Bulk Density
Summary
TLDRToday's lesson delves into the concept of bulk density and its impact on soil health. Bulk density, a key indicator of soil health, affects water infiltration, root penetration, and nutrient availability. The tutorial compares bulk density to particle density, explaining that bulk density includes both soil solids and pore spaces. The video guides viewers through calculating bulk density and porosity, illustrating how increased bulk density correlates with decreased porosity. It concludes with the effects of soil compaction on porosity, emphasizing the importance of proper soil management to maintain healthy soil.
Takeaways
- π± Bulk density is a key indicator of soil health, affecting water infiltration, root growth, and nutrient availability.
- π§ As bulk density increases, it becomes more difficult for microorganisms to break down organic matter, impacting soil fertility.
- π The average bulk density of soil is about 1.3 grams per cubic centimeter, including both solids and pore spaces.
- π Particle density, which excludes pore spaces, is typically around 2.6 grams per cubic centimeter and is a constant value.
- π Porosity can be calculated using the formula: percent porosity = (100 * (particle density - bulk density)) / particle density.
- πΎ Soil texture, such as silt loam, can be estimated based on bulk density readings, with different ranges indicating different textures.
- π Soil compaction, often caused by heavy equipment use or poor soil management, increases bulk density and decreases porosity.
- π± Compaction reduces the pore space available for water and nutrients, which can negatively impact plant growth and soil health.
- π‘οΈ The depth in the soil profile affects bulk density, with deeper layers typically having higher bulk density and lower water capacity.
- π± Maintaining proper soil porosity is crucial for optimal water infiltration, nutrient availability, and root development.
Q & A
What is bulk density and why is it important in soil health?
-Bulk density is a measure of the mass of dry soil per unit volume, including both the solid particles and the pore spaces. It is important in soil health because it affects infiltration, root growth, water capacity, nutrient availability, and the activity of microorganisms within the soil.
How does bulk density affect water infiltration and root growth?
-Higher bulk density reduces water infiltration as it decreases the pore spaces where water can enter. It also limits root growth because roots require these pore spaces to penetrate and access water and nutrients.
What is the average bulk density of soil, and how does it compare to particle density?
-The average bulk density of soil is about 1.3 grams per cubic centimeter, which includes both solids and pore spaces. Particle density, which only considers the solid particles, is around 2.6 grams per cubic centimeter.
How is the bulk density of soil measured?
-Bulk density is measured by taking a sample of soil, drying it to remove all moisture, and then weighing it. The mass is then divided by the volume of the soil sample to obtain the bulk density in grams per cubic centimeter.
What is the relationship between bulk density and soil texture?
-Soil texture can be inferred from bulk density. For example, a bulk density of 1.4 is typical for clay, while a density of 1.75 is more indicative of sandy loam. Soils with higher bulk density tend to be more compact and have less pore space.
How does porosity relate to bulk density?
-Porosity is inversely related to bulk density. As bulk density increases, porosity decreases because the soil becomes more compact with less space for water and air.
What is the formula for calculating porosity based on bulk density and particle density?
-The formula for calculating porosity is: Percent Porosity = (100 * (Particle Density - Bulk Density)) / Particle Density.
How does soil compaction affect porosity?
-Soil compaction increases bulk density, which in turn decreases porosity. This is because the soil particles are pressed closer together, reducing the space available for water, air, and root growth.
What is the impact of a bulk density of 1.85 grams per cubic centimeter on soil porosity?
-A bulk density of 1.85 grams per cubic centimeter results in a porosity of approximately 30.18%, indicating a soil that is less porous and more compact, likely a sandy soil.
How does soil management practices affect bulk density and porosity?
-Poor soil management practices, such as frequent driving of heavy equipment over wet soil, excessive cultivation, or reduction in organic matter, can lead to increased bulk density and decreased porosity, negatively impacting soil health.
Outlines
π± Introduction to Bulk Density and Soil Health
The first paragraph introduces the concept of bulk density in relation to soil health. It explains that bulk density is an indicator of soil compaction and its importance in infiltration, root growth, water capacity, and nutrient availability. The paragraph also distinguishes between bulk density and particle density, providing a calculation example where 1 cubic centimeter of soil with an average weight of 1.3 grams has a bulk density of 1.32 grams per cubic centimeter. The impact of bulk density on microorganisms is also discussed, highlighting how increased bulk density can hinder their activity.
π§ Calculating Porosity and Its Impact on Soil Texture
The second paragraph delves into the calculation of porosity and its relationship with bulk density. It uses a formula where porosity is calculated as the percentage of bulk density subtracted from particle density and then multiplied by 100. An example is given where a soil with a bulk density of 1.5 has a porosity of 43.39%, indicating a clay soil texture. The paragraph also discusses how increased bulk density can lead to decreased porosity, affecting soil's ability to hold water and nutrients. The impact of soil compaction on porosity is also explored, showing how changes in bulk density due to management practices can significantly alter soil texture and its properties.
