In-situ soil ammonium sensing system

Abstract

An in-situ, or interfacial, soil sensor is provided, which includes one or more electrodes. The soil sensor is configured to detect levels of ammonium in a sample of soil, the sensor including: a working electrode coated in a composite sensing film, where the composite sensing film includes: an active sensing component functionalized to attract ammonium, a physical stabilizer element, a sealant component, and an RTIL component.

Description

IN-SITU SOIL AMMONIUM SENSING SYSTEMCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Application 63 / 658,049 filed on June 10, 2024, the content of which is incorporated herein in its entirety.BACKGROUND

[0002] Soil and water are vital components of the Earth's ecosystem, both playing a major role in maintaining the ecological balance of the planet and sustaining mankind. For instance, the correct use of resources such as water and fertilizers in agriculture application has enormous societal (e.g., health, economic, etc.) importance as well as importance at an environmental level. Governments, corporations, and non-profit groups are working to develop paradigms in which soil and water are protected, regenerated and used more intelligently for the benefit of man and nature. For instance, "regenerative farming" concepts and practices have been proposed and implemented for improving soil health, increasing nutrient levels in crops, improving water use efficiency and reversing climate change through sequestering carbon.

[0003] For farmers, the systematic recording of a wide range of information about their fields helps them to implement quality regenerative farming systems, with the aim of improving the information which the farmers rely on for planning and decision-making to increase productivity, land quality, land assets and to reverse losses or inefficiencies in their farms. Optimization of regenerative agriculture is also important at a macro societal level, by protecting crop-producing land, water availability, quality and safety, and reversing negative environmental impacts due to degenerative, inefficient or careless farming practices.

[0004] Traditionally, analytical information for soil health has been obtained by means of manually taking soil samples from various accessible zones to represent various soil regions. The samples are then transported to a laboratory to conduct tests and measurements on these samples to better understand the individual nutrient levels in these soil samples and to estimate the overall soil health and water use efficiency in a whole field, farm or in wider regions. Such traditional measurement systems are both inefficient, suboptimal, and expensive, limiting the utility and affordability to the end-user farmers, and thereby limiting the accessibility and momentum needed to implement such "regenerative farming" methods at scale, among other example disadvantages.BRIEF DESCRIPTION OF FIGURES

[0005] FIG. 1 is a simplified block diagram showing an example soil sensor system including a soil ammonium sensor.

[0006] FIG. 2 is a simplified block diagram illustrating the measurement of ammonium content within a soil sample using an example soil ammonium sensor.

[0007] FIG. 3 is a simplified block diagram illustrating example manufacture of an example soil ammonium sensor.

[0008] FIG. 4A is a simplified block diagram illustrating an example deployment of an example soil ammonium sensor within an example environment.

[0009] FIG. 4B is a diagram illustrating a soil triangle.

[0010] FIG. 5 is a simplified block diagram illustrating an example deployment of an example soil ammonium sensor.

[0011] FIG. 6 is a simplified block diagram illustrating an example soil ammonium sensor system.

[0012] FIGS. 7A-7D show graphs illustrating an example calibration of an example soil ammonium sensor.

[0013] FIG. 8 is a flow diagram illustrating an example technique for measuring ammonium content within soil using an in-situ soil sensor.

[0014] Like reference numbers and designations in the various drawings indicate like elements.DETAILED DESCRIPTION

[0015] Sustainable agriculture is designed to answer the rapid rise in food demand which is straining global soil resources leading to desertification, food insecurity, and ecosystem imbalance. Sustainable agriculture would benefit from reliable systems capable of providing realtime soil health information to allow farmers to make better decisions around the management of their lands. In some implementations, an ion-selective electrode (ISE) electrochemical soil ammonium sensor may be utilized in connection with a soil health system and include the use of electrochemical impedance spectroscopy (EIS) for direct (in situ), real-time, continuous soil ammonium measurement without any soil pre-treatment.

[0016] Soil is a fundamental core element of the earth's environment and directly impacts the growth of plants, crops, and other vegetation in addition to having a relationship with other parts of the ecosystem including water and air. There is a major requirement for information related to the physical, chemical, and biological components of soil and thereby its vital association with soil health. Amongthese groups of parameters, understandingthe chemical profiles of a given volume of soil can be used to create a soil health index with a high degree of reliability in an in-situ manner. For instance, improved soil health systems may be implemented to derive soil chemistry readings using improved in-field probes that have a significant correlation and are also a function of the physical and biological parameters as well as activity in the soil matrix. Commercially, soil quality determines crop yields and cost of farmland. Accordingly, the availability of thorough dynamic and in-situ information about soil parameters that is synchronized in terms of geological location (space) and period (time) may be particularly valuable, for instance, due to the similarly dynamic variations associated with environmental andland use changes. The in-field use of dynamic, in-situ soil sensors may therefore be of particular benefit in characterizing multiple soil parameters related to soil health from a local as well as global environmental-impact standpoint.

[0017] Soil health / quality is defined by its capacity to function as a sustainable ecosystem that supports plants, animals, and humans alike. Typically, soil health includes three types of soil characteristics: biological, physical, and chemical. Although sometimes used interchangeably, soil quality, from a practical sense, refers to soil chemical and physical properties. For instance, soil health assessment is largely determined by the nutrient levels in soil. Hence, assessment of soil health parameters in an on-farm setting, facilitates quantification and recording of the soil's inherent physio-chemical and biochemical characteristics. Sufficient levels of soil nutrients are required for sustainable agricultural practices that typically increase the health of the overall agricultural ecosystem and boost crop yields, pasture growth, etc.

[0018] There is a wide number of primary and secondary micronutrients that are required by plants for growth in addition to the importance for plants and our environment of the soil organic matter pool. An important metric that needs to be considered here is that the rate of nutrient release for uptake by the crops or plants is affected by the availability of the various nutritional sources and other soil parameters. There are a number of electrochemically active and redox substances present in soil that exist in reduced state under ideal conditions (submerged) that contribute to electrochemical activity and in turn have a proportional effect on soil quality.

