NATURAL SCIENCE 3 REPORT

INVESTIGATE THE ROLE OF THE SOIL TO ORGANISM

Created by :

Group 4

Helda Arina Simatupang (12315244003)

Lady Wahyu Hapsari (12315244006)

Marta Asri Dewi (12315244009)

Wulan Ambar Pratiwi (12315244017)

Fitra Nugraha Tama (12315244026)

INTERNATIONAL SCIENCE EDUCATION

FACULTY OF MATHEMATICS AND NATURAL SCIENCE

YOGYAKARTA STATE UNIVERSITY

2014

INVESTIGATE THE ROLE OF THE SOIL TO ORGANISM

I. Objective

1. Investigating the role of the soil to organism

II. Literary Review

Soil helps to provide much of the food that humans consume. Only 25 percent of

the earth's surface is made up of soil and only 10 percent of that soil can be used to grow

food. Soil sustains life by helping plants to grow. It also harbors worms, beetles, fungi and

bacteria, providing them with the nutrients they need to live. Without soil, there would be

nowhere to grow food that is the sustenance of life. Soil contains food, water and air that is

needed by plants to grow. The healthier the soil, the more nutrients a plant can soak up. The

healthier the plant, the better it is for humans and animals to eat. The quality of the soil

ultimately affects the health of people and animals.

Soil is made up of organic matter, minerals and living organisms. Organic matter is

decaying material such as rotting leaves and dead animals. Minerals are crushed rocks or

bedrock. Living organisms include moles, worms and beetles, which churn through the earth

as well as essential bacteria that help to break down organic matter. Soil is more than just

the dirt under our feet. It is a home for living organisms and it provides nutrients and

stability for plants to grow. Without soil, the plants necessary for people and animals to

survive could not exist. By caring for our soil properly, we can ensure the longevity of both

animals and people. The use of crop rotation, limiting harsh chemicals and composting will

help to maintain a healthy balance of nutrients, living organisms and minerals in the soil. It

is important to remember that the fresh foods on which we feast affect our health. To the

question, "Why is soil so important", the simple answer is that we are what we eat.

The physical and chemical characteristics of a soil are different in different parts of

the soil profile. Generally, the upper layers of a soil have more organic matter and roots than

the lower layers. Other differences are related to the nature of the soil constituents, to

weathering processes and to past land management practices. The origin of the soil

determines the particle size distribution, which in turn affects the way the soil is packed,

creating spaces and surfaces that are either accessible or inaccessible to soil organisms. The

proportion of clay or sand influences the structural characteristics of soil and determines its

response to management practices.

The structure of a soil is related to the extent to which particles are aggregated into

relatively stable formations. Aggregates vary in size and the degree of soil aggregation

dictates the number and size of the pores within it. The type and quantity of organic matter

also influences the degree of soil aggregation. Soil structure determines the number and size

of air spaces and influences the water holding capacity and drainage properties of the soil.

Roots can also alter the soil environment for living organisms and play an important

role in supplying nutrients for organisms that live around them. Roots are dynamic

structures, especially when young, releasing carbon compounds that can be readily used as

an energy and carbon source by many soil organisms. However, over time roots change, and

older roots have different surface properties and release different compounds to younger

roots. As roots age, the outer layers of the root die, providing a source of organic material as

well as a habitat for soil organisms. It is important to consider the soil as a continually

changing and complex environment for organisms. Part of this complexity arises because

the organisms themselves contribute to the some of the changes that occur within the soil.

Soil Organism

The soil is a complex system of organic and inorganic matter. It consists of various

layers of this material, each varying in the amount of solid, gases, liquids, and organic

matter. A general analysis of soil shows that about 40% are rocks and minerals, 25% gases,

25% liquid, and 10% organic matter. This combination creates the soil environment, which

has several characteristics that make it worthwhile to study. It provides a place for plants to

secure themselves. Soil acts as a filter that helps purify the water, and it is the place where

many nutrients are recycled. Finally the topic of this paper, soil is the habitat for thousands

of different organisms around the world.

