A rapid method for measuring root volume in soil

Abstract

The present application belongs to the technical field of plant root determination, and particularly relates to a rapid determination method of root volume in soil, comprising the following steps: step one, obtaining a sample to be determined including roots and soil; step two, placing the sample to be determined into a measuring box to determine electrical parameters such as capacitance and resistance of the sample; step three, establishing a relationship between root volume and electrical parameters by using electrical parameters and root volume; and step four, substituting the electrical parameters into the relationship established in step three to calculate the root volume. The present application deduces a dielectric coefficient equation of a binary medium of roots and soil for the first time and simplifies the calculation process, and the root volume can be quickly calculated by using the electrical parameters of soil and roots measured at high frequency, so that the root cleaning process is avoided, and the determination efficiency is greatly improved compared with the traditional root washing determination mode.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of plant root determination, and particularly relates to a rapid determination method of root volume in soil. BACKGROUND

[0002] Roots directly affect the performance of the aboveground part of a plant, and in-depth understanding of roots will help to understand the overall performance of a plant, and therefore, root research is increasingly important. At present, in order to obtain morphological parameters such as root length, volume and surface area, the common practice usually includes several steps: washing the sample obtained by soil sampling; washing off the soil and other impurities in the sample; and measuring the root characteristics. This way can intuitively obtain root data, but the operation process is time-consuming and laborious, and it is difficult to quickly measure a large number of samples. SUMMARY

[0003] In order to solve the problems existing in the prior art, the present application provides a rapid determination method of root volume, which can avoid the time-consuming and laborious root washing process, and the volume parameter of the root can be quickly calculated and obtained by measuring the dielectric constant and conductivity of the root and the root growth medium under high frequency.

[0004] The specific technical scheme adopted by the present application is as follows:

[0005] A rapid determination method of root volume in soil, comprising the following steps,

[0006] Step 1: obtaining a sample to be measured including roots and soil;

[0007] Step 2: placing the sample to be measured into a measuring box and determining the electrical property parameters of the sample;

[0008] Step 3: establishing a relationship between the root volume and the electrical property parameters by using the electrical property parameters and the root volume data;

[0009] Step 4: substituting the electrical property parameters into the relationship established in Step 3 to calculate the root volume.

[0010] In Step 3, the volume of the root is calculated by using the electrical property parameters, and the electrical property parameters include capacitance and conductivity, and the calculation formula is:

[0011]

[0012] The derivation method of formula (12) is that the property of the interface polarization mechanism between the root and the soil can be expressed as the following formula based on the property of the interface polarization mechanism between the root and the soil:

[0013]

[0014] In formula (1),

[0015] ε mi* is the complex permittivity of the non-uniform system;

[0016] ε m * is the complex permittivity of the medium;

[0017] ε i * is the complex permittivity of the dielectric sphere in the medium;

[0018] Φ is the volume fraction of the spherical dispersion.

[0019]

[0020] Equation (2) is a general expression of the complex permittivity. Wherein, ε * is the complex permittivity; j is the imaginary unit; ε is the real part, k / (ωε0) is the imaginary part; ε0 is the vacuum permittivity; k is the conductivity; ω is the angular frequency; ω=2πf; f is the frequency. Equation (2) is substituted into equation (1), and the real part is separated to obtain equation (3):

[0021]

[0022] In equation (3), ε(ω) is the real part of the dielectric constant; ε ∞ is the limit of the dielectric constant under high frequency conditions, specifically expressed as the left half of equation (4); Δε is the increase of the dielectric constant, specifically expressed as the left half of equation (5); τ is the relaxation time, specifically expressed as the left half of equation (6); Considering that the volume fraction Φ of the root system occupied by the root is much smaller than 1, therefore, (Φ±1) multiplied by any one parameter γ can be simplified as γ(Φ±1)≈γ.

