A method of measuring thermodynamic parameters of soil

Abstract

The application discloses a kind of methods for measuring soil thermodynamic parameters, comprising: S1, taking the soil sample to be measured in experimental basin body;S2, the probe of volume water content sensor and water potential sensor is buried in the soil sample, and is connected with data collector;S3, the experimental basin body is placed in outdoor natural conditions for a period of time, after it is naturally leached, artificial rainfall and dynamic determination of soil water content and soil water potential data according to set frequency;S4, the data obtained by collection is fitted according to the relationship model of soil water potential and soil volume water content;S5, the soil thermodynamic parameter is calculated.The model parameter is less in the application, and the tedious data collection and arrangement work can be avoided, to provide technical support for real-time monitoring water technology.

Description

Technical Field

[0001] This invention relates to a method for measuring soil thermodynamic parameters, belonging to the field of soil thermodynamic parameter measurement technology. Background Technology

[0002] Soil is a natural and complex porous medium with a large specific surface area. When water comes into contact with the surface of soil particles, adsorption occurs, with the soil particles acting as adsorbents and the water as adsorbate, forming a layer on the surface. Essentially, the adsorption of water between soil and water is a phenomenon involving the interaction of bonding or adhesive forces between two heterogeneous interfaces. Similarly, like the adsorption of most heavy metals, the adsorption process between soil and water involves two processes: physical adsorption and chemical adsorption. However, under natural conditions, soil and water generally cannot meet the energy requirements of chemical adsorption (80–400 kJ / mol), while physical adsorption requires only 20 kJ / mol or less, relying primarily on van der Waals forces between the molecules to achieve this easily. Therefore, the process of water entering and being absorbed by soil in nature is a physical adsorption process, but this adsorption process is characterized by relatively weak bonding forces. Adsorption heat It is characterized by its small size and easy desorption. For example, when the soil is saturated with moisture due to rainfall, the gravitational water in the soil pores will seep out, and the water that is not firmly adsorbed will desorb.

[0003] All movements in nature are accompanied by energy changes, and the movement of soil water is no exception. Soil hydraulic properties are key factors regulating groundwater and solute transport. One of the most important hydraulic properties is the relationship between soil moisture content and soil water potential. The forms and pathways of water movement in the soil have a significant impact on soil properties. Recent studies by Hirmas et al. and Vereecken et al. argue for the urgent need to include soil structures that can significantly affect infiltration in ways that are unpredictable due to soil texture. Therefore, research on the hydraulic properties of soils with different textures is urgently needed. However, while the free energy of some simple molecules can be calculated using quantum chemistry or classical models, traditional chemical calculations are impractical for complex macromolecules like soil. Armindo and Wendroth's study on soil physical structure evaluation based on hydraulic energy functions showed that energy exponents and functions can be used to assess the energy related to soil physical structure. However, there is little research on the thermodynamic properties of soil, and existing studies have not yet been able to directly calculate soil thermodynamic parameters. Therefore, further research in this area is necessary.

[0004] Furthermore, soil moisture measurement methods can be categorized into three main types based on their research methods and scope (scale): sampling-location measurement methods, remote sensing monitoring methods, and model simulation methods. Among sampling-location measurement methods, the drying method, which is simple and highly accurate, is the most commonly used. Other methods include tensiometer methods, dielectric methods, neutron ray methods, and gamma-ray methods. Remote sensing monitoring primarily uses radiometers, followed by continuous wave (CW) spectroscopy, cameras, and THz time-domain spectroscopy (TDS). The relationship between soil water potential and soil moisture content is called the soil moisture characteristic curve, which reflects the water-holding and water-releasing characteristics of different soils. Currently, highly accurate models include the Van Genuchten model, the Fredlund and Xing model, the Brooks-Corey model, and the Gardner model. However, these models have numerous parameters, some of which are difficult to obtain, hindering real-time monitoring. Additionally, these models are ineffective in obtaining thermodynamic parameters of complex mixed soil components, such as the soil molar concentration conversion coefficient and the standard free energy of the soil. Summary of the Invention

[0005] Based on the above, the present invention provides a method for measuring soil thermodynamic parameters, which can quickly and accurately obtain soil thermodynamic parameters simply by measuring soil moisture content and soil water potential.

[0006] The technical solution of this invention is: a method for measuring soil thermodynamic parameters, comprising:

[0007] S1, Take the soil sample to be tested into the experimental basin;

[0008] S2, The probes of the volumetric water content sensor and the water potential sensor are buried in the soil sample and connected to the data acquisition device;

[0009] S3. Place the experimental basin outdoors under natural conditions for a period of time. After it is naturally compacted, measure the soil moisture content and soil water potential data dynamically at a set frequency after artificial rainfall.

[0010] S4. The collected data is fitted according to the soil water potential and soil volumetric water content relationship model, and the results are calculated. And the value of k, wherein the relationship model between soil water potential and soil volumetric water content is as follows:

[0011]

[0012] In the formula, constant θ and k are model parameters, where k is the soil property coefficient; θ is the soil volumetric water content. Soil water potential;

[0013] S5, calculate the soil thermodynamic parameters according to the following formula;

[0014]

[0015]

[0016] In the formula, M is the soil molar concentration conversion coefficient, G is the standard free energy of the soil, R is the gas constant, and T is the ambient temperature.