Soil Organisms are generally grouped into two categories: micro

fauna/microorganisms and macrofauna. The main soil microorganisms include bacteria,

fungi, and protozoa. The macro fauna include oligochaeta, arthropods, mollusks, and

nematods. There are many other organisms that spend some time in the soil, but usually just

for reproduction or feeding, and are not included in this paper. The organisms mentioned

above play an essential role in soil formation and the soil environment. The larger organisms

tend to depend more on the microorganisms that are part of the lower trophic levels.

Therefore microorganisms will be discussed first to provide background information.

Perhaps the most important microorganisms in the soil ecosystem are bacteria. They

are single-celled organisms that are responsible for many important processes. One thing

they do is decompose plant material as well as other organisms' waste. These waste

materials contain nutrients, and the bacteria's cells are able to convert them from an

unusable form into a form that can be used. One essential nutrient that is converted by

bacteria is nitrogen. Nitrogen-fixing bacteria are able to use the nitrogen that exists in the

atmosphere (N2) and change it through cellular processes into ammonia (NH3). Nitrifying

bacteria mix ammonia (NH3) with water (H2O) to create ammonium ion (NH4+) and nitrate

(NO3-), which can be used by other organisms. Protozoa are also present in the soil

environment and contribute to distributing ammonium into the soil for use by plants and

other organisms. They feed on bacteria but do not need as much nitrogen as the bacteria

provide, and therefore release the excess ammonium. Plants need this to grow, so much so,

that humans began putting more nitrogen into fertilizers through an industrial process

created by Fritz Haber and Carl Bosch. Denitrifying bacteria are responsible for putting the

nitrogen back into the atmosphere as N2.

Bacteria are also responsible for decomposing other compounds as well. One

phylum of bacteria called actinobacteria or actinomycetes are responsible for decomposing

chitin, cellulose, and other difficult materials in dead plants, animals and fungi. Other

organisms cannot disintegrate these materials because of their tough structure. The bacteria

are able to produce an enzyme allowing them to reduce the chitin, for example, from a

polymer into simple sugars and ammonia that other organisms can then use. Actinomycetes

are a type of bacteria that used to be considered as fungi. They were thought to be so

because they grow hyphae like fungi, and they can live in harsh environments in which other

bacteria usually do not survive, like higher pH levels and dryer conditions. They since were

reclassified and renamed actinobacteria. These bacteria give the soil its earthy scent, which

actually indicates a healthy environment. Bacteria such as this help to maintain healthy soil

environments for plants, allowing them to get the nitrogen they need, and decomposing

organic waste.

Fungi serve in a similar capacity in the soil environment. They tend to be more

abundant in places where the bacteria cannot thrive, such as environments that are acidic,

have low amounts of nitrogen, have low moisture, and high complex carbohydrates (bacteria

cannot break them down). Fungi fill the niche of decomposing tough organic matter such as

chitin, cellulose, keratin and lignins. Again, most organisms cannot digest these materials,

but fungi, like actinobacteria, can produce enzymes that allow them to degrade those strong

compounds into sugars that can be digested. Not only are they decomposers, but fungi also

are responsible for supplying nutrients to other organisms, in this case plants. Fungi form a

mutualistic relationship with plants called mycorriza, which allows both parties to benefit.

The fungi grow on or within (endopyhtic) the roots of the plant. Because of the hyphae's

high surface area to volume ratio, fungi are able to better access essential nutrients and

deliver them to the plants. The plants, in turn, give the fungi food in the form of glucose.

Already, the importance of these microorganisms is clear, but in addition to them converting

nutrients into usable forms, they also are the food source for many of the macro fauna in the

soil. The macro fauna depend on the nutrients that the microbes produce.

