Electrochemical sensors are amperometric of potentiometric devices that produce a voltage or signal relating to a chemical state or reaction. A large number of electrochemical sensors have been developed for a range of chemical properties suited to soil sensing (e.g. pH, NO3-, Na+, K+, Cl-, Ca+, Mg+ etc). There are four types of electrochemical sensors that are commonly used in PSS research.

1. Ion Selective Electrodes (ISEs) are a potentiometric sensor based on the ion selective membrane. When submerged in the electrolyte to be analysed, generates an electromotive force (emf) related to the activity of the targeted ionic species.

2. Ion Sensitive Field Effect Transistors (ISFETs) are pH sensors based on a Field Effect Transistor (FET). The gate insulator (oxide) of the FET is left exposed to the measured electrolyte so that current flow is regulated by proton interaction, and therefore pH of the solution.

3. Chemically modified ISFETs (CHEMFETs) are identical to the ISFET but with membrane layers applied to the gate oxide surface so sensitivity can be targeted at a specific ionic species (e.g. NO3-).

4. Metal Electrodes are essentially an ISE however the membrane is replaced with metals such as antimony (for pH) and cobalt (for phosphate). This offers increased durability over glass pH electrodes and other PVC membrane based ISEs.


On-the-go soil nutrient [1,2,3] and pH measurement [4,5]

Continuous monitoring of nutrient status [6].


Response characteristics of the ISEs are variable, requiring frequent calibration.

A suitable environment must be provided for ISE measurement (e.g. a soil slurry or soil extract solution) and therefore additional hardware is required to facilitate measurement. Commercial on-the-go soil pH measurement is available (Veris pH Manager) however measurement of other soil chemical properties is still under research.

Development Status

Sensor technology - Commercially available.

Proximal Soil Sensor - Research (with pH commercially available e.g. Veris pH manager).



1. Adsett, J.F. and Zoerb, G.C., 1991. Automated field monitoring of soil nitrate levels. In Proceedings ASAE symposium on Automated Agriculture for the 21st Century, 16-17 Dec., 1991, Chicago, IL. American Society of Agricultural Engineers, St. Joseph, MI, pp. 326-335.

2. Birrell, SJ, Hummel, JW, 2001. Real-time multi ISFET/FIA soil analysis system with automatic sample extraction. Computers and Electronics in Agriculture 32, 45–67.

3. Adamchuk VI, Lund ED, Sethuramasamyraja B, Morgan MT, Dobermann A, Marx DB (2005) Direct measurement of soil chemical properties on-the-go using ion-selective electrodes. Computers and Electronics in Agriculture 48, 272-294.

4. Adamchuk, V.I., Morgan, M.T. and Ess, D.R. (1999). An automated sampling system for measuring soil pH. Trans. ASAE 42(4):885–891.

5. Viscarra Rossel, R.A. and Walter, C. (2004). Rapid, quantitative and spatial field measurements of soil pH using an Ion Sensitive Field Effect Transistor. Geoderma 119:9–20.

6. Artigas, J., Beltran, A., Jimenez, C., Baldi, A., Mas, R., Domınguez, C., Alonso, J. 2001. Application of ion sensitive field-effect transistor based sensors to soil analysis Computers and Electronics in Agriculture 31: 281 – 293