Soil is a complex amalgum that, of necessity, has been defined from a variety of perspectives. It has been defined as: the unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants; the unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of such genetic and environmental factors as climate (including water and temperature effects), and macro- and microorganisms—conditioned by relief—acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics.
Additionally, soil has been defined as a natural body comprised of solids (minerals and organic matter), liquid, and gases that occurs on the land surface, occupies space, and is characterized by one or both of the following: horizons, or layers, that are distinguishable from the initial material as a result of additions, losses, transfers, and transformations of energy and matter; or the ability to support rooted plants in a natural environment.
Also, the upper limit of soil is the boundary between soil and air, shallow water, live plants, or plant materials that have not begun to decompose. Areas are not considered to have soil if the surface is permanently covered by water too deep (typically more than 2.5 meters) for the growth of rooted plants.
The lower boundary that separates soil from the nonsoil underneath is most difficult to define. Soil consists of horizons near the Earth's surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time. Commonly, soil grades at its lower boundary to hard rock or to earthy materials virtually devoid of animals, roots, or other marks of biological activity. For purposes of classification, the lower boundary of soil is arbitrarily set at 200 cm.
Groundwater inflow represents an important part of groundwater assessment methodology within the hydrological cycle. This article reviews chief methodology for estimating the...
NitrateLast Updated on 2013-08-11 10:09:48Nitrate is a polyatomic ion having a molecular formula NO3- and molecular mass of 62.0049 grams per mole. This ion is the conjugate base of HNO3, its geometry consistng of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries an electrical charge of minus one, arising from a combination formal charge in which each of the three oxygen atoms carries a fractional two thirds charge, whereas the nitrogen atom carries a plus one charge, all these adding up to minus one formal charge of the polyatomic nitrate ion. This atomic arrangement is often invoked as a classic example of chemical resonance. Similar to the isoelectronic carbonate ion, the nitrate ion can be represented by resonance structures.
Nitrate is a very important chemical soil amendment responsible for a major portion of the agricultural... More »
SoilLast Updated on 2013-06-30 09:50:56An important factor influencing the productivity of our planet's various ecosystems is the nature of their soils. Soils are vital for the existence of many forms of life that have evolved on our planet. For example, soils provide vascular plants with a medium for growth and supply these organisms with most of their nutritional requirements. Further, the nutrient status of ecosystem's soils not only limit both plant growth, but also the productivity of consumer type organisms further down the food chain.
Soil itself is very complex. It would be very wrong to think of soils as just a collection of fine mineral particles. Soil also contains air, water, dead organic matter, and various types of living organisms (Figure 1). The formation of a soil is influenced by organisms, climate, topography, parent material, and time. The following items describe some important features of a... More »
Burnt CapeLast Updated on 2012-06-29 00:00:00
The Burnt Cape is a limestone barren headland on the extreme northwest of the Northern Peninsula of Newfoundland, Canada. The prevailing harsh cold climate and [calcareous] soils have created a natural environment that is hospitable to certain extremophile plant species, many of which are rare or have limited geographic distribution. The site has experienced damage from gravel extraction in the latter part of the twentieth century, although most of the habitat remains [intact]. Due to the need to protect the biodiversity of Burnt Cape from mineral exploitation, the site has been designated as a protected area known as the Burnt Cape Ecological Reserve, by the Government of Newfoundland and Labrador. There are over 300 plant species present on this inhospitable site, with more than 30 being rare and two being near-endemics.
The dominant rock formation at Burnt Cape is... More »
Predators: influence over habitatsLast Updated on 2012-06-14 00:00:00
Study of grasshoppers' diets shows that animals are an important part of organic matter decomposition. While being hunted, prey animal diets may affect how soil releases carbon dioxide.
Predators Have Outsized Influence Over Habitats
A grasshopper's change in diet to high-energy carbohydrates while being hunted by spiders may affect the way soil releases carbon dioxide into the atmosphere, according to research results published in the journal Science.
Grasshoppers like to munch on nitrogen-rich grass because it stimulates their growth and reproduction. But when spiders enter the picture, grasshoppers cope with the stress from fear of predation by shifting to carbohydrate-rich plants, setting in motion dynamic changes to the ecosystem they inhabit, scientists have found.
"Under stressful conditions they go to different parts of the 'grocery store'... More »
Zambezi RiverLast Updated on 2012-03-20 00:00:00
The Zambezi River, Africa's fourth largest after the Nile, Zaire and Niger rivers, exhibits a length of 2700 kilometers prior to discharge to the Indian Ocean in Mozambique.
Zambezi River with Zambia in foreground and Zimbabwe in background. @ C.Michael Hogan
Zambezi River at the junction of Namibia, Zambia, Zimbabwe and Botswana. Source: Brian McMorrow
From headwaters in northwest Zambia, the river flows:
southeast through a portion of eastern Angola;
south through western Zambia;
east along the Zambia-Namibia (Caprivi Strip) border to the junction of Namibia, Zambia, Zimbabwe and Botswana;
east along the border between Zambia and Zimbabwe over the dramatic Victoria Falls and on to Lake Kariba
east into Mozambique and Lake Cahora Bassa
south west... More »
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