Method and device for measuring nitrate nitrogen concentration

Abstract

To enable more accurate measurement of nitrate nitrogen concentration in plants through non-destructive inspection.SOLUTION: A nitrate nitrogen concentration measurement method provided herein comprises irradiating a leaf blade 100 of a plant with first ultraviolet light L1 of a wavelength in a range of 280-320 nm to measure the amount of light transmitting through the leaf blade 100, and then calculating nitrate nitrogen concentration in the leaf blade 100 based on the amount of the transmitted first ultraviolet light L1.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for measuring the nitrate nitrogen concentration.

Background Art

[0002] In plant cultivation, nitrogen contained in fertilizers is a factor that greatly affects plant growth. Therefore, if the nitrate nitrogen concentration in plants becomes clear, it becomes possible to set appropriate fertilization timing and amount without being influenced by the experience of farmers. For example, by squeezing the leaves and stems of a plant to collect the squeezed juice and measuring the nitrate ion concentration contained in this squeezed juice, the nutritional status of the plant can be confirmed. However, such a destructive test is time-consuming.

[0003] For example, in Patent Document 1 below, a method is shown in which light is irradiated on vegetables, a spectroscopic absorption spectrum in the ultraviolet wavelength range of the reflected light is obtained, and the nitrate ion concentration in the vegetables is measured non-destructively by analyzing this spectroscopic absorption spectrum.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when detecting reflected light as described above, most of the irradiated ultraviolet light is reflected on the surface of the plant, so that nitrate ions inside the plant are hardly measured. Therefore, depending on the shape (especially the surface shape) and type of the plant and the distribution status of nitrate ions in the plant, there are variations in the measurement accuracy of the nitrate ion concentration.

[0006] Therefore, an object of the present invention is to more accurately measure the nitrate nitrogen concentration in plants by non-destructive inspection.

Means for Solving the Problem

[0007] To solve the above problems, the present invention provides a method for measuring the nitrate nitrogen concentration, which includes irradiating a plant with first ultraviolet light having a wavelength in the range of 280 to 320 nm and measuring the amount of transmitted light that has passed through the plant, and calculating the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light.

[0008] Further, the present invention provides a measuring device for nitrate nitrogen concentration, which includes a first light source that irradiates a plant with first ultraviolet light having a wavelength in the range of 280 to 320 nm, a first light receiving unit that detects the amount of transmitted light of the first ultraviolet light irradiated from the first light source and passing through the plant, and an arithmetic unit that calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit.

[0009] As described above, in the present invention, a plant is irradiated with first ultraviolet light having a wavelength near the maximum absorption wavelength (about 300 nm) of nitrate nitrogen, and the nitrate nitrogen concentration is calculated based on the amount of transmitted light of the first ultraviolet light that has passed through the plant. Thereby, since it is possible to measure the concentration including nitrate nitrogen existing not only on the surface of the plant but also inside the plant, the nitrate nitrogen concentration can be measured more accurately than the conventional technique that measures the amount of received reflected light.

[0010] The absorbance of nitrate nitrogen decreases as the wavelength becomes longer than the maximum absorption wavelength, and ultraviolet light in the wavelength range of 330 nm or more is hardly absorbed by nitrate nitrogen (see FIG. 3). Therefore, when a plant is irradiated with ultraviolet light having a wavelength of 330 nm or more, the influence of factors other than nitrate nitrogen on the amount of transmitted light becomes relatively large. Accordingly, if the nitrate nitrogen concentration in the plant is calculated based on the amount of transmitted light of the first ultraviolet light and the amount of transmitted light of second ultraviolet light having a wavelength of 330 nm or more, a measurement result excluding the influence of factors other than nitrate nitrogen can be obtained.

[0011] Based on the above findings, the above measurement method preferably includes a step of irradiating the plant with a second ultraviolet light having a wavelength of 330 nm or more and measuring the amount of transmitted light that has passed through the plant, and calculating the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light and the amount of transmitted light of the second ultraviolet light. Further, the above measurement device preferably includes a second light source that irradiates the plant with a second ultraviolet light having a wavelength of 330 nm or more, and a second light receiving unit that detects the amount of transmitted light of the second ultraviolet light that has been irradiated from the second light source and has passed through the plant, and the arithmetic unit calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit and the amount of transmitted light of the second ultraviolet light detected by the second light receiving unit.

