Method and apparatus 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 laborious.

[0003] For example, in Patent Document 1 below, a method for non-destructively measuring the nitrate ion concentration in vegetables is shown by irradiating the vegetables with light, obtaining the 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

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 almost no nitrate ions inside the plant are measured. Therefore, depending on the shape of the plant (especially the surface shape), the type, and the distribution status of nitrate ions in the plant, variations occur 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 aforementioned problems, the present invention provides a method for measuring nitrate nitrogen concentration, comprising the steps of: 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] Furthermore, the present invention 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 the amount of transmitted light of the first ultraviolet light 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 this invention, a plant is irradiated with first ultraviolet light having a wavelength near the maximum absorption wavelength of nitrate nitrogen (approximately 300 nm), 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. This makes it possible to measure the concentration of nitrate nitrogen, including that present not only on the surface of the plant but also inside the plant, thus enabling more accurate measurement of the nitrate nitrogen concentration than conventional techniques that measure the amount of reflected light received.

[0010] The absorbance of nitrate nitrogen decreases as the wavelength lengthens beyond the maximum absorption wavelength, and ultraviolet light in the wavelength range of 330 nm or longer is hardly absorbed by nitrate nitrogen (see Figure 3). Therefore, when ultraviolet light with wavelengths of 330 nm or longer is irradiated onto plants, the amount of transmitted light is relatively more influenced by elements other than nitrate nitrogen. Accordingly, by calculating the nitrate nitrogen concentration in plants based on the amount of transmitted light from the first ultraviolet light and the amount of transmitted light from the second ultraviolet light with wavelengths of 330 nm or longer, it is possible to obtain measurement results that exclude the influence of elements 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 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. Furthermore, 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 transmitted light of the second ultraviolet light irradiated from the second light source and passed through the plant, and that 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 second ultraviolet light detected by the second light receiving unit.

[0012] The amount of transmitted ultraviolet light decreases 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 transmitted light. 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 each time. For example, if we assume that the volume (thickness) of the plant is constant, we can calculate the nitrate nitrogen concentration, but there are concerns about a decrease in measurement accuracy.

[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 transmitted light that has passed through the plant, and that the nitrate nitrogen concentration in the plant is calculated based on the amount of transmitted first ultraviolet light and the amount of transmitted near-infrared light. Furthermore, 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 near-infrared light irradiated from the third light source and that has passed through the plant, and that the calculation unit calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted first ultraviolet light detected by the first light receiving unit and the amount of transmitted near-infrared light detected by the third light receiving unit.

[0014] Because water absorbs light highly in the near-infrared wavelength range (750-2500 nm), the relative amount of water contained in plants, and consequently the relative volume of the plants, 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 ultraviolet light and the amount of transmitted near-infrared light, information about the plant's volume is reflected in the measurement results, thus improving the accuracy of nitrate nitrogen concentration measurement.

[0015] Furthermore, 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 first ultraviolet light and the amount of transmitted visible light. Furthermore, 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 visible light irradiated from the fourth light source and passed through the plant, and the calculation unit preferably calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted first ultraviolet light detected by the first light receiving unit and the amount of transmitted visible light detected by the fourth light receiving unit.

[0016] In the absorption spectrum of plants, there is a wavelength range called the red edge wavelength range in the long wavelength range of visible light (600-700 nm) where the absorbance changes abruptly. It is known that when plants are subjected to stress such as water shortage, the red edge wavelength range shifts towards the shorter wavelength side (blue shift). Therefore, by measuring the amount of shift in the red edge wavelength range from the amount of transmitted visible light in the red edge wavelength range, it is possible to measure the relative value of the water content in the plant, and consequently the relative value of the plant's volume. Thus, as described above, by calculating the nitrate nitrogen concentration using the amount of transmitted ultraviolet light and the amount of transmitted visible light in the red edge wavelength range, information about the plant's volume is reflected in the measurement results, improving the accuracy of nitrate nitrogen concentration measurement. [Effects of the Invention]

[0017] As described above, the measurement method of the present invention allows for more accurate measurement of nitrate nitrogen concentration in plants using non-destructive testing.

