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SOIL COMPACTION

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Progressive Agriculture: Recent Trends and Innovation

CHAPTER-10

SOIL COMPACTION
Abhishek Patel1*, Mohit kumar2, Rohit Nalawade1, Aman
Mahore1, Avesh Kumar Singh3
1
Division of Agricultural Engineering, ICAR-CIAE, Bhopal, India
2
Division of Agricultural Engineering, ICAR-IARI, New Delhi, India
3
Department of Farm machinery & Power Engineering, PAU Ludhiana, India
*Email: abhishekpatel2910@gmail.com

Abstract

Soil compaction is an important physical limiting factor for root

emergence and the growth of plants. Soil compaction has been recognized as a
severe problem in mechanized agriculture and has an influence on many soil
properties and processes. As a result, it's critical to keep soil compaction under
control throughout the growing season, which is usually exacerbated by heavy
traffic in fields. Soil compaction is typically measured using regular cone
penetrometers, which come in a variety of designs. In most cases, particularly in
heavy soil conditions, measuring soil compaction with a standard hand operated
cone penetrometer is sufficient. There is measurement errors occur when the
penetrometer's cone cannot be pushed into the soil at a consistent rate. The main
objective of this chapter is to provide the information related to the soil
compaction and their types with its causes, diagnosis and prevention. It also
includes about the standard size of cone penetrometer rod which is used to
determine cone index as per the standards. The impact of compaction on soil and
plant properties, as well as the various relationships between shape size and
penetration resistance, are also discussed in this chapter. It includes a variety of
cone penetrometers, including hand-held, optical, and tractor-mounted, each with
its own set of functional and operational parameters for use in the field.

Keywords: Soil compaction, Causes, management, cone penetrometer,

penetration resistance

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Progressive Agriculture: Recent Trends and Innovation

Soil compaction is soil particle trapping into a smaller amount, thereby

reducing the pore space between water and air. Figure 1 shows the arrangement of
soil particles of compacted and non-compacted soil. The majority of the soils
consist of approximately 50% solids (organic matter, clay, sand and silt) and 50%
pore space. (McKenzie 2010).

Fig.1. Arrangement of Compacted and Non-Compacted soil particle

In India, the total geographical area is 328.7 million hectares, the gross
cropped area is 198.36 million hectareswith a cropping intensity of 141.5 per cent.
Out of which 140.13 million hectare is net sown area. The net irrigated area is
68.38 million hectares. Punjab has total geographical area of 5.03 million hectare
in which 4.1millionhectares area is under cultivation. The gross cropped area is
7.86 million hectares with cropping intensity of 190.8 per cent (Anon 2018).

Fig.2. Worldwide compaction level Source: FAO (2016)

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Progressive Agriculture: Recent Trends and Innovation

The primary cause for the high cropping intensity is intensive farming.
Crop intensive farming has expanded around the world, involving the use of
heavier machinery and reduced crop rotations, resulting in increased soil
compaction (Poesse 1992). The following are the major compaction processes:
The soil compaction is takes place in three processes are explained below:

Compression: It is the compacting of soil particles by comparatively vertical

forces, such as those seen under wheels or animal feet.

Shearing: It is the deformation of the soil mass caused by competing horizontal

forces such as spinning and slipping tractor wheels or hooves, as well as
equipment like ploughs.

Smearing: It is the process of realigning soil particles in a thin layer under the
base of mould board ploughs and revolving wheels from a random to a parallel
orientation.

Classification of Soil Compaction based on Penetration Resistance

The United States Department of Agriculture has classified the compaction

in various classes based on the penetration resistance of soil (Table 1). The classes
of soil compaction are as follow as:

Table1 Classification of soil compaction based on penetration resistance

Soil compaction class Penetration resistance (MPa)

Small < 0.10
Extremely low < 0.01
Very low 0.01 – 0.10
Intermediate 0.10 – 2.00
Low 0.10 – 1.00
Moderate 1.00 – 2.00
Large > 2.00
High 2.00 – 4.00
Very high 4.00 – 8.00
Extremely high > 8.00
(Source: USDA 1993)

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Stress on Soil by Various Power Sources

The stress acting on the soil by various power sources while performing
different agriculture operations are such as(The Science of Soil 2015):
Horses and cows: - 0.16-0.39MPa
Sheep/humans: - 0.06-0.10MPa
Small tractors: - 0.03-0.10MPa
Large tractors (2-axle): - 0.1-0.2MPa

Why Compaction is a Problem?

