Method for estimating the size of the wetted volume of soil in drip irrigation

Abstract

This invention discloses a method for estimating the size of soil wet bodies in drip irrigation. The process is as follows: Step 1, establish a soil wet body size estimation model; Step 2, simplify the model established in Step 1 into a dimensionless equation using dimensional analysis; Step 3, assume the relationship between the parameters in the dimensionless equation obtained in Step 2; Step 4, substitute the dimensionless equation obtained in Step 2 into the assumed relationship in Step 3 to obtain the soil wet body size estimation equation; Step 5, conduct simulation experiments using HYDRUS-2D / 3D software, and perform nonlinear regression analysis on the simulation results to determine the coefficients and exponents in the soil wet body size estimation equation obtained in Step 4. This invention solves the limitations of existing technologies that do not consider the influencing factor of initial moisture content, as well as the problems of inconvenient observation of the vertical wetting front movement distance of soil wet bodies during field irrigation, complex wet body size estimation methods, and low estimation accuracy.

Description

Technical Field

[0001] This invention belongs to the field of agricultural engineering technology and relates to a method for estimating the size of wetted soil bodies in drip irrigation. Background Technology

[0002] Drip irrigation is a common surface water-saving irrigation technology. Water is delivered to the soil near plant roots through orifices or drippers on plastic pipes, reducing water loss through evaporation and deep seepage, resulting in significant water savings. The similarity between the size of the soil wetting body and the distribution area of ​​the crop root system is a crucial measure for improving water use efficiency. The shape of the soil wetting body is approximately hemispherical or semi-ellipsoidal, and its size can be determined by the movement of the wetting front in the horizontal and vertical directions. Accurately obtaining the size of the soil wetting body is a fundamental basis for the rational design of drip irrigation systems and improving irrigation efficiency.

[0003] In actual irrigation processes, observational errors are significant, field conditions are complex, and the movement of vertical moist fronts is difficult to obtain, making it impossible to analyze the size of soil wetting bodies under different conditions. Furthermore, inappropriate irrigation parameters can easily lead to over- or under-irrigation, thus affecting crop growth and development. Researching methods for estimating irrigation wetting body size is crucial for achieving precision irrigation, reducing ineffective irrigation, and improving water resource utilization. Therefore, establishing a simple and rapid method for estimating soil wetting body size is essential.

[0004] There are many methods for estimating the size of wetting fronts, generally categorized into three main types: analytical methods, numerical methods, and empirical model estimation methods. Analytical methods are based on mathematical methods and physical laws under specific assumptions. Numerical methods are complex and require extensive calculations, and neither is suitable for variable field conditions. Empirical model estimation methods are widely used. They are built based on simple and easily measurable field data, containing fewer parameters (soil hydraulic properties and irrigation technology elements), but simplifying the complex water infiltration process. Therefore, the estimated results may differ from the measured results. However, the initial soil moisture content has a significant impact on wetting front transport. At low initial moisture content, the soil has a small matrix potential (negative), and the large potential energy difference leads to rapid water infiltration. The lower the moisture content, the longer it takes for the pores to fill with water, which not only slows down the wetting front transport rate but also increases the amount of water applied. As the moisture content increases, the potential energy difference gradually decreases, water infiltration slows down, but the time for the soil pores to fill with water decreases, the wetting front transport rate accelerates, and the amount of water applied decreases. This indicates that initial soil moisture content has a significant impact on soil water infiltration, and this influencing factor should be considered when estimating soil wet volume. However, existing estimation methods that include initial moisture content as a parameter are not yet perfect, which limits their application. Summary of the Invention

[0005] The purpose of this invention is to provide a method for estimating the size of soil wetting bodies in drip irrigation, which solves the limitations of existing technologies that do not consider the influencing factor of initial moisture content, as well as the problems of inconvenience in observing the vertical wetting front movement distance of soil wetting bodies during field irrigation, complex wetting body size estimation methods, and low estimation accuracy.

