What's in a soil name?

By Thembi Borras

You may be familiar with local forest soil names such as Bearwallow, Kibesillah, Ornbaun and/or Zeni. Soil names, also referred to as series names, are commonly used to connect to useful information such as soil descriptions that include potential annual production, permeability, erodability, depth and color, which may inform management decisions. Series names are easy to remember, pronounce and recognize. However, dig a little deeper and you learn behind each series name is a soil order, suborder, great group, subgroup and family, which when combined form a long and complex taxonomic classification that is brimming with information, such as particle size, temperature regime, moisture regime, characteristic soil horizons and origin.

For example, the Zeni series is a fine-loamy, mixed, isomesic Ultic Haplustalf. From this, I can glean that it is in the Alfisol order, an order that in part may be characterized by clay from upper horizons leaching to lower horizons where the clay accumulates in films. The moisture regime is ustic, which means moisture is limited, but is present at a time when conditions are suitable for plant growth. The temperature regime, is isomesic, which means the annual soil temperature is between 46 degrees F and 59 degrees F, measured at approximately 20" below the surface. Finally, I can glean something about the particle size; fine-loamy may be translated to clay loam. A loam is a mixture of sand, silt and clay that exhibits the properties of each in approximately equal proportions.

There are twelve orders of soils, Entisols are young soils with little or no morphological development. Inceptisols, Alfisols, and Ultisols are in ascending order in the development continuum, all of which locally can support timber. Mollisols are soils with a dark horizon rich in organic matter and can often be found supporting grasslands. Aridisols are desert soils. Vertisols are truly amazing as they invert themselves through the shrinking and swelling of the clays contained within them in response to soil moisture. Oxisols are highly weathered soils in subtropical or tropical environments; you can experience Oxisols in Florida. Andisols are soils formed in volcanic ash and are prevalent in the Andes. Spodosols are acid forest soils with a subsurface accumulation of metal-humus complexes. In our area, the pygmy forest grows from a Spodosol. Histosols are organic soils, peats are an example. Finally Gelisols are soils with a permafrost within 2 meters of the surface.

A portion of this production was gleaned from Keys to Soil Taxonomy published by the USDA and the Natural Resources Conservation Service, The Nature and Properties of Soils by Nyle Brady, the University of Idaho Soil Science Division website at http://soils.ag.uidaho.edu/soilorders/orders.htm and The Soil Survey Report for the western part of Mendocino County, available at http://www.ca.nrcs.usda.gov/mlra02/wmendo.html.