Soil compaction is an important physical limiting factor for the root growth
and plant emergence, decreasing crop production worldwide (Hummel et al 2004).
Soil compaction may significantly weaken the production capacity of soil by
reducing porosity, creating obstacles to air, water, nutrient movements and root
penetration (Raper 2001).Extreme soil compaction has negative impact on
agriculture and soil environment.It reduces pore size, increases the proportion of
water-filled pore space in the soil, and lowers soil temperature at field moisture.
Therefore, it reduces the rate of decomposition of soil organic matter and the
resulting release of nutrients, which influences the activity of soil microorganisms.
Compaction reduces infiltration, which leads to more runoff and the risk of
erosion.

Types of Soil Compaction

The soil compaction divided into two categories i.e., surface and
subsurface soil compaction. The detail cause and diagnosis are explained in detail
are as follow as:

1. Surface Compaction

This occurs when the surface soil or upper layer of soil is compacted. The
surface soil compaction occurs at the depth up to 15cm which is represent in
figure 3. This is mainly caused by the Compaction due to various field preparation
operations such as levelling of field, primary and secondary tillage. It may also
cause due to splash erosion or impact created on soil due to irrigation water.

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Fig.3 Surface Compaction

Causes

Soil tillage can destroy the granular structure of surface soils by burying
most of the protective soil residue cover (breaking or crushing of larger soil
aggregates). Splash erosion due to rainfall drops and impact energy of irrigation
water rainfall or irrigation may degrade and break down soil aggregates, allowing
soil particles to become trapped in water, flow together, and dry into a hard layer
soil crust. The germination of plants may also be limited by soil crust.

Assessment

Crusted soils can be managed easily by simply assessing the soil surface
check to see how the soil aggregates have broken down and formed a hard soil
crust. A plate like horizontal layered structure can be seen in the soil crust when
examined visually. If a crust forms after seeding and germinating seedlings and
that are unable to break through the surface soil crust indicates that soil is
compacted. This compaction is surface soil compaction. Therefore, the plant
population would be significantly reduced, lowering plant stand and crop yield
capacity.

Management

After seeding, a short-term remedy for soil crushing can be a little

harrowing or rolling with packers to gently crack the crust and to support seedling
emergence through crust. The crusting of the surface soil results from the exposure
of bare soil to splash erosion or irrigation water impact.

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The easiest way to avoid soil crusting in fields is to reduce tillage and
leave a protective coating of residue on the soil surface to withstand the effect of
water droplets until they strike and break down solid soil aggregates. Reduced
tillage and direct seeding activities can help in achieving these two objectives. To
decrease soil crusting and raise soil organic matter levels, these strategies leave
more residue on the soil surface, resulting in healthy surface soil structure. Crop
management strategies such as using forage in the crop rotation or increasing soil
organic matter levels by direct seeding would help in the growth of a healthy
granular-structured soil with greater resistance to breakdown. In irrigated areas, it
is also important to keep water application under control to avoid exceeding the
soil infiltration rate.

2. Subsurface Compaction

This type of soil compaction occurs at the sub surface level of soil having
depth more than 15 cm which is shown in fig 4. it is mainly caused due to
continuous operation of tillage tools to the surface soil so the sub surface soil gets
compacted and hard pans are created below surface soil.

Causes

A tillage-induced compaction layer, also known as a "hardpan" or "plough

pan," develops in the soil layer underneath the tillage level. It is due to repeated
cultivation of soil at same depth. The weight of tillage equipment such as discs or
cultivator shovels may cause soil compression and smearing at the point of contact
between the soil and the tillage implement. The thickness of soil compaction layer
is generally 2 to 3cm.

Fig.4Subsurface compaction and a graph plotted for cone index reading

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Compaction increases when soil has higher moisture content during tillage
operation or if silt and clay content is higher in the soil. In severe situations, the
compaction can affect significantly so that infiltration of water and movement of
root inside the soil get restricted. Whereas, in coarser textured soils the hardpan
seems to be weaker and friable so does not have effect on the productivity of crop.

