Microfluidic nutrient measurement sensor system, method for the direct automated measurement of nutrients from soil solution in a sensor system, and microfluidic nutrient measurement sensor system assembly

Abstract

The invention relates to a microfluidic nutrient measurement sensor system for the direct automated measurement of nutrients from soil solution, comprising a sensor box having at least one sensor; an energy supply; a controller; a soil solution extraction unit having a first pump; reservoirs for storing solutions; and a second pump, and is characterised in that the sensor is designed as a chip having microfluidics, the energy supply is designed having an internal current source, and the soil solution extraction unit is designed having a first pump and a suction head made of a porous ceramic. The invention additionally relates to a method for the direct automated measurement of nutrients from soil solution in a sensor system, and to a microfluidic nutrient measurement sensor system assembly.

Description

[0001] Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0002] September 10, 2025

[0003] 1

[0004] Microfluidic nutrient measurement sensor system. Method for the direct automated measurement of nutrients from soil solution in a sensor system and microfluidic nutrient measurement sensor system.

[0005] NETWORK

[0006] The invention relates to a microfluidic nutrient measurement sensor system for direct automated nutrient measurement from soil solution comprising a sensor box with at least one sensor, a power supply, a control unit, a soil solution extraction unit with a first pump, reservoirs for storing solutions and a second pump.

[0007] Furthermore, the invention relates to a method for the direct automated measurement of nutrients from soil solution in a sensor system and a microfluidic nutrient measurement sensor system combination.

[0008] Eutrophic waters, declining biodiversity, and nitrate-contaminated drinking water have brought agricultural fertilization practices into sharp focus, highlighting how improper fertilization is already causing significant environmental damage and heavily polluted soils. This focus is also reflected in stricter regulations, rules, and laws, particularly within the EU (for example, the EU Nitrates Directive (91 / 676 / EEC)), and is driving the need for better nutrient monitoring. In January 2023, the Common Agricultural Policy 2023-27 (CAP 2023-27) came into force, aiming to actively address these problems. A new EU Soil Health Directive is expected to be adopted. Furthermore, the revised Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV) has been in effect in Germany since August 1, 2023.

[0009] The need for data acquisition is also increasing in precision agriculture, as its foundation is fundamentally based on data analysis for optimizing agricultural processes. Temperature, humidity, and nutrient concentrations are particularly important here to ensure a sustainable supply of nutrients to plants, while increasing weather extremes, climate variability, international conflicts, and a growing global population threaten food security.

[0010] The determination and quantification of soil nutrients is therefore an important tool for agricultural applications as well as for soil remediation and soil monitoring.

[0011] According to the state of the art, there are various systems for determining soil nutrients, based on different methods such as the electrical Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0012] September 10, 2025

[0013] 2

[0014] Conductivity, near-infrared spectroscopy, capillary electrophoresis or UV / Vis spectroscopy are used.

[0015] Soil nutrients are determined using laboratory analyses, capillary electrophoresis, electrochemical potential analysis, infrared sensors, spectrometers, and optical sensors. Laboratory testing is the standard method for soil nutrient measurements. For laboratory tests, soil samples are taken from at least 16 different soil columns per field. These samples are homogenized, immediately frozen, and sent to an external laboratory. The laboratories use chemical digestion with strong acids or bases to extract the nutrients from the soil samples. The required standard methods for quantifying the nutrient parameters (e.g., grit assay, CAL method, DL method, Mehlich-3 method) depend on the nutrients being determined and the laboratory's preferences. Results are available within 2 to 3 days; however, longer analysis times are common during peak seasons (e.g., fertilization periods) due to high demand.

[0016] Document CN 104330401 A discloses a microsensor for the detection of nitrogen, phosphorus, and potassium in soil, belonging to the technical field of detection sensors. The sensor is characterized in that an encapsulation protective layer, a liquid flow channel layer, a substrate layer, and a printed circuit board layer are arranged sequentially, with a photoelectric sensor encapsulated in the encapsulation protective layer. A liquid inlet hole and a liquid outlet hole are each formed on two sides of the encapsulation protective layer. A liquid flow channel is integrated into the liquid flow channel layer and connected to both the liquid inlet hole and the liquid outlet hole. An on-chip light source is encapsulated in the substrate layer, and an operational amplifier, a microprocessor, and a liquid crystal display are distributed on the printed circuit board layer.

[0017] Furthermore, publication CN 117191698 A presents a high-precision automatic soil nutrient detection system and method, aiming to solve the technical problem of certain detection errors in current soil nutrient detection methods. Optimizing the flow path reduces the length of the pipeline and further shortens the detection time. The sample feeder pump is located downstream of the photoelectric detection unit, ensuring that changes in the mixture being detected within the pump do not adversely affect the accuracy of the detection result. Additionally, bubbles are injected into the pipeline at regular intervals by the bubble injection pump, thus reducing the influence of the solution flow velocity. (Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST)

[0018] September 10, 2025

[0019] 3

[0020] The flow velocity is relatively stable, the gas-liquid segmentation specification is reliable, tiny bubbles are hardly generated, and the stability and reliability of the test data are favorably improved.

[0021] From publication EP 3 063 886 B1, a radio signal-emitting node is known which is configured to emit a radio signal with a radio transmission power when buried in the ground, wherein the node comprises: an antenna; an integrated electronic circuit which is electrically connected to the antenna by means of a feed line; and at least one sensor for generating measurement data, wherein the integrated circuit is configured to operate the antenna so that it emits the radio signal containing the measurement data periodically or upon receiving a wireless request. The invention further relates to a sensor system with at least one of the aforementioned nodes.

[0022] Publication KR101325725 B1 discloses a device for analyzing water quality, capable of analyzing the components contained in water, and a method for analyzing water quality. The device comprises a platform, a plurality of chambers formed within the platform, and a valve arranged between the chambers, wherein a plurality of materials selected from the group consisting of nitrate, nitrite, silicate, phosphate, and ammonium salts are analyzed simultaneously, wherein a sample injection chamber connected to the analysis line and a filter unit for separating impurities contained in the sample are also connected to the sample injection chamber.