[0012] Since the amount of transmitted light of the first ultraviolet light attenuates in proportion to the number of nitrate nitrogen (nitrate ions) contained in the plant, the amount of nitrate nitrogen can be measured from this amount of transmitted light. In order to calculate the nitrate nitrogen concentration, it is necessary to measure the volume (thickness) of the plant, but it is troublesome to measure the volume of the plant every time. For example, if it is assumed that the volume (thickness) of the plant is constant, the nitrate nitrogen concentration can be calculated, but there is a concern about a decrease in measurement accuracy.

[0013] Therefore, the above measurement method preferably includes a step of irradiating the plant with near-infrared light and measuring the amount of transmitted light that has passed through the plant, and calculating the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light and the amount of transmitted light of the near-infrared light. Further, the above measurement device preferably includes a third light source that irradiates the plant with near-infrared light, and a third light receiving unit that detects the amount of transmitted light of the near-infrared light that has been irradiated from the third light source and has passed through the plant, and the arithmetic unit calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit and the amount of transmitted light of the near-infrared light detected by the third light receiving unit.

[0014] In the wavelength range of near-infrared light (750 to 2500 nm), since the absorbance of water is high, the relative value of the water content contained in the plant, and thus the relative value of the volume of the plant, can be measured from the amount of transmitted near-infrared light. Therefore, as described above, by calculating the nitrate nitrogen concentration using the amount of transmitted light of the first ultraviolet light and the amount of transmitted near-infrared light, information on the volume of the plant is reflected in the measurement result, so the measurement accuracy of the nitrate nitrogen concentration is improved.

[0015] Further, the above measurement method preferably includes a step of irradiating the plant with visible light having a wavelength in the red edge wavelength range and measuring the amount of transmitted light that has passed through the plant, and calculating the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light and the amount of transmitted visible light. Further, the above measurement device preferably includes a fourth light source that irradiates the plant with visible light in the red edge wavelength range, and a fourth light receiving unit that detects the amount of transmitted light of the visible light irradiated from the fourth light source and passing through the plant, and the calculation unit calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit and the amount of transmitted light of the visible light detected by the fourth light receiving unit.

[0016] Among the absorption spectra of plants, in the long wavelength range of visible light (600 to 700 nm), there is a wavelength range called the red edge wavelength range where the absorbance changes rapidly. It is known that when a plant is stressed such as water shortage, the red edge wavelength range shifts to the short wavelength side (blue shift). Therefore, by measuring the shift amount of the red edge wavelength range from the amount of transmitted light of visible light in the red edge wavelength range, the relative value of the water content in the plant, and thus the relative value of the volume of the plant, can be measured. Thus, as described above, by calculating the nitrate nitrogen concentration using the amount of transmitted light of the first ultraviolet light and the amount of transmitted light of visible light in the red edge wavelength range, information on the volume of the plant is reflected in the measurement result, so the measurement accuracy of the nitrate nitrogen concentration is improved.

Advantages of the Invention

[0017] As described above, according to the measurement method of the present invention, the nitrate nitrogen concentration in a plant can be measured more accurately by non-destructive inspection.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, the case of measuring the nitrate nitrogen concentration in the leaf blade of a plant, particularly the nitrate nitrogen concentration in the leaf blade of fruit vegetables such as tomatoes and cucumbers and leaf vegetables such as spinach by non-destructive inspection is shown.

[0020] First, as a preliminary preparation for measuring the nitrate nitrogen concentration, a correlation formula between the optical density and the nitrate ion concentration of the leaf blade is obtained by the following procedure.

[0021] (1-1) Measure the transmitted light quantity of the leaf blade Irradiate the leaf blade with ultraviolet light and measure the transmitted light quantity (optical density of the transmitted light) that has passed through the leaf blade. The specific measurement procedure for the transmitted light quantity (in this embodiment, the optical density difference D described later) is the same as the procedure shown in (2-1) to (2-4) described later.

