Comp Action Final

8/2/2019 Comp Action Final

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SEMINAR-II

CourseNo : 699 Date : 07/07/2011

TopicSOIL COMPACTION- ITS CAUSES, EFFECTS AND REMEDIES

SPEAKER:

ARINDAM SARKAR

CHAIRMAN:

Dr. P.K. BANDYOPADHYAY

SEMINAR LEADER:

Prof. B. MONDAL

Department of Agril. Chemistry & Soil Science

Bidhan Chandra Krishi Viswavidyalaya

Mohanpur, Dist.-Nadia,

West Bengal


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INDEX

1) INTRODUCTION2) DEFINITION OF SOIL COMPACTION3) TYPES OF SOIL COMPACTION4) VISIBLE SYMPTOMS OF SOIL COMPACTION5) PLANT SYMPTOMS OF SOIL COMPACTION6) METHODS OF DETERMINING SOIL COMPACTION7) CAUSES OF SOIL COMPACTION8) EFFECT OF MOISTURE AND AXLE LOAD ON COMPACTION9) EFFECT OF COMPACTION ON SOIL PHYSICAL PROPERTIES10)EFFECT OF COMPACTION ON CROP11)EFFECT OF COMPACTION ON PLANT GROWTH12)SOIL COMPACTION AND EROSION13)TECHNIQUES TO MINIMIZE SOIL COMPACTION14)CONCLUSION15)REFERENCE


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INTRODUCTION

One hundred years ago, Wollny (1898) described the positive effect of a favorable

soil structure on root growth, water availability, gas transport and soil strength. He

stressed that the mechanisms involved in the relationships between soil structure, plant

growth and crop yield should be investigated, not only to achieve higher crop yields

but also to further improve relevant soil properties. At that time, scientists generally

were concerned with research aimed at the optimization of crop yields and they were

not obliged to care about environmental problems. However, even in 1898, it was well

known that, under given environmental conditions, a favorable soil structure results in

consistent crop yields and it was recognized that, under the same conditions, soil

compaction usually will have negative effects on crop growth and/or yield,

Throughout the decades, this knowledge has repeatedly been confirmed by the results

of field experiments on the effects of soil compaction and, sometimes, also causes and

effects of compactive processes were established (Soane and Van Ouwerkerk, 1994).

Besides having intended positive effects, the interference of man with the natural

environment also causes changes which may unfavorably affect both the farm economy

and the environment. These phenomena are recognized as an effect of industrialproduction but they are also considered to be related to agricultural practices, which

embrace incomparably larger areas. At present, increasing attention is being paid to the

factors causing degradation of agricultural areas, including the agricultural activity

itself as a soil degrading factor. The importance of this factor depends mainly on the

type of farming and the intensity of agricultural production, including the level of

fertilization, degree of mechanization, the soil water status during field operations,

tillage and harvesting technologies, etc. (Domial et al., 1992). According to Miller ( 1990)

the maintenance of soil productivity is particularly hampered by water erosion, soil

structure degradation and compaction, phosphorus losses due to runoff from

agricultural areas and the leaching of nitrate compounds and pesticides to the ground

water.


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Soil compaction caused by traffic of heavy vehicles and machinery results in soil

structure deterioration, both in the topsoil and in the subsoil (Slowinska and Domial,

1991a,b). In soil compaction, not only pure static stresses, but also dynamic forces play a

role, caused by vibration of the engine and the attached implements and by wheel slip.Owing to dynamic loading, soil physical properties such as pore size distribution and

pore continuity are negatively affected, which entails decreases in air and water

permeability and results in increased soil strength or, in the presence of excess soil

water, decreased soil strength due to kneading. These changes may have a negative

effect on the soil biota, on physical-chemical equilibria and redox potential, on the soils

filtering and buffering capacity, on ground water recharge and, finally, on crop yield

(Domial and Hodara, 1992; Domial et al., 1992; Horn et al., 1994). Meanwhile,agricultural engineers developed much site-specific machinery but until now they were

not very successful in the prevention or long-lasting repair of compaction-induced soil

degradation.

In order to analyze soil degradation due to soil compaction in detail, the

relationships between internal soil strength and applied stress, the kind and intensity of

stress application and relevant soil parameters must be considered (Horn, 1988).

WHAT IS SOIL COMPACTION?

Soil compaction refers to the compression of unsaturated soil, during which the

density of the soil body increases and there is a simultaneous reduction in fractional air

volume. In other words, the effect of compaction on a soil body is a change in its

structure. That is why soil compaction is often described by the measures of bulk

density, void ratio, or total porosity, parameters that grossly quantify soil structure.

Other parameters used to describe soil compaction include applied force or applied

stress. Soil compaction occurs when soil particles are pressed together, reducing pore

space between them (Figure 1). Heavily compacted soils contain few large pores and

have a reduced rate of both water infiltration and drainage from the compacted layer.