[0019] Some soil properties often used to evaluate soil physical properties are bulk density, infiltration parameters, water holding capacity, and soil texture; on the other hand, parameters used for chemical evaluation typically include soil pH, plant available nutrients, soil nitrate, reactive carbon, soil organic matter, and electrical conductivity. Biological properties of soil systems include the diversity and quantity of soil organisms (soil food web), total organic carbon, soil respiration, and soil enzymatic activity. Overall, each of these individual parameters can be matched to provide information about the soil state, which is the end objective.

[0020] Currently, soil sampling and evaluation methods involve intrusive approaches to collect and then subsequently test the soil samples in a laboratory environment that differs from the point of collection. Among these, the combustion method is one of the most widely sought- after techniques to look at soil anatomy in laboratories. Even with the forthcoming research breakthroughs in non-destructive approaches like spectroscopy and tomography-based models, there remains a barrier in-terms of accuracy of the methods, especially at soil depths below 5-10 cm, given equipment complexity and availability, as well as high costs and high logistical overhead such as labor, among other issues.

[0021] As noted, traditional soil health measurement approaches often rely on transporting soil samples to remote laboratory facilities or relying on satellite imagery to perform soil salinity analysis, which are time-consuming and costly. Some soil sensors rely on electrochemical measurements, but such traditional electrochemical soil sensors rely on measuring charge accumulation or current changes within the solid soil electrolyte. In controlled environments (e.g., bench testing in a laboratory), such sensors may be effective, but in the field, or in-situ, such soil sensors (e.g., field effect transistor (FET)-based soil sensors) are prone to significant signal drift, due to uncontrolled variables in "wild" or out-of-bounds in-field settings, where such variables (e.g., fertilization conditions) can inadvertently cause charge in-flux or out- flux, creating variations in measurements collected by such FET-based sensors. Further, traditional electrochemical soil sensors are also dependent on the liquid (e.g., water) in the soil mass serving as the primary liquid electrolyte or transduction mechanism for the sensor, which is the medium upon which the sensor relies to function. While such sensors may be effective in certain in-situ environments where the soil has very high moisture content (e.g., a higher percentage of moisture than solid soil elements), such sensors have limited in-field applicability and versatility, particularly during times or in climates where soil moisture is low, as the sensor readings are prone to signal drift and other issues when soil moisture is low, among other example issues and shortcomings.

[0022] Improved sensors may be provided, which leverage soil electrochemistry to correlate soil health in terms of understandable electrochemical signals. Such sensors may beimplemented as integrated and miniaturized platforms along with reliable data output and transmission. For instance, a sensor device may be implemented as an on-chip in-situ diagnostic platform for continuously monitoring active parameters inside the dynamic soil ecosystem. Using such sensors, data sets may be collected and processed by the system to identify correlations between electrochemical activity and the presence of active substances that contribute to the soil nutrient cycle. Indeed, such improved in-situ soil sensors may permit soil health to be assessed and monitored at an interfacial level using a probe system. Accordingly, the soil matrix may be characterized using the resulting data in order to provide information in terms of various physio-chemical phenomena occurring at the electrode interface. Subsequently this information can be correlated with other useful data to understand soil fertility and bioavailability of nutrients for plants and other vegetation at the field level, among other example insights.

[0023] Turning to FIG. 1, a simplified block diagram 100 is shown illustrating an example soil sensing system implemented using one or a collection of computing and / or sensor devices. In one example system, a set of sensors (e.g., 105, 105a-d), such as discussed in the examples below, may be deployed in an agricultural plot 150 to test various areas, or samples (e.g., 110), of soil under various electrochemical modalities to thereby visualize the composite soil chemistry profile of the plot via a point measurement from different characterization perspectives. Such different perspectives may be collected utilizing a collection of sensors (e.g., 105, 105a-d), which includes sensors dispersed in various areas of the plot and / or different types of sensors (e.g., measuring the same or varied portions of the plot), as well as collecting measurements from the sensors on a rolling or continuous basis so as to survey the development of the soil's health attributes over time. Thus, improved data and resulting insights may be derived in such on-field applications due to the sensor devices capturing the dynamic behavior of soil through sensor readings in a range of temporal and spatial settings. Integration of these measurements from spread-out temporal and spatial points may be used by the system to compute a holistic soil profile for the corresponding region, among other example applications and potential benefits.

[0024] In some implementations, supplemental or cooperating computing systems may be provided to communicate with and consume data generated by the collection of sensors (e.g.,105, 105a-d). In one example, a gateway device or other I / O device (e.g., 115) may be utilized to collect signals and other data generated by the sensor devices (e.g., 105, 105a-d) and collect, aggregate, filter, and / or sort the data for consumption by other computing systems and logic. For instance, a computing system (e.g., 125) may be provided with computational logic to determine correlations between the readings of the sensors (e.g., 105, 105a-d) and corresponding soil attributes, which the sensors are configured to measure. For instance, a sensor (e.g., 105) may include one or more electrodes (e.g., 140), which are mounted on a portion 135 of the sensor 105 that is to be brought into contact with soil (e.g., 110) and measure electrochemical characteristics of the soil. The electrode(s) 140, in some implementations, may be coated in a specialized coating to enable the electrode 140 to function appropriately within the sensor 105 to enable the sensor to detect ammonium content within a given soil sample (e.g., 110). For instance, the sensor 105 may generate signals based on these measured electrochemical characteristics. The signals, by themselves, may not directly indicate the level of certain soil health attributes, but through analysis by a correlation engine 155 (e.g., implemented in software and / or hardware of a computing system (e.g., 125)), correlations between certain electrochemical characteristic measurements and corresponding levels of one or more soil health attributes may be determined. While FIG. 1 shows that correlation engine 155 may be executed by a processor 145 and stored in memory 150 of a computing system remote from the sensors (e.g., 105, 105a-d), in some implementations, the hardware and logic of system 125 may be integrated on the sensors themselves to allow this translation between electrochemical readings and various soil health attribute measurements to be determined locally. In some implementations, soil health attribute results determined by a correlation engine 155 may be shared with other computing systems for further storage and / or processing, such as a cloudbased soil-health analysis system (e.g., 130) among other example implementations.