Brief Description of the Drawings

[0018] [Figure 1] It 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 the destructive inspection. [Figure 2] It is a cross-sectional view of a nitrate nitrogen concentration measuring device according to an embodiment of the present invention. [Figure 3] It is the spectral spectrum of nitrate ions. [Figure 4] It is a cross-sectional view of a nitrate nitrogen concentration measuring device according to another embodiment. [Figure 5] It is a cross-sectional view of a nitrate nitrogen concentration measuring device according to still another embodiment.

Modes for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described based on 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 amount of the leaf blade Irradiate the leaf blade with ultraviolet light and measure the transmitted light amount (optical density of the transmitted light) that has passed through the leaf blade. The specific measurement procedure for the transmitted light amount (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 destructive inspection The nitrate ion concentration in the leaf blade, whose transmitted light intensity was measured in (1-1) above, is measured by destructive testing. Specifically, the leaf blade is squeezed with a juicer to collect the juice, and the nitrate ion concentration of this juice is measured using a commercially available nitrate ion concentration meter. In addition to the leaf blade, juice may also be collected from the petiole and stem.

[0023] (1-3) Obtain a correlation equation between optical density and nitrate ion concentration. Obtain a correlation equation between the transmitted light quantity obtained in (1-1) above and the nitrate ion concentration obtained in (1-2) above. For example, as shown in Figure 1, plot the results obtained in (1-1) and (1-2) above on a graph with the optical density of transmitted light on the horizontal axis and the nitrate ion concentration on the vertical axis. Calculate an approximate equation (a linear equation in the illustrated example) for these plots, and use this approximate equation as the correlation equation between optical density and nitrate ion concentration. For example, when the nitrate ion concentration is E, the optical density difference described later is D, and a and b are constants, perform multiple regression analysis to obtain: E = a·D + b The correlation formula represented by this formula is obtained. The correlation formula thus obtained is stored in the calculation unit 10, which will be described later.

[0024] Next, we will explain the procedure for measuring the nitrate ion concentration (nitrate nitrogen concentration) in the leaf blade using non-destructive testing.

[0025] (2-1) Installation of measuring device First, as shown in Figure 2, a nitrate nitrogen measuring device 1 according to one embodiment of the present invention is attached to the leaf blade 100 of a fruit vegetable, which is the target of nitrate nitrogen concentration measurement. The measuring device 1 is attached to a growing leaf blade 100 that 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 (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 (left side in the figure).

[0026] The first light source 2a emits first ultraviolet light. As shown in Figure 3, the absorption spectrum of nitrate ions is maximum at a wavelength of around 300 nm. The first ultraviolet light is ultraviolet light in the 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 emits ultraviolet light with a wavelength of 310 nm is used.

[0027] The second light source 2b emits a second ultraviolet light. As shown in Figure 3, the absorption spectrum of nitrate ions shows that the absorbance decreases as the wavelength increases from the maximum absorption wavelength (approximately 300 nm), and is hardly absorbed at wavelengths of 330 nm or higher. 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 where the absorbance is 20% or less of the absorbance at the maximum absorption wavelength (approximately 300 nm). In this embodiment, the second ultraviolet light has a wavelength of 330 nm or higher (preferably 340 nm or higher). 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, and in this embodiment, an LED that emits ultraviolet light with a wavelength of 340 nm is used.

[0028] The first light-receiving unit 3a is positioned to receive the first ultraviolet light irradiated from the first light source 2a, and the second light-receiving unit 3b is positioned to receive the second ultraviolet light irradiated from the second light source 2b. In the illustrated example, the first light-receiving unit 3a is positioned opposite the first light source 2a in the thickness direction (left-right direction in the figure) of the leaf blade 100, and the second light-receiving unit 3b is positioned opposite 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 the received light. 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 (for example, an aluminum substrate). The substrate 4 is connected to a light source control unit 5, which includes a power supply. By supplying power from the light source control unit 5 to either light source 2a or 2b via the substrate 4, light sources 2a and 2b can be selectively illuminated. A heat sink 6 is attached to the back of the substrate 4 (the side 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 measuring unit 8 (e.g., a multimeter) and a power supply 9 are connected to the IV conversion board 7. The measuring 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 measuring unit 8 via the IV conversion board 7, and the measuring unit 8 measures the received light voltage based on this electrical signal.

