SOILS

• Vegetated surface covers over 11.5 billion hectares of the 14.9 billion hectares of earth’s surface.

• SOILS: Sustain the terrestrial Biome– Supports plant growth– Filter or modify precipitation– Regulate amount of water entering ground.– Habitat for many organisms

What is Soil?

• a dynamic natural body composed of mineral and organic materials and living forms in which plants grow.

What are some of the uses for soils?• Medium for plant growth• recycling of nutrients and wastes• water supply and purification• habitat for soil organisms• engineering medium

What is soil composed of?

• mineral material (45%)• organic material (5%)• air (20-30%)• water (20-30%)

SOILS• Unconsolidated natural materials on the

earth surface that support rooted plant growth.

• Unconsolidated materials are produced by physical and chemical alteration of rocks (weathering) and mediated or modified by biotic processes.

Soil development is a function of Soil Forming Factors • climate • organisms• relief (topography)• parent material • time • HUMANS

Soil = f (clropth)

Parent Material

Geologic materialeg. - weathered rock (residual)

- glacial deposits- till (compacted)- outwash (loose)

- alluvial (river deposited)- loess (wind deposited)- marine, lacustrine, ash, mudflow,

organic

Climate

• Precipation &

• Temperature

Affects physical, chemical, & biological processes

Organisms

• Soil animals • Soil microbes • Vegetation

• * Interaction between Climate & Organisms

Relief (or topography)

• Affects:

– Water runoff– Colluvial movement – Solar radiation

Time

• Interacts with all other Soil Forming Factors

HUMANS

may increase or decrease the effects of the other soil forming factors

(many times even dramatically).

Different combinations and intensities of the different soil forming factors create different soils!

• These differences are a result of processes affected by the soil forming factors that directly and indirectly affect the soil properties.

Soil variability

• Vertical variations (soil horizons)• Variations across landscapes • Regional variation

SOIL PROFILE -HORIZONS

• Various soil forming processes lead to the formation of distinct layers - known as soil HORIZONS.

• The stacked layers produced a sequence that is typical of different types of soils - known as a soil PROFILE.

SOIL PROFILE

• ZONE OF ORGANIC MATTER ADDITIONS– O Horizon: Organic layer containing

decomposing plant material (dark brown - black).

– A Horizon: Mineral layer with significant organic matter. Materials are continuously being modified and removed (dark brown - brown).

TOPSOIL

• The O and A horizon(s)– Organic-rich – Nutrient -rich– Teaming with life

O horizon

A horizon

SOIL PROFILE

• ZONE OF LEACHING– O Horizon: Organic rich thin layer

containing decomposing plant material (dark brown - black).

– A Horizon: Mineral and Organic matter. Materials are continuously being modified and removed (dark brown - brown).

– E Horizon: present in many profiles a layer where many oxides (iron, manganese) have almost completely removed (light colored horizon).

SOIL PROFILE

• ZONE OF ACCUMULATION– B Horizon: layer in which materials

removed from the overlying horizons are accumulated.

– K Horizon: a layer common in many arid region soils formed by the accumulation of calcium carbonate (CaCO3 - calcite). Caliche

SUBSOIL

• The B (and K) horizons– rich in oxides (Fe, Mn)– may be clay rich– may contain salts, carbonate, or

be acidic– not as nutrient-rich as topsoil

SOIL PROFILE

– C Horizon: layer consisting of partially altered parent material. Commonly with oxides accumulated.

– R Horizon: unweathered (unaltered) parent material. i.e. Rock.

Exercise

SOIL TEXTURE

• Refers to the characteristic look and feel resulting from the variable amounts of SAND - SILT - CLAY.– SAND: grains that are 2 to 0.05 mm in

diameter– SILT: grains that are less than 0.05 mm

and as small as 0.002 mm in diameter– CLAY: grains that are smaller than 0.002

mm in diameter.

SOIL TEXTURE

• Loam - a material consisting of approximately 40 % sand, 40 % silt, and 20 % clay. Very common texture in nature.

