Analytical methods for soil mineral components

Abstract

The present invention provides a method for analyzing soil mineral components that can easily and accurately determine the quality and quantity of minerals contained in soil. [Solution] The method for analyzing soil mineral components of the present invention is characterized by comprising a powder X-ray diffraction pattern measurement step of measuring the powder X-ray diffraction pattern of a soil sample, a mineral qualification step of comparing the powder X-ray diffraction pattern of the soil sample measured in the powder X-ray diffraction pattern measurement step with a standard mineral powder X-ray diffraction pattern group including multiple powder X-ray diffraction patterns of reference mineral samples containing standard minerals and internal standards to identify the minerals contained in the soil sample, and a mineral quantification step of quantifying the minerals contained in the soil powder of the soil sample for the minerals identified in the mineral qualification step based on the internal standard contained in the soil sample and the reference mineral sample.

Description

[Technical Field]

[0001] The present invention relates to a method for analyzing soil mineral components. [Background technology]

[0002] In recent years, it has become increasingly recognized that quantifying minerals in soil is important for improving agricultural productivity. In particular, it is becoming increasingly recognized that it is important to understand the amount of potassium, one of the three essential nutrients for plants, along with nitrogen and phosphorus. Potassium is one of the three major nutrients for plants, and is essential for plant growth, including photosynthesis, regulating osmotic pressure within cells, and maintaining enzyme function.

[0003] Selective dissolution analysis is used to quantify minerals in soil. Patent Document 1 also discloses a method for analyzing soil fertility traits by irradiating air-dried soil samples with excitation light and analyzing the fluorescence spectra from the samples, which includes the steps of quantitatively analyzing multiple types of evaluation soils with different fertility traits to determine the quantitative values ​​of the fertility traits of each soil, irradiating the evaluation soils with the excitation light to obtain the fluorescence spectra of each soil, and calculating fluorescence analysis values ​​by analyzing the fluorescence spectra, and creating a calibration curve between the soil fertility traits and the fluorescence analysis values ​​based on the correlation between the quantitative values ​​and the fluorescence analysis values ​​of the soil fertility traits. The calibration curve is then used to analyze the soil fertility traits of the samples. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-240825 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the selective dissolution method is a method for quantifying minerals in soil based on the elemental content of a solution obtained by dissolving soil using known chemical treatments. Although it can accurately quantify the amount of elements contained in soil, it requires the use of dangerous chemical treatment agents, as well as complex procedures and takes a long time to quantify, making it unsuitable for analyzing large amounts of sample.

[0006] Furthermore, the method of analyzing soil fertility characteristics in Patent Document 1 also requires complicated operations and has the problem of being unsatisfactory in terms of measurement accuracy.

[0007] Generally, soil contains many minerals, and it is difficult to accurately qualify and quantify the minerals contained in soil using the above-mentioned methods. Even if it is possible to qualify and quantify the amount of minerals, it requires extremely complicated and time-consuming work, and therefore there is a demand for a method that can easily qualify and quantify the minerals in soil.

[0008] The present invention provides a method for analyzing soil mineral components that can easily and accurately determine the quality and quantity of minerals contained in soil. [Means for solving the problem]

[0009] The method for analyzing soil mineral components of the present invention includes: A powder X-ray diffraction pattern measurement step of measuring a powder X-ray diffraction pattern of a soil sample containing soil powder and an internal standard substance; a mineral qualification step of comparing the powder X-ray diffraction pattern of the soil sample measured in the powder X-ray diffraction pattern measurement step with a standard mineral powder X-ray diffraction pattern group including a plurality of powder X-ray diffraction patterns of the standard minerals, which are minerals contained in general soil, to identify the minerals contained in the soil sample; The method is characterized by including a mineral quantification step in which the mineral identified in the mineral qualification step is used as a reference mineral, the powder X-ray diffraction pattern of a reference mineral sample containing the reference mineral and an internal standard substance is compared with the powder X-ray diffraction pattern of the soil sample, and the minerals contained in the soil powder of the soil sample are quantified based on the peaks of the internal standard substance in the powder X-ray diffraction patterns of the reference mineral sample and the soil sample. [Effects of the Invention]

[0010] The method for analyzing soil mineral components of the present invention uses X-ray diffraction, which can accurately analyze mineral structures such as crystalline structure. Minerals contained in general soil (minerals generally contained in soil) are used as standard minerals, and powder X-ray diffraction patterns are measured in advance for each standard mineral. Powder X-ray diffraction patterns of multiple types of standard minerals are prepared in advance as a group of standard mineral powder X-ray diffraction patterns. By comparing this group of standard mineral powder X-ray diffraction patterns with the powder X-ray diffraction pattern of the soil sample, the minerals contained in the soil sample can be easily identified.

[0011] An internal standard substance is contained in the soil sample, and the mineral identified in the mineral qualification step is used as the reference mineral.A powder X-ray diffraction pattern of a reference mineral sample containing the internal standard substance is prepared in advance, and the mineral content of the soil powder of the soil sample can be easily measured based on the peaks of the internal standard substance that appear in the X-ray diffraction patterns of the soil sample and the reference mineral sample.

[0012] The method for analyzing soil mineral components of the present invention can identify minerals contained in soil and easily and accurately analyze their content.

[0013] In the above-mentioned method for analyzing soil mineral components, if the group of standard mineral powder X-ray diffraction patterns includes only the powder X-ray diffraction patterns of standard minerals that are likely to be contained in the soil powder of the soil sample, then by using only the powder X-ray diffraction patterns of standard minerals that are likely to be contained in the soil powder of the soil sample as the comparison object, the minerals contained in the soil powder can be more accurately qualified and quantified.

[0014] If the above-mentioned method for analyzing soil mineral components further includes a non-exchangeable potassium content estimation step of calculating the non-exchangeable potassium content in the soil powder of the soil sample based on the biotite content and muscovite content obtained in the mineral quantification step, the non-exchangeable potassium content in the soil can be measured easily and accurately, and the amount of potassium fertilizer applied can be controlled, making it easy to ensure that the potassium content in the soil is appropriate.

[0015] In the above-mentioned method for analyzing soil mineral components, if the non-exchangeable potassium content in the soil sample is estimated based on Equation 1 described below in the non-exchangeable potassium content estimation step, the non-exchangeable potassium content in the soil powder of the soil sample can be estimated with higher accuracy.

[0016] If the method for analyzing soil mineral components further includes a cation exchange capacity estimation step of calculating the total amount of allophane, humus, and phytoliths obtained in the mineral quantification step as the amorphous content in the soil sample and estimating the cation exchange capacity of the soil powder of the soil sample based on the amorphous content, the cation exchange capacity in the soil can be accurately estimated, and the fertilizer retention capacity of the soil can be easily confirmed. If the cation exchange capacity in the soil is low and the fertilizer retention capacity is low, measures can be quickly taken to improve the fertilizer retention capacity of the soil, such as by applying a soil improver to the soil.

