TECHNICAL FIELD OF THE INVENTION

The present invention relates to a leaf device, capable of determining the hydration state of a plant by leaf analysis, as well as a possible stress condition that has occurred, in order, for example, to establish the best irrigation strategy.

The present invention also relates to the method for obtaining this detection by means of the above leaf device.

STATE OF THE ART

Techniques that aim to determine the water content of a plant and/or leaf are known. However, these techniques are not suitable for evaluating the fluctuations of the water content due to the brightness incident on the leaf and the Applicant has instead shown that these fluctuations are to be taken into consideration in order to obtain a significant result from the measurements in question.

For many species, the evapo-perspiration, which occurs in the presence of light, temporarily changes the water balance of the plant. The species that are sensitive to light availability have stomata that open in the presence of light and close in the shade or in the dark, without the onset of changes in the amount of water available for the plant. This light-related process changes the water content of the individual leaf.

All the vital functions of the plant (such as respiration, photosynthesis, cell growth and multiplication, radical absorption, translocation and transformation of nutrients) are influenced by water availability. Consequently, these vital functions affect, albeit to a small extent, the water content of the individual leaf.

Although being among the various factors necessary for the life of a plant the one required in higher quantities, the water that enters the constitution of the plant and which is fixed in the organic substance corresponds to approximately 1-1.5% of the absorbed water from the root system. 99% of the absorbed water is instead eliminated into the atmosphere in the form of steam in the perspiration process. Therefore, a continuous passage of water from the soil, to the root hairs, to the vascular tissues, to the cells of the leaves and from these to the external atmosphere occurs. The loss of water vapor, which occurs mainly through the stomata in the leaves, is called perspiration. To limit the continuous loss of water entering the atmosphere, a layer of cuticle impermeable to water and C0 ₂ is present on the upper page of the leaf, while the lower page presents the stomata that regulate the leakage of water into the tissues of the leaf epidermis and the entry of C0 ₂ for photosynthesis.

The stomata comprise two guard cells, whose shape changes cause the opening and closing of the stomatal pore. The closure of the stomata prevents the loss of water vapor from the leaf and also prevents the C0 ₂ from entry. A certain amount of C0 ₂ is produced by the plant with respiration, and as long as light is available, this C0 ₂ can be used to allow limited photosynthetic activity even with closed stomata. Even if the loss of water remains the factor, among all others, that most influences the operation of the stomata, the stomatal movements can occur independently of the gain or loss of water by the plant. In fact, many species have stomata that open regularly in the morning and close in the evening, responding to the availability of light, even if in the meantime no change in the amount of water available for the plant has occurred. In general, the factors that can cause the closure of the stomata are water loss, a high concentration of C0 ₂ , for many species the dark, and temperatures higher than 30-35° C.

The plant must constantly face the need to maintain within it an amount of water suitable for its normal functions, opposing the continuous demand for water from the atmosphere and subtracting water from the soil, where reserves are often limited. This balance is referred to as the "water balance" and represents the difference between the water inlet and outlet in the plant.

Therefore, for many species, the evapo-perspiration, which occurs in the presence of light, temporarily changes the water balance of the plant.

By measuring and correlating the light incident on the leaf and the water content of the leaf being measured, the Applicant was able to calculate the fluctuation of the water content due to the value of the brightness incident on the leaf and estimate the theoretical water content of the leaf in light or dark conditions.

OBJECTS OF THE INVENTION

An object of the present invention is to provide a leaf device capable of measuring the water content of a plant and/or, in particular, of a leaf.

Another object of the present invention is to provide a leaf device capable of counting the fluctuations of the water content due to the brightness incident on the leaf, in order to obtain a significant result from the measurements of the water content under consideration.

Therefore, the present invention makes it possible to correlate the water content of the leaf and the brightness incident on the leaf to determine the fluctuations of the water content of the leaf precisely caused by the variation of the incident brightness. Another object of the present invention is to provide a leaf device which is easy and practical to use, both in the laboratory and on open and wider surfaces, such as for example in a field.

Another object of the present invention is to provide a leaf device capable of providing information on the presence of any water stress for the plant and/or in particular for the leaf.

In accordance with an aspect of the invention, a leaf device according to claim 1 is provided.

In accordance with a further aspect of the invention, a method is provided for the determination of the water content of the plant by means of a leaf device, according to claim 11.

The dependent claims refer to preferred and advantageous embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be more evident from the description of an embodiment of a leaf device, shown by way of illustration in the accompanying drawings in which:

figure l is a side view of a leaf device according to the present invention; figure 2 is a top view of a version of the leaf device of figure 1, applied to a leaf;

figure 3 shows a diagram of a version of the leaf device according to the present invention, in which the detector means in reflection and transmission at 890 nm (NIR band) with an angle of incidence at 45° are illustrated. In this specific version, the detector means can be silicon photodiodes;

figure 4 illustrates a diagram of a version of the leaf device according to the present invention, which illustrates the detector means in reflection and transmission at 1450 nm (SWIR band) with an angle of incidence at 45°. In this specific version, the reflection and transmission detector means can be silicon photodiodes for the wavelength of 890 nm and InGaAs photodiodes for the wavelength at 1450 nm;

