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 nitrate nitrogen concentration. [Background technology]

[0002] In plant cultivation, the nitrogen contained in fertilizer is a factor that greatly affects plant growth. Therefore, if the concentration of nitrate nitrogen in a plant is known, it becomes possible to set the appropriate timing and amount of fertilization without being influenced by the experience of the farmer. For example, the nutritional state of a plant can be confirmed by squeezing the leaves and stems of the plant to collect the juice and measuring the concentration of nitrate ions in the juice. However, such destructive testing is time-consuming.

[0003] For example, Patent Document 1 listed below shows a method for non-destructively measuring the nitrate ion concentration in vegetables by irradiating the vegetables with light, obtaining a spectroscopic absorption spectrum in the ultraviolet wavelength range of the reflected light, and analyzing this spectroscopic absorption spectrum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-101040 A Summary of the Invention [Problem to be solved by the invention]

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

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

[0007] In order to solve the above problem, the present invention provides a method for measuring a nitrate nitrogen concentration, comprising the steps of: irradiating a plant with a first ultraviolet light having a wavelength in the range of 280 to 320 nm and measuring an amount of light transmitted through the plant; and calculating a nitrate nitrogen concentration in the plant based on the amount of the first ultraviolet light transmitted through the plant.

[0008] The present invention also provides a nitrate nitrogen concentration measuring device comprising: 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 an amount of transmitted light of the first ultraviolet light that is irradiated from the first light source and transmitted through the plant; and a calculation 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 a 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 the first ultraviolet light transmitted through the plant. This makes it possible to measure the concentration of nitrate nitrogen present not only on the surface of the plant but also inside the plant, making it possible to measure the nitrate nitrogen concentration more accurately than the conventional technology 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 Figure 3). Therefore, when ultraviolet light having a wavelength of 330 nm or more is irradiated onto a plant, the amount of transmitted light is relatively more influenced by factors other than nitrate nitrogen. Therefore, 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 the second ultraviolet light having a wavelength of 330 nm or more, it is possible to obtain measurement results that exclude the influence of factors other than nitrate nitrogen.

[0011] Based on the above findings, it is preferable that the above measurement method 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 light transmitted through the plant, and calculates the nitrate nitrogen concentration in the plant based on the amount of light transmitted through the first ultraviolet light and the amount of light transmitted through the second ultraviolet light. Also, it is preferable that the above measurement device 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 light transmitted through the plant of the second ultraviolet light irradiated from the second light source, and a calculation unit that calculates the nitrate nitrogen concentration in the plant based on the amount of light transmitted through the first ultraviolet light detected by the first light receiving unit and the amount of light transmitted through the second ultraviolet light detected by the second light receiving unit.

[0012] The amount of transmitted light of the first ultraviolet light is attenuated in proportion to the number of nitrate nitrogen (nitrate ions) contained in the plant, so 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 a measurement is made. For example, if it is assumed that the volume (thickness) of the plant is constant, it is possible to calculate the nitrate nitrogen concentration, but there is a concern that the measurement accuracy will decrease.

[0013] Therefore, it is preferable that the above measurement method includes a step of irradiating the plant with near-infrared light and measuring the amount of light transmitted through the plant, and calculates 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. Also, it is preferable that the above measurement device 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 irradiated from the third light source and transmitted 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 near-infrared light detected by the third light receiving unit.

[0014] Since water has a high absorbance in the wavelength range of near-infrared light (750 to 2500 nm), the relative value of the water content contained in the plant, and therefore the relative value of the plant's volume, can be measured from the transmitted light amount of near-infrared light. Therefore, by calculating the nitrate nitrogen concentration using the transmitted light amount of the first ultraviolet light and the transmitted light amount of the near-infrared light as described above, the measurement result reflects information on the plant's volume, improving the measurement accuracy of the nitrate nitrogen concentration.