[0017] If the method for analyzing soil mineral components further includes a carbon dioxide capture capacity estimation step of estimating the carbon dioxide capture capacity of the soil powder of the soil sample based on the Ca-type plagioclase content, Na-type plagioclase content, and pyroxene content obtained in the mineral quantification step, the carbon dioxide capture capacity of the soil can be easily estimated. By determining the carbon dioxide capture capacity of the soil and, if it has decreased, supplying basalt rich in Ca-type plagioclase, Na-type plagioclase, and pyroxene to the soil, for example by scattering it, the carbon dioxide capture capacity of the soil can be stably maintained, and measures to combat global warming can be taken. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is an example of a powder X-ray diffraction pattern of a soil sample. [Figure 2] This is an example of a group of standard mineral powder X-ray diffraction patterns. [Figure 3] This is an example of a group of powder X-ray diffraction patterns of a reference mineral sample. [Figure 4] 1 is a graph showing the relationship between the total content of amorphous matter in soil measured in Example 4 and the cation exchange capacity of the soil. DETAILED DESCRIPTION OF THE INVENTION

[0019] An example of the method for analyzing soil mineral components of the present invention will be described with reference to the drawings. The method for analyzing soil mineral components of the present invention includes a powder X-ray diffraction pattern measurement step, a mineral qualification step, and a mineral quantification step. Each step is described below.

[0020] [Powder X-ray diffraction pattern measurement step] In the method for analyzing soil mineral components, the powder X-ray diffraction pattern measurement step involves powdering the soil to be measured and adding an internal standard substance to the soil powder to prepare a soil sample, and then measuring the powder X-ray diffraction pattern of this soil sample.

[0021] A soil sample is prepared, for example, as follows. The soil to be used for powder X-ray diffraction pattern measurement is preferably air-dried and then sieved to a size of 2 mm or less. Next, an internal standard and ethanol are added to the soil, and the soil is pulverized using a pulverizing ball. The soil is then allowed to dry at room temperature (20-25°C) without spraying or other treatment, and then lightly pulverized to prepare a soil sample containing soil powder and the internal standard. By pulverizing the soil to produce soil powder while avoiding the destruction of the crystalline structure of the minerals contained in the soil, a powder X-ray diffraction pattern can be obtained with high accuracy. For example, by performing the method in accordance with Srodon et al., "Quantitative X-ray diffraction analysis of clay-bearing rocks from random preparations," Clays and Clay Minerals 49.6 (2001): 514-528, a powder X-ray diffraction pattern of the minerals contained in the soil powder can be obtained with high accuracy.

[0022] The internal standard substance added to the soil is not particularly limited as long as it forms a powder X-ray diffraction pattern that does not overlap with the powder X-ray diffraction patterns of minerals contained in the soil, and corundum (α-Al2O3) is preferred. The content of the internal standard substance contained in the soil sample is preferably 10 to 40 parts by mass per 100 parts by mass of soil powder.

[0023] The powder X-ray diffraction pattern of the soil sample prepared as described above is measured to obtain the powder X-ray diffraction pattern of the minerals contained in the soil powder. Figure 1 shows an example of the powder X-ray diffraction pattern of a soil sample.

[0024] The measurement conditions for the powder X-ray diffraction pattern are preferably such that Cu Kα radiation is used, as this allows accurate measurement of the crystal structure of minerals in the soil, and the scan range 2θ is preferably from 5 to 65°.

[0025] The conditions for measuring the powder X-ray diffraction patterns of the soil sample, the standard minerals and the reference mineral samples described below are, for example, as follows. Measuring device: Miniflex600 (Rigaku) Tube: Cu Kα with Ni filter Scan speed: 60 seconds / 10° Step width: 0.01° / step

[0026] [Mineral Qualitative Analysis Step] The mineral qualification step of the method for analyzing soil mineral components involves comparing the powder X-ray diffraction pattern of the minerals contained in the soil powder of the soil sample measured in the manner described above (hereinafter simply referred to as the "powder X-ray diffraction pattern of the soil sample") with a group of standard mineral powder X-ray diffraction patterns containing multiple powder X-ray diffraction patterns of standard minerals to identify the minerals contained in the soil powder of the soil sample.

[0027] It is preferable that the standard minerals selected are minerals that may be contained in general soil (general soil), and minerals that are not normally contained in soil are excluded. Furthermore, even if a mineral is contained in soil in another region, if it is confirmed in advance that it is not contained in the soil to be measured, it is preferable to exclude such a mineral from the standard minerals. For example, if the soil to be measured is soil in Japan, it is preferable to select only minerals that may be contained in Japanese soil as standard minerals. Although minerals are generally identified by the same name, that category may contain multiple types of minerals with different crystal structures. If the powder X-ray diffraction patterns of multiple types of minerals differ, it is preferable to select a different standard mineral for each crystal structure.

[0028] By excluding minerals that have been confirmed in advance not to be contained in the soil being measured from the standard minerals, it is possible to prevent such minerals from being mistakenly identified as being contained, thereby improving the qualitative accuracy of minerals in the soil.

[0029] For example, in the case of Japanese soil, examples of minerals selected as standard minerals include biotite, muscovite, vermiculite, allophane, humus (including humic acid, fulvic acid, humin, etc.), silicon dioxide, feldspar (plagioclase such as Ca-type plagioclase and Na-type plagioclase, potassium feldspar, etc.), pyroxene, clay minerals (smectite, chlorite, talc, kaolinite, halloysite, etc.), carbonate minerals (calcite, dolomite, etc.), phosphate minerals (apatite, etc.), quartz, cristobalite, amphibole, olivine, etc.

[0030] For multiple types of minerals selected as standard minerals, powder X-ray diffraction patterns are measured for each standard mineral, and a powder X-ray diffraction pattern is obtained for each standard mineral. The powder X-ray diffraction patterns of the standard minerals are compiled into a database, and a group of standard mineral powder X-ray diffraction patterns containing multiple powder X-ray diffraction patterns of the standard minerals is prepared in advance.

[0031] Furthermore, for each of the multiple types of minerals selected as standard minerals, a standard mineral sample containing the standard mineral (standard mineral) and an internal standard substance is prepared, and a powder X-ray diffraction pattern is measured for each standard mineral sample to obtain a powder X-ray diffraction pattern for each standard mineral sample. The powder X-ray diffraction patterns of the standard mineral samples are compiled into a database, and a group of powder X-ray diffraction patterns of the standard mineral samples containing multiple powder X-ray diffraction patterns of the standard mineral samples is prepared in advance.

[0032] For example, Figure 2 shows an example of a set of standard mineral powder X-ray diffraction patterns. The set of standard mineral powder X-ray diffraction patterns includes the powder X-ray diffraction patterns of each standard mineral, and the powder X-ray diffraction patterns of each standard mineral and the powder X-ray diffraction patterns of soil samples are digitized so that they can be compared. The powder X-ray diffraction patterns shown in Figure 2 are those of each standard mineral.

[0033] Figure 3 shows an example of a set of powder X-ray diffraction patterns for reference mineral samples. The set of powder X-ray diffraction patterns for reference mineral samples includes the powder X-ray diffraction patterns of each reference mineral sample, and the powder X-ray diffraction patterns of each reference mineral sample are digitized so that they can be compared with the powder X-ray diffraction patterns of soil samples. The powder X-ray diffraction patterns shown in Figure 3 are those of each reference mineral sample.

[0034] When measuring the X-ray diffraction patterns of standard minerals and reference mineral samples based on powder X-ray diffraction, the standard mineral is finely pulverized using a high-speed grinder or an agate mortar. In the case of a reference mineral sample, the pulverized mineral is mixed with an internal standard substance in an arbitrary ratio. Using the standard mineral or reference mineral sample, the X-ray diffraction pattern is measured by powder X-ray diffraction in the same manner as in the measurement of the powder X-ray diffraction pattern of the soil sample described above.

[0035] Furthermore, by adjusting the ratio (R1 / R2) between the mass ratio R1 of the soil powder and internal standard substance content in the soil sample (soil powder content / internal standard substance content) and the mass ratio R2 of the mineral and internal standard substance content in the reference mineral sample (soil powder content / internal standard substance content) to be 0.9 to 1.1, the quantitative accuracy of minerals, as described below, can be improved.