The most beneficial, and probably most recognizable macro fauna in soil is the

earthworm. Oligochaeta, a subclass of annelids, or segmented worms, contribute to the

texture of soil as we know it. The earthworms burrow throughout the soil creating tunnels

and shafts. These openings loosen the soil structure providing spaces where other organisms

can travel and gain access to other areas. Water also fills these spaces, adding to the water

absorption of the soil, increasing moisture, which many organisms need, including

earthworms. When water gets absorbed into the ground there is less runoff on the surface.

While the worms burrow, they intake soil and dead plant material. They digest these

nutrient-rich materials and produce waste called castings. The castings contain all of the

nutrients that were present in the organic material: nitrogen, potassium, calcium,

phosphorus, and magnesium, and contain microorganisms, such as bacteria and fungi. The

protozoa and nematodes feed on the microorganisms within the castings and release the

nutrients within them. The worm castings are considered to be fertilizers because of their

positive effect on the soil: they help to balance the pH levels, retain moisture, improve

drainage, and control pathogens. Plant nurseries harvest and sell worm castings for this very

reason.

Other macro fauna include nematodes, mollusks, and arthropods. These include a

wide variety of animals that help to maintain a balance in the food web. Some of these

animals consume live or dead plant material, and some are predators of the microorganisms

mentioned above. The larger bugs gain and release some of the nutrients from bacteria when

they feed on them. In addition to this, macro fauna help maintain natural population sizes of

their prey. One very interesting relationship is between macro fauna and bacteria. As the

bacteria are eaten, the more their population grows. This is a negative feedback. This is

clearly supported in the relationship between the arthropods and fungi in the following

situation. Leaf cutter ants harvest basidiomycete fungi. They grow the fungi, feeding it

leaves, providing it with a desirable living condition and protection from other organisms. In

tern, the ants eat the fungi. The obvious question begs to be asked, wouldn't the fungi die off

if it is constantly being eaten? In actuality, when it is eaten, it is more stimulated to grow,

and it does just that. As long as it is fed (the leaves provided from the ants) it will continue

to grow, and be satisfied living in this situation. This is the same relationship with bacteria

and their predators.

Soil organisms are not always beneficial. organisms that pose a threat to plants and

microorganisms that aid the plants are viewed as pests. Fungi and bacteria have been known

for posing many problems to soil organisms. They can form parasitic relationships with

plants, attacking young or damaged roots and inhibiting their growth. The enzymes that

enable these microorganisms to digest tough plant materials are the same enzymes, such as

cellulase, that allow the bacteria and fungi to penetrate a plant's roots in a pathogenic

relationship. Macro fauna are not faultless. Nematodes can also be parasites, feeding on

plants and animals, including humans. They spread diseases and viruses amongst soil

organisms, posing many problems for farmers and gardeners. Larger nematodes are often

introduced as predators to smaller nematodes to control their population. An arthropod

called symphyla, or wire worms, are pests in greenhouses and gardens. They also feed on

plants and microorganisms. Mites pose similar concerns.

As is described above, the organisms in the soil contribute greatly to the wellness of

the plants that grow from the soil. They are dependent on each other and each has a niche to

fill to ensure that the environment stays well-balanced. Organisms do not always behave in a

helpful manner, but pesty organisms occur naturally in an ecosystem. Each type of organism

in the soil plays a role in keeping the soil an ecosystem that is diverse and worthy of our

attention.

The habitat available to a soil organism depends on its size: the soil environment of

bacteria will be quite different to that of an earthworm. For a bacterium, important aspects

of the soil environment include:

Microhabitat (structure)

• surfaces of soil particles

• pore spaces

• roots

• dead organic matter (plant, animal or microbial)

• water films

Physical and chemical characteristics

• the charge of soil particles (positive or negative)

• degree of aeration

• pH

• salinity

• temperature

• nutrients

Biological aspects

• other living organisms (including roots)

Bacteria are usually attached to the surfaces within soil pores or fragments of

organic matter. They may attach themselves using flagella or fine hair-like fribrillae,

although not all bacteria have these structures. Another method of attachment occurs

through the production of polysaccharide gums that are released through the cell wall of

some bacteria. Certain fungi also produce gums that actually help bacteria attach to soil

particles.

