SCSC301 chapter 1

what are the 5 major soil functions?

• medium for plant growth

• support for buildings and roads (engineering medium)

• habitats for organisms

• purification of waters and regulator of water supplies

• recycling system for nutrients and organic wastes

How is soil a medium for plant growth?

soil supplies physical support, minerals, nutrients, waters, detoxification, and ventilation

Essential Macronutrients

C, H , O , N , P, K , Ca, Mg, S

Essential Micronutrients

Fe, Mn, B , Zn, Cu, Cl, Mo, Ni

How are soils an engineering medium

soils differ but have the qualities of bearing strength, compressibility, hear strength, and stability. not all soils are the same and some are better for building than others

How are soils a habitat?

soils contain billions of organisms because of its rich microhabitats with oxygen, pH, temperature, and water

Pores : Habitat (Smalll)

round worms, diatoms, and rotifers

Larger pores: habitat

tiny insects, and mites

how do soils help with water purification

soils slow water flow, allowing for longer filtration and detoxification. water is purified as it moves toward a body of water

how do soils recycle?

animal and human waste becomes humus, Carbon dioxide, and nutrients available for plants

Regolith

unconsolidated debris layer (bottom most layer)

• can be transported from where it was formed and deposited

relationship between regolith and soil

soil forms where regolith meets air

Destructive biochemical processes

weathering/erosion and microbial decay of organic residues

synthetic biochemical processes

formation of minerals, formation of organic compounds, and aggregation

aggregation

process of which soil particles bind together to form larger couples. supports microbes, root growth, and structure

5 Soil Forming Factors

Climate, biota, parent material, topography, time

active factor

factor that is acting upon the soil all of the time.

• climate, and biota

Passive factor

factor that plays a role in the development of the soil but not hands on like an active factor.

• time, parent material

modifying factor

alters the structure or the formation of the soil. change the soil qualities

• topography

Soil definition

a dynamic natural body having properties derived from the combined effects of climate and biotic activities, as modified by topography and acting on parent material over periods of time

Lunar Soil

Moon is regolith (unconsolidated rock layer) and not soil.

• no known biota and very little climate

Soil Profile

vertical section exposing a set of layers called horizons that extend down to the parent material hori

horizons

layer of soil approx. parallel to the soil surface. differing in properties and characteristics from adjacent layers below or above it

• vary in thickness

  • may have irregular boundaries

parent material or regolith

deepest layers of soil that are relatively unaffected by soil forming processes

Topsoil (surface soil)

layer most affected by soil forming factors

• darker

• more plant roots

• porous

• aggerates (smaller)

  • less clay and more sand and silt

Subsoil

layers less affected by soil forming factors

• light in color (less organic matter)

• fewer plant roots

• more dense (less porous)

• larger aggregates

  • more clay

Solum

horizons above the C (not C) horizons affected by soil forming factors

O horizon

horizon of partially or wholly decayed organic materials that may occur over or in place of an A horizon

A

topmost mineral horizon

E

subsoil horizon that is a zone of eluviation (depletion)

• less clay, oxides, minerals

  • white or light colored

B

subsoil horizon that is a zone of accumulation

• usually more gain of clay, oxides, and minerals

C

regolith layer

R

rock layer

Pedon

smallest 3D soil unit with all the characteristic of the soil

• size can vary

Polypedon

group of similar pedons

4 major soil components

Air, Water, Mineral, Organic Matter

Pore Space

where water and air accumulate and organisms live in soil

• accounts for usually 50% of the soil

Particles in Soil

contains the mineral and organic matter of the soil.

• organic 5% of the soil

  • mineral accounts for 45% of the soil

Soil Air

differs from atmospheric air

• variable

• higher moisture (100% relative humidity)

• higher co2

• lower o2

Soil water (solution)

Determines the functioning of the soil

• organisms survival (plants, microbes)

• affects quality and quantity of water resources

Differs from drinking water

• soil particles affect flow

• dissolved organic and inorganic substances

  • differing acidity or alkalinity

pH

master variable in soils due to its influence on so many chemical and biological processes

• concentration of hydrogen ions in soil water

Nutrient Availability in soil

nutrient availability is usually tied to nutrients in the soil solution

as plants take up nutrients, they must be replenished from the soil

Root interception

root grows into the new areas that are not depleted

mass flow

ions are carried with the flow of water into the root from the soil

diffusion

ions move from areas of high concentration to areas of low concentration (area around the roots that depleted due to uptake)

replenishing mechanism

weathering

• degradation releasing nutrients

Soil Solution

• released nutrients in soil are available for uptake

Nutrients can also absorb particles

• particles can store nutrients back to soil solution via diffusion or mass flow

Soil size ranking (smallest to largest)

clay (<.002 mm) < sil (.002 - .05 mm) < Sand (.05 to 2 mm)

Sand

low attraction to water and each other

low ability to hold chemicals and nutriens

tend to act as individuals

loose gritty

silt

moderate attaction to water and each other

• modertae ability to hold nutrients

• tend to act mostly as individuals, some groupings

  • smooth powdery

Clay

high attraction to water and each other

high ability to hold

tend to act in groups

sticky, malleable, and can form hard clods

Soil Texture

relative amounts of primary particles

described based on categories that are based on percentages

soil structure

the arrangement of particles in soil

• classified by shape

• affects water movement in soil

Minerals

Homogenous inorganic compounds

have definite chemical formula

Primary mineral

formed as molten lava cools and solidifies

secondary minerals

recrystallization and or alteration of primary minerals

living biomass

plants and other organisms

• identifiable

Detritus

dead residues from living organisms

• identifiable

Humus (stabilized soil organic matter)

complex mixture of organic compounds that accumulate in soil

• no longer identifiable

• role in soil structure; binds mineral particles together

• holds water nutrients and chemicals

Interaction of Soil Components

• Organic affects organization of mineral particles

• organization of particles affects water movement

• water affects air distribution