[0036] To compare the powder X-ray diffraction pattern of the soil sample described above with a group of standard mineral powder X-ray diffraction patterns containing multiple types of powder X-ray diffraction patterns of standard minerals, single reflection methods such as full pattern summation (FPS method), which uses the entire powder X-ray diffraction pattern, or the mineral intensity factor (MIF) method (Moore & Reynolds, 1989; Srodon et al., 2001) can be used, but full pattern summation (FPS method), which uses the entire powder X-ray diffraction pattern, is preferred.

[0037] In detail, as the FPS method, for example, the automatic full pattern summation function afps() included in the powdR (Butler and Hillier 2020, “powdR: full pattern summation of X-ray powder diffraction data.” R package version 1.3.0. URL: https: / / CRAN.R-project.org / package=powdR) package version 1.3.0 (R Core Team, 2022) can be used.

[0038] The powder X-ray diffraction pattern of the soil sample is then aligned along the 2θ axis, and the powder X-ray diffraction pattern of the soil sample is processed by the least squares method without affecting the powder X-ray diffraction pattern. The processed powder X-ray diffraction pattern of the soil sample is compared with the powder X-ray diffraction patterns of each standard mineral included in the standard mineral powder X-ray diffraction pattern group of the standard minerals, and standard minerals having the same powder X-ray diffraction pattern as the soil sample are extracted, thereby identifying the minerals contained in the soil sample. In particular, by limiting the standard minerals to minerals that may be contained in the soil powder of the soil sample, the minerals contained in the soil powder of the soil sample can be identified accurately and without error.

[0039] [Mineral quantification step] The method includes a mineral quantification step in which the minerals identified in the mineral qualification step are quantified based on internal standard substances contained in the soil sample and the reference mineral sample, to quantify the minerals contained in the soil powder of the soil sample.

[0040] The standard mineral determined to be identical to the soil sample powder X-ray diffraction pattern in the mineral qualification step, i.e., the mineral identified as being contained in the soil sample, is used as the standard mineral, and the powder X-ray diffraction pattern of a standard mineral sample containing this standard mineral as the standard mineral is extracted from the group of powder X-ray diffraction patterns of the standard mineral sample. The intensity ratio between the peak of the standard mineral (standard mineral) and the peak of the internal standard substance appearing in the powder X-ray diffraction pattern of the standard mineral sample is calculated.

[0041] Since a reference mineral sample contains a reference mineral (standard mineral) and an internal standard substance in a specific ratio, the mineral content in the soil powder can be calculated from the peak intensity ratio of the mineral and the internal standard substance in the powder X-ray diffraction pattern of the soil sample.

[0042] As described above, the method for analyzing soil mineral components makes it possible to easily and accurately identify the minerals contained in the soil powder to be measured and analyze their content.

[0043] [Step to estimate non-exchangeable potassium content] As described above, the method for analyzing soil mineral components can accurately perform qualitative and quantitative analysis of minerals contained in soil. In particular, the present inventors have focused on biotite and muscovite contained in soil, and have found that the non-exchangeable potassium content in soil can be estimated with high accuracy based on the content of these minerals (non-exchangeable potassium content estimation step).

[0044] Potassium in soil is one of the three essential nutrients for plants, along with nitrogen and phosphorus. Potassium plays an essential role in photosynthesis, opening and closing stomata, and maintaining osmotic pressure within cells, making it an essential nutrient for plant growth.

[0045] The form that crops can absorb is water-soluble potassium ions, but when potassium ions in the soil decrease, they are replenished by non-exchangeable potassium contained in minerals. Non-exchangeable potassium is released into the soil from minerals due to weathering, etc., and is considered one indicator of the soil's potassium supply capacity. Accurately understanding and managing the non-exchangeable potassium content in the soil is important for crop cultivation. Furthermore, by optimizing the amount of potassium fertilizer applied to the soil, the amount of potassium fertilizer used can be reduced.

[0046] It has also been reported that non-exchangeable potassium in the soil inhibits crops from absorbing radioactive cesium in the soil, and understanding the content of non-exchangeable potassium in the soil is also effective in reducing contamination of crops with radioactive substances.

[0047] Among the potassium-containing minerals contained in soil, we focused on the contents (mass%) of biotite and muscovite measured in the mineral qualitative and mineral quantitative steps. In light of the fact that biotite has a superior potassium release capacity to muscovite, we found that the non-exchangeable potassium content in soil (mgK2O / 100g) can be accurately estimated by multiplying the biotite content by a correction coefficient X, which represents the superiority of biotite over muscovite. Specifically, the non-exchangeable potassium content in 100g of soil (soil powder) can be accurately estimated based on Equation 1.

[0048] Non-exchangeable potassium content (mgK2O / 100g) = α × [{100 × content of muscovite in soil powder (g) / 100 (g, mass of soil powder)} × {(atomic weight of K × ratio of K contained in muscovite (the standard mineral) to K in the ideal muscovite structure) / molecular weight of muscovite} × {(atomic weight of K × 2 + atomic weight of oxygen) / (atomic weight of K × 2)} × 1000 (mg KO / 100g) + {100 × content of biotite in soil powder (g) / 100 (g, mass of soil powder)} × {(atomic weight of K × ratio of K contained in biotite (the standard mineral) to K in the ideal biotite structure) / molecular weight of biotite} × {(atomic weight of K × 2 + atomic weight of oxygen) / (atomic weight of K × 2)} × 1000 (mgK2O / 100g) × correction factor X] + β (mgK2O / 100g) (Equation 1)

[0049] In Equation 1, "muscovite content (g) in soil powder" means the amount (g) of muscovite contained in 100 g of soil powder. "Biotite content (g) in soil powder" means the amount (g) of biotite contained in 100 g of soil powder. "100 (g, mass of soil powder)" means the mass of soil powder, 100 g.

[0050] In formula 1, "the ratio of K contained in the standard mineral muscovite to K in the ideal muscovite structure" is, for example, the ratio of K in the ideal muscovite structure KAl2(AlSi3)O shown below. 10 The content of K atoms in (OH,F)2 is taken as A (atom%), and the standard mineral muscovite [e.g., [(Si 3.7 ,Al 0.3 )(Al 1.2 ,Ti 0.1 ,Fe 2+ 0.2 ,Fe 3+ 0.1 Mg 0.3 )(K 0.8 ,Na 0.1 )O 10 When the content of K atoms in (OH)2 is B (atom%), this value is calculated as "B / A".

[0051] In formula 1, "the ratio of K contained in the biotite in the above standard mineral to K in the ideal biotite structure" refers to, for example, the ratio of K in the ideal biotite structure (K2, Mg, Fe) shown below. 2+ ,Fe 3+ )6(Si,Al)8O 20 The content of K atoms in (O,OH)4 is taken as C (atom%), and the standard mineral biotite [e.g., [(Si 2.91 ,Al 1.09 )(Al 0.69 ,Ti 0.10 ,Fe 2+ 1.24 ,Mg 0.47 ,Mn 0.01 ,Li 0.04 )(K 0.83 ,Na 0.04 ,Ca 0.01 )O 10 When the content of K atoms in (OH)2 is D (atom%), this is the value calculated as "D / C."

[0052] In Equation 1, the correction coefficient X by which the biotite content is multiplied is 7 to 11, and preferably 8 to 10. Multiplying the biotite content by the correction coefficient X makes it possible to properly evaluate the potassium release capacity and estimate the non-exchangeable potassium content in the soil with high accuracy.