This occurs because large pores are the most effective in moving water through the soil


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when it is saturated. In addition, the exchange of gases slows down in compacted soils,

causing an increase in the likelihood of aeration-related problems. Finally, while soil

compaction increases soil strength-the ability of soil to resist being moved by an applied

force-a compacted soil also means that roots must exert greater force to penetrate thecompacted layer.

Soil compaction changes pore space size, distribution, and soil strength. One way

to quantify the change is by measuring the bulk density. As the pore space is decreased

within a soil, the bulk density is increased. Soils with a higher percentage of clay and

silt, which naturally have more pore space, have a lower bulk density than sandier soils.

FIGURE 1- Effects Of Compaction On Pore Space.

There is an increased concern regarding the effect of compaction on crop

production in mechanized agriculture. Compaction effects on crop yield are due to

changes in soil physical, chemical, and biological processes that in turn are dependent

upon the structure of the soil. To separate beneficial from harmful compaction and to

provide guidelines on the range of applied stresses and water contents not conducive to

excessive compaction, we need to understand and quantify changes in soil structure

upon compaction (Gupta and Allmaras, 1987).


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FIGURE 2- Relationships Between Soil Compaction And Root Health; A Diagrammatic Guide.

SOURCE- Allmaras et al.., 1993.

TYPES OF SOIL COMPACTION:

Generally soil compaction affects the top 24 of the soil . Different types of

compaction may be cited as following-

Surface Crusting restricts seedling emergence and water infiltration, caused by

raindrops on weak soil aggregates. Soils with cover crops or high-residue cover are less

likely to form crusts.

Surface Compaction can occur from surface down to normal tillage depth, and can

be loosened by normal tillage, root growth and biological activity.

Tillage Pan a compacted layer several inches thick beneath the normal tillage depth

and develops when the depth of tillage is the same year after year.

Deep Compaction occurs beneath the level of tillage. Ground contact pressure and

total weight on the tire from the axle load significantly affect the amount of subsoil

compaction. It is difficult to eliminate and may permanently change soil structure.

Inherent Hardpans can form because of variations in soil particle size, consolidationof particles by rainfall, and certain organo-chemical factors. These pans are aggravated

by tillage and traffic.


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WHAT DOES COMPACTION LOOK LIKE?

Recent construction sites, farm fields, and soils with high clay content are most

commonly affected by compaction. Unfortunately, soil compaction can be difficult to

detect in the landscape because its symptoms can be caused by other site problems.

Some indicators include:

Standing water that implies a drainage problem

Physically dense soil that is hard to dig whether wet or dry (massive and platy like

structures)

Dark streaks in wheel tracks caused by moisture remaining for a longer time above

the compacted zone.

Increased runoff and soil erosion from water that cannot penetrate the soil.

Increased load on engine or need to gear down in portions of the field to maintain

speed.

Uneven plant stands and reduced plant height, especially in wheel tracks.

Difficulty in penetrating the soil with a firm wire (survey flag) or welding rod (18

long).

Soil scientists measure compaction with a device called a soil penetrometer. The

easiest way for a homeowner to test for soil compaction is to plunge a soil probe (or

hollow metal pipe) into the soil. If the probe barely enters, the soil is compacted.

PLANT SYMPTOMS OF COMPACTION

Compacted soils will affect crop production, because compacted soils are an

inferior medium for plant growth. The following symptoms can be caused by disease

and other plant stresses, but compaction is often the culprit.

Slow or poor plant emergence and thin stands can result from compacted soils with

increased strength. Often, the surface structure is broken down and a surface crust

develops. Seedlings have a difficult time penetrating the soil. As a result, root growth

and elongation can be constricted. Generally, this is the result of over-preparation of the

seedbed.


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Uneven early growth in the form of tall and short plants in adjacent rows can suggest

uneven compaction. It also may reflect restricted root growth due to compacted layers

or not enough oxygen for root respiration and soil microorganism activity.

Off-colored leaves may reflect nutrient deficiencies brought on by compacted soil,

restricting root growth, and water movement. Nitrogen starvation is one of the most

common symptoms.

Abnormal rooting patterns can suggest compaction. A shallow, fibrous root system

running horizontally above a compacted layer is a frequent symptom. Roots in

compacted soils are often flattened.

Premature drought stress often indicates a compaction problem. A shallow, restricted

root system cannot utilize stored subsoil moisture or plant nutrients below a compacted

layer.

METHODS O DETERMINING SOIL COMPACTION

There are several methods available when determining soil compaction. Some

possibilities are listed below:

Knife blade penetration when soil is dry. Dig a hole in the suspected area at least two

feet deep. Leave one side of the hole free of shovel marks. Press a knife blade into the

undisturbed side every inch or two, starting at the top. Any difficulty penetrating the

soil is probably evidence of compaction.

