JP7348652B2 - Computing method, computing device, and computing program - Google Patents

Description

The present invention relates to a calculation method, a calculation device, and a calculation program.

A method for evaluating the soil moisture environment has been proposed for agricultural crops for which soil moisture management is important during cultivation, and has been put into practical use in agricultural fields. For example, Non-Patent Document 1 discloses a method of estimating a change in soil moisture (volume water content) by estimating evapotranspiration in a field from a reference evapotranspiration and a crop coefficient. Irrigation support systems utilizing the method disclosed in Non-Patent Document 1 include the soybean irrigation support system "Soywater" in Nebraska, USA, described in Non-Patent Document 2, and the cultivation management support system described in Non-Patent Document 3. It has been adopted for soybean irrigation support information.

However, to evaluate water stress and water absorption of crops, soil water tension (hereinafter referred to as "pF value") is more useful than volumetric water content. The pF value represents the force of soil pores to retain water, or the force of water in soil to remain within the pores. Since soil moisture management is extremely important in the cultivation and management of mandarin oranges, where sugar levels increase due to water stress, there is a high level of interest in soil moisture evaluation technology at public research stations that have the production areas of mandarin oranges. , development of high-quality fruit production technology through appropriate soil moisture management is underway.

The pF value can be measured using existing sensors, but the sensors are expensive and their maintenance requires effort and time. Therefore, methods for estimating the pF value are being studied. For example, Non-Patent Document 4 discloses that the amount of change in soil moisture is evaluated from weather data, and the amount of change in soil moisture is evaluated using a pF moisture characteristic curve. Non-Patent Document 5 discloses that the volumetric moisture content of soil is evaluated from the reference evapotranspiration amount, and the pF value is estimated using a pF moisture characteristic curve determined by the pressure plate method.

Allen, R.G. et al., 1997, FAO Irrigation and Drainage Paper No.56 Etsushi Kumagai et al. 2016, Agriculture and Horticulture Vol. 91, No. 6, p.608-p.617 National Agriculture and Food Research Organization Agricultural Environmental Change Research Center 2019, Cultivation Management Support System Ver. 1.0. User manual p.120-p.127 Seino, F. 1990, Soil Physics No. 61, p.11-p.18 Daio Ito et al. 2013, Agricultural meteorology in Tohoku vol. 57, p.1-p.6

In order to estimate the pF value using the methods disclosed in Non-Patent Documents 4 and 5, it is necessary to create a pF moisture characteristic curve that shows the relationship between the volumetric moisture content and the pF value. Even if the soil is of the same type, it needs to be created for each field with different physical properties.

Furthermore, to create this pF moisture characteristic curve, it is necessary to apply different methods depending on the range and size of the pF value (e.g., sand column method, pressure plate method, centrifugation method, etc.); Even the method for measuring pF values requires expensive equipment and long measurement times. For this reason, the creation of pF moisture characteristic curves can only be carried out at some research institutions that have technicians with specialized knowledge and special equipment, and it is possible to create pF moisture characteristic curves by using conventional techniques at general agricultural sites beyond research sites. is difficult to introduce.

The present invention has been made in view of the above background, and one aspect of the present invention is to easily and inexpensively measure pF value without using existing pF value sensors that are expensive and require labor and time to maintain. The purpose is to realize a method that can estimate the value.

In order to solve the above problems, a calculation method according to one aspect of the present invention calculates the measured saturated moisture content or estimated saturated moisture content according to the following (1), the measured volumetric moisture content according to the following (2), and the following ( a relational equation preparation step of preparing a relational equation indicating the relationship between the volumetric water content and the water tension value for the field of interest, determined based on the actually measured water tension value related to 3);
(1) Calculate the regression equation between the measured saturated moisture content of the soil of the field of interest, or the measured saturated moisture content of multiple soils including soil other than the soil of the field of interest, and the measured dry density of the soil. the estimated saturated moisture content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual moisture tension value measured in advance for the soil of the field of interest;
An estimated water tension value of the soil of the field of interest based on the relational equation prepared in the relational equation preparation step and the estimated volumetric moisture content of the soil of the field of interest calculated based on the meteorological data of the point where the field of interest is located. This method includes a step of calculating an estimated water tension value.

In addition, in order to solve the above-mentioned problem, a calculation device according to another aspect of the present invention includes an actual measured saturated moisture content or an estimated saturated moisture content according to (1) below, and an actual measured volumetric moisture content according to (2) below. , and a relational equation preparation unit that prepares a relational equation indicating the relationship between the volumetric water content and the water tension value for the field of interest, which is determined based on the actually measured water tension value according to (3) below;
(1) Calculate the regression equation between the measured saturated moisture content of the soil of the field of interest, or the measured saturated moisture content of multiple soils including soil other than the soil of the field of interest, and the measured dry density of the soil. the estimated saturated moisture content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual moisture tension value measured in advance for the soil of the field of interest;
An estimated water tension value of the soil of the field of interest based on the relational equation prepared in the relational equation preparation section and the estimated volumetric moisture content of the soil of the field of interest calculated based on the meteorological data of the point where the field of interest is located. This configuration includes an estimated moisture tension value calculation unit that calculates the estimated water tension value.

According to one aspect of the present invention, it is possible to estimate the pF value easily and inexpensively without using an existing pF value sensor that is expensive and requires labor and time to maintain.

3 is a flowchart illustrating an example of a calculation method according to one aspect of the present invention. 1 is a block diagram showing a main part configuration of an arithmetic device according to Embodiment 1 of the present invention. FIG. 7 is a flowchart illustrating an example of a calculation method according to another aspect of the present invention. It is a figure showing the saturated moisture content of soil having 16 types of different properties. It is a correlation diagram showing the relationship between saturated moisture content and dry density for soils having 16 types of different properties. The results of Examples of the present invention are shown, and the curves obtained from the estimated saturated water content, measured volumetric water content, and measured water tension values for field A, and the curve obtained from the equation for calculating the estimated pF value using van Genuchten's model are shown. It is a diagram. It is a figure which shows the result of the Example of this invention, and represents the result of investigating the volumetric moisture content and pF value of the soil of the bare area of field A over time. It is a figure which shows the result of the Example of this invention, and represents the result of investigating the volumetric water content and pF value of the soil of the mulch area of field A over time.