π Summary of Porosity and Bulk Density Relationships
The third paragraph summarizes the key learnings about porosity and bulk density. It emphasizes the inverse relationship between the two, where an increase in bulk density leads to a decrease in porosity. The paragraph also discusses the consequences of poor soil management practices, such as compaction from heavy equipment, that can lead to a reduction in porosity. The importance of maintaining adequate porosity for water infiltration and nutrient availability is reiterated, and the video concludes with a reminder of the significance of these soil properties in agricultural practices.
Mindmap
Keywords
π‘Bulk Density
π‘Particle Density
π‘Porosity
π‘Infiltration
π‘Soil Texture
π‘Soil Compaction
π‘Root Penetration
π‘Water Capacity
π‘Microorganisms
π‘Soil Management
Highlights
Bulk density is an indicator of soil health.
Compaction affects infiltration and root penetration.
Bulk density impacts water capacity and nutrient availability.
As bulk density increases, it becomes more difficult for microorganisms to break down soil components.
Bulk density includes both solids and pore spaces in soil.
Particle density considers only the solid components of soil.
Bulk density is calculated by dividing the mass of dry soil by its volume.
Particle density is calculated by dividing the mass of the solids by half the volume.
Soil texture can be estimated from bulk density readings.
Porosity is calculated using the formula: percent porosity = (100 * (1 - (bulk density / particle density))).
Porosity and bulk density have an inverse relationship.
Increased bulk density leads to decreased porosity.
Compaction can be caused by poor soil management practices.
Cultivating soil too much can reduce organic matter and increase bulk density.
Corn roots are unable to penetrate soil with a bulk density of 1.85 g/cmΒ³.
Soil compaction can reduce porosity, affecting water infiltration and nutrient availability.
Understanding the relationship between porosity and bulk density is crucial for soil health management.
Transcripts
welcome today's lesson is on bulk
density before we get into the problem
sets I'd like to tell you a little bit
about what bulk density is one of the
things that VOC did density definitely
is an indicator of the soil health and
so compaction what we're gonna be doing
today is are going to be taking a look
at the relationship between volt entity
and also porosity some things that have
that bulk density affects it affects
things like infiltration like how water
percolate through the soil it it also
also dictates how far the roots can't
can actually stretch out and get down
into the soil to get water and nutrients
we also take a look at that water
capacity when we're talking about bulk
density the further you in the soil
profile you go the the heavier or the
more the greater bulk density and that
definitely impacts the water capacity
and as I said before nutrient
availability and that impacts a lot of
the microorganisms as the bulk density
increases it makes it much more
difficult for some of these
microorganisms to be able to break
things down so with that in mind let's
talk about porosity and also bulk
density before we get into porosity part
I just want to compare two things that
you know to be hearing out bulk density
versus particle density when we're
looking at bulk density what we're
looking at is a in the soil profile what
we're looking at one cubic centimeter of
soil in other words a length times width
times depth and when we take a look at
that just that one little cube of one by
one by one soil it weighs on average 1.3
grams so if you take that little bitty
cuba of soil and we dry it and it weighs
1.3 grams and we divide it by the volume
again that one by one by one centimeter
cube that's what we divide it by so when
we divide the one point three two by one
we get on average one point
three two that's our bulk density that
includes not only the solids but also
the pore spaces now we get on the
particle density side we just want to
look at the particles we just want to
look at the solid stuff of soil so we
take that same one cubic block and we
take essentially the pores out of it and
what you are left behind is with the
solids and that solids is is only about
half that cube that we've been talking
about so we take the mass of the solids
which is one point three two just as we
did in the bulk density but because the
volume only takes up half you divide 0.5
into 1/3 - you get a bulk excuse me a
particle density of 2.6 four or five
kind of whatever your preference is
that's a constant that same thing that
really doesn't change much because we've
already taken all the pores out so now
that you have a little bit understanding
about bulk density and particle density
let's take a look at problem number one
what is the bulk density of a soil that
760 grams of dry once when we dry the
dot all out and we put it on the scale
that's what away 765 grams and then the
volume is 510 cubic centimeters so let's
set it up
our our subscript B happens to be bulk
density so that's that's our basic
formula so let's go ahead and take a
look 765 is the mass the volume is 510
so we're gonna divide 510 into 765 and
we get a bulk intensity reading of 1.5
grams per cubic centimeters and if we
were to Crawford represent with the soil
textural triangle it's about where a
silt loam is silt loam soil so that
gives you kind of a perspective of how
we can look at bulk density in turn
of soil texture so this is a soil
texture chart and if you look on all of
those lines on there kind of like
reading a contour map and you can see
where some of those lines go like for
instance a 1.4 bulk density is kind of
in the clay range whereas a 1.75 is
