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Improving agricultural production relies on the decisions and actions of farmers and land managers, highlighting the importance of efficient soil monitoring techniques for better resource management and reduced environmental impacts. Despite considerable advancements in soil sensors, their traditional bulky counterparts cause difficulty in widespread adoption and large-scale deployment. Printed electronics emerge as a promising technology, offering flexibility in device design, cost-effectiveness for mass production, and a compact footprint suitable for versatile deployment platforms. This review overviews how printed sensors are used in monitoring soil parameters through electrochemical sensing mechanisms, enabling direct measurement of nutrients, moisture content, pH value, and others. Notably, printed sensors address scalability and cost concerns in fabrication, making them suitable for deployment across large crop fields. Additionally, seamlessly integrating printed sensors with printed antenna units or traditional integrated circuits can facilitate comprehensive functionality for real-time data collection and communication. This real-time information empowers informed decision-making, optimizes resource management, and enhances crop yield. This review aims to provide a comprehensive overview of recent work related to printed electrochemical soil sensors, ultimately providing insight into future research directions that can enable widespread adoption of precision agriculture technologies. 

Abstract Many applications in human health screening, soft robotics, and structural health monitoring require sensors that can accommodate large deformations and highly curved geometries, while providing reliable measurements across a range of frequencies. Ideally, such sensors will also be low cost and easy to manufacture. While prior studies achieve some of these goals, it is rare to achieve them all in a holistic manner. Here, a soft sensor that is easy to manufacture, affordable, and water compatible is presented. The sensor is made of a combination of carbon nanotubes and few‐layer graphene dispersed in a polydimethylsiloxane elastomer. The sensor's ability to detect a broad range of frequencies under both uniaxial stretch and bending is demonstrated. The sensor is effective in multiple configurations, including directly stretching the sensor, adhering the sensor to a deforming compliant substrate, and operating under water. Specifically, the sensor can accurately detect vibrational frequencies with amplitudes as small as 0.1% strain and excitation frequencies covering a broad range of 50–600 Hz with an average root mean square error (RMSE) of 0.16%. Even in the presence of large (≈ 20%) deformations and aqueous environments the sensor can recover the fundamental and higher order vibrational modes within less than 2% error. 

Abstract Agricultural intensification has increased the use of chemical fertilizers, promoting plant growth and crop yield. Excessive use of nitrogen fertilizers leads to nutrient loss and low nitrogen use efficiency. Management of nitrogen fertilizer input requires close to real‐time information about the soil nitrate concentration. While there is extensive work developing nitrate ion sensing solutions for liquid media, few allow for in‐soil measurements. This study introduces inkjet‐printed potentiometric sensors, containing 2 electrodes, the reference electrode (RE) and the nitrate‐selective film‐encapsulated working electrode (WE). The interaction between the nitrate‐sensitive membrane and soil nitrate ions causes a change in potential across the RE and WE. Additionally, a hydrophilic Polyvinylidene Fluoride (PVDF) layer ensures the long‐term functionality of the sensor in wet soil environments by protecting it from charged soil particles while simultaneously allowing water to flow from the soil toward the sensor electrodes. The sensors are tested in sand and silt loam soil, demonstrating their versatility across soil types. The potential change can be related to the nitrate concentration in soil, with typical sensitivities of 45–55 mV decade⁻¹. Overall, the use of the PVDF layer allows for direct sensing in moist soil environments, which is critical for developing soil nitrate sensors. 

Abstract The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g. via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g. printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world.