Compaction at the
base of tillage tool

Fig.5 Compaction created by implement

Assessment

The presence of a hardpan can be measured by carefully shaving the

surface soil that has been tilled up to depth of the tillage, until the top layer of the
hardpan is seen, with the help of a shovel or trowel. The hardpan can be visually
inspected if the roots of plants are expanding horizontally over the hardpan's
surface, which is a positive indication that roots are having trouble in passing
through the hardpan as shown in fig.5(McKenzie 2010).

Management

The sub surface compaction can be managed by breaking the hard pans
using a heavy-duty cultivator with spikes or subsoiler that reach just below the
hardpan in the comparatively dry soil. This tillage can mostly be done in the fall
while the soils are dry; however, careful caution must be taken to keep residue on
the soil surface, to avoid soil erosion and to avoid mixing subsoil with surface soil.
To prevent the formation of a tillage-induced hardpan, land should be direct
seeded so the tillage is minimized. In case where tillage is necessary carful action
is needed such that soil should not too moist since this can result in tillage induced
compaction. In addition to it, for cultivated soils, the formation of hardpan can be

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reduced by adjusting the depth and direction of tillage for each cultivation. For
land seeded to row or root crops, where tillage is required, soils should not be
worked when wet. Soils should not be worked when wet for root and row crops
where tillage is needed.

Factors Affecting Compaction

The soil compaction is affected by various factors some of are as follow as

(Quality and Sheet 1998):

(i) Compactive Effort

In modern construction projects, heavy compaction machinery is deployed

to provide compaction energy. Types of machinery required are decided based on
type of soil to be 2 compacted. The method of compaction is primarily of four
types such as kneading, static, dynamic or impact and vibratory compaction.
Different type of action is effective in different type of soils such as for cohesive
soils; sheeps foot rollers or pneumatic rollers provide the kneading action. Heavy
compaction machineries are used in modern construction projects to provide
compaction energy. The type of machinery needed is determined by the type of
soil to be compacted. Rigid, kneading, vibratory and dynamic compaction are the
most common methods of compaction. Various kinds of action are useful in
different soil types, such as kneading action provided by sheeps foot rollers or
pneumatic rollers in cohesive soils. Compaction of silty soils can be accomplished
with pneumatic rollers or a smooth wheel roller. Vibratory rollers are the most
powerful for compacting sandy and gravelly soil. Smooth wheel and pneumatic
rollers can also be used on granular soils with some fines.

(ii) Moisture Content

Proper regulation of moisture content of the soil is essential for

accomplishing the desired density. Maximum density with minimal compacting
effort can be attained by compacting soil at its OMC (Optimum Moisture
Content). If the moisture content of the soil is less than OMC, a measured quantity
of water can be applied to the soil using a sprinkler connected to a water tanker
and mixed in with the soil using a motor grader to achieve a consistent moisture
content. When moisture content of the soil is more than OMC, aeration is done to
get it up to OMC.

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(iii) Soil Type

The compaction characteristics of a soil are greatly influenced by its type.

Heavy clays, clays, and silt are typically more resistant to compaction, while
sandy soils and coarse-grained or gravelly soils are more compaction-friendly. In
contrast to clays, coarse-grained soils provide higher densities. It is possible to
compress a well-graded soil to a higher density.

(iv) Layer thickness

To achieve uniform thickness, each layer of soil must be of a suitable

thickness. The thickness of layer depends on soil type used, roller type, and weight
of roller and the contact pressure of its drums. In most cases, a layer thickness of
200-300 mm is ideal for achieving homogeneous compaction in the region.

(v) Contact Pressure

The contact pressure depends on the weight and contact area of the roller
wheel. For pneumatic roller, the contact pressure is determined by the tyre (tier)
inflation pressure as well as the tyre load. Higher contact pressure increases dry
density and decreases optimal moisture content.

(vi) Number of Roller Passes

The density of the soil raises as the number of roller passes increases, but
after a certain number of passes, any more increase in density is negligible for
additional number of passes. A field trial is necessary to determine the optimum
number of passes for a specific type of roller and optimum layer thickness at pre-
determined moisture content.