• Soil Texture affects or controls a number of important soil properties and its WORKABILITY (ease with which a soil can be cultivated).

SOIL STRUCTURE

• Natural aggregates (peds) in the soil. Form by clumping together of mineral grains. Organic matter important in the formation and stability of soil structure.

• Soil structure affects how big the spaces will be in the soil through which roots, air, and water may move

SOIL STRUCTURE

• Soils are modified by organisms and characteristic structure results through:– Addition of particulate materials, e.g. plant

litter, animal droppings, – Decomposition of organic matter by

detritus feeders and decomposers– (Above processes produce HUMUS)– Modification (clumps) of soil by ingestion

and addition of organic matter, e.g. earth worms.

SOIL PROPERTIES

• Water– Permeability: ability to allow water to pass

through the pores (open space between grains). Depends greatly on texture. Infiltration is the actual water that passes through the soil.

– Water-holding capacity: quantity of water that a soil can retain and is available for plant usage.

– Evaporative water loss: amount of water lost from a soil surface to evaporation

SOIL PROPERTIES

• Nutrients– Mineral Nutrients: element or compounds

derived from soil components and available for use by producers. Includes phosphate (PO4-3), potassium (K+), calcium (Ca++), and other.

– Nutrient-holding capacity: quantity of mineral nutrients retained by the soil (on the surface of grains). Cation Exchange Capacity - CEC

SOIL PROPERTIES

• Aeration– Ability to let air (atmospheric gasses) through.

• Acidity/Alkalinity– Presence absence of compounds releasing

protons (H+)- Acids, or binding protons - Bases (OH-).

• Salts– Salts tend to retain water and even extract water

from plants.

SOIL ECOSYSTEM

• The soil itself is a Habitat for numerous organisms living above and below the soil surface.

• The activities of the organism serve to modify a soil and it continuously evolve (i.e. it goes through various ecological successions).

• Soil properties depend on soil texture and biotic modifications.

SOIL and PLANTS

• PLANTS depend on soil for nutrients and water.

• SOILS are maintained by plants – plant litter replenishes organic matter– roots (aeration and infiltration).– nutrient recycling and regulation– protect the soil

• control erosions• control water loss.

Need to be concerned about our management or use of soils• erosion, • compaction,• pollution, • available water, • organic matter, • nutrients, • etc

• Soil is a resource that should be protected from misuse– because soil formation is generally considered in

terms of centuries

• Soils should be considered as a valuable resource– should be careful about our use or misuse of the

soils

SOIL ENVIRONMENTAL PROBLEMS• Environmental problems of soils caused by

utilization (agriculture, construction, mining..)

• Soil Degradation– EROSION - Soil loss

• Removal of vegetation, overgrazing and tilling– splash - sheet -gully

– NUTRIENT LOSS• Erosion, overcultivation, deforestation

Erosion control - Terracing

SOIL ENVIRONMENTAL PROBLEMS

• SALINIZATION– Irrigation with mineral rich groundwater

• DESERTIFICATION– Modified water-holding capacity and enhance

evaporative loss.• overgrazing, salinization

• SEDIMENTATION– Rivers, lakes, ocean are receiving too much sediment

from land.

Outlined region shows desertification due to overgrazing and irrigation (Israel).

Deserification along fenceline in Africa

Web sources

• http://www.wtamu.edu/~crobinson/DrDirt.htm (Excellent lab experiments to teach basic concepts!)

• http://ag.arizona.edu/OALS/watershed/beaver/soiltexture.gif (soil texture flowchart from workshop)

• http://soils.usda.gov/education/resources/k_12/lessons/profile/ (soil profile exercise from workshop)

• http://soils.usda.gov/technical/soil_orders/ (GREAT poster of the 12 main soil types)

• http://county-tx.tamu.edu/ (to find your local county extension office for county soil survey)

• http://soils.usda.gov/ (some soil surveys are digital and can be viewed online, also has some other great links)

• http://school.discovery.com/schooladventures/soil/down_dirty.html

• http://soil.gsfc.nasa.gov/