[0031] (2-2) Measurement of the amount of transmitted ultraviolet light (receiving voltage V1) First, with both light sources 2a and 2b turned OFF, the measurement unit 8 measures the received voltage V1(OFF) when the light sources are OFF, based on the amount of light received by the first light receiving unit 3a. Next, the first light source 2a is turned ON and the first ultraviolet light L1 is irradiated onto the leaf blade 100, and the transmitted light is received by the first light receiving unit 3a (see Figure 2). Based on the amount of light received by the first light receiving unit 3a at this time, the measurement unit 8 measures the received voltage V1(ON) when the first light source 2a is turned ON. Then, the calculation unit 10 calculates the difference between these received voltages V1(OFF) and V1(ON) and records this value as the received voltage V1 of the transmitted light of the first ultraviolet light L1. In this embodiment, the root mean square (RMS) value of the received voltages V1(OFF) and V1(ON), which are expressed by the following formula, is considered to be the received 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 amount of transmitted ultraviolet light (receiving voltage V2) Next, with both light sources 2a and 2b turned OFF, the measurement unit 8 measures the received voltage V2(OFF) when the light sources are OFF, based on the amount of light received by the second light receiving unit 3b. Next, the second light source 2b is turned ON and the second ultraviolet light L2 is irradiated onto the leaf blade 100, and the transmitted light is received by the second light receiving unit 3b (see Figure 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 voltage V2(ON) when the second light source 2b is turned ON. Then, the calculation unit 10 calculates the difference between these received voltages V2(OFF) and V2(ON) and records this value as the received voltage V2 of the transmitted light of the second ultraviolet light L2. In this embodiment, the root mean square (RMS) value of the received voltages V2(OFF) and V2(ON), which are expressed by the following formula, is considered to be the received 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 V1 and V2 values ​​measured above. In this embodiment, since the irradiation amounts of ultraviolet light 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 calculates the nitrate ion concentration E in the leaf blade 100 by substituting the value of the optical density difference D into the correlation formula (E=a·D+b) obtained in (1-3) above. From this nitrate ion concentration E, the nitrate nitrogen concentration of the leaf blade 100 is calculated.

[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 nitrate ions is measured, and the nitrate nitrogen concentration is calculated based on this transmitted light amount. 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, thus providing highly reliable measurement results.

[0036] Furthermore, 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 greatly influenced 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 measurement results that eliminate the influence of factors other than nitrate nitrogen, thereby improving measurement accuracy.

[0037] As described above, the nutritional status of the leaf blade, and by extension the nutritional status of the fruiting vegetable, can be inferred from the nitrate nitrogen concentration measured in the leaf blade. Therefore, subsequent growing conditions (e.g., fertilizer application rate) can be adjusted based on the measured nitrate nitrogen concentration. For example, by obtaining in advance the range of nitrate nitrogen concentration in leaf blades under good growth conditions, it is possible to maintain consistently good growth conditions by increasing the fertilizer application rate if the nitrate nitrogen concentration measured in the leaf blades during growth falls below this range, and decreasing the fertilizer application rate if the nitrate nitrogen concentration exceeds this range.

[0038] The present invention is not limited to the embodiments described above. Other embodiments of the present invention will be described below, but details similar to those of the embodiments described above will be omitted.

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

[0040] The third light source 2c emits near-infrared light (wavelength 750-2500 nm), for example, near-infrared light having a wavelength near the maximum absorption wavelength of water (for example, 1430-1470 nm or 1920-1960 nm). An LED is used as the third light source 2c, and in this embodiment, an LED that emits 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 allows any of the light sources 2a to 2c to be selectively emitted.

[0041] The third light-receiving unit 3c is positioned to receive near-infrared light irradiated from the third light source 2c. In the illustrated example, the third light-receiving unit 3c is positioned opposite the third light source 2c in the thickness direction (left-right direction in the figure) of the leaf blade 100. 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 substrate 7.

[0042] Using these third light source 2c and third light receiving unit 3c, the amount of transmitted 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 received light voltage V3(OFF) when the light sources are 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 leaf blade 100 with near-infrared light L3, and the transmitted light is received by the third light receiving unit 3c. Based on the amount of light received by 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) and V3(ON), and records this value as the received light voltage V3 of the transmitted near-infrared light L3. In this embodiment, the root mean square (RMS) values ​​of the received voltages V3(OFF) and V3(ON), expressed by the following formulas, are considered to be the received voltage V3 of the transmitted near-infrared light L3. V3 = √{V3(ON)^2 - V3(OFF)^2}