[0023] Furthermore, publication WO 2022 / 269388 A1 describes an automated, computer-controlled sampling system and associated procedures for collecting, processing, and analyzing agricultural samples for various chemical properties, such as plant-available nutrients. The sampling system allows for the processing of multiple samples and their simultaneous or semi-simultaneous analysis for different analytes or chemical properties. Advantageously, the system can process soil samples in their collected state without prior drying or grinding to create a sample slurry. The system includes a multi-layered microfluidic distribution substrate for chemical analysis, configured to deliver a temperature-compensated concentration of analytes or other sample-related chemical properties.For this purpose, the system uses a programmable controller, a temperature sensor, and an absorption meter. The system can be used to analyze various agricultural samples, such as soil, vegetation, manure, milk, or others. Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST.

[0024] September 10, 2025

[0025] 4

[0026] Document WO 2015 / 00975 A1 discloses a substrate for a carrier for bituminous membranes comprising two or more layers of fibers comprising a homogeneous mixture of organic and inorganic fibers, between which a reinforcing fabric is arranged, the fibers being aligned parallel to the longitudinal axis of the substrate and laid side by side and alternately.

[0027] From publication WO 2022 / 259074 A1, an automated, computer-controlled sampling system and associated methods for collecting, processing, and analyzing agricultural samples for various chemical properties, such as plant-available nutrients, are known. The sampling system allows for the processing of multiple samples and their simultaneous or semi-simultaneous analysis for different analytes or chemical properties. Advantageously, the system can process soil samples in their collected state without drying or grinding them to create a sample slurry. The system includes a chemical analysis subsystem that processes and analyzes the prepared slurry to quantify multiple analytes and / or chemical properties of the sample.The chemical analysis subsystem can be housed in a multi-layered microfluidic distribution substrate, which includes microfluidic devices that extract and quantify the concentration of analytes or other chemical parameters associated with the sample. The system can be used to analyze various agricultural samples, such as soil, vegetation, manure, milk, or others.

[0028] Furthermore, the publication WO 2022 / 264121 A1 describes a method for the real-time determination of a nitrate concentration level in a water sample collected from the soil at a specific location, wherein the water sample contains an unknown composition and an unknown concentration of DOC, the method comprising: (A) during an offline phase: obtaining a test sample from the soil, determining a first and a second wavelength, each correlated with concentration levels of DOC and nitrate in the test sample, and creating a calibration equation for that location; and (B) during real-time: separately striking a real-time water sample from the soil with light at the two wavelengths, determining the respective absorption values ​​by the real-time sample at the two wavelengths, and (c) substituting the respective absorption values ​​into the calibration equation to obtain the nitrate concentration in the real-time sample.

[0029] Publication WO 2022 / 264126 A1 discloses a system for reducing nitrate leaching into a sub-root zone of a crop, comprising: (a) an analytical unit for the repeated determination of a nitrate concentration level at least in a sub-root zone of the crop and for recording the Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0030] September 10, 2025

[0031] 5

[0032] nitrate concentration levels, (b) a controller configured to: (i) receive a recent recording of the nitrate concentration level below the root zone and at least one previous recording of the concentration level and determine a rate of change between the recent and the previous recording, and (ii) on the basis of the rate of change of the nitrate concentration, activate fertilization and irrigation at times and in periods that minimize the leaching of nitrate to below the root zone, the system comprising at least one water sample collection sensor positioned below the root zone of the crop and transmitting the sample to the analyzer.

[0033] Document WO 2023 / 161763 A1 describes a method that uses measuring devices to measure soil properties. Each measuring device comprises a position receiver, at least one soil sensor, a transmitter, a processor that communicates with the at least one soil sensor and the transmitter, a power source connected to the processor, and a rigid housing containing the at least one soil sensor, the transmitter, the processor, and the power source. The measuring devices can be moved during the cultivation of an agricultural field, for example, during plowing, planting, harvesting, etc.

[0034] Furthermore, publication WO 2023 / 016601 A1 discloses a soil water extraction device comprising at least one matrix body in which at least one channel for receiving a soil water sample is incorporated, and a porous, hydrophilic ceramic which is also incorporated into the matrix body and closes the channel flush with the matrix body on the soil side, and a hose which leads from the opposite side of the channel to a pump which is driven by a motor driver, wherein the motor driver is controlled by a microcontroller and the microcontroller is connected to at least one interface and moisture information is transmitted to the microcontroller via the interface and compared with stored setpoint values. The invention further relates to a method for extracting soil water.

[0035] In Alahi and Mukhopadhyay (2019), “Smart nitrate sensor: internet of things enabled real-time water quality monitoring (Vol. 35)”, Springer-Verlag, the authors propose a system for measuring nitrate in water.

[0036] In “Extraction of soil solution into a fluidic chip”, AgriEngineering, 2021, Vol. 3(4), pp. 783-796, Böckmann et al. describe a soil solution extraction device based on the combination of a porous ceramic filter with a microfluidic channel with a volume of 12 pL. The microfluidic chip is made of polydimethylsiloxane, measures 1.7 cm x 17 cm x 0.6 cm, and is bonded to a glass substrate. A hydrophilic aluminum oxide ceramic with a porosity of approximately 37 vol.% and an average [Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST]

[0037] September 10, 2025

[0038] 6

[0039] A pore size of 1 pm is integrated at the inlet. Soil water can be extracted from three soil types – silt, garden soil, and sand – by creating a vacuum with a pump at the other end of the microfluidic channel.

[0040] Furthermore, Titov et al. present a highly integrated design of organic optoelectronic devices for point-of-need (PON) nitrite (NO2-) measurement in “Monolithic integrated OLED-OPD unit for point-of-need nitrite sensing”, Sensors, 2022, Vol. 22(3), pp. 1-11. The spectrophotometric investigation of the nitrite concentration is performed using the common Griess reagent and a reflection-based photometric unit with an organic light-emitting diode (OLED) and an organic photodetector (OPD).

[0041] The problems with the current state of the art essentially lie in the fact that the existing method for measuring soil nutrient concentration requires additional procedural steps for taking and preparing soil samples. These procedural steps require manual intervention, are time-consuming, have a low measurement frequency, and provide an average result for the nutrient concentration of the taken soil samples without accounting for the heterogeneity of the soil (differentiated information for different soil locations within a field).

[0042] Furthermore, optical autonomous nutrient measurement systems measure the nutrient content in plant components, typically leaves, without manual sample preparation. Their use is limited to the presence of plants in the field. These systems cannot measure nutrient content over an entire growing season and are unable to indicate nutrient fluctuations in soil solutions (e.g., leaching) when no plants are present. Therefore, they do not provide insight into nutrient fluctuations over a whole growing season. Additionally, they have a lower measurement frequency due to the significant time required for the measurement process.

