Wk10_Module10C_GlobalSoils

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School

University of Cincinnati, Main Campus *

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108

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Geography

Date

Oct 30, 2023

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doc

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(Slide #1) Hello Class! In this short module we’ll talk about some different specific soil TYPES around the world. Just like we have discussed CLIMATE REGIONS and VEGETATION REGIONS, there are also patterns of SOIL DISTRIBTUION around the world, which help to determine the kinds of human activity that take place on the landscape. (Slide #2) As you can see in your textbook chapter that you’ve been reading this week, there are a LOT of SOIL CLASSIFICATIONS. They are organized by ORDER and SUBORDER. Soil scientists have CREATED and ORGANIZED these classifications by studying soil HORIZONS and determining distinctive PHYSICAL and CHEMICAL properties. This table from your book shows some of the main SOIL ORDERS: namely what we call the GROUP ONE soils. You notice that ALL the terms for the SOIL ORDERS end in the SUFFIX “S-O-L” or “SOL,” from the Latin “SOLUM” which one of the Latin words meaning “ground” or “Bottom,” and is the same Latin word from which we get “the word “SOLE,” as in the “SOLE” of the FOOT. Each of these GROUP ONE soils is summarized on this table. (Slide #3) The table continues with the GROUP TWO AND GROUP THREE soils. Now your text goes through details of ALL these soil groups, and I’m NOT going to do that. But I AM going to talk about some of the more significant ones. (Slide #4) We’ve seen this sort of map before, a map showing the GLOBAL DISTRIBUTION of some specific FEATURE of PHYSICAL GEOGRAPHY. In this case, we are looking at the GLOBAL DISTRIBUTION of SOIL types. This map indicates the DOMINANT soil order in these areas, and any SPECIFIC location is likely to be somewhat more COMPLEX, affected by certain local VARIABLES. This map includes most of the GROUP ONE soil orders, as well as several important SUBORDERS. (Slide #5) First, let’s look at OXISOLS and ULTISOLS. They are associated with the hot climates of the Equatorial, tropical, and subtropical regions. They

develop over LONG time periods and are very REDDISH from the presence of MINERAL OXIDES. (Slide #6) Next we have ALFISOLS. ALFISOLS are present in a WIDE DISTRIBUTION around the world, at MANY latitudes and across an enormous range of CLIMATE TYPES. There are FOUR important SUBORDERS of ALFISOLS, which are listed here, and which you see included in the global soils map that I just showed. ALFISOLS have a HIGH presence of those important BASE ELEMENTS that we talked about earlier in this week’s material – those BASE NUTRIENTS of calcium, potassium, magnesium, and sodium, which are so important for AGRICULTURE. So ALFISOLS can be very productive and you generally find a lot of agriculture in areas with alfisols. (Slide #7) Next we have SPODOSOLS. They are the soils of the COLD NEEDLELEAF FORESTS, typically in the HIGHER latitudes. CONSEQUENTLY, spodosols are quite ACIDIC. Recall that we talked about how CONIFEROUS needleleaf forests give rise to ACIDIC soil. ALSO, spodosols tend to correspond to areas that were once covered by ICE SHEETS or GLACIERS. So they are the soils of the NORTHERN LATITUDES, the northern BOREAL FOREST. (Slide #8) Next we have ANDISOLS. This is a really INTERESTING soil order! ANDISOLS are associated with the DRAMATIC landscapes of VOLCANIC ACTIVITY. The main PARENT MATERIAL of andisols is VOLCANIC ASH. Andisols can be in a lot of places, anywhere that has VOLCANOS. There is also a lot of CARBON in Andisols. Andisols can be very FERTILE. They can be found in the TROPICS, but also in the HIGHER LATITUDES, again, anywhere that has had relatively recent VOLCANIC activity. In this image you see a PINEAPPLE field in HAWAII – volcanic ANDISOL soil. (Slide #9) MOLLISOLS are an important soil order, the one that is associated with the productive short-grass PRAIRIE grasslands of the American MIDWEST.

MOLLISOLS are a very productive soil order, due to their thick active ORGANIC layer and their HIGH concentration of BASE elements. (Slide #10) Like ALFISOLS, MOLLISOLS are also quite WIDESPREAD over a lot of climates and latitudes. So there are several important SUBORDERS of mollisols, which are listed here. You see slightly different MOLLISOLS from the northern plains to the eastern plains to the western plains at the base of the Rockies to the open agricultural lands of the Mediterranean climate. The different MOLLISOL suborders help to explain the crop distributions in these various areas – from corn to wheat to vegetables and fruits and so on. (Slide #11) FINALLY, we have ARIDISOLS. Aridisols are the DESERT soils, with WEAKLY developed layers or HORIZONS. In ARIDISOLS, the surface layer can often have CALCIUM CARBONATE or some sort of soluble SALT. ARIDISOLS may not SEEM very viable for agriculture, but in fact with IRRIGATION, they can be VERY productive. A LOT of desert areas, both here in the US and across the world, have IRRIGATED ARIDISOLS that produce a wide VARIETY of crops. (Slide #12) OK, so now you should have gained a better sense of the amazing diversity of SOIL CATEGORIES throughout the world. From the volcanic ANDISOLS like we see here, to desert’s ARIDISOLS to the rich MOLLISOLS and ALFISOLS of the midlatitudes to the acidic SPODOSOLS of the boreal forest to the OXISOLS and UDISOLS of the tropics, we’ve covered quite a bit of range. SOIL is the BASIS for human existence. It gives humans the PLATFORM on which they live and grow food. By looking at the diversity of SOIL ORDERS we gain a better appreciation of why human cultures THEMSELVES are so VARIED. So that’s it for this short module! Next we’ll be moving on deeper into the LITHOSPHERE to begin talking about EARTH MATERIALS and LANDFORMS. Thanks for your attention!

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