Abstract Mehlich 3 (M3) is a widely used extractant for evaluating plant available phosphorus (P) in soils and may be quantified using colorimetric or inductively coupled plasma (ICP) spectroscopic methods. Analysis by ICP has recently become increasingly popular in soil‐testing labs primarily due to its ability to simultaneously measure multiple elements. Despite the versatility and efficiency of ICP, some laboratories hesitate to use ICP to determine P in M3 extracts because (1) fertilizer recommendations were developed using colorimetric analysis, and (2) differences have been reported between P analyzed colorimetrically and by ICP. This study documented the differences between M3 P measured colorimetrically using a flow injection auto‐analyzer and by ICP (ICP‐P) for approximately 6400 routine soil samples analyzed by the Soil, Water and Forage Analytical Laboratory at Oklahoma State University. Potential factors contributing to the difference in colorimetric P and ICP‐P were also examined using anothe...