[0022] (1-2) Measure the nitrate ion concentration of the leaf blade by a destructive test The nitrate ion concentration in the leaf blade, whose transmitted light quantity was measured in the above (1-1), is measured by a destructive inspection. Specifically, the leaf blade is squeezed with a juicer to collect the squeezed juice, and the nitrate ion concentration of this squeezed juice is measured with a commercially available nitrate ion concentration measuring device. Note that squeezed juice may be collected not only from the leaf blade but also from the petiole and the stem.

[0023] (1-3) Obtain a correlation formula between the optical density and the nitrate ion concentration A correlation formula between the transmitted light quantity obtained in the above (1-1) and the nitrate ion concentration obtained in the above (1-2) is obtained. For example, as shown in FIG. 1, the results obtained in the above (1-1) and (1-2) are plotted on a graph with the optical density of the transmitted light on the horizontal axis and the nitrate ion concentration on the vertical axis. An approximate formula (a linear formula in the illustrated example) of these plots is calculated, and this approximate formula is used as the correlation formula between the optical density and the nitrate ion concentration. For example, when the nitrate ion concentration is E, the optical density difference to be described later is D, and a and b are constants, by multiple regression analysis, E = a·D + b A correlation formula represented by this is obtained. The correlation formula thus obtained is stored in the arithmetic unit 10 to be described later.

[0024] Next, a procedure for measuring the nitrate ion concentration (nitrate nitrogen concentration) in the leaf blade by a non-destructive inspection will be described.

[0025] (2-1) Mounting the measuring device First, as shown in FIG. 2, a nitrate nitrogen measuring device 1 according to an embodiment of the present invention is mounted on a leaf blade 100 of a fruit vegetable that is an object of measurement of the nitrate nitrogen concentration. The measuring device 1 is mounted on the growing leaf blade 100 that has not been separated from the stem. The measuring device 1 includes a first light source 2a and a first light receiving unit 3a, and a second light source 2b and a second light receiving unit 3b. The light sources 2a and 2b are arranged on one side in the thickness direction of the leaf blade 100 (the right side in the figure), and the light receiving units 3a and 3b are arranged on the other side in the thickness direction of the leaf blade 100 (the left side in the figure).

[0026] The first light source 2a irradiates first ultraviolet light. As shown in FIG. 3, the absorption spectrum of nitrate ions reaches a maximum near a wavelength of 300 nm. The first ultraviolet light is ultraviolet light in a wavelength range near the maximum absorption wavelength, specifically, ultraviolet light having a wavelength of 280 to 320 nm. As the first light source 2a, for example, an LED is used. In this embodiment, an LED that irradiates ultraviolet light with a wavelength of 310 nm is used.

[0027] The second light source 2b irradiates second ultraviolet light. As shown in FIG. 3, the absorption spectrum of nitrate ions decreases in absorbance as the wavelength becomes longer from the maximum absorption wavelength (about 300 nm), and is hardly absorbed at wavelengths of 330 nm or more. The second ultraviolet light is ultraviolet light in a wavelength range that is hardly absorbed by nitrate ions. For example, it is ultraviolet light in a wavelength range where the absorbance is 20% or less of the absorbance at the maximum absorption wavelength (about 300 nm). The second ultraviolet light in this embodiment is ultraviolet light having a wavelength of 330 nm or more (preferably 340 nm or more). The wavelength of the second ultraviolet light is preferably 20 nm or more (preferably 30 nm or more) longer than the wavelength of the first ultraviolet light. As the second light source 2b, for example, an LED is used. In this embodiment, an LED that irradiates ultraviolet light with a wavelength of 340 nm is used.

[0028] The first light receiving part 3a is arranged at a position to receive the first ultraviolet light irradiated from the first light source 2a, and the second light receiving part 3b is arranged at a position to receive the second ultraviolet light irradiated from the second light source 2b. In the illustrated example, the first light receiving part 3a is arranged at a position facing the first light source 2a in the thickness direction of the leaf blade 100 (the left-right direction in the figure), and the second light receiving part 3b is arranged at a position facing the second light source 2b in the thickness direction of the leaf blade 100. The light receiving parts 3a and 3b detect the amount of received light (intensity). In this embodiment, photodiodes that convert the intensity of the received light into an electrical signal are used as the light receiving parts 3a and 3b.