[0017] Preferably, the bottom of the experimental basin is provided with a seepage hole, and the upper part of the experimental basin is provided with a radial runoff pipe, and the soil sample is parallel to the wall of the runoff pipe.

[0018] Preferably, the derivation process of the model relating soil water potential and soil volumetric water content is as follows:

[0019] Current model for the relationship between soil water potential and water content:

[0020] (1)

[0021] In this formula The soil moisture content is the mass of the soil, while in this invention, the soil moisture content is the volumetric water content. Formula (1) is modified, and the relationship model between soil water potential and soil volumetric water content is obtained from the Gibbs free energy formula. The derivation of the modified model is as follows:

[0022] Because volumetric water content θ = soil water volume V w Total soil volume V0, Total soil volume V0 = Soil water volume V w + Soil volume V s Then it can be launched:

[0023] (2-1)

[0024] According to Moore's Law, the molar concentration C of the solute is... The volume of the solution V = the amount of solute n, therefore: Substitute We can obtain:

[0025] (2-2)

[0026] And because n / V s Let M be the soil molar concentration conversion coefficient. The above formula is then transformed into:

[0027] (2-3)

[0028] Depend on ,Will Substitution We can obtain:

[0029] (2-4)

[0030] Equation (2-4) can be transformed into:

[0031] (2-5)

[0032] In the formula, Ψs is the soil water potential to be measured, kPa; θ is the soil moisture content to be measured, m. 3 / m 3 G is the standard free energy of the soil; M is the soil molar concentration conversion coefficient.

[0033] make , Then equation (2-5) can be written as:

[0034] (2-6)

[0035] constant θ and k are model parameters, where k is the soil property coefficient. When θ is zero, Ψ0 represents the inherent water potential, which reflects the soil's ability to absorb water; that is... , Based on the parameters Ψ0 and k, the soil molar concentration conversion coefficient M and the standard free energy of the soil can be calculated.

[0036] The beneficial effects of this invention are:

[0037] 1. Based on previous research, this invention uses the Gibbs free energy formula to derive the relationship curve between the volumetric water content (θ) and water potential (Ψ) of two types of soil after rainfall. In practice, it is only necessary to simulate the soil state through pot experiments and measure the volumetric water content and water potential online after artificial rainfall. The thermodynamic parameters of complex mixed soil components, namely the soil molar concentration conversion coefficient and the standard free energy of the soil, can be obtained quickly.

[0038] 2. Traditional methods for measuring soil mass moisture content require drying and other means, and cannot be performed online. However, this invention uses soil volumetric moisture content, which can be measured online using only a volumetric moisture sensor, making the operation simpler and faster.

[0039] 3. The present invention uses fewer model parameters, which on the one hand facilitates the prediction of water conditions, and on the other hand avoids tedious data collection and processing work, providing technical support for real-time water monitoring technology. Attached Figure Description

[0040] Figure 1 A schematic diagram of the experimental basin from one perspective;

[0041] Figure 2A schematic diagram of the experimental basin from another perspective;

[0042] Figure 3 Curves showing the changes in soil moisture content and soil water potential over time for the two soil types;

[0043] Explanation of reference numerals in the attached figures:

[0044] 1. Experimental basin, 2. Flow pipe, 3. Drainage hole. Detailed Implementation

[0045] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0046] 1. Soil sample collection

[0047] Soil samples were taken from the topsoil layer (0-20 cm) near Zhanjie Town, Qingzhen City, Guizhou Province (26°33'N, 106°24'E; 26°34'N, 106°25'E), and were classified as dryland soil within cultivated land. The physicochemical properties of the two soil samples are shown in Table 1. Based on the International Soil Texture Classification (ISC) according to particle size distribution, soil sample 1 was identified as silty loam (Ld), and soil sample 2 as silty clay loam (Lc).

[0048]

[0049] Note: The values ​​are expressed as the average of 3 repetitions ± SD.

[0050] 2. Design of the experimental setup

[0051] A hole was drilled at a height of 17 cm in the experimental basin. After connecting the drainage pipe, the outflow volume was the surface runoff. The outflow volume was determined by uniformly drilling seepage holes at the bottom. The experimental basin had a height of 20.5 cm and a bottom diameter of 18.5 cm.

[0052] 3. Experimental Design

[0053] A pot experiment was conducted using the two types of soil mentioned above as the research subjects. After soil collection, the soil was brought back to the laboratory, ground, impurities removed, and mixed thoroughly before being placed into experimental pots to simulate different soil habitats. Due to the different textures of the two soils, the soil volume in each pot was kept consistent, filling them to a height of 17 cm (parallel to the runoff pipe wall). Soil moisture content (θ, m³) was measured. 3 / m 3Soil water potential (Ψ, kPa) was measured using a ZL6 data logger (Meter, Decagon, USA) connected to a TEROS 12 volumetric water content sensor and a TEROS 21 water potential sensor (Meter, USA). Both sensor probes were buried 10 cm deep in the soil. After 45 days of natural outdoor conditions to allow for natural compaction, two soil samples with identical moisture content and weight were selected for a rainfall experiment. The rainfall intensity was 60 mm / h, and the rainfall duration was 1 hour to maximize the soil moisture content in the experimental container. Data were dynamically collected at a frequency of 10 min / time to determine θ and Ψ.

