Soil

1
Soil
Tuesday 21st March 2006

• Learning Objectives
• To understand soil formation.
• To understand the characteristics of two soil
  types brown earths and podsols.
• To know about azonal, intrazonal soils and the
  role of topography soil catena.

2
Definitions

• Soil forms the thin surface layer of the earths
  crust. It provides the foundation for plant and,
  consequently, animal life on land.
• The soil is a natural body of animal, mineral
  and organic constituents differentiated into
  horizons of variable depth which differ from the
  material below in morphology, physical make up,
  chemical properties and composition, and
  biological characteristics (Joffe, 1949).
• Soil results from the interrelationships between,
  and interaction of, several physical, chemical
  and biological processes all of which vary
  according to different natural environments.

3
The soil system
4
The soil system

• Open system inputs, stores, outputs and
  recycling or feedback loops.
• Inputs include
• Water from the atmosphere or through flow from
  higher up the slope.
• Gases from he atmosphere and the respiration of
  soil animals.
• Mineral nutrients from weathered parent material,
  which are needed as plant food.
• Organic matter and nutrients from decaying plants
  and animals and
• Solar energy and heat.
• Outputs include
• Water lost to the atmosphere through
  evapotranspiration.
• Nutrients taken up by plants as food.
• Nutrients lost through leaching and throughflow
  and
• Loss of soil particles through soil creep and
  erosion.

5
Soil Formation

• The process of soil formation is called
  pedogenesis and it is the product of three
  processes
• The weathering or breakdown of minerals.
• The incorporation of decomposed organic matter
  (humus).
• The movement of water through the soil.

Bowen and Pallister, page 116/7.
6
Factors which affect soil formation

• Climate
• Vegetation
• Topography
• Time
• Parent material
• Fauna
• Human activity

Bowen and Pallister, page 119.
7
Topography (relief)
A catena the relationship between soil and
slope.
Waugh, page 239.
8
Relative proportions, by volume, of components in
a normal soil.
Waugh, page 240.
9
The soil profile

• The soil profile is a vertical section through
  the soil showing its different horizons.

Waugh, page 240.
10
Soil Classification

• Zonal soils Mature soils. They result from the
  maximum effects of climate and living matter
  (vegetation). They have had time to develop
  distinctive profiles and, usually, clear
  horizons.
• Azonal soils Have a more recent origin and are
  said to be immature as they occur where
  soil-forming processes have had insufficient time
  to operate fully. These soils show
  characteristics of their origin (i.e. parent
  rock), do not have well defined horizons and are
  not associated with specific climatic-vegetational
  zones.
• Intrazonal soils Reflect the dominance of a
  single local factor, such as parent rock. As
  they are not related to general climatic
  controls, they are not found in zones. They can
  be divided into Calcimorphic or calcareous
  soils Hydromorphic soils or Halomorphic soils.

11
The characteristics of soils

• Brown earths
• Podsols
• Page 122 125
• Questions
• Shade in a world map to show the distribution of
  these soil types.
• Describe the distribution in Britain.
• Draw a soil profile.
• Describe the soil characteristics.
• Explain the role of climate and vegetation in the
  formation of each soil type.
• Discuss the impact of human activities.

12
Homework

• Make notes on British Soils, using the Geo
  Factsheet.
• Due next Wednesday.