Understanding soil and plant properties in real-time and at high-spatial resolution is critical for optimizing agricultural input use (such as irrigation water and fertilizer) as well as for general assessment of soil and plant health. However, obtaining such information can be a challenge, thereby limiting management approaches and potentially leading to excess input and energy use. Many important materials of interest (such as soil nitrate), show significant spatial variation (on the order of 10s of meters). As such novel instrumentation that can directly sample soil at high spatial density is needed to capture current conditions and enable optimized management strategies.
Printing approaches are well suited for the manufacture of sensor systems to address these concerns, since large numbers of devices can potentially be economically produced and distributed over a wide area to capture appropriate spatial information. In this presentation, several recently developed printed devices (capacitive, ion-selective, and enzyme/microbe selective) for real-time, in-situ, high-spatial density monitoring of soil conditions such as moisture, ion concentration, and microbial activity will be discussed. These sensors are fabricated using biodegradable materials for substrates, conductors, encapsulants, and stimuli-responsive materials, so that the sensors degrade into the environment when no longer required, allowing large numbers to be used without the production of excess waste or the need for maintenance and collection. In addition, ion-selective organic electrochemical transistor-based sensors for determining ion concentrations in whole plant sap will also be discussed.