[0025] The rapid rise in food demand is straining our soil to the point that the United Nations (UN) have named food insecurity, desertification, land degradation, and ecosystem imbalance as some of the critical problems to conquer in their Sustainable Development Goals (SDG) report. A major solution to these problems is sustainable agriculture. The National Instituteof Food and Agriculture (NIFA) defines sustainable agriculture as a system that integrates plants and animal production that over the long term would satisfy human food requirements, protects the environment and enhances its natural resources, makes efficient use of nonrenewable resources complimented by the natural biological cycle, and improves the quality of life for society and farmers. However, to achieve this goal, farmers need to know the health of their soil on a continuing basis (e.g., throughout the year).

[0026] Ammonium and nitrate are two forms of nitrogen in soil that are useable by plants. Unused ammonium is converted to nitrate which in excess starts leaching to nearby or underground water bodies which accelerates eutrophication, causing damaging increases in aquatic plant growth and changes in the types of plants and animals that live in nearby water bodies. Ammonium on the other hand, would reach an equilibrium state of ammonia and ammonium in water. Ammonia is highly toxic to marine life even at ultra-low concentrations. Indeed, over-fertilization is one of the major byproducts of inadequate farming techniques. This leads to an imbalance in the soil ecosystem affecting carbon sequestration, plant-available nutrients, and microorganisms. Sustainable agriculture on the other hand, efficiently uses the soil with minimal fertilizer inputs and increased crop rotation to prevent soil erosion. Improvements to soil sensing technologies would enable the realization of these goals.

[0027] Current techniques to quantify soil ammonium is either based on extensive soil sampling for analyzing in the laboratory or using proximal sensing methods, which lack accuracy. In an improved implementation, in situ soil sensors provide accurate in-situ measurements to fundamentally improve soil ammonium assessment and monitoring. Such improved sensors may continuously monitor, in real time, ammonium levels in soil to thereby inform and facilitate the more efficient use of fertilizers, which has the added benefit of reducing the financial burden on farmers. This may lead to higher crop yields and in turn reduce the occurrence of food shortages worldwide. A soil sensing platform that incorporates the improved soil sensor discussed herein may monitor ammonium levels on a daily or weekly basis to derive benefits towards governance perspectives for technical assistance, financial incentives, and environmental monitoring, verification, and reporting, among other example applications.

[0028] Currently, the standard for measuring soil ammonium is the spectrophotometric method after extraction with potassium chloride. This approach requires days to dry the soil sample, then treatment of the soil through mixture with potassium chloride before measuring the ammonium concentration. Such soil analysis techniques may be expensive resulting in farmers testing their land infrequently (e.g., once every two to five years). A common technique is image analysis using drone or satellite images. Other methods include optical sensors that have good sensitivity, but greatly suffer from bulky spectrometer hardware, site-specific calibration, and a lack of accuracy for detecting nutrients that are not fully observed in the Vis-NIR region. Another approach uses a robotic platform that scans a specific field detecting different vegetation and assessing irrigation cycles for the different fields. These techniques, however, require collecting thousands of images stitched together and large processing power to analyze the data. Such demanding hardware may limit the viability, economics, and deployment of such solutions, limiting their utility and adoption.

[0029] In improved implementations, miniaturized sensors may be provided to perform accurate in-situ measurements and deliver readings of soil ammonium on a continuous basis. Such sensor devices may include a microcontroller and a battery in a handheld device to measure the soil nutrients. The simplicity of the hardware allows for weeks or months of data collection before the batteries need to be replaced. The sensors may be calibrated on the soil samples ensuring high measurement accuracy in-situ. In some implementations, such improved in-situ sensor devices may include screen printed electrodes (SPE) enabling low cost manufacture, as well as portability and easy insertion in soil. Such improved soil sensors for accurate in-situ measurements could fundamentally improve soil ammonium assessment and monitoring. Continuously monitoring ammonium levels in soil allows efficient use of fertilizers which reduces financial burden on farmers. This leads to higher crop yield and in turn reducing food shortage worldwide. Tracking ammonium levels in soil also highlights any leaching of nitrate deeper into the soil polluting underground water source or runoff water with high nitrate concentrations into surrounding water bodies turning them toxic to marine life. This sort of sensing platform that monitors ammonium levels on a daily or weekly basis would be greatly beneficial towardsgovernance perspectives for technical assistance, financial incentives and, just from an environmental standpoint, monitoring, verification, and reporting, among other example advantages.

[0030] In one example, an improved sensor is provided configured to perform real-time continuous in-situ soil ammonium measurement through the use of electrochemistry. Some approaches have used open circuit potential (OCP) to measure the concentration of various components within soil. However, open circuit potential measures the equilibrium state of soil which technically depicts bulk micro-environment and is not able to gauge dynamic soil phenomenon. Further, OCP is limited to measuring the equilibrium state of soil which is highly susceptible to environmental noise, signal drift, and moisture content in soil. As such, OCP-based sensors are not suitable for long term in-situ measurement. In an improved implementing, electrochemical impedance spectroscopy (EIS) may instead be utilized to gauge the soil dynamics, which is not only scientifically significant, but also relevant to build an internet of things (loT)- enabled impedimetric platform for soil signal quantification.

[0031] An improved soil sensor may incorporate a sensor design including an electrode system with a composite coating engineered in a in a manner to support selective measurement of ammonium ions directly from soil. Electrochemical signals may be generated at the soil sensor based on the presence of ammonium ions in the soil contacting the improved soil sensor. The electrochemical signal is transduced from the composite coating to a reportable measurement of ammonium in a soil sample (e.g., portion of ground or volume of soil in which the improved in situ soil sensor is inserted). Turning to FIG. 2, a simplified block diagram is shown illustrating an example improved soil sensor 105. In this example, the soil sensor 105 may implement a three- electrode system towards selective detection of ammonium ions in various soil textures. In one example, interfacial-chemical detection of ammonium ions is provided on the sensor using a specialized chemical layer 205 modified surface for ammonium measurement. In FIG. 2, a diagrammatic representation of an example three-electrode sensor is shown with the chemical coating on the working electrode (140), together with a counter electrode (215), and a reference electrode (210), with the working electrode 140 functionalized by the coating (e.g., 205) to bindwith ammonium ions. As such the functionalized sensor coating 205 is deposited precisely to cover only the working electrode 140 to facilitate the generation of electrochemical signals based on the presence and concentration of ammonium ions within a soil sample.