[0053] Muscovite is generally KAl2(AlSi3)O 10 It is a mineral with the chemical composition (OH,F)2, for example, [(Si 3.7 ,Al 0.3 )(Al 1.2 ,Ti 0.1 ,Fe 2+ 0.2 ,Fe 3+ 0.1 Mg 0.3 )(K 0.8 ,Na 0.1 )O 10 (OH)2]. Muscovite includes those in which a small amount of potassium has been replaced by sodium, and those containing small amounts of Ti, Fe, or Mg. The amount of potassium substituted for sodium is so small that it can be ignored compared to the potassium content in muscovite, and does not affect the non-exchangeable potassium content.

[0054] Biotite is generally composed of (K2, Mg, Fe 2+ ,Fe 3+ )6(Si,Al)8O 20 It is a mineral with the chemical composition (O,OH)4, for example, [(Si 2.91 ,Al 1.09 )(Al 0.69 ,Ti 0.10 ,Fe 2+ 1.24 ,Mg 0.47 ,Mn 0.01 ,Li 0.04 )(K 0.83 ,Na 0.04 ,Ca 0.01 )O 10 (OH)2]. In biotite, Fe and Mg are often replaced by Al. In addition, Fe and Mg are often replaced by Mn, Fe 3+ ,Ti 4+These include those in which K has been replaced by Na, those in which OH has been replaced by F, and those containing small amounts of Li and Ca. The amount of K substituted for Na is so small that it can be ignored compared to the K content in biotite, and does not affect the non-exchangeable potassium content.

[0055] In Equation 1, the correction coefficient X multiplied by biotite is 7 to 11. The correction coefficient X is adjusted appropriately depending on the particle size of the biotite contained in the soil powder, and the correction coefficient X should be adjusted to be smaller as the average particle size of the biotite increases. For example, when the average particle size of the biotite is about 20 to 212 μm, the correction coefficient X should be set to 9.

[0056] The average particle size of biotite can be measured using several sieves with different mesh sizes as specified in JIS Z8801-1:2019. Specifically, after vibrating for 5 minutes using the sieves specified in JIS Z8801-1:2019, the 50% average diameter of the undersize mass distribution measured by the sieving method is calculated, and this is the average particle size. Specifically, using the sieves specified in JIS Z8801-1:2019, the sieves are stacked on a tray in order from smallest to largest mesh size. 100 g of biotite is added to the top sieve, the sieves are capped, and the sieves are attached to a low-tap sieve shaker (e.g., tapping: 156 times / min, rolling: 290 times / min). After vibrating for 5 minutes, the mass of biotite remaining on each sieve and on the tray is measured, and the mass percentage (%) of biotite on each sieve is calculated. The mass percentages of the biotite on the sieves with the smallest openings are added up from the tray, and the particle size at which the total is 50 mass% is taken as the average particle size.

[0057] In Equation 1, the correction coefficient α is 0.02 to 0.2. The correction coefficient α is appropriately adjusted based on the average particle size of the biotite, and the correction coefficient α should be adjusted so that the larger the average particle size of the biotite, the smaller the correction coefficient α. For example, when the average particle size of the biotite is 20 to 212 μm, the correction coefficient α should be set to 0.1.

[0058] In Equation 1, the correction coefficient β is 25 to 31 mgK2O / 100 g. The correction coefficient β is appropriately adjusted based on the average particle size of the biotite, and the larger the average particle size of the biotite, the smaller the correction coefficient β should be. For example, when the average particle size of the biotite is 20 to 212 μm, the correction coefficient β should be set to 30 mgK2O / 100 g.

[0059] For example, the chemical composition of muscovite contained in the soil powder is [(Si 3.7 ,Al 0.3 )(Al 1.2 ,Ti 0.1 ,Fe 2+ 0.2 ,Fe 3+ 0.1 Mg 0.3 )(K 0.8 ,Na 0.1 )O 10 (OH)2], and the chemical composition of biotite is [(Si 2.91 ,Al 1.09 )(Al 0.69 ,Ti 0.10 ,Fe 2+ 1.24 ,Mg 0.47 ,Mn 0.01 ,Li 0.04 )(K 0.83 ,Na 0.04 ,Ca 0.01 )O 10 (OH)2], the non-exchangeable potassium content in the soil powder is estimated based on Equation 1 as follows:

[0060] Non-exchangeable potassium content (mgK2O / 100g) = 0.1 × [{100 × content of muscovite in soil powder (g) / 100} × {(39.10 × 0.80) / 400.8} × {(39.10 × 2 + 16.00) / (39.10 × 2)} × 1000 (mgK2O / 100g) + {100 × content of biotite in soil powder (g) / 100} × {(39.10 × 0.83) / 444.1} × {(39.10 × 2 + 16.00) / (39.10 × 2)} × 1000 (mgK2O / 100g) × correction factor X] + 30 (mgK2O / 100g) However, the correction coefficients α and β vary as the correction coefficient X varies.

[0061] [Cation exchange capacity estimation step] It is preferable that the method for analyzing soil mineral components further includes a cation exchange capacity estimation step of calculating the total amount of the allophane content, the humus content, and the phytolith content obtained in the mineral quantification step as the amorphous content (mass%) in the soil powder, and estimating the cation exchange capacity in the soil powder of the soil sample based on the amorphous content.

[0062] When water-soluble chemical fertilizers such as ammonium sulfate, ammonium chloride, ammonium phosphate, and potassium are applied to rice paddies or fields, positively charged fertilizer components (cations) such as ammonium and potassium ions dissolve from the water-soluble chemical fertilizer into the water. These dissolved fertilizer components are adsorbed by the negative charges on the surface of soil colloids due to electrostatic forces. Fertilizer components adsorbed to soil colloids are less likely to be washed out by irrigation or rainfall and can remain in the soil for a certain period of time. Cations adsorbed to soil colloids and easily replaced by other cations (except hydrogen ions) are most easily absorbed by crops. Therefore, soils containing large amounts of these cations are more fertile. The amount of cations that soil can hold is known as its cation exchange capacity (CEC), which correlates with the soil's ability to adsorb and retain fertilizer components (fertilizer retention capacity).

[0063] According to the above-described method for analyzing soil mineral components, the allophane content, humus content, and phytolith (silicon dioxide) content in soil can be easily and accurately estimated.

[0064] The total amount of allophane, humus (including humic acid, fulvic acid, and humin), and phytoliths (silicon dioxide) is defined as the amorphous content, and it has been found that this amorphous content correlates with the cation exchange capacity (CEC) of the soil. Based on the amorphous content, the cation exchange capacity of the soil can be easily estimated, and if the cation exchange capacity is insufficient, efforts can be made to enrich the soil by applying soil conditioners or compost.

[0065] The cation exchange capacity (cmol / kg) of soils at multiple locations (soils with low, medium, and high cation exchange capacities) is measured in advance using known methods, and the amorphous content (mass%) in these soils is measured using powder X-ray diffraction using the method described above.A linear function that serves as a calibration curve is then calculated, with the cation exchange capacity (cmol / kg) in the soil on the vertical axis and the amorphous content (mass%) on the horizontal axis.

[0066] The amorphous content of the soil to be measured is then measured using powder X-ray diffraction as described above, and the cation exchange capacity of the soil can be estimated using this measured amorphous content based on the calibration curve.

[0067] If the cation exchange capacity in the soil is below the required standard, it is assumed that the cation exchange capacity is insufficient, and soil improvement can be easily achieved by applying soil conditioners or the like to the soil.