[0043] Other systems, in turn, use electrical conductivity (EC) to measure the nutrient content in solution. These systems cannot be calibrated, which limits their measurement accuracy. They also require a constant energy supply.

[0044] Other soil nutrient sensors known from the prior art require an irrigation system to measure the nutrient content in soil solution.

[0045] Existing methods that indirectly measure nutrient content, such as using aerial photographs, suffer from approximation problems that lead to inaccurate measurements.

[0046] Predicting the mineralization of urea, organic fertilizer, cover crops, or crop residues is difficult due to uncontrollable factors. It requires time series of nutrient and soil data, which are not feasible with current solutions. Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0047] September 10, 2025

[0048] 7

[0049] The object of the invention is to provide a system and a system utilization method for fully automatic, high-frequency, accurate and reliable measurement of the nutrient content in the soil solution without manual process steps.

[0050] Another task is to provide a system and a system usage procedure that enables the measurement of nutrient content in the soil solution when no plants are present in the field. This will make it possible to carry out nutrient content measurements over the entire season, at least for up to one year.

[0051] Furthermore, improving the measurement accuracy during the evaluation of the measurements is a task.

[0052] Another task is to provide a system that can be operated without an external energy supply.

[0053] Furthermore, it is a task to provide a system that enables high-frequency measurements and wireless transmission of the data collected from the ground.

[0054] Another task is to enable efficient sampling of the soil solution by providing a system.

[0055] The system should also make it possible to map the nutrient content in the immediate vicinity of the plant root, thus enabling a better approximation of the actually available nutrient content.

[0056] Furthermore, another task is to provide a system that delivers quasi-real-time data using discrete, high-frequency measurements, enabling precise adjustment of fertilizer applications to soil availability and plant needs, and solving the problem of mineralization prediction better than the current state of the art.

[0057] The tasks are solved by a microfluidic nutrient measurement sensor system for direct automated nutrient measurement from soil solution, comprising a sensor box with at least one sensor, a power supply, a control system, a soil solution extraction unit with a first pump, reservoirs for storing solutions and a second pump, wherein it has

[0058] - the sensor as a chip, a microfluidic,

[0059] - the energy supply an internal power source,

[0060] - the soil solution extraction unit, the first pump, and a suction head made of a porous ceramic, wherein the suction head serves as an inlet to the microfluidics and is directly connected to it without additional connecting pieces, and the suction head protrudes from the sensor box, Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0061] September 10, 2025

[0062] 8 and furthermore exhibits microfluidics

[0063] - Microfluidic channels,

[0064] - a soil solution reservoir,

[0065] - a mixing system comprising at least a first mixer and a second mixer, wherein the first mixer is used for mixing a chemical assay and the second mixer is used for mixing the chemical assay with the drawn-in soil solution from the soil solution reservoir, and comprising an optical measuring unit with a measuring chamber, wherein the second mixer is arranged spatially in the flow direction upstream of the optical measuring unit and downstream of the merging of the microfluidic channels from the first mixer and the soil solution reservoir, and further comprising

[0066] - the measuring chamber contains a temperature sensor and a heating element,

[0067] - the control system includes at least one circuit board for pump, valve and heating control and one circuit board for carrying out optical measurements, wherein

[0068] - Valves are present in the individual microfluidic channels and the second pump is connected to the outlet of the solutions from the microfluidics in the flow direction after the optical measuring unit;

[0069] - during operation, the first pump draws soil solution through the suction head into the soil solution reservoir of the microfluidics system,

[0070] - during operation, the second pump directs solutions in the microfluidics.

[0071] Alternatively, the microfluidic nutrient measurement sensor system for direct automated nutrient measurement from soil solution can comprise a sensor box with at least one sensor, a power supply, a control unit, a soil solution extraction unit with a first pump, reservoirs for storing solutions and a second pump, wherein

[0072] - the sensor, as a chip, is designed with a microfluidic system,

[0073] - the energy supply is designed to have an internal power source,

[0074] - the soil solution extraction unit comprising a first pump and a suction head made of a porous ceramic, wherein

[0075] - the suction head is designed as an inlet to the microfluidics and is directly connected to it without additional connecting pieces,

[0076] - the suction head protrudes from the sensor box,

[0077] - exhibiting microfluidics

[0078] - Microfluidic channels,

[0079] - a soil solution reservoir, Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0080] September 10, 2025

[0081] 9

[0082] - a mixing system with at least one first and one second mixer and an optical measuring unit with a measuring chamber or

[0083] - an optical measuring unit comprising a measuring chamber and means for mixing the chemical components in the measuring chamber, wherein

[0084] - Valves are present in the individual microfluidic channels,

[0085] - the measuring chamber is designed to include a temperature sensor and a heating element,

[0086] - the second pump is designed to be connected to the outlet of the solutions from the microfluidics in the flow direction after the optical measuring unit,

[0087] - the control at least

[0088] - a circuit board for pump, valve and heating control and

[0089] - a circuit board for carrying out the optical measurements, wherein

[0090] - when the first pump is in operation, soil solution can be drawn through the suction head into the soil solution reservoir of the microfluidics system,

[0091] - when the second pump is in operation, solutions in the microfluidics are conductive, and

[0092] - in the mixer system with at least the first and second mixers and the optical measuring unit with a measuring chamber:

[0093] - a chemical assay is miscible in the first mixer,

[0094] - in the second mixer, the chemical assay is miscible with the soil solution drawn from the soil solution reservoir,

[0095] - the second mixer is spatially arranged in the direction of flow upstream of the optical measuring unit and after the merging of the microfluidic channels from the first mixer and the soil solution reservoir, or

[0096] - in the optical measuring unit with the measuring chamber and the means for mixing the chemical components in the measuring chamber:

[0097] - a chemical assay is miscible in the measuring chamber,

[0098] - in the measuring chamber, the chemical assay is miscible with the soil solution drawn from the soil solution reservoir, and

[0099] - the optical measuring unit is calibratable with the chemical assay and a standard solution and a blank solution, Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0100] September 10, 2025

[0101] 10

[0102] - in the optical measuring unit, the measurement for sample analysis can be carried out after prior calibration, and wherein the microfluidic nutrient measurement sensor system is designed for the nutrient measurement of at least one nutrient.

[0103] The reservoirs may include, in particular, at least one reservoir as a waste collection container, at least one reservoir for a rinsing solution, at least one soil solution reservoir, reservoirs for assay starting materials, at least one reservoir for a standard solution, and at least one reservoir for a blank solution, wherein the standard solution and blank solution are available for carrying out the calibration.