(vii) Speed of Rolling

The speed at which the rollers are rolled has a significant impact on the
roller performance. Higher the speed of rolling the longer the length of
embankment that can be compacted in single day, since the frequency of
vibrations per minute is unrelated to the forward motion of vibratory rollers, speed
was discovered to be a significant factor. As a result, the slower the travel speed,
the more vibrations at a given point and the less passes needed to achieve a given
density (Ministry of Railways 2005).

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Soil Compaction Measurement

Measurement of soil compaction is important to make correct management

of soil based on the compaction level. Soil compaction can be measured with the
help of cone penetrometer. The cone penetrometers are available in various variety
such as hand operated, tractor operated and automation based are described in
detail in this section.

Cone Penetrometer

The penetrometer is a good tool for determining soil penetration resistance

(SPR) values. A penetrometer consists a rod with a cone tip on one end (Lowery
and Morrison 2002). The cone diameter, cone angle, roughness, and
penetrometer's penetration rateare all important variables in determining SPR
values (Bradford 1986). Compaction is usually a problem in the top 24 inches of
the soil. Measuring penetration resistance using a commercially available cone
penetrometer and measuring soil bulk density using other instruments are two
quantitative methods for detecting compaction.

When calculating bulk density, the texture of the soil must be taken into
account. For soils with a large percentage of clay, a bulk density of 1.50 g/cc is
root limiting, however sandy soils are not root limiting up to bulk density of
1.85g/cc (Muckel2004). The moisture content of the soil has a major effect on
penetrometer readings. Data must be analyzed in terms of moisture content and
penetrometer type, with special emphasis paid to the size and shape of the
penetrometer tip.

The penetration resistance recorded is affected by a number of parameters

i.e., size and shape of cone, the rate at which penetrometer is inserted into soil, and
the surface roughness. As a result, the American Society of Agricultural and
Biological Engineers has set standards for soil cone penetrometer testing for both
uniformity in testing and ease in interpreting the data.

The standard diameter suggested for determining SPR values in manually

operated cone penetrometer is 20.27 mm in soils with SPR values less than 2 MPa
(soft soils) and 12.83 mm in places with SPR values up to 5 MPa (hard soils)
(ASABE, 2006b). The maximum permitted wear in comparison to the standard
cone diameter is 3%.

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Standards of Soil Cone Penetrometer at 30⁰ Cone Angle shown in fig. 6

(ASABE standard S313.2)

1. Base area of cone 323 mm2 and 20.27mm base diameter with a 15.88mm
diameter probe for soft soil.
2. Base area of cone 130 mm2 and 12.83 mm base diameter with a 9.53 mm
diameter probe for hard soil.

Maximum force (N) = cone index (N⁄mm2 )× base area of cone (mm2 )

Hand Operated Manual Cone Penetrometer

A hand operated cone penetrometer was developed by the Waterways

Experiment Station in 1948 to assess off-road vehicle mobility. The penetrometer
had a circular cone with an apex angle of 30° and a base area of 1.61 cm2. It was
mounted on a graduated shaft with a diameter of 0.95 cm and a length of 91.4 cm.
On the top of the shaft was a proving ring with a dial scale to show penetration
resistance and a handle. The dial gauge was calibrated to measure soil resistance
in terms of force per unit area, or cone index, using the proving ring. In 1954,
WES standardization a cone penetrometer with 3.23 cm2 for field application
(Okello 1991). When conducting penetration tests, the dial indicator is initially set
to zero. Dial gauge readings are taken at every 2.5 cm penetration of the rod as the
penetrometer is pressed into the soil. A constant rate of 30mm/s should be used to
press the cone into the soil.

Fig.6 Standard size of cone penetrometer

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Progressive Agriculture: Recent Trends and Innovation

Hand Operated Recording Cone Penetrometer

An electronic hand-operated recording penetrometer was developed by

Prather et al., in 1970. A cone having base area of 0.2square inch and cone angle
of 300 was used. The cone and shaft were attached to a load cell that was placed in
a rigid housing linked to the handle to determine the force. An unbounded strain
gauge load cell having capacity of 200 pound and a total displacement of 0.12 mm
was used to measure the force, and the output signal was proportional to the
applied forceon the cone with respect to handle of the penetrometer. For
recording, a simple two-bar X-Y recorder is used. A servo motor was used to drive
and stabilize the axes.

