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What is soil

What is soil?


Discoveryschool com

discoveryschool.com

  • What’s the difference between soil and dirt? Dirt is what you find under your fingernails. Soil is what you find under your feet. Think of soil as a thin living skin that covers the land. It goes down into the ground just a short way. Even the most fertile topsoil is only a foot or so deep. Soil is more than rock particles. It includes all the living things and the materials they make or change.


Discoveryschool com cont d

discoveryschool.com, cont’d

  • There is no soil on Mars or Venus. How come? Those planets have plenty of rocks. Mars has windstorms that erode rocks into dust. Venus has an acid atmosphere that cooks rocks into new chemicals. But there's still something missing. Without life, there is no soil. Living things haven't just made a home in the soil on our planet. Life actually made the soil as we know it.


Definitions hillel introduction to soil physics 1982

Definitions, Hillel, Introduction to Soil Physics, 1982

  • Soil refers to the weathered and fragmented outer layer of the earth’s terrestrial surface.

  • The soil is a heterogeneous, polyphasic, particulate, disperse, and porous system, in which the interfacial area per unit volume can be very large. The disperse nature of the soil and its consequent interfacial activity give rise to such phenomena as adsorption of water and chemicals, ion exchange, adhesion, swelling and shrinking, dispersion and flocculation, and capillarity.


Definition soil taxonomy 2 nd ed

Definition, Soil Taxonomy, 2nd ed.

  • The lower boundary that separates soil from the nonsoil underneath is most difficult to define. Soil consists of horizons near the earth's surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time. Commonly, soil grades at its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or other marks of biological activity. For purposes of classification, the lower boundary of soil is arbitrarily set at 200 cm.


What is soil

Unsaturated System

Zone of Aeration

Vadose Zone

Unsaturated Zone

Three phase system – air, water, rock


Infiltration percolation rates

Infiltration & Percolation Rates

  • The rate that water enters (infiltrates) a soil and then moves through the soil profile (percolates) depends partly on soil structure.

    • Rapid infiltration with granular and loose, single grained structureless soil.

    • Moderate infiltration with block-like and prismatic structure.

    • Slow infiltration with platy and solid, massive structure-less structure.


Internal drainage

Internal Drainage

  • If permeability is slow or very slow, water stays in the pore spaces and air cannot enter.

  • Soils with poor internal drainage and aeration are mostly gray with some red or yellow streaks.

  • Soils with fair to good internal drainage and aeration are yellow-brown or reddish-brown with some gray spots (mottlings)


What is soil

Infiltration

The process of water entry into the soil

Partitions water at surface between storm runoff and recharge

Plants depend on infiltrated water

Infiltration rate

volume (flux) of water per unit area

that enters the soil, per unit time

Infiltration capacity

the maximum rate at which

infiltration can occur under specific

moisture conditions.


What is soil

When rain hits a dry soil,

surface effects between the soil

and water exert a tension that

draws moisture into the soil

As the capillary forces

diminish with increased

soil-moisture content,

the infiltration capacity

decreases

As more water infiltrates,

the amount of water that

can be infiltrated during

the latter stages of a

precipitation event is less

than at the beginning


How soils are formed

How Soils are Formed

  • Soil is formed from rock (Parent material)

    • Rock is slowly broken down or fragmented by

      • Weathering processes

        • Biological

        • Chemical

        • Physical

    • Topography helps control how fast parent material is broken down.

      • Steep slopes – very little or no soil

      • Moderate slope – deep soil formation


Physical weathering breaks rocks into small mineral particles

Physical weathering breaks rocks into small mineral particles.


Chemical weathering dissolves and changes minerals at the earth s surface

Chemical weathering dissolves and changes minerals at the Earth’s surface.


Decomposing organic material from plants and animals mixes with accumulated soil minerals

Decomposing organic material from plants and animals mixes with accumulated soil minerals.


