EVALUATION OF NITRATE AND POTASSIUM ION-SELECTIVE MEMBRANES FOR SOIL MACRONUTRIENT SENSING

Abstract

On-the-go, real-time soil nutrient analysis would be useful in site-specific management of soil fertility. The rapidresponse and low sample volume associated with ion-selective field-effect transistors (ISFETs) make them good soil fertilitysensor candidates. Ion-selective microelectrode technology requires an ion-selective membrane that responds selectively toone analyte in the presence of other ions in a solution. This article describes: (1) the evaluation of nitrate and potassiumion-selective membranes, and (2) the investigation of the interaction between the ion-selective membranes and soilextractants to identify membranes and extracting solutions that are compatible for use with a real-time ISFET sensor tomeasure nitrate and potassium ions in soil. The responses of the nitrate membranes with tetradodecylammonium nitrate(TDDA) or methlytridodecylammonium chloride (MTDA) and potassium membranes with valinomycin were affected by bothmembrane type and soil extractant. A TDDA-based nitrate membrane would be capable of detecting low concentrations in soils to about 10-5 mole/L NO3 -. The valinomycin-based potassium membranes showed satisfactory selectivity performancein measuring potassium in the presence of interfering cations such as Na+, Mg2+, Ca2+, Al3+, and Li+ as well as provideda consistent sensitivity when DI water, Kelowna, or Bray P1 solutions were used as base solutions. The TDDA-based nitratemembrane and the valinomycin-based potassium membrane, used in conjunction with Kelowna extractant, would allowdetermination of nitrate and potassium levels, respectively, for site-specific control of fertilizer application.