CN1793881A - Automatic determination device of soil moisture solute moving parameter - Google Patents

Abstract

The invention discloses an automatic measuring device for soil moisture and solute migration parameters, comprising a water and solute supplier, a three-way solenoid valve, a pressure sensor, a soil level column, a probe, an automatic collector and a computer control unit; the computer control unit Connect the pressure sensor, three-way solenoid valve, probe and solution collector through the connection line to control the automatic switching of water and solute in the water and solute supplier, and automatically collect the liquid signal in the solution collector to obtain different soils. Conductivity and infiltration of soil samples at different positions in the horizontal column, and automatically calculate the soil wetting front, solute front position and infiltration over time based on the collected data. The device uses the same soil sample to automatically measure soil hydraulic parameters and solute migration parameters, and the parameters obtained from the measured data are consistent with the actual situation.

Description

Automatic measuring device for soil moisture and solute transport parameters

Technical field

The invention belongs to the field of soil and water conservation research, and relates to a measuring device, in particular to a device for automatically measuring soil moisture and solute migration parameters.

Background technique

The shortage of water resources in arid and semi-arid areas is an important factor restricting the development of industry and agriculture and the overall progress of society. Efficient use of limited water resources has become an important means to alleviate water shortages, achieve sustainable industrial and agricultural development, and ecological restoration. Soil is the supply and storage place of various energy required for crop growth. Prediction and forecasting and timely regulation of the material cycle process in soil are important contents for the implementation of efficient agricultural water use and ecological environment construction. Soil moisture is not only the solvent and carrier of various nutrient elements of crops, but also one of the nutrient elements necessary for crop growth. It plays a key role in rationally regulating the material cycle process in the soil, so it reveals the characteristics of soil moisture movement and reasonably regulates soil moisture. Conditions are the foundation of ecological environment construction.

Scholars at home and abroad have done a lot of research work on soil moisture and solute measurement technology, soil moisture movement and solute transport theory, and gradually developed from simple experimental research to using mathematical models to predict soil moisture and solute transport processes. As far as mathematical simulation is concerned, the Richards equation is commonly used to describe the characteristics of soil water movement, and the convection-dispersion theory is used to describe the migration process of soil solutes. The accuracy of simulation calculations directly depends on the reliability and accuracy of the hydraulic parameters and soil solute migration parameters involved. The main hydraulic parameters involved are soil moisture characteristic curve, unsaturated hydraulic conductivity, diffusivity, and solute transport parameters include hydrodynamic diffusion coefficient and retention factor. At present, there are two methods for determining parameters: direct measurement method and indirect derivation method. The direct measurement method for measuring hydraulic parameters mainly uses tensiometer, pressure membrane, and centrifuge to measure soil moisture characteristic curve, and uses rainfall infiltration, evaporation and ponding water infiltration methods to measure unsaturated hydraulic conductivity. These methods have clear concepts, but time-consuming, expensive experiments, parameter uncertainties, and soil spatial variability often limit the application of these methods in the field. At the same time, the sample for measuring the moisture characteristic curve is not consistent with the sample for soil moisture movement research, resulting in sample error. There are serious problems with the application of these methods if the soil has a layered structure and preferential flow paths. In recent decades, in order to overcome the shortcomings of direct measurement methods, people have sought to use simple methods to estimate soil water movement parameters, such as using soil particle composition to estimate soil water characteristic curves (Arya et al., 1999), and using the existing The relationship between the established soil moisture characteristic curve and unsaturated hydraulic conductivity is used to predict the unsaturated hydraulic conductivity. However, since the hydraulic characteristics of soil are affected by soil bulk density and soil structure, the use of particle composition to determine the soil moisture characteristic curve is still in the theoretical exploration stage. In addition, people can use the soil moisture motion equation and the corresponding experimental data to invert the parameters through the mathematical model, but a large number of studies have shown that the non-uniqueness of the parameters and the convergence of the method caused by this method limit the development and development of this method. application. Ming'an Shao (1998) developed an integral method to determine soil moisture movement parameters (van Genuchten model, 1980). Wang Quanjiu (2002) developed a method for deriving the parameters of the Brooks-Corey (1964) model using horizontal one-dimensional infiltration tests. This method only needs to measure the time-varying process of infiltration and wetting front, which provides a basis for determining soil hydraulic parameters. valid theory.

At present, the direct measurement method of measuring hydraulic parameters mainly uses tensiometer, pressure membrane and centrifuge to measure soil moisture characteristic curve, and uses rainfall infiltration, evaporation and ponding water infiltration method to measure unsaturated hydraulic conductivity. These methods have clear concepts, but time-consuming, expensive experiments, parameter uncertainties, and soil spatial variability often limit the application of these methods in the field. At the same time, the sample for measuring the moisture characteristic curve is not consistent with the sample for soil moisture movement research, resulting in sample error. There are serious problems with the application of these methods if the soil has a layered structure and preferential flow paths.

