Bulk Density May 2016
Summary
TLDRThis educational video script explains the process of collecting soil samples to measure bulk density, a key indicator of soil compaction affecting plant growth and water infiltration. It details the importance of careful sample collection to avoid altering density readings and discusses the impact of soil moisture on density measurements. The script also includes a laboratory demonstration to illustrate how water content affects bulk density, emphasizing the need for standardized, moisture-free samples to ensure accurate soil analysis.
Takeaways
- đ± **Soil Sampling for Bulk Density**: College students learn to collect soil samples to measure bulk density, which indicates how compacted the soil particles are.
- đ **Importance of Bulk Density**: Bulk density is crucial for understanding soil chemistry, water infiltration, and plant growth as it reflects soil compaction.
- âïž **Correct Sample Collection**: To ensure accurate bulk density measurements, students must carefully cut off excess soil without pressing it into the cylinder to avoid falsely high readings.
- đ **Volume Measurement**: The volume of the soil sample, including both particles and pore space, is a key factor in calculating bulk density, with the cylinder volume given as 347.5 cubic centimeters.
- đż **Soil Composition**: Soil is composed of solid particles with varying shapes and sizes, and the space between them, called pores, can be filled with air or water.
- đ§ **Impact of Water Content**: The water content in soil can significantly affect bulk density measurements, as it adds weight and can vary due to weather and precipitation.
- đ§ïž **Soil Saturation**: During rainfall, soil can become saturated, filling all pore spaces with water, which is a critical condition for understanding how water affects soil density.
- đ„ **Moisture Elimination**: To standardize bulk density measurements, soil samples are dried in an oven at 105 degrees Celsius to remove moisture content and measure dry weight.
- đ§Ș **Laboratory Demonstration**: A demonstration using pebbles and a beaker illustrates how adding water to a soil sample increases its mass and affects bulk density calculations.
- đ **Bulk Density Calculation**: Bulk density is calculated as the mass of the dry soil sample divided by its volume, providing a standardized measure of soil compaction.
Q & A
What is the purpose of collecting a soil sample for bulk density testing?
-Collecting a soil sample for bulk density testing helps to understand how compacted the soil particles are, which significantly affects soil chemistry, water infiltration, and plant growth.
How is a soil sample collected for bulk density measurement?
-The soil sample is collected by driving a hollow cylinder into the ground, ensuring that the soil is cut off level with the cylinder without pressing it in to avoid falsely high bulk density readings.
What is the significance of bulk density in soil science?
-Bulk density is significant in soil science as it measures soil compaction and is an important concept in both soil physics and soil chemistry.
What is included in the volume of a soil sample when calculating bulk density?
-The volume of a soil sample for bulk density calculation includes both the soil particles and the pore space between the soil particles.
Why is the term 'bulk' used in the context of soil density?
-In soil science, 'bulk' refers to the whole sample, which includes soil particles, plant roots, and the air space between them, representing the density of the soil matrix.
How does the presence of water in soil pores affect the calculation of bulk density?
-Water in soil pores can significantly affect the calculation of bulk density because the mass of water is about one gram per cubic centimeter, which is not negligible and can change the mass of the soil sample.
How can changes in soil moisture content impact the measurement of bulk density?
-Changes in soil moisture content can cause fluctuations in the mass of bulk soil samples, making the bulk density measurements inconsistent and less representative of the soil matrix.
What is the laboratory demonstration used to understand the effect of water content on bulk density?
-The laboratory demonstration uses pebbles in a beaker to represent a soil sample, where water is added to the pore space to simulate rainfall and saturation, demonstrating how water content can increase the mass and affect bulk density.
How is the bulk density of a soil sample calculated?
-Bulk density is calculated using the formula: bulk density equals the mass of the sample divided by the volume of the sample. The mass is determined after drying the sample to remove moisture content.
Why is it necessary to dry the soil samples before calculating bulk density?
-Drying the soil samples is necessary to remove moisture content and ensure that the mass measured represents the dry weight of the soil particles, allowing for standardized and accurate bulk density measurements.
What is the expected bulk density range for soil samples taken from the same field?
-The expected bulk density range for soil samples taken from the same field is likely to be close to each other since they are from a similar soil matrix and have been oven-dried to remove soil moisture for standardized results.
Outlines
đ± Understanding Soil Bulk Density
This paragraph introduces the concept of soil bulk density, explaining its significance in soil chemistry, water infiltration, and plant growth. Students are shown collecting soil samples using a hollow cylinder to measure compaction. The process emphasizes careful cutting to avoid altering the sample's density. The paragraph reviews the formula for density, noting that bulk density accounts for both soil particles and the pore space between them. It also discusses the impact of water content on bulk density, highlighting the need to standardize measurements by eliminating moisture.
