Towards the implementation of ISFET sensors for in-situ and real-time chemical analyses in soils: A practical review

Estimating available nutrients and pH in soils has been considered an essential step to improve soil fertility for better crop growth and yield. Classical or conventional laboratory analyses are time-consuming, expensive and expose chemical agents to the environment, hence, do not fulfil the requirement of high sampling resolution data for Precision Agriculture (PA) applications. Proximal Soil Sensing (PSS) allows generating high-volume data quickly and cost-effectively. A functional technology under PSS is the Ion-Sensitive Field-Effect Transistor (ISFET) sensor, which is based on electrochemical principles and can estimate pH and available nutrients in soils. However, their use in PA is limited, compared to other disciplines, e.g., biomedical sciences. This paper presents a state-of-the-art review of ISFET sensors and their use in soil nutrients and pH analyses, highlighting the technical potential and limitations related to implementation. The review focuses on essential concepts (e.g., basic operation principle, algorithms, sensor representations, behavioral model, and simulation example), performance characteristics (e.g., relevant variables, non-idealities, and electronic instrumentation), application examples in PA, and some perspectives of implementation. The goal is to raise awareness of ISFET sensors in the agriculture community and to offer a starting point to those who plan to adopt ISFET sensors in PA.