figure 5 illustrates a diagram of a version of the leaf device according to the present invention, in which the detector means in reflection and transmission at 890 nm (NIR band) and at 1450 nm (SWIR band) with an angle of incidence at 45° are illustrated-. In this specific version, the reflection and transmission detector means can be silicon photodiodes for the wavelength of 890 nm and InGaAs photodiodes for the wavelength at 1450 nm;

figure 6 illustrates a version of the leaf device according to the present invention in transmission only. Also in this case, the reflection and transmission detector means can be silicon photodiodes for the wavelength of 890 nm and InGaAs photodiodes for the wavelength at 1450 nm;

figure 7 illustrates a graph of the dependence between the ratio of the brightness transmitted at 1450 nm and 890 nm (line A) with the brightness incident on the leaf (line B);

figure 8 illustrates a graph relating to the brightness and brightness coefficients incident on the leaf. These are experimental data obtained by means of the present invention and correlation function obtained by performing a fit of the data. The brightness in Lux is on the abscissa, while the brightness coefficient is on the ordinate; figure 9 shows a graph of the values of the ratio L _trans (l ₁₄₅₀ ) / L _trans (l ₈₉₀ ) in ordinate on the time measured in seconds on the abscissa, without the correction of the luminance coefficients (line B) and with the correction (line A).

In the attached drawings equal parts or components are marked by the same reference numbers;

figure 10 illustrates a perspective view of a version of the leaf device according to the present invention;

figure 11 shows a side view of the leaf device of figure 10;

figures 12 and 13 show enlarged details of the leaf device of figures 10 and 11.

EMBODIMENTS OF THE INVENTION

The present invention relates to a leaf device indicated as a whole with 1, capable of correlating with each other the water content of a leaf F of a plant and the value of the brightness incident on the leaf itself.

In this way, it is possible to determine and/or measure the fluctuations of the water content of the leaf due precisely to the values of the brightness incident on the leaf. In the rest of this discussion, the formulas applied by the Applicant to the leaf device 1 will be reported, correlating the incident brightness with the measurement of the water content by means of appropriate correlation coefficients. For plants tested with the present invention, the correlation coefficients were obtained through a specific test procedure, which could also prove the effectiveness of the present invention.

The device 1 according to the present invention comprises a first portion 2 and a second portion 3. The first and second portions 2, 3 constitute two arms or plates, for example with a shape of gripper or clamp; moreover, the first portion 2 is suitable for being positioned in use at the upper face F1 of the leaf while the second portion 3 is suitable for being positioned in use at the lower face F2 of the leaf.

The leaf device 1 can be made of a plastic, possibly light and/or suitable for resisting humidity or bad weather, eventually biodegradable material.

The first and second portions 2, 3 of the leaf device 1 can be joined and/or constrained at one of their ends or fulcrum (indicated as la in figure 1), while their second end (indicated with lb in figure 1) is adapted to be coupled in a removable manner, after the leaf device 1 has been positioned on the leaf where the measurement should take place.

The first and second portions 2 and 3 can be joined with each other by screws or by gluing or other suitable means (as illustrated in figures 10 to 13).

In an alternative version, not shown in the attached figures, portions 2 and 3 have both ends la, lb released from each other but constrainable to each other in order to block inside them the leaf to be analyzed. In particular, in at least one version of the invention, the ends la of the first and second portions 2, 3 are separated from each other but are joined and/or constrained with each other so that the leaf device 1 can be made.

Therefore, the two portions 2 and 3 are movable one with respect to the other, and in particular they can be approached, so as to block or tighten the thickness of a leaf inside them, or they can be moved away from each other, in order to free the leaf, for example at the end of the measurement. The movement of the first portion 2 and the second portion 3 is thus reversible.

In particular, in one version, the first portion 2 moves in relation to the second portion 3 by rotating around a fulcrum or rotation axis X which passes for example at two joined ends la of these portions 2 and 3. In particular, the rotation axis is perpendicular to the rotation plane of the portions 2, 3.

In a further version, the two portions 2, 3 move relative to each other, translating on two substantially parallel planes with respect to each other.

Therefore, the two portions 2 and 3, in their approached position, are spaced apart from each other by a very thin space D, corresponding approximately to the thickness of the leaf.

In a particular version, in which the portion 2 and the portion 3 are approached to each other even in the absence of a leaf, they can come into contact, actually canceling the space between them.

At the end lb of the leaf device 1, an element for removable constraining the portions 2, 3 can be provided, for example shaped like a clip, screw with bolt, pin or nail equipped with a respective housing seat and/or interlocking, or by means of a band, a closure system such as adhesive, etc.

The leaf device l is a device for measuring the water content of a leaf and/or a plant. The first portion 2 and the second portion 3 have a substantially elongated conformation, capable of "enclosing" the entire transverse extension of the leaf to be measured. Given that the size of the leaves of plants of different species can vary widely, each portion 2, 3 will have a length varying between 5 cm and 20 cm. If necessary, one can also opt for a different shape or size of the leaf device, to meet the specificity of the leaf.

However, the conformation of the first portion 2 and the second portion 3 makes it possible to "enclose" and/or come into contact in use with a large leaf surface, thereby effectively facilitating the operation of the leaf device 1.

The first portion 2 and the second portion 3 also have a substantially cylindrical or prismatic or preferably parallelepiped conformation.

