A soil profile is a view of the different layers of soil from the side, so it’s easy to separate each one. These layers are also called horizons, and there are four main ones that our text mentions- O, A, B, and C. Page 49 of our text has a good description as well. http://soils.usda.gov/education/resources/lessons/profile/profile.jpg
Each of the horizons have distinct qualities that separate them from the others:
- O- This is made up of the seasoned, dead organic matter known as “leaf litter.” It contains detritivores, and other small insects. The material we collected during the Davidson field trip was the O layer.
- A- This is the topsoil. Combined with the O and E, which isn’t necessary to know, layers it makes up the zone of leaching. Humus is also found in this horizon. Humus is the nutrient-rich soil that is dark brown in color.
- B- This is the subsoil and the zone of accumulation.
- C- This is the parent material, which is made up of weathered, larger rocks. The R horizon lies below the C and is known as bedrock, but it isn’t necessary to know this layer either.
We then went on to make our own ice cream version. First we added cookies, which were the R layer, next was the ice cream, which was the C layer. On top of that we put whipped cream as the B layer and pudding represented the A layer. The O layer was a combination of nuts, chocolate chips, and other toppings. This helped us to visualize what makes up each of the horizons.
We also reviewed a soil triangle; it might be nice to make sure you know how to read one- clay is read on the horizontal, and silt and sand are read on the diagonal.
A review over the qualities of sand, silt, and clay:
Sand- It is the largest of the three and is very permeable, so it doesn’t retain water well. This results in lots of leaching, which causes nutrients to be lost because they are “leached” downwards through the horizons. This causes sand to have poor nutrient retention. On the other hand, it has very good water infiltration (absorption), but poor aeration.
Silt- It is the second largest and retains water and nutrients fairly well. Its aeration and ability to absorb water are fair too.
Clay- It is the smallest of the three, and retains water and nutrients well. However, it has poor water absorption and aeration.
A combination of the three soils makes the “best” type of soil, which is known as loam. Loam exhibits the best qualities of all three particles, which is why it’s so good.
That was about it, so I hope this helps anyone who needed a review of soil!