Plant rooting patterns. Observe the side of the hole for the location and predominance

of roots at different depths. Look for masses of roots running horizontal and the

absence of roots below certain depths. This is also good evidence of compaction.

Soil sampling tube or steel rod. Simply push the tube into the soil and note resistance.

Penetrometer. This is a pointed steel rod with a gauge that records the pressure

needed to penetrate the soil. It provides specific readings, but requires adjustments for

moisture. Its reading must be carefully interpreted.

WHAT CAUSES SOIL COMPACTION?

There are several forces, natural and man-induced, that compact a soil. This

force can be great, such as from a tractor, combine or tillage implement, or it can come


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from something as small as a raindrop. Listed below are several causes of soil

compaction.

Raindrop Impact - This is certainly a natural cause of compaction, and we see it as a soil

crust (usually less than 1/2 inch thick at the soil surface) that may prevent seedling

emergence. Rotary hoeing can often alleviate this problem.

Tillage Operations - Continuous moldboard plowing or disking at the same depth will

cause serious tillage pans (compacted layers) just below the depth of tillage in some

soils. This tillage pan is generally relatively thin (1-2 inches thick), may not have a

significant effect on crop production, and can be alleviated by varying depth of tillage

over time or by special tillage operations.

Wheel Traffic - This is without a doubt the major cause of soil compaction. With

increasing farm size, the window of time in which to get these operations done in a

timely manner is often limited. The weight of tractors has increased from less than 3

tons in the 1940's to approximately 20 tons today for the big four-wheel-drive units.

This is of special concern because spring planting is often done before the soil is dry

enough to support the heavy planting equipment.

Minimal Crop Rotation - The trend towards a limited crop rotation has had two effects:

1.) Limiting different rooting systems and their beneficial effects on breaking subsoil

compaction, and 2.) Increased potential for compaction early in the cropping season,

due to more tillage activity and field traffic.

FIGURE 3- Reduced Root Growth Due To Compaction From Raindrop Impact, Tillage,

And Wheel Tracks.

SOURCE- Compaction-Soil Management Series 2. University of Minnesota Extension

Service, BU-7400.


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FIGURE 4- Soil Compaction Produced By Primary Tillage Tools In a Long-term Tillage

System And Measured With a Cone Penetromete (after).

SOURCE- Swan et al., 1987.

EFFECT OF SOIL MOISTURE AND AXLE LOAD ON DEPTH OF

COMPACTION

Greater axle loads and wet soil conditions increases the depth of compaction in

the soil profile. Compaction caused by heavy axle loads (greater than 10 tons per axle)

on wet soils can extend to depths of two feet or more (Figure 5 and 6). Since this is well

below the depth of normal tillage, the compaction is more likely to persist compared to

shallow compaction that can be largely removed by tillage.

(Tire pressure remained at 12 psi for all tire sizes) (Tire size 11 x 28, load 1,650 lbs, pressure 12 psi)

FIGURES 5 and 6- Depth Of Compaction As (5) Axle Load And (6) Soil moisture Increases .

SOURCE- Unger et al., 1982.


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Total axle load, as well as contact pressure between the tire and soil, affects

subsoil compaction. Historically, as equipment weight increases, tire size also increases.

This avoids drastic increases in contact pressure (pounds per square inch (psi) of

pressure exerted by the tire on the soil surface).

EFFECT OF SOIL COMPACTION ON SOIL PHYSICAL PROPERTIES

Depending upon the experimental objectives, soil properties in the literature

could be grouped into those describing (1) pore geometry or (2) soil matrix. Scientists

concerned with water, solute, and gas movement have characterized soil structure in

terms of pore geometry, i.e., pore size distribution and pore continuity. Soil

morphologists and scientists working in soil erosion research have concentrated on the

understanding of soil matrix, i.e., aggregate size distribution and aggregate strength.

A. PORE GEOMETRY

Measurements that describe pore geometry include the water retention

characteristic curve, permeability/infiltration rate, soil-water diffusivity, sorptivity, air

permeability, and gas diffusion.

1 . Water Retention Characteristic CurveThe water retention characteristic (WRC) curve is the relationship between the

quantity of water in soil pores to the energy with which this water is held in these

pores. Soil structure greatly affects the water retention characteristics of soils.

Aggregated soils generally retain more water than sands at a given soil matric potential.