Fungi experience a similar soil environment to that of bacteria, but the scale is

greater. Fungi spread much further through the soil than do bacteria and will encounter a

greater variety of soil environments. Also, bacteria have access to smaller pore spaces than

most fungi. Protozoa and mites both feed on bacteria but only the protozoa are small enough

to enter some soil pores. Mesofauna such as mites and collembola cannot enter smaller soil

pores and therefore bacteria that occur there are protected. The smallest soil pores are

inaccessible to bacteria and may contain organic matter that is protected from degradation.

While the soil environment obviously has a great effect on soil organisms they, in

turn, may affect their physical environment. The breakdown of organic matter by soil

organisms changes the structure of the soil, which leads to changes in the habitats available

for soil organisms. The chemical environment of soil organisms can also be of their own

making. Some bacteria and fungi initiate many of the biochemical reactions that occur in

soil. The decomposition of leaves requires the enzyme cellulase, which is produced by soil

organisms. The activity of cellulase changes with time, with the main peak in activity

occurring soon after the addition organic matter, such as red maple leaves, to soil .

This reflects the increased production of cellulase by soil organisms in response to

organic matter. Cellulase enzymes occur within the organisms (endocellulase), but can also

be excreted into the soil (exocellulase). Thus, the data reflect the greater cellulase activity

during the early stages of decomposition. Waste products excreted by soil organisms

provide substances that can be degraded further by other organisms. Alternatively, the

wastes may be toxic to some organisms and inhibit their growth.

Some organisms tolerate a wide range of conditions whereas others are adapted to a

more limited environment. For example, cyanobacteria are rarer in acidic soils than in soils

of pH 7 to 8. The abundance of bacteria is less in acidic soils than in soils of higher pH.

Generally, there is not such a strong relationship between soil pH and fungi as there is

between soil pH and bacteria, although individual fungi can have a marked pH preference.

Soil habitats differ greatly depending on land use. For a similar soil type within the

same climate zone, a forest soil will generally have a greater diversity of habitats for soil

organisms than a cultivated agricultural soil. These differences are primarily associated with

a greater diversity of plant species and heterogeneity of the soil itself and the characteristics

of organic matter produced in natural and agricultural ecosystems.

The size of soil pores, and therefore the habitat available to bacteria etc, depends on

soil structure. For example, soils with high levels of clay have a greater proportion of small

pores less than 0.2 µm in diameter than loams on sandy soils. The very small pores are too

small for bacteria to enter, providing protection to organic matter.

Soils with a higher number of small, but not too small, pores (e.g. 0.2 to 6 µm in

diameter) have more bacteria than do those with fewer pores in this size category. This is

because bacteria survive best within aggregates of soil rather than on the surfaces of soil

particles outside aggregates. Bacteria exposed on surfaces are likely to be eaten by soil

animals such as mites and springtails (collembola) or damaged by extreme cycles of wetting

and drying. Therefore, a clayey soil would be expected to have a greater number of bacteria

than a sandy soil under similar land use. For one of the soils studied by Hassink et al.

(1993), there was a close relationship between the biomass of bacteria and the percentage of

the pore volume in soil that was in the size class 0.2 to 1.2 µm. Bacteria and fungi

commonly occur within aggregates of soil, although they are not distributed evenly in all

size fractions of soil aggregates. Most bacteria in this study were present in soil aggregates

that ranged from 2 to 20 µm in diameter.

The number of soil organisms varies greatly between the surface and very deep

layers in the soil profile. The main reason for this is because the supply of plant organic

matter that is essential for many soil organisms is almost absent lower in the soil profile.

However, it needs to be remembered that organisms do occur at great depths within the

regolith, even though their numbers are much reduced compared with communities at the

soil surface.