[0068] [Carbon dioxide capture capacity estimation step] It is preferable that the method for analyzing soil mineral components further includes a carbon dioxide trapping capacity estimation step of estimating the carbon dioxide trapping capacity of the soil sample based on the Ca-type plagioclase content, the Na-type plagioclase content, and the pyroxene content obtained in the mineral quantification step.

[0069] Ca-type plagioclase, Na-type plagioclase (Ca-type plagioclase and Na-type plagioclase are sometimes collectively referred to as "plagioclase"), and pyroxene have a high carbon dioxide trapping capacity and are found in large quantities in basalt. Ca-type plagioclase, Na-type plagioclase, and pyroxene can trap carbon dioxide as carbonate by reacting with carbon dioxide, and the trapped carbon dioxide is removed from the air by remaining in the soil or flowing into the ocean. For this reason, scattering basalt containing a large amount of Ca-type plagioclase, Na-type plagioclase, and pyroxene on soil is being considered as one of the measures to combat global warming.

[0070] According to the above-described method for analyzing soil mineral components, the contents of Ca-type plagioclase, Na-type plagioclase, and pyroxene in soil can be easily and accurately estimated.

[0071] Ca-type plagioclase, Na-type plagioclase, and pyroxene have high carbon dioxide capture capacities, and the carbon dioxide capture capacity of soil can be easily estimated based on the content of Ca-type plagioclase, Na-type plagioclase, and pyroxene. It is easy to confirm whether basalt containing a large amount of Ca-type plagioclase, Na-type plagioclase, and pyroxene that has been spread on soil is decreasing over time by capturing carbon dioxide, and if the carbon dioxide capture capacity of the soil is decreasing, measures such as spreading additional basalt on the soil can be taken quickly.

[0072] The contents of Ca-type plagioclase, Na-type plagioclase, and pyroxene in the soil to be measured are measured as described above, and the carbon dioxide capture capacity of the soil can be estimated based on Equation 2 using the measured contents of Ca-type plagioclase, Na-type plagioclase, and pyroxene. Note that this is based on the reaction equations in which 1 mole of Ca-type plagioclase, Na-type plagioclase, and pyroxene reacts with 2 moles, 1 mole, and 4 moles of carbon dioxide, respectively (Equations 1 to 3). Note that 278.22, 262.22, and 216.55 represent the molecular weights of Ca-type plagioclase, Na-type plagioclase, and pyroxene, respectively, and 44.01 represents the molecular weight of carbon dioxide.

[0073] Carbon dioxide capture capacity (g / kg) = {100 × content of Ca-type plagioclase in soil powder (g) / 100 (g, mass of soil powder)} × 10 (g / kg) × 2 × 44.01 (g / mol) / 278.22 (g / mol) + {100 × content of Na-type plagioclase in soil powder (g) / 100 (g, mass of soil powder)} × 10 (g / kg) × 1 × 44.01 (g / mol) / 262.22 (g / mol) + {100 × content of pyroxene in soil powder (g) / 100 (g, mass of soil powder)} × 10 (g / kg) × 4 × 44.01 (g / mol) / 216.55 (g / mol) (Equation 2)

[0074] In Equation 2, the content (g) of Ca-type plagioclase in the soil powder means the amount (g) of Ca-type plagioclase contained in 100 g of soil powder. In Equation 2, the content (g) of Na-type plagioclase in the soil powder means the amount (g) of Na-type plagioclase contained in 100 g of soil powder. In Equation 2, the content (mass%) of pyroxene in the soil powder means the amount (g) of pyroxene contained in 100 g of soil powder.

[0075] 2CO2+3H2O+CaAl2Si2O8 →Al2Si2O5(OH)4+Ca 2+ +2HCO3 - Reaction scheme 1 (Ca-type plagioclase)

[0076] 2CO2+11H2O+2NaAl2Si3O8 →Al2Si2O5(OH)4+2Na + +2HCO3 - +4H4SiO4 Reaction scheme 2 (Na-type plagioclase)

[0077] 4CO2+2H2O+CaMgSi2O6 →2SiO2+Ca 2+ +Mg 2+ +4HCO3 - Reaction 3 (pyroxene)

[0078] If the soil's carbon capture capacity falls below the required standard, measures such as spreading basalt on the soil can be taken immediately.

[0079] According to the above-mentioned method for analyzing soil mineral components, the content of minerals contained in the soil to be measured can be easily estimated from the powder X-ray diffraction pattern of the soil sample and the powder X-ray diffraction patterns of the standard mineral and the standard mineral sample, thereby enabling accurate understanding of the soil condition and soil management. [Example]

[0080] The present invention will be described in more detail below using examples, but the present invention is not limited thereto. Specific numerical values ​​of blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or more than") of the corresponding blending ratios (content ratios), physical property values, parameters, etc. described in the "Description of Embodiments."

[0081] (A) Powder X-ray diffraction method [Powder X-ray diffraction pattern measurement step] (Measurement of powder X-ray diffraction patterns of soil samples) Soil samples were collected from the surface layer of cultivated land (0-15 cm below the ground surface) in Japan. The soil samples were air-dried and then sieved to a 2 mm or smaller sieve. Next, 0.25 g of corundum (α-Al2O3) as an internal standard and 7 mL of ethanol were added to 1 g of soil sample. The mixture was then ground in a grinder using corundum grinding balls for 10 minutes and allowed to dry at room temperature (25°C) without spraying. The dried mixture was then lightly ground to obtain a uniform powdered soil sample containing the soil powder and the internal standard.

[0082] The obtained soil samples were loaded onto the sample plate of an XRD instrument (Rigaku Corporation, product name "Miniflex 600") using the front-loading method, avoiding preferred orientation. Powder X-ray diffraction patterns were obtained using a Ni-filtered Cu Kα beam and a one-dimensional silicon strip detector (Rigaku Corporation, product name "Rigaku D / teX Ultra 2"), covering the range of 5–65° (2θ) at a scan rate of 60 s / 10° and a step of 0.01°. Measurement results for pure phases confirmed that contamination from the grinding balls did not affect the overall XRPD pattern. Powder X-ray diffraction patterns were normalized to a maximum intensity of 10,000 counts / sec without background correction.

[0083] (Measurement of powder X-ray diffraction patterns of standard minerals) The standard minerals prepared were biotite, muscovite, vermiculite, quartz, potassium feldspar, Ca-type plagioclase, Na-type plagioclase, allophane, humus, phytolith (silicon dioxide), smectite, chlorite, talc, kaolinite, halloysite, quartz, cristobalite, amphibole, olivine, and pyroxene. Each of the standard minerals was finely ground using a high-speed grinder or an agate mortar. Muscovite was measured using [(Si 3.7 ,Al 0.3 )(Al 1.2 ,Ti 0.1 ,Fe 2+ 0.2 ,Fe 3+ 0.1 Mg 0.3 )(K 0.8 ,Na 0.1 )O 10 (OH)2], and biotite is [(Si 2.91 ,Al 1.09 )(Al 0.69 ,Ti 0.10 ,Fe 2+ 1.24 ,Mg 0.47 ,Mn 0.01 ,Li 0.04 )(K 0.83 ,Na 0.04 ,Ca 0.01 )O 10 (OH)2].

[0084] Powder X-ray diffraction patterns of the standard minerals were obtained in the same manner as for the soil samples, except that 1 g of the standard mineral was used instead of 1 g of soil sample and 0.25 g of internal standard. The powder X-ray diffraction patterns of the standard minerals were normalized to a maximum intensity of 10,000 counts / sec without background correction.