[0054] 4. Data Processing

[0055] All data were plotted and statistically analyzed using Excel 2010, IBM SPSS 18.0, Systat Sigma Plot 12, and Origin 2023. The experiment was set up with three replicates; the following data are the mean or mean ± standard deviation of the three replicates.

[0056] 5. Thermodynamic property analysis

[0057] Figure 3 The graphs show the changes in soil moisture content and soil water potential over time for two types of soil after rainfall. It is evident from the graphs that in the early stages, due to soil saturation from rainfall, seepage occurs, leading to a significant decrease in both soil water potential and moisture content. After seepage ceases, both soil moisture content and soil water potential exhibit a slow downward trend. Furthermore, it is clearly visible that the water potential value changes with the soil moisture content, and both maintain a consistent downward trend.

[0058] The soil water potential (Ψ) and corresponding water content (θ) of the two soil types were fitted using the above formula (2-6). Table 2 shows that formula (2-6) can well fit the relationship between soil water potential and volumetric water content after precipitation, and the coefficient of determination R for the two soil types is [value missing]. 2 All are above 0.99.

[0059]

[0060] Note: Ψs is soil water potential, θ is soil moisture content, M is the soil molar concentration conversion coefficient, and G is the soil standard free energy.

[0061] The parameters k and Ψ0 values ​​of the two soils are not significantly different, when At that time, the Ψ0 values ​​of Ld and Lc, i.e., the intrinsic water potential values, were -9.1885 kPa and -9.5771 kPa, respectively, with little difference. In the model deriving the relationship between soil volumetric water content and soil water potential using the Gibbs free energy formula, the values ​​of k and Ψ0 were defined, from which the soil molar concentration conversion coefficient (M) and the standard free energy (G) of the soil can be obtained. As can be seen from Table 2, the molar concentration conversion coefficient (M) and the standard free energy (G) of the two soils are very close. This is because both silty loam (Ld) and silty clay loam (Lc) are silty loams, with very similar soil types, and therefore similar thermodynamic characteristics, indicating that the present invention is effective.

[0062] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for measuring soil thermodynamic parameters, characterized in that, include: S1, Take the soil sample to be tested into the experimental basin; S2, The probes of the volumetric water content sensor and the water potential sensor are buried in the soil sample and connected to the data acquisition device; S3. The experimental basin is placed outdoors under natural conditions for a period of time. After it is naturally waterlogged, artificial rainfall is carried out and the soil moisture content and soil water potential data are dynamically measured at a set frequency. S4. The collected data is fitted according to the soil water potential and soil volumetric water content relationship model, and the results are calculated. And the value of k, wherein the relationship model between soil water potential and soil volumetric water content is as follows: In the formula, constant and k are model parameters, where k is the soil property coefficient; θ is the soil moisture content. Soil water potential; S5, calculate the soil thermodynamic parameters according to the following formula; In the formula, M is the soil molar concentration conversion coefficient, G is the standard free energy of the soil, R is the gas constant, and T is the ambient temperature.

2. The method for measuring soil thermodynamic parameters according to claim 1, characterized in that, The bottom of the experimental basin is provided with a seepage hole, and the upper part of the experimental basin is provided with a radial runoff pipe, with the soil sample parallel to the wall of the runoff pipe.

3. The method for measuring soil thermodynamic parameters according to claim 1, characterized in that, The derivation process of the model relating soil water potential and soil volumetric water content is as follows: Model of the relationship between soil water potential and water content: （1） In this formula To determine the soil mass water content, formula (1) is modified, and the relationship between soil water potential and soil volumetric water content is obtained from the Gibbs free energy formula. The derivation of the modified model is as follows: Because volumetric water content θ = soil water volume V w Total soil volume V0, Total soil volume V0 = Soil water volume V w + Soil volume V s Then it can be launched: （2-1） According to Moore's Law, the molar concentration C of the solute is... The volume of the solution V = the amount of solute n, therefore: Substitute We can obtain: （2-2） And because n / V s Let M be the soil molar concentration conversion coefficient. The above formula is then transformed into: （2-3） Depend on ,Will Substitution We can obtain: （2-4） Equation (2-4) can be transformed into: （2-5） In the formula, Ψs is the soil water potential to be measured, kPa; θ is the soil moisture content to be measured, m. 3 / m 3 G is the standard free energy of the soil; M is the soil molar concentration conversion coefficient. make , Then equation (2-5) can be written as: （2-6） constant θ and k are model parameters, where k is the soil property coefficient. When θ is zero, Ψ0 represents the inherent water potential, which reflects the soil's ability to absorb water; that is... , Based on the parameters Ψ0 and k, the soil molar concentration conversion coefficient M and the standard free energy of the soil can be calculated.

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