In the latter case, it is possible to identify, for each portion 2, 3, an internal base 2a, 3a, and an external base 2b, 3b. In use, the internal base 2a of the first portion 2 faces and is suitable for contacting and/or abutting with the internal base 3a of the second portion 3. When the leaf is present, the bases 2a, 3a are in contact respectively with the upper face FI and the lower face F2 of the leaf.

The external bases 2b, 3b, on the other hand, are opposite to the internal bases 2a, 3 a and face in use in a direction opposite to that of the leaf.

The first portion 2 comprises at least one emitter means 5, capable of emitting a light at a given wavelength. Therefore, the emitter means 5 is a light source.

Such at least one emitter means is capable of emitting at a wavelength equal to 890 nm (emitter means 5a) or 1450 nm (emitter means at 1450 nm).

In a version of the invention, two emitter means 5 are present, one 5a capable of emitting a wavelength equal to 890 nm and one 5b capable of emitting a wavelength equal to 1450 nm.

The 890 nm radiation provides information on the appearance of the leaf, makes it possible to estimate the amount of reflected light and the state of stress, while the 1450 nm radiation is used to estimate the hydration state of the plant.

In this description, the term "stress" means an identifiable biochemical condition of the leaf and/or plant, for example a condition that requires water in order to take it back to a normal or hydrated condition.

The at least one emitter means 5, in a version of the invention, is an LED light source that emits in a given wavelength.

The first portion 2 and/or the second portion 3 also comprises at least one detector means 6. In a version of the invention, the at least one detector means 6 comprises at least one photodiode, for example a SWIR photodiode, a NIR photodiode, a photodiode for the visible, for example a silicon (typical photodiode material for the visible and for NIR (890 nm)) or InGaAs (typical photodiode material for SWIR (1450 nm)) photodiode.

The at least one detector means 6 is powered, according to a version of the invention, in reverse current (i.e. the mode of operation of the photodiode is powered in reverse current, but can also be unpowered) and connected to a load resistance (other technical solutions can be that of connecting the photodiode to an operational amplifier for example).

The at least one detector means 6 is able to detect a wavelength after it has interacted with the leaf. In particular, the present invention can have at least one reflection detector means 6a, for example of the wavelength at 890 nm (reflection detector means 6al) or at 1450 nm (reflection detector means 6a2), in particular positioned at the first portion 2 of the leaf device 1.

Furthermore or alternatively, the at least one detector means 6 comprises at least one transmission detector means 6b, placed for example at the second portion 3 of the leaf device 1.

Therefore, the analysis by means of the leaf device 1 can be carried out in transmission and/or reflection and the detector means 6 are arranged on the same face of the emitter means 5 (to receive the reflected radiation) and/or on the face opposite to that on which the emitter means 5 are arranged (to receive the transmitted radiation).

By getting into the details, the leaf device 1 according to the present invention can comprise:

- in a first version of the invention, an emitter means 5a of a wavelength equal to 890 nm and an emitter means 5b of a wavelength equal to 1450 nm as well as a transmission detector means 6b 1 for the wavelength wave equal to 890 nm and a transmission detector means 6b2 for the wavelength equal to 1450 nm. It is thus a leaf device 1 which determines an analysis in transmission-only at 890 nm and at 1450 nm;

- in a second version of the invention, an emitter means 5a with a wavelength equal to 890 nm as well as a reflection detector means 6al and a transmission detector means 6b 1 for a wavelength equal to 890 nm. It is therefore a leaf device 1 which determines an analysis in reflection and transmission at 890 nm;

- in a third version of the invention, an emitter means 5b with a wavelength equal to 1450 nm as well as a reflection detector means 6a2 and a transmission detector means 6b2 for a wavelength equal to 1450 nm. It is therefore a leaf device 1 which determines an analysis in reflection and transmission at 1450 nm;

- in a fourth version of the invention, an emitter means 5a of a wavelength equal to 890 nm and an emitter means 5b of a wavelength equal to 1450 nm as well as a reflection detector means 6al and a transmission detector means 6b 1 for the wavelength equal to 890 nm and a reflection detector means 6a2 and a transmission detector means 6b2 for the wavelength equal to 1450 nm. It is therefore a leaf device 1 which determines an analysis in reflection and transmission at 890 nm and at 1450 nm.

Therefore, the leaf device 1 according to the present invention makes it possible to determine an analysis of the hydration and/or stress state of a plant and/or leaf and to monitor in real time the hydration state of the plant and thus, in this way and based on the results of the analysis carried out, to intervene appropriately in order to vary the irrigation and/or watering of the plant according to the real needs of the same. Therefore, in the first version the detector means 6 are positioned on the opposite portion (for example on the second portion 3) to that on which the emitter means 5 are positioned (for example on the first portion 2). In this case there are also two emitter means 5 and two detector means 6 (makes it possible to carry out analysis in transmission at both wavelengths).

In the second and third versions, an emitter means 5, on the same portion (for example the first portion 2) a reflection detector means 6a and on the opposite portion (for example the second portion 3) the transmission detector means 6b (allows to carry out reflection and transmission analysis at a single wavelength) are present.

