Soil Forming Factors

 So I have focused a lot of my time discussing many management strategies that help promote soil health, but I realized today that in order to make sound management decisions you first need to know what your working with. What I mean by this is that not all soils are the same, soils are often generalized but they are very much different from each other. So what makes soils different? This is where the famous ClORPT saying comes into play . If you have ever watched a soil talk or researched the basics of soil probably one of the first things you learned about was ClORPT. If you have ever watched a soil talk or researched the basics of soil, probably one of the first things you learned about was the 5 soil forming factors or what we at NDSU say ClORPT.

ClORPT strands for...

Cl- Climate

O- Organisms

R-Relief

P- Parent Material

T- Time

I like to start with the P component or the Parent Material, because soil has to be made and it has to come from another material through weathering processes. Just like us soils have parents, called parent materials. These are the underlying materials that the soil was formed from after thousands to millions of years of weathering. Some might form from sandstone giving the soils sandy characteristics or from limestone giving the soils excess calcium carbonate. All soils take on characteristics from their parents but other factors help to influence these "traits" and make them individually unique from their parents and siblings.

The Cl or the Climate component is a real driving factor in molding these traits and developing them into stable soils.  Below is a figure showing major climatic regions in the world.

 

Each of these regions have unique characteristic's help drive soil characteristics. For example in areas that are humid and see significant amounts of precipitation we might see extremely leached soils. In areas with an arid climate or semi-arid climate we might see soils that have very little profile development showing only one or two horizons. You'd also see little organic matter or the "dark stuff" due to little vegetation on the soil, because in these areas there is not enough precipitation to support active plant growth.  These two contrasting examples should really bring home how climate influences soil formation.

Leached Soil

Arid-Semiarid Soil

 These two figures here are two soils that represent the two examples I provided above. The one on the left shows an extremely leached soil due to plentiful amounts of precipitation. The white area is the defining factor that we look for when determining if the soil is heavily leached. We call this the E horizon. The figure on the right shows an example of a soil that you would most likely see in an arid or semi-arid area. This is an example of a Aridisol. An Aridisol is a soil order ( this is a way of classifying soils, which I may discuss in a later post) that represents little profile development and little organic matter that dominate deserts. Much like we discussed above.


The O component or Organisms is another factor that may be harder to conceptualize. We know that soils are in fact living, they have millions of little organisms living in them that help make many processes function. It's said that in one tablespoon of soil there is more organisms than there are people on Earth. Now if you look at a soil profile down to 60 inches, imagine how many living organisms there are! So with that big of an influence it's hard not to say their making an impact. These organisms help to bind soil aggregates and really start to make soil structures. They help with many processes that involve plants, that help to provide nutrients back into the soil. All of these processes really start to determine soils and their functions. Below is a link to a video to on soils biology, it's a lengthy video (25 minutes) but if your interested in learning more about this aspect of soil health its worth a view.

http://www.bing.com/videos/search?q=soil+biology&qs=n&form=QBVR&pq=soil+biology&sc=8-8&sp=-1&sk=#view=detail&mid=67CE654F7E75399564B167CE654F7E75399564B1

 The R component or Relief component is another factor that defines how a soil forms. The best way to understand this component is to use a hill scenario. Say we have a hill and we take a soil cores from the top of the hill, the side/middle of the hill and one at the bottom of the hill. What would we expect to see? Well we know that after a rainfall event all the water at the top of the hill will most likely end up at the bottom of the hill due to gravitational movement and the path of least resistance so how does that effects soil formation. Well after many years of this type of event we would start to see erosion processes take place on the top and side of the hill, meaning that we would see a shorter or thinner A horizon and less organic matter than the bottom core. Similar to what we discussed in the climate section we would see more leaching going on in the bottom core due to more active water entering the soil system.

One of the most important factors is time! Just like Rome wasn't built in a day, soil takes thousands to millions of years to form. In order for all the of the processes discussed above to effectively influence the soil it needs a plentiful amount of time for these processes to take shape.