[0029] The first light source 2a and the second light source 2b are connected to a substrate 4 (e.g., an aluminum substrate). The substrate 4 is connected to a light source control unit 5 including a power supply. By supplying power from the light source control unit 5 to either of the light sources 2a, 2b via the substrate 4, the light sources 2a, 2b can be selectively irradiated. A heat sink 6 is attached to the back surface of the substrate 4 (the surface opposite to the light sources 2a, 2b).

[0030] The first light receiving unit 3a and the second light receiving unit 3b are connected to an IV conversion substrate 7. A measurement unit 8 (e.g., a multimeter) and a power supply 9 are connected to the IV conversion substrate 7. The measurement unit 8 is connected to an arithmetic unit 10 (e.g., a computer). When the light receiving units 3a, 3b detect light, an electrical signal corresponding to the intensity of the light is transmitted to the measurement unit 8 via the IV conversion substrate 7, and the measurement unit 8 measures the received light voltage based on this electrical signal.

[0031] (2-2) Measurement of the transmitted light quantity of the first ultraviolet light (received light voltage V1) First, with both light sources 2a, 2b turned off, the measurement unit 8 measures the received light voltage V1(OFF) when the light source is off based on the light reception amount by the first light receiving unit 3a. Next, the first light source 2a is turned on to irradiate the leaf blade 100 with the first ultraviolet light L1, and the first light receiving unit 3a receives the transmitted light (see Fig. 2). Based on the light reception amount of the first light receiving unit 3a at this time, the measurement unit 8 measures the received light voltage V1(ON) when the first light source 2a is turned on. Then, the arithmetic unit 10 calculates the difference between these received light voltages V1(OFF), V1(ON), and records this value as the received light voltage V1 of the transmitted light of the first ultraviolet light L1. In this embodiment, the root mean square (RMS) value of the received light voltages V1(OFF), V1(ON) represented by the following formula is taken as the received light voltage V1 of the transmitted light of the first ultraviolet light L1. V1 = √{V1(ON)^2 - V1(OFF)^2}

[0032] (2-3) Measurement of the transmitted light quantity of the second ultraviolet light (received light voltage V2) Next, with both light sources 2a and 2b turned off, the measurement unit 8 measures the received light voltage V2(OFF) when the light source is off based on the amount of light received by the second light receiving unit 3b. Next, the second light source 2b is turned on to irradiate the leaf blade 100 with the second ultraviolet light L2, and the second light receiving unit 3b receives the transmitted light (see Fig. 2). Based on the amount of light received by the second light receiving unit 3b at this time, the measurement unit 8 measures the received light voltage V2(ON) when the second light source 2b is turned on. Then, the calculation unit 10 calculates the difference between these received light voltages V2(OFF) and V2(ON), and records this value as the received light voltage V2 of the transmitted light of the second ultraviolet light L2. In the present embodiment, the root mean square (RMS) value of the received light voltages V2(OFF) and V2(ON) represented by the following formula is used as the received light voltage V2 of the transmitted light of the second ultraviolet light L2. V2 = √{V2(ON)^2 - V2(OFF)^2}

[0033] (2-4) Calculation of optical density difference D The calculation unit 10 calculates the optical density difference D between the transmitted light of the first ultraviolet light L1 and the transmitted light of the second ultraviolet light L2 from the values of V1 and V2 measured above. In the present embodiment, since the irradiation amounts of the ultraviolet lights L1 and L2 by both light sources 2a and 2b are equal, the optical density difference D is represented by the following formula. D = log 10 (V1) - log 10 (V2)

[0034] (2-5) Calculation of nitrate ion concentration (nitrate nitrogen concentration) Then, the calculation unit 10 substitutes the value of the optical density difference D into the correlation formula (E = a·D + b) obtained in the above (1-3) to calculate the nitrate ion concentration E in the leaf blade 100. From this nitrate ion concentration E, the nitrate nitrogen concentration of the leaf blade 100 is calculated.

