In a previous study (Kim et al., 2007), we established the ability
of ISEs and Kelowna extractant (pH = 4.0) to simultaneously quantify
NO3–N, P and K ions in a set of 37 soils. We developed methods
(baseline correction and two-point normalization) that standardized
ISE response and allowed application of a single calibration
equation across multiple ISEs fabricated simultaneously. A test
stand with an array of ISEs was constructed and used to analyze
soil extracts obtained through a standard Kelowna-based extraction
process in the laboratory.