[0023] Wherein: ε ∞ , Δε, τ can be calculated from the right half of equations (4), (5) and (6) respectively:

[0024]

[0025]

[0026]

[0027] In equations (5) and (6), k m is the conductivity of the medium; k i is the conductivity of the dielectric sphere. In order to simplify the expression, three coefficients are used instead:

[0028] a=ε m k i -ε i k m (7)

[0029] b = 2ε m + ε i (8)

[0030] c = 2k m + k i (9)

[0031] Put the formula (4) ~ (9) into the formula (3), the formula (10) can be obtained:

[0032]

[0033] From the above formula (10), in the non-uniform dispersion system, the dielectric constant of the whole system is linearly positively correlated with the volume fraction of the dispersion. Assuming that a dielectric sphere composed of cells has no order of magnitude difference in conductivity with the medium conductivity, in the beta relaxation frequency range, the dielectric constant of the biological tissue (about 10 4 ~ 10 5 ) is much larger than the dielectric constant of the common growth medium (such as soil, water, etc.) (about 10 ~ 200), that is, ε m is much smaller than ε i , so a ≈ - ε i k m , b ≈ ε i .

[0034] Therefore, in the beta relaxation frequency range, the relationship between the dielectric constant of the medium and the volume fraction can be approximated as formula (11):

[0035]

[0036] Replace the dielectric sphere with the root system and the medium with the soil, the relationship between the soil capacitance of the sample and the root volume can be obtained (12):

[0037]

[0038] In formula (12), EC is the soil capacitance; RV represents the root volume; d represents the distance between the electrodes; EC m represents the soil capacitance without root system.

[0039] In the step one, the method for taking soil to obtain the sample to be measured is: preselecting the plant to be measured, digging the soil around the plant to be measured according to the cross section of the measuring box, taking out the columnar soil sample wrapped with the root system of the plant, and dividing the soil sample into block samples to be measured along the height direction according to the height of the measuring box.

[0040] In the step two, the block sample to be measured is placed in the measuring box, water is poured, the soil moisture of the block sample in the measuring box is saturated, the capacitance and resistance of the block sample are measured by the electrodes arranged on the opposite sides in the measuring box, and the resistance can be used to calculate the conductivity.

[0041] The beneficial effects of the present application are:

[0042] The present application deduces the dielectric coefficient equation of root-soil binary medium, effectively simplifies the calculation process, and can quickly calculate and obtain the volume of root system through the soil and root system capacitance and resistance parameters measured at high frequency. Compared with the traditional determination method, the washing process of the root system is omitted, and the determination efficiency is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 The dielectric constant of root system, the dielectric constant of different medium and the dielectric constant of root system in medium change with frequency, and the shadow part represents the frequency range of 30-100 kHz;

[0044] Figure 2 The error between the calculated capacitance value based on the dielectric constant of medium, the dielectric constant of root system, the conductivity of medium and the conductivity of root system and the measured capacitance value changes with frequency;

[0045] Figure 3 The correlation between root system volume and medium capacitance changes with frequency;

[0046] Figure 4 The relationship between the capacitance of soil sample obtained from different soil layers in the field and the root system volume and the relationship between the root system volume estimated using soil capacitance and the measured root system volume;

[0047] Figure 5 The relationship between the capacitance of soil sample obtained from different soil layers in the field and the root system volume and the relationship between the root system volume estimated using soil capacitance and the measured root system volume; DETAILED DESCRIPTION

[0048] The present application will be further described below in combination with the drawings and specific implementation examples.

[0049] The present application is a kind of root system volume rapid determination method, comprising the following steps:

[0050] Step one, obtain the sample to be measured including root system and soil;

[0051] Step two, place the sample to be measured into the measuring box, and determine the electrical parameters such as capacitance and resistance of the sample;

[0052] Step three, use the electrical parameters and root system volume data to establish the relationship between root system volume and electrical parameters;

[0053] Step four, substitute the electrical parameters into the relationship established in step three to calculate and obtain the root system volume.