Thereafter another cone penetrometer was developed by Hendrick (1969).

It was comprising of two components i.e., force and depth measuring component.
The relative movement of the penetrometer shaft and foot-plate shaft as the tip
was thrust into the soil provided depth measurement. A 300angle cone with a base
area of 1.29 cm2 used as the penetrometer tip.

Tractor Operated Cone Penetrometer

A Tractor mounted multiple probe soil cone penetrometer (MPSCP) was

developed by Raperet al (2001), to find out the strength of soil profiles across the
row quickly and efficiently. The cone penetrometer probe tip and shaft were
designed according to ASAE (American Society of Agricultural Engineers)
standard (ASAE, 1998). For design there were two sizes available for use;
diameter of conical base was 20.27mm and diameter of shaft was 15.88-mm for
softy soils and the diameter of conical base is 12.83mm with the diameter of shaft
is 9.53mm for hardy soils.

It was hydraulically regulated and movement in row spacing’s of up to 1.2

m to found the cone index they mounted five probes across the row. Ordinary
depths and length of probe had been 0.91 m or 0.76 m with the structure having a
limitation of marginally more than 1m. They used Lebow type of load cells and
had a maximum capacity of 226 kg. Cone index was measured by each load cells
and its maximum capacity of approximately 7 MPa, which was hardpan of soil.
Flow chart of tractor operated soil cone penetrometer is shown in fig. 7.

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Progressive Agriculture: Recent Trends and Innovation

Fig.7 Flow chart of tractor operated cone penetrometer

Microcomputer Based Cone Penetrometer

A microcomputer-based, tractor hydraulic operated cone penetrometer was

developed by Williford et al., (1972). The hydraulic cylinder was used to insert
penetrometer into the soil. Penetration data was recorded in x-y graph and
comprising of force and depth relationship at any point across three,one-meter
rows. Two men were required to collect data for their designed penetrometer. The
data was automatically recorded in the microcomputer in excel format. Similar
kind of cone penetrometer was developed by Wilkerson et al (1982). It was
designed to work up to depth of 61cm over a 4-row width.To actuate all moving
mechanisms and automatically record the data on a magnetic tape, a
microprocessor-based control unit was used shown in fig.9.

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Progressive Agriculture: Recent Trends and Innovation

A B C
Fig.8 (a) Ring type (b) Digital type (c) Tractor operated type cone
penetrometer

Fig.9 Operating panel and controls of digital type penetrometer

Relation of Cone Parameters with Penetration Resistance

The cone penetration resistance varies with various cone parameters such
as shape and size of cone, cone angle and penetration rate. The relationship of
these parameters with the penetration and resistance are covered in this section.

1. Relationship between Cone Diameter, Base Area and Penetration

Resistance

The shape and size of the cone will influence the determination of SPR
values in undisturbed soil samples. The insertion of the penetration rod in

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undisturbed soil samples obtained in rigid cylinders facilitates soil containment on

the cylinder walls, which may change the SPR values (Bengough and Mullins
1990). As a result, measurements of the maximum cone diameter in contrast to the
diameter of undisturbed samples should be observed to prevent overestimation of
SPR values. The soil confinement caused by the cone insertion has an impact on
SPR values, particularly in clay-rich soils. This confinement effect is lower in
compressible soils (low density), since a small quantity of soil can support both
rod and penetration cone volumes (Bengough and Mullins 1990). Furthermore, the
existence of structural discontinuities (root or biological pores) as well as pieces of
materials with varying compressive properties (stones) favors variations in SPR
values (Misra and Li 1996). This confinement effect is lower in compressible soils
(low density), since a small quantity of soil can support both rod and penetration
cone volumes (Bengough and Mullins 1990). Furthermore, the existence of
structural discontinuities (root or biological pores) as well as pieces of materials
with varying compressive properties (stones) favors variations in SPR values
(Misra and Li 1996). To solve these problems, the gap between the SPR values
measuring position and the structural discontinuity must be at least eight times
greater than the cone diameter (Misra and Li 1996). As a result, if a cone with a
diameter of 4 mm is used, the undisturbed soil sample should have a diameter of at
least 32 mm. In this case, it's important to use the proper cone diameter in
undisturbed soil samples in order to obtain accurate SPR values.