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

[0044] Then, the measuring device 1 is attached to the leaf blade 100, which is the object 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 of near-infrared light L3 (receiving voltage V3) are measured. By substituting these optical density difference D and receiving voltage V3 into the correlation formula (E=a1·D+a2·V3+b) above, 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 readily absorbed by water, the relative amount of water contained in the leaf blade 100 can be estimated from the amount of transmitted near-infrared light irradiated from light source 2c. In this embodiment, by measuring not only the amount of transmitted first ultraviolet light L1 but also the amount of transmitted near-infrared light L3, the amount of water in the leaf blade 100, and consequently the nitrate ion concentration E based on the volume (thickness) of the leaf blade 100, can be measured. This improves the accuracy of nitrate nitrogen concentration measurement.

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

[0047] The fourth light source 2d emits visible light in the red edge wavelength range. The red edge wavelength range is the wavelength range in the long wavelength range (600-700 nm) of the absorbance spectrum of the leaf blade 100 in which the absorbance rate changes abruptly. Therefore, the spectral spectrum of the leaf blade 100 of the plant to be measured is obtained in advance to identify the red edge wavelength range, and a fourth light source 2d is prepared that emits visible light with wavelengths within that red edge wavelength range. For example, an LED can be used as the fourth light source 2d, and in this embodiment, an LED that emits visible light with a wavelength of 650 nm is used.

[0048] The fifth light source 2e emits near-infrared light (wavelength 750-2500 nm), and in this embodiment, for example, an LED emitting near-infrared light at 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 allows any of the light sources 2a to 2e to be selectively emitted.

[0049] The fourth light-receiving unit 3d and the fifth light-receiving unit 3e are positioned 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 positioned opposite the fourth light source 2d and the fifth light source 2e in the thickness direction (left-right direction in the figure) of the leaf blade 100, respectively. In this 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 board 7.

[0050] The amount of transmitted visible light L4 in the red edge wavelength range can be measured using the fourth light source 2d and the fourth light receiving unit 3d. Specifically, first, with all light sources 2a to 2e turned OFF, the measurement unit 8 measures the received light voltage V4(OFF) when the light sources are 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 range, 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 visible light L4. In this embodiment, the root mean square (RMS) values ​​of the received light voltages V4(OFF) and V4(ON), which are expressed by the following formulas, are considered to be the received light voltage V4 of the transmitted visible light L4. V4 = √{V4(ON)^2 - V4(OFF)^2}

[0051] Furthermore, the amount of transmitted near-infrared light L5 can be measured using the fifth light source 2e and the fifth light receiving unit 3e. Next, the amount of transmitted near-infrared light L5 is measured. Specifically, first, with all light sources 2a to 2e turned OFF, the measurement unit 8 measures the received light voltage V5 (OFF) when the light sources are OFF, based on the amount of light received by the fifth light receiving unit 3e. Next, the fifth light source 2e is turned ON and the near-infrared light L5 is irradiated onto the leaf blade 100, and the transmitted light is received by the fifth light receiving unit 3e. Based on the amount of light received by 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 near-infrared light L5. In this embodiment, the root mean square (RMS) values ​​of the received light voltages V5(OFF) and V5(ON), expressed by the following formulas, are considered to be the received light voltage V5 of the transmitted 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 V4 and V5 values ​​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 by considering not only the amount of transmitted light of the first ultraviolet light L1, but also the amount of transmitted light of visible light L4 in the red edge wavelength range (optical density difference d in this embodiment). Specifically, first, in step (1-1) above, 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 near-infrared light L3 (receiving voltage V3), and the optical density difference d between the amount of transmitted light of visible light L4 in the red edge wavelength range and the amount of transmitted light of near-infrared light L5 are measured. Then, in step (1-2) above, the nitrate ion concentration E is expressed by an approximate formula with optical density difference D, receiving voltage V3, and optical density difference d as variables. For example, by multiple regression analysis, E = a1·D + a2·V3 + a3·d + b Obtain the correlation equation represented by (a1, a2, a3, and b are constants).

