Physical Properties Of Soil | Texture, Structure, Porosity, Bulk Density
Summary
TLDRIn this educational video, T Simmons from Agriculture Explained explores the physical properties of soil, focusing on texture, structure, porosity, and bulk density. Simmons explains how soil texture, derived from parent rock, influences soil behavior and crop growth, with clay, silt, and sand particles playing crucial roles. The video further delves into soil structure types, from single grains to massive soils, emphasizing the importance of balanced structure for gas exchange, water infiltration, and root growth. Porosity, or the air and water space in soil, is highlighted as essential for plant and microbial respiration, with an ideal 50% pore space recommended. Lastly, bulk density, which affects root growth, varies by soil texture, with methods to measure it provided for both home and lab settings.
Takeaways
- 🌱 The video discusses the physical properties of soil, focusing on its texture, structure, porosity, and bulk density.
- 📊 Soil texture is crucial as it influences soil behavior and crop growth, originating from parent rock composition and age.
- 🔍 There are three primary soil particles: clay (<0.002 mm), silt (0.002 to 0.05 mm), and sand (0.05 to 2 mm), each with different properties.
- 💧 Clay particles have a negative charge, attracting positively charged nutrients, while silt and sand do not contribute to cation exchange capacity.
- 🌤️ Soil structure refers to how particles clump together, affecting characteristics like water flow, gas exchange, and root penetration.
- 🏖️ Single grain is typical for sandy soils, while blocky, platy, and prismatic structures are indicative of more compacted soils.
- 💨 Porosity, or the amount of pore space in soil, is vital for air and water movement, with an ideal goal of around 50%.
- 📐 Bulk density measures the mass of soil in a given volume, with ideal densities varying based on soil texture, affecting root growth.
- 🧪 A simple method to estimate bulk density at home involves using a cylinder, water, and measuring the displacement to calculate density.
- 🌱 The video is part of a series by T Simmons from Agriculture Explained, aiming to educate on soil science for better agricultural practices.
Q & A
What are the main four physical properties of soil discussed in the video?
-The main four physical properties of soil discussed in the video are texture, structure, porosity, and bulk density.
What is soil texture and why is it important?
-Soil texture refers to the individual grains of soil, which are classified as clay, silt, and sand. It is important because it determines how soil behaves under different circumstances and the types of crops that can grow on it.
How does the parent rock affect soil texture?
-The parent rock affects soil texture by determining the amount of clay, silt, and sand in the soil, as well as its age.
What is the significance of the charge on clay particles in soil?
-Clay particles have a negative charge which attracts positively charged nutrients, contributing to the soil's cation exchange capacity.
How can soil texture be described using the soil texture triangle?
-Soil texture can be described using the soil texture triangle by determining the percentage of clay, silt, and sand in the soil and plotting these on the triangle to find the corresponding soil type.
What are the different types of soil structure and which one is considered the best?
-The different types of soil structure include single grains, granular, blocky, platy, prismatic, and massive. Granular structure is considered the best as it provides a good balance between compaction and aeration.
Why is soil porosity important for plant growth?
-Soil porosity is important for plant growth because it affects the amount of air and water that can flow into the soil, which is essential for gas exchange, water infiltration, and root exploration.
What is bulk density and how does it relate to soil structure?
-Bulk density is the mass of soil per unit volume and it relates to soil structure by indicating how compact the soil is. Ideal bulk density varies with soil texture and affects root growth and soil function.
How can you measure bulk density at home without scientific equipment?
-You can measure bulk density at home by using two measuring jugs, one filled with water to measure the volume displaced by the soil, and the other to weigh the soil. The bulk density is then calculated by dividing the mass of the soil by the volume it displaces.
What are the ideal bulk densities for different soil textures?
-The ideal bulk density varies with soil texture: for sandy soils, it's less than 1.4 g/cm³; for loamy soils, it's 1.6 g/cm³; and for clay soils, it's less than 1.1 g/cm³.