Physical Properties of Soil

Soil quality is determined by physical and biological state of soil and harmony of

fertility. If the consistency ceases, the living conditions of plant deteriorate too. The efforts

for soil quality amelioration, conservation, retain –coincide with the objectives of

sustainable management. In the sustainable management, the crop cultivation may be based

such a cultivation methods that creates, saves and keeps favourable physical and biological

condition of the soil.

The physical properties of a soil are those characteristics which can be seen with the

eye or felt between the thumb and fingers. They are the result of soil parent materials being

acted upon by climatic factors (such as rainfall and temperature), and affected by

topography (slope and direction, or aspect) and life forms (kind and amount, such as forest,

grass, or soil animals) over a period of time. A change in any one of these influences usually

results in a difference in the type of soil formed. Important physical properties of a soil are

color, texture, structure, drainage, depth, and surface features (stoniness, slope, and erosion).

The physical properties and chemical composition largely determine the suitability

of a soil for its planned use and the management requirements to keep it most productive. To

a limited extent, the fertility of a soil determines its possible uses, and to a larger extent, its

yields. However, fertility level alone is not indicative of its productive capacity, since soil

physical properties usually control the suitability of the soil as growth medium. Fertility is

more easily changed than soil physical properties.

a. Soil Color

When soil is examined, color is one of the first things noticed. It indicates extremely

important soil conditions. In general, color is determined by: (1) organic matter content, (2)

drainage conditions, and (3) degree of oxidation (extent of weathering).

Surface soil colors vary from almost white, through shades of brown and gray, to

black. Light colors indicate a low organic matter content and dark colors can indicate a high

content. Light or pale colors in the surface soil are frequently associated with relatively

coarse texture, highly leached conditions, and high annual temperatures. Dark colors may

result from high water table conditions (poor drainage), low annual temperatures, or other

conditions that induce high organic matter content and, at the same time, slow the oxidation

of organic materials. However, soil coloration may be due to the colors imparted by the

parent material. Shades of red or yellow, particularly where associated with relatively fine

textures, usually indicate that subsoil material has been incorporated in the surface layer.

Subsoil colors, in general, are indications of air, water, and soil relationships and

the degree of oxidation of certain minerals in the soil. Red and brown subsoil colors indicate

relatively free movement of air and water allowed by the soil. If these or other bright colors

persist throughout the subsoil, aeration is favorable. Some subsoils that are mottled (have

mixed colors), especially in shades of red and brown, are also well-aerated.

Yellow-colored subsoils usually indicate some drainage impediment. Most mottled

subsoils, especially those where gray predominates, have too much water and too little air

(oxygen) much of the time. The red-to-brown color of subsoils comes from iron coatings

under well-aerated conditions. In wet soils with low oxygen levels, the iron coatings are

chemically and biologically removed, and the gray color of background soil minerals shows.

Color IndicationsRed Brown Good DrainageYellow Some DrainageGrey Poor Drainage

b. Soil Texture

Texture refers to the relative amounts of differently sized soil particles, or the

fineness/coarseness of the mineral particles in the soil. Soil texture depends on the relative

amounts of sand, silt, and clay. In each texture class, there is a range in the amount of sand,

silt, and clay that class contains.

The coarser mineral particles of the soil are called sand. These particles vary in size.

Most sand particles can be seen without a magnifying glass. Sand particles feel gritty when

rubbed between the thumb and fingers. Relatively fine soil particles that feel smooth and

floury are called silt. When wet, silt feels smooth but is not slick or sticky. When dry, it is

smooth, and if pressed between the thumb and finger, will retain the imprint. Silt particles

are so fine that they cannot usually be seen by the unaided eye and are best seen with a

microscope. Clays are the finest soil particles. Clay particles can be seen only with the aid of

a very powerful (electron) microscope. They feel extremely smooth when dry, and become

slick and sticky when wet. Clay will hold the form into which it is molded. Soils high in

clay content often show pronounced surface cracking when dried.