In aggregated soils, a large proportion of soil water at high matric potential is in the

voids formed by aggregates, whereas soil at low matric potential is in voids formed by

soil particles. Since soil compaction alters the aggregate size distribution, we expect a

shift in the proportion of inter- and intra-aggregate voids during compaction. Thus, the

shape of the WRC curve is a good indicator of alterations in soil structure or soil pore

geometry due to compaction.As reported by Assouline et al. (1997) for matric potential

100 MPa, the volumetric water content in the compacted soils is somewhat lower and


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can be attributed to the reduced potential of surfaces. Some studies indicated that an

increase in soil compaction results in lower gravimetric water content at high matric

potential range (from 0 to approximately 16 kPa) and higherat low values of the

potentials (from 50 to 1550 kPa) (Walczak, 1977 and Domzal, 1983). Only a slighteffect occurred at the intermediate potential range. These are reflected in flattening of

soil water retention curve (SWRC) and they are indicators that as the proportion of

large pores decreases, the proportion of small pores increases (Van Dijck and Van Asch,

2002). Changes in volumetric water contents at given potentials affect the hydraulic

conductivity.

FIGURE. 7- Relationships Between Suction And Water Content For A Silty Sand At Two

Densities.SOURCE- Croney and Coleman, 1954.

FIGURE 8- Soil Matric Water Potential As A Function Of Days After Planting.

SOURCE- Lipiec et al., 2003.


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TABLE 1- Pore Size Distribution In A Nicollet Clay Loam At Four Levels Of Soil Compaction

SOURCE- Vorhees, 1992.

2. Permeability/Infiltration Rate

Laliberte and Brooks (1967) measured the effect of compaction on permeability of

three soil materials. Relative permeability is defined as the ratio of permeability to

saturated permeability.

A soil at a given bulk density can have several different pore geometries,

depending upon the water content and the applied stresses at the time of compaction.

In addition to these two factors, methods of soil compaction also have important effects

on the changes in soil pore geometry. Davies et al. (1973) measured the effects of normal

applied loads versus wheelslip on infiltration rates in Boxworth clay loam. The

reduction in the infiltration rate was much greater due to wheel slippage than to anincreased load. Decrease in the water entry rate due to wheel slippage is a result of

increased compaction by realignment of particles in an orientation parallel to the

direction of shear forces.

FIGURE 8- Effect Of Soil Compaction On Permeability

SOURCE- Vorhees, 1992.


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3. Saturated Flow

Saturated hydraulic conductivity (Ksat) is often used to characterize the effect of

soil compaction on water flow. A drastic reduction of Ksat with increasing compaction

has been reported in many studies (Dawidowski and Koolen, 1987). The ratio of Ksat orwater infiltration rate of loose and compacted soil range from several (Young and

Voorhees, 1982) to several hundreds (Arvidsson, 1997).

A reduced Ksat will enhance runoff and soil erosion (Fleige and Horn, 2000). The

critical limit for adequate Ksat (as measured with a constant head method) for poorly

drained fine-textured soils in cropping systems was established at 1.0106 m s1

(McQueen and Shepherd, 2002). However, in highly permeable and conducive-to-

leaching sandy soils, reduced Ksat conductivity may improve their water status (Lipiec

et al.,1996) and reduce NO3N leaching losses (Agraval, 1991).

The effect of soil compaction on saturated water flow is largely governed by

larger pores (preferential flow) (Lipiec et al., 1996), which are negatively related to soil

compaction (Carter, 1990). Research indicates that compaction may reduce not only the

volume of macropores but also their continuity.

FIGURE. 9. Percent Of Stained Areal Porosity Relative To Total Area And Number Of Stained

Pores In Horizontal Sections (0.036 m2) In The Silty Loam At Various Tractor-Wheel Traffic.

SOURCE- Lipiec and Hkansson, 2000.


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4. Unsaturated Flow

Unsaturated flow largely affects the dynamic processes of water and solute

movement in the vadose zone. Experimental data relating the effect of soil compaction

on unsaturated flow is very limited. It has been reported (Horton et al., 1994) thathydraulic conductivity, as a function of soil wetness, generally decreases with

compaction; however, at some compaction range and low water potentials, the

conductivity is higher in compacted versus non-compacted soil. Analysis of the

relations between hydraulic conductivity and water ratio indicates the effect of soil

compaction on hydraulic conductivity by increasing the contact surface between

aggregates and by formation of the relict structural pores that do not contribute to

water movement (Richard et al., 1999).

The effect of soil compaction on unsaturated hydraulic conductivity in

undisturbed soil cores can be well characterized using the instantaneous profiles of

moisture and matric potentials in the tensiometric range (Walczak et al., 1996).

Unsaturated hydraulic conductivity, together with root length density, is the

main factor affecting hydraulic resistance in unsaturated compacted soil (Lipiec and

Tarkiewicz, 1988).

5. Soil Water Diffusivity

The soil-water diffusivity versus soil-water content relationship is often needed

to describe non-steady state water movement in soils. Soil-water diffusivity as a soil-

water transmission property reflects the pore size distribution of soil. Jackson (1963)

studied the effect of compaction on the soil-water diffusivity function of various soil

and concluded that high-clay soils showed greater change in soil water diffusivity due

to compaction than low-clay soils like.


