Week 4: Important soil physical properties

1
Important Soil Physical Properties for Engineers and Agricultural
Professionals
C.K. Saxena
Senior Scientist, Central Institute of Agricultural Engineering,Bhopal 462 038
Introduction
Soil is a natural upper-mostlayer of the earth’s crust and is made up of inorganic and organic matter which
is capable of supporting plants. The earth consists of 71% water and 29% land. Of this 29%, agricultural
land covers about33% of the world's land area as per the estimates by the FAO's arable land representing
about 9.3% of the world's land area, while the rest areas are dry, cold ice deserts; warm sand and rock
deserts and steep uncultivable lands.This 9.3% of land with an approximately 1m deep layer of soil to feed,
house and sustain all the people of the earth (FAO, 2014). Soil is developed as a result of dynamic
pedogenic processes during and after weathering of mineral rocks and organic constituents, possessing
definite chemical,physical,mineralogical and biological properties, which provides a medium for plan growth
for land plants. Soils are comprised of solids, liquid, and gas.
Soil is developed as a resultof dynamic pedogenic processes during and after weathering of mineral rocks
and organic constituents, possessing definite chemical, physical, mineralogical and biological properties,
which provides a medium for plan growth for land plants. Soils are comprised of solids, liquid, and gas. The
inorganic components of soil are weathered rock, air, water and minerals. The organic matter is the
decomposing contribution from plants and animals.The voids between the small particles that make up the
soil are filled with air or water. Living plants and animals do live in the soil and improve aeration and
drainage. Some organisms, like bacteria, play an important role in converting plant foods or nutrients, e.g.
nitrogen (helps leaves and stems grow), phosphate (helps roots and fruits develop) and potassium
(stimulates overall plant health). When plants die, they return the nutrients they initially absorbed from the
soil, back to the soil, and enrich the soil. In this way soil plays a very important role in the recycling of
nutrients (Enviro Facts, 1999).Soil may take thousands of years to develop from the parent rock – 10mm of
soil takes between 100 and 1000 years to form. This time depends on the speed of weathering (parent rock
being broken down into small particles). Weathering can be physical (frost, temperature changes, salt
crystallization), chemical (chemical action of water, oxygen, carbon dioxide and organic acids) or biological
(tree roots that widen crevices and cracks).
Soil Sampling Techniques
Properly collecting soil samples is the most important step in understanding of any soil nutrient or
amendment management exercise. Soil sample must be true representative of the field or the part of the
field being tested. This chapter discusses many methods used for taking an accurate soil sample using
various methods among several types of tillage conditions as well as their analysis for physical properties .
The most commonly used method for soil sampling is generally based on soil types. Fields could be split
carefully chosen sampling numbers from the areas that contain similar soils’ conditions (Eberhardt and
Thomas,1991;Pennock,2004). In general sampling may be planned just before the sowing or planting; or
after the harvest of the crops. Each sample should be labelled describing field identification, farmer’s or
experiment’s name and address, previous crops, date and the present status etc. Augers with a core
diameter of 1–2 cm are convenient, but small spades can also be used (Figure 1). In any case, a uniform
slice of soil should be taken from top to bottom of the desired sampling depth. About 20 cores are taken
from a field of 1 ha. In absence of an auger, a V-shaped cut 15-20 cm deep and 1 cm slice from the smooth
side could be cut using field spade. Trim sides with a sharp blade or a pen knife leaving a 2 cm strip. A
number ofsuch samples are collected into a clean bucket to make a composite sample. In the laboratory or
it is air dried, ground using a rubber pestle in an agate mortar and sieved (2 mm sieve).
Fields in India, where micro-irrigation systems have been installed are generally have a s maller sampling
area. The sampling could be done for laboratory experiments too from that of an experiment on nutrient, salt
and moisture movementas well as their accumulation. Such samples are collected in a smaller vertical as
well as horizontal grids or arrays and their representative samples are built, for the purpose ofdetermination
of physical as well as chemical properties of soils. Several plans and layouts have been tried by several
researchers for the collection of soil samples starting from 2.5 to 15 cm in depth and width away from the
point source of drip used in different experiments (Ben-Asher et al., 1986; Nehra et al.,1991; Angelakis et

