Friday, October 3, 2014

I'll take an order of the Andisol, please.

To understand and characterize soils better United States soil taxonomists (those who define and name) came up with a a system that divides soils by various distinct and unique features. Soils in their broadest sense are grouped into divisions called orders. There are twelve soil orders in the USDA system of naming (yes, different countries and organizations have different ways of naming soils, just to make life more interesting!). In alphabetical order they are as follows:

Alfisols - Andisols - Aridisols - Entisols - Gelisols -
 Histosols - Inceptisols - Mollisols - Oxisols -Ultisols -Vertisols

Twelve Orders of Soil Taxonomy poster
Photo credit USDA NRCS - http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/edu/?cid=nrcs142p2_053588. 
This poster can be downloaded or purchased from this link. 


Since the Japanese volcano, Mt. Ontake, erupted just recently, I thought it would be appropriate to begin with andisols! Soil orders are grouped by their major diagnostic horizons (layers within the soil that have specific characteristics), minerology (minerals present in the soil), soil moisture and temperature regimes. Andisols are unique in that they typically form from volcanic materials (ash or tephra, pumice, lava, and cinders) which have a very different type of mineralogy than other soils types. I'll forgo a long-winded discussion about this, but you may have seen volcanic glass (e.g. obsidian) and noticed how it doesn't look like a typical rock. As this glassy material weathers (breaks down) it creates a soil - an Andisol. The rocks int the volcanic explosions (tephra) also contribute to these soils.

Soil with volanic deposits that many many years from now could turn into an Andisol. 
Photo Credit: D. Beaudette USDA-NRCS. 

Obsidian - cooled volcanic material that appears "glassy."

The complex mineralogy (glassy and rocky materials) in these soils allow for high fertility (lots of nutrients for plants). However, in cooler climates, many of the andisols are on steep slopes this high fertility is limited to production of forests. For anyone who has visited the Pacific Northwest's Cascade Mountains, you have seen these soils in action.  Some of the great trees in these areas can attribute their size these soils. In warmer climates these soils are used for agriculture. However, a draw back of this soil is it's capacity to "fix" phosphorus making it unavailable to plants. Additions of more phosphorus fertilizer often do not help either. This would be similar to buying flour at the store, bringing it home, and placing it on a high shelf in your kitchen, and then throwing away the step-stool you used to place it there. You have flour to make cookies, but cannot access it (lets just pretend you have no other chairs and cannot climb on the counters to get at it). You go to the store and buy more flour, come home and place it on the high shelf again removing the step stool once again. Continue this process over and over and you will begin to understand this issue with phosphorus fertilization in andisols. Some creative solutions have been approached, such as soaking potato tubers in a phosphate solution prior to planting so that they have access to phosphorus.

Because andisols occur in many different climates the resulting soils can look very different. Below is the distribution in the United States and a few examples.



                   
http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447032&topicorder=12&maxto=16





                                                     
From top to bottom - Andisols found in Idaho, New Zealand, and Iceland. 
http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447032&topicorder=12&maxto=16
http://www.cals.uidaho.edu/soilorders/andisols_02.htm

Interested in the major soil order near you? 
Post the location in the comments and I'll address
it the next time I blog on soil orders!  

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