Most agricultural penetrometers have cone diameters ranging from 2.15

mm in laboratory equipment (Mihra and Li 1996) to 20.27 mm in field versions
(ASABE, 2006b). Penetration rods with a needle-like diameter (0.5-1.0 mm) may
also be used (Schimitd et al 2013). In this way, the cone is a source of SPR
variance since different basal areas and angles exist based on the model (Torres
and Saraiva 1999).

2. Relationship between Cone Angle and Penetration Resistance

Penetrometers used to obtain SPR values in agriculture have different cone

angles that, most commonly, vary from 30º to 60º (Serafimet al 2008). The
ASABE standards (ASABE, 2006b) for the use of penetrometers determine that
the cone angle must be 30º. This standardization is due to the fact that SPR values
depend on the cone angle (Bradford 1986). The cone angles of 30º determine the
lowest SPR values in relation to either greater or lower angles.

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Penetrometers used in agriculture to determine SPR values have varying

cone angles, which most usually range from 300 to 600 (Serafim et al 2008). The
cone angle must be 30o according to the ASABE criteria (ASABE, 2006b) for the
use of penetrometers. Since SPR values are influenced by cone angle, this
standardization is essential (Bradford 1986). The lowest SPR values are
determined by cone angles of 300 in comparison to greater or lesser angles.
Whereas, Cone angles of 600, in combination with smaller diameters
(approximately 4 mm), produced better correlation with root growth of plant
(Serafim et al 2008). The values of SPR in undisturbed soil samples are measured
using bench top penetrometers (Tormena et al 1998). Moreover, the use of cones
suggested by is impractical due to the limited amount of soil samples typically
used cylinders of 5 cm diameter and 5 cm height.Therefore, in undisturbed soil
samples to measure SPR values the cone with base area of about 5 cm, must be
standardized and measuredwith the help of penetrometers having cone of 4 mm
diameter and angle of 60º angle (Tormenaet al 1998).

3. Relationship between Penetration Rate and Penetration Resistance

The impact of water movement across soil pores, favours variations in SPR
values, hence an acceptable value for the penetration rate in a soil with high
moisture content is critical (Bengough and Mullins 1991). Due to non-uniformity
among the adopted penetration rates is an issue that is frequently encountered
when comparing multiple studies in the literature. However, it is well understood
that establishing a penetration rate that can be used under all conditions is difficult
because rate increases can boost, decrease, or have no effect on SPR values,
depending on the soil properties and moisture conditions of the profile (Bradford
1986).

The ASABE, by means of the EP542 standard, describes technical

standards for the achievement of SPR values with cone penetrometers (ASABE,
2006b). This standard indicates, as the penetration rate limit, the uniform value of
30 mm s-1, with readings at depth intervals of less than 0.05 m. However, for field
readings, the best results have been obtained with the use of rates of less than 8.3
mm s-1(Lowery and Morrison 2002).

The ASABE defines specifications for achieving SPR values with cone
penetrometers via the EP542 standard (ASABE, 2006b). This specification
specifies a standardized value of 30 mm/s uniform penetration rate, at depth of
less than 0.05 m. Whereas, for field readings, lower rates of less than 8.3 mm s-1

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have yielded the best results (Lowery and Morrison 2002). According to Torres
and Saraiva (1999), the higher the insertion rate is, the lower the recorded SPR
values are. This same evidence was obtained by Kim et al (2008), In this sense,
impact penetrometers and/or penetrometers of constant penetration rate tend to
minimize this problem (Torres and Saraiva 1999). At higher insertion rate, less
SPR values were obtained, according to Torres and Saraiva (1999). In this context,
impact penetrometers or constant penetration rate penetrometers appear to mitigate
this problem, according to Kim et al (2008). (Torres and Saraiva 1999).

