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A key to developing a real time, automated soil nutrient sensor depends on the ability to effectively extract soil nutrients from a soil sample and precisely detect them in a very short time period. An ion-selective field effect transistor (ISFET) chip has proven to be a good candidate for use in real-time soil nutrient sensing because of its rapid response and low sample volume. This paper describes the evaluation of nitrate ionselective membranes and the investigation of the interaction between the ion-selective membranes and soil extracting solutions. The response characteristics of the membranes and their suitability for use for real-time soil nutrient sensing were investigated through evaluation of their sensitivity and selectivity using 16 ion selective electrodes (ISEs) in a computer-controlled system. All membranes showed an approximately linear Nernstian response when nitrate concentrations were above 10-3 M, irrespective of extracting solution type. At low nitrate concentrations, below 10-4 M, both the extracting solution and ligand types significantly affected the sensitivity and selectivity of each membrane. A TDDA-NPOE membrane showed greater sensitivity to nitrate than did the MTDA-NPOE and MTDA-TOTM membranes. In addition, the selectivity of the TDDA membrane was superior to that of the MTDA membranes when bicarbonate, chloride, and bromide were considered as the interfering ions.