[0035] As described above, in the present embodiment, the amount of transmitted light of the first ultraviolet light L1 having a wavelength near the maximum absorption wavelength of nitrate ions is measured, and the nitrate nitrogen concentration is calculated based on this amount of transmitted light. As a result, not only the surface of the leaf blade 100 but also the concentration including nitrate nitrogen existing inside the leaf blade 100 can be measured, so that highly reliable measurement results can be obtained.

[0036] Also, in the present embodiment, as described above, the transmitted light amount of the second ultraviolet light L2 having a wavelength of 330 nm or more is measured. Since the second ultraviolet light is hardly absorbed by nitrate ions, the absorbance of the transmitted light of the second ultraviolet light is greatly affected by factors other than nitrate ions. Therefore, by calculating the nitrate nitrogen concentration based on the difference (optical density difference D) between the transmitted light amount of the first ultraviolet light L1 and the transmitted light amount of the second ultraviolet light L2, it is possible to obtain a measurement result excluding the influence of factors other than nitrate nitrogen, and thus the measurement accuracy is improved.

[0037] From the nitrate nitrogen concentration in the leaf blade measured as described above, the nutritional state of the leaf blade, and thus the nutritional state of the fruit vegetable, can be estimated. Therefore, based on the measured nitrate nitrogen concentration, the subsequent growth conditions (for example, the amount of fertilizer application) can be adjusted. For example, in advance, obtain the range of the nitrate nitrogen concentration in the leaf blade in a good growth state, and if the nitrate nitrogen concentration in the leaf blade measured during growth is below the above range, increase the amount of fertilizer application, and if the nitrate nitrogen concentration is above the above range, reduce the amount of fertilizer application, so that it is possible to always maintain a good growth state.

[0038] The present invention is not limited to the above-described embodiment. Hereinafter, other embodiments of the present invention will be described, but descriptions of the same points as the above-described embodiment will be omitted.

[0039] The measuring device 1 shown in FIG. 4 further includes a third light source 2c and a third light receiving unit 3c.

[0040] The third light source 2c irradiates near-infrared light (wavelength 750 to 2500 nm), for example, near-infrared light having a wavelength near the maximum absorption wavelength of water (for example, 1430 to 1470 nm, or 1920 to 1960 nm). As the third light source 2c, for example, an LED is used, and in the present embodiment, an LED that irradiates near-infrared light with a wavelength of 1450 nm is used. The third light source 2c is connected to the light source control unit 5 via the substrate 4, and the light source control unit 5 enables any one of the light sources 2a to 2c to be selectively irradiated.

[0041] The third light-receiving unit 3c is arranged at a position for receiving the near-infrared light irradiated from the third light source 2c. In the illustrated example, the third light-receiving unit 3c is arranged at a position facing the third light source 2c in the thickness direction of the leaf blade 100 (the left-right direction in the drawing). In the present embodiment, a photodiode is used as the third light-receiving unit 3c. The third light-receiving unit 3c is connected to the IV conversion substrate 7.

[0042] Using these third light source 2c and third light-receiving unit 3c, the amount of transmitted light of the near-infrared light L3 can be measured. Specifically, first, with all the light sources 2a, 2b, 2c turned off, the measurement unit 8 measures the received light voltage V3(OFF) when the light sources are off based on the amount of received light by the third light-receiving unit 3c. Next, the third light source 2c is turned on to irradiate the leaf blade 100 with the near-infrared light L3, and the third light-receiving unit 3c receives the transmitted light thereof. Based on the amount of received light of the third light-receiving unit 3c at this time, the measurement unit 8 measures the received light voltage V3(ON) when the third light source 2c is turned on. Then, the calculation unit 10 calculates the difference between these received light voltages V3(OFF), V3(ON), and records this value as the received light voltage V3 of the transmitted light of the near-infrared light L3. In the present embodiment, the root mean square (RMS) value of the received light voltages V3(OFF), V3(ON) represented by the following formula is taken as the received light voltage V3 of the transmitted light of the near-infrared light L3. V3 = √{V3(ON)^2 - V3(OFF)^2}