In the fourth version, two emitter means 5, two reflection detector means 6a placed on the same face of the emitter means 5 (for example on the first portion 2) and, on the opposite face (for example on the second portion 3), two transmission detector means 6b (allows to carry out reflection analysis and transmission at two wavelengths) are present.

In the versions of the invention in which the analysis is carried out in transmission and also in reflection, it is possible that the emitter means 5 emit a radiation at the indicated wavelength, in which the radiation hits the leaf with an inclined direction with respect to the perpendicular of the leaf, for example with an angle of incidence equal to 45° or less or in any case different from 45°. In this case, also the emitter means 5 and/or the detector means 6 are positioned inclined, for example arranged on an plane inclined at an angle of 45° or less or in any case different from 45°. Furthermore, the present invention is characterized by the presence, in the leaf device 1, of a sensor 8 of brightness incident on the leaf.

Such at least one incident brightness sensor 8 is adapted to detect the intensity of the radiation of an artificial or natural light source such as the sun, which hits the leaf and/or is a photodiode, for example silicon, or a photoresistor, a digital brightness sensor or a photodiode with germanium or InGaAs or with two or more substrates, i.e. silicon germanium, germanium InGaAs, silicon InGaAs or silicon germanium and InGaAs, with a detection spectrum in the visible or in the enlarged visible, i.e. also including the infrared IR and/or ultraviolet UV radiation.

Of course, the sensor 8 does not detect the light emitted by the emitter means 5 (which can always be considered a light source) but only the radiation emitted by a light source external to the leaf device 1, such as a lamp, the sun or other.

Therefore, the sensor 8 detects the brightness incident on the leaf.

The measurement carried out by means of the leaf device according to the present invention can, in fact, be carried out directly in the place where the plant is located (therefore also in a field) or in a greenhouse or laboratory or in any other suitable place.

The incident brightness sensor 8 on the leaf is positioned at the external base 2b of the first portion 2. In this case, the incident brightness sensor 8 must always be directed towards the light source.

Alternatively, the or a sensor 8 could also be placed on the internal base 2a of the first portion 2, for example by making a through hole in the first portion 2 which goes from the internal base 2a to the external base 2b, the sensor 8 can be placed on the inside or on the end of such hole at the internal base 2a.

According to a less preferred alternative, instead of a hole, a waveguide component could be provided which conveys the light or incident brightness to the sensor 8 which is placed on the internal base 2a of the first portion 2, which waveguide component is extends from one side or external base 2b to the other side or internal base 2a of the first portion 2.

Of course, the sensor 8 could also be on the internal base 3a or external 3b of the second portion 3 or at the end or fulcrum la of union and/or constraint of the first 2 and of the second 3 portion.

If desired, a sensor 8 could also be provided inside or in the volume of the first portion 2 or of the second portion 3, this being possible for example by making a non-through hole in the first 2 or in the second portion 3, which hole ends or it is open towards the outside of the first 2 or second 3 portion or towards the external base 2b, 3b and placing the sensor 8 on the blind bottom of this non-through hole. Alternatively, the first 2 or the second 3 portion or better an external portion thereof could be made in a material that does not reflect or alter the light or at least such as not to reflect it or alter it in a sensitive way, then embedding the sensor in such portion 2, 3 or in this external portion.

In this way, the present invention overcomes the drawbacks of the prior art, since it can take into account the fluctuations in the water content of the leaf precisely in relation to the value of the incident light received by the sensor 8.

The present invention also provides a method for determining the water content of a leaf of a plant by at least one leaf device 1 according to the present invention, comprising the following steps:

providing a leaf device 1, suitable for being applied in use to a leaf F of a plant, comprising a first portion 2, a second portion 3, at least one emitter means 5 and at least one detector means 6,

applying the leaf device 1 to the leaf by positioning the first portion 2 at an upper face F1 of the leaf and the second portion 3 at a lower face F2 of the leaf, activating the at least one emitter means 5 so as to emit radiation at a wavelength equal to 890 nm and / or 1450 nm,

detecting this radiation reflected and/or transmitted by the leaf F by the at least one detector means 6,

actuating at least one incident brightness sensor 8 on the leaf positioned on the leaf device 1,

sending the data collected by the at least one incident brightness sensor 8 and by the at least one detector means 6 to a processing and control unit to determine the water content of the leaf F.

The processing and control unit (not shown in the accompanying drawings), can be positioned in the leaf device 1 or can be external to it, connected to the latter by means of cables or by means of a data transmission technology without cable, such as WiFi or Bluetooth, or by means of radio frequency identification technology or RFID (Radio-Frequency IDentification). Preferably, the data is acquired by a microcontroller that measures the voltage across the load resistance of the photodiodes and acquires the measurement of a digital incident brightness sensor (i.e. with an integrated meter, the data supplied to the microcontroller is not analog, but digital. Alternatively, it could also be an analog data and measured directly by the microcontroller). The microcontroller can send the data to a receiving system (gateway and then internet, server, computer) via a modem (via radio or cable) or send the data directly to a computer.

The collected data are then processed, considering both what has been received from the at least one detector means 6 and from the at least one incident brightness sensor 8, in order to determine the water content of the plant while assessing the fluctuations in the water content due to the variation of the brightness incident on the leaf and detected by the sensor 8.