Soil composition

Soil Composition

  • Soil is composed of four major parts:

    • Mineral particles

    • Organic matter

    • Water

    • Air

  • When organisms die, bacteria and other soil organisms decompose the dead material, returning the nutrient minerals to the soil.


Mineral portion

Mineral Portion

  • Comes from weathered rock

  • Constitutes most of what we call soil.

  • Mineral content is determined by the type of parent material.

  • Age of soil affects its mineral content.

  • Older soils are more weathered and have poorer mineral nutrient content.

  • Young soils formed in the area of volcanoes have many essential nutrient mineral ions available.


What is soil

Parent material (bedrock) undergoes weathering to become regolith (soil + saprolite).


What is soil

Soil is a mixture of mineral and organic matter lacking any inherited rock structure.

Soil


What is soil

Saprolite is weathered rock that retains remnant rock structure.

Saprolite


What is soil

Saprolite


Organic matter

Organic Matter

  • Organic material is composed of:

    • Litter

      • Dead leaves

      • Branches

    • Animal dung

    • Dead remains of plants, animals and microorganisms.

  • Microorganisms (bacteria and fungi) decompose the materials into basic nutrients in the soil

  • Organic matter increases the soil’s ability to retain moisture.

  • Humus is the black or dark brown organic material remains after much decomposition.


Water and air

Water and Air

  • Soil has numerous pore spaces around and among the soil’s particles.

  • The pore spaces occupy roughly 50% of a soil’s volume and are filled with varying proportions of water (soil water) and air (soil air).

  • Both are necessary to produce a moist but aerated soil.


Soil water

Soil Water

  • Soil water originates as precipitation which drains downward until it reaches the groundwater level.

  • Soil water contains low concentrations of dissolved nutrient mineral salts that enter the roots of plants.

  • Water not bound to soil particles or absorbed by plant roots, percolates through the soil taking the mineral nutrients with it.


Soil water1

Soil Water

  • Leaching is the removal of dissolved materials from the soil by water percolating down through it.

  • Illuviation is the deposition of leached material in the lower layers of the soil.


Soil air

Soil Air

  • Soil air contains the same gases as atmospheric air, although the are usually present in different proportions.

  • As a result of cellular respiration by soil organisms, there is more carbon dioxide and less oxygen than in atmospheric air.

  • Nitrogen is used by nitrogen-fixing bacteria.

  • Carbon dioxide is turned into carbonic acid and is used in weathering of soil and bedrock.


What is soil

6 – 12 inches of water are added to the hole

and the time per inch of decline is measured

Time can’t be too long (>60 min) or too short (<3 min)


What is soil

Infiltration Rates in Soils


Soil horizons

Soil Horizons

  • A soil profile is a vertical section from the surface to parent material.


What is soil

  • Gley soil in soil science is a type of hydric soil which exhibits a greenish-blue-grey soil color due to wetland conditions. On exposure to the air, gley colors are transformed to a mottled pattern of reddish, yellow or orange patches. During gley soil formation (a process known as Gleying), the oxygen supply in the soil profile is restricted due to soil moisture at saturation. Anaerobic micro-organisms support cellular respiration by using alternatives to free oxygen as electron acceptors. This is most often the case when the sesquioxide of iron, ferric oxide is reduced to ferrous oxide by the removal of oxygen. These reduced mineral compounds produce the gley soil color.


What is soil

if more than 2-3 inches thick –

probably been plowed


What is soil

light colored, leached horizon

typically present only in forests


What is soil

:

zone of accumulation

Iron bearing leached from above

and precipitated in B

Yellowish brown to strong brown color


Ideal soil horizon

IDEAL SOIL HORIZON


Finding and describing horizons

Finding and Describing Horizons

Soil Pit Technique

Starting from top, observe profile to determine properties and differences between horizons.

Place golf tee or marker at the top and bottom of each horizon to clearly identify it.

Look for: different colors, shapes, roots, the size and amount of stones, small dark nodules (called concretions), worms, or other small animals and insects, worm channels, and anything else that is noticeable.