2
al.,1993; Lubana and Narada, 2001; Cote et al., 2003; Mmolawa and Or, 2003; Li et al.,2004; and
Provenzano, 2007). While it covered up to a varying vertical and horizontal distances largely depending
upon the extent of interest, which generally dependent of root zone. In general, the laboratory studies
covered a smaller sample size in comparison to the field samples.
The Soil Texture
In general, soil consists of approximately 45% mineral material, 5% organic matter, and 50% pore space
through which liquids and gases move. The amount of pore space is determined by the size and
arrangement of the soil particles. The proportion of pore space is low when soil particles are very close
together (e.g., compacted soil) and is higher when soils have high organic matter.Sandy soils normallyhave
35-50% pore space, while medium to fine-textured soils have 40-60% pore space. Pore space decreases
with soil depth because subsoil tends to be more compacted than topsoil. Soil solids (mineral particles and
organic material) comprise roughly 50% of the total soil volume. The remainder is made up of soil water
(25%) and soil air (25%). The relative amounts and sizes of mineral particles in a given soil determine soil
texture. Soil texture is not determined by organic material, soil water or soil air. Soil texture refers to the
relative amounts of three well-defined soil particle size separates: sand, silt, and clay. Sand refers to a
discretelydefined particle size between 2.0 and 0.05 mm in diameter.The siltfraction is defined as particles
with a diameter between 0.05 and 0.002 mm in diameter, and clay is defined as particles with a diameter
less than 0.002 mm. Therefore, it is the relative percentages of the sand, silt, and clay that determine the
soil textural class (e.g.“clay loam”).Particles larger than 2 mm in diameter are not considered in soil texture
determinations, but act as modifiers for designated textural class names (e.g. gravelly clay loam). Soil
texture impacts soil properties including chemical reactions, water and gas movement.
The Soil Textural Triangle
Soils are grouped into 12 textural classes depending on their proportions of sand, silt, and clay, which are
expressed as percentages as shown in the soil textural triangle (Figure 3). Notice that the clay size class
dominates the textural triangle. A soil with 55% clay is considered a clay soil, but it requires 85% sand
content for a soil to be considered a sand. This reflects the ability of clay particles to dominate soil
properties. In other words, “a little clay goes a long way.”
To determine a soil’s textural class, we need know only the
percentages of each size class (sand, silt, or clay). The
region at which these percentages intersect on the textural
triangle defines the soil texture. For example, for a soil with
30% clay, 20% siltand 50% sand,the lines drawn based on
the 3 axes of the triangle intersect in the “sandy clay loam”
region. Note how the lines are drawn relative to the major
axes that define the soil separates (sand, silt and clay).
Obviously, these designations are fairly generalized, but an
astonishing amountofinformation aboutsoil properties can
be conveyed by the soil’s textural class. For example, soils
dominated by the sand fraction tend to be better drained,
less chemically active, less fertile, etc. One of our goals in
this course will be to link soil properties to their textural
classes in order to facilitate decision-making relative to
agriculture and the environment.
Figure 3. The soil textural triangle.
Figure 1 Various augers/samplers Figure 2 Different sampling plans

