Challenges of polymer‐based pHsensing in soil

It is well established that plants need a range of soil nutrients to grow. In farming, these nutrients are generally added to the soil in the form of fertilizers. However, depending on the soil conditions (such as temperature, water content, pH, and soil type), nutrients may not be in the right form for plant uptake. Determining the availability of nutrients in the soil for plant growth is therefore critical for the yield and productivity of modern farming. A considerable amount of research and knowledge has been developed that shows the importance of the soil pH on the availability (or not) of nutrients. Furthermore, pH plays a crucial role in controlling the availability of potential toxic elements, such as aluminum and manganese. This review article discusses recent research aimed at real‐time and continuous soil pH measurement in‐situ. More specifically, it focuses on the development of polymer materials that will ultimately enable pH measurements for the specific application of in‐ground pH sensing. Given the breadth of the polymeric sensor research field, this review has a narrowed focus on optical and electrochemical transduction methods.