Soil formed under very dry or arid conditions in New Mexico, USA


Finding and describing horizons1

Finding and Describing Horizons

Exposed Profile (Road Cut) Technique

Obtain permission to take samples from the road cut, excavation, or other soil profile exposed by others. Obey any and all safety precautions requested.

Expose a fresh soil face by scraping approximately 2cm off of the vertical surface of the soil profile.

Follow Soil Pit Technique directions.


Recognizing soil texture structure

Recognizing Soil Texture & Structure


Terminology

Terminology

  • Texture – physical property of soil referring to the relative amounts of sand, silt, and clay; how a soil feels.

  • Sand – largest individual soil particle

  • Silt – medium sized individual soil particle


Terminology1

Terminology

  • Clay – smallest individual soil particle

  • Peds – natural grouping of soil particles

  • Clods – artificial grouping of soil particles

  • Infiltration – movement of water into the soil


Terminology2

Terminology

  • Mechanical analysis – process of separating a soil into its various parts to permit study.

  • Mottlings – indication of internal drainage & aeration; soil exhibits spots of color.

  • Percolation – movement of water through the soil.

  • Permeability – characteristic of soil which permits variations in the speed of air & water movement.


Soil texture

Soil Texture

  • Soil texture = proportions of sand, silt and clay

  • Property of the soil controlled by the size of individual grains or particles

  • Soil is usually made up of particles of widely varying sizes.

  • Soil texture expresses the average or combined effect of all these grain sizes


Texture

Texture

  • At the most basic level, soil texture can be determined by feel & described as one of the following:

    • Coarse

    • Moderately Coarse

    • Medium

    • Moderately Fine

    • Fine


Specific soil textures from coarsest to finest determined by mechanical analysis

Specific Soil Textures (from Coarsest to Finest) determined by Mechanical Analysis

  • Sand (Coarse)

  • Loamy Sand (Moderately Coarse)

  • Sandy Loam (Moderately Coarse)

  • Loam (Medium)

  • Silt Loam (Medium)

  • Silt (Medium)

  • Sandy Clay Loam (Medium)


Specific soil textures continued from coarsest to finest

Specific Soil Textures continued (from Coarsest to Finest)

  • Clay Loam (Moderately Fine)

  • Silty Clay Loam (Moderately Fine)

  • Sandy Clay (Moderately Fine)

  • Silty Clay (Fine)

  • Clay (Fine)


Specific soil textures determined by feel

Specific Soil Textures determined by Feel

  • Sand – Dry = no clods. Moist = easily crumbled ball, does not ribbon, does not stain fingers.

  • Loamy Sand – Dry = very weak clods. Moist = easily crumbled ball, does not ribbon or stain fingers.


Felt textures cont

Felt textures cont…

  • Loam (most difficult) – Dry = clods slightly hard to break. Moist = forms firm ball, ribbons poorly, poor fingerprint

  • Silt – Dry = clods moderately difficult to break; ruptures suddenly. Moist = Smooth, slick feel; forms firm ball, slight ribbon; good fingerprint.


Felt textures cont1

Felt textures cont…

  • Silt Loam – Dry = clods moderately difficult to break; ruptures suddenly. Moist = Smooth, slick feel; forms firm ball, slight ribbon; good fingerprint.

  • Sandy Clay Loam – Dry = clods break with some difficulty. Moist = forms firm ball that dries moderately hard; ½” ribbon.


Felt textures cont2

Felt Textures cont…

  • Clay Loam – Dry = clods break with difficulty. Moist = forms firm ball that dries moderately hard; ½” ribbon.

  • Silty Clay Loam – Dry = resembles clay loam, only stickier. Moist = shows good fingerprint; forms firm ball drying moderately hard. ½” thin ribbon.


Felt textures continued

Felt Textures continued…

  • Sandy Clay – Dry = clods broken with extreme pressure. Moist = forms very firm ball drying quite hard. Thin, long, somewhat gritty ribbon.

  • Silty Clay – Dry = clods broken with extreme pressure. Moist = forms very firm ball drying quite hard. Thin, long, smooth ribbon.