Soil textural classes take their names from the particle size categories (sand, silt,

and clay) and also from the category called loam. Loam is a textural class of soil that has

moderate amounts of sand, silt, and clay. Loam contains approximately 7% to 27% clay,

28% to 50 % silt, and 23% to 53% sand. It is smooth to the touch when dry, but when moist,

it becomes somewhat slick/ sticky. Most surface soils fall into five general textural classes.

Each class name indicates the size of the mineral particles that are dominant in the soil.

Intermediate texture soils are called loams. Texture is determined in the field by rubbing

moist-to-wet soil between the thumb and fingers. These observations can be checked in the

laboratory by mechanical analysis which separates particles into clay, silt, and various-sized

sand groups.

c. Soil Structure

The term texture is used in reference to the size of individual soil particles but when

the arrangement of the particles is considered the term structure is used. Structure refers to

the aggregation of primary soil particles (sand, silt and clay) into compound particles or

cluster of primary particles which are seperated by the adjoining aggregates by surfaces of

weakness. Structure modifies the effect of texture in regard to moisture and air relationships,

availability of nutrients, action of microorganisms and root growth. E.g. a highly plastic clay

(60% clay) is good for crop product if it has a well developed granular structure which

facilitates aeration and water movement. Similarly a soil though has a heavy texture, can

have a strongly developed structure, thus making it not very satisfactory for aquaculture as a

result of this soil allowing high seepage losses.

The soil separates can become aggregated together into discrete structural units

called “peds”. These peds are organized into a repeating pattern that is referred to as soil

structure. Between the peds are cracks called “pores” through which soil air and water are

conducted. Soil structure is most commonly described in terms of the shape of the individual

peds that occur within a soil horizon.

Structure is the arrangement of primary sand, silt and clay particles into secondary

aggregates called peds or structural units which have distinct shapes and are easy to

recognize. These differently shaped aggregates are called the structural type. 

1. There are 5 basic types of structural units: 

a) Platy: Plate-like aggregates that form parallel to the horizons like pages in a book. 

1. This type of structure may reduce air, water and root movement. 

2. common structure in an E horizon and usually not seen in other horizons.

b) Blocky: Two types--angular blocky and subangular blocky 

1. These types of structures are commonly seen in the B horizon. 

2. Angular is cube-like with sharp corners while subangular blocky has rounded

corners.

c) Prismatic: Vertical axis is longer than the horizontal axis. If the top is flat, it is

referred to as prismatic. If the top is rounded, it is called columnar. 

d) Granular: Peds are round and pourous, spheroidal. This is usually the structure of A

horizons. 

e) Structureless: No observable aggregation or structural units. 

1. Single grain-sand 

2. Massive-solid mass without aggregates

2. Grade of structure - Describes stability of the aggregates. 

a) structureless 

b) weak 

c) moderate 

d) strong

3. Class of structure - Describes size of the aggregates. 

a) very fine 

b) fine 

c) medium 

d) coarse 

e) very coarse

The size of each category varies with the type of structure. 

4. Formation of soil structure 

a) freeze / thaw 

b) wetting / drying 

c) root pressure 

d) microorganisms 

e) cementing by clay, organic matter, iron and aluminum compounds

5. Importance of Soil Structure 

a) Increases infiltration of water, thus reducing runoff and erosion and increases the

amount of plant available water. 

b) Improves seedling emergence, root growth and rooting depth. 

c) Large continuous pores increase permeability.

6. Maintaining Soil Structure 

a) Till soil only at the proper moisture contents. Never till when the soil is too wet. This

will cause the soil to become cloddy. Aggregates are easily destroyed. 

b) Add the proper amounts of lime and fertilizer. Proper plant growth will lead to the

development of good soil structure. 

c) Grow grasses and legumes. These plants may help form unstable aggregates and

their organic matter will help stablize the aggregate. 

d) Growth of legumes will also give the soil more microorganisms which give certain

beneficial fungi which will stabilize peds. 

e) Maintain or increase organic matter contents of Ap horizon. 

