Why do we classify soil? Classifying has always been important in a scientists life. We mainly do it to easily understand the relationship between soils and the factors responsible for their character. We organize our knowledge about soil with soil surveys, and we use the identifications of soils for practical purposes. 

I have been wondering what the difference between the expressions “soil Taxonomy” and “soil Classification” is. What I believe now after looking it up it seems like soil classification includes the soil taxonomy. And the soil taxonomy is basically only about the relationships between soil. Classifications are there so that the humans can classify the soil by their purposes. Soil classes in soil taxonomy are defined by properties that can be measured quantitatively. Some properties used to classify soils are soil depth, moisture, temperature, texture, structure, cation exchange capacity, base saturation, clay mineralogy, organic matter content and salt content.

The classification system is divided in 6 groups: Order (there are 12 soil orders), Suborders, Great groups, Subgroups, Family, and Series. Looking at the picture we can for example see how many more series there are than orders.

So how do people name soil? The basic components of soil are sand, silt, clay and humus. When they are in perfect condition it’s called loam. The 12 soil orders are names of which combinations the soil has of sand loam and clay. Loam is the ideal soil type and is; if you could analyze one square foot of loam soil, you’d find it was composed of 10% clay, 20% silt, 20% sand and 50% air space!

These are the three very basic types of soil: Sandy Soils are loose. They tend to be low in nutrients and more acidic than loams and clays. Loamy Soils is somewhere between sand and clay soils.  They are composed of many different sized soil particles, and are rich in organic matter. Loamy soils is very good for growing most plants. Clay Soils consist of very small, tightly packed particles.  They tend to be dense and hard to work. Clays are usually rich in nutrients, and have a high water-holding capacity.

I read about two tests that one can do by themselves to determine what soil type they have, without testing in a lab. It was just pretty funny to read so I’m writing it down so you can read. 

The Feel Test: What you do is that you basically pick up some soil and rub it back and forth between your fingers. If it is a clay soil it will feel very slick and smooth. A sandy soil will be gritty and will not feel stick together so well. And a loamy soil will feel like flour, and will stick together easily (but not as easy as clay)

The Squeeze test: Here you can pick up a hand full of soil in your hand and squeeze it. The soil has to be a little moistly. It is really easy and of course the sandy soil is going to feel more “sandy” than how a clay soil feels. the loam soil will be dark brown and will feel spongy in texture. 

I thought these tests were pretty lame and of course it can be a way of knowing what kind of soil you have in your own yard, but if you’re a scientist you would probably want to be a little bit more exact in your “guess” of soil type. 
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One Response to Soils

  1. amalderm says:

    I also believe that soil classification is very important. My favorite reason for classifying soil is to identify it for practical reasons. It is important to know which type of soil you are building a structure on. You would like to build on a soil that is going to withstand the weathering and erosion of time as well as the shrinking and swelling that soil is subject to throughout the year. As for the squeeze test, I believe that you would have to know a great deal about soil to tell what type it is from just rubbing it in your hand. I guess a soil scientist could figure it out though.

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