  • Clay – Dry = clods often can’t be broken. 2”-3” ribbon


Feel that soil

Feel that soil!

  • Sand: In the moist condition sand should feel gritty and will be loose and single grained. Squeezed when wet, it will fall apart when the pressure is released

  • Clay: when moist is quite plastic and sticky when wet. When the moist soil is squeezed out between the thumb and fore finger, it will form long flexible ribbons.

  • Silty Soil: when dry and pulverized will feel soft and floury. When wet the soil readily runs together and puddles. When squeezed between the thumb and finger it will ribbon but the ribbon will appear checked and cracked.


Soil structure

Soil Structure

The combination or arrangement of primary soil particles into secondary particles, units, or peds (which are separated from adjourning aggregates by surfaces of weakness)


Soil aggregation

Soil Aggregation

The cementing or binding together of several soil particles into a secondary unit, aggregate, or granule

**clods are different – they are caused by some disturbance such as plowing or digging


Consistence

Consistence

The resistance of a material of deformation or rupture – the degree of cohesion or adhesion of the soil mass


Structureless soil

Structureless soil

Soil where the particles of coarse soil fail to cling together, when fine soil breaks into large clods, or when the soil is massive, a single compacted substance


Platy structure

Platy Structure

Soil aggregates developed along the horizontal direction: flaky


Prismatic structure

Prismatic Structure

A soil structure type with a long vertical axis that is prism shaped, vertical faces are well defined, without rounded caps


Columnar structure

Columnar Structure

Vertically oriented, round-topped structural prisms – rounded caps


Granular structure

Granular Structure

A natural soil ped or aggregate – have plane or curved surfaces which have slight or no accommodation to the faces of surrounding peds


Types of soil structure

Types of Soil Structure

  • Platy

  • Prismatic

  • Columnar

  • Angular Blocky: Block-like – three dimensions of same magnitude

  • Subangular blocky: same as angular except the vertices are more rounded

  • Granular

  • Crumb: similar to granular except the peds are porous


Class of structure

Class of Structure

Size of individual ped


Good soil structure

Good Soil Structure

  • Good Soil Structure:

  • Necessary for good water penetration into the soil

  • Water holding capacity

  • Ease of working the soil

  • Good root penetration

  • Favorable movement of soil air

  • Availability of plant nutrients

  • Good internal drainage


Binding agent in the soil

Binding Agent in the soil

  • Organic matter converted to humus is the chief binding agent for stable soil structure.

  • Continuous cultivation and never plowing under any organic matter tends to destroy structure


Soil structure is fragile

Soil structure is fragile.

  • Soil structure can be damaged or destroyed by:

    • Working soil that is too wet

    • Repeated movement of heavy objects or animals over the soil

    • Use of equipment at the same depth of the soil

    • Continual flooding of the soil


Improving soil structure

Improving soil structure

  • Leave it alone. Given enough time nature will repair damaged structure

  • Planting green manure crop

  • Incorporate plant residue into the soil


What is soil

Soil Taxonomy

and

Taxonomic Names


What is soil

Soil Orders

Alfisols-- high to med. base saturation. Older landscapes but not extensively leached. Not as weathered as Ultisols

Andisols--volcanic parent material. Non crystalline clays, high organic matter

Aridisols -- Arid environment. Light colored A horizon. Some B horizon development.

Entisols-- young soil, lacking horizon development

Gelisols-- showing freeze/thaw mixing

Histosols-- large organic horizon


What is soil

Soil Orders

Inceptisols -- young, weakly weathered. Few diagnostic horizons

Mollisols--well developed horizons, high in organic matter and calcium. High base saturation.

