The Nature of Soil

Tara D. Weldon
GENS 320 Physical Geography
August 2, 2015
Soil is a nearly infinitely varying mixture of weathered mineral particles, decaying organic matter, living organisms, gases, and liquid solutions. There are five principal soil forming factors responsible for soil development: Geology, climate, topography, biology, and time.
(geologycafe, 2015)
Geologic Factor: Over many years (thousands and/or millions) a stony surface can be broken down by weather, such as rain, wind and ice. This process is known as weathering.
Climatic Factor: Warmer temperatures and an abundance of water have a tendency to speed up the formation of soil. Cooler temperatures and less precipitation slow down soil formation. Topographic Factor: In areas that are flat, soil tends to get deeper quicker than the surface erodes away. Which typically have deeper, more mature soil layer. On steep slopes, erosion takes place quicker than the formation of new soil. Which have thin layer of soil that is immaturely developed.
Drainage is also a factor. Some locations become waterlogged. This blocks oxygen, which is important for soil formation. In those locations soil formation can become severely hindered.
Biological Factor: Living organisms have an extensive impact on soil. A small fraction of soil contains living and dead lifeforms. However, the role of these lifeforms can't be underestimated. Roots from plant life dig deep into the soil, creating passages for water and air. Animals such as ants, earthworms, rodents and snakes dig and till the soil extensively. Plants and animals provide nutrients to the soil in the form of waste products and dead bodies. A variety of micro-organisms perform important jobs in the soil that help to decompose living materials, and that give richness to the soil.

(Cuny, 2015)
Time Factor: Soil forms over thousands and/or millions of years. A newly exposed surface will have little or no soil, while old surfaces will have much deeper soil.
Mollisols (Dark, Soft Soils for Grasslands) The distinctive characteristic of Mollisols is the presence of a mollic epipodon, which is a mineral surface horizon that is dark and thick, contains abundant humus and basic cations, and retains a soft character (rather than becoming hard and crusty) when it dries out. Mollisols can be thought of as transition soils that evolve in regions not dominated by either humid or arid conditions. They are typical of the midlatitude grasslands and are thus most common in central Eurasia, the North American Great Plains, and the pampas of Argentina.
The grassland environment generally maintains a rich clay-humus content in a Mollisol soil. The dense, fibrous mass of grass roots permeates uniformly through the epipedon and to a lesser extent into the subsurface layers. There is almost continuous decay of plant parts to produce a nutrient-rich humus for the living grass.
Mollisols on the whole are probably the most productive soil order. They are generally derived from loose parent material rather than from bedrock and tend to have favorable structure and texture for cultivation. Because they are not overly leached, nutrients are generally retained within reach of plant roots. Moreover, Mollisols provide a favored habitat for earthworms, which contribute to softening and mixing of the soil.
Alfisols (Clay-Rich B Horizons, High Base Status) the widest ranging of the mature soils, Alfisols occur extensively in low and middle latitudes. They are found in a variety of temperature and moisture conditions and under diverse vegetation associations. They tend to be associated with transitional environments and are less characteristic of regions that are particularly hot or cold or wet or dry. Their global distribution is extremely varied. They are also widespread in the United States, with particular concentrations in the Midwest.
Alfisols are distinguished by a subsurface clay horizon and a medium to generous supply of basic cations, plant nutrients, and water. The epipedon is ochric (light-colored), but beyond that, it has no characteristics that are particularly diagnostic and can be considered an ordinary eluviated horizon. The relatively moderate conditions under which Alfisols develop tend to produce balanced soils that are reasonably fertile. Alfisols rank second only to Mollisols in agricultural producti (America, 2015)

Bibliography
America, S. S. (2015, August 2). K-12 Soil Science Teacher Resources. Retrieved from soils4teachers.org: http://www.soils4teachers.org/lessons-and-activities/teachers-guide/world-soils
Cuny, H. (2015, August 2). chapter.4.outline. Retrieved from geography.hunter.cuny.edu: http://www.geography.hunter.cuny.edu/tbw/ncc/Notes/chapter.4.outline.html geologycafe. (2015, August 2). Weathering and Erosion. Retrieved from geologycafe.com: http://geologycafe.com/erosion/weathering.html