[0054] In the third step, the volume of the root system is calculated by the electrical parameters, including capacitance, conductivity, and dielectric constant, which are calculated by capacitance and resistance, respectively, with the formula:

[0055]

[0056] The derivation method of formula (12) is that the polarization mechanism between the root system and the soil can be expressed as follows:

[0057]

[0058] In formula (1),

[0059] ε mi * is the complex dielectric constant of the non-uniform system;

[0060] ε m * is the complex dielectric constant of the medium;

[0061] ε i * is the complex dielectric constant of the dielectric sphere in the medium;

[0062] Φ is the volume fraction of the spherical dispersion.

[0063]

[0064] Formula (2) is a general expression of the complex dielectric constant. Wherein, ε * is the complex dielectric constant; j is the imaginary unit; ε is the real part, k / (ωε0) is the imaginary part; ε0 is the vacuum dielectric constant; k is the conductivity; ω is the angular frequency; ω=2πf; f is the frequency. Formula (2) is substituted into formula (1), and the real part is separated to obtain formula (3):

[0065]

[0066] In formula (3), ε(ω) is the real part of the dielectric constant; ε ∞ is the limit of the dielectric constant under high frequency conditions, specifically expressed as the left half of formula (4); Δε is the increase of the dielectric constant, specifically expressed as the left half of formula (5); τ is the relaxation time, specifically expressed as the left half of formula (6); Considering that the volume fraction Φ is much smaller than 1, therefore, (Φ±1) multiplied by any one parameter (γ) can be simplified as γ(Φ±1)≈γ.

[0067] Wherein: ε ∞ , Δε, τ can be calculated from the right half of (4), (5) and (6) respectively:

[0068]

[0069]

[0070]

[0071] In formula (5) and (6), k m is the medium conductivity; k i is the dielectric sphere conductivity. In order to simplify the expression, three coefficients are used to replace;

[0072] a = ε m k i - ε i k m (7)

[0073] b = 2 ε m + ε i (8)

[0074] c = 2 k m + k i (9)

[0075] Bringing formula (4) to (9) into formula (3), formula (10) can be obtained:

[0076]

[0077] From the above formula (10), in the non-uniform dispersion system, the dielectric constant of the whole system is linearly positively correlated with the volume fraction of the dispersion; assuming that a dielectric sphere composed of cells has no order of magnitude difference in conductivity with the medium conductivity, in the beta relaxation frequency range, the dielectric constant (about 10 4 ~ 10 5 ) of the biological tissue is much larger than the dielectric constant (about 10~200) of the common growth medium (such as soil, water, etc.), that is, ε m is much smaller than ε i , so a ≈ - ε i k m , b ≈ ε i .

[0078] Therefore, in the beta relaxation frequency range, the relationship between the dielectric constant of the medium and the volume fraction can be approximately formula (11):

[0079]

[0080] Replacing the dielectric sphere with the root system and replacing the medium with the soil, the relationship between the soil capacitance of the sample and the root system volume can be obtained (12):

[0081]

[0082] In equation (12), EC represents soil capacitance; RV represents root volume; d represents the distance between electrodes; EC m This represents the soil capacitance when there are no roots.

[0083] In step one, the method for obtaining the soil sample to be tested is as follows: pre-select the plant to be tested, excavate the soil around the plant to be tested according to the cross-section of the measuring box, take out the columnar soil sample containing the plant roots, and divide the soil sample into block samples to be tested along the height direction according to the height of the measuring box.

[0084] In step two, the block sample to be tested is placed in the measuring box and watered to saturate the soil moisture in the measuring box. The capacitance and resistance of the block sample are measured by electrodes placed on opposite sides inside the measuring box.