3
Particle Size and Surface Area
The mostimportant aspect of soil texture is the large surface area supplied by the many soil particles. For
soil particles comprising the same mass, surface area increases as the size of the particles decrease. For
example,the surface area of the cube below is doubled by breaking itup into 8 identical particles (Figure 4).
Thus, smaller particles have a greater surface area for the same mass of soil. For example, one hundred
particles weighing a total of one gram have a far greater surface area than a single particle weighing one
gram. Surface area ultimately determines the size of the interface between the soil particle and the
surrounding environment,which in turn dictates the magnitude and rate of many soil chemical and physical
properties.
Specific surface area is the surface area per unit mass. Table A indicates the three primary particle size
fractions and their specific surface areas. Note that the units for specific surface area are expressed as
surface area per unit mass (cm2
/g). Clay particles can have surface areas that are 100,000 times greater
than for sand-sized particles. Imagine the implications in terms of their relative abilities to interact with the
environment. These interactions will take place at the mineral surface; therefore, a small amount of clay-
sized particles can have an enormous impacton soil properties. As we will learn in this exercise, increased
surface area means greater potential interaction with the environment. Therefore, this property has vast
implications for the physical and chemical properties of soils, many of which will be examined in later lab
exercises.
Table 1. Soil particle size fractions and specific surface area.
Soil Separate Diameter (mm) Specific Surface Area (cm2
/g)
Sand 2.0 – 0.05 30
Silt 0.05 – 0.002 1,500
Clay <0.002 3,000,000
Laboratory Determination of Soil Texture
A reliable method for determining the proportions of each soil separate
(sand,silt,or clay) employs sedimentation.The rate at which particles settle
out of aqueous suspensions is dependent upon their size, or more directly,
their surface area.Particles with large specific surface areas (such as clay)
experience greater “drag” or resistance to settling than particles with smaller
specific surface areas (such as sand). Therefore, if both types of particles
are suspended in water, those with a small specific surface area (such as
sand) will settle out first according to Stokes’ law.
A simplified equation (based on Stokes’ law) indicates that the settling velocity of a soil particle in water is
proportional to the square of the particle diameter.
𝑉 = 𝑘𝐷2
Where: V= settling velocity of a spherical particle with diameter D, and k = constant (11,241 cm-1
sec-1
)
Stokes’ law is indirectly used by allowing particles to settle out of suspension for predetermined time
periods. Since the larger particles (sand) settle out first and the smallest (clay) settle last, this would
determine the relative amounts ofsand,silt and clay in a soil sample. To accomplish this, a calibrated float
Figure 5. Hydrometer
Figure 4. The large cube represents surface area of a sand size particle, while the smaller cubes
show how the surface area increased when smaller siltor clay sized particles constitute the same
mass