[0032] When a potential is applied to the electrode, while the electrode of the ammonium soil sensor is inserted into a mass, or bulk, of soil, an electrical double layer (e.g., 240) is formed above the coating on the electrolyte within the electrolyte bulk of the soil sample. From this electrical double layer, measurement of ammonium ions within the soil sample by the soil sensor is achieved. The surface coating on the working electrode is selective towards detection of ammonium ions in various soil textures and facilitates interfacial chemical detection of ammonium ions 245. In one example, the chemical coating to be deposited on the working electrode 140 of the improved sensor 105 may be composed of four primary components as follows:

[0033] Component 1: An ammonium attracting agent such as an ammonium ionophore (e.g., Ammonium Ionophore I), which promotes binding / interaction that is captured using electrochemical impedance spectroscopy to track soil ammonium. This is the main sensing element of the system.

[0034] Component 2: Serves as a physical stabilizer element in the composite coating, such as a plasticizer that permits electrochemical activity at the electrode. In one example, plasticizer Bis(2-ethylhexyl)sebacate is added to enhance the coating's durability and flexibility providing better longevity and resilience against variations in temperature.

[0035] Component 3: A polymeric sealant serving as both a hydrophobic sealant and support electrolyte (e.g., to preserve Component 1 in a dispersed form). In one example, the compound includes polymeric entities (e.g., polyvinyl chloride (PVC), polymethyl methacrylate ( PMMA), polyaniline, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and similar analogues) which are added into the composite coating precursor to act as a film sealant that holds the composite against the electrode layer in a functionalized manner, this acts a support electrolyte layer in this modified electrochemical sensor structure.

[0036] Component 4: A component to amplify electrochemical readings and reduce resistive noise characteristics within soil. For instance, a room-temperature Ionic liquid (RTIL) system or other ionic transducer compound may be utilized to enhance the ionic conductivity of the membrane improving signal strength and reducing resistive noise.

[0037] The composite material (e.g., Components 1, 2, 3, 4) are mixed to form a near homogeneous-like physical structure, for instance, by pipette-action, then vortexed (e.g., for 20 minutes) and sonicated (e.g., for 20 minutes) to form a gel-like physical structure. The resulting composite ink may then be coated onto the sensor (e.g., precisely on the working electrode of the sensor) by drop-casting, screen-printing, spin-coating, or another deposition technique to form a functionalized layer on the working electrode of the 3-layer electrode system.

[0038] In one specific example implementation, illustrated in FIG. 3, to prepare an ammonium-selective coating for deposition on a working electrode of an improved soil sensor, a respective amount of a polymeric sealant (e.g., PVC) and a respective amount of plasticizer component (e.g., Bis(2-ethylexyl) sebacate, dioctyl sebacate, etc.)) are dissolved in a respective amount of solvent (e.g., tetra hydrofuran (THF)) (e.g., as illustrated at 305). The solution is mechanically stirred for 30 minutes followed by 20 minutes of sonication (e.g., in a water bath) or until a clear homogenous solution 320 is obtained. Afterwards (as shown in 310), an amount of the ammonium-attracting agent (e.g., Ammonium Ionophore I) and an amount of an amplification component (e.g., an RTIL such as of BMIMTF2N) are added to the solution 320 in a new glass vial. The new solution is prepared (as shown in 310) by mechanically stirring the components for 15 minutes followed by sonication in a water bath for 15 minutes (or until a clear homogenous solution is obtained). The resulting sensor coating may be drop-casted or otherwise deposited (at 315) onto the working electrode 140 of the sensor and left overnight to dry at room temperature, among other example techniques and implementations.

[0039] FIG. 4A is a representation of a comparison between traditional soil analysis techniques and improved, which may be facilitated through miniaturized sensors 105 for in-situ monitoring, such as described herein. FIG. 4A further shows an illustration 400a of the electrical double layer 240 formed at the interface between the soil and the electrode surface 140. Theion-selective coating 210 of the sensor allows the diffusion or binding of a specific target ion only, which in this case is ammonium. Further, as soil textures may vary from location to location and sample to sample, the sensors may be calibrated to various soil types. As an example, a multicalibrated dose-response may be built using three (or more) different soil textures, such that the soil ammonium sensor is calibrated to accurately measure (e.g., within a defined margin of error) ammonium content within any one of these multiple different soil textures. In one example, the three soil textures are clay, sandy loam, and loamy clay as indicated in FIG. 4B. In other implementations, the soil ammonium sensor may be calibrated for a specific soil texture or type. An example in-situ sensing system may be validated using test samples of different soil types obtained from the field and reference ammonium levels (and corresponding electrochemical sensor response) may be correlated to validate and calibrate the sensor to derive ammonium content signals for specific soil types. As an example, a three calibrated dose-response may be built based on cross-correlation of sensor values in three different soil textures (e.g., to configure the sensor readings to correct ammonium level values in any one of these three soil textures, as well as more generally to soil more generally (e.g., soil textures other than, but possessing some similar characteristics of the three correlated soil textures).

[0040] As shown in the simplified block diagram 500 of FIG. 5, an in-situ sensing system with probe integration may be provided and one or more multiple ammonium soil sensor device (e.g., 105) may be inserted within a soil mass 505 to continuously monitor ammonium levels within the soil mass in real-time to enhance agricultural and environmental planning and deployment through real-time tracking of the dynamic soil ecosystem. In some implementations, measurement of the soil ammonium may include impedimetric double layer analysis and modelling to study the interactions at the sensing film and soil ammonium interface and correlate modulations towards ammonium levels (e.g., Electrochemical Impedance Spectroscopy-EIS analysis). As shown in the simplified diagram 500 of FIG. 5, a sensor device 105 may be inserted within a mass of soil and a potential applied at the sensor (e.g., using a cooperating computing system 125) to form an interface between the soil system (analyte) and the functionalized sensor 105. This interface is probed using an impedance-based detection technique (e.g., a correlationengine executed on computing system 125). The presence of increasing levels of soil ammonium in the soil 505 may correlate to corresponding changes / modulation in impedance signals, and this information may be extracted at a specific frequency signature determined experimentally to detect only soil ammonium variations and thereby detect ammonium presence within the soil 505. For instance, the improved ammonium sensor 105 may be inserted in the soil which contains ammonium ions that will bind to the chemical coating on the three-electrode system. The other end of the sensor may be connected to a portable potentiostat system (e.g., 125) for in-situ on demand measurement and analysis, among other example features.