[0104] The rinsing solution can be used in particular for cleaning soil solution reservoirs and microfluidics.

[0105] In a preferred embodiment, solutions can be introduced and collected in the waste collection container after use, and the waste collection container can be located spatially in the direction of flow at the outlet of the microfluidics system after the optical measuring unit.

[0106] Each microfluidic channel can be configured to include a valve.

[0107] In addition, the part of the suction head protruding from the sensor box can preferably be rounded.

[0108] The first mixer and / or the second mixer can be designed in particular as serpentine mixers.

[0109] The optical measuring unit can be designed, in particular, as a photometric measuring unit.

[0110] The optical measuring unit can also be configured to include a light-emitting diode and photodetector / photodiode, in particular LED / OPD pairs, or the optical measuring unit can be configured to include exactly three LED / OPD pairs.

[0111] Preferably, the control system can be configured to include an analog-to-digital converter and / or a microprocessor and / or a telemetry system.

[0112] The microfluidic nutrient measurement sensor system can be switched between normal operation and standby mode via the control unit.

[0113] Furthermore, the sensor box can be configured to include one sensor for measuring a single nutrient, multiple sensors for measuring multiple nutrients, or one sensor for measuring multiple nutrients. Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0114] September 10, 2025

[0115] 11

[0116] The system can be specifically designed to measure nitrate and / or ammonium and / or phosphate.

[0117] Furthermore, the tasks are solved by a method for the direct automated measurement of nutrients from soil solution using a microfluidic nutrient measurement sensor system comprising at least the following steps:

[0118] - Receiving a measurement order by the control system,

[0119] - Switching the sensor system from standby mode to normal mode,

[0120] - Performing a soil solution extraction and collecting soil solution,

[0121] - Preparation of a calibration fluid using a chemical assay,

[0122] - Feeding calibration fluid into the measuring chamber,

[0123] - Temperature control of the calibration fluid in the measuring chamber,

[0124] - Performing at least one calibration measurement in the optical measuring unit,

[0125] - Draining the calibration fluid from the measuring chamber,

[0126] - Mixing the collected soil solution with the chemical assay,

[0127] - Directing the mixture of soil solution and chemical assay into the measuring chamber,

[0128] - Performing a measurement in the optical measuring unit,

[0129] - Tempering the mixture of soil solution and chemical assay in the measuring chamber,

[0130] - Performing a measurement in the optical measuring unit,

[0131] - Determining the nutrient concentration from the results of measurements in the optical measuring unit,

[0132] - Cleaning the sensor system and

[0133] - Switching the sensor system from normal mode to waiting mode.

[0134] The measurement order can be received via a transmitter / receiver in the control system or carried out at preset time intervals.

[0135] In addition, liquid drawn from the measuring chamber can be collected in a waste collection container.

[0136] The steps of soil solution extraction and calibration can take place simultaneously or sequentially, with a time delay.

[0137] In a particularly preferred configuration, the sensor box can be placed in the ground at root level before measurements begin and remain there for a defined period with a defined number of measurement tasks. Alternatively, the measurement data can be transmitted directly and autonomously to a receiver, or the data can be collected and transmitted manually or at specific times. Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0138] September 10, 2025

[0139] 12

[0140] At least two microfluidic nutrient measurement sensor systems placed in the soil can form a microfluidic nutrient measurement sensor system network if they are interconnected via a wireless standard.

[0141] The microfluidic nutrient measurement sensor system according to the invention consists of a unique combination of components.

[0142] In a preferred embodiment, this includes a soil solution extraction unit, at least two pumps, at least seven reservoirs for storing solutions, a soil solution reservoir, at least one chemical assay, at least one blank and one standard solution for calibration, at least two mixers, at least one measuring chamber, at least eleven valves, at least one heating element, at least one temperature sensor, at least one optical measuring unit, preferably consisting of three LED / OPD pairs, a circuit board for valve and heating control, at least one circuit board for optical measurements, a pressure sensor and a power source.

[0143] It may include a transceiver and a microprocessor for improved data management. If the sensor system is used for autonomous data transmission, a telemetry system is preferably provided. For this purpose, modems and antennas for radio standards such as RF, cellular, SigFox, LoRaWAN, or narrowband can be used.

[0144] The LoRaWAN standard, in particular, can be used for underground-to-underground (UG2UG) communication in addition to underground-to-aboveground (UG2AG) and above-ground-to-underground (Aboveground-to-Underground) communication due to its signal strength. When using multiple microfluidic nutrient measurement sensor systems simultaneously, this enables data transfer between the individual sensor systems via UG2UG communication, meaning that only one collection point is needed to receive all sensor data, thus significantly simplifying data transmission, especially of measurement data.

[0145] According to the invention, no additional elements or steps for soil sampling or preparation are included. All components are housed in a sensor box, which may have dimensions of 10 cm x 10 cm x 20 cm.

[0146] Instead of soil sampling and preparation, the soil solution is automatically extracted.

[0147] The sensor system according to the invention is installed in the soil, particularly below a working depth of at least 30 cm, without an external power supply. Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0148] September 10, 2025

[0149] 13

[0150] Unlike conventional measurement methods, photometric analysis is used in conjunction with a chemical assay. The measurement is fully automated and requires no sample preparation. The soil solution extraction unit is integrated into the microfluidic nutrient measurement sensor system, whereas other sensors that extract soil solution use an external suction unit connected to tubing for extraction.

[0151] The suction head used in the soil solution extraction unit on this site is already used in a similar form in, for example, commercial suction candles.

[0152] The use and combination of such a suction head with microfluidics has so far only been described in publication WO 2023 / 016601 A1.

[0153] To perform relevant nutrient measurements, the microfluidic nutrient measurement sensor system is inserted into the soil at root level. The soil solution extraction unit draws in the surrounding soil solution for measurement and collects it in the soil solution reservoir. A calibration measurement is first performed within the sensor system. For this, a blank solution and then a standard solution containing a chemical assay are mixed, and the nutrient concentration of both is determined. Subsequently, the chemical assay and the soil solution sample are mixed, and the concentration is again determined using the optoelectronic measuring unit. After completion of the measurement, the result can be transmitted from the soil to the receiver via a wireless standard. Possible wireless standards include, as previously mentioned, RF, cellular networks, SigFox, LoRaWAN, or narrowband.