4
(or bobber) hydrometer is essentially used (Figure 5) and is buoyed up in dense suspensions. In other
words, the greater the amount of material in a suspension, the higher the hydrometer will float.
Determining Soil Texture and Particle Size Distribution (Hydrometer Method)
A hydrometer (ASTM 152H with scale in g/l) measures the density (mass/unit volume) of a suspension.
During the lab exercise,the hydrometer directly measures the mass ofparticles remaining suspended in a 1-
L volume, not the amount of particles that have settled out. Due to the settling of particles, the density of a
soil suspension changes with time. The cylinder on the left in Figure 6 represents the condition moments
after soil was added.The cylinder on the right in Figure 6 shows the condition at some time later,after some
of the soil has settled outof suspension.Scale markings on the stem allow directreading of the suspension
density in g/L. The scale reads zero in pure water at 18ºC.
Dispersion of Soil Particles
Small,clay-sized soil particles are held together by weak electrostatic linkages. We
can break these linkages by adding a chemical dispersant (sodium
hexametaphosphate (NaPO
3
)
6
) and the use of mechanical stirring so that each
particle settles separately and in accordance with its own size. Organic matter can
also prevent complete dispersion of the soil particles. Typically, we would remove
organic matter from the soil prior to sedimentation using hydrogen peroxide.
Peroxide oxidizes the organic matter in the soil, converting it to gaseous carbon
dioxide and water, leaving soil particles free to settle.
Temperature
Density and viscosity of water change with temperature. This results in faster or
slower settling velocities for particles depending on the temperature. Hydrometers
are calibrated at the factory to read accurate densities at 18ºC. Therefore, readings
at other temperatures mustbe corrected.For each degree above 18ºC, we add 0.25
g/L to the observed hydrometer reading. Similarly for each degree below 18ºC, we
subtract0.25 g/L from the observed hydrometer reading. For example, if the reading
at 20ºC was 10 g/L, the temperature-corrected reading would be 10 g/L + (2 × 0.25
g/L) or 10.5 g/L.
Particle Size Distribution by Hydrometer Method
1. Weigh 40 g of the provided soil (oven dried and 2 mm sieved) into a metal stir cup.
2. Fill the metal cup half-full with deionized water. Add 20 ml of sodium hexametaphosphate dispersing
solution.
3. Place cup on the mechanical stirrer for 5 minutes.
4. Quantitatively transfer all the soil suspension from the metal wash cup into a 1000 mL cylinder. (Use a
wash bottle to rinse the contents of the metal stir cup into the cylinder to ens ure you don’t lose any soil
material.)
5. Fill the cylinder up to the 1000 mL (1L) level using D.I. water.
6. Insert the plunger into the cylinder and move it up and down several times to thoroughly mix the soil.
(Take care not to spill the suspension!)
7. Remove the plunger and immediatelystarta timer. Lower the hydrometer into the suspension carefully.
(Do not allow the hydrometer to bob excessively.)
8. Read the hydrometer when the timer reaches 40 s. Record the reading (g/L).
9. Repeat steps 6 through 8.
10. Measure the temperature of the suspension.
11. Apply a temperature correction to your 40 s hydrometer readings ifneeded.For each degree over 18ºC,
add 0.25 g/L to the average 40 s hydrometer reading. For each degree below 18ºC, subtract 0.25 g/L
from the average 40 s hydrometer reading. Record the temperature-corrected average reading. The
40-second reading gives the amount of silt and clay still suspended after the sand particles have
settled.
Figure 6. The density
of the soil suspension
changes with time as
the solids settle.

5
12. A 2-hour hydrometer reading is also required. While waiting, complete the remaining exercises. Once
the timer reaches 2 hr, insert the hydrometer into the solution and report the value in Table 1.
13. Measure the temperature of the suspension. (Please use care and do not drop the thermometer!)
14. Apply a temperature correction to your 2-hr hydrometer readings ifneeded. For each degree over 18ºC,
add 0.25 g/L to the average 40 s hydrometer reading. For each degree below 18ºC, subtract 0.25 g/L
from the average 40 s hydrometer reading. Record the temperature-corrected average reading.
15. Determine the weight and proportion of sand, silt and clay in the sample. Use the texture triangle to
determine the texture of the soil sample.
16. Determine total surface area of the soil. First, determine the surface area of each separate. For
example, if you determine that the sample had 20 g of sand, 5 g of silt and 15 g of clay, multiply the
mass ofthe separate by the surface area of that separate to obtain its surface area in the sample.Then,
add them together to obtain the total soil surface area.
Example: 20 g sand × 30 cm2
/g = 600 cm2
sand surface area
5 g silt × 1500 cm2
/g = 7,500 cm2
silt surface area
15 g clay × 3,000,000 cm2
/g = 4.5 x 107
cm2
clay surface area
45,008,100 cm2
total surface area
Sample Calculations for the Hydrometer Method of Determining Soil Texture
A 40 g soil sample was used to determine soil particle analysis using the hydrometer method. The soil
sample was dispersed and suspended in 1 L of water in the cylinder. The cylinder was shaken well and the
following measurements made:
At 40 seconds, all of the sand-sized particles will have settled out of the suspension leaving only silt- and
clay-sized particles.So there are 10 g of our original soil sample (40 g) remaining in the suspension (which
is equivalentto silt and clay fraction). Since we know that it is the sand-sized particles that have settled out,
we know by subtraction that there were 30 g of sand in the original sample.
Mass sand: 40 g original soil - 10 g silt and clay remaining in suspension = 30 g sand
Percent sand: 30 g sand/40 g original soil = 0.75; the fraction of sand in the sample = 0.75 x 100 = 75%
sand
The 2-hour hydrometer reading was 2 g/L, this means that there are 2 grams of material left in the
suspension.We know that this must be clay, since the sand and silt have settled out. Therefore, there were
2 g of clay in the original soil sample.
Percent clay: 2 g clay/40 g original soil = 0.05; the fraction of clay in the sample = 0.05 x 100 = 5 % clay.
So, now we know the fractions or percentages ofsand- and clay-sized particles that were in the original soil
sample. The only remainder is the silt. We can determine this by simple subtraction.
Percent silt: 40 g (original soil) - (30 g sand + 2 g clay) = 8 g silt
8 g silt/40 g original soil = 0.20 = fraction of silt in the sample
0.20 × 100 = 20% silt
Alternatively: 100% (original soil) - (75% sand + 5% clay) = 20% silt