Outlines
🌱 Understanding Soil Texture
The first paragraph introduces the topic of soil texture, emphasizing its importance for agricultural production. It explains that soil texture is derived from parent rock and is categorized into three main particle sizes: clay (less than 0.002 mm), silt (0.002 to 0.05 mm), and sand (0.05 to 2 mm). The paragraph also touches on the concept of soil charge, particularly the negative charge of clay particles that can attract positively charged nutrients. The video aims to educate viewers on how to identify and understand the texture of their soil, which is crucial for crop growth and soil management.
🌿 Soil Structure and Its Impact on Plant Growth
The second paragraph delves into soil structure, which refers to how soil particles clump together. It outlines different types of soil structures, including single grains, granular, blocky, platy, prismatic, and massive. Each structure type has implications for soil's ability to retain air, water, and support root growth. The paragraph highlights the importance of an optimal soil structure for gas exchange, water infiltration, and root exploration, which are vital for plant health. It also discusses the challenges posed by compacted soils, such as reduced water and air movement, which can limit plant growth.
💧 Measuring Soil Porosity and Bulk Density
The third paragraph focuses on soil porosity, which is the amount of empty space in the soil, and bulk density, which is the mass of soil per unit volume. It explains the significance of these properties for plant growth, as they affect water and air availability in the soil. The paragraph provides a method for measuring bulk density at home using a simple water displacement technique. This method involves weighing soil, displacing water with it, and calculating the bulk density based on the volume of water displaced. The ideal bulk density varies depending on soil texture, with different thresholds for root growth and soil compaction. The paragraph concludes with a practical example of how to perform this measurement, emphasizing its relevance for assessing soil health.
Mindmap
Keywords
💡Soil Texture
💡Clay
💡Silt
💡Sand
💡Soil Structure
💡Pore Space
💡Bulk Density
💡Vertisols
💡Cation Exchange Capacity (CEC)
💡Compaction
💡Agricultural Production
Highlights
Soil texture is crucial for understanding soil behavior and crop growth.
Soil texture originates from parent rock, affecting clay, silt, and sand composition.
Clay particles are the smallest and have a negative charge, which is important for nutrient attraction.
Silt particles are larger than clay and do not contribute to cation exchange capacity.
Sand particles are the largest and, like silt, do not have any charge.
Soil texture can be described as clayey, sandy clay, silty clay, or sandy loam, among others.
A soil texture triangle can be used to determine the soil's composition based on percentages of clay, silt, and sand.
Soil structure, such as single grains, granules, and blocky forms, affects erosion, water flow, and root growth.
Granular soil structure is ideal as it provides a balance between compaction and erosion resistance.
Compacted soils, like platey and prismatic structures, limit gas and water exchange, hindering plant growth.
Pore space or void space in soil is essential for air and water flow, affecting plant and microbial respiration.
Ideal pore space in soil should aim for 50% to ensure optimal gas exchange and water infiltration.
Bulk density is a measure of soil mass per volume and varies with soil texture, affecting root growth.
A simple method to measure bulk density at home involves using a cylinder and water displacement.
Different soil textures have different ideal bulk densities, with clay soils requiring the lowest.
Understanding soil properties is vital for agricultural production and soil health management.
