Soil morphology
[3] Since the origin of agriculture, humans have understood that soils contain different properties which affect their ability to grow crops.
Pedons generally occupy between 1 and 10 m2 of surface land area and are the fundamental unit of field-based soil study.
These horizons are distinguishable from adjacent layers by their changes in morphological properties as the soil naturally forms.
Boundary topography refers to the horizontal variation of the border, which is often not parallel to the soil surface and may even be discontinuous.
Organic-rich soils tend to be dark brown or even black due to organic matter accumulating on the mineral particles.
When soil is saturated for prolonged periods, oxygen availability is limited and iron may become a biological electron acceptor.
When iron reduction and/or depletion makes gray the dominant matrix color, the soil is said to be gleyed.
The soil is then rolled into a ball nearing 1-2 inches in diameter and squeezed between the thumb and side of the index finger.
The relative smoothness or grittiness indicates the sand percentage, and with practice, this technique can provide accurate textural class determinations.
The mineral texture can be obfuscated by high soil organic matter, iron oxides, amorphous or short-range-order aluminosilicates, and carbonates.
In order to precisely determine the amount of clay, sand and silt in a soil, it must be taken to a laboratory for analysis.
This consists of mixing the pretreated soil with water and then allowing the mixture to settle, making note of the hydrometer reading.
[9] Porosity of topsoil is a measure of the pore space in soil which typically decreases as grain size increases.
The table below displays the deal bulk densities that both allow and restrict root growth for the three main texture classifications.
[11] While micromorphological descriptions may begin in the field with the use of a 10x hand lens, much more can be described using thin sections made of the soil with the aid of a petrographic polarizing light microscope.
More recently, the science has expanded to encompass the characterization of all archeological soils and sediments and has been successful in providing unique cultural and paleoenvironmental information from a whole range of archaeological sites.
[16] Soils are formed from their respective parent material, which may or may not match the composition of the bedrock that they lie on top of.
Increased runoff can inhibit soil formation as the upper layers continue to get stripped off because they are not developed enough to support root growth.
Most often, biological processes work to disrupt existing soil formation which leads to chemical translocation.
