Soils

Soil Composition

Most soils are composed water, air, organic matter, and sand silt and clay with sand being the largest particle and can be seen with the naked eye.

Sand is great for

drainage and allowing oxygen to enter soils.

Clay is…

the smallest and is great at holding nutrients in the soil due to surface area

silt is…

indistinguishable from clay by sight but clay sticky while silt is not

CL - Climate

Different climates cause soils to form at different speeds Warm wet climates will form soil horizons faster than cold dry climates.

O - Organisms

Plant roots help prevent erosion and help carry water and nutrients into deeper soils. Animals like earthworms and burrowing animals break down organic matter making it accessible to micro organisms as well as decompacting soils making water infiltration easier

R - Relief/Topography

Where your soil is located determines how it forms. Soils that form on flat ground with good drainage will develop greater topsoil horizons (O/A) than a soil that forms on hill that has water constantly running on top of it eroding the topsoil.

P - Parent Material

where the original material for the soil came from 5 types residuum, colluvium, recent alluvium, old alluvium, Coastal Plain sediments.

T - Time

Time forms soil horizons the longer a soil is exposed to erosion or other forming factors the more defined the horizons become. Soil age is not liner and is dependent on how developed the horizons are.

Residuum

Formed in place from bedrock being broken down from weathering and erosion normally well developed horizons.

Colluvium

Soil and rock fragments that fell downhill either by water or gravity, commonly found beneath hills and mountains jagged and anguraly rocks.

Recent Alluvium

Caused by streams or rivers flooding and depositing sediments along the floodplain does not form distinct horizons due to constant additions.

Old Alluvium

Found on terraces and have had time to form well developed horizons.

Coastal Plain Sediments

In Maryland these sediments mostly came from the erosion of the Appalachian mountains and were brought down here by water. Have formed developed horizons but have not had time to be compressed and form bedrock.

Position

Where the soil is located will help you decide which management practice that area is best suited for

Floodplains

 near streams flood often limits their uses.

Terrace

used to be a floodplain old alluvial parent material.

Upland depressions-

water ponds in these areas has a high organic matter content.

Upland-

not affected by stream activity and is at an higher elevation than surrounding land.

Soil forming processes

The processes that change parent material into soil

Additions

Organic matter such as dead plants and leafs add to the very top of a soil also adds carbon to soil. Other additions include soil deposited by streams and wind and rain adding nitrogen.

Losses

Water moving through a soil dissolves minerals and moves them into deeper horizons, this is called leaching. Calcium and salt are affected by this. Plants take in nutrients from the soil and erosion takes the topsoil away

Translocations

when leaching is incomplete due to low rainfall or high temperatures layers of previously dissolved minerals gets deposited in layers causing hardpans. 

Transformations

Microorganisms change organic matter into humus iron rusts causing the red tint or reduced by being in waterlogged soil and leached out.

Soil horizons

distinct layers that form as soil develops over time, each with its own composition and appearance.

O Horizon

Organic, Made up of fresh and decayed plant material leafs and wood. Can be distinguished by either identifiable plant material like individual leafs or a dark brown or black layer.

A horizon

Topsoil, brown due to a high organic makeup but contains no identifiable plant material. This layer is where roots and microorganisms are most active.

E Horizon

Eluvial, light white or bleached colored horizon is caused by soluble minerals being leached from that layer into deeper layers. Clay and Iron are the most notable losses from this horizon. Will contain mostly sand and silt.

B horizon

Subsoil, Light colored mostly red and yellow will contain splotches of grey if not well drained. Will have a higher clay content that surrounding horizons.

C horizon

Will contain sediments that have not been weathered as much as above horizons so will have a high sand content and may have rounded gravel. Will look most like parent material.

Redoximorphic Features

are caused by a high water table or poor drainage and look like grey splotches or “molts” That do not change color when moistened.

The grey color is caused…

when iron is reduced due to being wet for long periods of time and leeches down to lower layers. Will decided drainage class 

Hydric soil

form when the water table is near the surface for long periods of time. Will be very grey and might have a very deep and black O horizon. You will most likely be standing in water

Texture

determines how well the soil holds water, resistance to erosion, how permeable and quick water drains through the soil. Trying to distinguish between sand silt and clay particles.

Coarse

Feels gritty and does not hold water when moist. Very permeable but can contain enough silt and clay to hold nutrients.

Moderately Coarse

feels gritty but holds together in ball great for agriculture if irrigated and construction if well drained.

Medium

feels smooth but not sticky will form a short ribbon due to some clay. The best texture for agricultural and septic systems.

Moderatley fine

feels slightly sticky and slightly plastic will form a good ribbon.

Fine

feels very smooth and sticky will form a large ribbon and form clods when dry

Structure and permeability

Soils will naturally form different structured based on how they formed and what materials they are made up of. These structures will affect how water drains throughout the soil.

Excessively drained

Water gets removed rapidly due to coarse texture or steep slopes. Poor for agriculture not redox depletions

Well drained

Subsoil colors are bright normally red and yellow with no redoximorphic features above 40 inches.

Moderately well drained

Subsoil color similar to well drained but grey molts are found between 20 and 40 inches. Good for agriculture as during droughts crops have access to water.

Somewhat poorly drained

Redoximorphic features occur within 10 to 20 inches. Soil experiences prolonged periods of wetness may be caused by a high water table. Drainage needs to be implemented for agriculture to be successful.

Poorly drained

Dark and deep surface horizons and grey subsoil. Redox feature are found above 10 inches. High water table. Not suitable for agriculture and construction.

Very poorly drained

found in depressions or other low lying areas. Very dark and deep surface horizons with high organic content. Subsoil is grey.

Land capability classes

each represents how useful a soil is and what management practice should be used to best improve that area.