[0006] The technical solution adopted in this invention is a method for estimating the size of wetted soil bodies in drip irrigation, which is implemented according to the following steps:

[0007] Step 1: Establish a soil wet body size estimation model;

[0008] Step 2: Simplify the model established in Step 1 into dimensionless equations using dimensional analysis.

[0009] Step 3: Assume the relationship between the parameters in the dimensionless equation obtained in Step 2;

[0010] Step 4: Substitute the dimensionless equation obtained in Step 2 into the assumed relationship in Step 3 to obtain the soil wet body size estimation equation.

[0011] Step 5: Conduct simulation experiments using HYDRUS-2D / 3D software, and perform nonlinear regression analysis on the simulation results to determine the coefficients and exponents in the soil wet body size estimation equation obtained in Step 4.

[0012] The invention is further characterized in that,

[0013] In step 1, the soil wet body size estimation model is as follows:

[0014]

[0015] In equation (1), X is the horizontal movement distance of the wetting front (cm); Z is the vertical movement distance of the wetting front (cm); and θ0 is the initial soil moisture content (cm). 3 cm -3 V represents the amount of water applied, in L; q represents the dripper flow rate, in L / h. -1 ;K s For saturated hydraulic conductivity, cm h -1 .

[0016] In step 2, the dimensionless equation is:

[0017] (1) Dimensionless horizontal movement distance of the moistening front X * The expression is:

[0018]

[0019] (2) Dimensionless vertical direction wet front transport distance Z * The expression is:

[0020]

[0021] (3) Dimensionless water application volume V * The expression is:

[0022]

[0023] In step 3, the relationship between the parameters is as follows:

[0024]

[0025] In equation (5), a1 and a2 are coefficients; n1 and n2 are exponents.

[0026] In step 4, the equation for estimating the size of the soil wetted body is:

[0027]

[0028] In step 5, the model used by the HYDRUS-2D / 3D software for the simulation experiment is:

[0029] (1) Soil water flow governing equation:

[0030]

[0031] In equation (8), x is the horizontal coordinate; z is the vertical coordinate; and θ is the soil moisture content (cm). 3 cm -3 t represents time; D(θ) represents the unsaturated diffusivity, in cm / h. -1 K(θ) is the unsaturated hydraulic conductivity, in cm / h. -1 ;

[0032] (2) Soil hydraulic properties were described using the van Genuchten-Mualem model:

[0033]

[0034]

[0035]

[0036] m = 1 - 1 / n (11)

[0037] In equations (8)-(11), h is the pressure head, in cm; θ r Residual soil moisture content, in cm 3 cm -3 ;θ s Soil saturation moisture content, cm 3 cm -3 Se α represents relative saturation; n and m represent soil air intake; l represents soil shape parameters; and l represents porosity correlation.

[0038] The specific process of step 5 is as follows: In HYDRUS-2D / 3D, set the geometric surface as an axisymmetric vertical plane. Considering the symmetry, set the dripper position as point A. The horizontal distance adopts the dripper spacing in the drip irrigation design. The vertical distance is selected as the length from the soil surface to the crop root system and the depth that does not affect irrigation. The simulation area is set as a rectangular plane of 100cm×100cm. Establish a coordinate system according to the above settings.

[0039] In the simulation experiment, soil moisture content was selected as the initial condition, the simulation time was set to 10h, the minimum time step was 0.01h, the maximum time step was 0.02h, the upper boundary was connected to the atmosphere and set as the atmospheric boundary, the left and right boundaries were both set as zero flux boundaries, and the lower boundary was set as the free drainage boundary.

[0040] The simulation area was divided into triangular meshes by FE-Mesh finite element analysis and the meshes were refined. The maximum diameter of the circumcircle of the finite element triangle was set to 1 cm. The hydraulic parameters of the soil were then input to obtain the horizontal and vertical wet front migration distances. The obtained horizontal and vertical wet front migration distances were then substituted into formula (6) and the values ​​of coefficients a1 and a2 and exponents n1 and n2 were obtained through nonlinear regression analysis.