đ§ Impact of Water Content on Soil Bulk Density
The second paragraph delves into how water content in soil affects bulk density. It uses a laboratory demonstration with pebbles in a beaker to illustrate the concept. The dry weight of the pebbles is measured, then water is added to simulate rainfall, filling the pore spaces. The saturated sample's weight is then compared to the dry weight, showing a significant increase due to the added water. The paragraph explains how this affects bulk density calculations and the importance of using dry weight for standardized measurements.
đ Calculating and Standardizing Soil Bulk Density
The final paragraph focuses on the process of calculating bulk density by using the dry weight of soil samples. It describes how samples are oven-dried to remove moisture, ensuring standardized results. The paragraph provides an example calculation using a sample's dry weight and the known volume of the sample container, resulting in a bulk density of 1.3 grams per cubic centimeter. It concludes by emphasizing the importance of standardized bulk density measurements for understanding soil characteristics.
Mindmap
Keywords
đĄSoil Sample
đĄBulk Density
đĄPore Space
đĄSoil Compaction
đĄSoil Chemistry
đĄWater Infiltration
đĄPlant Growth
đĄSoil Matrix
đĄSoil Saturation
đĄOven Drying
Highlights
Students learn to collect soil samples for bulk density testing.
Bulk density indicates soil compaction levels, affecting soil chemistry, water infiltration, and plant growth.
Soil sample collection involves driving a hollow cylinder into the ground without pressing soil into it.
Bulk density is calculated using the formula mass over volume, with the volume of the cylinder being 347.5 cubic centimeters.
Soil is composed of solid particles with varying shapes and sizes, and the space between them, called pores.
Bulk density accounts for both soil particles and the pore space, which can be filled with air or water.
The term 'bulk' in soil science refers to the entire sample, including soil particles, plant roots, and air spaces.
More pore space results in a less dense soil sample.
Soil moisture content can change frequently, affecting the mass and bulk density of soil samples.
During rainfall, soil pores can become saturated with water, displacing air and affecting bulk density.
A laboratory demonstration uses pebbles in a beaker to simulate the effect of water content on bulk density.
Saturation of soil pores with water increases the mass of the sample, thus affecting bulk density calculations.
To standardize bulk density measurements, soil samples are dried in an oven at 105 degrees Celsius to remove moisture.
Drying samples allows for the use of dry weight in bulk density calculations, providing standardized results.
Bulk density is a key measurement for identifying different soil types and understanding soil matrix characteristics.
Sample 14, after oven drying, has a bulk density of 1.3 grams per cubic centimeter, indicating soil compaction.
Similar bulk density results from multiple samples suggest a consistent soil matrix in the sampled field area.
Transcripts
these college students are learning how
to collect a soil sample that will be
tested for bulk density the soil sample
is collected by driving a hollow
cylinder into the ground bulk density
tells us how compacted particles are in
the soil and that compaction has a
significant effect on such things as
soil chemistry water infiltration and
plant growth here you see the students
cutting off excess soil and plant root
the soil is cut off level with the
cylinder the students must be careful to
cut off the soil rather than pressing it
into the cylinder remember bulk density
is a measurement of soil compaction so
pressing the excess soil into the
cylinder would cause our bulk density
reading to be slightly higher than it is
in the field bulk density is an
important concept in both soil physics
and soil chemistry so let's review this
concept to make sure that you have a
good understanding of how to determine
the bulk density of a soil you will
remember from high school that the
formula for the simple density of a
material is mass over volume the volume
of the cylinder is three hundred and
forty seven point five cubic centimeters
so we're already halfway there in
calculating our bulk density but when it
comes to determining the mass of the
sample bulk density is a little more
complicated than the simple disa T that
you're used to working with in order to
understand the difference let's review a
few basic facts about soil we know that
soil is made up of solid particles that
have different shapes and sizes and in
between these particles there is
empty space and that empty space we call
pores so the first thing you need to
remember about bulk density is that the
volume of the sample includes both the
soil particles and the pore space
between the soil particles if the word
bulk is a little confusing to you don't
worry about that actually it is a rather
odd word to use in this context just
keep in mind that in soil science the
word means hole and bulk density means
the density of the whole sample which
includes soil particles plant roots and
the air space in between them another
term we could use his soil matrix
density we could say that bulk density
is the density of the soil matrix and is
representative of the field from which
we took the sample obviously the more
empty space or pore space that you have
in your sample the less dense the sample
will be and there's another reason why
pore spaces are important to the
calculation of bulk density these empty
spaces in the soil can be filled either
with air or with water we won't worry
about the weight or mass of the air
because that's negligible but the weight
or mass of water as you will remember is