[0054] Then, the measuring device 1 is attached to the leaf blade 100, which is the target of measurement, 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, the transmitted light amount of near-infrared light L3 (receiving voltage V3), and the optical density difference d between the transmitted light amount of visible light L4 in the red-edge wavelength range and the transmitted light amount of near-infrared light L5 are measured. By substituting these optical density differences D, receiving voltage V3, and optical density difference d into the correlation formula (E=a1·D+a2·V3+a3·d+b) above, 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] As described above, by measuring the amount of transmitted visible light (receiving voltage V4) in the red edge wavelength range, the shift amount in the red edge wavelength range and, consequently, 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 visible light L3 in the red edge wavelength range, the water content in the leaf blade 100 and, consequently, the nitrate ion concentration taking into account the volume (thickness) of the leaf blade 100 can be measured. This improves the accuracy of the measurement of nitrate nitrogen concentration. In this embodiment, if there is no particular need, the measurement of transmitted near-infrared light L3 by the third light source 3c and the third light receiving unit 3c may be omitted.

[0056] The above embodiments show a case where multiple light sources emitting light of different wavelengths are used, but the invention is not limited to this, and for example, a single light source capable of emitting multiple light sources of different wavelengths may be used. In this case, there may be only one light receiving unit. [Explanation of Symbols]

[0057] 1. Nitrate nitrogen measuring device 2a~2e light source 3a~3e Light receiving part 4 circuit boards 5. Light source control unit 6 Heat sink 7 IV Conversion Board 8 Measurement Unit 9 Power supply 10 Arithmetic section 100 leaf blades L1 First ultraviolet light L2 Second ultraviolet light L3 Near-infrared light L4 visible light L5 Near-infrared light

Claims

1. A process of irradiating a plant with first ultraviolet light having a wavelength in the range of 280 to 320 nm from a single LED, and measuring the amount of transmitted light that passes through the plant without spectrally analyzing it for each wavelength, The process involves irradiating the plant with near-infrared light having a wavelength near the maximum absorption wavelength of water, and measuring the amount of light transmitted through the plant. A method for measuring nitrate nitrogen concentration, comprising the step of calculating the nitrate nitrogen concentration in the plant based on the amount of first ultraviolet light transmitted and the amount of near-infrared light transmitted.

2. The process includes irradiating the plant with a second ultraviolet light having a wavelength of 330 nm or more from a single LED, and measuring the amount of transmitted light that passes through the plant without spectrally separating it by wavelength. A method for measuring nitrate nitrogen concentration in a plant according to claim 1, wherein the nitrate nitrogen concentration in the plant is calculated based on the amount of first ultraviolet light transmitted and the amount of second ultraviolet light transmitted.

3. The process involves irradiating the plant with visible light in the red-edge wavelength range and measuring the amount of transmitted light that passes through the plant without spectrally separating it by wavelength. A method for measuring nitrate nitrogen concentration in a plant, according to claim 1 or 2, wherein the nitrate nitrogen concentration in the plant is calculated based on the amount of first ultraviolet light transmitted and the amount of visible light transmitted.

4. A first light source consisting of a single LED 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 passed through the plant without spectrally separating it by wavelength, The plant is irradiated with a third light source that emits near-infrared light having a wavelength near the maximum absorption wavelength of water, A third light receiving unit that detects the amount of transmitted light of the near-infrared light irradiated from the third light source and passed through the plant, A device for measuring nitrate nitrogen concentration, comprising a calculation unit that calculates the nitrate nitrogen concentration in the plant based on the amount of transmitted ultraviolet light detected by the first light receiving unit and the amount of transmitted near-infrared light detected by the third light receiving unit.

5. The plant is irradiated with a second light source consisting of a single LED having a second ultraviolet light with a wavelength of 330 nm or more, It has a second light-receiving unit that detects the amount of transmitted light of the second ultraviolet light irradiated from the second light source and passed through the plant without spectrally separating it by wavelength, The nitrate nitrogen concentration measuring device according to claim 4, wherein the calculation unit calculates the nitrate nitrogen concentration in the plant based on the amount of first ultraviolet light transmitted by the first light receiving unit and the amount of second ultraviolet light transmitted by the second light receiving unit.

6. The plant is provided with a fourth light source that irradiates it with visible light in the red edge wavelength range, It has a fourth light-receiving unit that detects the amount of visible light transmitted through the plant, irradiated from the fourth light source, without spectrally separating it by wavelength, The nitrate nitrogen concentration measuring device according to claim 4 or 5, wherein the calculation unit calculates the nitrate nitrogen concentration in the plant based on the amount of first ultraviolet light transmitted by the first light receiving unit and the amount of visible light transmitted by the fourth light receiving unit.

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