[0015] The above-mentioned measuring 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 light transmitted through the plant, and calculates 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 visible light. The above-mentioned measuring 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 transmitted through the plant, and the calculation unit preferably 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] In the absorption spectrum of plants, the long wavelength region of visible light (600 to 700 nm) has a wavelength region called the red edge wavelength region where the absorbance changes rapidly. It is known that when a plant is stressed due to lack of water, the red edge wavelength region shifts to the short wavelength side (blue shift). Therefore, by measuring the shift amount of the red edge wavelength region from the transmitted light amount of visible light in the red edge wavelength region, the relative value of the water content in the plant, and further the relative value of the volume of the plant, can be measured. Therefore, as described above, by calculating the nitrate nitrogen concentration using the transmitted light amount of the first ultraviolet light and the transmitted light amount of visible light in the red edge wavelength region, the measurement result reflects information on the volume of the plant, thereby improving the measurement accuracy of the nitrate nitrogen concentration. Effect 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 testing. [Brief description of the drawings]

[0018] [Figure 1] 1 is a graph showing the correlation between the measured value of the transmitted light amount (optical density) of the first ultraviolet light and the nitrate ion concentration by destructive testing. [Diagram 2] 1 is a cross-sectional view of a nitrate nitrogen concentration measuring device according to one embodiment of the present invention. [Diagram 3] This is the spectroscopic spectrum of nitrate ions. [Figure 4] FIG. 4 is a cross-sectional view of a nitrate nitrogen concentration measuring device according to another embodiment. [Diagram 5] FIG. 11 is a cross-sectional view of a nitrate nitrogen concentration measuring device according to still another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment 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 in the leaf blade of fruit vegetables such as tomatoes and cucumbers and leafy vegetables such as spinach, by non-destructive testing will be described.

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

[0021] (1-1) Measuring the amount of light transmitted through the leaf blade The leaf blade is irradiated with ultraviolet light, and the amount of light that passes through the leaf blade (optical density of the transmitted light) is measured. The specific procedure for measuring the amount of transmitted light (in this embodiment, optical density difference D described later) is the same as the procedures shown in (2-1) to (2-4) described later.

[0022] (1-2) Measuring nitrate ion concentration in leaf blades by destructive testing The nitrate ion concentration in the leaf blade, whose amount of transmitted light was measured in (1-1) above, is measured by destructive testing. Specifically, the leaf blade is squeezed with a juicer to obtain a juice, and the nitrate ion concentration of the juice is measured with a commercially available nitrate ion concentration meter. Note that juice may be obtained not only from the leaf blade, but also from the petiole and stem.

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

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

[0025] (2-1) Installation of measuring device First, as shown in Fig. 2, a nitrate nitrogen measuring device 1 according to one embodiment of the present invention is attached to a leaf blade 100 of a fruit vegetable which is to be measured for nitrate nitrogen concentration. The measuring device 1 is attached to a growing leaf blade 100 which has not been separated from the stem. The measuring device 1 has 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 the first ultraviolet light. As shown in FIG. 3, the absorption spectrum of nitrate ions is maximum at a wavelength of about 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. For example, an LED is used as the first light source 2a, and in this embodiment, an LED that irradiates ultraviolet light with a wavelength of 310 nm is used.

[0027] The second light source 2b irradiates the second ultraviolet light. As shown in FIG. 3, the absorption spectrum of nitrate ions shows that the absorbance decreases as the wavelength increases 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, ultraviolet light in a wavelength range in which the absorbance is 20% or less of the absorbance at the maximum absorption wavelength (about 300 nm). The second ultraviolet light of 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. For example, an LED is used as the second light source 2b, and in this embodiment, an LED that irradiates ultraviolet light with a wavelength of 340 nm is used.