[Calculation method]
The calculation method according to one aspect of the present invention is based on the measured saturated moisture content or estimated saturated moisture content according to (1) below, the measured volumetric moisture content according to (2) below, and the measured water tension value according to (3) below. a relational expression preparation step of preparing a relational expression indicating the relationship between the volumetric moisture content and the water tension value for the field of interest, determined based on the
(1) Calculate the regression equation between the measured saturated moisture content of the soil of the field of interest, or the measured saturated moisture content of multiple soils including soil other than the soil of the field of interest, and the measured dry density of the soil. the estimated saturated moisture content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual moisture tension value measured in advance for the soil of the field of interest;
An estimated water tension value of the soil of the field of interest based on the relational equation prepared in the relational equation preparation step and the estimated volumetric moisture content of the soil of the field of interest calculated based on the meteorological data of the point where the field of interest is located. This configuration includes an estimated moisture tension value calculation step of calculating the estimated water tension value.

In the calculation method according to one aspect of the present invention, the first soil of the field of interest is calculated based on the measured volumetric water content and meteorological data of the point where the field of interest is located at the time when the measured volumetric water content is measured. a crop coefficient preparation step of preparing a crop coefficient for the field of interest determined based on the estimated standard evapotranspiration;
a second estimated standard evapotranspiration calculation step of calculating a second estimated standard evapotranspiration of the soil of the field of interest based on meteorological data at the point where the field of interest is located at the time of calculating the water tension value;
Based on the second estimated standard evapotranspiration calculated in the second estimated standard evapotranspiration calculation step and the crop coefficient prepared in the crop coefficient preparation step, calculate the estimated actual evapotranspiration of the field of interest. An estimated actual evapotranspiration calculation step;
further comprising an estimated volumetric water content calculation step of calculating an estimated volumetric water content of soil in the field of interest based on the estimated actual evapotranspiration calculated in the estimated actual evapotranspiration calculation step,
The estimated volumetric water content calculated in the estimated volumetric water content calculation step may be used in the estimated water tension value calculation step.

Here, a calculation method according to one aspect of the present invention will be described using FIGS. 1 and 2. FIG. 1 is a flowchart illustrating an example of a calculation method according to an aspect of the present invention, and FIG. 2 is a block diagram illustrating an example of a calculation device that executes the processing shown in the flowchart.

First, in step S101, the relational expression preparation unit 11 calculates the measured saturated water content or estimated saturated water content according to (1) below, the measured volumetric water content according to (2) below, and the measured water tension according to (3) below. Prepare a relational expression that indicates the relationship between the volumetric water content and water tension value for the field of interest determined based on the values (relational equation preparation step):
(1) Calculate the regression equation between the actually measured saturated moisture content of the soil of the field of interest, or the actually measured saturated moisture content of a plurality of soils including soil other than the soil of the field of interest, and the actually measured dry density of the soil. the estimated saturated water content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual water tension value measured in advance for the soil of the field of interest.

Specifically, the relational expression indicating the relationship between the volumetric water content and the water tension value (hereinafter also referred to as "pF value") for the focused field is obtained from the relational expression database (DB) 4, and the Prepare the above relational expression. The relational expression preparation section 11 supplies the obtained relational expression to the estimated water tension value calculation section 14.

The data of the relational expression (hereinafter referred to as "estimated pF value calculation formula") indicating the relationship between the volumetric moisture content and the pF value for the field of interest is stored in a database such as the relational expression DB4, for example. . The relational expression DB4 may store data on formulas for calculating estimated pF values for a plurality of types of fields, including formulas for calculating estimated pF values for the field of interest. In the relational equation preparation step, the relational equation preparation unit 11 acquires data of the equation for calculating the estimated pF value for the field of interest from the relational equation DB 4 as needed, thereby preparing the equation for calculating the estimated pF value for the field of interest. Prepare. The relational expression DB4 may be stored on the hard disk of the arithmetic device 1 or may be stored on a server.

A formula for calculating the estimated pF value for the field of interest is determined in advance based on the actually measured saturated moisture content or the estimated saturated moisture content, the actually measured volumetric moisture content, and the actually measured pF value. The value of the saturated water content used to determine the formula for calculating the estimated pF value for the field of interest may be the actually measured saturated water content, or may be the estimated saturated water content, which is the estimated value.

Here, the "actually measured saturated moisture content" is an actually measured value of the saturated moisture content of soil. To determine the saturated moisture content of soil, for example, measure the saturated weight (g) and dry weight (g) of 100 ml of soil collected with a sampling tube, and calculate the saturated moisture content (%) from the following formula (1). be able to. The method for measuring the "actually measured saturated water content" is not limited to this method.

The "estimated saturated moisture content" is determined by using a regression equation between the actually measured saturated moisture content of a plurality of soils, including soils other than the soil in the field of interest, and the measured dry density of the soil. This is a value calculated from the measured value of the actually measured dry density. The "measured dry density" is an actual value of the dry density of soil. The above-mentioned "dry density" represents the dry weight of soil per fixed volume. The dry density of soil can be measured, for example, by the method shown in the Examples below.

As will be specifically explained in the examples below, the present inventors found that the saturated moisture content and dry density of soil are correlated, and developed a regression equation showing the relationship between the saturated moisture content and dry density. By using this method, it was revealed that the saturated moisture content can be estimated based on the dry density of soil. Conventional methods for measuring saturated moisture content involve many steps, and it takes time and effort to obtain saturated moisture content. On the other hand, dry density can be easily determined by simply measuring the weight of soil before and after drying per fixed volume. Therefore, by calculating the saturated moisture content based on the actually measured dry density of the soil using a regression equation that shows the relationship between the saturated moisture content and the dry density, the saturated moisture content can be calculated simply by measuring the dry density of the soil. It can be estimated easily and quickly.

The "measured volumetric moisture content" is an actual measured value of the volumetric moisture content of soil. The volumetric moisture content of soil can be measured using, for example, an existing moisture sensor, soil moisture meter, or the like.

The "actually measured pF value" is the actually measured pF value of soil. The pF value of soil can be measured using, for example, an existing tensiometer, pF sensor, or the like. As will be specifically explained in the examples described below, according to the calculation method according to one aspect of the present invention, the pF value measured using a tensiometer can be suitably used to create the calculation formula for the estimated pF value. I can do it. Then, the pF value can be estimated with high accuracy using the formula for calculating the estimated pF value created in this way. Tensiometers are more preferable than existing expensive pF sensors because they are easier to obtain and can be easily handled even by non-researchers.

Specifically, the "formula for calculating the estimated pF value" is based on van Genuchten's model (Reference 1: van Genuchten, M. Th. 1980, Soil Sci. Soc. Am. J., VOL. 44:892- The formula for calculating the estimated pF value according to (898) is the following formula (2):

(In the above formula (2), Se is the relative moisture content expressed by the following formula (3).

In the formula (3), θ represents the volumetric water content, θs represents the saturated water content, and θr represents the residual water content. ).