Transcripts
if I asked you to describe your soil
what would you try and describe it as if
you don't know what you'd say this is
perfect for you today in this video
we'll be talking about the physical
properties of soil what are the main
four uh and what we can basically learn
from looking at these characteristics of
our soul in terms of what it means for
our production my name is T Simmons I
run this channel agriculture explained I
also run agol which is a regenerative
agriculture Consulting business I make
these videos for free just to share um
information about s science and help
grows um is completely for free so so if
you like the content make sure to
subscribe and it would do me a big favor
if you could also share this with
someone that you think would enjoy learn
about s science um or some of the other
things we have on the channel cool all
right let's get into it so texture
texture is so important for us all
because it determines so many things in
terms of how it behaves and how it acts
under different circumstances and the
crops that can grow on it now originally
all soil texture comes from its parent
rock depending on the rock that the soil
formed from will determine the amount of
clay Sil and sand as well as its age
we'll have a whole another video in the
future uh talking about pent rock
material and how it contributes to so
characteristics but starting off there's
texture now texture if you think of it
if you reached down to some soil and you
pulled out um a bit of soil and you felt
and you and you feel the individual
grains texture just describes the
individual grains of soil so the
individual soil um
particles and there's three topes
there's clay clay is super small .2 m in
size or in diameter uh this is our
smallest Clay is also quite special
because it has negatively charged SS on
on the clay most Clays do um which
attracts nutrition effectively or
positively charged nutrition could cat
IR so CL small so we have silt silt a
bit larger it's
from2
2.02 m millim in diameter and then we
have sand which is quite large um so
Sand's quite large it's from 02 to 2 m
and then if you get larger than 2 Ms
it's it's classified as um
gravel now sand and silk don't have any
charge and so they do not contribute to
our cattin exchange capacity which is
what I was talking about with the um the
positively charged nutrition we got a
whole another video on chemical
properties of soil so you can check that
out on the channel as well effectively
they are three soil textures but they
but they are our three soil particles
that make up all all of our soils so one
really good way we can um describe our
soils and our soil texture
is basically the combination of these
words as well as um l so L is basically
equal mix of all three but effectively
we have clayy soil we have Sandy clay
soil Sandy clay lomy soil uh sandy lomy
soil so that's how that's what we can
use to describe the texture so we have
Clay um silty Sandy and LOM this
triangle can help us determine which of
those is our soil so to read this
triangle is quite confusing but
effectively if you can see the arrows on
my diagram they point a particular way
say you have a soil with uh 50% clay you
would go on our clay side 50% now clay
reads AC Crossways so it would go 50%
and then read across which means it
could be either so if we if we knew it
was 50% clay um it could either be a
Sandy clay clay or Sil clay so if we
know it was for example
50% or 40% sand sand reads up on an
angle like that so this soil would be a
Sandy clay it also mean that we have 10%
silk because if we have 50% clay 40%
sand 10% silk that equals 100 and so
we're
happy likewise if you had say 40% sand
which raids up this way you had
say
20% clay so you're about here R across
sand going up You' be a Sandy loone and
then 50% or whatever the remaining per
clay and whatever the remaining per silt
is so that's how you read this so this
is super important for determining a lot
of our other um so characteristics CU
each of these will behave differently in
and the amount of these particles in our
s will determine how our soul behaves so
for example vertisols which are very
high in clay so 35% clay they have a
shrink swell action so the soil cracks
up a lot um Clays tend to disperse quite
easily which means you can get surface
cealing all these things are determined
by our texture from texture we have
structure structure is how these soil
particles Clump together which also
determines a whole range of different
characteristics of that so so first we
have single grains which is just
individual bits think of the Sandy Beach
you can actually see individual bits of
sand that is the first typ of structure
uh single grains very typical sand very
Sandy soils next we have granula granula
is about um half a cm in size this is
actually probably the best um structure
you can get it's nice granulated soil
it's not too compact it's not too light
means that we're not going to be able to
erode this away easy with a single grain
there's a big risk of erosion because
none this is held together and so it can
be you know washed away by water or
Blown Away by wind grula is good it's a
bit of clumping bit of aggregation to
hold it all together uh it's not going
to prevent water flow gas exchange um or
rot moving throughout the soil this is
what we need to try and Achieve then we
have blocky this is
um slightly more compact compacted soil
but it's a bit more on the granul side
so there are limitations but it's not
too bad typically blocky soil is between
uh 1.5 to 5
cm next we have platey soil plate is
very typical of compacted soils and
basically you form these plates on the