[0154] The sensor chip manufacturing process influences the possible usable mixer structures. For the sensor chip manufacturing process of the microfluidic nutrient measurement sensor system according to the invention, photolithography is preferably used. In this method, a silicon wafer is coated with a negative photoresist, and structures are selectively cured with UV light using a photomask. The uncured photoresist is then dissolved using a developer, thus producing a positive for casting with silicone. This process allows, in particular, the production of microstructures in a single plane, which are also selected for the mixer in this case.

[0155] Another factor in choosing the mixer structure is the low required flow rate of just a few pL / min in the microfluidics on the sensor chip. At these speeds, the flow is purely laminar and not turbulent. However, many known mixer structures utilize turbulent flow for better mixing and are therefore unsuitable. Furthermore, the miniaturization and autonomy of the sensor system impose clear requirements. The dead volume in the mixer should be minimized without external [Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST].

[0156] September 10, 2025

[0157] 14

[0158] Power consumption and limited power and space capacities must be kept as low as possible for complete mixing. Serpentine mixers, in particular, have proven suitable for this purpose, as mixing in serpentine mixers occurs solely through diffusion and path length. Furthermore, serpentine mixers have an acceptable dead volume and are relatively simple to manufacture.

[0159] A groundbreaking step compared to other state-of-the-art methods is the direct measurement of nutrient content from soil solution through a unique combination of components. Almost all other methods measure from prepared soil samples or via electrical conductivity in soil matrices.

[0160] No other currently known solution integrates soil water extraction into the sensor box. This innovation results in the following improvements: elimination of time-consuming sampling and preparation with chemical analysis, construction of time series of nutrient concentrations, and faster measurement execution and results presentation. The soil solution extraction unit in combination with a microfluidic chip is also new and was only mentioned in publication WO 2023 / 016601 A1.

[0161] Automation and stationary measurement as a time series not only enable more frequent measurements, as cumbersome sampling and preparation are avoided, but also eliminate all associated measurement errors.

[0162] Nutrient measurement from soil solution also enables, for the first time, the measurement of plant-available nutrient concentrations compared to the total nutrient concentration in the soil, which is normally measured and leached out by chemical treatments. This allows, for the first time, a reference-based assessment of cultivation techniques such as fertilization or irrigation, based on continuous data acquisition.

[0163] The majority of nitrogen in the soil is chemically bound as a component of organic matter ("humus") and is not directly available to plants. Complex, primarily biological processes convert small portions of the nitrogen from organic matter into ammonium, then into nitrate, and finally a small portion into nitrous oxide ("mineralization"). Conversely, nitrate and ammonium are incorporated into organic matter through biological processes ("demineralization"). A dynamic equilibrium exists in the soil between organically bound nitrogen and mineralized nitrogen (ammonium and nitrate = N₂). m (in) - This balance is determined by many factors, such as the carbon content of the soil, the N mThe soil's pH is influenced by various factors, including nutrient content, soil life (bacteria, fungi, earthworms, etc.), soil temperature, soil moisture, redox potential, other available nutrients and micronutrients, and many others. When nitrogen fertilizers—both organic and mineral—are applied, the soil's pH is affected. (Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST)

[0164] September 10, 2025

[0165] 15 this balance is disturbed, and some of the nitrogen is incorporated into the organic matter of the soil, another part contributes to the water-soluble ammonium and nitrate fraction (Nmin), and a small amount can be emitted as nitrous oxide.

[0166] To achieve a good crop yield and the desired quality at acceptable costs, farmers must ensure an adequate nitrogen supply to their plants during the growing season. An oversupply of nitrogen can negatively impact yield and quality, leading to greater nutrient losses and environmental damage, while an undersupply results in lower yields and can also affect crop quality, and does not necessarily lead to less loss, as fewer plants absorb less nitrogen.

[0167] The amount of plant-available nitrogen fluctuates considerably over time due to mineralization. For optimal agronomic and sustainable fertilization, farmers need to know the current status through frequent, standardized measurements with immediate results. While farmers can predict the effects of nitrogen fertilization relatively well, the mineralization of urea, organic fertilizers, cover crops, or crop residues depends on uncontrollable factors such as soil temperature and moisture and is therefore difficult to predict.

[0168] The microfluidic nutrient measurement sensor system can provide soil nutrient data at defined intervals throughout the entire season. The sensor system can remain in the soil for up to a year without maintenance, where it regularly measures nutrient concentrations in the soil water when sufficient soil moisture is present.

[0169] The data enables the farmer to precisely adjust nitrogen fertilization in terms of timing and quantity to the soil supply ("mineralization") and the needs of the plants, thereby optimizing crop yields and quality while significantly reducing environmental impact.

[0170] The method for the direct, automated measurement of nutrients in soil solution allows for discrete, high-frequency measurements to obtain timely results (quasi-real-time data), enabling quick and timely decisions and immediate action, even with volatile nutrients. This is particularly valuable when there is no visible vegetation in the field and optical nutrient measurements of chlorophyll are not possible.

[0171] The proposed system enables the measurement of plant-available nutrients in the soil solution, thus providing a more precise measurement of available nutrients. The system maps the nutrient content in the immediate vicinity of the plant roots, thereby representing a good approximation of the actually available nutrient content. Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0172] September 10, 2025

[0173] 16

[0174] The sensor system according to the invention enables the quantification of nutrient concentrations in a wide measuring range.

[0175] The measurement accuracy of the optical measuring unit is improved compared to the state of the art by using a standard solution in conjunction with a blank measurement and high-frequency discrete measurements. The information content is enhanced by representing nutrient fluctuations in soil solution using time series data and enabling direct feedback after interventions (such as heavy rainfall or fertilization).

[0176] Furthermore, the discrete measurements do not require a continuous energy supply (normal operation and standby operation), so longer system runtimes are possible and data on nutrient concentrations can be collected for an entire growing season.

[0177] Soil cultivation is not affected, as the sensor system according to the invention is preferably installed below the cultivation depth. Furthermore, no manual handling or maintenance is required, since the sensor system measures automatically. This drastically reduces the workload for users and lowers the cost per measurement.

[0178] The sensor system measures in aqueous solution and can also be used for water analysis, including but not limited to drinking water and groundwater measurements. A particularly noteworthy feature of the sensor system according to the invention is the unique combination of automatic time-series recording of critical nutrient concentrations in the soil without the need for manual steps. The system provides non-invasive measurements before visible plant growth begins and delivers results with a high frequency.