[0041] In one example implementation, the sensor system may include the sensor electrode that is inserted or deployed into the soil which is functionalized as aforementioned to detect soil ammonium entities in the soil sample, and the sensor device may be connected to an electronic hardware platform (e.g., 125). In one example, the hardware platform may include a portable potentiostat system capable of measurements explained previously as well as recording and analyzing output data. Examples of commercially available portable potentiostat systems that the sensor system can be compatible with including but are not limited to: Palmsens emstat series, sensit / sensit BT, pocketstat 2, Metrohm PSTAT mini.; among others. In one example implementation of an improved sensor devices, a screen printed three-electrode with a gold working and counter electrodes and silver reference electrode are used. In one example, the functionalized coating to be provided on the electrode may be constructed to include the components of ammonium Ionophore I, high molecular weight Poly (vinyl chloride) (PVC), Bis(2- ethylhexyl) sebacate (DOS), Tetra hydrofuran (THF) stabilized with BHT, and ammonium chloride. FIG. 6 is a simplified block diagram 600 of hardware components included in an example implementation of a soil ammonium sensor system including sensor device (e.g., 105) and supporting hardware platform, such as discussed herein.

[0042] A soil sensor functionalized to detect ammonium within an amount of soil, such as discussed herein, may be subjected to impedimetric double layer analysis and modelling to study the interactions at the sensing film-soil ammonium interface and correlate modulations towards ammonium levels. For instance, the interface formed between the soil system (analyte)and the functionalized sensor may be probed using an impedance-based detection technique. The functionalized sensor operates such that the presence of increasing levels of soil ammonium correlate to corresponding change / modulation in impedance signals. The readings of the sensor are extracted at a specific frequency signature determined experimentally to detect only soil ammonium variations.

[0043] Turning to FIGS. 7A-7D, graphs 700a-d are presented showing example readings in connection with an example calibration of an example soil sensor device functionalized to detect the presence of ammonium within a soil sample, such as discussed above. For instance, a soil sensor functionalized to detect ammonium within an amount of soil, such as discussed herein, may be subjected to impedimetric double layer analysis and modelling to study the interactions at the sensing film-soil ammonium interface and correlate modulations towards ammonium levels. For instance, the interface formed between the soil system (analyte) and the functionalized sensor is probed using an impedance-based detection technique. The functionalized sensor operates such that the presence of increasing levels of soil ammonium correlate to corresponding changes / modulations in impedance signals. The readings of the sensor are extracted at a specific frequency signature determined experimentally to detect only soil ammonium variations.

[0044] In one example, an example soil ammonium sensor, such as discussed herein, is calibrated against known spiked doses prepared to cover the range from 0 ppm to 32 ppm of ammonium. In this example, a PVC membrane containing ammonium ionophore I is used. As such, in this example, ammonium ions have the highest probability of binding to the ionophore. During calibration, the changing charge on the electrode surface can be measured using EIS, such as depicted in the graphs 700a-d of FIGS. 7A-7D, for the various ammonium content levels. As illustrated, as the ammonium concentration in soil increases, the impedance of the electrical double layer (EDL) decreases, as measured at the sensor. More particularly, FIG. 7A shows a Nyquist plot showing measured EIS in sandy loam soil of varying ammonium concentrations using an example soil ammonium sensor. FIG. 7B shows the measured versus spiked concentrations in sandy loam soil with a Pearson correlation r = 0.9951, while FIG. 7C shows a similar comparisonfor clay (with Pearson r = 0.9917), and FIG. 7D shows a similar comparison for loamy clay soil (with Pearson r = 0.9981), among other example implementations (which may include calibrations in other soil types and with comparable, but different results). Once calibrated, an impedance value generated at the sensor may be properly interpreted to correlate (e.g., for a corresponding soil type) to a corresponding soil ammonium content level, allowing ammonium content level to be generated through the sensor for further processing or transmission to soil health analytics tools or services.

[0045] In some implementations, the soil sensor devices may be hardwired or connect wirelessly (e.g., via an integrated wireless communication module) to supporting hardware capable of recording or performing analytics on the data generated by and received from the sensor devices. In some implementations, such systems may be locally deployed. In other implementations, such systems may include cloud-based computing systems (e.g., which the sensor devices may communicate with via a local gateway devices). In still other implementations, data storage and analytics / interpretation logic may be included on the sensor devices, among other example implementations. As one example, sensor devices may connect to a potentiostat system (e.g., a portable or battery-powered system) capable of performing calculations on measurements obtained from the sensor devices (e.g., discussed in the first and second approaches above), as well as recording and analyzing output data.

[0046] While the examples above illustrate example soil sensor implementations, it should be appreciated that these are presented as illustrative examples only and that a variety of other, additional interfacial soil sensors may be implemented based on and applying the principles described herein, including sensors with varying form factors and substrates, sensors applying different active, stabilizer, RTIL, and / or sealant layers or coatings, and sensors capable of being used to measure other attributes of soil health (e.g., organic carbon, nitrate, salinity, etc.). Moreover, multiple sensor designs may be applied and integrated within a single sensor device to enable the device to concurrently measure multiple different soil health attributes for a corresponding soil sample matrix and multi-variant analysis of the subject soil. Indeed, an array of soil health attributes may be advantageously measured using soil sensor systems such asdescribed herein to develop measurements of the overall health of a plot of ground (e.g., farmland, ranch land, orchard plots, vineyards, and the like).

