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Soil is our life support system. Soils anchor roots, hold water and store nutrients. Soils are home to earthworms, termites and a myriad of micro-organisms that fix nitrogen and decompose organic matter. We build on soil as well as with it.
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- Soils in ecosystems
- Carbon and nitrogen cycles
- Soils and global warming
An ecosystem is a collection of organisms and the local environment with which they interact. For the soil scientist studying microbiological processes, ecosystem boundaries may enclose a single soil horizon or a soil profile. When nutrient cycling or the effects of management practices on soils are being considered, the ecosystem may be as large a...
An ecosystem is a collection of organisms and the local environment with which they interact. For the soil scientist studying microbiological processes, ecosystem boundaries may enclose a single soil horizon or a soil profile. When nutrient cycling or the effects of management practices on soils are being considered, the ecosystem may be as large a...
Soils are dynamic, open habitats that provide plants with physical support, water, nutrients, and air for growth. Soils also sustain an enormous population of microorganisms such as bacteria and fungi that recycle chemical elements, notably carbon and nitrogen, as well as elements that are toxic. The carbon and nitrogen cycles are important natural processes that involve the uptake of nutrients from soil, the return of organic matter to the soil by tissue aging and death, the decomposition of organic matter by soil microbes (during which nutrients or toxins may be cycled within the microbial community), and the release of nutrients into soil for uptake once again. These cycles are closely linked to the hydrologic cycle, since water functions as the primary medium for chemical transport.
Nitrogen (N), one of the major nutrients, originates in the atmosphere. It is transformed and transported through the ecosystem by the water cycle and biological processes. This nutrient enters the biosphere primarily as wet deposition to the soil surface (throughfall), where plants, microbial decomposers, or nitrifiers (microbes that convert ammonium [NH4+] to nitrate [NO3−]) compete for it. This competition plays a major role in determining the extent to which incoming nitrogen will be retained within an ecosystem.
Carbon (C) also enters the ecosystem from the atmosphere—in the form of carbon dioxide (CO2)—and is taken up by plants and converted into biomass. Organic matter in the soil in the form of humus and other biomass contains about three times as much carbon as does land vegetation. Soils of arid and semiarid regions also store carbon in inorganic chemical forms, primarily as calcium carbonate (CaCO3). These pools of carbon are important components of the global carbon cycle because of their location near the land surface, where they are subject to erosion and decomposition. Each year, soils release 4–5 percent of their carbon to the atmosphere by the transformation of organic matter into CO2 gas, a process termed soil respiration. This amount of CO2 is more than 10 times larger than that currently produced from the burning of fossil fuels (coal and petroleum), but it is returned to the soil as organic matter by the production of biomass.
A large portion of the soil carbon pool is susceptible to loss as a result of human activities. Land-use changes associated with agriculture can disrupt the natural balance between the production of carbon-containing biomass and the release of carbon by soil respiration. One estimate suggests that this imbalance alone results in an annual net release of CO2 to the atmosphere from agricultural soils equal to about 20 percent of the current annual release of CO2 from the burning of fossil fuels. Agricultural practices in temperate zones, for example, can result in a decline of soil organic matter that ranges from 20 to 40 percent of the original content after about 50 years of cultivation. Although a portion of this loss can be attributed to soil erosion, the majority is from an increased flux of carbon to the atmosphere as CO2. The draining of peatlands may cause similarly large losses in soil carbon storage.
Soils and climate have always been closely related. The predicted temperature increases due to global warming and the consequent change in rainfall patterns are expected to have a substantial impact on both soils and demographics. This anticipated climatic change is thought to be driven by the greenhouse effect—an increase in levels of certain trace gases in the atmosphere such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). The conversion of land to agriculture, especially in the humid tropics, is an important contribution to greenhouse gas emissions. Some computer models predict that CH4 and N2O emissions will also be very important in future global change. About 70 percent of the CH4 and 90 percent of the N2O in the atmosphere are derived from soil processes. But soils can also function as repositories for these gases, and it is important to appreciate the complexity of the source-repository relationship. For example, the application of nitrogen-containing fertilizers reduces the ability of the soil to process CH4. Even the amount of nitrogen introduced into soil from acid rain on forests is sufficient to produce this effect. However, the extent of net emissions of CH4 and N2O and the microbial trade-off between the two gases are undetermined at the global scale.
Perhaps the most notable and pervasive role of soils in global warming is the regulation of the CO2 budget. Carbon that is stored in terrestrial plants mainly through photosynthesis is called net primary production or NPP and is the dominant source of food, fuel, fibre, and feed for the entire population of Earth. Approximately 55 billion metric tons (61 billion tons) of carbon are stored in this way each year worldwide, most of it in forests. About 800 million hectares (20 billion acres) of forestland have been lost since the dawn of civilization; this translates to about 6 billion metric tons of carbon per year less NPP than before land was cleared for agriculture and commerce. This estimated decrease in carbon storage can be compared to the 5–6 billion metric tons of carbon currently released per year by fossil fuel burning. One is left with the sobering conclusion that reforestation of the entire planet to primordial levels would have only a temporary counterbalancing effect on carbon release to the atmosphere from human consumption of natural resources.
- Garrison Sposito
Soil is fundamental to all life on earth. It filters our water and grows our crops. 95 percent of the food we eat is grown in the fertile topsoil that is fast being degraded by...
- Jon Heggie
- 2 min
Why is soil important? Soil carries out a range of functions and services without which human life would not be possible. It provides an environment for plants (including food crops and timber wood) to grow in, by anchoring roots and storing nutrients.
Nov 8, 2024 · Soil is one of the principal substrata of life on Earth, serving as a reservoir of water and nutrients, as a medium for the filtration and breakdown of injurious wastes, and as a participant in the cycling of carbon and other elements through the global ecosystem.
- Garrison Sposito
- Soil is the biologically active and porous medium that has developed in the uppermost layer of Earth’s crust. It serves as the reservoir of water a...
- The grain size of soil particles are categorized into three groups: clay, silt, and sand. Clay measures less than 0.002 mm (0.0008 inch) in diamete...
- The evolution of soils and their properties is called soil formation, and according to pedologists, five fundamental soil formation processes influ...
- Soils have a unique structural characteristic that distinguishes them from mere earth materials: a vertical sequence of layers produced by the comb...
Soils are the environment in which seeds grow. They provide heat, nutrients, and water that are available for use to nurture plants to maturity. These plants form together with other plants and organisms to create ecosystems.
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Nov 11, 2024 · Soil is an important source of food and medicine, it filters and purifies our water, reduces flooding and plays a crucial role in the fight against climate change. Learn more about this miraculous substance.