[0179] Other known systems either require manual sampling (for example, Pessl Instruments Dualex, Stenon FarmLab, Phytoprove yield e, Citizen Sensor, Agro Cares F series scanner, Yara N Sensor and N Tester) or cannot be efficient and / or remain on arable land for at least one full growing season (Pessl Instruments, JXCT Tech., Teralytic, Phytoprove, Citizen Sensor, Agro Cares, TerrAquat GmbH, cropx, Yara).

[0180] The system proposed by Alahi and Mukhopadhyay (Alahi and Mukhopadhyay (2019), “Smart nitrate sensor: internet of things enabled real-time water quality monitoring (Vol. 35)”, Springer-Verlag) is used to measure nitrate in water and also relies on pumps and valves to draw water from a sample, analyze it with a sensor controlled by a microcontroller and circuit board, and connected to a power supply and an antenna. However, this system lacks the porous inlet for drawing in soil solution. Furthermore, it does not include a microfluidic chip for miniaturization. Therefore, this system is not capable of drawing in soil solution. Christian-Albrechts-Universität zu Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0181] September 10, 2025

[0182] 17

[0183] Furthermore, the system uses an impedimetric sensor, while the proposed system uses an optical sensor.

[0184] The microfluidic nutrient measurement sensor system according to the invention has some similarities with existing publications, but is unique in the combination of components.

[0185] The following similarities with the sensor system according to the invention can be identified in the following publications:

[0186] The publication CN 104330401 A has four common features: a test for analysis, a measuring chamber / channel, an optical measuring device, and a microcontroller.

[0187] The printed document CN 117191698 A has five common attributes: pumps, a chemical analysis method, mixers, measuring chamber and optical measuring device.

[0188] The printed document EP 3 063 886 B1 has two features in common: a microcontroller and a radio modem with an antenna.

[0189] The publication KR101325725 B1 shares the following seven attributes: a soil solution extraction unit, chemical assays for measurements, a mixer, a measuring chamber / channel, valves, an optical measuring device, microfluidics.

[0190] The publication WO 2022 / 269388 A1 has six common features: pumps, valves, an optical measuring device, a microcontroller, a radio modem with antenna, and microfluidics.

[0191] Document WO 2015 / 002975 A1 shares eleven features with the sensor system according to the invention: pumps, containers, a test for measurements, a calibration solution, mixers, a measuring chamber / channel, valves, heating elements, an optical measuring device, a microcontroller, and microfluidics. However, this document is aimed at medical applications that use biological tests and biological analytes, in particular cell samples, and is not geared towards soil samples.

[0192] Document WO 2022 / 259074 A1 is aimed at an agricultural application and has the following common features: pumps, tanks, chemical test for measurements, calibration solutions, mixers, measuring channel / chamber, valves, an optical measuring device, a microcontroller and the integration of microfluidics.

[0193] Publication WO 2022 / 264121 A1 shares six characteristics. The sensor system described here requires no soil sampling or preparation and comprises a water sampling unit, container, calibration solution, an optical measuring device, and a microcontroller. Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0194] September 10, 2025

[0195] 18

[0196] The publication WO 2022 / 264126 A1 also does not specify soil sampling and preparation and adds a further attribute compared to the previously mentioned publication by including pumps.

[0197] Document WO 2023 / 161763 A1 features a microcontroller, a radio modem with antenna and a power source in accordance with the microfluidic nutrient measurement sensor system according to the invention.

[0198] The invention is described below with reference to the accompanying figures in the figure description, which are intended to illustrate the invention and are not to be considered limiting. They show:

[0199] Fig. 1 shows a flowchart of the process of nutrient measurement from soil solution using a sensor system;

[0200] Fig. 2 shows an exemplary detailed schematic representation of a microfluidic nutrient measurement sensor system according to the invention, without showing the control system and power supply.

[0201] Fig. 3 shows an exemplary rough schematic representation of a microfluidic nutrient measurement sensor system according to the invention.

[0202] Figure 1 shows a flowchart of the process for measuring nutrients from soil solution using a sensor system. The sensor system consists of a sensor box with at least one sensor, a controller for the system, a soil solution extraction unit, and an optical measuring unit with a measuring chamber. The process includes at least the following steps:

[0203] - Receipt of a measurement order by control unit A,

[0204] - Switching the sensor system from standby mode to normal mode,

[0205] - Performing a soil solution extraction B and collecting soil water,

[0206] - Preparation of a calibration fluid using a chemical assay,

[0207] - Feeding calibration fluid into the measuring chamber,

[0208] - Temperature control of the calibration fluid in measuring chamber C

[0209] - Performing at least one calibration measurement in the optical measuring unit D, E

[0210] - Draining the calibration fluid from the measuring chamber,

[0211] - Mixing the collected soil solution with the chemical assay,

[0212] - Directing the mixture of soil solution and chemical assay into the measuring chamber,

[0213] - Performing a measurement in the optical measuring unit,

[0214] - Tempering the mixture of soil solution and chemical assay in measuring chamber F,

[0215] - Performing a measurement in the optical measuring unit G, Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0216] September 10, 2025

[0217] 19

[0218] - Determining the nutrient concentration from the results of measurements in the optical measuring unit H,

[0219] - Cleaning of sensor system I and

[0220] - Switching the sensor system from normal mode to waiting mode J.

[0221] The nutrient measurement from soil solution, carried out with a microfluidic nutrient measurement sensor system 0 according to the invention, can proceed, for example, as described below. It begins with the system's controller receiving a measurement command A and the system switching from standby mode (sleep mode) to normal operation. In this process, either a transmitter / receiver of the controller can receive a measurement command via radio, or the measurement process can be started at preset time intervals.

[0222] The first pump 7 is then switched on and begins to draw the soil solution from the surrounding soil pores into the soil solution reservoir via the suction head of the soil solution extraction unit B and collect it there.

[0223] Additionally, a calibration measurement E is performed. The second pump 8 draws the chemical assay into the first mixer 6. The individual assay reactants are drawn from reservoirs 2, 3, 4 together with the blank solution 12, first mixed in the second mixer 13 and then drawn into the measuring chamber 10. The heating element for the measuring chamber 15 has already heated the measuring chamber 10 at this point C. After a defined waiting time for the assay reaction, the optical measuring unit is switched on and begins an optical calibration measurement D, E. The second pump 8 draws further assay reactants 2, 3, 4 into the first mixer 6, which are then mixed with standard solution 11 in the second mixer 13 and drawn further into the measuring chamber 10 for optical analysis, as described above. The optical measuring unit measures D, E again. The calibration measurement E and the soil solution sampling B can be performed sequentially or in parallel.

