Comparison of Conventional and Automated Procedures for Nitrogen, Phosphorus, and Potassium Analysis of Plant Material Using a Single Digestion1

Abstract Nitrogen content in 10 plant samples of widely varying concentrations of N, P, and K was measured by a H 2 SO 4 —H 2 O 2 ashing procedure and the AutoAnalyzer system and found comparable to nitrogen content obtained by conventional Kjeldahl analysis. Phosphorus content measured by the AutoAnalyzer system on the same H 2 SO 4 ‐H 2 O 2 ashing was similar to that obtained by dry‐ashing combined with the molybdo‐vanadate procedure. Potassium analyses on the solutions from the two ashing procedures by atomic absorption spectroscopy were comparable. Details are presented for simultaneous N and P analysis by the AutoAnalyzer and for K analysis by atomic absorption on plant material performed on a single H 2 SO 4 ‐H 2 O 2 digest at a rate of 160 samples per week by one technician.