Ms. LacrossApril 2015

Agriscience and Technology I

Introduction to Soil Science

After this unit you will be able to:

Identify and Identify and describe soildescribe soil

Describe the Describe the importance importance

of soil of soil Describe Describe

and draw a and draw a soil profilesoil profile

Soil Introduction

Soil Origin and Development

• Pedology: The study of soil formation

• V. V. Dokuchaev (Russian) is credited with laying the foundation of modern Pedology– published a careful study of

Russian Soils in 1883

• Hans Jenny (US) published the Factors of Soil Formation in 1941 developed 5 factors of soil formation

Soils Perform Several Vital Functions

Sustaining plant and Sustaining plant and animal life below and animal life below and above the surfaceabove the surface

Regulating and Regulating and partitioning water and partitioning water and

solute flowsolute flow

Filtering, buffering, Filtering, buffering, degradingdegrading, immobilizing, and , immobilizing, and detoxifyingdetoxifying

Storing and cycling Storing and cycling nutrientsnutrients

Providing Providing supportsupport to to structuresstructures

What is Soil?

Soil Components

The Soil Body

• Soil is a – collection of natural bodies of

the earths surface– contains living matter that is able

to support growth of plants

• Soil varies across the landscape• Pedon: Is a small section of soil

extending from the surface to the depth of root penetration

Soil Vs Dirt

Soil Dirt

Material which nourishes and supports growing plants

Soil out of place

Compilation of minerals, air, water, animals and other living matter

Unable to serve its original purpose

Contains an equal amount of Sand, Silt and Clay

Can not support plant life

Parent Material

• Soil Genesis = the process of creating soil from parent material

• Soils form directly from bed rock• Transported soils: developed from weathered

material and are transported from their place of original origin – glacial ice: carried parent materials over the northern

part of America– wind– water – gravity

Parent Material

• Soil Genesis = the process of creating soil from parent material

• Soils form directly from bed rock• Transported soils: developed from weathered

material and are transported from their place of original origin – glacial ice: carried parent materials over the northern part

of America– wind– water – gravity

Physical Properties of SoilColor, Texture, Structure and Horizons

Soil Components and Texture

• Soil Texture describes the portion of three sizes of soil particles– Sand – largest– Silt- medium– Clay- smallest

12 Texture Classes

• The United States Department of Agriculture (USDA) has identified 12 soil texture classes

Importance of Soil Texture

Texture is important because it affects:• Water-holding capacity—the ability of a soil to retain

water for use by plants• Permeability—the ease with which air and water may

pass through the soil• Soil workability—the ease with which soil may be

tilled and the timing of working the soil after a rain• Ability of plants to grow—some root crops like carrots

and onions will have difficulty growing in a fine-textured soil

Soil Texture Triangle

• Way of showing proportions of sand, silt and clay in the soil

• Texture determines practices that should be used.

Soil Texture by Feel

• Texture class can be determined by feel

• To determine texture a person MUST be familiar with the composition of soils

• Gather a bit of soil and add water droplets until the soil is moldable

Soil Particles

• Soil is made of solid particles• particles largely consist of

mineral matter and organic matter

• between these soil particles are open spaces called pore space

• the arrangement of the solid particles and the pore space is called the soil matrix

Soil Structure

Aggregate: clumps of soil particles held together by moist clay, organic matter, by organic compounds

Soil Color

• Described by comparing the color of a soil horizon with a Munsell color chart

• Soil horizons have several colors

• Dark colored horizons have MORE organic matter than lighter ones

Soil Color

• Dark = organic matter• Red = iron• Brown = well drained• Grey (gley) = poorly drained• Mottled: redoximorphic concentrations,

depletions = restricted aeration, poor drainage

Soil Horizons

• System for naming soil horizons

• A, B and C are the master horizons

• Each layer is identified by a code: O, A, E, B, C and R

Soil Profile

O: Organic MatterA: Top Soil

– Surface mineral layer where organic matter accumulates

E: Zone of Eluviation– depleted in clay, chemicals

and organic matter– light colored – many soils do not have this

horizon

Soil ProfileB: Subsoil

– “zone of accumulation”: where chemicals leached out of the A horizon accumulates. lower organic matter content than top soil

C: Weathered/aged parent material

– little touched by soil-forming processes

– soft, weathered bedrockR: Hard Bedrock

– limestone, sandstone or granite

Soil Taxonomy

Soils Taxonomy

• Soil is as variable as leaves so we use a system to name soils

• Soil Taxonomy: – Six categories: order, suborder, great group,

subgroup, family and series– Twelve orders in the world– More than 17000 series in the US

Soil Taxonomy: 6 Groups

• Soil orders are defined on the basis of horizons and materials– Suborder: based on soil moisture regimes– Great Group and Subgroup: based on the presence or

absence of certain kinds of soil horizons– Family: based on particle-size, temperature of subsoil

horizons– Soil Series: based on a wide set of properties and are

named for the local community in which the soil was first identified

Twelve Soil Orders

• Gellisols• Histosols• Spodosols• Andisols• Oxisols

• Vertisols

• Aridisols• Ultisols

• Mollisols• Alfisols

• Inceptisols• Entisols

Soil Orders

Alfisols•Soils with a subsoil accumulation of silicate clay that are moderately weathered•Abbreviation: ALF

Andisols•Soils formed from volcanic materials•Abbreviation: AND

Soil Orders

Aridisols•Soils of Arid Environments•Arid = dry, climates lacking vegetation •Abbreviation: AID

Entisols•Very weakly developed soils •Including sandy soils•Abbreviation: ENT

Soil Orders

Histosols•Soils formed from organic materials•Abbreviation: IST

Inceptisols•Weakly developed soils•Excluding sandy soils•Abbreviation: EPT

Soil Orders

Mollisols•Soils wit thick, dark surface horizons•They are high in organic matter•Abbreviation: OLL

Oxisols•Highly weathered soils or tropic areas•Are high in Iron and aluminum-oxide •Abbreviation: OX

Soil Orders

Spodosols•Soils with a subsoil accumulation or aluminum, organic matter and Iron•Abbreviation: OD

Ultisols•Soils with a subsoil accumulation of clay that are highly weathered•Abbreviation: ULT

Soil Orders

Vertisols•Soils that undergo shrinking and swelling•Abbreviation: ERT

Gellisols•Soils of a very cold

climates that contain permafrost within the

soils surface•Abbreviation: EL

Soil Quality

Soil Quality

• Soil Quality = the capacity of a specific soil to provided needed functions for human or natural ecosystems over the long term–can sustain plant and animal growth–can maintain air and water quality–support human health

Soil Quality

• Soil degradation = The loss of soil quality• Soil connects intimately to water this also

means water problems• How to fix it?

– BMP’s or Best Management Practices– involve keeping the soil covered as much as

possible– employing management methods like mulching

and cover cropping

Soil and Climate

• Carbon sequestration: the process of storing carbon in soils, plans and elsewhere