Effect of Soil Compaction on Soil and Crop Properties

Soil compaction is greatly influencing soil and their properties. The effect
of soil compaction on various soil and parameters are explained through the flow
chart shown in fig 10.

Fig.10 Flow chart of effect of soil compaction on soil and plant properties

(a) Soil Properties

The oven dry mass of soil per unit volume is referred to as bulk density.
Increased soil macro aggregates and porosity characterize good soil structures.

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Progressive Agriculture: Recent Trends and Innovation

Since compacting forces compress the volume of soil by removing pore spaces,
the bulk density rises with increased soil compaction. High penetration resistance,
reduction in infiltration rate, greater runoff, and more soil erosion are all possible
consequences of increased bulk density due to compaction. Soil compaction
results in a substantial reduction in soil porosity and aeration, as well as stunted
root growth and poor root proliferation. The reduction of soil macropores caused
by compaction resulted in the creation of anoxia conditions, which hampered crop
growth and development.

(b) Plant Properties

The consequences of soil compaction include restricted root growth,

decreased nutrient accessibility, runoff, increased nutrient loss by leaching, and
gaseous losses to the environment which may have an impact on plant growth.

Table 2. Bulk density of different soil texture(Quality and Sheet 1998)

Texture Bulk Density (g/cc)

Coarse, medium, and fine sand and loamy sands 1.80
other than loamy very fine sand
Very fine sand, loamy very fine sand 1.77
Sandy loams 1.75
Loam, sandy clay loam 1.70
Clay loam 1.65
Sandy clay 1.60
Silt, silt loam 1.55
Silty clay loam 1.50
Silty clay 1.45
Clay 1.40

The soil is sorrow from other types of degradation such as the salinity,
drastic belongings of the soil compaction on the plant growth and crop. It also
effects on seedling emergence, plant roots and plant shoots. Other forms of
erosion are wreaking havoc on the soil, such as salinity and the drastic effects of
soil compaction on plant growth and yield (Fig.11). Seedling germination, plant
shoots and plant roots are also affected by soil compaction.

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Fig.11 Effect of soil compaction on crop yield

Causes of Soil Compaction

Most field operations in modern agriculture, from sowing to harvesting,

are performed mechanically, with heavy wheeled machines that compress the soil
at each pass.Generally, the soil compaction by a machine is determined by the soil
strength and the machine's load. The moisture content, organic matter, texture and
soil composition all these parameters influence soil strength, whereas loading is
influenced by number of tyres, axle load, tyre dimensions and interaction between
soil and tyre (Thakur R 2010). The more strain applied to the soil, the more likely
it is to become compacted. By increasing the number of machine passages over
the soil which shows the results of increasing dry bulk density and cone index
under the surface soil compaction with the reduction seed germination.However,
the first or early passages of the machineries are responsible for a large portion of
overall soil compaction, and 10 passes may impact soil up to a depth of the 50 cm.
Soil compaction and degradation can be caused by animal trampling.

The soil compaction caused by grazing animals through hoof action is

likely to be more widespread within the paddocks as compared to the soil
compaction caused by mechanical implements which is limited under the tracks.
Physical deterioration by grazing animals depends on the trampling intensity, soil
moisture, plant cover, land slope, and land use type. Animal caused the soil
compaction could range from 5 to 20 cm and might affect the soil bulk density,
hydraulic conductivity, macro pore volume, and penetration resistance of the soil.
In comparison to soil compaction caused by mechanical implements, which is

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confined under the tracks, soil compaction due to grazing animals by hoof action
is likely to be more extensive within the paddocks. Soil moisture content,
trampling intensity, ground slope, land use type and plant cover all influence
physical deterioration of soil caused by grazing animals. Soil compaction caused
by animals can vary from 5 to 20 cm and it may affect the bulk density of soil,
macropore volume, penetration resistance and hydraulic conductivity. Harvesting
operations in the forest, in comparison to cultivated fields, induce more soil
compaction due to:

1. Raindrop Impact

This is a natural cause of compaction, and this can be seen as soil crust that
can hinder seedling emergence. This problem is often alleviated by rotary hoeing.

2. Heavy Machinery

Heavy agricultural machinery results in more permanent damage to the soil

than previously believed by researchers. This may lead to poorer crop yields and
increased pollution. (The Research Council of Norway. (2011).