somewhere in the sandy loam areas and
then problem number two now what we're
gonna do is take a look at porosity in
bulk dense and see what the relationship
is because that's one of the things that
we're trying to do in this video as to
what what relationship the bulk density
have porosity so when we look at problem
set number two what we want to do is we
want to know that the porosity is soil
number one which had a bulk density of
1.5 again our constant we're going to be
using is our particle density and that's
at two point six five so the equation
for calculating porosity is percent
porosity equals 100 to a - bulk density
divided into particle density density
that you multiply by 100 with so let's
take a look at that looks like 1 point 5
divided by 2 6 5 times 100 and as you
can see dividing 1 point 5 by 2 6 5 bulk
density divided by our particle density
point 5 6 6 0 3 and then we multiply
that by 100 we get 56 point six zero
three so that's going to help us
calculate the percentage and when we
subtract that for 500 you're going to
get forty three point three nine percent
so again what does that have in terms of
a soil texture so when we take a look at
that porosity at 43% a little bit over
three percent it's going to be in the
range of a clay soil I mean that that
range coming near the top third of our
our triangle so we can calculate
porosity based on obviously our bulk
density so but there's some some other
problems that we want
look at again I just want to remind you
that the answer came from 1.5 which was
which was question number one will be
calculated already problem three though
is research has shown that corn roots
are unable to penetrate a layer of soil
having a bulk density of one point eight
five grams per cubic centimeters what is
the porosity in this dense soil well
what we're going to be doing is division
is gonna drop in the 1.85 into our
equation and we divided by two six five
and when we do that we get a point six
nine eighty one and we'll multiply that
by a hundred when we do that we're gonna
get a number of sixty nine point eight
one subtract that and then our bulk
excuse me our porosity is thirty point
one eight or a little over thirty
percent and again what does that have to
do what does that take us probably going
to take us somewhere in a sandy soil and
it definitely does because of the pore
spaces are really large you put any kind
of pressure on sand it's gonna push all
of those particles down into the the
pores and drive out some of the air and
potentially drive out some of the water
that's there as well so it's not gonna
be able to hold as much water either
so and problem number four we've talked
about compaction how does compaction
manipulate porosity and the way we do
that is we're just gonna let's say for
instance you have the soil it's a clay
kind of a soil it's one point two grams
per cubic centimeter since in the clay
range and what would happen if because
of our implements in the way we managed
our soil our bulk density change from
one point two to one point seven in the
root zone what what would happen to that
how much how much porosity will be will
we lose in this such scenario so when we
do that we're gonna again put drop
everything in our bulk density and
particle density formula and one point
two divided by two six five times one
and of course subtract 100 and we'll
just fly by that forty five point two
eight and we subtract that by a hundred
and we get fifty-four percent which in
in our net estimation that's going to be
somewhere in the clay range and then
what we're gonna do is what happened to
it we did some practice and now our bulk
density is one point seven instead of
one point two so we're about one point
seven divided by 2 6 5 times 100 and
when we do that we get a number sixty
four point one five subtract that by 100
and basically what we're having here is
a percentage percentage change
we went from clay to a more sandy soil
we in the process we lost 18 percent of
our porosity which means there's the
less pore space for a nutrients and
water and also what's gonna happens
because there's a less pore space for
the water it's the water infiltration is
going to be lessened as well so let's
summarize what we learned today number
one is that 100 in our equation really
stands for the total so volume that's
the minerals it's the solids it's also
the pore spaces so we take that into
account and then our bulk density
divided by our particle density well
that has to do it's just the solid
portion of it so if we take out the
solids by subtracting it by 100 which is
the total what we're going to have left
really are just the pores the pore
spaces the things that holds the water
the things that that helps get nutrients
from the soil into the plant so and we
want to try to keep as much as that as
possible the second thing that we
learned is a relationship between
porosity and also bulk density we
basically learned in increased in bulk
density is going to mean a decrease in
our porosity kind of a corresponding
decrease I might add so it's an inverse
relationship but what causes this well
primarily poor management such as that
we
in soil compaction driving heavy
equipment on the field over and over
again we want a lesson that the amount
of time our equipment stays on top of
the soil second of all maybe you get it
too wet and when you do to which you
smash down the soil particles into the
pore spaces an organic matter reduction
maybe you cultivate too much I hope
that's helped and I hope that you help
understand how to do the problem sets as
well as the relationship between
porosity and bulk density well thanks
for watching and we'll see you in the
lab
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