6
Knowing the percentages ofsand, silt, and clay we can use the soil textural triangle (Figure 3) to determine
the soil’s textural class--loamysand. We will use this procedure in the lab to determine the textural class of
soils collected in the field.
Estimating Soil Texture in the Field
Field estimates of soil texture can be made
using the “texture-by-feel” method. In essence,
the method involves manipulating moist soil
samples to determine roughly the proportions
of sand, silt, and clay based on grittiness,
smoothness, and plasticity, respectively. This
is a subjective skill that takes practice.
Opportunities to hone your talents will be
provided in this lab exercise. Historically,
students have been quite surprised at their
ability to estimate soil texture with this method.
Other, more precise, methods also will be
examined, but the texture-by-feel method is a
handy first approximation, especially under
field conditions.
Soil Texture - Feel Method
1. Follow the provided flowchart to practice determining the texture of the soils samples.
2. Record the texture of the unknown soils as estimated using the texture-by-feel method.
The ability of the soil to hold and transmit water and air is impacted by the (1) amount of pore space in the
soil and (2) pore size distribution. Soil pores can be classified into three main groups depending on the
diameter of the individual pore. Macropores are large diameter pores (≥ 0.1 mm) that tend to be freely
draining and are prevalent in coarse textured or sandysoils. Mesopores are medium sized pores (0.03 mm
– 0.1 mm) that are common in medium-textured soils or loamy soils. Micropores are small diameter pores
(<0.03 mm) that are important for water storage and are abundant in clay soils. It is sometimes helpful to
envision soil pore space as a network of tiny tubes of varying diameter.Imagine how the diameters of those
tubes would impact the movement of gasses and liquids relative to aeration, drainage, and infiltration.
Soil Color
Soil color originates from a number of processes leading to the concentration or removal of a variety of soil
constituents including various metal oxides, organic matter, and clay (Figure 7). It is an important
determinant of many soil chemical and physical properties. For example, together with other criteria, soil
color can be used to assess the drainage class of a soil, its season high water table, or its redox status.
Soil color is determined using a Munsell soil color book.The book consists ofa number of pages containing
color chips used for comparison of soil color. The pages are labeled according to the dominant spectral
color or hue. For example,many soils in Florida have associated colors which match well with the 7.5 YR or
10 YR hues. The designation YR indicates “yellow-red”. In this case, the 10 YR page is dominated by chip
containing less red and more yellow colors than the 7.5 YR page. Similarly, the 5 YR page is more red and
less yellow than the 7.5 YR page. Munsell color books will be provided in the lab for your use.
On each page of the Munsell color book is also a designation referring to the amount of reflected light or
grey scale, called the “value” and the intensity of the color called the “chroma”. A page of the Munsell color
book is shown in Figure 8.
Figure 7. Soil color may vary throughoutthe profile based
on the physico-chemical and biological properties ofthe soil.