[0224] After calibration measurement E, sample analysis H takes place. The assay reactants 2, 3, 4 are again drawn by the second pump 8 into the first mixer 6. The mixed chemical assay, however, is now drawn together with the soil solution sample from the soil solution reservoir 5 into the second mixer 13. As in calibration step E, the resulting solution, after mixing, is drawn into the measuring chamber of the optical measuring unit 10. There, a third measurement is performed to correct for any coloration of the soil solution. The chamber is then heated for a specific time F to complete the chemical reaction of the assay, and the nutrient concentration is obtained via a fourth measurement (after correction with the previous measurements). Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0225] September 10, 2025

[0226] 20

[0227] In cleaning step I, the soil solution reservoir 5 and the microfluidic channels are rinsed with rinsing solution 1, and all previously used solutions are pumped into the reservoir designed as a waste collection container 16.

[0228] The measurement data can then be transmitted from the transmitter or receiver in the soil, or the data can be collected and read out manually or at specific times. After cleaning, the microfluidic nutrient measurement sensor system according to the invention switches back to standby mode J.

[0229] The assay starting material can vary in number, substance, and quantity depending on the nutrient and chemical assay to be used.

[0230] Fig. 2 shows an exemplary schematic representation of a microfluidic nutrient measurement sensor system 0 according to the invention, without showing the control unit 60 and the power supply 40.

[0231] The following should be noted: The connections shown between the liquid containers 1-4, 11, 12, 16, the pumps 7, 8, 9, and the sensor chip do not necessarily correspond to hoses, but merely indicate the connection points. In a preferred embodiment, no hoses are present in the soil solution extraction unit 9. All lines shown on the sensor chip represent microfluidic channels, which in this example have dimensions of 50 µm in width and 80 µm in height. The suction head of the soil solution extraction unit 9 is a ceramic cylinder (6 mm wide and 13 mm long) that protrudes from the sensor box, with the protruding part of the suction head being rounded. The soil solution extraction unit 9 is thus directly connected to the microfluidic system of the sensor chip.

[0232] The soil solution is drawn in through the porous inlet of the soil solution extraction unit 9 by the first pump 7, which requires a suction pressure between -500 mbar and -950 mbar, and collected in the soil solution reservoir 5, which measures 7 mm x 10 mm. The soil solution reservoir 5 is connected to the reservoir for rinsing solution 1 via valve 17. The soil solution reservoir 5 also has a third connection via valve 24 to the channel for the standard solution 11, which in turn is connected via a crossover to the channel between the first mixer 6 and the second mixer 13. The reservoir for rinsing solution 1 is also connected via valve 18 to the channels for the assay chemicals 18, 19, and 20, which converge before the first mixer 6.The liquids are stored in vials with a volume of 5 ml, the assay components 2, 3, 4 are connected via the valves 19-21 to the first mixer 6, the Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST.

[0233] September 10, 2025

[0234] 21 is preferably serpentine in shape and in this example has a length of 48.5 mm.

[0235] The blank solution or sample 12 is connected via valve 26 to the sample / standard solution channel and the assay channel after the first mixer 6 at a junction. From there, the liquids are drawn to the second mixer 13, which has a length of 48.5 mm, and then into a measuring chamber 10. In this example, the measuring chamber 10 is 5 mm wide, 8.5 mm long, and 1 mm high. From there, the solutions are pumped into the waste collection container 16, located downstream of the second pump 8.

[0236] Fig. 3 shows an exemplary rough schematic representation of a microfluidic nutrient measurement sensor system according to the invention.

[0237] The microfluidic nutrient measurement sensor system 0 consists of three compartments: power supply 40, microfluidics 50 (including, in particular, the soil water extraction unit 9 and the optical measuring unit 10), and control unit 60 (including, in particular, circuit boards 61 and, in this example, also the microprocessor 62 and antenna 63). The antenna 63 can also be integrated within the system, so that fewer or no parts protrude, thus making the system more robust. Pumps, valves, etc., are not shown in this simplified diagram.

[0238] The microfluidic nutrient measurement sensor system according to the invention enables efficient sampling of soil solution through a porous inlet in conjunction with microfluidics, liquid containers, pumps and valves.

[0239] The integration of at least one microprocessor and / or microcontroller, radio transmitter or receiver, at least one signal processing unit, antenna and power supply enables high-frequency measurements and wireless transmission of the data acquired from the ground.

[0240] Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST 10.09.2025

[0241] 22

[0242] Reference symbol list:

[0243] 0 Microfluidic nutrient measurement sensor system

[0244] 1 rinsing solution, reservoir for rinsing solution

[0245] 2 Assay reactant A, reservoir for assay reactant A

[0246] 3 Assay reactant B, reservoir for assay reactant B

[0247] 4 Assay reactant C, reservoir for assay reactant C

[0248] 5 Groundwater reservoir

[0249] 6 First mixer

[0250] 7 First pump

[0251] 8 Second pump

[0252] 9 soil water extraction unit

[0253] 10 Measuring chamber of the optical measuring unit, optical measuring unit

[0254] 11 Standard solution, reservoir for standard solution

[0255] 12 Empty solution, reservoir for empty solution

[0256] 13 Second mixer

[0257] 14 Temperature sensor

[0258] 15 Heating element for the measuring chamber

[0259] 16 waste collection containers, reservoir for waste

[0260] 17 Valve for the flushing solution towards the groundwater reservoir

[0261] 18 Valve for the rinsing solution towards the mixer for the chemical assay

[0262] 19 Valve for Assay Educt A

[0263] 20 Valve for Assay Receptacle B

[0264] 21 Valve for assay reactant C

[0265] 22 Valve for pump for groundwater intake

[0266] 23 Valve for soil water extraction

[0267] 24 Valve for sampling from soil water reservoir

[0268] 25 Valve for standard sample

[0269] 26 Valve for empty solution

[0270] 40 Energy supply

[0271] 50 Microfluidics

[0272] 60 Control

[0273] 61 circuit boards

[0274] 62 microprocessor

[0275] 63 Antenna

[0276] A measurement order

[0277] B Soil Water Extraction Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST

[0278] September 10, 2025

[0279] Temperature adjustment for calibration

[0280] Optical measurement for calibration

[0281] E Calibration measurement

[0282] F Temperature adjustment for sample G Optical measurement for sample analysis