Parameters α, n, m, and θr in the equation for calculating the estimated pF value are determined based on the actually measured saturated moisture content or the estimated saturated moisture content, the actually measured volumetric moisture content, and the actually measured pF value. Specifically, a curve obtained from the measured saturated water content or the estimated saturated water content, the measured volumetric water content, and the measured pF value, and the calculated formula for the estimated pF value include the measured saturated water content or the estimated pF value. The values of each parameter in the equation for calculating the estimated pF value may be adjusted so that the curve obtained by substituting the estimated saturated water content and the measured volumetric water content match.

The data sets of the measured volumetric moisture content and the measured pF value used to determine the formula for calculating the estimated pF value for the field of interest are the data sets of the measured volumetric moisture content and the measured pF value, respectively, for the soil of the field of interest under different moisture conditions ranging from a wet state to a dry state. Just get it. For example, several sets (for example, 3 to 4 Point) Just measure it. The number of sets of measured data of the measured volume water content and the measured pF value is not particularly limited, but reliable data can be obtained by obtaining at least two or more points.

The relational expression preparation unit 11 may accept an instruction or input from a user via an input unit (not shown) to start the process of step S101, or may periodically execute the process of step S101 at preset intervals. You may start. The "instruction or input by the user" may be, for example, the name of the field of interest, the position information of the field of interest, the date and time of calculation of the pF value, etc.

Next, in step S102, the crop coefficient preparation unit 12 calculates the first estimate of the soil of the field of interest calculated based on the measured volumetric water content and the meteorological data of the point where the field of interest is located at the time when the measured volumetric water content is measured. A crop coefficient for the field of interest determined based on the standard evapotranspiration is prepared (crop coefficient preparation step). Specifically, the crop coefficient preparation unit 12 prepares crop coefficients for the field of interest by acquiring crop coefficients for the field of interest from the crop coefficient database (DB) 3. The crop coefficient preparation unit 12 supplies the acquired crop coefficients to the parameter calculation unit 13.

The crop coefficient data for the field of interest is stored in a database such as crop coefficient DB3, for example. The crop coefficient DB3 may store data on crop coefficients of a plurality of types of fields, including the crop coefficient for the field of interest. In the crop coefficient preparation step, the crop coefficient preparation unit 12 prepares crop coefficients for the field of interest by acquiring crop coefficient data for the field of interest from the crop coefficient DB 3 as necessary. The crop coefficient DB3 may be stored in the hard disk of the arithmetic device 1, or may be stored on the server.

The crop coefficient for the field of interest is the first estimated standard evaporation of the soil of the field of interest, which is calculated based on the measured volumetric moisture content and the meteorological data of the point where the field of interest is located at the time when the measured volumetric moisture content is measured. It is determined in advance based on the amount of dispersion.

Here, the "actually measured volumetric water content" is the measured volumetric water content used when determining the calculation formula for the estimated pF value in the above-mentioned relational equation preparation step.

The "first estimated standard evapotranspiration" is the estimated standard evapotranspiration of the soil of the field of interest, which is calculated based on the meteorological data of the point where the field of interest is located at the time when the actual volumetric water content is measured. The "standard evapotranspiration" represents the standard value (mm) of potential evapotranspiration (Non-Patent Document 3: National Agriculture and Food Research Organization Agricultural Environmental Change Research Center 2019, Cultivation Management Support System Ver. 1.0. User's Manual p.120-p.127). In the FAO guidelines on irrigation (Non-patent Document 1: Allen, R.G. et al., 1997, FAO Irrigation and Drainage Paper No. 56, commonly known as "FAO-56"), it is described as Reference evapotranspiration (ETo).

As a method for calculating the standard evapotranspiration amount from meteorological data, for example, a method using the Priestly-Taylor method (PT method) using the following formula (4) can be mentioned.

(In the above formula (4), s: slope of the saturated water vapor pressure curve, γ: psychrometer constant, G: underground heat transfer amount, Rn: net radiation amount.)
Each coefficient of this model formula (4) (net radiation amount, psychrometer constant, slope of saturated water vapor pressure curve) can be calculated from the air temperature and the amount of solar radiation using the formula described in FAO-56. The amount of underground heat transfer can be ignored. FAO-56 recommends evapotranspiration by the Penman-Monteith method (PM method) as the standard evapotranspiration, but (i) the PM method requires wind speed data, and (ii) the PT method It has been reported that radiation methods such as the above yield good results in humid climates, and (iii) that the PT method was closest to observed values compared to other methods, including the PM method. Douglas et al. 2009, J Hydrology 373) Therefore, it is preferable to calculate the standard evapotranspiration using the PT method.

In addition, as another method for calculating standard evapotranspiration from meteorological data, it is possible to use, for example, the farmland environment estimation system provided by the West Japan Agricultural Research Center (Reference 2: "A farmland environment estimation system that estimates precise weather data from AMeDAS etc.", West Japan Agricultural Research Center 2017 Research results information; Reference 3: Ueyama et al. 2018, Biology and Weather, vol. 18, p. 76-p. 85) . According to the farmland environment estimation system, meteorological data of the target area (daily maximum temperature, daily minimum temperature, daily average temperature, daily average relative humidity, daily cumulative solar radiation, daily It is possible to obtain the cumulative precipitation amount, daily cumulative precipitation amount up to the relevant time, 6 hours ahead precipitation amount, and daily cumulative standard evapotranspiration amount.

The meteorological data used to calculate the first estimated standard evapotranspiration include, for example, daily maximum temperature, daily minimum temperature, daily cumulative solar radiation, wind speed, etc. Preferably, a combination of amounts is used. From the combination of daily maximum temperature, daily minimum temperature, and daily cumulative solar radiation, the shortwave radiation balance (difference between downward shortwave radiation and upward shortwave radiation) and longwave radiation balance ( The difference between the amount of downward longwave radiation and the amount of upward longwave radiation) can be estimated. Estimating formulas for the shortwave radiation budget and longwave radiation budget can be calculated using the formulas described in FAO-56. The shortwave radiation budget is calculated from the albedo, which is the reflectance of the solar radiation on the ground surface, and the daily cumulative solar radiation. The longwave radiation budget is calculated from daily maximum temperature, daily minimum temperature, daily cumulative solar radiation, water vapor pressure (estimated from daily maximum temperature and daily minimum temperature), and clear-sky solar radiation (estimated from altitude and extraatmospheric solar radiation). In these estimation formulas, it is also possible to use actually measured values instead of estimated values. Adoption of the FAO-56 estimation formula is practical because the net radiation amount can be calculated using only general meteorological data such as daily maximum temperature, daily minimum temperature, and daily integrated solar radiation. Although an example has been described in which the first estimated standard evapotranspiration is calculated from weather data, the first estimated standard evapotranspiration can also be calculated based on the amount of rainfall or the amount of irrigation.

