Soil Basics: Structure


[MUSIC] Now we’re gonna talk about the last
component and that’s soil structure. Soil structure is the arrangement of the
sand, silt and clay particles in a soil. There are actually six types of
soil structure that you can have. The first structure is granular structure. It’s these fine particles,
which are actually stuck together by organic matter, and
fungal hyphae and things like that. Gives you good granular structure. So the more organic matter that you have, the better your granular
structure is going to be. The next type of structure that you have
is something called platy structure. Looks just like a series of plates. The technical term for
it is actually lenticular structure. And what’s interesting about having
platy structure in your soil is that, think about it for a minute. You have a water droplet, water coming
down hitting the top of this plate. It has to move in a horizontal direction,
Right? Falls, hits the next plate, has to
move in another horizontal direction. So when you have lots of
platy structure in your soil, chances are you’re gonna have
a poorly drained soil situation. And actually, you can get platy
structure to form in your soil, by the type of tillage
practice that you do. You do a lot of mobile plowing or
conventional tillage, you’re gonna get the formation
of platy structure. So in the B horizon we actually
have two types of structure. We have what is called subangular blocky
structure,and angular blocky structure. And with subangular blocky structure, the edges of the blocks
are actually rounded off. Versus angular blocky structure
where you have these sharp angles, which occur in the blocky structures. Also in the B horizon, you could have
what is called prismatic structure. And prismatic structure is long
in the vertical direction, sort of short in the horizontal,
it’s got sharp edges. You can also have prisms that are smaller. You can have small prisms,
you can have large prisms. The size of the structural unit
is pretty irrelevant, because you can have all sorts of different sizes
for these different types of structures. The other type of structure
that we have in the B horizon, is something called columnar structure. And columnar structure is not so
common here in Indiana, but we do see it. It’s where you have a lot
of salt in your soil. And what happens is that, that salt
causes the tops of the prisms to disperse and sort of round off and you end up
with what’s called columnar structure. What’s the situation down in the C
horizon, where the parent material is? Actually we do have what is called
structuralist units in the C horizon. And usually that consists of sand or it consists of a massive
type of structure, everything just kind of glued together. So let’s conclude by looking at the soil
structures in a soil monolith or soil profile. Top of the soil profile, the A horizon,
that’s where you find granular structure. In the E horizon, that’s principally
where you’re gonna find platy structure. Down here below the E horizon
going into the B horizon, that’s where you have subangular blocky. In the B horizon itself,
this is prismatic structure. And down below, this is where we
find angular blocky structure. And then, as I mentioned in my discussion,
in the C horizon, there’s no structure. It’s a structureless condition, but we
have a massive condition in the C horizon. [MUSIC]

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