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FIGURE 10- Soil-Water Diffusivity Versus Relative Water Content Of Adelanto Loam,

Pachappa Loam, And Pine Silty Clay At Three Bulk Densities. SOURCE- Jackson, 1963.

6. Sorptivity

Sorptivity is a measure of the uptake of water by soil without gravitational

effects (Philip, 1957). Sorptivity values depend upon the structure and the antecedent

water content of the soil. Figures 11 show the changes in sorptivity as influenced by

different levels of applied stress and antecedent soil water contents. Starting from a dry

condition, sorptivity increased with increasing soil water content, reached a peak, and

then decreased. Sorptivity can be a useful index that measures the combined effect of

applied stress and water content on pore geometry.

FIGURE 11- Sorptivity As A Function Of Soil-Water Content At Various Levels Of Applied

Static Pressure.

SOURCE- Walker and Chong, 1986.


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7. Air Permeability And Gas Diffusion

The response of air permeability, being a measure of the ability to transport gas

by convection, to compaction is related to soil structure and pore size and pore

continuity. Air permeability reflects the size and continuity of air filled pores . At the

same level of compactness, air permeability was greater for coarse structure (4 8 mm

peds) compared to fine structure (


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FIGURE 13-Air Permeability Versus Moisture Content For a Ruston Fine Loamy Sand.

SOURCE- Bowen, I966.

B. SOIL MATRIX

Effects of soil compaction on soil solid-solid interaction have been characterizedin terms of aggregate size distribution, aggregate density, and wet and dry aggregate

stabilities.

1 . Aggregate Size Distribution

Voorhees et al. (1979) studied the effect of field traffic (compaction) on aggregate

size distribution and random roughness following tillage. Figure 14 shows the

aggregate size distribution following tillage in wheel-tracked and non-tracked areas of a

Nicollet silty clay loam and indicate an increase in the proportion of large aggregates

when compacted Nicollet silty clay loam soil was subsequently tilled.

FIGURE 14-Aggregate Size Distribution Of Subsequently Tilled Non-Tracked And Wheel

Tracked Nicollet Silty Clay Loam, After Planting, May 1975.

SOURCE- Voorhees et al., 1979.


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TABLE 2 -Clod Density As Affected By Wheel Traffic.

SOURCE- Voorhees et al., 1979.

2. Aggregate Stability

Power and Skidmore (1984) studied the effect of compaction on wet and dry

aggregate stability. They defined dry aggregate stability as the energy needed to crush

the compacted sample between two parallel plates. Wet stability is defined as the

amount of soil left on a 0.25-mm sieve (60-mesh) after a sample has been lowered and

raised through a distance of 27mm, 25 times per minute, in a tank of water.

TABLE 3- Physical Properties Of Yolo Fine Sandy Loam As Influenced By Compaction

Treatment

SOURCE- Flocker et al., 1958.

Table 4 shows that dry aggregate stability of Reading silt loam increased as a

result of compaction for both cultivated and uncultivated samples. Differences in soil-

water content (m = - 33 and - 100 kPa) at the time of compaction had a minimal effecton dry aggregate stability. Power and Skidmore (1984) attributed the increase in dry

aggregate stability of compacted soils to an increase in bonding of particles because

these particles were forced into closer proximity during compaction.


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TABLE 4- Dry And Wet Aggregate Stabilities Of Uncompressed And Compressed Readings

Silt Loam

SOURCE- Powers and Skidmore (1984).

3. Structural Arrangement

Measurements of pore space are increasingly used to quantify the effects of soil

compaction on the soil structure (Douglas and Koppi, 1997). To evaluate the soil

compaction effects on pore and aggregate structure, images of resin-impregnated soil

are used (Lipiec et al., 1996). Morphological analysis of the images revealed that

compaction of loamy soil by tractor pass reduced larger pores, but mainly the elongated

and continuous transmission pores (50500 m) and to lesser extent those


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EFFECT OF COMPACTION ON CROP

Fontaine (1959) has pointed out that productivity of compacted soils is affected

by the increased mechanical impedance, reduced aeration, altered moisture availability

and heat flux which follow from increased soil density and reduced pore space. At anyone time one or more of these factors may become critical for the growth of plants.

Which of the factors actually does become critical will depend upon the soil type, the

climatic conditions, the plant species, and possibly upon the stage of development of

the plant when its roots encounter compact soil conditions. Whether a given density

increment will hamper or improve plant growth depends then upon whether the soil is

looser than, at, or more compact than, the optimal density for the season and stage of

growth of the crop growing in the soil. Plant response has, however, been related to

specific soil physical phenomena that arise as the result of soil compaction.