The "crop coefficient" is a coefficient unique to each crop, and varies depending on the growth stage. In FAO-56, it is explained as Crop coefficient (Kc). The "crop coefficient" can be calculated by calculating the actual evapotranspiration from the measured volumetric water content and dividing the obtained actual evapotranspiration by the first estimated standard evapotranspiration.

Next, in step S103, the parameter calculation unit 13 receives meteorological data at the point where the field of interest is located from the meteorological data measuring device 2.

Next, in step S104, the parameter calculation unit 13 calculates the second estimation standard evapotranspiration of the soil of the field of interest based on the meteorological data of the point where the field of interest exists at the time of water tension value calculation (second estimation standard Evapotranspiration calculation process). Specifically, the parameter calculation unit 13 calculates the second estimated standard evapotranspiration of the soil in the field of interest based on the meteorological data acquired in step S103.

The "second estimated standard evapotranspiration" is the estimated standard evapotranspiration of the soil of the field of interest, which is calculated based on the meteorological data of the point where the field of interest is located at the time of calculating the pF value. The method of calculating the reference evapotranspiration of the field of interest from meteorological data was explained in the section of "Crop coefficient preparation process" above, but there are calculation methods using the PT method and the farmland environment provided by the West Japan Agricultural Research Center. Estimation systems can be used. Note that the second estimated standard evapotranspiration can also be calculated based on the amount of rainfall or the amount of irrigation, similarly to the first estimated standard evapotranspiration.

Next, in step S105, the parameter calculation unit 13 calculates the target field based on the second estimated standard evapotranspiration calculated in the second estimated standard evapotranspiration calculation step and the crop coefficient prepared in the crop coefficient preparation step. Calculate the estimated actual evapotranspiration of (estimated actual evapotranspiration calculation step). Specifically, the parameter calculation unit 13 calculates the estimated actual evapotranspiration of the field of interest based on the second estimated reference evapotranspiration calculated in step S104 and the crop coefficient acquired in step S102.

The above-mentioned "actual evapotranspiration" represents the estimated value (mm) of actual evapotranspiration taking into account the growth stage of the crop and the dryness of the cultivated soil (Non-Patent Document 3: National Agriculture and Food Research Organization, Agricultural Environmental Change Research Center) 2019, Cultivation Management Support System Ver. 1.0. User Manual p.120-p.127). In FAO-56, it is explained as Crop evapotranspiration under non-standard conditions (ETc adj).

The estimated actual evapotranspiration of the field of interest can be calculated by multiplying the second estimated standard evapotranspiration calculated in step S104 by the crop coefficient obtained in step S102 (non-representative evapotranspiration). (See Patent Document 1).

Next, in step S106, the parameter calculation unit 13 calculates the estimated volumetric water content of the soil in the field of interest based on the estimated actual evapotranspiration calculated in the estimated actual evapotranspiration calculation step (estimated volumetric water content calculation step). ). Specifically, the parameter calculation unit 13 calculates the estimated volumetric moisture content of the soil in the field of interest based on the estimated actual evapotranspiration calculated in step S105. The parameter calculation unit 13 supplies the calculated estimated volume water content to the estimated water tension value calculation unit 14.

Specifically, as a method for calculating the estimated volumetric water content, first, when the pF measurement target day is day t, the estimated actual evapotranspiration calculated in step S105 from the precipitation amount (mm) in the field of interest on day t. By subtracting (mm), the amount of increase in soil moisture (mm) in the surface layer of the field of interest on day t is calculated. Next, the increase in soil moisture in the surface layer of the field of interest on day t is divided by the thickness (mm) of the surface layer of the field of interest, and this is calculated as the volumetric water content of the day before the pF measurement target day (day t-1). By adding, the estimated volumetric water content on day t can be calculated.

Next, in step S107, the estimated water tension value calculation unit 14 uses the relational expression prepared in the relational expression preparation step and the estimated volumetric moisture content of the soil of the focused field calculated based on the meteorological data of the point where the focused farm exists. Based on this, the estimated water tension value of the soil in the field of interest is calculated (estimated water tension value calculation step). Specifically, the estimated water tension value calculation unit 14 calculates the estimated pF value of the soil in the field of interest based on the relational expression obtained in step S101 and the estimated volumetric water content calculated in step S106. The estimated water tension value calculation unit 14 supplies data of the calculated estimated pF value to the output control unit 16.

Next, in step S108, the output control unit 16 outputs the acquired estimated pF value data. The output control unit 16 may output the estimated pF value of the soil of the field of interest calculated in step S107 to an external display device such as a display, a smartphone, or a tablet terminal via communication such as the Internet. Thereby, the user can grasp the estimated pF value of the soil of the field of interest displayed on the display device. The obtained estimated pF value can be used for quality control of agricultural products, such as determining the timing of irrigation. It is said that there is a relationship between fruits with high sugar content and pF values, and understanding pF values is important in quality control of agricultural products.

According to the calculation method according to one aspect of the present invention, the pF value can be estimated easily and inexpensively without using existing pF value sensors that are expensive and require labor and time to maintain. In general agricultural fields, it becomes possible to realize advanced cultivation management based on soil moisture data such as pF values.

Further, according to the calculation method according to one aspect of the present invention, if the volumetric moisture content and the pF value are measured when determining the calculation formula for the estimated pF value for the field of interest, the pF value is not measured thereafter. Both methods have the advantage that the pF value can be estimated from weather data using the formula for calculating the estimated pF value for the field of interest. Further, the volumetric water content and pF value used to determine the formula for calculating the estimated pF value can be easily measured with an inexpensive measuring device such as a moisture sensor or a tensiometer, and do not require an expensive sensor. Furthermore, the calculation method according to one aspect of the present invention has an excellent effect in that it becomes possible to estimate pF values of pF2.7 or more, which could not be measured with conventional tensiometers.

(Variation example of calculation method)
The calculation method according to another aspect of the present invention includes a soil moisture change amount estimation step of estimating the amount of soil moisture change in the field of interest based on the estimated pF value calculated by the estimated water tension value calculation step. It is good also as a structure which further includes.

With this configuration, it is possible to estimate the amount of change in soil moisture in the field of interest based on the pF value, so it is possible to achieve advanced cultivation management according to changes in the estimated pF value.

A calculation method according to another aspect of the present invention will be described using FIGS. 2 and 3. FIG. 3 is a flowchart illustrating an example of a calculation method according to another aspect of the present invention. In this modification, instead of outputting the data of the estimated pF value calculated in step S107 in step S108, the amount of change in soil moisture in the field of interest is estimated based on the estimated pF value calculated in step S107 (step S301 ), the calculation method is different from the calculation method shown in FIG. 1 in that the estimated moisture change amount is output (step S302). Therefore, step S301 and step S302 will be explained, and the explanation of the other steps S101 to S107 will be omitted.