[0028] The first light receiving unit 3a is disposed at a position where it receives the first ultraviolet light irradiated from the first light source 2a, and the second light receiving unit 3b is disposed at a position where it receives the second ultraviolet light irradiated from the second light source 2b. In the illustrated example, the first light receiving unit 3a is disposed at a position where it faces 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 unit 3b is disposed at a position where it faces the second light source 2b in the thickness direction of the leaf blade 100. The light receiving units 3a and 3b detect the amount (intensity) of light received. In this embodiment, photodiodes that convert the intensity of the received light into an electrical signal are used as the light receiving units 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 source. By supplying power from the light source control unit 5 to either the light source 2a or 2b via the substrate 4, the light source 2a or 2b can be selectively irradiated. A heat sink 6 is attached to the rear surface of the substrate 4 (the surface opposite to the light sources 2a and 2b).

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

[0031] (2-2) Measurement of the transmitted light amount of the first ultraviolet light (received voltage V1) First, with both light sources 2a and 2b turned off, the measuring unit 8 measures the light receiving voltage V1(OFF) when the light source is turned off based on the amount of light received by the first light receiving unit 3a. Next, the first light source 2a is turned on to irradiate the first ultraviolet light L1 onto the leaf blade 100, and the first light receiving unit 3a receives the transmitted light (see FIG. 2). Based on the amount of light received by the first light receiving unit 3a at this time, the measuring unit 8 measures the light receiving voltage V1(ON) when the first light source 2a is turned on. Then, the calculation unit 10 calculates the difference between these light receiving voltages V1(OFF) and V1(ON), and records this value as the light receiving voltage V1 of the transmitted light of the first ultraviolet light L1. In this embodiment, the root mean square (RMS) value of the light receiving voltages V1(OFF) and V1(ON) expressed by the following formula is set as the light receiving 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 amount of the second ultraviolet light (received voltage V2) Next, with both light sources 2a and 2b turned off, the measuring unit 8 measures the light receiving voltage V2(OFF) when the light source is turned 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 second ultraviolet light L2 onto the leaf blade 100, 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 measuring unit 8 measures the light receiving voltage V2(ON) when the second light source 2b is turned on. Then, the calculation unit 10 calculates the difference between these light receiving voltages V2(OFF) and V2(ON), and records this value as the light receiving voltage V2 of the transmitted light of the second ultraviolet light L2. In this embodiment, the root mean square (RMS) value of the light receiving voltages V2(OFF) and V2(ON) expressed by the following formula is set as the light receiving 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 this embodiment, since the irradiation amounts of the ultraviolet lights L1 and L2 from both light sources 2a and 2b are equal, the optical density difference D is expressed 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 equation (E=a·D+b) obtained in (1-3) above to calculate the nitrate ion concentration E in the leaf blade 100. The nitrate nitrogen concentration in the leaf blade 100 is calculated from this nitrate ion concentration E.

[0035] As described above, in this embodiment, the amount of transmitted light of the first ultraviolet light L1 having a wavelength near the maximum absorption wavelength of the nitrate ion is measured, and the nitrate nitrogen concentration is calculated based on this amount of transmitted light. This makes it possible to measure the concentration of nitrate nitrogen present not only on the surface of the leaf blade 100 but also inside the leaf blade 100, thereby obtaining highly reliable measurement results.

[0036] In this embodiment, as described above, the amount of transmitted light 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 largely affected by factors other than nitrate ions. Therefore, by calculating the nitrate nitrogen concentration based on the difference (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, it is possible to obtain a measurement result that excludes the influence of factors other than nitrate nitrogen, thereby improving the measurement accuracy.

[0037] From the nitrate nitrogen concentration of the leaf blade measured as described above, the nutritional state of the leaf blade, and therefore the nutritional state of the fruit vegetable, can be estimated. Therefore, the subsequent growth conditions (e.g., the amount of fertilizer) can be adjusted based on the measured nitrate nitrogen concentration. For example, by acquiring in advance the range of nitrate nitrogen concentration in the leaf blade in a good growth state, and increasing the amount of fertilizer if the nitrate nitrogen concentration in the leaf blade measured during growth is below the above range, and decreasing the amount of fertilizer if the nitrate nitrogen concentration is above the above range, it is possible to maintain a good growth state at all times.