[0085] The powder X-ray diffraction patterns of the standard mineral samples were obtained in the same manner as for the soil samples, except that 1 g of the standard mineral was used instead of 1 g of soil sample. The powder X-ray diffraction patterns of the standard mineral samples were normalized to a maximum intensity of 10,000 counts / sec without background correction.

[0086] The standard mineral powder X-ray diffraction pattern group (standard mineral sample powder X-ray diffraction pattern group) included the powder X-ray diffraction patterns of the following standard minerals (standard mineral samples): biotite, muscovite, vermiculite, quartz, potassium feldspar, Ca-type plagioclase, Na-type plagioclase, allophane, humus, phytoliths (silicon dioxide), smectite, chlorite, talc, kaolinite, halloysite, quartz, cristobalite, amphibole, olivine, and pyroxene.

[0087] [Mineral Qualitative Analysis Step] Powder X-ray diffraction analysis was performed using the Full Pattern Summarization (FPS) method using the automatic full pattern summation function afps() in the powdR package (Butler and Hillier 2020, “powdR: full pattern summation of X-ray powder diffraction data.” R package version 1.3.0. URL: https: / / CRAN.R-project.org / package=powdR) (R Core Team, 2022).

[0088] Instead of the libraries installed in the powdR package, we used the standard mineral powder X-ray diffraction patterns and the standard mineral sample powder X-ray diffraction patterns measured above. After aligning the powder X-ray diffraction pattern of the soil sample along the 2θ axis, we processed the powder X-ray diffraction pattern of the soil sample using the least-squares method while avoiding any influence on the powder X-ray diffraction pattern. We then compared the powder X-ray diffraction pattern of this processed soil sample with the powder X-ray diffraction patterns of each standard mineral included in the standard mineral powder X-ray diffraction pattern set using the FPS method to identify the minerals contained in the soil powder.

[0089] [Mineral quantification step] The powder X-ray diffraction patterns of the reference mineral samples, which contained standard minerals determined to be identical to the powder X-ray diffraction patterns of the soil samples in the mineral qualification step, were extracted from the group of powder X-ray diffraction patterns of the reference mineral samples.

[0090] The intensity ratio of the peak of the standard mineral to that of the internal standard was calculated in the powder X-ray diffraction pattern of the reference mineral sample. Based on this intensity ratio, the mineral content in the soil powder was quantified from the intensity ratio of the mineral to the internal standard in the powder X-ray diffraction pattern of the soil sample.

[0091] (B) Selective dissolution method [Quantitative determination of mica] Ten grams of soil powder was added to a 50 mL centrifuge tube containing 30 mL of 6% by mass sodium hypochlorite adjusted to pH 8 with hydrochloric acid. After manual shaking several times over a period of 6 hours, the suspension was centrifuged and the supernatant was decanted. This procedure was repeated four times.

[0092] The residue was then washed twice with 30 mL of 1 M sodium chloride, three times with deionized water, and freeze-dried. After freeze-drying, the pulverized sample was subjected to selective lysis (Jackson et al., 1986).

[0093] The mica content in the soil was calculated by applying the amount of potassium (K) released by reductive dissolution of mica using sodium hydrogen sulfate to the structural formula of mica (Jackson et al., "Oxides, hydroxides, and aluminosilicates." Methods of Soil Analysis: Part 1 Physical and Mineralological Methods 5 (1986): 101-150.) (Equations A and B).

[0094] [Quantitative determination of quartz] The quartz content in the soil was calculated by dissolving silicate minerals other than quartz using hexafluorosilicic acid after the above procedure and measuring the weight of the quartz after treatment (Jackson et al., "Hexafluorosilicic acid reagent modification for quartz isolation," Soil Science Society of America Journal, Vol. 40, No. 6 (1976): 958-960).

[0095] [Quantitative analysis of potassium feldspar and plagioclase] The contents of potassium feldspar and plagioclase in the soil were calculated by applying the amounts of elements released by total soil digestion using hydrofluoric acid to their respective structural formulas (Prat 1965, "Digestion with hydrofluoric and perchloric acids for total potassium and sodium." Methods of Soil Analysis: Part 2 Chemical and Microbiological Properties 9 (1965): 1019-1021.) (Formulas C and D).

[0096]

number

[0097] In formula A, 39.10 is the atomic weight of K, and 444.1 is the mass of biotite [(Si 2.91 , Al 1.09 )(Al 0.69 ,Ti 0.10 , Fe 2+ 1.24 , Mg 0.47 , Mn 0.01 , Li 0.04 )(K 0.83 , Na 0.04 , Ca 0.01 )O 10 (OH)2].

[0098] In formula B, 39.10 is the atomic weight of K, and 400.8 is the mass of muscovite ([(Si 3.7 , Al 0.3 )(Al 1.2 , Ti 0.1 , Fe 2+ 0.2 , Fe 3+ 0.1 Mg 0.3 )(K 0.8 , Na 0.1 )O 10 (OH)2]).

[0099] In formula C, 39.10 represents the atomic weight of K, and 278.33 represents the molecular weight of potassium feldspar [K(AlSi3O8)].

[0100] In formula D, 22.99 and 40.08 represent the atomic weights of Na and Ca, respectively, and 262.22 and 278.21 represent the molecular weights of Na-type plagioclase [Na(AlSi3O8)] and Ca-type plagioclase [Ca(Al2Si2O8)], respectively.

[0101] Example 1 Soil samples were collected from 79 agricultural soil sites in Japan. The mica, quartz, potassium feldspar, and plagioclase contents were measured for each of the 79 soil samples according to the powder X-ray diffraction method described above, and the calculated average (arithmetic mean) values ​​for each mineral were calculated. The calculated mineral contents (arithmetic mean values) are shown in the "Powder X-ray Diffraction" column in Table 1. The mica content was the total amount of muscovite and biotite.

[0102] In Example 1 and the examples described below, the 79 agricultural soil locations were one or two locations in Hokkaido, Aomori Prefecture, Iwate Prefecture, Miyagi Prefecture, Akita Prefecture, Yamagata Prefecture, Fukushima Prefecture, Ibaraki Prefecture, Tochigi Prefecture, Gunma Prefecture, Saitama Prefecture, Niigata Prefecture, Fukui Prefecture, Nagano Prefecture, Gifu Prefecture, Aichi Prefecture, Shiga Prefecture, Osaka Prefecture, Hyogo Prefecture, Tottori Prefecture, Okayama City, Hiroshima Prefecture, Kochi Prefecture, Fukuoka Prefecture, Miyazaki Prefecture, Kagoshima Prefecture, and Okinawa Prefecture.

[0103] In addition, using the same soils as those measured by the powder X-ray diffraction method, the mica, quartz, potassium feldspar, and plagioclase contents were measured for each of the 79 soils according to the procedure of the selective dissolution method described above, and the calculated average (arithmetic mean) values ​​for each mineral were calculated. The calculated mineral contents (arithmetic mean values) are shown in the "Selective Dissolution Method" column in Table 1.

[0104] The conventional selective dissolution method can accurately measure the mineral content in soil, but it has the drawback of being time-consuming and labor-intensive. The mineral content measured by powder X-ray diffraction is close to that measured by selective dissolution, demonstrating that the mineral content in soil can be measured easily and accurately.

[0105] [Table 1]

[0106] Example 2 Using a mineral sample containing 10.0 mass% mica, 60.0 mass% quartz, 10.0 mass% potassium feldspar, and 20.0 mass% plagioclase, the contents of mica, quartz, potassium feldspar, and plagioclase were measured according to the procedures of the selective dissolution method and powder X-ray diffraction method described above.

