A Half Century of Changes in Soil Taxonomy

Abstract

Core Ideas This is the first comprehensive documentation of changes to Soil Taxonomy. Changes to the higher taxa in soil taxonomy have been irregular. Four periods during its development had distinctly different trajectories. The Seventh Approximation emerged in 1960, and the first edition of Soil Taxonomy was published in 1975. Through the years, as intended in its original architecture, revisions have been made at all levels in the system. This has resulted in the addition of two new orders and a multitude of classes at other categorical levels. Four distinct and contrasting periods can be identified and described with regard to the magnitude of changes in taxa at various levels. The most dramatic changes occurred between the mid‐1980s and publication of the second edition of Soil Taxonomy, when numerous international committees that had been charged with investigating particular taxonomic questions were completing and publishing their final reports and findings. Not surprisingly, most of these revisions resulted in the addition of taxonomic classes, although occasionally (especially in the 1998 Keys to Soil Taxonomy) there were notable reductions in the number of classes within certain orders. This review documents the nature and magnitude of changes that have occurred in the development of the US soil taxonomy during its 54‐yr history to provide a context within which to better understand how the current state of our soil classification system has evolved.