1. Mechanical Impedance To Root

A common response of root system to increasing compaction level is decreased

root size, retarded root penetration and smaller rooting depth (Glinski and Lipiec,

1990). This is mostly due to excessive mechanical impedance and insufficient aeration

depending on soil wetness. Decreased root size results in greater distances between theneighboring roots and affects water and nutrient uptake. However, absorption of water

and nutrients usually takes place in the soil adjacent to the root surface from 2 to 8 mm,

depending on soil and nutrient types (Yamaguchi and Tanaka, 1989). This leads to

reduced water and nutrient uptake, oxygen deficiency and crop yield.

TABLE 5 -Average Minimum Bulk Densities That Restrict Root Penetration In Soils Of

Various Textures.

SOURCE- http://osufacts.okstate.edu


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FIGURE 15 - Effect Of Compaction On Root Density

SOURCE - http://osufacts.okstate.edu

2. Soil Moisture

A comprehensive review of the interrelationships of soil moisture and plant

growth has been given by Richards and Wadleigh (1952). Baver (1938) demonstrated

that compaction of a soil causes an increase in the percentage of moisture at any suction

greater than approximately 60 millibars. Heinonen ( 1954) has remarked that bulk

density (over a relatively small range in natural soils) is positively correlated with the

available water of sands and silts and negatively correlated with other textures. On the

other hand, at extreme bulk densities a diminution of the capillary pore space may

occur to such extent as to decrease the available water content of a soil. Such a condition

was described by Veihmeyer and Hendrickson (1946).

3. Heat Transport

High thermal conductivity and heat capacity characterize solid and water phases

in contrast to air phase of soil. Therefore, any soil management practice affecting soil

compactness and thus relative proportion of each phase will have an effect on the

thermal properties and propagation of heat (Usowicz et al., 1996).

As can be seen in Fig. 16, the thermal conductivity, heat capacity and thermal

diffusivity (ratio of the thermal conductivity and volume heat capacity) increase with

increasing soil compaction to higher extent in wetter soil. Guerif et al. (2001) reported a


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similar effect of compaction on thermal properties. Increase in soil thermal properties

with compaction is attributed to mostly improved contact between soil particles.

Alterations in the thermal properties due to compaction affect the soil

temperature and its temporal and spatial variability. The effect of compaction was

reflected in the lower rate of warming and cooling, the daily temperature fluctuations

and the values of the noon temperature in the topsoil (Boone and Veen, 1994). Soil with

high thermal conductivity compared to low thermal conductivity can exhibit lower

surface temperature amplitudes under equal heat flux densities (Abu-Hamdeh, 2000).

At greater depths, however, a higher temperature was noted in compacted soil. The

differences can be attributed to greater volumetric heat capacity and thermal

conductivity in compacted soil at similar soil water content (Lipiec et al., 1996).

Relatively large wetness and associated evaporation from the compacted soil (Nassar

and Horton, 1999) will enhance this effect on topsoil temperature.

When soil temperature decreases with depth, a commonly deeper root system in

loose soil may experience a lower temperature than a shallow root system in compacted

soil.

FIGURE. 16- Thermal Properties And Coefficient Of Variation (CV) Of Loamy Sand As

Affected By Tractor Passes.

SOURCE- Usowicz et al., 1996.


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4. WATER AND NUTRIENT UPTAKE

Reduced and unevenly distributed roots in compacted soil affect uptake rate (per

unit of root) and total uptake of water and nutrients. Increased water uptake rate in

compacted soil was reported for bean (Smucker and Aiken, 1992), maize (Veen et al.,

1992), barley (Lipiec et al.,1996) and rice (Glinski and Lipiec, 1990). This increase was

mostly attributed to a greater rootsoil contact and to a higher unsaturated hydraulic

conductivity and a greater water movement towards the roots.

The increased root water uptake rate of Kentucky Bluegrass in poorly aerated

compacted soil was linked to higher root porosity and thus increased root permeability

(Agnew and Carrow, 1985). In most experiments, however, increased water uptake ratewas not sufficient to compensate entirely for the reduction in total root length and

resulted in reduced total water uptake. Similarly, greater nutrient inflow rate per unit

length and root soil contact area without additional nutrient application were not

sufficient to compensate for reduced root size (Lipiec and Stepniewski, 1995).

5. STOMATA DIFFUSIVE RESISTANCE

Root systems grown in compacted soil are often subjected to wetting and drying

which influence the stomata functioning. An experimental system using water-filled

ceramic tubes under controlled pressure below atmospheric for controlling soil water

potentials (over the tensiometric range) has been found to be useful for studying

stomata behavior in response to varying water status in variously compacted soil

(Lipiec et al., 1996). Fig. 17 shows that with transient wetting, the stomata resistance and

its variation over the growth period were considerably higher in a severely compacted

soil than in low or medium compacted soil. A substantial increase of stomata resistance

in most compacted soil occurred when soil matric potential increased from 415 to 220

hPa due to poor aeration. The highest stomata diffusive resistance in most compacted

soil has also been reported in droughty period. (Ali et al., 1999) reported that the


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increased leaf stomata resistance occurred even before a measurable change in leaf

water potential.

