceeds 7 days, it can be directly frozen and stored at below -18°C after filtering.

[0067] Step S06, testing the soil sample solution on a machine: testing the solution on a machine according to the measured indicators (the specific method of testing the solution on a machine depends on the needs of the user).

[0068] Example:

[0069] (1) Implementation background:

[0070] ①Soil texture: sandy clay loam;

[0071] ② Crops planted: corn;

[0072] ③ Determination of nutrient indicators: exchangeable ammonium nitrogen and exchangeable nitrate nitrogen;

[0073] ④Number of soil sampling points: 20;

[0074] ⑤Soil sampling depth: 0~10cm;

[0075] ⑥ Measurement method of soil ammonium nitrogen and nitrate nitrogen: extraction-UV spectrophotometry, the extractant is distilled water.

[0076] (2) Implementation steps:

[0077] ① Take original soil samples at 20 sampling points and repeat 3 times;

[0078] ② Bring the sample back to the laboratory and place it in distilled water for saturation treatment for 36 hours;

[0079] ③ After wiping off the water from the saturated soil sample, put it in a ziplock bag, adjust the oven to 70℃, preheat it until the actual temperature in the oven is 70℃, put the sample in, and bake for 1 hour until the soil sample reaches 55℃;

[0080] ④Take out the sample, squeeze it and obtain the soil sample solution;

[0081] ⑤ Filter the solutions separately to obtain clear solutions, put them into bottles, mark them, and store them in the freezer;

[0082] ⑥ Test on the computer, using an ultraviolet spectrophotometer to measure and obtain the measurement results of exchangeable ammonium nitrogen and exchangeable nitrate nitrogen.

[0083] (3) Data results:

[0084] After the data were processed by the mean, the results are shown in Table 2.

[0085] Table 2 is a table showing the results of the physical separation method for the nutrient content of sandy clay loam in this embodiment.

[0086]

[0087] Comparative Example:

[0088] (1) Implementation background:

[0089] ①Soil texture: sandy clay loam;

[0090] ② Crops planted: corn;

[0091] ③ Determination of nutrient indicators: soil ammonium nitrogen content, soil nitrate nitrogen content, corn root ammonium nitrogen content, corn root nitrate nitrogen content;

[0092] ④Number of soil sampling points: 20;

[0093] ⑤Soil sampling depth: 0~10cm;

[0094] ⑥ Regarding the measurement method of soil ammonium nitrogen and nitrate nitrogen: the conventional method is extraction-ultraviolet spectrophotometry, the extractant can be 0.01 mol / L CaCl2 solution or CaSO4 solution, 1 mol / L KCl solution, 2 mol / L NaCl solution, etc., and the quantitative method of the target nutrients in the leachate can be ultraviolet spectrophotometry, phenol disulfonic acid spectrophotometry (nitrate nitrogen), indigo blue colorimetry (ammonium nitrogen), etc. This comparative example uses 1 mol / L KCl solution extraction-ultraviolet spectrophotometry.

[0095] ⑦ Regarding the measurement of ammonium nitrogen and nitrate nitrogen content in the root system: use an interval analyzer for detection.

[0096] (2) Implementation steps:

[0097] ① Collect loose soil samples and root samples at 20 sampling points, and repeat 3 times;

[0098] ② Preparation of soil extract

[0099] At each sampling point, 5 g of fresh soil sample (passed through a 2 mm sieve) was weighed, placed in a plastic bottle, and extracted with 50 mL of KCl extractant;

[0100] ③ Quantification of ammonium nitrogen and nitrate nitrogen in soil leachate

[0101] The soil leachate was taken separately and measured with an ultraviolet spectrophotometer to obtain the final result;

[0102] ④ The ammonium nitrogen and nitrate nitrogen in the root system are measured according to the requirements of the interval analyzer and the results are obtained.

[0103] (3) Data analysis:

[0104] The data results and the comparative analysis with the examples are shown in Table 3. At the same time, the correlation between the physical extraction method proposed by the present invention and the results of the traditional method (R 2 ) are all higher than 0.99. Figure 2 , 3 .

[0105] Table 3 is a comparative analysis table of the nutrient content of sandy clay loam under two kinds of extracts in the comparative example.

[0106]

[0107] At the same time, the ammonium nitrogen and nitrate nitrogen content of crop roots were measured during the same period. Because the ammonium nitrogen absorbed by crop roots is generally 2%~8% of the ammonium nitrogen in the soil, and the nitrate nitrogen absorbed by crop roots is generally 80%~90% of the soil, it can be analyzed. By analyzing the measurement results, Table 4 is obtained. It can be seen that the difference between the two methods in the absorption of ammonium nitrogen by crops is small, but it can be seen that the average value obtained by the physical separation method is 3.23%, which is higher than the chemical separation method. And from the nitrate nitrogen index, it can be clearly seen that the proportion of crop absorption and soil content under the physical separation method is higher than 80%, while the average proportion of crop absorption and soil content under the chemical separation method is 70%.

[0108] Table 4: Comparative analysis of soil nutrient results and crop absorption using two separation methods in the comparative example.

[0109]

[0110] This proves that the results of the physical separation method under distilled water extraction can better represent the actual absorption of crops and are superior to the results of the chemical separation method.

[0111] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. Alterations, modifications, substitutions and variations of the above embodiments by a person skilled in the art are all within the scope of the present invention.

Claims

1. A method for extracting exchangeable nutrients from soil interface, characterized in that: The steps include: Step S01, collecting undisturbed soil samples; Step S02, saturating the soil samples: soaking all the original soil samples in distilled water until the soil is saturated; Step S03, heating the soil sample: wipe the saturated soil sample dry, seal it, put it in an oven, and heat it at 60-70°C for 1-1.5 hours until the soil sample reaches 55°C; Step S04, extracting soil sample solution: compacting the soil sample after the heating treatment in step S03, and collecting the solution flowing out of the soil sample; Step S05, filtering the soil sample solution: filtering the collected solution and retaining it; Step S06, testing the soil sample solution on a machine: testing the solution on a machine according to the measured indicators.

2. A soil interface exchangeable nutrient extraction method according to claim 1, characterized in that: In step S01, an in-situ soil sampling calibrator is used to collect soil samples in an in-situ state, and the sampling is repeated three times.

3. The method for extracting exchangeable nutrients from soil interface according to claim 1, characterized in that: In step S02, the sandy soil is soaked for at least 24 hours, the loamy soil is soaked for at least 36 hours, and the clay soil is soaked for at least 48 hours.

4. The method for extracting exchangeable nutrients from soil interface according to claim 1, characterized in that: In the step S03, the sealing is to put the soil sample into a ziplock bag and heat it in an oven at 70° C. for 1 hour.

5. The method for extracting exchangeable nutrients from soil interface according to claim 1, characterized in that: In the step S04, the soil sample after the heating treatment is taken out and quickly squeezed by a compacting device to make the solution in the soil sample flow out, and the solution is collected.

6. The method for extracting exchangeable nutrients from soil interface according to claim 1, characterized in that: The retention in step S05 is refrigerated if the test is to be performed on the machine within 7 days, and is directly frozen and stored below -18°C after filtration if the test is to be performed on the machine beyond 7 days.

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