soil uh this is very bad for gas
exchange and water exchange as well as
roots trying to explore the profile
because if you think about it if you
have water heat here it's not going to
be able to se uh seep down into the soil
it has to continue along the plate until
it finds opening and then flows down
this is very bad for uh water
infiltration which is very important for
plant
growth next we have Prismatic Prismatic
is almost a larger blocky type structure
they're just very long blocky Aggregates
basically quite long um not very good
finally we have massive soils there is
no structure it's all clumped together
very bad for um trying to do anything
with so all of these determine the
amount of gas that flow into our soil
which is very important for our plants
to breathe and our microbes to breathe
as well as water that flows into our
soil and a roots to explore so typically
you want a nice amount of um space in
our soil for all of that having massive
platey and Prismatic soils is going to
prevent that and this this is a sign of
compaction which is very typical of clay
soils see it flows
across however single grain is very
typical of Sandy soils so we don't want
to be on either end we want to be in the
middle here cuz single grains can either
compress really easily and so then you
get surface ceiling which is typical of
clay or in C soils actually doesn't stop
the water so it go straight through and
then washes out we don't keep any of it
now all of this flows on to the next one
parity parity is the amount of um air
space or what's called pore space or
void space in our soil so this is
everything other than the mineral
component of our soil which is the soil
particle component that's oranic matter
component so this is basically all the
empty space if we took all the water out
so you can see here we have a
effectively a soil that has maybe 50%
pore space this is really good because
we can get air to flow in we get water
to flow in it's going to have really
good water infiltration rates roots are
going to be able to move all the way
through this profile whereas if we have
a profile like this which might only be
20% poor space water's not going to be
able to get in and what does it's
actually not that much A lot of it's
going to flow off Our Roots can't
explore that much it's going to be quite
Limited in what we can do so we're going
to want to try and aim for 50% P space
to ensure that we get all those benefits
like gas exchange and water water
flow finally we have bulk density bulk
density is the amount of mass of soil in
a particular volume so it's a it's the
density of the soil and we can use our
bulk density to describe almost our
paracity the units of bulk density can
either be G per CM squ or it could be
Meg per M squ or tons per me squ all the
same so if you have a
1.4 G per CM squ that's going to equal
the same
meag and tons it's all the same now the
ideal bulk density varies with our s
texture so for a s the ideal bulk
density is
1.6 and Roots start to stop um
effectively growing or they start to
struggle in about 1.8 whereas in a loan
it's the ideal is less than 1.4 and
Roots start to stop at 1.8 again and in
really clay so soils it's ideal to have
a very low
um bulk density less than
1.1 and Roots start to stop growing at
1.47 so there's a really scientific way
we can measure Bo density um and there's
also not and that way is basically get a
cylinder you smack it into the ground
there a couple calculations on it so if
we're at home or on the farm and you
just want to get a simple roughly right
calculation of the bulk density and
there will be errors in it but if we
want to get it roughly what we can do is
get two measuring jugs fill one up with
say 100 m of water and what we're going
to do is going to try and get some
undisturbed soil so if you put your
shovel in uh get a bit carefully move
that out you don't really want to break
it up because that's going to disturb
the structure
paracity of the soil what you're going
to do is you're going to first weigh The
Jug tear it add the soil into it so we
can find out what the actual mass of the
soil is that's what we're trying to get
we're trying to get the mass so if you
get the underbed soil put into The Jug
way that and then we're going to get our
other jug with the water in it about 100
about 100 m of water add that in and
then what we're going to do is we're
going to measure that water rise so this
is what it's going to look like so we
have uh the soil here originally the
water level was at 100 but it's
increased to
173 now before we weighed the soil it
weighed about 98 G now the water level
increased to
173 which means that that the soil has
displaced about 73 CM s of water now
this is very important you want to make
sure that the soil is sitting on the
bottom otherwise it's not going to quite
work you want it to be sitting on the
bottom so that it's displacing its
volume but effectively this volume here
the water that goes up is going to be
equal roughly equal to the volume of
this soil then to work out a bulk
density we're going to get the weight
put it over our volume or go
weight divid by volume to get our bu
density and for this example it's
1.34 and say for example it's a Loney so
that's going to be pretty good otherwise
you can do it in the lab and it's a bit
more
complicated awesome well that's it for
the chemical properties of our soil at
least the four major properties if you
enjoyed this make sure to share with a
friend uh and to subscribe to the
channel awesome thanks for watching my
name is steal cheese
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