FIGURE 17- Stomata Resistance In Maize

SOURCE- Lipiec et al., 1996.

EFFECT OF SOIL COMPACTION ON PLANT GROWTH

Soil compaction can have both desirable and undesirable effects on plant growth.

Desirable Effects-

Slightly compacted soil can speed up the rate of seed germination because it

promotes good contact between the seed and soil. In addition, moderate compaction

may reduce water loss from the soil due to evaporation and, therefore, prevent the soil

around the growing seed from drying out. Corn planters have been designed

specifically to provide moderate compaction with planter mounted packer wheels that

follow seed placement.

A medium-textured soil, having a bulk density of 1.2 grams per cubic centimeter

(74 pounds per cubic foot), is generally favorable for root growth. (Note: a soil bulk

density of 1.2 grams per cubic centimeters is comparable to a non-tracked soil after a

secondary tillage operation.) However, roots growing through a medium-textured soil

with a bulk density near 1.2 grams per cubic centimeter will probably not have a high

degree of branching or secondary root formation. In this case, a moderate amount of


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compaction can increase root branching and secondary root formation, allowing roots

to more thoroughly explore the soil for nutrients. This is especially important for plant

uptake of non-mobile nutrients such as phosphorus.

Undesirable Effects-

Excessive soil compaction impedes root growth and therefore limits the amount

of soil explored by roots. This, in turn, can decrease the plant's ability to take up

nutrients and water. From the standpoint of crop production, the adverse effect of soil

compaction on water flow and storage may be more serious than the direct effect of soil

compaction on root growth.

In dry years, soil compaction can lead to stunted, drought stressed plants due todecreased root growth. Without timely rains and well-placed fertilizers, yield

reductions will occur. Soil compaction in wet years decreases soil aeration. This results

in increased denitrification (loss of nitrate-nitrogen to the atmosphere). There can also

be a soil compaction induced nitrogen and potassium deficiency (Figures 17 and 18).

Plants need to spend energy to take up potassium. Reduced soil aeration affects root

metabolism. There can also be increased risk of crop disease. All of these factors result

in added stress to the crop and, ultimately, yield loss.

In a dry year, at very low bulk densities, yields gradually increase with an

increase in soil compaction. Soon, yields reach a maximum level at which soil

compaction is also optimal for the specific soil, crop, and climatic conditions. However,

as soil compaction continues to increase beyond optimum, yields begin to decline. With

wet weather, yields are decreased with any increase in compaction.


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Figure 18 and 19- Nitrogen And Potassium Deficiency Symptoms In Corn.

Now the desirable and undesirable effect can be shown in a graph (figure 20).

FIGURE 20. Effects Of weather On Crop Yield Response To Compaction Level

SOURCE- Ali et al., 1999.

FIGURE 21- Effect of Compaction on Seed Germination.

SOURCE- Ali et al., 1999.


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FIGURE 22 - Effects Of Compaction In The Topsoil (a) and Upper Part Of The Subsoil (b) Are

Temporary, Whereas Deep Subsoil Compaction (c) Is Virtually Permanent.

SOURCE- Voorhees et al.. 1979.

TABLE 6- Effect Of Soil Compaction On Sugarbeet And Total Recoverable Sugar Yields.

*Compaction increased yields because of a higher final stand (108 vs. 79 beets/100 ft. of

row for compacted and non-compacted treatments respectively).

SOURCE- Lipiec, 1992.

SOIL COMPACTION AND EROSION

Soil compaction in the surface layer can increase runoff, thus increasing soil and

water losses. However, when the compacted layer is tilled with a moldboard or chisel

plow, the resulting rough, cloddy surface can decrease runoff and erosion. While it

sounds contradictory, both effects are possible, depending on the soil and soil

conditions encountered.

Soil Properties

Probe Resistance

(lbs/inch2)

1990* and 1991

Average

Tons/Acre

Beets Sugar

Compacted 133 11.5 1.53

Noncompacted

78 10.5 1.42


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FIGURE 23 - Reduced Water Infiltration In Wheel Tracks.

TECHNIQUES TO MINIMISE SOIL COMPACTION

1) Addition of Organic Matter

Ideally, cultivate organic soil amendments into the top six to eight inches of the soil.