7
Figure 8. The 10 YR page of the Munsell color book.
Soil color determination
Soil color is determined by matching the soil color with one of the chips and reporting the soil hue, value,
and chroma ratings that make up the soil color
1. Place a small amount of dried soil into your hand. Use the Munsell color book to determine the color
(hue, chroma and value) of each sample.
2. Record the hue, chroma, and value of each soil.
3. Repeat steps 1 and 2, but moisten the soil.
Soil Density
Density is the relationship between the mass (m) and volume (V) of a substance.
𝐷 =
𝑚
𝑉
Based on this relationship,an objector substance thathas high mass in relation to its size (or volume) also
has a high density (D).
The solid (mineral and organic) particles that make up a soil have specific particle density (Dp), which is
defined as the mass of solid particles in a unit volume.
𝐷 𝑝 =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑜𝑖𝑙
𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑𝑠
The particle density of a soil is not affected by particle size or arrangement; rather it depends on the type of
solid particles presentin the soils.Because mineral soil particles are heavier than organic matter, they have
a higher particle density on a unit volume basis. The average particle density of a mineral surface soil is
about 2.65 g cm-3
, which is the average density of quartz.
(Source: Harris, 2014)

8
Soil bulk density (Db) is a measure ofthe mass ofsoil per unitvolume (solids + pore space) and is usually
reported on an oven-dry basis.
𝐷 𝑏 =
𝑚𝑎𝑠𝑠 𝑜𝑓 𝑑𝑟𝑦 𝑠𝑜𝑖𝑙
𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑𝑠 & 𝑝𝑜𝑟𝑒 𝑠𝑝𝑎𝑐𝑒𝑠
Unlike the measurementofparticle density, the bulk densitymeasurementaccounts for the spaces between
the soil particles (pore space) as well as the soil solids. Soils with a high proportion of pore space have
lower mass per unit volume, and therefore have low bulk density. Typical mineral soils have bulk densities
that range from 1.0 to 1.6 g cm-3
. A bulk densitygreater than 1.6 g cm-3
may indicate soil compaction, which
means these soils have a low proportion of pore space and,therefore, low porosity. Alternatively, soils with a
high proportion of organic matter tend to have bulk densities that are less than 1.0 g cm -3
.
The bulk density of different soils varies based largely on soil texture and the degree of soil compaction.
Sandy soils with low organic matter tend to have higher bulk density than clayey or loamy soils. Soil bulk
densityis usuallyhigher in subsurface soils than in surface horizons,in part due to compaction by the weight
of the surface soil.
Bulk Porosity
The bulk density indirectly provides a measure of the soil porosity (amount of pore space). Soil porosity is
the ratio of the volume of soil pores to the total soil volume. In general, clayey soils have an abundance of
very small pores (micro-pores) that give them a higher total porosity compared to sands, which are
dominated by larger, but fewer pores. Consider the relative sizes of a single sand grain and several clay
particles existing as an aggregate (Figure 9). Low porosity tends to inhibitroot penetration,water movement,
and gas movement.
There are more pore spaces between the clay than sand particles because clayparticles are much smaller.
Thus, clay soils tend to have a higher total porosity than sandy soils all else being equal. However, the
relationship between texture and bulk density is tenuous and depends on a variety of factors such as
organic matter content and depth in the soil profile.
Bulk density (Db) is closely related to the soil porosity through the following relationship:
𝑷𝒐𝒓𝒐𝒔𝒊𝒕𝒚 = 𝟏 −
𝑫 𝒃
𝑫 𝒑
Soil porosity values range from 0 to 1. Soils with a high bulk density have low total porosity because empty
pores do not have any mass. Figure 10 illustrates the overall relationship between porosity and bulk density.
When the bulk densityis zero, porosity equals 1,meaning there are no particles. If the bulk density is equal
to the particle density, then there are no pores and porosity is zero. Between these two extremes are the
values for soils. Clayey soils tend to have lower bulk densities and higher porosities than sandy soils.
Figure 9. The relationship between soil particle size and soil porosity.