The determination of soil solute transport parameters is often determined by breakthrough curves, which is time-consuming and laborious. The boundary layer theory proposed by Shao Ming'an provides an effective theory for determining solute transport parameters. However, due to the limitations of the experimental system and research methods, the soil samples used in the determination of hydraulic parameters and solute transport are inconsistent, resulting in sample errors. Therefore, it is necessary to develop a device that uses the same soil sample to measure hydraulic parameters and solute transport parameters.

Contents of invention

The object of the present invention is to provide an automatic measuring device for soil moisture and solute transport parameters.

In order to achieve the above tasks, the technical solution adopted by the present invention is: an automatic measuring device for soil moisture and solute transport parameters, characterized in that the device includes:

A water and solute feeder is used to provide water and solution to the soil column. The feeder consists of two plexiglass tubes filled with water and solute, and a constant water head can be maintained by the principle of the Martens bottle. Each plexiglass tube is connected to a switch that controls the outflow of water or solute, and is connected to a three-way solenoid valve through a pipeline; at the liquid outlet of each plexiglass tube, there are pressure sensors for monitoring the outflow of water or solute ;

A soil level column, which is used to place the soil sample to be tested. The probes for measuring conductivity are evenly distributed on the soil level column. One end of the soil level column is connected with the solute supplier through a three-way solenoid valve and a pipeline, and the bottom of the other end is There is a solution collector for the effluent;

A computer control unit, the computer control unit is respectively connected with the pressure sensor, the three-way solenoid valve, the probe and the solution collector through the connection line, and is used to control the automatic switching of water and solute of the water and solute supplier, and to control the solution collector. The liquid signal in the soil is automatically collected to obtain the electrical conductivity and infiltration of soil samples at different positions in different soil horizontal columns, and automatically calculate the soil wetting front, solute front position and infiltration over time based on the collected data.

The device of the present invention has the following functions:

(1) Using the same soil sample to automatically measure soil hydraulic parameters and solute migration parameters;

(2) Adopt computer automatic control to realize man-machine dialogue;

(3) According to the relevant variables measured, the computer automatically calculates the relevant parameters.

Description of drawings

Fig. 1 is a schematic view of the device structure of the present invention;

Fig. 2 is the change process of the soil wetting front of two kinds of textures with time; among them, picture (a) is the change map of loess soil wetting peak with time; picture (b) is the change map of loess soil peak with time.

Figure 3 is the solute penetration curves of soils with different textures, in which picture (a) is black loam, picture (b) is sandy soil, picture (c) is loam soil, and picture (d) is yellow cotton soil.

The present invention will be further described in detail below in conjunction with the accompanying drawings and the working principle and process of the device.

Detailed ways

Referring to Fig. 1, soil moisture of the present invention, solute transport parameter automatic measuring device, are made up of three parts:

(1) Water and solute supplier. This part adopts the principle of Martens bottle to provide water and solution to the soil horizontal column. It is composed of two plexiglass tubes, and has a switch to control the outflow of water or solute, and through the pipeline and The three-way solenoid valve is connected, and there are pressure sensors for monitoring the infiltration of water or solute at the liquid outlet of each plexiglass tube.

(2) Soil level column, which is a plexiglass tube with a length of 60 cm and an inner diameter of 5 cm, on which a probe is inserted at an interval of 8 cm to measure the conductivity. One end is the inlet of water or solution, and the other end is the outlet. , below the outflow port, there is an automatic solution collector for the outflow liquid.

The probes are fixed on the probe in groups of 5, with a length of 3.5 cm and a diameter of 1 mm. The four probes are distributed around a square with a distance of 1 cm, and one is in the center.

(3) Computer control unit, the computer control unit is respectively connected with the pressure sensor, the three-way solenoid valve, the probe and the solution collector through the connection line, and is used to control the automatic switching of the water and the solute of the water and solute supplier, and the solution The liquid signal in the collector is automatically collected to obtain the conductivity and infiltration of soil samples at different positions in different soil horizontal columns, and automatically calculate the soil wetting front, solute front position and infiltration over time based on the collected data.

The solution collector chooses the BS-100A model of Shanghai Qingpu Huxi Instrument Factory. The solution collector is controlled by a single-chip microcomputer chip and displayed by a six-digit digital tube. It can perform timing control from 1 second to 9 hours, 59 minutes and 59 seconds. The test process is shown in Figure 4:

The test process is as follows: firstly, according to a certain bulk density, the soil sample to be tested is loaded into the soil horizontal column, the soil sample is air-dried and passed through a 2mm sieve, the conductivity probe is inserted into the soil horizontal column, and connected to the computer control unit. Fill the water and solute supplies with distilled water and solute, respectively.