about one gram per cubic centimeter and
that is significant it definitely will
affect our calculation of bulk density
so the water content of the soil is a
problem it can change from day to day
and even hour to hour depending on
weather conditions and the amount of
precipitation this means that the mass
of bulk soil samples taken from the same
field could fluctuate significantly from
day to day and therefore our calculation
of bulk density would also fluctuate so
it wouldn't tell us very much about the
actual care
heuristics of the soil matrix in the
field where we're sampling so how do we
eliminate the random changes in bulk
density that are caused by changes in
soil moisture content to answer that
question let's take a closer look at
what happens during a rainfall event
during prolonged dry periods soil
moisture is evaporated then the pore
spaces of the soil become filled with
air this is especially true with the top
six inches of soil now let's talk about
what happens when a storm system moves
into the area and there is an extended
rainfall the rainwater moves down
through the soil because of gravity and
begins to fill the pore space pushing
out the air if it rains long enough all
of the pores in the soil will be filled
with water this is referred to as soil
saturation or saturated conditions when
the soil is saturated rainfall can no
longer be absorbed have become surface
water runoff if it continues to rain
streams will rise and flooding will
occur
now let's conduct a laboratory
demonstration that will help us to
further understand how water content in
a soil sample will affect bulk density
the pebbles in this beaker will
represent a bulk soil sample the pebbles
themselves will represent the soil
particles and it's easy to see the pore
space in between them the weight of the
beaker and the pebbles is two hundred
and eight point two grams the weight of
the beaker by itself which is our tare
weight is fifty one point eight grams if
we subtract that from the weight of the
beaker and the pebbles then we get the
weight of the pebbles by themselves
which is 156 point four grams we would
call this the dry weight of our sample
because there's no water or moisture
content that we have to worry about all
the pore space is filled with air now we
will simulate a rainfall by pouring
water into the pore space of the sample
at the 100 milliliter mark all of the
pore space has been filled with water
and our imaginary soil sample is
completely saturated the weight of the
pebbles the water and the beaker is two
hundred forty eight point two grams once
again we will subtract the tare weight
of the beaker and we find that the
pebbles and the water weigh one hundred
ninety six point four grams compare that
to our dry weight of the pebbles which
was 156 point four grams and we see that
the water that we poured into the beaker
simulating a rainfall added 40 grams of
weight to our sample keep in mind we are
assuming that our laboratory scales are
properly calibrated so that weight has
the same number as mass therefore adding
the water to our sample also increase
the mass of the sample by 40 grams now
let's calculate the bulk density of both
our dry sample
and our saturated sample this should
help us to understand how moisture
content and the pores of the soil can
affect our bulk density reading here is
our formula bulk density equals the mass
of the sample over the volume of the
sample the volume we already know
because we filled the beaker up to the
100 milliliter level we also know that
100 milliliters is the same volume as
100 cubic centimeters density is almost
always given in grams per cubic
centimeters so let's use that unit of
volume now we will plug in our
measurements of mass our dry weight
measurement was 150 6.4 grams and the
weight of the saturated sample was 196
point 4 grams when we do the bath we see
that there is a significant difference
in our results and that difference is
significant enough to make our bulk
density readings virtually worthless
bulk density is one of the measurements
used to identify different types of
soils so we want our calculation of bulk
density to be both accurate and
standardized the only way we can achieve
this is by getting rid of the moisture
content in the sample but how are we
going to do that
well what if we simply heat up the
sample and evaporate the moisture then
we would always be using the dry weight
of the sample as the mass and in fact
that is exactly what's done to determine
bulk density the samples are placed in
an oven with a temperature of about 105
degrees Celsius the samples will stay in
the oven for several hours or even
several days if necessary to remove
virtually all of the moisture content so
when the samples come out of the oven
and our way to determine mass
we will be measuring their dry weight if
all of the samples are dried and the
mass then is given to us in dry weight
we can then standardize the results and
the bulk density then will give us
important information about the soil
matrix from which the samples were taken
now that we know what bulk density is
and how it's determined let's calculate
the bulk density of one of the samples
taken by the college students let's say
the sample 14 is taken out of the oven
and weighed and the weight is 450 1.75
grams
this would be the samples dry weight and
we would then plug this number into our
formula as the mass of the sample the
result is a bulk density of 1.3 grams
per cubic centimeter we would expect the
other samples to have a bulk density
close to sample 14 this is because they
were all taken close together in the
same field so it is likely that their
soil matrix is very similar and they
were all oven dried to remove soil
moisture which will give us standardized
results
5.0 / 5 (0 votes)