[0041] The beneficial effects of this invention are that the method for estimating the size of the wetted soil body in drip irrigation takes into account the influence of the initial soil moisture content on the size of the wetted body, thereby improving the accuracy and universality of the estimation method and making the method simple. Attached Figure Description

[0042] Figure 1 This is a diagram showing the boundary conditions of the simulated region in this invention;

[0043] Figure 2 This is a diagram showing the relationship between the dimensionless water application volume V* and the horizontal and vertical wetting fronts X* and Z* in this invention.

[0044] Figure 3 This is a comparison chart of the measured values ​​of the horizontal and vertical wetting front migration distances and the estimated values ​​obtained by the method of this invention;

[0045] Figure 4 This is a comparison chart of simulated values ​​of horizontal and vertical wetting front migration distances with estimated values ​​obtained by the method of this invention. Detailed Implementation

[0046] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0047] This invention provides a method for estimating the size of the wetted soil body in drip irrigation, specifically implemented according to the following steps:

[0048] Step 1: Establish a soil wet body size estimation model;

[0049] The soil wet body size estimation model is as follows:

[0050]

[0051] In equation (1), X is the horizontal movement distance of the wetting front (cm); Z is the vertical movement distance of the wetting front (cm); and θ0 is the initial soil moisture content (cm). 3 cm -3 V represents the amount of water applied, in L; q represents the dripper flow rate, in L / h. -1 ;K s For saturated hydraulic conductivity, cm h -1 ;

[0052] Step 2: In order to reduce the number of parameters, the model established in Step 1 is simplified into dimensionless equations using dimensional analysis.

[0053] (1) Dimensionless horizontal movement distance of the moistening front X * The expression is:

[0054]

[0055] (2) Dimensionless vertical direction wet front transport distance Z * The expression is:

[0056]

[0057] (3) Dimensionless water application volume V * The expression is:

[0058]

[0059] Step 3, assuming the relationship between the parameters in the dimensionless equation obtained in Step 2, as shown;

[0060]

[0061] In equation (5), a1 and a2 are coefficients; n1 and n2 are exponents;

[0062] Step 4: Substitute the dimensionless equation obtained in Step 2 into the assumed relationship in Step 3 to obtain the soil wet body size estimation equation.

[0063]

[0064] Step 5: Conduct simulation experiments using HYDRUS-2D / 3D software. Perform nonlinear regression analysis on the simulation results to determine the coefficients and exponents in the soil wetting body size estimation equation obtained in Step 4, such as... Figure 2 As shown;

[0065] The model used in the simulation experiment by HYDRUS-2D / 3D software is:

[0066] (1) The soil water movement under drip irrigation conditions is simplified to a two-dimensional movement on a vertical plane with a single source axisymmetric about the dripper as the center of symmetry. Assuming that the soil is homogeneous and isotropic, and ignoring the effects of temperature, solute potential, etc., and neglecting the water lag effect, the soil flow control equation adopts the two-dimensional Richards equation:

[0067]

[0068] In equation (8), x is the horizontal coordinate; z is the vertical coordinate; and θ is the soil moisture content (cm). 3 cm -3 t represents time; D(θ) represents the unsaturated diffusivity, in cm / h. -1 K(θ) is the unsaturated hydraulic conductivity, in cm / h. -1 ;

[0069] (2) When conducting simulation experiments, the parameters in the soil moisture characteristic curve are required, including soil retained water content, soil saturated water content, soil shape parameters, soil air suction, saturated water content, and soil pore connectivity coefficient. The soil hydraulic properties parameters are described using the van Genuchten-Mualem model:

[0070]

[0071]

[0072]

[0073] m = 1 - 1 / n (11)

[0074] In equations (8)-(11), h is the pressure head, in cm; θ r Residual soil moisture content, in cm 3 cm -3 ;θ s Soil saturation moisture content, cm 3 cm -3 S e α represents relative saturation; α represents soil air intake; n and m are soil shape parameters; l represents porosity correlation.

