Physical Properties Of Soil | Texture, Structure, Porosity, Bulk Density

Summary

In 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

00:00

🌱 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.

05:02

🌿 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.

10:04

💧 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.

Keywords

💡Soil Texture

Soil texture refers to the relative proportions of different-sized mineral particles in the soil, which are sand, silt, and clay. It is crucial for understanding how soil behaves under various conditions and which crops can grow on it. In the video, T Simmons explains that soil texture originates from parent rock and determines the soil's behavior and its suitability for agriculture. The script mentions that clay particles are very small and have a negative charge, which is important for nutrient retention, while sand and silt do not contribute to cation exchange capacity.

💡Clay

Clay is the smallest soil particle, with a diameter less than 0.002 mm. It has a significant impact on soil fertility due to its negative charge, which attracts positively charged nutrients. The video script describes clay as having a special property of being able to retain nutrients effectively, making it a key component in soil fertility and structure.

💡Silt

Silt is a soil particle larger than clay but smaller than sand, with a diameter ranging from 0.002 to 0.05 mm. It is neutral in charge and does not contribute to cation exchange capacity. The script mentions silt as part of the soil texture triangle, which helps in classifying and understanding soil types and their properties.

💡Sand

Sand is a larger soil particle with a diameter between 0.05 and 2 mm. It is also neutral in charge and does not contribute to cation exchange capacity. The video explains that sand and silt are important for soil structure but do not have the same nutrient-retaining properties as clay. Sand is also mentioned in the context of soil structure, where single grains of sand are indicative of sandy soils.

💡Soil Structure

Soil structure refers to how individual soil particles clump together. It affects soil aeration, water infiltration, and root growth. The video script discusses different types of soil structure, such as single grains, granular, blocky, and massive, each with different implications for soil function and management.

💡Pore Space

Pore space, also known as void space, is the empty space within the soil that is not occupied by soil particles. It is critical for air and water movement in the soil. The video script emphasizes the importance of maintaining adequate pore space for healthy soil function, such as gas exchange and water infiltration, which are essential for plant growth.

💡Bulk Density

Bulk density is the mass of dry soil per unit volume and is an indicator of soil compaction. It affects root penetration and soil aeration. The video script explains how to measure bulk density and provides ideal bulk density ranges for different soil textures, highlighting the importance of this property in soil management.

💡Vertisols

Vertisols are a type of soil high in clay content, which exhibit a shrink-swell behavior. This means they crack and disperse easily, leading to potential issues like surface sealing. The video script uses vertisols as an example to illustrate how soil texture influences soil behavior and agricultural practices.

💡Cation Exchange Capacity (CEC)

Cation Exchange Capacity is a measure of a soil's ability to retain nutrients, primarily through the negative charge of clay particles. It is an important property for soil fertility. The video script mentions that clay's negative charge contributes to its CEC, which is essential for nutrient availability to plants.

💡Compaction

Soil compaction refers to the reduction of pore space between soil particles, which can limit root growth, water infiltration, and gas exchange. The video script discusses how different soil structures, like massive or platey, can be signs of compaction, which is detrimental to soil health and plant growth.

💡Agricultural Production

Agricultural production is the process of cultivating plants and livestock for food and other products. The video script connects soil properties to agricultural production by explaining how soil texture, structure, and other characteristics influence crop growth and management practices.

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