The step of activating the at least one emitter means 5 comprises activating at least one emitter means 5a which emits radiation at a wavelength equal to 890 nm which is detected in reflection by at least one reflection detector means 6a, 6al of the wavelength at 890 nm and/or which is detected in transmission by at least one transmission detector means 6b, 6b 1 of the wavelength at 890 nm.

In addition or alternatively, the step of activating the at least one emitter means 5 comprises activating at least one emitter means 5b which emits radiation at a wavelength equal to 1450 nm which is detected in reflection by at least one reflection detector means 6a , 6a2 of the wavelength at 1450 nm and/or which is detected in transmission by at least one transmission detector means 6b, 6b2 of the wavelength at 1450 nm.

According to one version, the leaf device 1 is left applied to the leaf under examination during the various moments of the day or during the various moments of the test, since the brightness incident on the leaf and detected by the sensor 8 can vary both according to the position of the leaf, and during the day or test period. The present invention also refers to the use of the leaf device 1 for the determination of the water content of a leaf F of a plant taking into account the variation in the incident brightness.

Therefore, the determination of the water content of the leaf includes the determination of the state of hydration and/or stress of the plant and/or of the leaf and/or real-time monitoring of the state of hydration of the plant and/or of the leaf, adjust irrigation and/or watering the plant itself.

In fact, if the water content of the plant was within a certain range of parameters, defined as hydration of the plant, it would be possible to postpone or avoid the watering or irrigation phase.

If instead the water content of the plant was outside the hydration range of the plant, thus recalling a condition of water stress, it would be possible to anticipate or perform the watering or irrigation phase.

The data processed by the processing and control unit can then be sent to the staff who takes care of the plant in question or, automatically, to a watering/irrigation management system of the plant itself.

Another possible use, by determining the water content of the leaf, is to determine the presence of any diseases of the leaf and/or plant (for example, seeing that regardless of the irrigation or watering interventions, the water content of the leaf does not change) or even the presence of any substances present in the leaf and therefore in the plant, such as heavy metals, contaminants, etc. In this way, it is also possible to evaluate the health of the plant. For this point it is necessary to define specific reflection or absorption wavelengths for the substances to be searched, for example cadmium at a wavelength of 672.6 nm or lead at 416.8 nm, etc.

Advantageously, both the emitter means 5 and the detector means 6 are positioned at the internal bases 2a, 3a of the first portion 2 and of the second portion 3, respectively, according to a version in correspondence one above the other, when transmission detector means 6b are present.

In this way, the radiation emitted directly hits the leaf (in particular its upper face FI) and is transmitted according to a substantially rectilinear path from the lower face F2, where the detector means 6b is present.

Alternatively, the emitter means 5 and/or the detector means 6 can be provided at the external bases 2b, 3b of the first portion 2 and/or of the second portion 3, this being possible for example by making a through hole in the first 2 or in the second portion 3 and placing the means 5 and/or 6 at the outside of a respective through hole.

If desired, the emitter means 5 and/or the detector means 6 are provided inside or in the volume of the first portion 2 and of the second portion 3, this being possible for example by making a non-through hole in the first 2 or in the second portion 3, which hole ends or is open towards the inside of the first 2 of the second 3 portion or towards the internal base 2a, 3a and placing the means 5 and/or 6 on the blind bottom of a respective non-through hole.

Alternatively, the first 2 or the second 3 portion could be made or better an internal portion thereof it in a material that does not reflect or alter the light or at least such as not to reflect it or alter it in a sensitive way, then embedding the means 5 and/or 6 in said portion 2, 3 or in this internal portion.

Clearly, if the emitter means 5 is inclined by a certain angle with respect to the perpendicular of the leaf, the respective detector means 6b will be positioned on the internal base 3b inclined by an angle equal to 90° + the angle of incidence, so as to make it possible to receive the transmitted radiation (which as said moves in a substantially rectilinear direction).

Similarly, when the reflection detector means 6a are present, they will be positioned on the same internal base as the emitter means 5, i.e. the internal base 2a. When the emitter means 5 is inclined by a certain angle with respect to the perpendicular of the leaf, the respective detector means 6a will be positioned on the same internal base 2a inclined by an angle equal to 90° + the angle of incidence, so as to allow reception of the reflected radiation (which is usually reflected by forming an angle of about 90° with respect to the direction of incidence).

The leaf device 1 according to the present invention could also be equipped with at least one temperature and/or humidity sensor to detect any environmental changes. Such at least one temperature and/or humidity sensor can be positioned on the first and/or on the second portion 2, 3 or it could also not be positioned on the leaf device 1, but near the same. Temperature and/or humidity, in fact, can affect the condition of the leaf. In general, in fact, the factors that can cause the closure of the stomata are the loss of water, a high concentration of C0 ₂ , for many species the darkness, and temperatures higher than 30-35 ° C.

We report below the process of given calculations by the Applicant to determine and/or calculate the water content of a leaf and its variation over time, including the parameters that define the water content of a leaf according to at least one version of the present invention.

