Soil

developed in glacial till in Northern Ireland Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil. Soil consists of a solid collection of minerals and organic matter (the soil matrix), as well as a porous phase (Pore space) that holds gases (the soil atmosphere) and a liquid phase that holds water and dissolved substances both organic and inorganic, in ionic or in molecular form (the soil solution). Accordingly, soil is a complex three-state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development through numerous physical, chemical, and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm 3 , though the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm 3 .…

developed in glacial till in Northern Ireland Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from soil by restricting the former term specifically to displaced soil. Soil consists of a solid collection of minerals and organic matter (the soil matrix), as well as a porous phase (Pore space) that holds gases (the soil atmosphere) and a liquid phase that holds water and dissolved substances both organic and inorganic, in ionic or in molecular form (the soil solution). Accordingly, soil is a complex three-state system of solids, liquids, and gases. Soil is a product of several factors: the influence of climate, relief (elevation, orientation, and slope of terrain), organisms, and the soil's parent materials (original minerals) interacting over time. It continually undergoes development through numerous physical, chemical, and biological processes, which include weathering with associated erosion. Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm 3 , though the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm 3 . Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean. Collectively, the Earth's body of soil is called the pedosphere. The pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, and the biosphere. Soil has four important functions: as a medium for plant growth as a means of water storage, water supply, and water purification as a modifier of Earth's atmosphere as a habitat for soil organisms All of these functions, in their turn, modify the soil and its properties. Soil science has two basic branches of study: edaphology and pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation, description (morphology), and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which also includes other loose material that lies above the bedrock, as can be found on the Moon and other celestial objects. ==Functions== Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, and a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains a prominent part of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species, mostly microbial and largely still unexplored. Soil has a mean prokaryotic density of roughly 10 8 organisms per gram, whereas the ocean has no more than 10 7 prokaryotic organisms per milliliter (gram) of seawater. Organic carbon held in soil is eventually returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter; tillage usually increases the rate of soil respiration, leading to the depletion of soil organic matter. Since plant roots need oxygen, aeration is an important characteristic of soil. This ventilation can be accomplished via networks of interconnected soil pores, which also absorb and hold rainwater making it readily available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can effectively remove impurities, kill disease agents, and degrade contaminants, this latter property being called natural attenuation. Typically, soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, air, water, temperature moderation, nutrients, and protection from toxins. Soils provide readily available nutrients to plants and animals by converting dead organic matter into various nutrient forms. Soil is a major component of the Earth's ecosystem. The world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, with effects ranging from ozone depletion and global warming to rainforest destruction and water pollution. With respect to Earth's carbon cycle, soil acts as an important carbon reservoir, and it is potentially one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback (amplification). This prediction has, however, been questioned on consideration of more recent knowledge on soil carbon turnover. Cation exchange capacity is the soil's ability to remove cations from the soil water solution and sequester those to be exchanged later as the plant roots release hydrogen ions to the solution. CEC is the amount of exchangeable hydrogen cations (H + ) that will combine with 100 grams dry weight of soil and whose measure is one milliequivalent per 100 grams of soil (1 meq/100 g). Hydrogen ions have a single charge and one-thousandth of a gram (1 mg) of hydrogen ions per 100 grams dry soil gives a measure of one milliequivalent of hydrogen ion. Calcium, with an atomic weight 40 times that of hydrogen and with a valence of two, converts to = 20 milliequivalents of hydrogen ion per 100 grams of dry soil or 20 meq/100 g. The modern measure of CEC is expressed as centimoles of positive charge per kilogram (cmol/kg) of oven-dry soil. Most of the soil's CEC occurs on clay and humus colloids, and the lack of those in hot, humid, wet climates (such as tropical rainforests), due to fast leaching and decomposition, respectively, explains the apparent lack of fertility of tropical soils. Live plant roots also have some CEC, linked to their specific surface area. ==Classification== One of the first soil classification systems was developed by the Russian scientist Vasily Dokuchaev around 1880. It was modified a number of times by American and European researchers and was developed into the system commonly used until the 1960s. It was based on the idea that soils have a particular morphology based on the materials and factors that form them. In the 1960s, a different classification system began to emerge which focused on soil morphology instead of parental materials and soil-forming factors. Since then, it has undergone further modifications. The World Reference Base for Soil Resources aims to establish an international reference base for soil classification. In the United States, the system of Soil Taxonomy is used. This system was established by the United States Department of Agriculture: Natural Resource Conversation Service and is currently on its second edition, released in 1999¹ by the Soil Survey Staff. ==See also== ==Sources== ==Bibliography== ==Further reading== Soil-Net.com A free schools-age educational site teaching about soil and its importance. Adams, J.A. 1986. Dirt. College Station, Texas: Texas A&M University Press Certini, G., Scalenghe, R. 2006. Soils: Basic concepts and future challenges. Cambridge Univ Press, Cambridge. Montgomery, David R., Dirt: The Erosion of Civilizations (U of California Press, 2007), Faulkner, Edward H. Plowman's Folly (New York, Grosset & Dunlap, 1943). LandIS Free Soilscapes Viewer Free interactive viewer for the Soils of England and Wales Jenny, Hans. 1941. Factors of Soil Formation: A System of Quantitative Pedology Logan, W.B. Dirt: The ecstatic skin of the earth (1995). Mann, Charles C. September 2008. " Our good earth" National Geographic Magazine ==External links== Photographs of sand boils. Soil Survey Division Staff. 1999. Soil survey manual. Soil Conservation Service. U.S. Department of Agriculture Handbook 18. Soil Survey Staff. 1975. Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. USDA-SCS Agric. Handb. 436. United States Government Printing Office, Washington, DC. Soils (Matching suitable forage species to soil type), Oregon State University Janick, Jules. 2002. Soil notes, Purdue University LandIS Soils Data for England and Wales a pay source for GIS data on the soils of England and Wales and soils data source; they charge a handling fee to researchers.

Text derived from https://en.wikipedia.org/w/index.php?oldid=1377313926 under CC BY-SA 4.0; modifications have been made.