[0075] The specific process is as follows:

[0076] In HYDRUS-2D / 3D, the geometric surface is set as an axisymmetric vertical plane. Considering symmetry, the dripper position is set to point A. The horizontal distance adopts the dripper spacing in drip irrigation design, and the vertical distance is selected as the length from the soil surface to the crop root system and the depth that does not affect irrigation. The simulation area is set as a 100cm × 100cm rectangular plane. A coordinate system is established based on the above settings, such as... Figure 1 As shown;

[0077] In the simulation experiment, soil moisture content was selected as the initial condition, that is, the initial soil moisture content was set, the simulation time was set to 10h, the minimum time step was 0.01h, the maximum time step was 0.02h, the upper boundary was connected to the atmosphere and set as the atmospheric boundary, the left and right boundaries were both set as zero flux boundaries, and the lower boundary was set as the free drainage boundary.

[0078] The simulation area was divided into triangular meshes by FE-Mesh finite element analysis method, and the meshes were refined. The maximum diameter of the circumcircle of the finite element triangle was set to 1 cm (15600 nodes in total). Then, the hydraulic parameters of the soil were input to obtain the horizontal and vertical wet front migration distances. The obtained horizontal and vertical wet front migration distances were then substituted into formula (6) and the values ​​of coefficients a1, a2 and exponents n1, n2 were obtained through nonlinear regression analysis.

[0079] Different initial soil moisture contents can be set by changing the percentage of maximum available soil water, which is the difference between field capacity (FC) and wilting factor (PWP).

[0080] Based on the soil field capacity and wilting coefficient provided by the U.S. Department of Agriculture, the maximum available water (AW) of 12 soil types was determined as shown in Table 1. 30%, 50%, and 70% of the maximum available water were set as the initial moisture content of different soil types. Three commonly used dripper flow rates were set for each group of simulation experiments. The input variables in HYDRUS-2D / 3D are shown in Table 2.

[0081] Table 1. Hydraulic parameters of 12 typical soil types

[0082]

[0083] Table 2 Initial simulation conditions for drip irrigation infiltration in Hydrus-2D / 3D

[0084]

[0085] The final equation for estimating the size of the soil wet body is as follows:

[0086]

[0087] Example 1

[0088] To verify the feasibility of the method of the present invention, the experimental data and the simulation test results in HYDRUS-2D / 3D software were used for verification. The parameters required in the experiment included hydraulic parameters of different soil textures and irrigation technology elements, as detailed in Table 3.

[0089] Table 3 Soil hydraulic properties and irrigation techniques used in the experiment

[0090]

[0091] 40% and 60% of the maximum available soil water content (AW) were selected as the initial soil moisture content in the HYDRUS-2D / 3D simulation test. The soil hydraulic characteristics parameters are shown in Table 1, and the simulation test details are shown in Table 4. The test included 2 initial soil moisture contents, 12 soil structures, and 3 dripper flow rates, totaling 72 groups. The simulation time was 10 hours.

[0092] Table 4 Soil hydraulic properties and irrigation techniques used in the simulation experiment.

[0093]

[0094] In this invention, the performance of the estimation method is evaluated using mean absolute error (MAE), mean relative error (MRE), and root mean square error (RMSE). The calculation equations are as follows:

[0095]

[0096]

[0097]

[0098] Where i is an integer ranging from 1 to N, N represents the total number of data points, and y ei It is the i-th estimated value, y si It is the i-th measured or simulated value. If MAE and RMSE are close to 0 and MRE is less than ±10%, it indicates that the model fit is good.

[0099] The estimated values ​​of this invention are compared with the measured values ​​and simulated values, respectively. Figure 3 and Figure 4 The errors are shown in Table 5. The results indicate that the estimation results describe the horizontal and vertical wetting front movement distances well under different soil textures, demonstrating that the estimation method of this invention can be used to estimate the size of the wetting body in drip irrigation soil.

[0100] Table 5 Error Analysis of Measured, Simulated, and Estimated Values ​​of Soil Moisture Body in Drip Irrigation

[0101]

[0102] Through the above examples, the soil wetting body size estimation method of the present invention considers the influence of initial moisture content, determines the estimation parameters through simulation results of 12 soil textures, establishes an improved empirical model, calculates the horizontal and vertical wetting front transport distances, and improves the universality and accuracy of the estimation results while simplifying the soil moisture infiltration process.