[0047] FIG. 8 is a simplified flow diagram 800 illustrating an example technique involving the use of an example in-situ soil sensor. The sensor may be deployed in a particular soil sample (either isolated in a container or representing a portion of a large plot of ground or soil). Electrodes of the soil sensor may be in prolonged and direct contact with the soil and may be configured to react to, measure, or detect chemical properties of the soil based on electrochemical reactions measured at the electrodes of the sensor. The sensor, through the electrodes, may generate signals 805 based on a sensing film or coating (such as discussed above) applied to one or more electrodes of the sensor (e.g., only the working electrode of a three electrode sensor). The film may include an active sensing element, stabilizer, sealant, and RTIL and may enable the sensor to generate signals corresponding to ammonium levels of the soil. The signals may be sent 810 to a cooperating computing device, which includes computer processing hardware and logic to determine 815 correlations between the generated signals and the ammonium level of the soil sample. In some implementations, the cooperating computing device may be different from and remote from the sensor device. In other implementations, the computing device and its hardware may be integrated with the sensor device. Measurement data may be generated 820 based on the determined correlation to indicate a measure of the corresponding soil ammonium level. In some implementations, a soil sensor device may include multiple sensor elements, including the ammonium sensor discussed herein, so that the soil sensor device may detect the presence of multiple different chemical attributes of the soil, such as carbon content, nitrate content, salinity content, among other example soil health attributes. This information may be further used, stored, shared, or tracked to assess, on a continuing basis, the ammonium level in this portion of the soil, and through the deployment of multiple such sensors in multiple nearby soil samples, the overall ammonium attributes of a plot of land and its soil, among other example applications and benefits.

[0048] Note that in this document, references to various features (e.g., elements, structures, modules, components, steps, operations, characteristics, etc.) included in "oneembodiment", "example embodiment", "an embodiment", "another embodiment", "some embodiments", "various embodiments", "other embodiments", "alternative embodiment", and the like are intended to mean that any such features are included in one or more embodiments of the present disclosure, but may or may not necessarily be combined in the same embodiments. Furthermore, the words "optimize," "optimization," and related terms are terms of art that refer to improvements in speed and / or efficiency of a specified outcome and do not purport to indicate that a process for achieving the specified outcome has achieved, or is capable of achieving, an "optimal" or perfectly speedy / perfectly efficient state.

[0049] In general, computing systems, which interface with a biosensor via a wired or wireless communication channel, can include electronic computing devices operable to receive, transmit, process, store, or manage data and information associated with the biosensor and other subsystems of the computing system. As used in this document, each of the terms "computer," "processor," "processor device," "microcontroller," or "processing device" is intended to encompass any suitable data processing apparatus. For example, while the microcontroller may be implemented, in some examples, as a single device within the computing system, in other implementations the processing functionality of the system may be implemented using a plurality of computing devices and processors, such as a fog computing system, server pools, a cloud computing system, or other distributed computing system including multiple computers. Further, any, all, or some of the computing devices may be adapted to execute any operating system, including Linux, UNIX, Microsoft Windows, Apple OS, Apple iOS, Google Android, Windows Server, etc., as well as virtual machines adapted to virtualize execution of a particular operating system, including customized and proprietary operating systems.

[0050] In some implementations, all or a portion of a computing platform may function as a wearable device, standalone biosensor device, or other sensor device. A sensor device may connect to and communicate with other computing devices through wired or wireless network connections. For instance, wireless network connections may utilize wireless local area networks (WLAN), such as those standardized under IEEE 802.11 family of standards, home-area networks such as those standardized under the Zigbee Alliance, personal-area networks such as thosestandardized by the Bluetooth Special Interest Group, cellular data networks, such as those standardized by the Third-Generation Partnership Project (3GPP), and other types of networks, having wireless, or wired, connectivity. For example, an endpoint device may also achieve connectivity to a secure domain through a bus interface, such as a universal serial bus (USB)-type connection, a High-Definition Multimedia Interface (HDMI), or the like.

[0051] The following examples pertain to embodiments in accordance with this Specification. Example 1 is an apparatus including: a sensor to detect levels of ammonium in a sample of soil, the sensor including: a working electrode coated in a composite coating, where the composite coating includes: an active sensing component functionalized to attract ammonium; a physical stabilizer element; a sealant component; and a room temperature ionic liquid (RTIL) component; and another electrode.

[0052] Example 2 includes the subject matter of example 1, where the physical stabilizer element comprises a plasticizer that permits electrochemical activity at the working electrode.

[0053] Example 3 includes the subject matter of any one of examples 1-2, where the sealant component acts as a support electrolyte for electrochemical transduction.

[0054] Example 4 includes the subject matter of any one of examples 1-2, where the other electrode includes a reference electrode.

[0055] Example 5 includes the subject matter of example 4, where the sensor further includes a counter electrode.

[0056] Example 6 includes the subject matter of any one of examples 4-5, where the composite coating is layered over only the working electrode.

[0057] Example 7 includes the subject matter of any one of examples 1-6, where the composite coating is drop-cast over the working electrode.

[0058] Example 8 includes the subject matter of any one of examples 1-6, where the composite coating is drop-cast over the working electrode.

[0059] Example 9 includes the subject matter of any one of examples 1-8, where the composite coating includes a mixture of the active sensing component, the active sensing component, the physical stabilizer element, the sealant component, and the RTIL component.

[0060] Example 10 includes the subject matter of any one of examples 1-9, further including circuitry to: apply a voltage; and detect impedance at the sensor based on presence of ammonium in the soil sample.

[0061] Example 11 includes the subject matter of example 10, where the voltage includes a pulsed voltage signal applied across the working electrode and reference electrode.

[0062] Example 12 includes the subject matter of example 11, where the pulsed voltage signal is applied according to a particular frequency associated with detection of varied levels of ammonium.

[0063] Example 13 includes the subject matter of any one of examples 1-12, further including a communication module to send a signal to another computing device to communicate the detected impedance.

[0064] Example 14 includes the subject matter of any one of examples 1-13, further including a second sensor to detect another chemical property of the soil.

[0065] Example 15 includes the subject matter of any one of examples 1-14, where the sensor includes an in-situ soil sensor.

[0066] Example 16 includes the subject matter of any one of examples 1-15, where the physical stabilizer element includes plasticizer Bis(2-ethylhexyl)sebacate.

[0067] Example 17 includes the subject matter of any one of examples 1-16, where the sealant component includes polyvinyl chloride (PVC).

[0068] Example 18 includes the subject matter of any one of examples 1-17, where the RTIL component includes BMIMTF2N.