3. Tillage Operations

In certain soils, continuous mold board ploughing or disking at the same

depth can result in tillage pans (compacted layers) just below the tillage depth.
This tillage pan is usually thin (1 to 2 inches), has no impact on crop yield, and
can be mitigated by adjusting tillage depth over time or using special tillage
operations.

4. Wheel Traffic

Without a doubt, wheel traffic is the leading cause of soil compaction.

With the scale of the farm growing, there is only a finite amount of time to
complete these tasks. The weight of large four-wheel-drive tractors has risen from
less than three tonnes in the 1940s to about 20 tonnes today. This is especially
concerning since spring planting is often carried out before the soil has dried
enough to accommodate the heavy planting machinery.

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5. Minimal Crop Rotation

The trend towards a limited crop rotation has had two effects(Thakur R
2010):
• Limiting various rooting processes and their beneficial impact on breaking
subsoil compaction
• Due to more tillage operation and field traffic early in the cropping season,
there is a greater risk of compaction.

The most extreme soil compaction is exacerbated by machine-assisted

thinning and clear-felling operations, which can compress the soil to a depth of 60
cm and last for more than three years. The use of light-weight multi-function
machines can help in minimizing passages and, as a result, decrease in soil
deterioration. Natural causes of soil compaction (precipitation, tree roots, seasonal
cycles etc.) are not as damaging as anthropogenic causes: natural causes of soil
compaction are restricted to the top 5 cm of the soil, while urban pressure and
trampling on a site can compress the soil up to 20 cm and mechanical activities
can compact the soil to a depth of 60 cm.

Best Management Practices to Prevent Soil Compaction

The suggestive measures to reduce soil compaction are as follow as:

1. Controlled Traffic

Generally, more than 90% of the areas of field are tracked by machineries
and equipment in a normal year. Controlled traffic is based on the idea of limiting
the amount of soil travelled through using the same wheel tracks, controlled and
uncontrolled traffic shown in fig. 12. On the first pass across the field, 70 to 90
percent of the plough layer compaction happens. The tracked field would have a
slightly deeper compaction as a result of traffic management, but the surface
between the tracks will not be compacted (Hughes 2018).

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Progressive Agriculture: Recent Trends and Innovation

Fig.12 Field coverage by normal annual field operations and controlled

traffic situation

2. Manage Axle Loads and Tyres Pressure

Another way to manage compaction is to maintain tyre inflation rates and

reducing axle loads. The depth of compaction can be increased by heavy axle
loads and moist soil conditions. The potential to compact the soil beyond the
tillage layer increases as the load per axle exceeds 10 tonnes.

3. Choose the Right Equipment

Compaction may be caused by any piece of machinery, whether it has

tracks or tyres. Choosing machinery that produces the least amount of compaction
is influenced by a number of factors, such as
• Availability of the land
• Size of the land
• Matching implement
• Tractor size
• Tyre size and their type

Conclusion

Soil compaction is the most severe form of land deterioration that reduces
agricultural production, and given current trends, it is likely to become more

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common. As more and heavier agricultural equipment or animals per unit of land
surface area, increasing the soil compaction. Soil compaction and a decline in soil
fertility have resulted from the strengthening of the farming system, especially in
rainfed/ dryland areas. Soil compaction has a negative impact on soil fertility,
rising soil bulk density, reducing porosity, and increasing soil pressure. It also
decreases the crop production and fertilizer efficiency, create water logging
problem, soil degradation and runoff. The practices include minimum (and zero)
tillage, minimizing traffic, combining more than one farmhouse operation
instantaneously using the same machine to minimize number of passes, traffic,
intensity of grazing and number of animals per grazing for reducing compaction.
By maintaining vegetative soil cover, loosening compacted soil by deep ripping
accompanied and using a rotation which includes deep and strong rooting plants
able to penetrate relatively compacted soils, in this way we can reduce soil
compaction significantly. Cumulative soil organic matter over stubble retention,
green and brown manure, addition of plant/animal organic matter from external
sources is also important in decreasing bulk density of the soil and acting as a
buffer preventing or lessening the transmission of compaction to subsoil from
external loads acting on the earth.

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