A Rapid In‐Field Soil Extraction Procedure to Measure Plant‐Available Soil P and K Using an ISFET Multi‐Sensor

ABSTRACT Background Knowledge of plant‐available soil nutrients is important for determining fertilizer requirements. Collecting this data rapidly and directly in the field could be beneficial for improving nutrient utilization efficiency. Aim Evaluation of the comparability of plant‐available soil phosphorus (P pa ) and potassium (K pa ) measurements with a newly developed rapid soil extraction procedure based on a nutrient measurement system using an ISFET (ion‐sensitive field‐effect transistor) multi‐sensor module (“FieldLab”) under quasi‐realistic field conditions with the results of a lab‐based soil analysis. Methods Following calibration of the FieldLab measurement system with the calcium‐acetate‐lactate (CAL) extraction method commonly used in Germany, the ability of the ISFET multi‐sensor module to measure P pa and K pa under in‐field conditions was investigated. For this purpose, a set of dried soil samples from 15 fields in northwest Germany was used, representing very different soil nutrient levels as well as various soil texture and soil organic matter contents. The soils were assessed using the standard lab procedure or the rapid FieldLab extraction, followed by lab measurements or nutrient quantification with the ISFET multi‐sensor, respectively. Results Soil extraction using the FieldLab procedure showed a high correlation with the lab results ( R 2 0.97 and 0.92 for P pa and K pa , respectively). The combination of the rapid soil extraction followed by the ISFET measurement revealed significant correlations with the laboratory data ( R 2 0.80 and 0.79 for P pa and K pa , respectively). Conclusion The developed ISFET‐based FieldLab procedure is an innovative and reliable approach for rapid in‐field nutrient analysis of P pa and K pa , and it has the potential to enable the timely calculation of P and K fertilizer recommendations.