[0085] When the root growth medium is soil, it can be seen from equation (12) that, without considering the influence of root absorption on soil capacitance, soil capacitance is directly proportional to root volume. Therefore, soil capacitance under high-frequency conditions has the potential to directly measure root volume, and further has the potential to measure root size and distribution.

[0086] To verify the correctness of the above formula derivation, a root addition verification experiment was conducted. Equal amounts of washed roots (20 grams fresh weight) were added to different media, and the capacitance of the media with and without roots was measured to verify whether the addition of roots significantly affected the dielectric constant of the medium. Figure 1 The results show that when the frequency is greater than 1 kHz, the dielectric constant of the root system is much greater than that of the medium (where the horizontal axis represents the relative dielectric constant; the vertical axis represents the frequency; and SWC represents the soil moisture content), which confirms the rationality of simplifying equations (7) and (8). At the same time, the addition of roots significantly increases the dielectric constant of the medium, which verifies the hypothesis that there is potential for measuring root volume based on the dielectric capacitance.

[0087] To verify whether equations (11) and (12) are correct, we examine the root dielectric constant ε. i Root conductivity k i Dielectric constant ε m Dielectric conductivity k m Measurements were performed and the dielectric capacitance was calculated. For wheat roots, the estimation error of soil capacitance was less than 10% when the measurement frequency was between 9 and 38 kHz. Figure 2 a, Figure 2 b); For the main root of a carrot, when the frequency is greater than 100kHz, the estimation error of the dielectric capacitance is about 20%. Figure 2 c. Figure 2d). These results show that the formula we derived is applicable when the root volume fraction is small (<0.1, which is satisfied for most crop roots). In addition, as shown in Figure 3 Figure 6, the correlation between the root volume (RV) and the medium capacitance (EC) as a function of frequency further confirms this (where Figure 3 the ordinate represents the linear correlation coefficient; the abscissa represents the frequency).

[0088] Figure 2 Figure 7 shows the error between the calculated capacitance value based on the medium dielectric constant, the root dielectric constant, the medium conductivity, the root conductivity and the root volume fraction and the measured capacitance value as a function of frequency, where the abscissa represents the frequency and the ordinate represents the relative error Figure 2 a, Figure 2 c) and the average relative error Figure 2 b, Figure 2 d), Figure 2 a and Figure 2 b represent wheat roots with different volume fractions (RVD) and the medium is soil with a saturated water content; Figure 2 c and Figure 2 d represent carrot main roots with different volume fractions and the medium is distilled water; the shaded part indicates that the error between the estimated capacitance and the measured capacitance is less than 10%.

[0089] In practical applications, the implementation of the method for measuring root volume based on soil capacitance without washing can be divided into two types:

[0090] 1. When there is a good linear relationship between soil capacitance and root volume, the root volume can be directly predicted using the empirical model between the two (as in Application Example 1);

[0091] 2. When the relationship between root volume and soil capacitance is poor (e.g., the determination coefficient is less than 0.8) due to the change in the soil background value caused by root uptake, the empirical model can be calibrated using formula (12).

[0092] Application Example 1: Corn is planted in the field, and a measurement frequency of 17 kHz is used as an example.

[0093] First, soil samples with different root volumes are taken from different soil layers during the corn filling stage (root drill diameter is 10 cm, and one layer is taken every 10 cm to create soil containing different root volumes), a total of 140 samples; then, equal amounts of soil are placed in a measurement box (the measurement box has electrodes at both ends to measure capacitance); then, the soil is irrigated to saturation; finally, the capacitance at different frequencies is measured. After the operation is completed, the roots are cleaned and the root volume is measured. The relationship between soil capacitance and root volume is established using 90 measurement data to determine the values of the slope and the intercept (modeling), as shown in Figure 4a. The model was then used to calculate the root volume from the 50 additional measured soil capacitance data. Figure 4 b. The calculated root volume values agreed well with the measured root volume values (R 2 = 0.91, P < 0.0001), and the normal distribution of the residuals indicated that the errors were caused by random factors. These results indicated that the empirical relationship between soil capacitance and root volume could be used to quickly measure the root volume in soil.

