Assessment of hand held ion selective electrode technology for direct measurement of soil chemical properties

Access to real-time information on soil chemistry would assist farmers in making decisions about nutrient management. Hand held Ion Selective Electrodes (ISE) are commercially available for testing pH, sodium (Na), potassium (K), and nitrate-nitrogen (NO3-N). To date, there has been some success in adapting hand held ISE devices for testing plant sap nutrient levels. The objective of our study was to determine if these devices could be used to directly measure ion content in soils. Two different soils, a Quincy sand and a Warden silt loam, made into slurries by adding water to achieve 50, 40, 30, 27.5, 25, 22.5, 20, 17.5, or 15% soil water content by volume. The slurries were directly applied to the hand held ISE (Cardy meter) five times for each soil texture and moisture content. In addition, soil solution was also sorbed onto absorbent paper and the paper placed directly on the Cardy meter surface. The results were compared to soil NO3-N, K, Na. and pH determined by conventional methods. The hand held soil pH meter worked exceptionally well on soil slurries and did not fail in making measurements even after over 500 readings, For K, the Cardy meter readings were consistent with conventional measurements in both soils between 20-25% water content using direct measurement of a soil slurry. For Na, the Cardy meter worked reliably between 20-30% soil water content on the Warden silt loam, but did not perform well on the Quincy sand. However, Cardy meter values for soil NO3-N greatly exceeded conventional measurements and was not suitable for use regardless of soil moisture content.