Free Resource: Keys to Soil Taxonomy

Like many archaeologists I’ve worked with, my knowledge of soil taxonomy had largely been a mish-mash. It was a mix of what I remembered from my field school and what I was able to learn from the more experienced hands I’ve worked with over the years. This approach led me to learning “just enough to be dangerous” and likely resulted in exclamations of “what the…” from more than a few Principle Investigators (PIs) reviewing paperwork. I know this because I’ve had the same reaction reviewing forms for projects where I’ve acted as PI. This experience led me to an appreciation of accurate and consistent soil descriptions.

There are many paid and free guides to soil taxonomy and description available. These range from online slide shows to specialty books aimed at archaeologists (a hard to find favorite of mine being this book by Gary Vogel, 2002). However, for a clear, concise, comprehensive, and free resource, the USDA’s Keys to Soil Taxonomy stands out.

USDA Keys to Soil Taxonomy Cover Image (Source:

This 372 page resource provides a comprehensive overview of soil taxonomy with an emphasis on agriculture. Designations for Horizons and Layers (Chapter 18, p. 335) is the chapter I most often reference in the field and while reporting. In the book, the nine (9) master soil horizons (O, L, A, E, B, C, R, M, and W) are discussed in enough detail to describe their identifiable characteristics, and the process(es) that lead to their formation. The thirty-four (34) subordinate distinctions of master soil horizons are also described in the same detail. The conventions for naming soil horizons is also covered. I find this very valuable in decoding information included in geomorphology reports and double-checking the horizon designations included in my reports will make sense to readers.

Since I’ve begun making copies of Designations for Horizons and Layers (Chapter 18) from this resource available to field personnel on Phase II and Phase III CRM projects, I’ve found that soil descriptions are presented in a more accurate and consistent manner. This has realized a significant reduction in the amount of corrections made to field forms while preparing reports, freeing up more time for interpretation and analysis.


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