1. plant cover crops in fall and winter 

2. plant more grasses 

3. turn under crop residue 

4. add manure

Graphic

ExampleDescription of Structure Shape

Granular – roughly spherical, like grape nuts. Usually 1-10 mm in diameter. Most

common in A horizons, where plant roots, microorganisms, and sticky products of

organic matter decomposition bind soil grains into granular aggregates

Platy – flat peds that lie horizontally in the soil. Platy structure can be found in A,

B and C horizons. It commonly occurs in an A horizon as the result of compaction.

Blocky – roughly cube-shaped, with more or less flat surfaces. If edges and

corners remain sharp, we call it angular blocky. If they are rounded, we call it

subangular blocky. Sizes commonly range from 5-50 mm across. Blocky

structures are typical of B horizons, especially those with a high clay content.

They form by repeated expansion and contraction of clay minerals.

Prismatic – larger, vertically elongated blocks, often with five sides. Sizes are

commonly 10-100mm across. Prismatic structures commonly occur in fragipans.

Columnar – the units are similar to prisms and are bounded by flat or slightly

rounded vertical faces. The tops of columns, in contrast to those of prisms, are

very distinct and normally rounded.

d. Soil Consistence

Soil consistence refers to the ease with which an individual ped can be crushed by

the fingers. Soil consistence, and its description, depends on soil moisture content. Terms

commonly used to describe consistence are:

Moist soil:

1. loose – noncoherent when dry or moist; does not hold together in a mass

2. friable – when moist, crushed easily under gentle pressure between thumb and forefinger

and can be pressed together into a lump

3. firm – when moist crushed under moderate pressure between thumb and forefinger, but

resistance is distinctly noticeable

Wet soil:

1. plastic – when wet, readily deformed by moderate pressure but can be pressed into a

lump; will form a “wire” when rolled between thumb and forefinger

2. sticky – when wet, adheres to other material and tends to stretch somewhat and pull

apart rather than to pull free from other material

Dry Soil:

1. soft – when dry, breaks into powder or individual grains under very slight pressure

2. hard – when dry, moderately resistant to pressure; can be broken with difficulty between

thumb and forefinger

Chemical Properties of Soil

a. Cation Exchange Capacity (CEC)

Some plant nutrients and metals exist as positively charged ions, or “cations”, in the

soil environment. Among the more common cations found in soils are hydrogen (H+),

aluminum (Al+3), calcium (Ca+2), magnesium (Mg+2), and potassium (K+). Most heavy

metals also exist as cations in the soil environment. Clay and organic matter particles are

predominantly negatively charged (anions), and have the ability to hold cations from being

“leached” or washed away. The adsorbed cations are subject to replacement by other cations

in a rapid, reversible process called “cation exchange”.

Cations leaving the exchange sites enter the soil solution, where they can be taken

up by plants, react with other soil constituents, or be carried away with drainage water. The

“cation exchange capacity”, or “CEC”, of a soil is a measurement of the magnitude of the

negative charge per unit weight of soil, or the amount of cations a particular sample of soil

can hold in an exchangeable form. The greater the clay and organic matter content, the

greater the CEC should be, although different types of clay minerals and organic matter can

vary in CEC.

Cation exchange is an important mechanism in soils for retaining and supplying

plant nutrients, and for adsorbing contaminants. It plays an important role in wastewater

treatment in soils. Sandy soils with a low CEC are generally unsuited for septic systems

since they have little adsorptive ability and there is potential for groundwater.

b. Soil Reaction (pH)

By definition, “pH” is a measure of the active hydrogen ion (H+) concentration. It is

an indication of the acidity or alkalinity of a soil, and also known as “soil reaction”. The pH

scale ranges from 0 to 14, with values below 7.0 acidic, and values above 7.0 alkaline. A pH

value of 7 is considered neutral, where H+ and OH- are equal, both at a concentration of 10-

7 moles/liter. A pH of 4.0 is ten times more acidic than a pH of 5.0.

