Bulk Density

Summary

Today'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

• 🌱 Bulk density is a key indicator of soil health, affecting water infiltration, root growth, and nutrient availability.
• 💧 As bulk density increases, it becomes more difficult for microorganisms to break down organic matter, impacting soil fertility.
• 📊 The average bulk density of soil is about 1.3 grams per cubic centimeter, including both solids and pore spaces.
• 🔍 Particle density, which excludes pore spaces, is typically around 2.6 grams per cubic centimeter and is a constant value.
• 📏 Porosity can be calculated using the formula: percent porosity = (100 * (particle density - bulk density)) / particle density.
• 🌾 Soil texture, such as silt loam, can be estimated based on bulk density readings, with different ranges indicating different textures.
• 🚜 Soil compaction, often caused by heavy equipment use or poor soil management, increases bulk density and decreases porosity.
• 🌱 Compaction reduces the pore space available for water and nutrients, which can negatively impact plant growth and soil health.
• 🌡️ The depth in the soil profile affects bulk density, with deeper layers typically having higher bulk density and lower water capacity.
• 🌱 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

00:00

🌱 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.

05:01

💧 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.

10:02

🔍 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.

Keywords

💡Bulk Density

Bulk density refers to the mass of dry soil per unit volume, including both the solid particles and the pore spaces. It is a key indicator of soil health and is crucial in understanding how water, air, and nutrients are held within the soil. In the video, bulk density is used to assess soil compaction and its impact on root penetration and water infiltration. For instance, a bulk density of 1.3 grams per cubic centimeter is mentioned as an average for soil, and different soil types like silt loam are discussed in relation to their bulk density.

💡Particle Density

Particle density is the mass of the soil's solid particles alone per unit volume, excluding the pore spaces. It is a constant value that does not change much because it only considers the soil's solid components. In the script, particle density is contrasted with bulk density to illustrate the difference between the total mass of soil and just the solid components. A particle density of 2.65 grams per cubic centimeter is given as an example, which is used to calculate the porosity of soil.

💡Porosity

Porosity is the percentage of voids or spaces in a material that can contain air or water. In the context of soil, it is an important factor for water infiltration, root growth, and nutrient availability. The video explains how porosity can be calculated using the formula involving bulk density and particle density. A decrease in porosity, as seen when bulk density increases, can lead to soil compaction and reduced water and nutrient availability, as illustrated by the example of corn roots being unable to penetrate soil with a high bulk density.

💡Infiltration

Infiltration refers to the process by which water penetrates the soil surface and moves into the ground. The video script discusses how bulk density affects infiltration rates, with higher densities leading to reduced water penetration. This is significant for agriculture as it impacts the water available to plant roots and the overall health of the soil.

💡Soil Texture

Soil texture is determined by the relative proportions of sand, silt, and clay in the soil. It influences the soil's physical properties, such as water retention, aeration, and nutrient availability. The script uses soil texture as a context for interpreting bulk density measurements, with different textures correlating to different ranges of bulk density values. For example, a bulk density of 1.4 is associated with clay, while 1.75 is linked to sandy loam.

💡Soil Compaction

Soil compaction is the process by which soil particles are pressed together, reducing the pore spaces and increasing the bulk density. This can be caused by heavy machinery or improper soil management. The video explains how compaction negatively impacts porosity and, consequently, the soil's ability to support plant growth by reducing the availability of water and nutrients.

💡Root Penetration

Root penetration refers to the ability of plant roots to grow and spread through the soil. The script mentions that certain bulk densities can hinder root penetration, which is essential for plants to access water and nutrients. An example given is that corn roots cannot penetrate soil with a bulk density of 1.85 grams per cubic centimeter.

💡Water Capacity

Water capacity is the amount of water that a soil can hold against the force of gravity. The video script explains that bulk density affects water capacity, with higher densities leading to reduced capacity. This is important for plant growth as it influences the availability of water to the roots.

💡Microorganisms

Microorganisms play a vital role in soil health by breaking down organic matter and cycling nutrients. The script discusses how increased bulk density can negatively affect these organisms by reducing the pore spaces, making it more difficult for them to function effectively. This can impact the overall nutrient cycling and health of the soil.

💡Soil Management

Soil management refers to the practices and strategies used to maintain and improve soil health and productivity. The video script touches on the importance of proper soil management to prevent soil compaction and maintain optimal bulk density and porosity. It suggests that avoiding heavy equipment use when the soil is wet and minimizing tillage can help preserve soil structure and function.

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/cm³.

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