[0038] The present invention is not limited to the above embodiment. Other embodiments of the present invention will be described below, but the description of the same points as the above embodiment will be omitted.

[0039] The measurement 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, irradiates near-infrared light having a wavelength near the maximum absorption wavelength of water (for example, 1430 to 1470 nm or 1920 to 1960 nm). For example, an LED is used as the third light source 2c, and in this 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 can selectively irradiate any of the light sources 2a to 2c.

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

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

[0043] In this embodiment, the nitrate ion concentration E is measured taking into consideration not only the amount of transmitted light of the first ultraviolet light L1 having a wavelength range near the maximum absorption wavelength of the nitrate ion, but also the amount of transmitted light of the near-infrared light L3 (received 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 voltage V3) are measured. Then, in the above step (1-2), the nitrate ion concentration E is expressed by an approximation equation with the optical density difference D and the received voltage V3 as variables. For example, by multiple regression analysis, E = a1 D + a2 V3 + b Obtain the correlation equation expressed as (a1, a2, and b are constants).

[0044] Then, the measuring device 1 is attached to the leaf blade 100 to be measured, and 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. The optical density difference D and received light voltage V3 are substituted into the above correlation equation (E=a1·D+a2·V3+b) to calculate the nitrate ion concentration E in the leaf blade 100. The nitrate nitrogen concentration in the leaf blade 100 is calculated from this nitrate ion concentration E.

[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 amount of transmitted light of the near-infrared light irradiated from the light source 2c. In this embodiment, by measuring not only the amount of transmitted light of the first ultraviolet light L1 but also the amount of transmitted light of the near-infrared light L3, it is possible to measure the amount of water in the leaf blade 100, and further the nitrate ion concentration E taking into account the volume (thickness) of the leaf blade 100. This improves the measurement accuracy of the nitrate nitrogen concentration.

[0046] The measurement device 1 shown in FIG. 5 further includes a fourth light source 2d, a fifth light source 2e, a fourth light receiving unit 3d, and a fifth light receiving unit 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 where the absorptivity changes rapidly in the long wavelength range (600 to 700 nm) of visible light in the absorption spectrum of the leaf blade 100. Therefore, the spectrum of the leaf blade 100 of the plant to be measured is acquired in advance to identify the red edge wavelength range, and the fourth light source 2d is prepared to irradiate visible light of a wavelength within the red edge wavelength range. For example, an LED can be used as the fourth light source 2d, and in this embodiment, an LED that irradiates visible light with a wavelength of 650 nm is used.

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

[0049] The fourth light receiving unit 3d and the fifth light receiving unit 3e are disposed 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 disposed 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 figure). In this embodiment, photodiodes are used as the light receiving units 3d and 3e. The light receiving units 3d and 3e are connected to an IV conversion board 7.

[0050] Using the fourth light source 2d and the fourth light receiving unit 3d, the amount of transmitted light of 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 measuring unit 8 measures the light receiving 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 leaf blade 100 with visible light L4 in the red edge wavelength region, and the fourth light receiving unit 3d receives the transmitted light. Based on the amount of light received by the fourth light receiving unit 3d at this time, the measuring unit 8 measures the light receiving voltage V4(ON) when the fourth light source 2d is turned on. Then, the calculation unit 10 calculates the difference between these light receiving voltages V4(OFF) and V4(ON), and records this value as the light receiving voltage V4 of the transmitted light of visible light L4. In this embodiment, the root mean square (RMS) value of the light receiving voltages V4(OFF) and V4(ON) expressed by the following formula is set as the light receiving voltage V4 of the transmitted light of visible light L4. V4=√{V4(ON)^2-V4(OFF)^2}