Claims

1. A method for estimating the size of wetted soil bodies in drip irrigation, characterized in that, The specific steps are as follows: Step 1: Establish a soil wet body size estimation model; In step 1, the soil wet body size estimation model is as follows: （1） In equation (1), X The distance of the horizontal movement of the moistening front is expressed in cm. Z The vertical distance of the moistening front, expressed in cm; θ 0 represents the initial soil moisture content, in cm. 3 cm -3 ; V The amount of water applied is expressed in L; q For dripper flow rate, L h -1 ; K s For saturated hydraulic conductivity, cm h -1 ; Step 2: Simplify the model established in Step 1 into dimensionless equations using dimensional analysis. In step 2, the dimensionless equation is: (1) Dimensionless horizontal distance of the moistening front The expression is: （2） (2) Dimensionless vertical distance of the moistening front The expression is: （3） (3) Dimensionless water application The expression is: （4） Step 3: Assume the relationship between the parameters in the dimensionless equation obtained in Step 2; In step 3, the relationship between the parameters is as follows: （5） In equation (5), a 1. a 2 is the coefficient; n 1. n 2 is the exponent; Step 4: Substitute the dimensionless equation obtained in Step 2 into the assumed relationship in Step 3 to obtain the soil wet body size estimation equation. In step 4, the equation for estimating the size of the soil wetted body is: （6） Step 5: Conduct simulation experiments using HYDRUS-2D / 3D software, and perform nonlinear regression analysis on the simulation results to determine the coefficients and exponents in the soil wet body size estimation equation obtained in Step 4.

2. The method for estimating the size of the wetted soil body in drip irrigation according to claim 1, characterized in that, In step 5, the model used by the HYDRUS-2D / 3D software for the simulation experiment is: (1) Soil water flow governing equation: （7） In equation (8), x The horizontal coordinate; z Vertical coordinates; θ Soil moisture content, in cm 3 cm -3 ; t For time; D(θ) The unsaturated diffusivity is expressed in cm h. -1 ; K(θ) The unsaturated hydraulic conductivity is expressed in cm h. -1 ; (2) Soil hydraulic properties were described using the van Genuchten-Mualem model: （8） （9） （10） （11） In equations (8)-(11), h is the pressure head, in cm; θ r Residual soil moisture content, in cm 3 cm -3 ; θ s Soil saturation moisture content, cm 3 cm -3 ; S e Relative saturation; α This refers to the soil air intake value. n and m For soil shape parameters; l For porosity correlation.

3. The method for estimating the size of the wetted soil body in drip irrigation according to claim 2, characterized in that, The specific process of step 5 is as follows: In HYDRUS-2D / 3D, the geometric surface is set as an axisymmetric vertical plane. Considering the symmetry, the dripper position is set as point A. The horizontal distance adopts the dripper spacing in the drip irrigation design. The vertical distance is selected as the length from the soil surface to the crop root system and the depth that does not affect irrigation. The simulation area is set as a rectangular plane of 100 cm × 100 cm. A coordinate system is established according to the above settings. In the simulation experiment, soil moisture content was selected as the initial condition, the simulation time was set to 10 h, the minimum time step was 0.01 h, the maximum time step was 0.02 h, the upper boundary was connected to the atmosphere and set as the atmospheric boundary, the left and right boundaries were both set as zero flux boundaries, and the lower boundary was set as the free drainage boundary. The simulation region was divided into triangular meshes using the FE-Mesh finite element analysis method, and the meshes were refined. The maximum diameter of the circumcircle of the finite element triangles was set to 1 cm. Then, the hydraulic parameters of the soil were input to obtain the horizontal and vertical wetting front migration distances. These distances were then substituted into formula (6), and the coefficients were obtained through nonlinear regression analysis. a 1. a 2 and index n 1. n The value of 2.

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