[0094] Example 2: Winter wheat was planted in pots, and the measurement frequency was 100 kHz.

[0095] Measurement procedure: After the winter wheat was cultured for 44 days, the soil was saturated with water, and the soil capacitance and resistance were measured. After the measurement, the root volume was harvested and measured.

[0096] Figure 5 a. The results showed that there was a significant linear relationship between soil capacitance and root volume under pot culture conditions, but the correlation was low. This was because the absorption of the root system reduced the soil conductivity and the background capacitance. As shown in equation (12), the soil conductivity and the soil background dielectric constant can be used to calibrate the relationship between soil capacitance and root volume.

[0097] In most cases, the effects of soil properties (such as water content, ions, etc.) on soil conductivity (G) and soil capacitance (EC m ) are consistent, and the effects of the root system itself on soil conductivity can be ignored. Therefore, it is assumed that EC m ∝ G (ε m ∝ k m , k m ≈ k, k is the conductivity of the root-matrix system), G = 1 / ER (matrix resistance); in addition, it is difficult to accurately measure the root conductivity and dielectric constant in the entire soil body, and the variation is large. We combined the above relationship with equation (12) and proposed a semi-empirical equation (13) for calibrating the relationship between root volume and soil capacitance based on soil resistance:

[0098]

[0099] In the equation, RV is the root volume; EC and ER are the capacitance and resistance of the root-soil system; β1, β2, β3, β4, β5, β6, and K are fitting parameters.

[0100] After multiple tests, we fitted equation (14):

[0101] RV = β1EC x ER 2 + K (14)

[0102] As Figure 5As shown in b, the empirical relationship between soil capacitance and root volume was calibrated using Formula 14. The results showed that there was a highly significant linear relationship between the calibrated estimate of root volume and the measured root volume (R = 0.93, with a slope of 1 and no significant difference between the intercept and 0, indicating that the calibration effect was very good).

[0103] Methods for determining the optimal measurement frequency:

[0104] Since different types of root systems have different impedances at different times, their impact on dielectric capacitance (EC) also varies. Here, we provide a method for determining the optimal measurement frequency:

[0105] Before measurement, a root-planting experiment is conducted, in which a root system addition experiment is performed in the soil. The increase in soil capacitance (soil capacitance with roots minus soil capacitance without roots, then divided by soil capacitance without roots) is compared with frequency. The frequency with the largest increase can be determined as the optimal measurement frequency.

[0106] Figure 4 The relationship between capacitance and root volume of soil samples obtained from different soil layers in the field ( Figure 4 a. This figure is used for modeling, where the vertical axis represents root volume and the horizontal axis represents soil capacitance. ) and based on Figure 4 The model established in section a uses soil capacitance to estimate the root volume and compares it with the measured root volume. Figure 4 b); Figure 4 In b, the horizontal axis represents the actual measured root volume, the vertical axis represents the calculated root volume, and the dashed line represents the 1:1 line. Figure 4 c represents the residuals from modeling and the residual distribution of the model test set.

[0107] Figure 5 The relationship between soil capacitance and root volume before calibration under potted conditions is shown in (a), and the relationship between root volume estimated by the model after soil resistance calibration and measured root volume is shown in (b); the dashed line represents the 1:1 line.

Claims

1. A rapid method for determining root volume in soil, characterized in that: Includes the following steps, Step 1: Obtain the sample to be tested, including the root system and soil. Step 2: Place the sample to be tested into the measuring box and measure the sample's electrical parameters; Step 3: Using electrical parameters and root volume data, establish the relationship between root volume and electrical parameters; Step 4: Substitute the electrical parameters into the relationship established in Step 3 to calculate the root volume; In step three, the volume of the root system is calculated using electrical parameters, including capacitance and conductivity, which are calculated using the following formula: In equation (12), EC represents soil capacitance; RV represents root volume; d represents the distance between electrodes; EC m ε represents the soil capacitance when there are no roots. m ε represents the dielectric constant of the medium; i k represents the root dielectric constant. m k is the dielectric conductivity. i ε0 is the root conductivity; ε0 is the vacuum permittivity; ω is the angular frequency.