The most important effect of pH in the soil is on ion solubility, which in turn affects

microbial and plant growth. A pH range of 6.0 to 6.8 is ideal for most crops because it

coincides with optimum solubility of the most important plant nutrients. Some minor

elements (e.g., iron) and most heavy metals are more soluble at lower pH. This makes pH

management important in controlling movement of heavy metals (and potential groundwater

contamination) in soil.

In acid soils, hydrogen and aluminum are the dominant exchangeable cations. The

latter is soluble under acid conditions, and its reactivity with water (hydrolysis) produces

hydrogen ions. Calcium and magnesium are basic cations; as their amounts increase, the

relative amount of acidic cations will decrease. Factors that affect soil pH include parent

material, vegetation, and climate. Some rocks and sediments produce soils that are more

acidic than others: quartz-rich sandstone is acidic; limestone is alkaline. Some types of

vegetation, particularly conifers, produce organic acids, which can contribute to lower soil

pH values. In humid areas such as the eastern US, soils tend to become more acidic over

time because rainfall washes away basic cations and replaces them with hydrogen. Addition

of certain fertilizers to soil can also produce hydrogen ions. Liming the soil adds calcium,

which replaces exchangeable and solution H+ and raises soil pH.

Lime requirement, or the amount of liming material needed to raise the soil pH to a

certain level, increases with CEC. To decrease the soil pH, sulfur can be added, which

produces sulfuric acid.

III. Setting

1. Place and time

Place : Sleman (Wulan’s house)

Time : Thursday, October 23th 2014

2. Tools and Materials

Tools: Materials:

- Higrometer - Soil

- Thermometer - Water

- pH stick

- Ruler

- Hoe

- Pen

- Camera

3. Procedures

a. Perparing the material and tools

b. Mencangkul tempat sampah yang akan diobservasi sampai terlihat bagian tanah

c. Mengukur kedalaman tanah yang sudah digali

d. Mengamati organisme yang berada di dalam tanah

e. Mengukur kelembaban tanah

f. Mengukur suhu tanah

g. Mengambil sample tanah

h. Memasukan ke dalam tabung reaksi dan menambahkan air untuk mengamati jenis

tanah

i. Mengukur pH tanah

IV. Data of The Result

ObjekKedalaman

tanahOrganisme Kelembaban Suhu

pH

tanahLapisan tanah

Tempat

sampah 1

23 cm Uler gagak (++)

Kecoa kecil (+)

Semut (+++)

62 % 300 5 Debu = 10%

Pasir = 60%

Batuan kecil = 30 %

Tempat

sampah 2

20 cm Gonteng (++)

Semut (+++)

57% 310 6 Pasir halus = 40%

Pasir kasar = 60%

Tempat

sampah 3

28 cm Tidak ada 57% 30,50 5,5 Debu = 8%

Pasir halus = 72%

Pasir kasar = 20%

V. Discussion

VI. Conclussions

VII. References

Darmawijaya, Isa. 1990. Klasifikasi Tanah. Yogyakarta: Gadjah Mada University Press.

Hanafiah, Kemas Ali. 2005. Dasar-Dasar Ilmu Tanah. Jakarta: PT. Raja Grafindo

Persada.

Hardjowigeno, Sarwono. 2003. Ilmu Tanah. Jakarta: CV. Akademika Pressindo.

Sutedjo, Mul Mulyani dan Kartasapoetra. 2005. Pengantar Ilmu Tanah. Jakarta: PT.

RINEKA CIPTA.

Mulder, E. G. 1971. Soil Biology. USA: UNESCO.

Ma’shum, M. 2003. Biologi Tanah. Jakarta: Departemen Pendidikan Nasional. Jakarta.

Lynch, J. M. 1983. Soil Biotecnology, Microbiologycol Factors in Crop Production.

Blackwell Scientific Publication. London: Oxford.