9
Soil Sampling to Determine Bulk Density
Soil sampling to determine bulk densityis quite simple,butrequires patience and care because obtaining an
accurate volume of soil is critical.The samples are obtained by driving a container of known volume into the
soil.The container is then oven-dried and weighed. Dividing weight of soil (g) obtained by the volume of the
container (cm3
) gives the soil bulk density value (g cm-3
).
Figure 11 illustrates a typical bulk density sampler. The construction allows the sample container to be
driven into the soil without undue disturbance or compaction. Compaction increases the mass in a given
volume,which increases the measured bulk density.Accidental compaction during sampling can lead to an
overestimation of bulk density.
Determination of bulk Density (Core Method)
1. Drive the soil core into the ground and remove the intact core. After
collecting, weigh the soil core and report the mass (g) to 2 decimals.
Label the soil core with your group number and place the intact core in
the drying oven.
2. Soil core samplers are 10 cm in diameter and 10 cm high. Calculate
the volume of the soil core sampler using the equation: V = π r2
h,
where V = volume (cm3), r = the radius ofthe core sampler (cm) and h
is the height of the core sampler (cm). Record the volume of the soil
sampler.
3. Remove soil core from the drying oven and weigh. Report this value
(in g) to 2 decimal places.
4. Remove the soil from the core sampler and clean the container. Do
not discard the soil; store the soil in the provided container labeled
with the soil information and your lab group name.
5. For each soil,weigh the soil core sampler.Reportthis value (in g) to 2
decimal places in Table 2.
6. Determine the mass (or weight) of the oven-dry soil by subtracting the
weightof the core sampler (line 4) from the weightof the core sampler
+ dry soil (line 3). Record the weight of the oven dry soil (g) to 2
7. Calculate the bulk density of your samples (Db = M/V) and record the value in Table 1.
8. Determine the mass (or weight) of the moist soil by subtracting the weight of the core sampler (line 4)
from the weight of the moist soil + core sampler (line 1). Record the weight of the moist soil (g) to 2
9. Using the weight of the moist sample and oven-dry sample, calculate the amount of water that was
removed by drying.
Figure 10. The relationship between soil bulk density and porosity.
Figure 11. Soil bulk density
sampler

10
Particle Density and Porosity
In the examples and procedures here,the porosityis calculated for the soil thatwas used in the bulk density
exercise.
1. Obtain a clean, dry 100 mL volumetric flask. Weigh the flask and record the weight in Table 3.
2. Using a funnel, carefully fill the flask with water to the line indicated. Dry the outside of the flask. Weigh
the flask plus water and record the weight in Table 3.
3. Determine the weight of the water by subtracting the weight of the flask + water from the weight of the
flask. Record the weight in Table 3.
4. Empty the flask and dry the outside.
5. Carefully add 25 g of soil provided to the flask. Fill the flask approximately½ way and swirl the contents
gently to remove air bubbles.
6. Slowly add water to the flask and soil to the line indicated. Dry the outside of the flask. Weigh and
record the mass of soil, water, and flask and record the mass in Table 3.
7. Determine the weight of the water in the flask containing soil by subtracting the weight of the soil from
the weight of the flask + water + soil. Record the weight in Table 3.
8. Record the difference in the weightof water in the flask with and withoutsoil. Record this value in Table
2.
9. Determine the volume of water that was displaced by the sand. (Use the conversion 1 g water = 1 cm 3
of water.) This value represents the volume of soil solids. Record this volume in Table 3.
10. Calculate the particle density (Dρ) of the soil using the formula: Dρ = mass of dry soil/volume of soil
solids. Record this value in Table 3.
11. Calculate the porosity of the sample using the formula: Porosity (%) = 1 – (Db/ Dρ). Record the porosity
in Table 1. (Use the Db values you calculated using the core method to calculate porosity.)
Table 2. Soil Bulk Density– Core Method
Soil Bulk DensityParameter Soil sample
1. Weight of moistsoil + core sampler
2. Volume of soil
3. Weight of dry soil + container
4. Weight of soil core sampler
5. Dry weightof soil (3-4)
6. Soil bulk density
7. Weight of moistsoil (1-4)
8. Weight of water removed (7-5)
Table 3. Soil Particle Density and Porosity
Soil Parameter Soil 1 Soil 2
1. Weight of flask
2. Weight of flask + water
3. Weight of water (2-1)
4. Weight of soil
5. Weight of flask + water + soil
6. Weight of water (5-4)
7. Difference in mass ofwater (3-6)
8. Volume of soil solids (= volume of water displaced by

