Notes 24-36 Soil Composition and Properties Cont.

APES 2024

Can affect porosity, permeability, and fertility of soil

Can affect porosity, permeability, and fertility of soil

Particle size and composition of each soil horizon

Porosity

How many pores or holes a soil has

Permeability

The property of the soil to transmit water and air

Soil may be porous but if the pores are not connected then

Permeability is low

Most permeable

Sand

Least permeable

Clay

Highest porosity

Clay

Lowest porosity

Varies

The permeability of soil depends on

Texture ex. sand has large and loosley packed particles, drains quickly; clay drains much more slowly

Soil that is too sandy

Drains too much water, and roots will dry out

Clay heavy soil retains water, but

Does not get to roots or waterlogs roots causing suffocation

The ideal soil

Loam

Loam

Has a balance of porosity and can hold water

The chemical properties of soil help determine

How a soil functions

Cation exchange capacity (CEC)

The ability of particular soil to adsorb and release cations

CEC depends on

The amount of clay particles (clay is negatively charged)

Soil with a lot of clay can provide

Cations to plants and is good for agriculture

If there is more than 20% clay

It will hold too much water

Adsorb

Individual molecules, atoms, or ions gathering on surfaces

Molecules and ions can

Interact with a surface and “stick” or adsorb

Calcium, potassium, and sodium are soil bases because

They can neutralize or counteract soil acids such as aluminum and hydrogen

Soil acids tend to prohibit

Plant growth

Plant growth is encouraged by

Soil bases

When soil has a high CEC it can

Retain and release plant nutrients

A soil that has a high CEC and high base saturation will likely

Support high plant productivity

Soil fertility

Ability of soil to support plant growth

Soil nutrients

Nitrogen, phosphorus, magnesium, calcium, and sodium

What increases soil nutrients

• Organic matter

• Humus (holds & releases)

• Decomposers

• Clay (negative charge bonds positive nutrients)

• Bases (ex. calcium carbonate: limestone)

What decreases soil nutrients

• Acids (leach positively charged nutrients)

• Excessive rain or irrigations leach nutrients

• Excessive farming depletes nutrients

• Topsoil erosion

Groups of organisms that account for most of the biological activity in soil (80-90% of soil)

• Fungi

• Bacteria

• Protozoans

Other organisms that do biological activities in soil

• Snails

• Slugs

• Insects

• Worms

• Rodents

Types of soil

• Agricultural

• Urban

• Desert

• Tundra

• Volcanic

• Mountainous

• Forest

• Coastal

• Wetland

Agricultural

Barren fields, compact soil, less infiltration, fewer streams

Urban

Natural water flow pattern, altered, high runoff, vulnerable to flooding, fixed land use

Desert

Often has a b horizon, made up o fcalcium carbonate, gypsum and/or salts, usually light colored, little rainfall=no stream devolopment, limited ground water recharge

Tundra

Often barren, some trees but are small, soils are permafrost

Permafrost

Permanently frozen, thaw during summer for a short growing seasos store a lot of carbon

Volcanic

Often rich in nutrients and hold water well, darker in color, can be acidic

Mountainous

Steep gradient, less porous soil (more rocky), less infiltration, high runoff, downstream are vulnerable to flooding

Forest

Evapotranspiration dominant, high inflitration, little runoff

Evapotranspiration

Sum of all processes by which water moves from the land surface to the atmosphere via evaporation and transpiration

Coastal

High rainfall, no channel control, local flooding, high water table, saltwater intrusion

Wetland

Water is not a limiting factor, high rainfall, high runoff, dominant evaporation

Vegetation

Adds organic matter to soil

Tree litter protects the

Soil’s surface

Roots prevent

Erosion

Canopy keeps

Water cool to prevent thermal pollution

Reduces the force of rain and wind speed

Canopy

Plant cover provides

Food and protection for organisms

Riparian zone

Buffers water from runoff (sediment, chemicals, nutrients)