On compacted /clayey soils, anything less can lead to a shallow rooting system with

reduced plant growth, lower vigor, and lower stress tolerance. General application rate

for organic soil amendments is based on the type of product and the salt content. Do not

leave compost in chunks, as this will interfere with root growth and soil water

movement. As the soil organic content builds in a garden soil, the application rate

should be reduced to prevent ground water contamination issues. Five ways soil

organic matter resists soil compaction-

Surface residue resists compaction. Acts like a sponge to absorb weight andwater.

Organic residues are less dense (0.3-0.6 g/cm3) than soil particles (1.4-1.6g/cm3).

Roots create voids and and spaces for air and water. Roots act like a biological valve to control oxygen in the soil. Roots supply exudates to glue soil particles together to form macro-aggregates

and supply food for microbes.

2) Manage Traffic Flow

Traffic over the soil is the major contributor to soil compaction. For example a

moist soil could reach 75% maximum compaction the first time it is stepped on, and


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90% by the forth time it is stepped on. Raised bed gardening techniques, with

established walkways, eliminate compaction in the growing bed. On fine-textured

clayey soils, limit routine traffic flow to selected paths. Soils are more prone to

compaction when wet. Soil water acts as a lubricant allowing the soil particles to readilyslide together reducing large pore space.

3) Use Mulches

Some types of mulch effectively reduce the compaction forces of traffic. For

example, three to four inches of wood or bark chip will minimize the effect of foot

traffic. Mulch minimizes the compaction forces of rainfall and sprinkler irrigation. On

fine-textured clayey soil, keep garden beds mulched year round to minimize the

compaction forces of summer and winter storms. Organic mulches create an ideal home

for beneficial earthworms and soil microorganisms, which play a key role in improving

soil tilth.

4) Soil Aeration

In areas, where organic matter cannot be cultivated into the soil, reduce

compaction with soil aeration. Make enough passes with the aerator to have plugs at

two-inch intervals.

5) Avoid Excessive Cultivation

Avoid cultivating fine-textured clayey soils except to incorporate organic matter

and fertilizer, and to prepare a seedbed. Use mulches to help manage weeds.

6) Avoid Cultivating Overly Wet or Dry Soils

Never cultivate a clayey soil when wet since this will destroy soil structure; thedirt clods created by tilling wet clay may last for years. To check dryness, take a handful

of soil and gently squeeze it into a ball. If the soil is dry enough to crumble, it may be

cultivated. If the ball only reshapes with pressure, it is too wet for cultivation. On some

clayey soils, there may be only a few days (or even hours) between the time when the


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soil is too wet and too dry (too hard) to cultivate. In years when frequent spring rains

prevent the soil from drying, planting will be significantly delayed.

7) Avoid Fill Over Compacted Soil

Adding a thin layer of topsoil over compacted soil is a common practice that

leads to future landscape management problems. It is often justified as a way to get

plants established. However, root growth into the compacted layer will be restricted or

even minimal. Do not create a layer with added topsoil that is of a different texture than

the soil below. This change in texture (actually pore space) interferes with water

movement and root spread. Where additional fill is desirable, lightly mix the fill with

the soil beneath.

8) Reduction of Stresses (e.g. enlarged tire width, reduced machine weight or reducedbunker filling under wet soil conditions)

9) Improvement of Soil Stability (e.g. by reduced tillage, no tillage or conservationtillage)

10) Further Development of Techniques (e.g. regulation of tire inflation pressure, low-pressure tires)

11) Adaptation of Farming Procedures (e.g. the adaptation of row width to enlarged tirewidth)

CONCLUSION

There is increased concern regarding the effect of compaction on crop production

in mechanized agriculture. Compaction effects on crop yield are due to changes in soil

physical, chemical, and biological processes. These processes, in turn, are dependent on

the soil structure. In order to provide guidelines for appropriate soil management, weneed to understand and quantify changes in soil structure due to compaction.

Soil compaction processes and the corresponding changes in soil physical

properties may be described by the value of the precompression stress, the type and

intensity of stress application and the resulting changes in soil strength. Repeated


32/39

wheeling causes the consecutive destruction of the inter- and intra-aggregate pores,

which results in the formation of a massive, dense pore system and/or in a loss of soil

strength. It further results in reduced aeration, water infiltration and root development

and in a drastic decline in soil strength and worsening of pore functions, such asfiltering and buffering capacities. The formation of dense, platy aggregates due to

repeated wheeling may induce a more pronounced horizontal flux of water, which may

cause soil erosion. Compaction-induced soil degradation is still more severe if, due to

dynamic forces influencing the matric potential, additional soil swelling occurs. This

does not only result in a complete loss of soil strength but it also worsens the ecological

parameters. These phenomena occur especially in silt and clay soils, which are most

susceptible to compaction processes. Only if the soil aggregates and the total soilstructure are strong enough to withstand applied soil stresses, will soil physical

properties remain unchanged. Therefore, soil loading should be limited in accordance

with the internal strength of the weakest horizon of the soil profile.


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