Soil #16

Soils are critical for life on Earth; they are not just dirt.
3% of the planet's surface is suitable for arable agricultural production.
An alarming statistic indicates that 75 billion tons of fertile soil is degraded worldwide.
It takes 500 years to form just 1 inch of soil in the United States.

Our existence depends on a thin layer of topsoil, typically six inches, and the availability of rain.

Soil is defined as a dynamic body of natural materials, which is capable of supporting a vegetative cover.
Fertility is the soil's usefulness, specifically its effectiveness in producing crops or plants.

Comprise insoluble rock and mineral fragments:
- Quartz, feldspar, and mica (forms sand and silt).
- Oxides of aluminum and iron combined with silica (forms clay).
Includes soluble minerals held in solution:
- Most common: silica, aluminum, oxygen, iron.
- Most important nutrients: carbon, hydrogen, nitrogen, sodium, potassium, zinc, copper, and iodine.

Refers to the process of adding nutrients or other constituents to meet the specific soil conditions required by certain plants.

Texture is determined by the particle sizes present in the soil:
- Particles greater than 2.0 mm include pebbles and gravel, important for infiltration.
- Large particles allow for aeration while small particles may lead to waterlogged conditions.

Visual representation categorizing soil types based on their percentage of sand, silt, and clay:
- Demonstrates how combinations of these particles affect soil characteristics and functions.

Porosity is defined as the amount of space within a soil volume.
Permeability determines the ease with which air and water move through soil.
- Percentage values help quantify these properties.

Infiltration plays a key role in dissolving materials, making them available for plants:
- Gravitational water drains through the soil due to gravity impacts.
- Capillary water refers to water stored in the soil, which is accessible to plants.
Precipitation contributes to soil moisture alongside organic additions and soil faunal activity.

Water table is the surface where the ground becomes fully saturated with water.
Leaching is the process of nutrient depletion due to percolation, while eluviation refers to the downward removal of solids, and illuviation is the deposition of materials in the subsoil.
Hardpan is a dense subsoil clay layer that restricts percolation.

Soil Profile refers to the vertical differentiation of soil into various horizons:
- O Horizon: Leaf litter and organic debris.
- A Horizon: Known as topsoil, dark in color and high in organic matter.
- E Horizon: Zone of eluviation or leaching, light in color and low in mineral content.
- B Horizon: Accumulation zone rich in minerals and clay; also known as the illuviation zone.
- C Horizon: Partly weathered parent material.
- R Horizon: Bedrock or solid rock layer.

Spring: Natural outlet of groundwater.
Aquifer: Underground layer of water-bearing rock.
Zone of Saturation: Undersaturated area where the soil's voids are filled with water.
Zone of Aeration: The layer above the water table where soil pores are filled with air rather than water.

Soil color can indicate essential physical and chemical characteristics:
- Brown or black indicates high organic material (humus).
- Light gray or white suggests leached soils with lower fertility.
- Indicators of drainage issues may appear as blue-gray.
pH scale (0-14):
- Low pH indicates acidic soils; high pH indicates alkaline soils.
- Most plants prefer a pH range between 4 and 10.

Occurs in humid tropical climates with high temperatures and precipitation:
- Results in laterite, a red clayey soil horizon rich in iron and aluminum oxides.

Found in coniferous forests at high latitudes, it leads to highly leached, acidic soils with distinct layering.

Observed in drier climates, it causes the upward movement of calcium and soluble salts, creating nutrient-rich topsoils.

Occurs in areas with high evaporation rates, leading to salt build-up in the soil profile, particularly in arid regions.

Happens in cold, humid environments, resulting in soil formation in waterlogged conditions.

Alfisols: Fertile forest soils found in temperate regions.
Andisols: Developed from volcanic ash, highly fertile and moisture-retaining.
Aridisols: Dry soils with potential nutrient accumulations, primarily in arid and semi-arid areas.
Entisols: Recent soils with little developed horizon, found in young landscapes.
Gelisols: Associated with permafrost and poorly drained cold environments.
Histosols: Extremely organic in nature and form in wetland environments.
Inceptisols: Young soils showing early stages of development in varying climates.
Mollisols: Exceptionally fertile grassland soils.
Oxisols: Characterised by extensive weathering in tropical climates, low fertility.
Spodosols: Sandy soils subjected to leaching, not suitable for agricultural uses.
Ultisols: Older, weathered soils which are acid and nutrient-poor without proper management.
Vertisols: Clay-rich soils that expand and contract dramatically with moisture changes.

Understanding the variety of soil types and their characteristics is vital for effective soil management and sustainable agricultural practices. Each soil type presents unique challenges and opportunities regarding land use and ecological balance.