Real-time Soil Nitrate Sensing

Abstract

Soil nitrate is an important factor in the farming industry as it influences how well a cropwill grow and yield. Nitrate can vary widely spatially and temporally due to weather conditions, soilcharacteristics and the height of the surrounding water table. Providing an automated process of soilcollection along with a real-time nitrate sensor would contribute to the optimization of nitrate fertilizerapplication. This paper outlines the development of a nitrate sensing process utilizing ion selectiveelectrode technology and an automated soil extraction system. The sample soil requires a simplepretreatment of potassium chloride solution to obtain extractant solution containing the sample soilsmacronutrient ions. This paper contains the laboratory comparisons of extracting solutions, varyingsample soil sizes and methods to quantify amounts of nitrate ions found in soil samples. A range ofdifferent nitrate sensing methods are investigated including: colorimetric and ISE technology. Thecolorimetric method proved to need a very small sample size (magnitude of 50L) as well as havinga high repeatability rate but lacked the speed needed for real-time analysis. The ISE analysis methodproved to require less pretreatment of sample soil and relatively fast, about 30-60 seconds; however, the electrodes robustness is questionable for field measurement. Data obtained pointed to thenitrate ISE holding an advantage over the colorimetric technique in time, the amount of pretreatmentof samples and ease of use. For the purpose of real-time measurement, results indicated using anitrate ISE to be a feasible method.