Soil: One of Our Natural Resources

Charity I. Mulig

Soil

• The portion of regolith that can support plant growth.– Inorganic/mineral matter– Humos/organic matter– Air and water

• A dynamic interface which responds to changes in the different parts of the earth system

Soil Texture

• refers to the proportions of different particle sizes.

• Influences the ease of soil’s cultivation as well as the susceptibility of soil’s erosion; also affects the porosity and permeability of the soil

Soil Structure

• Describes the way soil forms clumps or peds (platy, prismatic, blocky or spheroidal)

• Influences the ease of soil’s cultivation as well as the susceptibility of soil’s erosion; also affects the porosity and permeability of the soil.

Controls of Soil Formation

Parent Material

• Affects the rate of weathering and fertility of the soil– Residual soil the parent material is

the underlying bedrock– Transported soil soils develop from

unconsolidated sediments; generally form faster than residual soil

Time

• “the longer the soil has been forming, the thicker it becomes and the less it resembles the parent material”– More time climate has more effect on

soil characteristics– Short time parent material has more

effect on the soil characteristics

Climate

• The most influential control of soil formation• Influence the type of plant and animal life in

the region• Temperature and Precipitation have the

greatest effect on soil formation.– Precipitation influences the degree of leaching and

therefore the soil fertility.

Plants and Animals

• Furnish soil with organic matter which aids in water retention

• Microorganisms in organic matter also aids in decomposition and nitrogen fixation while burrowing animals mix minerals and humus in the soil.

Slope

• Inclination influences the amount of erosion and water retention

• Orientation influences the amount of sunlight

• “The optimum terrain for soil development is a flat-to-undulating upland surface.”

Soil Profile

• Soil horizons are zones or layers of soil.

• A soil profile is a vertical section through all the soil horizons.

Soil TypesPedalfer (pedon + Al

+ Fe)Pedocal (pedon +

calcite)Laterite

•Accumulation of iron oxides and aluminum-rich clays in the B horizon •Found in midlatitude areas where there is abundant percipitation.•Soil is brown to reddish brown•Best developed under forest vegetation

•Accumulates calcium carbonate •Associated with drier grasslands and brush vegetation•Forms caliche (a calcium-enriched soil)

•Forms in hot, wet tropical climates where chemical weathering is intense as well as leaching of soluble minerals such as silica•Removal of silica results to increase concentration of iron and aluminum oxides giving the soil its orange to red color•Poor for growing crops