[0069] Example 19 includes the subject matter of any one of examples 1-18, where the active sensing component includes ammonium Ionophore I.

[0070] Example 20 is a method including: applying a voltage across a working electrode and reference electrode of an in-situ soil sensor deployed in a soil sample, where the workingelectrode is coated with a composite coating including an active sensing component, a physical stabilizer element, a sealant component, and a room temperature ionic liquid (RTIL) component; and generating impedance signals at the in-situ soil sensor, where the impedance signals are generated based on concentration of ammonium in the soil sample, where the active sensing component is configured to detect the ammonium.

[0071] Example 21 includes the subject matter of example 20, further including determining, from the impedance signals, a concentration of ammonium within the soil sample.

[0072] Example 22 includes the subject matter of example 21, further including transmitting a signal to another computing device to identify the impedance signals to the other computing device, where the other computing device determines the concentration of ammonium within the soil sample.

[0073] Example 23 includes the subject matter of any one of examples 20-22, where the voltage forms an electrical double layer above the composite coating.

[0074] Example 24 includes the subject matter of any one of examples 20-23, where the in-situ soil sensor includes the apparatus of any one of examples 1-19.

[0075] Example 25 is a system including means to perform the method of any one of examples 20-24.

[0076] Example 26 includes the subject matter of example 25, where the means include a non-transitory machine-readable storage medium with instructions stored thereon, the instructions executable by a machine to cause the machine to perform at least a portion of the method of any one of examples 20-24.

[0077] Example 27 is a method to manufacture a soil ammonium sensor, the method including: mixing (i) an active sensing component functionalized to attract ammonium, (ii) a physical stabilizer element, (iii) a sealant component, (iv) and a room temperature ionic liquid (RTIL) component to generate a composite coating solution; coating a working electrode of the soil ammonium sensor with the composite coating solution; and drying the composite coating solution to form a film on the working electrode of the soil ammonium sensor.

[0078] Example 28 includes the subject matter of example 27, where the mixing includes mechanical stirring followed by sonication.

[0079] Example 29 includes the subject matter of any one of examples 25-28, where the soil ammonium sensor includes a plurality of electrodes and the composite coating solution is precision coated on the working electrode to coat only the working electrode.

[0080] Example 30 includes the subject matter of example 29, where the plurality of electrodes include the working electrode, a counter electrode, and a reference electrode.

[0081] Example 31 includes the subject matter of any one of examples 27-30, where coating the working electrode of the soil ammonium sensor with the composite coating solution includes drop-casting the composite coating solution on the working electrode.

[0082] Example 32 includes the subject matter of any one of examples 27-30, where coating the working electrode of the soil ammonium sensor with the composite coating solution includes spin-coating the composite coating solution on the working electrode.

[0083] Example 33 includes the subject matter of any one of examples 27-30, where coating the working electrode of the soil ammonium sensor with the composite coating solution includes screen printing the composite coating solution on the working electrode.

[0084] Example 34 includes the subject matter of any one of examples 27-33, where the physical stabilizer element includes plasticizer Bis(2-ethylhexyl)sebacate.

[0085] Example 35 includes the subject matter of any one of examples 27-34, where the sealant component includes polyvinyl chloride (PVC).

[0086] Example 36 includes the subject matter of any one of examples 27-35, where the RTIL component includes BMIMTF2N.

[0087] Example 37 includes the subject matter of any one of examples 27-36, where the active sensing component includes ammonium Ionophore I.

[0088] Example 38 includes the subject matter of any one of examples 28-37, where tetrahydrofuran (THF) is mixed with the active sensing component, the physical stabilizer element, the sealant component, and the RTIL component to generate a composite coating solution

[0089] Example 39 includes the subject matter of any one of examples 27-38, where the soil ammonium sensor includes the apparatus of any one of examples 1-19.

[0090] Example 40 is a product manufactured by a process including the method of any one of examples 27-38.

[0091] Example 41 is a system including: a sensor device including: a plurality of electrodes, where the plurality of electrodes includes a working electrode coated in a composite sensing coating, where the composite sensing coating includes an active sensing component, a physical stabilizer element, a sealant component, and a room temperature ionic liquid (RTIL) component; and circuitry to generate an impedance based on concentration of ammonium in a soil sample when in contact with the working electrode; and an analysis system including: a processor; and analytics logic executable by the processor to determine, from the impedance, a value of the concentration of ammonium in the soil sample.

[0092] Example 42 includes the subject matter of example 41, further including a plurality of sensor devices deployed in a plurality of soil samples within an environment.

[0093] Example 43 includes the subject matter of any one of examples 41-42, where the sensor device includes an in situ soil sensor.

[0094] Example 44 includes the subject matter of any one of examples 41-43, where the sensor device includes the apparatus of any one of examples 1-19.

[0095] It is also important to note that the operations and steps described with reference to the preceding figures illustrate only some of the possible scenarios that may be executed by, or within, the system. Some of these operations may be deleted or removed where appropriate, or these steps may be modified or changed considerably without departing from the scope of the discussed concepts. In addition, the timing of these operations may be altered considerably and still achieve the results taught in this disclosure. The preceding operational flows have been offered for purposes of example and discussion. Substantial flexibility is provided by the system in that any suitable arrangements, chronologies, configurations, and timing mechanisms may be provided without departing from the teachings of the discussed concepts.

[0096] Although the present disclosure has been described in detail with reference to particular arrangements and configurations, these example configurations and arrangements may be changed significantly without departing from the scope of the present disclosure. Numerous other changes, substitutions, variations, alterations, and modifications may be ascertained to one skilled in the art and it is intended that the present disclosure encompass all such changes, substitutions, variations, alterations, and modifications as falling within the scope of the appended claims.

Claims

CLAIMS:

1. An apparatus comprising: a sensor to detect levels of ammonium in a sample of soil, the sensor comprising: a working electrode coated in a composite coating, wherein the composite coating comprises: an active sensing component functionalized to attract ammonium; a physical stabilizer element; a sealant component; and a room temperature ionic liquid (RTIL) component; and another electrode.

2. The apparatus of Claim 1, wherein the physical stabilizer element comprises a plasticizer that permits electrochemical activity at the working electrode.