[0051] In addition, the fifth light source 2e and the fifth light receiving unit 3e can be used to measure the amount of transmitted light of the near-infrared light L5. Next, the amount of transmitted light of the near-infrared light L5 is measured. Specifically, first, with all the light sources 2a to 2e turned OFF, the measurement unit 8 measures the light receiving voltage V5 (OFF) when the light source is OFF based on the amount of light received by the fifth light receiving unit 3e. Next, the fifth light source 2e is turned ON to irradiate the leaf blade 100 with the near-infrared light L5, and the fifth light receiving unit 3e receives the transmitted light. Based on the amount of light received by the fifth light receiving unit 3e at this time, the measurement unit 8 measures the light receiving voltage V5 (ON) when the fifth light source 2e is turned ON. Then, the calculation unit 10 calculates the difference between these light receiving voltages V5 (OFF) and V5 (ON), and records this value as the light receiving voltage V5 of the transmitted light of the near-infrared light L5. In this embodiment, the root mean square (RMS) value of the light receiving voltages V5(OFF) and V5(ON) expressed by the following formula is set as the light receiving 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 ​​V4 and V5 measured above. This optical density difference d is expressed by the following formula. d=log 10 (V4)-log 10 (V5)

[0053] In this embodiment, the nitrate ion concentration E is measured taking into consideration 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 range (optical density difference d in this embodiment). Specifically, first, in the above step (1-1), 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, the transmitted light amount of the near-infrared light L3 (received light voltage V3), and the optical density difference d between the transmitted light amount of the visible light L4 in the red edge wavelength range and the transmitted light amount of the near-infrared light L5 are measured. Then, in the above step (1-2), the nitrate ion concentration E is expressed by an approximation equation with 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 Obtain the correlation equation expressed as (a1, a2, a3, and b are constants).

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

[0055] As described above, by measuring the amount of transmitted light (received light voltage V4) of visible light in the red edge wavelength range, the shift amount of 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 amount of transmitted light of the first ultraviolet light L1 but also the amount of transmitted light of 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. This improves the measurement accuracy of the nitrate nitrogen concentration. 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, a case where a plurality of light sources that irradiate light with different wavelengths are used has been described, but the present invention is not limited to this, and for example, a single light source that can irradiate a plurality of light with different wavelengths may be used. In this case, the number of light receiving units may be one. [Explanation of symbols]

[0057] 1. Nitrate nitrogen measuring device 2a~2e light source 3a~3e Light receiving part 4. Board 5 Light source control section 6 Heat sink 7 IV conversion board 8. Measurement section 9 Power supply 10 Arithmetic section 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 a first ultraviolet light having a wavelength in the range of 280 to 320 nm and measuring an amount of light transmitted through the plant; irradiating the plant with second ultraviolet light having a wavelength of 330 nm or more and measuring the amount of light transmitted through the plant; a step of irradiating the plant with near-infrared light and measuring an amount of the near-infrared light transmitted through the plant; irradiating the plant with visible light having a wavelength in a red edge wavelength range and measuring the amount of light transmitted through the plant; and calculating a nitrate nitrogen concentration in the plant based on the amount of transmitted light of the first ultraviolet light, the amount of transmitted light of the second ultraviolet light, the amount of transmitted light of the near-infrared light, and the amount of transmitted light of the visible light.

2. A first light source that irradiates a plant with a first ultraviolet light having a wavelength in the range of 280 to 320 nm; a first light receiving unit that detects an amount of the first ultraviolet light that is irradiated from the first light source and transmitted through the plant; 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 an amount of the second ultraviolet light that is irradiated from the second light source and transmitted through the plant; a third light source that irradiates the plant with near-infrared light; a third light receiving unit that detects an amount of the near-infrared light that is irradiated from the third light source and transmitted through the plant; A fourth light source that irradiates the plant with visible light having a wavelength in a red edge wavelength range; a fourth light receiving unit that detects an amount of the visible light that is irradiated from the fourth light source and transmitted through the plant; a calculation unit that calculates a 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, the amount of transmitted light of the second ultraviolet light detected by the second light receiving unit, the amount of transmitted light of the near-infrared light detected by the third light receiving unit, and the amount of transmitted light of the visible light detected by the fourth light receiving unit.

Images