In step S301, the soil moisture estimation unit 15 estimates the amount of change in soil moisture in the field of interest based on the estimated pF value calculated in step S107. The soil moisture amount estimating section 15 supplies the data of the moisture change amount estimation result to the output control section 16.

Next, in step S302, the output control unit 16 outputs the obtained data of the moisture change amount estimation result to a display device (not shown). As a method for estimating the amount of change in soil moisture in the field of interest, as shown in the example described later, the pF value is estimated and recorded over time to determine how the moisture content of the soil in the field of interest changes. It is possible to estimate whether

[Arithmetic device]
The calculation method according to each aspect of the present invention can be implemented by the calculation device 1. A calculation device according to one aspect of the present invention will be described below. However, regarding content that overlaps with the content explained in the above-mentioned calculation method, the explanation will not be simplified or repeated.

FIG. 2 is a block diagram showing the main part configuration of the arithmetic device 1 according to the first embodiment of the present invention. As shown in FIG. 2, the calculation device 1 includes a relational expression preparation section 11, a crop coefficient preparation section 12, a parameter calculation section 13, an estimated moisture tension value calculation section 14, a soil moisture content estimation section 15, and an output control section 16. ing. The calculation device 1 is a device that calculates the estimated pF value of the soil in the field of interest. The arithmetic device 1 includes, for example, an arithmetic unit (a processor, a CPU (Central Processing Unit), etc.) and a storage unit (a main memory such as a RAM, a storage such as an HDD/SDD, a register, a cache memory, etc.). The storage unit may store data necessary for each process, such as data acquired from a database (DB). The arithmetic device 1 may further include an input unit (not shown) that accepts instructions from the user.

The arithmetic device 1 is wirelessly or wired connected to a weather data measuring device 2, a crop coefficient database 3 (hereinafter referred to as "crop coefficient DB3"), and a relational expression database 4 (hereinafter referred to as "relational expression DB4").

The meteorological data measuring device 2 measures meteorological data at a point where the field of interest is located. The crop coefficient DB3 stores data on one or more crop coefficients including at least the crop coefficient of the field of interest. The relational expression DB4 stores data on one or more relational expressions including a relational expression indicating the relationship between the volumetric water content and the pF value for at least the field of interest. Further, although not shown, the arithmetic device 1, the weather data measurement device 2, the crop coefficient DB3, and the relational expression DB4 are equipped with a communication section or a connection section for realizing wireless connection or wired connection.

The relational expression preparation unit 11 prepares the relational expression for the field of interest by acquiring from the relational expression DB 4 a relational expression indicating the relationship between the volumetric water content and the pF value for the field of interest. Specifically, the relational expression preparation unit 11 performs the process of step S101 in FIG. 1 or 3. Further, the relational expression preparation section 11 supplies the obtained relational expression for the field of interest to the estimated water tension value calculation section 14.

The crop coefficient preparation unit 12 prepares crop coefficients for the field of interest by acquiring crop coefficients for the field of interest from the crop coefficient DB3. Specifically, the crop coefficient preparation unit 12 performs the process of step S102 in FIG. 1 or 3. Further, the crop coefficient preparation unit 12 supplies the acquired crop coefficients for the field of interest to the parameter calculation unit 13.

The parameter calculation unit 13 calculates the estimated standard evapotranspiration, estimated actual evapotranspiration, and estimated volumetric water content of the soil of the field of interest. Specifically, the parameter calculation unit 13 performs the processes from step S103 to step S106 in FIG. 1 or 3. In order to calculate these parameters, the parameter calculation unit 13 acquires meteorological data at the point where the field of interest is located from the meteorological data measuring device 2, and acquires crop coefficients for the field of interest from the crop coefficient preparation unit 12. Further, the parameter calculation section 13 supplies the calculated estimated volumetric water content to the estimated water tension value calculation section 14 .

The estimated water tension value calculation unit 14 acquires the estimated pF value calculation formula for the field of interest from the relational expression preparation unit 11, and calculates the estimated pF value from the estimated volumetric water content using the estimated pF value calculation formula. . Specifically, the estimated water tension value calculation unit 14 performs the process of step S107 in FIG. 1 or 3. Furthermore, the estimated water tension value calculation section 14 supplies the calculated estimated pF value to the soil moisture content estimation section 15.

The soil moisture estimation unit 15 estimates the amount of change in soil moisture in the field of interest based on the estimated pF value. Specifically, the soil moisture amount estimating unit 15 performs the process of step S301 in FIG. 3.

The output control unit 16 controls the output of the calculation result from the calculation device 1. Specifically, the soil moisture amount estimating unit 15 performs the process of step S108 in FIG. 1 or step S302 in FIG. 3. The output control unit 16 may display the calculation results from the calculation device 1 on a display device (not shown) connected wirelessly or wired to the calculation device 1, or may display data of the calculation results from the calculation device 1. may be output. The calculation results include the numerical value of each parameter calculated by the parameter calculation unit 13, the estimated pF value calculated by the estimated water tension value calculation unit 14, and the amount of moisture change estimated by the soil moisture content estimation unit 15.

[Example of implementation using software]
The control blocks of the arithmetic device 1 (especially the relational expression preparation section 11, the crop coefficient preparation section 12, the parameter calculation section 13, the estimated water tension value calculation section 14, the soil moisture content estimation section 15, and the output control section 16) are integrated circuits ( It may be realized by a logic circuit (hardware) formed on an IC chip, etc., or it may be realized by software.

In the latter case, the arithmetic device 1 includes a computer that executes instructions of a program that is software that implements each function. This computer includes, for example, one or more processors and a computer-readable recording medium storing the program. Then, in the computer, the processor reads the program from the recording medium and executes it, thereby achieving the object of the present invention. As the processor, for example, a CPU (Central Processing Unit) can be used. As the recording medium, in addition to "non-temporary tangible media" such as ROM (Read Only Memory), tapes, disks, cards, semiconductor memories, programmable logic circuits, etc. can be used. Further, the computer may further include a RAM (Random Access Memory) for expanding the program. Further, the program may be supplied to the computer via any transmission medium (communication network, broadcast wave, etc.) that can transmit the program. Note that one aspect of the present invention can also be realized in the form of a data signal embedded in a carrier wave, in which the program is embodied by electronic transmission.