2. The method for rapid determination of root volume in soil according to claim 1, characterized in that: The derivation method of the above equation (12) is as follows: based on the properties of the interfacial polarization mechanism between the root system and the root growth medium, it can be expressed as the following equation (1): In equation (1), ε mi * For a non-uniform system, the complex permittivity is given. ε m * is the complex permittivity of the dielectric. ε i * Let be the complex permittivity of the dielectric sphere; Φ is the volume fraction of the spherical dispersion; Equation (2) is the general expression for the complex permittivity; where ε * ε is the complex permittivity; j is the imaginary unit; ε is the real part; k / (ωε0) is the imaginary part; ε0 is the vacuum permittivity; k is the conductivity; ω is the angular frequency; ω=2πf; f is the frequency; Substituting equation (2) into equation (1), we obtain equation (3) by separating the real part: In equation (3), ε(ω) is the real part of the dielectric constant; ε ∞ The limit of the dielectric constant under high frequency conditions is expressed as the left half of equation (4); ∆ε is the increase of the dielectric constant, expressed as the left half of equation (5); τ is the relaxation time, expressed as the left half of equation (6); Considering that the volume fraction Φ of the root system in the root-soil system is much less than 1, (Φ±1) multiplied by any parameter γ can be simplified to γ(Φ±1)≈γ; Where: ε ∞ ∆ε and τ can be calculated from the right halves of (4), (5) and (6) respectively: In equations (5) and (6), k m k is the dielectric conductivity. i The conductivity of the dielectric sphere; To simplify the expression, three coefficients are used instead: Substituting equations (4) to (9) into equation (3), we obtain equation (10): From equation (10) above, it can be seen that in a non-homogeneous dispersion system, the dielectric constant of the entire system is linearly positively correlated with the volume fraction of the dispersion. Assuming a dielectric sphere composed of cells, its conductivity is not orders of magnitude different from that of the medium. Within the β relaxation frequency range, the dielectric constant of biological tissue is much greater than that of the growth medium, i.e., ε m Much smaller than ε i Therefore, a≈-ε i k m b≈ε i ; Therefore, within the β relaxation frequency range, the relationship between the dielectric constant and the volume fraction of the medium can be approximated by equation (11): ε m ε represents the dielectric constant of the medium; i This represents the root dielectric constant.

3. The method for rapid determination of root volume in soil according to claim 2, characterized in that: By replacing the dielectric sphere with the root system and the medium with soil, the relationship between the soil capacitance and the root volume of the sample can be obtained (12): In equation (12), EC represents soil capacitance; RV represents root volume; d represents the distance between electrodes; EC m ε represents the soil capacitance when there are no roots. m ε represents the dielectric constant of the medium; i k represents the root dielectric constant. m k is the dielectric conductivity. i ε0 is the root conductivity; ε0 is the vacuum permittivity; ω is the angular frequency.

4. The method for rapid determination of root volume in soil according to claim 1, characterized in that: In step one, the method for obtaining the soil sample to be tested is as follows: pre-select the plant to be tested, excavate the soil around the plant to be tested according to the cross-section of the measuring box, take out the columnar soil sample containing the plant roots, and divide the soil sample into block samples to be tested along the height direction according to the height of the measuring box.

5. The method for rapid determination of root volume in soil according to claim 4, characterized in that: In step two, the block sample to be tested is placed in the measuring box and watered to saturate the soil moisture in the measuring box. The electrical parameters of the block sample are measured by electrodes placed on opposite sides inside the measuring box.

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