[0043] In the present embodiment, the nitrate ion concentration E is measured in consideration of not only the amount of transmitted light of the first ultraviolet light L1 having a wavelength range near the maximum absorption wavelength of nitrate ions but also the amount of transmitted light of the near-infrared light L3 (received light voltage V3). Specifically, first, in the above step (1-1), the optical density difference D between the amount of transmitted light of the first ultraviolet light L1 and the amount of transmitted light of the second ultraviolet light L2, and the amount of transmitted light of the near-infrared light L3 (received light voltage V3) are measured. Then, in the above step (1-2), the nitrate ion concentration E is expressed by an approximate formula using the optical density difference D and the received light voltage V3 as variables. For example, by multiple regression analysis, E = a1·D + a2·V3 + b a correlation formula represented by (where a1, a2, b are constants) is obtained.

[0044] Then, the measuring device 1 is attached to the leaf blade 100 to be measured, and the optical density difference D between the transmitted light amount of the first ultraviolet light L1 and the transmitted light amount of the second ultraviolet light L2, and the transmitted light amount (received light voltage V3) of the near-infrared light L3 are measured. By substituting these optical density difference D and received light voltage V3 into the above correlation formula (E = a1·D + a2·V3 + b), the nitrate ion concentration E in the leaf blade 100 is calculated. From this nitrate ion concentration E, the nitrate nitrogen concentration of the leaf blade 100 is calculated.

[0045] Since near-infrared light is easily absorbed by water, the relative value of the amount of water contained in the leaf blade 100 can be estimated from the transmitted light amount of the near-infrared light irradiated from the light source 2c. In the present embodiment, by measuring not only the transmitted light amount of the first ultraviolet light L1 but also the transmitted light amount of the near-infrared light L3, the nitrate ion concentration E based on the amount of water in the leaf blade 100 and thus the volume (thickness) of the leaf blade 100 can be measured. Thereby, the measurement accuracy of the nitrate nitrogen concentration is improved.

[0046] The measuring device 1 shown in FIG. 5 further includes a fourth light source 2d, a fifth light source 2e, a fourth light receiving part 3d, and a fifth light receiving part 3e.

[0047] The fourth light source 2d irradiates visible light in the red edge wavelength range. The red edge wavelength range is a wavelength range in which the light absorption rate changes rapidly in the long wavelength range (600 to 700 nm) of the visible light of the light absorption spectrum of the leaf blade 100. Therefore, in advance, the spectral spectrum of the leaf blade 100 of the plant to be measured is acquired to specify the red edge wavelength range, and a fourth light source 2d that irradiates visible light having a wavelength within the red edge wavelength range is prepared. As the fourth light source 2d, for example, an LED can be used, and in the present embodiment, an LED that irradiates visible light with a wavelength of 650 nm is used.

[0048] The fifth light source 2e irradiates near-infrared light (wavelength 750 to 2500 nm), and in the present embodiment, for example, an LED that irradiates near-infrared light with a wavelength of 940 nm is used. The fourth light source 2d and the fifth light source 2e are connected to the light source control unit 5 via the substrate 4, and the light source control unit 5 enables any one of the light sources 2a to 2e to be selectively irradiated.

[0049] The fourth light-receiving unit 3d and the fifth light-receiving unit 3e are arranged at positions to receive visible light irradiated from the fourth light source 2d and the fifth light source 2e, respectively. In the illustrated example, the fourth light-receiving unit 3d and the fifth light-receiving unit 3e are arranged at positions facing the fourth light source 2d and the fifth light source 2e, respectively, in the thickness direction of the leaf blade 100 (the left-right direction in the drawing). In the present embodiment, photodiodes are used as the light-receiving units 3d and 3e. The light-receiving units 3d and 3e are connected to the IV conversion substrate 7.