[0107] The contents of mica, quartz, potassium feldspar, and plagioclase in the mineral samples, as determined by powder X-ray diffraction and selective dissolution, are shown in Table 2.

[0108] [Table 2]

[0109] Example 3 [Estimation of non-exchangeable potassium content by powder X-ray diffraction (non-exchangeable potassium content estimation step)] Soil samples were collected from 79 agricultural soil sites in Japan. The biotite and muscovite contents of each soil were measured using the powder X-ray diffraction method described above. The arithmetic mean biotite and muscovite contents in the soils from the 79 sites were 0.3% and 2.1% by mass, respectively. Using these arithmetic mean biotite and muscovite contents, the non-exchangeable potassium content of the soil was calculated using Equation 1, which was 73.5 mg KO / 100 g. Since the average particle size of biotite in the soil ranged from 20 to 212 μm, the correction factors in Equation 1 were: X = 9, α = 0.1, β = 30, the ratio of K in the standard mineral muscovite to K in the ideal muscovite structure was 0.80, and the ratio of K in the standard mineral biotite to K in the ideal muscovite structure was 0.83.

[0110] [Measurement of non-exchangeable potassium content by known methods] (Measurement of plant available potassium content) On the other hand, the non-exchangeable potassium content of the same soil as that measured by the powder X-ray diffraction method was measured as follows.

[0111] 2.5 g of soil was collected in an Erlenmeyer flask, and 25 mL of 1 M nitric acid was added to the soil. Next, a mini funnel was placed on top of the Erlenmeyer flask to prevent evaporation of the solution. The Erlenmeyer flask was placed on a hot plate and gently heated to a boil. Exactly 15 minutes after the first visual boiling was confirmed, the Erlenmeyer flask was removed from the hot plate.

[0112] After removing the Erlenmeyer flask from the hot plate and allowing it to cool for exactly 5 minutes, the suspension was poured onto filter paper (placed on top of a funnel placed on top of the volumetric flask), and the filtrate was collected in the volumetric flask.

[0113] The Erlenmeyer flask was washed with 15 mL of 0.1 M nitric acid, and the washings were also passed through the filter paper and poured into the measuring flask. This procedure was repeated four times, after which the filter paper was rinsed out and the solution was adjusted to 100 mL with 0.1 M nitric acid to prepare the test solution (the nitric acid concentration at this stage was 0.33 M). The test solution in the measuring flask was diluted appropriately (generally about 25 times).

[0114] The potassium concentration (hot nitric acid extractable K concentration) of the obtained test solution was measured using an atomic absorption spectrometer. The plant available potassium content (solution K concentration) was calculated using the following formula. Hot nitric acid extracted K concentration (mg / kg-soil) =Solution K concentration (mg / L: before dilution)×0.1(L) / 2.5g-soil

[0115] (Measurement of exchangeable potassium content) The non-exchangeable potassium content of the same soil as that measured by the powder X-ray diffraction method was measured in the following manner.

[0116] Five grams of soil was weighed and placed in a centrifuge tube (50 mL). 25 mL of a 1 mol / L aqueous solution of ammonium acetate was added to the tube using a pipette or dispenser, and the tube was shaken for 30 minutes using a reciprocating shaker (120 reciprocations per minute). The tube was then centrifuged at 2000 rpm for 5 minutes.

[0117] The supernatant was transferred to a 100 mL volumetric flask using No. 6 filter paper. 25 mL of a 1 mol / L aqueous solution of ammonium acetate was added to the residue, and the precipitate was completely disrupted using a stirrer or ultrasonic generator.

[0118] The above procedure was repeated twice, except that 5 g of soil was added to the centrifuge tube (50 mL volume).

[0119] Next, 25 mL of a 1 mol / L aqueous solution of ammonium acetate was added to the volumetric flask, and after stirring, the mixture was centrifuged at 2000 rpm without shaking, and the supernatant was transferred to a 100 mL volumetric flask. A 1 mol / L aqueous solution of ammonium acetate was added up to the marked line to prepare the stock solution for the exchangeable base extraction. The stock solution for the extraction was diluted up to 10 times as necessary.

[0120] 10 mL of the extract was placed in a 100 mL measuring flask and demineralized water was added to make the total volume 100 mL.

[0121] A standard stock solution containing 1000 ppm of K was prepared and left at room temperature for 1 hour. The required amount of standard stock solution was placed in a cleaned vial. 1 mL of the standard stock solution was placed in a measuring flask (100 mL capacity) and the volume was adjusted to the desired volume with demineralized water to prepare solution A (10 ppm solution). Solution A was used to prepare a K calibration curve (0, 0.2, 0.5, 1.0, 2.0 ppm).

[0122] The extract was analyzed by atomic absorption spectrometry, and the exchangeable potassium content was measured using a K calibration curve.

[0123] The non-exchangeable potassium content in each soil was calculated by subtracting the exchangeable potassium content from the plant-available potassium content. The arithmetic mean of non-exchangeable potassium content in the soil at 79 sites was 72.6 mg KO / 100 g. This value is similar to the arithmetic mean of non-exchangeable potassium content in the soil at 79 sites, 73.5 mg KO / 100 g, calculated using the powder X-ray diffraction method described above. This demonstrates that powder X-ray diffraction can be used to easily and accurately estimate the non-exchangeable potassium content in soil.

[0124] Example 4 [Estimation of cation exchange capacity by powder X-ray diffraction (cation exchange capacity estimation step)] The soil samples were collected from 79 agricultural soil sites in Japan. The contents of allophane, humus, and phytoliths (silicon dioxide) in each sample were measured according to the powder X-ray diffraction method described above.

[0125] [Measurement of cation exchange capacity by known methods] (Washing out excess ammonium ions) The soil samples to be measured were collected from 79 agricultural soil sites in Japan (the same soil samples as those measured using powder X-ray diffraction). Five grams of each soil was weighed out and placed in a centrifuge tube (50 mL). 25 mL of a 1 mol / L aqueous solution of ammonium acetate was added to the tube using a pipette or dispenser, and the tube was shaken for 30 minutes using a reciprocating shaker (120 strokes per minute). The tube was then centrifuged at 2000 rpm for 5 minutes.

[0126] The supernatant was transferred to a 100 mL volumetric flask using No. 6 filter paper. 25 mL of a 1 mol / L aqueous solution of ammonium acetate was added to the residue, and the precipitate was completely disrupted using a stirrer or ultrasonic generator.

[0127] The above procedure was repeated twice, except that 5 g of soil was added to the centrifuge tube (50 mL volume).

[0128] Next, 25 mL of a 1 mol / L aqueous solution of ammonium acetate was added to the volumetric flask, stirred, and then centrifuged at 2000 rpm without shaking. 10 mL of demineralized water was added to the residue, which was then thoroughly stirred in a thermomixer. The mixture was then centrifuged at 2000 rpm for 10 minutes, and the supernatant was removed.

[0129] 10 mL of 80% by weight ethyl alcohol was added to the centrifuge tube and thoroughly stirred using a thermomixer. The mixture was centrifuged at 2000 rpm for 10 minutes and the supernatant was removed. This process of adding ethyl alcohol to the centrifuge tube, centrifuging, and removing the supernatant was repeated two more times.

