Plant Science Chapter 5 Soils

Define Soil

composed of weather rock, air, and decomposed organic material and various organisms

Components of Soil:

• solid fractions - rock fragments and materials

• Organic fraction - decayed plant residue, microbes, and soil animals

• liquid fraction - water and dissolved minerals

• soil atmosphere of soil air

• voids between solid core - half water half air

• parent rock - minerals found in soil

• field capacity

Types of Parent rock

Igneous rock - from molten rock

sedimentary rock - transported and deposited by wind, water or glaciers

metamorphic rock - igneous and sedimentary rock changed by high temps and pressure

Composition of Rock

·       20 – 30 % air

·       20-30% water

·       45% mineral

·       5% Organic (organic minerals are on top)

Factors in Soil Formation

• Accumulation and breakdown of parent material (major process)

• Breakdowns into different layers called “horizons”

• Soil profile – vertical section of soil that extends through the horizion

Han Jenny’s Model Components

Soil Formation

• breakdown of parent material

• Chemical weathering

• climate effects

• biology

• fungi

• animals

• topography

• time

Soil Profile Characteristics

A Horizon - The upper soil layer where most roots are found and where there are large amounts of organic matter.

B Horizon - The subsurface soil layer where materials such as nutrients and fine particles from upper layers accumulate.

C Horizon - The soil layer beneath the B horizon that consists largely of relatively unweathered parent material.