Description of the measurement of the parameters necessary to define the water content of a leaf

The water content of the leaf is estimated starting from the measurement of the attenuation of light in the low wavelength infrared radiation band (or Short-Wave Infra-Red - SWIR) that interacts with the leaf. By measuring the attenuation of light that interacts with the leaf in other bands, by way of non-exclusive example the light in the near infrared band (or Near Infra-Red - NIR), it is possible to estimate the characteristics of the leaf, such as the composition, structure, thickness, etc. in order to improve the measurement of the water content of the leaf. Specifically, to determine the water content of a leaf, the present invention uses two emitter means 5 (for example two LED light sources), one at 890 nm (NIR light) and one at 1450 nm (SWIR light). The emitter means 5a at 890 nm is used as a reference to estimate the absorption of light linked to all the molecules - except the water - that make up the leaf in question given the little attenuation of the water at these frequencies. Instead, at 1450 nm the light is much absorbed by the water, and therefore the change in intensity of this wavelength is a good indicator for estimating the amount of water present in the leaf.

The same result can be obtained by using at least one emitter means 5 or a different light source, coupled with filters to select the same spectral bands.

Other functional elements, useful for the leaf device 1, can be instruments placed on the at least one emitter means 5, such as for example at least one filter and/or at least one lens, and/or sensors suitable for improving the measurement.

Figure 1 shows a version of the present invention, in which the leaf device 1 has two emitter means 5 in correspondence with the upper face F1 of the leaf, perfectly aligned with the respective detector means 6 (or light sensors) positioned on the lower face F2 of the same leaf. The light generated by each emitter means 5 that affects the leaf is reflected, absorbed and finally transmitted to detector means 6 which measure its intensity through an appropriate electronic circuit. The emitter means 5 and the detector means 6, as well as the incident light sensor 8, present on the leaf device 1, are connected to an electronic processing system (not shown in the figures).

When the detector means 6 is illuminated by an emitter means 5 such as a narrow band light source (e.g. LED) centered at the wavelength l, then the voltage across the load resistance (to which the detector means 6 can be connected) depends approximately on the brightness detected by the detector means 6 by law (1): V _R =L _det ×S×R (1) where V _R is the voltage across the resistance, L _det is the detected brightness and S the spectral sensitivity at the wavelength l (R is the load resistance). The measurement of the voltage across the load resistance, operated by a suitable electronic circuit, allows to calculate the brightness detected by the photodiode, or detector means 6, and transmitted by the leaf according to the following formula

(2):

Description of the calculation of the water content starting from the measured parameters

When a beam of light passes through a section of leaf of thickness x and area A, the relationship between the incident brightness and brightness transmitted at a certain wavelength l is expressed by law (3): where m _w is the water absorption coefficient at the wavelength l, x _w is the equivalent water thickness in the leaf, is the total absorption coefficient of the substances that form the leaf with the exception of water at the length wave l, W _f is the mass fraction of the substances that form the leaf with the exception of water, r is the density of the leaf and r _f is the density of the substances that form the leaf with the exception of water.

L _trans (l) is the intensity of the light transmitted by the leaf, while L _inc (l) is the light incident on the leaf.

In the non-limiting example considered in figure 1, L _trans (l) is approximatable to the light detected by the photodiode (L _trans (l) =L _det ), and L _inc (l) is approximatable to the radiation generated by the light source. The equivalent water thickness (x _w ) corresponds to the ratio between the volume of water contained in the section of leaf crossed by the light beam and area A, so:

where M _w means the mass of water crossed by light, V _w the volume of water crossed by light and p _w the density of water. Using formula (3) the relationship between transmitted and incident brightness can be rewritten as follows (5):

where l _a means the wavelength of light radiation with non-negligible water absorption coefficient (e.g. light at 1450 nm). In the event that the light that interacts with the leaf has negligible water absorption coefficient (e.g. light at 890 nm) the formula (5) is further simplified:

where l _n eans the wavelength of light radiation with negligible water absorption coefficient (e.g. 890 nm). By analyzing the same leaf section or two very similar sections of the same leaf with two beams of light at different wavelengths it is possible to combine the formulas (5) and (6) together, obtaining the following (7): the mass of water (M _w ) contained in the illuminated section of the leaf will therefore be:

where by R _inc is meant the ratio between the incident luminosities ( R _inc = L _inc (l _n )/

L _inc (l _a )), which once set the leaf device 1 is constant.

Description of the calculation of the change in water content

Starting from formula (5) the ratio between two luminosities transmitted through the leaf in two different moments and at a wavelength sensitive to water (l _a ) is:

where by M _w (t _k ) it is to be meant as the mass of water at the instant t _k in the leaf section crossed by the light and x(t _k ) the thickness at the instant t _k in the leaf section crossed by the light. If the light is not at a wavelength (l _n ) sensitive to water, the formula is simplified into:

By analyzing the same section of leaf or two very similar sections of the same leaf with two different light beams and combining the formulas (9) and (10) the following is obtained:

where with DM _w (t ₀ , t ₁ ) (= M _w (t ₁ )— M _w (t ₀ )) it is intended the variation in the mass of water in the section of leaf crossed by the light.

Starting from formula (11) and measuring the light transmitted through the leaf at the wavelengths l _a and l _n in two different instants t ₀ and t ₁ , the mass of water relative to the instant t ₁ with respect to the instant t ₀ will be:

with constant C and equivalent to:

Other possible versions of the leaf device 1 may include measuring only the light reflected by the leaf or simultaneously the reflected light and the light transmitted by the leaf, in the SWIR band only, in the NIR band only (in this case also in transmission only) or together with other bands (NIR, visible, etc.).