[0050] Using the fourth light source 2d and the fourth light-receiving unit 3d, the amount of transmitted light of the visible light L4 in the red edge wavelength region can be measured. Specifically, first, with all the light sources 2a to 2e turned off, the measurement unit 8 measures the received light voltage V4(OFF) when the light source is off based on the amount of light received by the fourth light-receiving unit 3d. Next, the fourth light source 2d is turned on to irradiate the visible light L4 in the red edge wavelength region onto the leaf blade 100, and the transmitted light is received by the fourth light-receiving unit 3d. Based on the amount of light received by the fourth light-receiving unit 3d at this time, the measurement unit 8 measures the received light voltage V4(ON) when the fourth light source 2d is turned on. Then, the calculation unit 10 calculates the difference between these received light voltages V4(OFF) and V4(ON), and records this value as the received light voltage V4 of the transmitted light of the visible light L4. In the present embodiment, the root mean square (RMS) value of the received light voltages V4(OFF) and V4(ON) represented by the following formula is taken as the received light voltage V4 of the transmitted light of the visible light L4. V4 = √{V4(ON)^2 - V4(OFF)^2}

[0051] In addition, the transmitted light amount of the near-infrared light L5 can be measured using the fifth light source 2e and the fifth light-receiving unit 3e. Next, the transmitted light amount of the near-infrared light L5 is measured. Specifically, first, with all the light sources 2a to 2e turned off, based on the received light amount by the fifth light-receiving unit 3e, the measurement unit 8 measures the received light voltage V5(OFF) when the light source is off. Next, the fifth light source 2e is turned on to irradiate the leaf blade 100 with the near-infrared light L5, and the transmitted light is received by the fifth light-receiving unit 3e. Based on the received light amount of the fifth light-receiving unit 3e at this time, the measurement unit 8 measures the received light voltage V5(ON) when the fifth light source 2e is turned on. Then, the calculation unit 10 calculates the difference between these received light voltages V5(OFF) and V5(ON), and records this value as the received light voltage V5 of the transmitted light of the near-infrared light L5. In the present embodiment, the root mean square (RMS) value of the received light voltages V5(OFF) and V5(ON) represented by the following formula is used as the received light voltage V5 of the transmitted light of the near-infrared light L5. V5 = √{V5(ON)^2 - V5(OFF)^2}

[0052] Then, the calculation unit 10 calculates the optical density difference d between the values of V4 and V5 measured above. This optical density difference d is represented by the following formula. d = log 10 (V4) - log 10 (V5)

[0053] In the present embodiment, not only the transmitted light amount of the first ultraviolet light L1 but also the transmitted light amount of the visible light L4 in the red edge wavelength region (the optical density difference d in the present embodiment) is considered to measure the nitrate ion concentration E. Specifically, first, in the above step (1-1), the optical density difference D between the transmitted light amounts of the first ultraviolet light L1 and the second ultraviolet light L2, the transmitted light amount of the near-infrared light L3 (received light voltage V3), and the optical density difference d between the transmitted light amounts of the visible light L4 in the red edge wavelength region and the near-infrared light L5 are measured. Then, in the above step (1-2), the nitrate ion concentration E is expressed by an approximate formula using the optical density difference D, the received light voltage V3, and the optical density difference d as variables. For example, by multiple regression analysis, E = a1·D + a2·V3 + a3·d + b a correlation formula represented by (where a1, a2, a3, and b are constants) is obtained.

[0054] Then, the measuring device 1 is attached to the leaf blade 100 to be measured, and the optical density difference D between the transmitted light amounts of the first ultraviolet light L1 and the second ultraviolet light L2, the transmitted light amount of the near-infrared light L3 (received light voltage V3), and the transmitted light amounts of the visible light L4 in the red edge wavelength range and the near-infrared light L5 are measured. By substituting these optical density differences D, received light voltage V3, and optical density difference d into the above correlation formula (E = a1·D + a2·V3 + a3·d + b), the nitrate ion concentration in the leaf blade 100 is calculated. From this nitrate ion concentration, the nitrate nitrogen concentration of the leaf blade 100 is calculated.