3. The apparatus of any one of Claims 1-2, wherein the sealant component acts as a support electrolyte for electrochemical transduction.

4. The apparatus of any one of Claims 1-2, wherein the other electrode comprises a reference electrode.

5. The apparatus of Claim 4, wherein the sensor further comprises a counter electrode.

6. The apparatus of any one of Claims 4-5, wherein the composite coating is layered over only the working electrode.

7. The apparatus of any one of Claims 1-6, wherein the composite coating is drop-cast over the working electrode.

8. The apparatus of any one of Claims 1-6, wherein the composite coating is drop-cast over the working electrode.

9. The apparatus of any one of Claims 1-8, wherein the composite coating comprises a mixture of the active sensing component, the active sensing component, the physical stabilizer element, the sealant component, and the RTIL component.

10. The apparatus of any one of Claims 1-9, further comprising circuitry to: apply a voltage; and detect impedance at the sensor based on presence of ammonium in the soil sample.

11. The apparatus of Claim 10, wherein the voltage comprises a pulsed voltage signal applied across the working electrode and reference electrode.

12. The apparatus of Claim 11, wherein the pulsed voltage signal is applied according to a particular frequency associated with detection of varied levels of ammonium.

13. The apparatus of any one of Claims 1-12, further comprising a communication module to send a signal to another computing device to communicate the detected levels of ammonium.

14. The apparatus of any one of Claims 1-13, further comprising a second sensor to detect another chemical property of the soil.

15. The apparatus of any one of Claims 1-14, wherein the sensor comprises an in-situ soil sensor.

16. The apparatus of any one of Claims 1-15, wherein the physical stabilizer element comprises plasticizer Bis(2-ethylhexyl)sebacate.

17. The apparatus of any one of Claims 1-16, wherein the sealant component comprises polyvinyl chloride (PVC).

18. The apparatus of any one of Claims 1-17, wherein the RTIL component comprises BMIMTF2N.

19. The apparatus of any one of Claims 1-18, wherein the active sensing component comprises ammonium Ionophore I.T120. A method comprising: applying a voltage across a working electrode and reference electrode of an in-situ soil sensor deployed in a soil sample, wherein the working electrode is coated with a composite coating comprising an active sensing component, a physical stabilizer element, a sealant component, and a room temperature ionic liquid (RTIL) component; and generating impedance signals at the in-situ soil sensor, wherein the impedance signals are generated based on concentration of ammonium in the soil sample, wherein the active sensing component is configured to detect the ammonium.

21. The method of Claim 20, further comprising determining, from the impedance signals, a concentration of ammonium within the soil sample.

22. The method of Claim 21, further comprising transmitting a signal to another computing device to identify the impedance signals to the other computing device, wherein the other computing device determines the concentration of ammonium within the soil sample.

23. The method of any one of Claims 20-22, wherein the voltage is applied to form an electrical double layer above the composite coating.

24. The method of any one of Claims 20-23, wherein the in-situ soil sensor comprises the apparatus of any one of Claims 1-19.

25. A system comprising means to perform the method of any one of Claims 20-24.

26. The system of Claim 25, wherein the means comprise a non-transitory machine- readable storage medium with instructions stored thereon, the instructions executable by a machine to cause the machine to perform at least a portion of the method of any one of Claims20-24.

27. A method to manufacture a soil ammonium sensor, the method comprising: mixing (i) an active sensing component functionalized to attract ammonium, (ii) a physical stabilizer element, (iii) a sealant component, (iv) and a room temperature ionic liquid (RTIL) component to generate a composite coating solution; coating a working electrode of the soil ammonium sensor with the composite coating solution; and drying the composite coating solution to form a film on the working electrode of the soil ammonium sensor.

28. The method of Claim 27, wherein the mixing comprises mechanical stirring followed by sonication.

29. The method of any one of Claims 27-28, wherein the soil ammonium sensor comprises a plurality of electrodes and the composite coating solution is precision coated on the working electrode to coat only the working electrode.

30. The method of Claim 29, wherein the plurality of electrodes comprise the working electrode, a counter electrode, and a reference electrode.

31. The method of any one of Claims 27-30, wherein coating the working electrode of the soil ammonium sensor with the composite coating solution comprises drop-casting the composite coating solution on the working electrode.

32. The method of any one of Claims 27-30, wherein coating the working electrode of the soil ammonium sensor with the composite coating solution comprises spin-coating the composite coating solution on the working electrode.

33. The method of any one of Claims 27-30, wherein coating the working electrode of the soil ammonium sensor with the composite coating solution comprises screen printing the composite coating solution on the working electrode.

34. The method of any one of Claims 27-33, wherein the physical stabilizer element comprises plasticizer Bis(2-ethylhexyl)sebacate.

35. The method of any one of Claims 27-34, wherein the sealant component comprises polyvinyl chloride (PVC).

36. The method of any one of Claims 27-35, wherein the RTIL component comprises BMIMTF2N.

37. The method of any one of Claims 27-36, wherein the active sensing component comprises ammonium Ionophore I.

38. The method of any one of Claims 27-37 , wherein tetra hydrofuran (THF) is mixed with the active sensing component, the physical stabilizer element, the sealant component, and the RTIL component to generate the composite coating solution.

39. The method of any one of Claims 27-38, wherein the soil ammonium sensor comprises the apparatus of any one of Claims 1-19.

40. A product manufactured by a process comprising the method of any one of Claims 27-39.

41. A system comprising: a sensor device comprising: a plurality of electrodes, wherein the plurality of electrodes comprises a working electrode coated in a composite sensing coating, wherein the composite sensing coating comprises an active sensing component, a physical stabilizer element, a sealant component, and a room temperature ionic liquid (RTIL) component; and circuitry to generate an impedance based on concentration of ammonium in a soil sample when in contact with the working electrode; and an analysis system comprising: a processor; analytics logic executable by the processor to determine, from the impedance, a value of the concentration of ammonium in the soil sample.

42. The system of Claim 41, further comprising a plurality of sensor devices deployed in a plurality of soil samples within an environment.

43. The system of any one of Claims 41-42, wherein the sensor device comprises an in situ soil sensor.

44. The system of any one of Claims 41-43, wherein the sensor device comprises the apparatus of any one of Claims 1-19.