These examples are illustrated in figures 3, 4 and 5.

In particular, in the version illustrated in figure 3, the location of the LEDs and photodiodes for the reflection and transmission configuration at 890 nm is illustrated. The arrangement of the sensors is optimized to detect the light in reflection (detector means 6al) and in transmission (detector means 6b 1), from which it is then possible to calculate the light absorbed by the leaf and determine its water status, and/or define the state of stress in which the leaf is located.

Two other possible versions of the invention consist of arranging LEDs and photodiodes with angles of incidence, transmission and reflection small or at 45°. The factor distinguishing the two versions is i) whether to favor transmission (through small angles) or ii) reflection (through angles at 45 degrees).

Figure 4 shows the location of the LED and photodiodes for the reflection and transmission configuration at 1450 nm. Also in this case, the arrangement of the sensors is optimized to detect the light in reflection (detector means 6a2) and in transmission (detector means 6b2), from which it is then possible to calculate the light absorbed by the leaf and determine its water state.

As for the previous version, two other possible embodiments consist of arranging LEDs and photodiodes with angles of incidence, transmission and reflection small or at 45°.

Figure 5 shows the configuration with reflection and transmission at 890 and 1450 nm. This type of arrangement allows to take advantage of the benefits of both frequencies but has, as a disadvantage, that of using twice the energy consumption compared to the previous ones, as well as that of needing a large leaf area.

Calculations of the correlation between leaf water content and incident brightness Figure 6 shows a possible (but not limiting) embodiment of the invention. This configuration provides LEDs (emitter means 5a, 5b) and photodiodes at 890 nm (NIR band) and at 1450 nm (SWIR band), i.e. detector means 6bl, 6b2, facing the leaf in transmission only, as well as a sensor 8 for the incident light on the external part of the leaf device 1, for example at the external base 2b of the first portion 2. Also in this case, additional functional elements may be present, useful for the leaf device 1, such as instruments (e.g. filters and/or lenses) placed on the brightness sensor 8 designed to improve the measurement. In this embodiment, and starting from formula (8), it is possible to determine the water content of the leaf using the following equation (14):

with constant A _w and B _w , L _trans (l ₁₄₅₀ ) is the light transmitted by the leaf at a wavelength of 1450 nm and L _trans (l ₈₉₀ ) is the light transmitted by the leaf at a wavelength of 890 nm. Correction of the parameters to define the water content of the leaf

As previously highlighted in formula (14) the A _w and B _w components are constants. It can therefore be noted that the only non-constant component present is the ratio between the brightness transmitted L _trans (l ₁₄₅₀ )/L _trans (l ₈₉₀ )

The test results, shown in the graph in figure 7, underline how the ratio L _trans (l ₁₄₅₀ )/ L _trans (l ₈₉₀ ) depends on the brightness incident on the leaf. In particular, line A represents the measurement of the ratio L _trans (l ₁₄₅₀ )/L _trans (l ₈₉₀ ), while line B is the brightness incident on the leaf. The data have been appropriately scaled along the y axis so as to be superimposable on a single graph in order to show the effect highlighted by the tests.

For this reason, it is clear that all other current techniques for measuring the water content of the leaf are affected by a fluctuation, which is not considered in the calculations, due to the effect of the incident light on the leaf. These fluctuations are due to the opening of the stomatic pore which allows the transpiration of the leaf (and/or other variations in the leaf due to a change in the state of the leaf, etc.). The present invention allows to estimate the fluctuation of the water content due to the incident light, to define the relative water content and to evaluate the basic or baseline water content. The fluctuation of water content due to incident light is estimated starting from the ratio between the light intensities transmitted by the leaf at the two wavelengths (890 nm and 1450 nm), using the following formula (15):

where L _leaf , means the intensity of the light incident on the leaf, IS

the ratio between the intensity of the light transmitted by the leaf to the two wavelengths (890 nm and 1450 nm) after correcting the fluctuation and is the ratio between the intensities of light transmitted by the leaf

to the two wavelengths (890 nm and 1450 nm) and measured by the leaf device 1. In its simplest form the formula (15) can be rewritten: with K(L _leaf ) conversion coefficents from

Description of the methods by which the brightness coefficients have been obtained By measuring the signal at the same time as the brightness incident on the leaf (by means of the sensor 8) during a rapid transition from dark to light, it was possible to measure the variation of the signal itself in relation to the variation in brightness. In this way it is possible to distinguish the variation due exclusively to the incident brightness, excluding other factors (e.g. internal variations of the leaf). This measurement is carried out quickly bringing the plant, to which the leaf being measured is attached, from a dark state (closed box, closed room, covered plant, etc.) to a state with a certain brightness, artificial or natural, incident on the leaf (open box, open room, uncovered plant, light on in the room, etc.). By analyzing the data, it is possible to determine a fit function to correlate the signal variation with the brightness. By repeating this procedure for different plants it is possible to generate a database with correlation functions for the different species.

The database is important in order to obtain the water status of the plant, according to at least one version of the invention. Each species to be subjected to analysis by the leaf device 1 requires a database that relates the cross-correlation between the water state and the brightness incident on the leaf. The database has been built and will be expanded on the basis of repeated experiments using the method described below which alternates two phases of darkness with one of light.