11
soil).1 g = 1 cm3
9. Particle density(Dρ) of soil
10. Bulk density(Db) of soil (From Table 1)
11. Porosity
References / Suggested readings
Angelakis,A.N., Kadir,T.N. and Rolston,D.E. 1993.Time-dependentsoil-water Distribution under a Circular
Trickle Source. Water Resources Management. 7:225-235.
Ben-Asher J, Charach CH, Zemel A. 1986. Infiltration and water extraction from trickle irrigation source: the
effective hemisphere model. Soil Science Society of America Journal 50: 882–887.
Brady, N.C. and R.R. Weil. 2008 The nature and properties of soil (14th
Ed.). Prentice Hall. Upper Saddle
River, N.J., Chapter 4.
Cote, C. M., K. L. Bristow, P. B. Charlesworth, F. J. Cook, and P. J. Thorburn. (2003). Analysis of soil
wetting and solute transport in subsurface trickle irrigation. Irrigation Science. 22: 143-156.
FAO (2014) initiative brings global land cover data under one roof for the first time.
http://www.fao.org/news/story/en/item/216144/icode/
Li, Jiusheng, Yoder, R.E., Odhiambo, L.O. and Zhang, J. 2004. Simulation of nitrate distribution under drip
irrigation using artificial neural networks. Irrigation Science. 23: 29-37.
Lubana, Prit Pal Singh and Narda, N. K. 2001. SW-Soil and Water:Modelling Soil Water Dynamics under
Trickle Emitters - A Review. Biosystems Engineering. 78 (3):217-232.
Mmolawa, Khumoetsile and Or, Dani. 2003. Experimental and Numerical Evaluation of Analytical Volume
Balance Model for Soil Water Dynamics under Drip Irrigation Soil Science Society of America Journal.
67 (6):1657-1671.
Nehra,V.S., Singh,Jaspal and Tyagi, N.K. 1991. Simulation ofsoil moisture distribution pattern under trickle
source through analytical approach, Ind. Jr. of Power and River valley Development, 41(1); 12-16.
Provenzano, G. 2007.Using HYDRUS-2D Simulation Model to Evaluate Wetted Soil Volume in Subsurface
Drip Irrigation Systems. Journal of Irrigation and Drainage Engineering 133: 342-349.
Singer,M.J. and D.N. Munns. 2006.Soils:An Introduction (6th Ed.). Pearsons Prentice Hall,N.J., Chapters 2
and 3.
Soil Science Society of America. 2010. Glossary of soil science terms. SSSA. Madison, WI. Available at:
https://www.soils.org/publications/soils-glossary
Villasmil, Y. 2014. The Soil. Republica de Venezuela. Santiago. CI 20.832.723
Harris WG. 2014. Handy Reference Material. Soil and Water Science Department, University of Florida, PO
Box 110290, Gainesville, FL, USA 32611http://wgharris.ifas.ufl.edu/SEED/10yr.jpg

Week 4: Important soil physical properties

More Related Content

What's hot

Similar to Week 4: Important soil physical properties

More from Suyog Khose

Recently uploaded

Week 4: Important soil physical properties