Oxisols--highly weathered soil, Fe, Al oxides. Low CEC

Spodosols--leached E horizon. B horizon with organics, Al, Fe oxides

Ultisols --Low base saturation. Weathered soils, but not as much as Oxisols

Vertisols --high shrink/swell clay content. Cracks


Soil orders in florida

Soil Orders in Florida

  • Entisols – little development, usually A-C horizons, ochric epipedon

  • Inceptisols – A little more development, Bw horizons, ochric, umbric epipedon

  • Alfisols – Argillic/Kandic horizon (Bt) less than 2 m, base saturation is > 35%

  • Ultisols – Argillic/Kandic horizon (Bt) less than 2 m, base saturation is < 35%

  • Mollisols – Mollic epipedon, dark, high organic matter

  • Spodosols – Spodic horizon (Bh), illuvial O.M., ochric, umbric epipedon

  • Histosols – Organic soil, histic epipedon


What is soil

State Soil of Florida: Myakka Series

Sandy, siliceous, hyperthermic

Aeric Alaquods

Surface layer: gray fine sand

Subsurface layer: light gray fine sand

Subsoil: dark reddish brown fine sand with organic stains

Substratum: brown and yellowish brown fine sand

http://soils.usda.gov

http://www.fao.org


Soil orders

Soil Orders

Weathering and

development

slight

Strong

Entisols

Histosols Inceptisols Andisols Gelisols

Aridisols Vertisols

Alfisols Mollisols

Ultisols Spodosols

Oxisols

The Florida state soil is a spodosol: Myakka fine sand


What is soil

Extent of Florida Soil Orders

Spodosols8.4 million acres

Entisols7.5

Ultisols6.9

Alfisols4.6

Histisols4.0

Inceptisols1.0

Mollisols1.0

Myakka fine sand


What is soil

Taxonomy

The last syllable in the taxonomic

name indicates the soil order

Apopkaloamy, siliceous, hyperthermic grossarenic paleudult

Ledwith fine, smectitic, hyperthermic mollic albaqualf

-ent-oll-od-ept


Soil taxonomy

Soil Taxonomy

Order

Suborder

Great group

Sub group

Family

Series

12

Soil forming processes / diagnostic horizons

Genetic similarity: Wetness, climate, vegetation

63

250

1400

8000

19,000


What is soil

Moisture Conditions

Suborder

Wet

Dry

Aquic – poor aeration, reduced iron

Udic- dry < 90 total days

Ustic - limited but is present

Aridic- moist <90 total days

Xeric - dry

Order

Suborder

Great group

Sub group

Family

Series

Temperature Conditions

Family

cold

Hot

Cryic – icy cold

Frigid – lower than 8oC

Mesic – between 8 and 15oC

Thermic – between 15 and 22oC

Hyperthermic - > 22oC


What is soil

Suborders

moisture, diagnostic horizons

Suborder Examples

Order

Suborder

Great group

Sub group

Family

Series

Aquodvery wet spodosol

Udultwet ultisol

Udollwet mollisol

Xerolldry mollisol

Psammentsandy entisol

Ochrept

Umbrept

Alboll


What is soil

Great Groups

Based on diagnostic horizons

and their arrangements or

other features like age, color, texture

Order

Suborder

Great group

Sub group

Family

Series

Arg - argillic horizon present

Pale - old

Kand - kandic horizon present

Hapl - minimum horizonation

quartzi – quartz sand

Hum - humid


What is soil

SuborderGreat Group

Udultpaleudult

Aquollargiaquoll

Udalfpaleudalf

Udulthapludult

Order

Suborder

Great group

Sub group

Family

Series

Aquic – poor aeration, reduced iron

Udic- dry < 90 total days

Ustic - limited but is present

Aridic- moist <90 total days

Xeric - dry


What is soil

Sub group

Expresses the core concept of the great group

Moisture, sandiness, depth, color

Order

Suborder

Great group

Sub group

Family

Series

Typic (typifies the great group)

Arenic (sandy)

Grossarenic (deep sandy)

Aquic (aquic moisture)

Rhodic (red color)

