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Soil Horizons• O Horizon
– The top, organic layer of soil, made up mostly of leaf litter and humus (decomposed organic matter).
– O horizons are subdivided according to the degree of organic material decomposition. These horizons are not common and are mostly restricted to moist or cool environments
– Not always present!
Soil Horizons
• A Horizon
– The layer called topsoil; it is found below the O horizon and above the E horizon. Seeds germinate and plant roots grow in this dark-colored layer..
– Consists of one or more surface mineral horizons with some accumulation of organic materials (less than O horizons). A horizons are usually darker than underlying horizons but they may also be horizons that are lighter colored or have a lower content of clay when compared to underlying horizons.
Soil Horizons• E Horizon (aka A2)
– This eluviation (leaching) layer is light in color; this layer is beneath the A Horizon and above the B Horizon. It is made up mostly of sand and silt, having lost most of its minerals and clay as water drips through the soil (in the process of eluviation).
– The A2, has less organic matter, sesquioxides or clay than the horizons above or below. It is a pale horizon, and various degrees of bleaching are recognized with white or near white layers being referred to as sporadically or conspicuously bleached depending on its extent.
– Not always present!
Soil Horizons• B Horizon
– Also called the subsoil - this layer is beneath the E Horizon and above the C Horizon. It contains clay and mineral deposits (like iron, aluminum oxides, and calcium carbonate) that it receives from layers above it when mineralized water drips from the soil above.
• They have one or more of the following:– concentration of clay, iron, aluminum or organic material; – a structure or consistence unlike the A horizon above
and different to the horizons below; or – stronger colors than the horizons above or below. – The B1 horizon is a transitional layer between the A and
B horizons but it is more like the B horizon. Similarly, a B3 horizon is a transitional layer to the underlying material.
Soil Horizons
• C Horizon
– Also called regolith: the layer beneath the B Horizon and above the R Horizon. It consists of slightly broken-up bedrock. Plant roots do not penetrate into this layer; very little organic material is found in this layer.
Soil Horizons
• R Horizon
– The un-weathered rock (bedrock) layer that is beneath all the other layers.
Determining Horizons
• Notice 3 things within a soil pit– Color change– Texture change– Structure change
Illinois Soils
TamaDrummer
BlufordFlanagan
Stronghurst Traer
Hoyleton Bloomfield
Muscatine Ava
SableFayette
Hosmer