〔summary〕
The calculation method according to aspect 1 of the present invention is based on the actually measured saturated moisture content or estimated saturated moisture content according to the following (1), the actually measured volumetric moisture content according to the following (2), and the actually measured water tension value according to the following (3). a relational expression preparation step of preparing a relational expression indicating the relationship between the volumetric moisture content and the water tension value for the field of interest, determined based on the
(1) Calculate the regression equation between the measured saturated moisture content of the soil of the field of interest, or the measured saturated moisture content of multiple soils including soil other than the soil of the field of interest, and the measured dry density of the soil. the estimated saturated moisture content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual water tension value measured in advance for the soil of the field of interest;
An estimated water tension value of the soil of the field of interest based on the relational equation prepared in the relational equation preparation step and the estimated volumetric moisture content of the soil of the field of interest calculated based on the meteorological data of the point where the field of interest is located. This method includes a step of calculating an estimated water tension value.

In the calculation method according to aspect 2 of the present invention, in aspect 1, the attention field is calculated based on the actually measured volumetric moisture content and the meteorological data of the point where the attention field is located at the time when the actual volumetric moisture content is measured. a crop coefficient preparation step of preparing a crop coefficient for the field of interest determined based on a first estimated standard evapotranspiration of soil in the field;
a second estimated standard evapotranspiration calculation step of calculating a second estimated standard evapotranspiration of the soil of the field of interest based on meteorological data at the point where the field of interest is located at the time of calculating the water tension value;
Based on the second estimated standard evapotranspiration calculated in the second estimated standard evapotranspiration calculation step and the crop coefficient prepared in the crop coefficient preparation step, calculate the estimated actual evapotranspiration of the field of interest. An estimated actual evapotranspiration calculation step;
further comprising an estimated volumetric water content calculation step of calculating an estimated volumetric water content of soil in the field of interest based on the estimated actual evapotranspiration calculated in the estimated actual evapotranspiration calculation step,
The estimated volumetric water content calculated in the estimated volumetric water content calculation step may be used in the estimated water tension value calculation step.

The calculation method according to aspect 3 of the present invention may be a method in which in aspect 1 or 2, the weather data is daily maximum temperature, daily minimum temperature, and daily cumulative solar radiation.

The calculation method according to aspect 4 of the present invention is, in any one of aspects 1 to 3, based on the estimated moisture tension value calculated in the estimated moisture tension value calculation step, the amount of change in soil moisture in the field of interest. The method may further include a step of estimating the amount of soil moisture change.

The computing device according to aspect 5 of the present invention calculates the measured saturated moisture content or estimated saturated moisture content according to (1) below, the measured volumetric moisture content according to (2) below, and the measured water tension value according to (3) below. a relational equation preparation unit that prepares a relational equation that indicates the relationship between the volumetric moisture content and the water tension value for the field of interest, which has been determined based on the
(1) Calculate the regression equation between the measured saturated moisture content of the soil of the field of interest, or the measured saturated moisture content of multiple soils including soil other than the soil of the field of interest, and the measured dry density of the soil. the estimated saturated moisture content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual moisture tension value measured in advance for the soil of the field of interest;
An estimated water tension value of the soil of the field of interest based on the relational equation prepared in the relational equation preparation section and the estimated volumetric moisture content of the soil of the field of interest calculated based on the meteorological data of the point where the field of interest is located. This configuration includes an estimated moisture tension value calculation unit that calculates the estimated water tension value.

The arithmetic device according to each aspect of the present invention may be realized by a computer, and in this case, the arithmetic device is realized by the computer by operating the computer as each section (software element) included in the arithmetic device. An arithmetic program for an arithmetic device and a computer-readable recording medium on which it is recorded also fall within the scope of the present invention.

The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. are also included within the technical scope of the present invention.

The present invention will be described in more detail below based on Examples, but the present invention is not limited to these Examples.

[Preliminary investigation on the relationship between saturated moisture content and dry density]
The inventors of this application have published the physical property database of agricultural soil in Japan, SolphyJ (Reference document 4: Main research results of 2010, Agricultural Environmental Change Research Center, National Agriculture and Food Research Organization (NARO), [searched on January 28, 2020], Internet < We focused on data on soil saturated moisture content and dry density, which is included in URL: https://www.naro.affrc.go.jp/archive/niaes/sinfo/result/result27/result27_60.html＞) . FIG. 4 is a graph showing the saturated moisture content of soils having 16 different properties recorded in SolphyJ (number of data N=706).

Therefore, for 689 soil samples out of 706 soil samples shown in Figure 4, the relationship between saturated moisture content and dry density is shown in the correlation diagram in Figure 5. The plots shown are almost on a straight line, and it is clear that there is a high correlation between the dry density and saturated moisture content of the soil. Then, the following regression equation (5) was obtained by regression analysis of the saturated water content and dry density of the soil.
Saturated moisture content (%) = -0.359 x dry density + 0.972... (5)
Conventional methods for measuring saturated moisture content involve many steps, and it takes time and effort to obtain saturated moisture content. On the other hand, it has become clear that by using the regression equation showing the relationship between saturated moisture content and dry density, it is possible to easily and quickly estimate the saturated moisture content simply by measuring the dry density.

[Example 1]
A citrus field (hereinafter referred to as "Field A") at the Shikoku Research Center of the National Agriculture and Food Research Organization, an independent administrative agency, was selected as a field of interest, and the amount of soil moisture change in Field A was estimated.

[Preliminary investigation procedure]
As a preliminary investigation to estimate the amount of soil moisture change in field A, the parameters and crop coefficients of the formula for calculating the estimated pF value for field A were determined using the following steps (A) to (E).

<(A) Measurement of volumetric moisture content and pF value of soil in field A>
The volumetric water content and pF value of soil in field A (mulched area or bare area) were measured under different moisture conditions ranging from wet to dry conditions, and three to four data sets were obtained.

The volumetric moisture content was measured using a moisture sensor (manufactured by A.R.P. Co., Ltd., model number WD-3-W-5Y). The pF value was measured using a tensiometer (manufactured by Takemura Electric Co., Ltd., model number DM-8HG-100). The moisture condition was set to a degree of dryness (pF of about 2.7 or less) that could be measured by a tensiometer. At the same time as measuring the volumetric water content and pF value, the standard evapotranspiration of the soil in field A was also observed.

<(B) Calculation of dry density of soil in field A>
100 ml of soil collected with a soil collecting tube (100 ml) was dried, and the dry density (g/cm ³ ) was calculated from the dry weight. As a result, the measured dry density of the mulch area in field A was 1.432 g/cm ³ , and the measured dry density of the bare area of field A was 1.638 g/cm ³ .