Typichapludult

Grossarenic quartzipsamment


What is soil

Families

Properties important to growth of plant roots

Particle sizemineralogytemperature oC

Siliceous

Kaolinitic

Smectitic

Oxidic

Sandy

Loamy

Fine loamy

Clayey

Frigid< 8

Mesic 8-15

Thermic 15-22

Hyperthermic > 22


What is soil

Series

Horizon number, order, thickness, texture, structure,

Color, Organic matter, pH, accumulations

Order Sub-order G. Group Sub-group Family Series

Mollisol Aquoll Argiaqoll typic Argiaquolltypic argiaquoll Brookston

loamy siliceous Cordova

Westland


What is soil

Horizon Properties

Soil Structure

Soil structure is the shape that the soil takes based on its physical and chemical properties. Each individual unit of soil structure is called a ped. Possible choices of soil structure are:

With Structure:

Blocky

Granular

Actual size

Actual size

Columnar

Platy

Prismatic

Actual size

Single Grained

Massive

Structureless:

See hands for relative size

Pencil is 19 cm


What is soil

Horizon Properties

Soil Color

Munsell Notation

The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils’ color.

7.5 YR 4/3

The first set of number and letter symbols represents the hue.

F Hue represents the position of the color on the color wheel (Y=Yellow, R=Red, G=Green, B=Blue, YR=Yellow Red, RY=Red Yellow).


What is soil

Horizon Properties

Soil Color (continued)

Munsell Notation

The Munsell code below each color in the GLOBE color chart is a universal notation that describes the soils’ color.

7.5 YR 4 / 3

The number before the slash is the Value.

The number after the slash is the Chroma.

F Value indicates the lightness of a color. The scale of value ranges from 0 for pure black to 10 for pure white.

F Chroma describes how the “intensity” of a color. Colors of low chroma values are sometimes called weak, while those of high chroma are said to be highly saturated, strong, or vivid. the scale starts at zero, for neutral colors, but there is no arbitrary end to the scale.


What is soil

Hue

Value

Chroma

Horizon Properties

Soil Color (continued)

Munsell Notation

Hue

Value

Soil Color Chart Pages

Chroma


What is soil

Horizon Properties

Soil Color (continued)

1.Take a ped of soil from each horizon and note on the data sheet whether it is moist, dry or wet. If it is dry, moisten it slightly with water from your water bottle.

3.Break the ped and compare the color of the inside surface with the soil color chart.

2.Stand with the sun over your shoulder so that sunlight shines on the color chart and the soil sample you are examining.

Note: Sometimnes, a soil sample may have more than one color. Record a maximum of two colors if necessary, and indicate (1) the Main (dominant color) and (2) the Other (sub-dominant color).


What is soil

Factors of Soil Formation

Parent Material

Climate

Vegetation

Topography

Time


What is soil

• Horizons are split or

differentiated by changes

in color, texture, roots,

structure, rock fragments


Soil ph

Soil & pH

(Remember pH is a scale of 0-14 that measures acidity)

  • Soil solution has a unique pH

  • Plants grow best at a certain pH

  • Nutrients are not available to plants at certain pH levels


Plant ph needs

Plant pH Needs

  • Goldenrod 5.0-7.5

  • Sugar Maple Tree 6.0-7.5

  • Soybean 6.0 and 7.0

  • Apple Tree 5.0-6.5

  • Blueberry Bush 4.0-5.0


Some soil organisms

Some Soil Organisms

  • Fungus

  • Worms

  • Insects

  • Bacteria


The biotic living part of soil

The Biotic (Living) Part of Soil


What is soil

  • In one tablespoonful of soil, there are more bacteria than there are people on the entire planet!


Soil organisms what can they do

Soil Organisms: What can they do?

  • Mix organic matter from the surface deeper

  • Break down large compounds into plant food

  • Make space in the soil for air and water


Summary

Summary

  • Soil provides support for plants and is a major site of decomposition.

  • Soil has an abiotic and a biotic part.

  • Tons of Fungus, Bacteria, Insects, and Worms live in the soil.

  • Soil organisms can mix organic matter deeper into the soil, break down large compounds, and make space for air& water in the soil.


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