[0055] By measuring the transmitted light amount (received light voltage V4) of the visible light in the red edge wavelength range as described above, the shift amount in the red edge wavelength range, and thus the relative value of the water content in the plant can be estimated. In this embodiment, by measuring not only the transmitted light amount of the first ultraviolet light L1 but also the transmitted light amount of the visible light L3 in the red edge wavelength range, the water content in the leaf blade 100, and thus the nitrate ion concentration based on the volume (thickness) of the leaf blade 100 can be measured. Thereby, the measurement accuracy of the nitrate nitrogen concentration is improved. Note that in this embodiment, if not particularly necessary, the measurement of the transmitted light of the near-infrared light L3 by the third light source 3c and the third light receiving unit 3c may be omitted.

[0056] In the above embodiment, the case of using a plurality of light sources that irradiate lights with different wavelengths is shown. However, the present invention is not limited to this, and for example, one light source capable of irradiating a plurality of lights with different wavelengths may be used. In this case, the light receiving unit may be one.

Explanation of Reference Numerals

[0057] 1 Nitrate nitrogen measuring device 2a~2e Light sources 3a~3e Light receiving units 4 Substrate 5 Light source control unit 6 Heat sink 7 IV conversion substrate 8 Measuring unit 9 Power supply 10 Arithmetic unit 100 Leaf blade L1 First ultraviolet light L2 Second ultraviolet light L3 Near-infrared light L4 Visible light L5 Near-infrared light

Claims

1. Irradiating a plant with first ultraviolet light having a wavelength in the range of 280 to 320 nm, and measuring the amount of transmitted light that has passed through the plant; A method for measuring the nitrate nitrogen concentration in a plant, comprising calculating the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light.

2. Irradiating the plant with second ultraviolet light having a wavelength of 330 nm or more, and measuring the amount of transmitted light that has passed through the plant, The method for measuring the nitrate nitrogen concentration according to claim 1, wherein the nitrate nitrogen concentration in the plant is calculated based on the amount of transmitted light of the first ultraviolet light and the amount of transmitted light of the second ultraviolet light.

3. Irradiating the plant with near-infrared light, and measuring the amount of transmitted light that has passed through the plant, The method for measuring the nitrate nitrogen concentration according to claim 1 or 2, wherein the nitrate nitrogen concentration in the plant is calculated based on the amount of transmitted light of the first ultraviolet light and the amount of transmitted light of the near-infrared light.

4. Irradiating the plant with visible light in the red edge wavelength region, and measuring the amount of transmitted light that has passed through the plant, The method for measuring the nitrate nitrogen concentration according to any one of claims 1 to 3, wherein the nitrate nitrogen concentration in the plant is calculated based on the amount of transmitted light of the first ultraviolet light and the amount of transmitted light of the visible light.

5. A first light source that irradiates a plant with first ultraviolet light having a wavelength in the range of 280 to 320 nm; A first light receiving unit that detects the amount of transmitted light of the first ultraviolet light irradiated from the first light source and passing through the plant; A measuring device for nitrate nitrogen concentration, comprising an arithmetic unit that calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit.

6. A second light source that irradiates the plant with second ultraviolet light having a wavelength of 330 nm or more; A second light receiving unit that detects the amount of transmitted light of the second ultraviolet light irradiated from the second light source and passing through the plant; The measuring device for nitrate nitrogen concentration according to claim 5, wherein the arithmetic unit calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit and the amount of transmitted light of the second ultraviolet light detected by the second light receiving unit.

7. A third light source that irradiates the plant with near-infrared light; A third light receiving unit that detects the amount of transmitted light of the near-infrared light irradiated from the third light source and passing through the plant; The nitrate nitrogen concentration measuring device according to claim 5 or 6, wherein the calculation unit calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit and the amount of transmitted light of the near-infrared light detected by the third light receiving unit.

8. a fourth light source that irradiates the plant with visible light in the red edge wavelength region; a fourth light receiving unit that detects the amount of transmitted light of the visible light irradiated from the fourth light source and transmitted through the plant; The nitrate nitrogen concentration measuring device according to any one of claims 5 to 7, wherein the calculation unit calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light detected by the first light receiving unit and the amount of transmitted light of the visible light detected by the fourth light receiving unit.

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