<(C) Calculation of saturated moisture content of field A>
The following regression equation showing the relationship between the measured dry density obtained in (B) above and the saturated moisture content and dry density prepared in the section "Preliminary investigation on the relationship between saturated moisture content and dry density" (5), the saturated moisture content (estimated saturated moisture content) of the soil in field A was calculated.
Saturated moisture content (%) = -0.359 x dry density + 0.972... (5)
As a result, the estimated saturated moisture content of the mulched area of field A was 0.458 (45.8%), and the estimated saturated moisture content of the bare area of field A was 0.384 (38.4%). The actual measured values of the saturated moisture content were 43.1% in the mulch area and 36.1% in the bare area, and there was no large discrepancy between the estimated saturated moisture content calculated using regression equation (5) and the actual value. It did not occur. From this, it has been proven that the estimated saturated moisture content of soil can be easily and accurately estimated from the following regression equation (5) showing the relationship between saturated moisture content and dry density and the measured dry density.

<(D) Preparation of formula for calculating estimated pF value for field A>
A curve obtained from the estimated saturated water content obtained in the above (C), the measured volume water content obtained in the above (A), and the measured water tension value obtained in the above (A) (solid line graph shown in FIG. 6) ) and the calculation formula for the estimated pF value (the following formula The parameters in the equation for calculating the estimated pF value are adjusted so that the curve (broken line graph shown in FIG. 6) obtained by substituting the estimated saturated water content and the measured volume water content into (2)) matches the curve obtained by substituting the estimated saturated water content and the measured volumetric water content. It was determined. The solid line graph shown at 1061 in FIG. 6 represents the curve obtained from the estimated saturated water content, the measured volume water content, and the measured water tension value of the multi plot in field A, and the solid line graph shown at 1062 in FIG. , represents a curve obtained from the estimated saturated water content, measured volumetric water content, and measured water tension value of the bare area of field A.

(In the above formula (2), Se is the relative moisture content expressed by the following formula (3).

In the above formula (3), θ represents the volumetric water content, θs represents the saturated water content, and θr represents the residual water content. )
As a result, the parameters in the equation for calculating the estimated pF value for the multi-section of field A were determined to be α: 0.32, θr: 0.05, n: 1.32, and m: 0.242. Furthermore, the parameters in the formula for calculating the estimated pF value for the bare area of field A were determined to be α: 0.15, θr: 0.09, n: 1.35, and m: 0.259.

Based on the above results, the formula for calculating the estimated pF value for the multi plot in field A was determined to be the following formula (6).

(In the above formula (6), Se is the relative moisture content expressed by the following formula (7).)

In addition, the formula for calculating the estimated pF value for the bare area of field A was determined to be the following formula (8).

(In the above formula (8), Se is the relative moisture content expressed by the following formula (9).)

<(E) Preparation of crop coefficients for field A>
Based on the actual volumetric moisture content of the soil in field A measured in (A) above and the standard evapotranspiration (first estimated standard evapotranspiration) determined from the meteorological data at the point where field A is located, the crops for field A are determined. The coefficient was calculated. In order to obtain numerical values that can be applied even under different moisture conditions, the crop coefficient was calculated as the average value of observed values for 28 days without rain, rather than data for one day. However, if this method is used by extension workers in actual agricultural fields rather than for research purposes, the crop coefficient should be calculated as the average value of observed values over several days (or several locations) with different soil dryness conditions. Bye.

Calculation of standard evapotranspiration from meteorological data was performed using the farmland environment estimation system provided by the West Japan Agricultural Research Center (Reference 2: "Estimating precise meteorological data for hilly and mountainous areas from AMeDAS etc." "Farmland Environment Estimation System", West Japan Agricultural Research Center 2017 Research Results Information). As meteorological data, the daily maximum temperature, daily minimum temperature, and daily cumulative solar radiation at the point where field A exists, which were observed when measuring the actual volumetric water content in (A) above, were used. The net radiation amount was calculated using the FAO-56 formula from the actual measured values of daily maximum temperature, daily minimum temperature, and daily integrated solar radiation. As a result, the first estimated standard evapotranspiration amount was 1.58 mm/day for both the mulch area and the bare area in field A. Furthermore, the measured volumetric moisture content of the mulched area of field A was 11.9%, and the measured volumetric moisture content of the bare area of field A was 17.5%.

The crop coefficient was calculated by calculating the actual evapotranspiration from the measured volumetric water content measured in (A) above, and dividing the obtained actual evapotranspiration by the first estimated standard evapotranspiration. As a result, the crop coefficient in the mulched area of field A was 0.18, and the crop coefficient in the bare area of field A was 0.94.

[Implementation procedure]
Next, calculate the volumetric water content and pF value of the soil in the mulched and bare areas of field A using the steps (a) to (d) below, and calculate the volumetric water content and pF value of the soil in the mulched and bare areas of field A. pF values were investigated over time over 15 days.

<(a) Calculation of standard evapotranspiration for field A>
Using the method explained in the above section "(E) Preparation of crop coefficients for field A," the pF value is calculated from the meteorological data at the point where field A is located at the time of implementation, and the standard evapotranspiration of field A on each survey day is calculated. (Second estimated standard evapotranspiration) was calculated. Although we will not disclose the numerical value of the second estimated standard evapotranspiration on each survey day, the average value of the second estimated standard evapotranspiration over 15 days is 1.59 mm for both the mulch plot and the bare plot in field A. / day.

<(b) Calculation of actual evapotranspiration of field A>
The actual evapotranspiration (estimated actual evapotranspiration) of field A on each survey day was calculated from the second estimated standard evapotranspiration obtained in (a) above and the crop coefficient prepared in (E) above. Actual evapotranspiration was calculated according to the method described in FAO-56. Although we omit the disclosure of actual evapotranspiration values for each survey day, the average value of actual evapotranspiration over 15 days is 0.28 mm/day in the mulch area of field A, and 0.28 mm/day in the bare area of field A. It was 1.48 mm/day.

<(c) Calculation of volumetric moisture content of field A>
From the estimated actual evapotranspiration calculated in (b) above, the volumetric water content (estimated volumetric water content) of the soil in field A on each survey day was calculated. Although we omit the disclosure of the estimated volumetric moisture content on each survey day, the average value of the estimated volumetric moisture content over 15 days is 11.2% in the mulch area of field A, and 11.2% in the bare area of field A. It was 15.9%.

<(d) Calculation of estimated pF value of soil in field A>
The estimated pF value of the soil in field A on each survey day was calculated from the estimated volumetric water content calculated in (c) above and the equation for calculating the estimated pF value prepared in (D) above.

Figure 7 shows the results of an investigation of the volumetric water content and pF value of the soil in the bare area of field A over time. 1071 in Figure 7 shows the estimated pF value of the soil in the bare area of field A estimated from the meteorological data using the above implementation procedure, and a pF sensor (manufactured by METER, model number TEROS-) to verify the accuracy of the estimated pF value. The actual pF value of the soil in the bare area of field A measured using 21) is shown. The pF sensor used for verification is a high-performance sensor that can measure pF up to about 3.5, unlike the tensiometer used to measure the pF value in (A) above.