Turn on the control program (SWSP) of the computer control unit, the water and solute supplier first starts to supply water, the control program will automatically open the three-way control valve to supply water to the soil level column, and the pressure sensor starts to automatically sample and record the infiltration into the soil level column , Probes at different positions on the soil level column automatically record the change process of conductivity to determine the position of the wetting peak. After the water penetrates into the last probe of the soil level column, the outflow of the soil level column has a solution flowing out, which is collected by the solution collector, and the automatic solution collection system of the computer control unit starts to run, and collects the outflow liquid of the soil level column ( That is, the liquid flowing into the solution collector). When the conductivity of the last probe is stable, it means that the soil level column is completely saturated at this time, and the saturated hydraulic conductivity can be obtained according to the solution volume and time in the solution collector. At this time, the control program stops the water supply, switches the switch, and the water and solute supplier starts to supply the solution. The computer control unit also collects the infiltration amount of the solute flowing into the horizontal column of the soil and the solute peak data with the above procedure, and the collected outflow solution can be analyzed to compare and determine the accuracy of the automatic calculation parameters of the instrument.

Test verification:

Using the device of the present invention to measure the wet peak, when the moisture has not reached the detection point of the last probe, the reading of the device is very small, and the relative conductivity value of the dry soil is between 3 and 6 readings. When the humidity peak reaches the monitoring point, the reading of the device increases suddenly, and the time when the reading increases suddenly is the time when the humidity peak reaches the monitoring point. Comparing the measured time of the device with the curve drawn by the position of the wet peak and the curve obtained by manual monitoring, the two curves almost overlap, indicating that the device is used to determine the relationship between the wet peak and time is very accurate (see Figure 2).

When the soil sample in the soil horizontal column was saturated and the solution outflow was stable, it was replaced with KCl solution for Cl ^- migration research. When the solute peak surface does not reach the detection point, the relative conductance value displayed by the device is basically a constant value. When the solute peak surface arrives, the displayed value begins to rise gradually, which is reflected in the soil salinity, that is, the concentration of the soil solution begins to increase, and the drawn curve is similar to The change of the breakthrough curve shows the feasibility of using the device to detect the solute peak surface. Table 1 shows the position of the probe at each detection point and the arrival time of the solute peak.

Table 1 Measurement data detection point Soil Loess soil black clay sand d(t) t d(t) t d(t) t d(t) t 1 3 5.33 3 0.60 3 2.75 3 0.53 2 7 16.20 7 1.42 7 9.92 7 1.73 3 11 29.20 11 2.58 11 16.58 11 2.53 4 15 39.00 15 3.42 15 22.08 17 3.90

The measurement data in Table 2 below are processed according to the cubic expression of the boundary layer theory, and the quadratic polynomial fitting is performed to obtain the mathematical expression of the solute peak in several soils:

Table 2 soil sample Fit Mathematical Expression R ² Yantu (Yangling) y=1.4042x ² -0.4583x 0.9942 Sand (Wei River) y= ^{0.1896x2-0.7674x} 0.9176 black clay y=0.5731x ² -0.2911x 0.9866 Loess soil y=0.2618x ² -1.0579x 0.6658

Since the solute is non-reactive Cl ^- , first assume that R = 1, and the obtained D value is shown in Table 3:

table 3 parameter Soil sand black clay Loess soil BTC boundary layer BTC boundary layer BTC boundary layer BTC boundary layer D. 0.07 0.06 0.29 0.44 0.14 0.15 0.29 0.32

It can be seen that, except for sandy soil, the D value obtained through the boundary layer in Table 3 is very close to the value obtained from the soil solute breakthrough curve. The parameters obtained by using the boundary layer method were brought into the CXTFIT program to calculate the soil solute breakthrough curve and the soil solute breakthrough curve obtained by the traditional method (titration of the effluent concentration change) was drawn simultaneously in the figure, as shown in Figure 3. It can be seen from the figure that the parameters obtained from the measured data of the device are consistent with the actual situation.

Claims (2)

1. a soil moisture, solute transfer parameter apparatus for automatically measuring is characterized in that this device comprises:

One water and solute feeder are used for providing water and solution to earth pillar, and this feeder is made up of two plexi-glass tubulars that water and solute are housed, and each plexi-glass tubular is connected with the switch of control water or solute outflow, and are connected with three-way solenoid valve by pipeline; At each plexi-glass tubular liquid outlet, be useful on the pressure transducer of the infiltration capacity of monitoring water or solute respectively;

One horizontal soil column, be used to place tested pedotheque, be evenly distributed with the probe of measuring conductivity on this horizontal soil column, horizontal soil column one end is communicated with the solute feeder by three-way solenoid valve and pipeline, and there is a solution catcher that the flow liquid body below of the other end;

One computer control unit, computer control unit is connected with pressure transducer, three-way solenoid valve, probe and solution catcher respectively by connecting line, be used to control the water of water and solute feeder, the automatic switchover of solute, and the liquid signal in the solution catcher gathered automatically, obtain the conductivity and the infiltration capacity of the pedotheque of diverse location in the different soils horizontal columns, and automatically according to the data computation soil wetting front, solute front position and the infiltration capacity that collect change procedure in time.

2. device as claimed in claim 1 is characterized in that, the long 3.5cm of the probe of described mensuration conductivity, and diameter 1mm is one group with per 5 and is fixed on the probe that 4 probes wherein are square profile with spacing 1cm, foursquare center is placed 1.

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