[0283] H Sample analysis

[0284] I Cleaning of the microfluidics

[0285] Return to sleep mode

Claims

Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST September 10, 2025 24 REQUIREMENTS 1. Microfluidic nutrient measurement sensor system (0) for direct automated nutrient measurement from soil solution comprising a sensor box with at least - a sensor; - an energy supply (40); - a control (60); - a soil solution extraction unit (9) with a first pump (7); - Reservoirs for storing solutions (1-5, 11 , 12, 16); - a second pump (8); wherein has - the sensor as a chip a microfluidic (50), - the energy supply an internal power source, - the soil solution extraction unit (9), the first pump (7), and a suction head made of a porous ceramic, wherein the suction head serves as an inlet to the microfluidic (50) and is directly connected to it without additional connecting pieces, and the suction head protrudes from the sensor box, and furthermore the microfluidic (50) - Microfluidic channels, - a soil solution reservoir (5), - a mixing system comprising at least a first mixer (6) and a second mixer (13), wherein the first mixer (6) serves to mix a chemical assay and the second mixer (13) serves to mix the chemical assay with the drawn-in soil solution from the soil solution reservoir (5), and comprising an optical measuring unit with a measuring chamber, wherein the second mixer (13) is arranged spatially in the direction of flow upstream of the optical measuring unit (10) and downstream of the merging of the microfluidic channels from the first mixer (6) and the soil solution reservoir (5), and further comprising - the measuring chamber includes a temperature sensor (14) and a heating element (14), - the control (60) at least a printed circuit board for pump, valve and heating control and a printed circuit board for carrying out optical measurements, wherein - Valves are present in the individual microfluidic channels and the second pump (8) is connected to the outlet of the solutions from the microfluidic system (50) in the flow direction to the optical measuring unit (10); - during operation, the first pump (7) pumps soil solution through the suction head into the Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST September 10, 2025 25 soil solution reservoir (5) of the microfluidics (50) is drawn in, - during operation the second pump (7) directs solutions into the microfluidics (50).

2. Microfluidic nutrient measurement sensor system (0) according to claim 1 , characterized in that the reservoirs - at least one reservoir as a waste collection container (16); - at least one reservoir for a rinsing solution (1); - Reservoirs for assay starting materials (2-4); - at least one soil solution reservoir (5); - at least one reservoir for a standard solution (11) and - at least a reservoir for an empty solution (12); include.

3. Microfluidic nutrient measurement sensor system (0) according to claim 1 or 2, characterized in that the rinsing solution (1) is used to clean the soil solution reservoir (5) and microfluidic system (50).

4. Microfluidic nutrient measurement sensor system (0) according to one of the preceding claims, characterized in that solutions are introduced and collected in the waste collection container (16) after their use and the waste collection container (16) is arranged spatially in the direction of flow at the outlet of the microfluidic system (50) after the optical measuring unit (10).

5. Microfluidic nutrient measurement sensor system (0) according to one of the preceding claims, characterized in that - each microfluidic channel is designed to have a valve and / or - the first mixer (6) and / or the second mixer (13) are designed as serpentine mixers and / or - the part of the suction head protruding from the sensor box is rounded. Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST September 10, 2025 26 6. Microfluidic nutrient measurement sensor system (0) according to one of the preceding Claims characterized in that - the optical measuring unit (10) is designed as a photometric measuring unit and / or - the optical measuring unit (10) includes a light-emitting diode and photodetector / photodiode and / or - the optical measuring unit (10) is configured to have LED / OPD pairs or the optical measuring unit (10) is configured to have exactly three LED / OPD pairs.

7. Microfluidic nutrient measurement sensor system (0) according to one of the preceding Claims characterized in that the control - an analog-to-digital converter and / or a microprocessor and / or - is equipped with a telemetry system.

8. Microfluidic nutrient measurement sensor system (0) according to one of the preceding Claims characterized in that the system (0) is switched to normal operation or standby operation via the control system.

9. Microfluidic nutrient measurement sensor system (0) according to one of the preceding Claims, characterized in that the sensor box comprises - a sensor for measuring a nutrient or - multiple sensors for measuring multiple nutrients or - is equipped with a sensor for measuring multiple nutrients.

10. Microfluidic nutrient measurement sensor system (0) according to one of the preceding Claims, characterized in that the system (0) is used for measuring Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST September 10, 2025 27 - Nitrate and / or - Ammonium and / or - Phosphate is formed.

11. Method for the direct automated measurement of nutrients from soil solution, using a microfluidic nutrient measurement sensor system (0) according to any one of claims 1 to 10, comprising at least the steps of: - Receiving a measurement order by the controller (A); - Switching the sensor system from standby mode to normal mode; - Performing a soil solution extraction and collecting soil water (B); - Preparation of a calibration fluid using a chemical assay; - Feeding calibration fluid into the measuring chamber; - Temperature control of the calibration fluid in the measuring chamber (C, E); - Performing at least one calibration measurement in the optical measuring unit (D, E); - Draining the calibration fluid from the measuring chamber; - Mixing the collected soil solution with the chemical assay; - Directing the mixture of soil solution and chemical assay into the measuring chamber; - Performing a measurement in the optical measuring unit; - Tempering the mixture of soil solution and chemical assay in the measuring chamber (F); - Performing a measurement in the optical measuring unit (G); - Determining the nutrient concentration from the results of measurements in the optical measuring unit (H); - Cleaning the sensor system (I) and - Switching the sensor system from normal mode to waiting mode (J).

12. Method according to the preceding claim, characterized in that - the measurement order (A) is received via a transmitter / receiver in the control system or takes place at preset time intervals and / or - liquid drawn from the measuring chamber is collected in a waste collection container.

13. Method according to one of the two preceding claims, characterized in that Christian-Albrechts-University of Kiel CAU IPR_2024_0127_WO - DESC, CLMS, ABST September 10, 2025 28 - the sensor box is placed in the ground at root level before the procedure is carried out and remains in the ground for a defined period with a defined number of measurement tasks and / or - a direct autonomous transmission of the measurement data to a receiver takes place, or the measurement data is collected and transmitted manually or at specific times.

14. Microfluidic nutrient measurement sensor system (O)-combination comprising at least two microfluidic nutrient measurement sensor systems (0) according to one of claims 1 to 10, introduced into the soil and interconnected via a radio standard.

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