In addition, 1072 in Fig. 7 shows the estimated volumetric moisture content of the soil in the bare area of field A estimated from the meteorological data using the above implementation procedure, and the actual volume of soil in the bare area of field A measured using a moisture sensor. moisture content.

As shown in FIG. 7, no large deviation occurred between the estimated value and the observed value (actually measured value) regarding the volumetric water content. Further, regarding the pF value, there was no large difference between the estimated value estimated from the estimated volumetric water content and the observed value.

From this, it is possible to create a formula for calculating the estimated pF value using a tensiometer that is easily available and can be easily handled by non-researchers, without using existing expensive pF sensors. It was proved that the pF value can be estimated with high accuracy from the formula for calculating the estimated pF value created in the above manner and the estimated volumetric water content. It should be noted that in the high pF value range, there was a tendency for the difference between the estimated value and the observed value to become large, but this was due to the fact that the measurement limit of the pF sensor (pF3.5) was exceeded. It was thought that the difference between the estimated value and the observed value was increasing. From the above results, it is clear that the calculation method according to one embodiment of the present invention makes it possible to accurately estimate the volumetric water content and pF value of soil from meteorological data without using existing expensive pF sensors. Ta.

In addition, the results of investigating the volumetric moisture content and pF value of the soil in the mulch plot of field A over time are shown in FIG. 1081 in Figure 8 shows the estimated pF value of the soil in the mulch area of field A estimated from the meteorological data using the above-mentioned implementation procedure, and a pF sensor (manufactured by METER, model number TEROS-) to verify the accuracy of the estimated pF value. The actual pF value of the soil in the mulch area of field A measured using 21) is shown.

In addition, 1082 in FIG. 8 shows the estimated volumetric moisture content of the soil in the mulch area of field A estimated from the meteorological data using the above-mentioned implementation procedure, and the actual volume of soil in the mulch area of field A measured using a moisture sensor. moisture content.

As shown in FIG. 8, as a result of investigating the volumetric moisture content and pF value of the soil over time in the mulched plot of field A, both the volumetric moisture content and the pF value could be estimated. Regarding the volumetric water content, there was no large difference between the estimated value and the observed value. On the other hand, regarding the pF value, the observed value and estimated value did not match very well in the mulch plot, probably because the soil was always quite dry (moisture content below 12%) and the changes were small. However, the accuracy of the pF sensor is guaranteed only up to about pF 3.5 or less, and the observed values of the pF sensor exceeding pF 3.5 are not useful as a reference, so the observed and estimated pF values shown in Figure 8 The difference between is not indicative of the accuracy of the pF value estimate.

INDUSTRIAL APPLICABILITY The present invention can be used at public testing stations, agricultural sites, etc. where crop cultivation is managed by evaluating water stress and water absorption of crops.

1 Arithmetic device 2 Meteorological data measurement device 3 Crop coefficient database 4 Relational expression database 11 Relational expression preparation section 12 Crop coefficient preparation section 13 Parameter calculation section 14 Estimated moisture tension value calculation section 15 Soil moisture content estimation section 16 Output control section

Claims (6)

The volumetric moisture content of the field of interest determined based on the measured saturated moisture content or estimated saturated moisture content related to (1) below, the measured volumetric moisture content related to (2) below, and the measured moisture tension value related to (3) below. a relational equation preparation step of preparing a relational equation showing the relationship between the ratio and the water tension value;
(1) Calculate the regression equation between the measured saturated moisture content of the soil of the field of interest, or the measured saturated moisture content of multiple soils including soil other than the soil of the field of interest, and the measured dry density of the soil. the estimated saturated moisture content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual moisture tension value measured in advance for the soil of the field of interest;
An estimated water tension value of the soil of the field of interest based on the relational equation prepared in the relational equation preparation step and the estimated volumetric moisture content of the soil of the field of interest calculated based on the meteorological data of the point where the field of interest is located. an estimated water tension value calculation step for calculating the
An arithmetic method characterized by comprising: Determined based on the measured volumetric water content and a first estimated standard evapotranspiration of the soil of the field of interest, which is calculated based on meteorological data at the point where the field of interest is located at the time when the measured volumetric water content is measured. a crop coefficient preparation step of preparing crop coefficients for the field of interest;
a second estimated standard evapotranspiration calculation step of calculating a second estimated standard evapotranspiration of the soil of the field of interest based on meteorological data at the point where the field of interest is located at the time of calculating the water tension value;
Based on the second estimated standard evapotranspiration calculated in the second estimated standard evapotranspiration calculation step and the crop coefficient prepared in the crop coefficient preparation step, calculate the estimated actual evapotranspiration of the field of interest. An estimated actual evapotranspiration calculation step;
an estimated volumetric water content calculation step of calculating an estimated volumetric water content of soil in the field of interest based on the estimated actual evapotranspiration calculated in the estimated actual evapotranspiration calculation step;
further including;
2. The calculation method according to claim 1, wherein the estimated volumetric water content calculated in the estimated volumetric water content calculating step is used in the estimated water tension value calculating step. 3. The calculation method according to claim 1, wherein the weather data is a daily maximum temperature, a daily minimum temperature, and a daily cumulative amount of solar radiation. The method further comprises a soil moisture change amount estimating step of estimating a soil moisture change amount in the field of interest based on the estimated water tension value calculated in the estimated water tension value calculation step. 3. The calculation method according to any one of 3. The volumetric moisture content of the field of interest determined based on the measured saturated moisture content or estimated saturated moisture content related to (1) below, the measured volumetric moisture content related to (2) below, and the measured moisture tension value related to (3) below. a relational equation preparation unit that prepares a relational equation showing the relationship between the ratio and the water tension value;
(1) Calculate the regression equation between the measured saturated moisture content of the soil of the field of interest, or the measured saturated moisture content of multiple soils including soil other than the soil of the field of interest, and the measured dry density of the soil. the estimated saturated moisture content calculated from the measured dry density of the soil of the field of interest;
(2) Actual volumetric water content measured in advance of the soil of the field of interest;
(3) Actual moisture tension value measured in advance for the soil of the field of interest;
An estimated water tension value of the soil of the field of interest based on the relational equation prepared in the relational equation preparation section and the estimated volumetric moisture content of the soil of the field of interest calculated based on the meteorological data of the point where the field of interest is located. an estimated water tension value calculation unit that calculates the
An arithmetic device comprising: An arithmetic program for causing a computer to function as the arithmetic device according to claim 5, the arithmetic program for causing the computer to function as the relational expression preparation section and the estimated water tension value calculation section.

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