[0130] (Ammonium ion extraction) 30 mL of 10% by weight NaCl aqueous solution was added to the centrifuge tube, and the precipitate was completely crushed and stirred using a thermomixer. After shaking the centrifuge tube for 1 hour, it was centrifuged at 2000 rpm for 10 minutes. The supernatant was filtered using No. 6 filter paper and transferred to a 100 mL volumetric flask. This process of adding saline to the centrifuge tube, centrifuging, and transferring the supernatant to a 100 mL volumetric flask was repeated two more times. Next, the solution was diluted to 100 mL with 10% by weight NaCl aqueous solution to prepare a sample solution.

[0131] (Ammonium ion (NH4 + -N) quantification) [Preparation of indophenol A solution] 30 g of 2-hydroxybiphenyl sodium salt tetrahydrate and 0.12 g of sodium nitroprusside dihydrate were dissolved in water to make 1 L, to prepare indophenol A solution.

[0132] [Preparation of indophenol B solution] Indophenol B solution was prepared by dissolving 40 g of trisodium citrate (sodium citrate) dihydrate, 4 g of sodium hydroxide, and 8 mL of sodium hypochlorite solution (antiformin) in water to make 1 L.

[0133] [Preparation of standard solutions] 0.955 g of NH4Cl that had been oven-dried (110°C for 12 hours) was dissolved in water to make 250 mL (1000 mg NH4-N / L). This solution was diluted 100 times to make a 10.0 mg NH4-N / L solution, which was then further diluted to make standard solutions (standard solutions of 0, 0.2, 0.5, 1.0, 1.5, 2.0, and 3.0 mg NH4-N / L).

[0134] (Cation exchange capacity determination) 2.5 mL of sample solution and 2.5 mL of solution A were added to a test tube. The amount of NH4-N was adjusted to be 0.5 to 6 μg in 2.5 mL of sample solution.

[0135] After covering the top of the test tube with parafilm and shaking vigorously, 5 mL of solution B was added to the test tube and shaken thoroughly. Sixty minutes after shaking was completed, colorimetric determination was performed at 625 nm using atomic absorption spectrometry, and the cation exchange capacity was calculated.

[0136] Figure 4 shows a graph of soil samples collected from 79 locations. The horizontal axis represents the total content (mass%) of amorphous matter (allophane, humus, and phytoliths (silicon dioxide)) in the soil, as measured by powder X-ray diffraction for each of the 79 locations, and the vertical axis represents the cation exchange capacity (cmol / kg) of each soil, as measured by a known method. Circles indicate soil samples measured by powder X-ray diffraction. The straight lines represent regression lines obtained from the total content of amorphous matter measured by powder X-ray diffraction and the cation exchange capacity measured by a known method. As shown in Figure 4, the cation exchange capacity of each soil measured by powder X-ray diffraction correlates well with the cation exchange capacity measured by a known method, demonstrating that the cation exchange capacity of a soil can be easily estimated based on the total content (mass%) of allophane, humus, and phytoliths in the soil measured by powder X-ray diffraction. In Figure 4, *** indicates a 0.1% significance level.

[0137] Example 5 [Estimation of soil carbon dioxide capture capacity using powder X-ray diffraction (carbon dioxide capture capacity estimation step)] Soil samples were collected from 79 agricultural soil sites in Japan. The contents of Ca-type plagioclase, Na-type plagioclase, and pyroxene in each soil were measured using the powder X-ray diffraction method described above. The arithmetic mean values ​​of the Ca-type plagioclase, Na-type plagioclase, and pyroxene contents in the soil from the 79 sites were 16.8 mass%, 6.7 mass%, and 1.2 mass%, respectively. Using the arithmetic mean values ​​of the Ca-type plagioclase, Na-type plagioclase, and pyroxene contents based on Equation 2 above, the carbon dioxide capture capacity of the soil was estimated to be 74.2 g / kg.

[0138] The carbon dioxide capture capacity of soil can be easily estimated based on the content of Ca-type plagioclase, Na-type plagioclase, and pyroxene in soil quantified by powder X-ray diffraction.

Claims

1. a powder X-ray diffraction pattern measurement step of measuring a powder X-ray diffraction pattern of a soil sample containing soil powder and an internal standard; a mineral qualification step of comparing the powder X-ray diffraction pattern of the soil sample measured in the powder X-ray diffraction pattern measurement step with a standard mineral powder X-ray diffraction pattern group including a plurality of powder X-ray diffraction patterns of the standard minerals, which are minerals contained in general soil, to identify the minerals contained in the soil sample; A method for analyzing soil mineral components, characterized by including a mineral quantification step in which the mineral identified in the mineral qualification step is used as a reference mineral, the powder X-ray diffraction pattern of a reference mineral sample containing the reference mineral and an internal standard substance is compared with the powder X-ray diffraction pattern of the soil sample, and the minerals contained in the soil powder of the soil sample are quantified based on the peaks of the internal standard substance in the powder X-ray diffraction patterns of the reference mineral sample and the soil sample.

2. The method for analyzing soil mineral components described in claim 1, characterized in that the group of standard mineral powder X-ray diffraction patterns includes only powder X-ray diffraction patterns of standard minerals, which are minerals that may be contained in the soil powder of the soil sample.

3. 3. The method for analyzing soil mineral components according to claim 1, further comprising a non-exchangeable potassium content estimation step of estimating the non-exchangeable potassium content in the soil powder of the soil sample based on the biotite content and muscovite content obtained in the mineral quantification step.

4. 4. The method for analyzing soil mineral components according to claim 3, wherein in the non-exchangeable potassium content estimation step, the non-exchangeable potassium content in the soil sample is estimated based on the muscovite content (% by mass) in the soil powder, the biotite content (% by mass) in the soil powder, and a correction coefficient X, where X is 7 to 11.

5. 4. The method for analyzing soil mineral components according to claim 3, wherein in the step of estimating the non-exchangeable potassium content, the non-exchangeable potassium content in the soil sample is estimated based on Equation 1. In Equation 1, the correction coefficient X is 7 to 11, the correction coefficient α is 0.02 to 0.2, and the correction coefficient β is 25 to 31 mgK. 2 0 / 100g. Non-exchangeable potassium content (mgK 2 0 / 100g) = α × [{100 × content of muscovite in soil powder (g) / 100 (g, mass of soil powder)} × {(atomic weight of K × ratio of K contained in muscovite, the standard mineral, to K in the ideal muscovite structure) / molecular weight of muscovite} × {(atomic weight of K × 2 + atomic weight of oxygen) / (atomic weight of K × 2)} × 1000 (mg K 2 0 / 100g) + {100 × content of biotite in soil powder (g) / 100 (g, mass of soil powder)} × {(atomic weight of K × ratio of K contained in biotite, the standard mineral, to K in the ideal biotite structure) / molecular weight of biotite} × {(atomic weight of K × 2 + atomic weight of oxygen) / (atomic weight of K × 2)} × 1000 (mg K 2 0 / 100g) × correction factor X] + β (mgK 2 O / 100g) (Formula 1)

6. 3. The method for analyzing soil mineral components according to claim 1, further comprising a cation exchange capacity estimation step of calculating the total amount of allophane content, humus content, and phytolith content obtained in the mineral quantification step as the amorphous content in the soil powder, and estimating the cation exchange capacity in the soil powder of the soil sample based on the amorphous content.

7. 3. The method for analyzing soil mineral components according to claim 1, further comprising a carbon dioxide trapping capacity estimation step of estimating the carbon dioxide trapping capacity of the soil powder of the soil sample based on the Ca-type plagioclase content, the Na-type plagioclase content, and the pyroxene content obtained in the mineral quantification step.

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