Data acquisition procedure

The method involves to start positioning the leaf device 1 on a leaf of a hydrated plant. Once the device values for the species have been calibrated, the plant is left to get acclimatize in the dark for 10 minutes. The test involves cycles of 30 minutes of measurement in which two periods of darkness and one of light of 10 minutes alternate. The cycles are separated by 10-minute breaks in which the plant remains in a dark condition. In the present discussion, the term "dark" corresponds to a situation in which the detected brightness settles around values of 1 lux. The cycle begins with a first dark phase. Afterwards, the plant is suddenly exposed to direct natural light. In the third and final phase, the plant is quickly brought back to dark conditions. The entire cycle must be repeated in order to record the response of the plant to different light intensities. If one works with natural light, the cycle must be repeated at all stages of the day. Subsequently, the variation factor of the signal recorded during the various changes from dark to light is calculated. This datum allows to correct the measured signal, obtaining the relative state of hydration of the leaf in the presence of natural incident light.

Data analysis in order to eliminate the fluctuations in the water content measurements through the leaf device of the present invention

Using equation (16) and the data previously acquired by the invention, a functional relationship can be defined between the brightness coefficients and the brightness incident on the leaf. Using equation (16) it is possible to express the brightness coefficients such as the ratio between the measured brightness and the baseline, according to the equation:

Approximating baseline values to the average of the

measurements taken in the dark in each cycle and considering that are the measurements made with light and therefore subject to the

fluctuation of the incident light, it is possible to determine, from the measurements made with the leaf device 1, the brightness coefficients of the leaf.

By performing a fit of the brightness coefficients, obtained from the measurements of the leaf device 1 and the brightness incident on the leaf, directly measured by the leaf device according to the present invention, it is possible to determine a correlation function between the brightness coefficients and the brightness incident on the leaf. Figure 8 shows the experimental data, obtained from the leaf device 1, of the brightness coefficients and of the brightness incident on the leaf and the correlation function between the data. The fit function used is:

With P ₀ = 1,123 x 10 ⁵ ± 2359 obtained by analyzing the brightness coefficients. The fit regression line has a determination coefficient of R ² = 0,9933.

By applying the brightness coefficients obtained from formula (18) it is possible to obtain the baseline values of the ratio between the brightness transmitted at 1450 starting from the measured brightness values

The graph in figure 9 illustrates how the baseline values (line A) are not affected by the fluctuation due to the brightness incident on the leaf with respect to the measured values (line B). Given that the luminosity coefficients are species-specific, the data shown in this document refer, by way of explanation, to the species Anthurium andraeanum.

In addition, the calculations that take into account the area of the leaf approximate the surface of a leaf, which has depressions and veins, to a uniform surface of the same size.

Finally, the difference in mass between the turgid leaf and the dry leaf will only refer to the water present in the leaf.

The mass of water measured by the invention in the area under test can be calculated starting from equation (14). Depending on whether the ratio between baseline or measured brightness is considered, the water mass will be:

Known devices calculate only the measured water mass and not the baseline water mass, as they do not have a leaf device like that of the present invention, capable of measuring the light incident on the leaf. By combining the formulas (16), (19) and (20) we obtain that the difference between the measured and baseline mass is:

with A the area of the leaf under test, m _w =2.860 mm ^-1 the water absorption coefficient (at 1450 nm) and p _w =1 g /cm ³ =1 mg /mm ³ the density of the water. The mass variation between measured values and baseline per square millimeter will be: At 1000 lux of incident brightness, the brightness coefficient is K (1000)=1.00895, ln(K (1000 ))=0.009 and the mass variation per square millimeter IDM _W I/A =0.003 mg /mm ² . The greater the area of the leaf, the greater the difference between the measured mass of water and the baseline. Multiplying the change in mass per square millimeter (0.003 mg /mm ² ) by the surface of the leaf i (S _i ) the change in water mass due to the incident brightness for that specific leaf was obtained. Dividing the change in mass (Dmi) by the water contained in the leaf i (mi) the change in relative water mass due to brightness is obtained. Considering the difference in mass between the turgid leaf and the dry leaf as the water contained in the leaf, the relative mass change in water due to the incident brightness of 1000 lux will be: with DR _i (1000 lux) the percentage variation of relative mass of the leaf i at the incident brightness of 1000 lux, S _i the area of the leaf i under test, FT _t the weight of the leaf i turgid, FD _i the weight of the leaf i dehydrated and Dm _i (1000 lux) the change in mass of water at 1000 lux for the leaf i.

By applying formula (23) to a sample of leaves under test (table 1) and calculating the average of the values found, an average value of relative mass variation of the leaf at 1000 lux of incident light was calculated. The estimated variation is therefore 1%, a significant value from a practical point of view if one takes into account the fact that a loss of 10% of water mass in the leaf irreparably compromises its vitality.

Table 1 : Data relating to the analysis of a sample of 10 Anthurium andraeanum leaves

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the inventive concept.

The features presented for one version or embodiment can be combined with the features of another version or embodiment, without departing from the scope of the present invention.

Furthermore, all the details can be replaced by other technically equivalent elements. In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to requirements without thereby departing the scope of the following claims.