User:Paleorthid/Sandbox/Pedogenesis Section Soil Article
From Wikipedia, the free encyclopedia
[edit] Soil formation
It is probably fair to conclude, at least from his reputation today, that Jenny’s greatest scientific achievement is his classic book Factors of Soil Formation. A System of Quantitative Pedology. It is also probably his most misunderstood achievement, a fact reflected in that few people ever cite the full name of the publication (and the second sentence is an essential component of the book), and that many recent pedological texts continue to incorrectly state the premise of the book, and its famous equation: s = f(cl, o, r, p, t, ...)
where s - soil properties; cl - regional climate; o - potential biota, r - topography; p - parent material; t - time
Jenny left the ellipsis open to indicate that there might other variables in the function. As Jenny once remarked, ‘‘It looks easy, but it’s not.’’
This was in no way an original idea, since V. V. Dokuchaev, and others after had proposed and refined climate and biological factors for many decades prior. Jenny's achievment was to consolidate this thinking.
- Jenny, Hans (1994) Factors of Soil Formation. A System of Quantitative Pedology. New York: Dover Press. (Reprint, with Foreword by R. Amundson, of the 1941 McGraw-Hill publication). pdf file format.
- Amundsen, R., 2004, History of Soil Science: Hans Jenny, pdf format, in Encyclopedia of Soils in the Environment. Hillel, D., J.L.. Hatfield, D.S. Powlson, C. Rosenweig, K.M. Scow, M.J. Singer and D.L. Sparks. Editors. (2004) Four-Volume Set, Volume 1-4, ISBN 0-12-348530-4
Although many of us don't think about the ground beneath us or the soil that we walk on each day, the truth is soil is a very important resource. Processes take place over thousands of years to create a small amount of soil material. Unfortunately the most valuable soil is often used for building purposes or is unprotected and erodes away. To protect this vital natural resource and to sustain the world's growing housing and food requirements it is important to learn about soil, how soil forms, and natural reactions that occur in soil to sustain healthy plant growth and purify water. Soil is important to the livelihood of plants, animals, and humans. However, soil quality and quantity can be and is adversely affected by human activity and misuse of soil.
Certain soils are best used for growing crops that humans and animals consume, and for building airports, cities, and roads. Other types of soil have limitations that prevent them from being built upon and must be left alone. Often these soils provide habitats for living creatures both in the soil and atop the soil. One example of soils that have use limitations are those that hold lakes, rivers, streams, and wetlands. Humans don't normally establish their homes in these places, but fish and waterfowl find homes here, as do the wildlife that live around these bodies of water.
Natural processes that occur on the surface of Earth as well as alterations made to earth material over long periods of time form thousands of different soil types. In the United States alone there are over 50,000 different soils! Specific factors are involved in forming soil and these factors vary worldwide, creating varied soil combinations and soil properties worldwide:
The Five Soil Forming Factors
- Regional climate: Heat and moisture affect rates of biological activity and chemical reactions. Seasonal patterns of heat flux, water content and water movement influence the depth and pattern of removal (elluviation) and accumulation (illuviation) of soluble and colloidal constituents in soil. Climatic extremes, such as ice and wind, can cause physical weathering, soil erosion as well as deposition and accumulation of soil parent material. Stable, humid climates cause deep soil development.
- Potential biota: Each soil has a unique combination of microbial, plant, animal and human influences acting upon it. Microorganisms are particularly influential in the mineral transormations critical to the soil forming process. Additionally, some bacteria can fix atmospheric nitrogen and some fungi are efficient at extracting deep soil phosphorus and increasing soil carbon levels in the form of glomalin. Plants hold soil against erosion, and accumulated plant material build soil humus levels. Plant root exudation supports microbial activity. Animals serve to decompose plant materials and mix soil thrugh bioturbation. Man can import, or extract, nutrients and energy in ways that dramatically change soil formation. Aceelerated soil erosion, and manure input driven soil formation are two examples.
- Topography: The location of a soil on a landscape can affect how the climatic processes impact it. Soils at the bottom of a hill will get more water than soils on the slopes, and soils on the slopes that directly face the sun will be drier than soils on slopes that do not. Also, mineral accumulations, plant nutrients, type of vegetation, vegetation growth, erosion, and water drainage are dependent on topographic relief.
- Parent material: The primary material from which the soil is formed. Soil parent material could be bedrock, organic material, an old soil surface, or a deposit from water, wind, glaciers, volcanoes, or material moving down a slope.
- Time: All of the above factors assert themselves over time, often hundreds or thousands of years. Soil profiles continually change from weakly developed to well developed over time.
