Application of ion sensitive field effect transistor based sensors to soil analysis

Standard methods to measure nutrient levels in soil are complex and time consuming due to the extraction and pre-treatment processes involved. Besides, the instrumentation used for these measurements is also expensive. Therefore, the use of chemical sensors warrants investigation since they can be placed directly in the soil and results can be provided in real or quasi-real time at a moderate cost. The control of nutrients with sensors will permit an optimisation of irrigation and fertilisation management systems and thus will be useful for reducing the environmental impact caused by the runoff of nutrients into surface and ground waters. In this work, the use of chemical sensors based on ion sensitive field effect transistors (ISFETs) for soil analysis is proposed. These devices are fabricated with microelectronic technology - providing some important advantages such as robustness, small size, low output impedance and mass production. Fabrication of pH, Ca2+, K+ and NO3 ISFETs with photocurable polymeric membranes and their evaluation in aqueous solutions is reported. Studies of their response in horticulture soils and comparison with standard methods have been performed. The results confirm the feasibility of ISFET based sensors for in-soil monitoring and the promising future applications they have. © 2001 Elsevier Science B.V.