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In geology and particularly in sedimentology, a nodule is a small, irregularly rounded knot, mass, or lump of a mineral or mineral aggregate that typically has a contrasting composition from the enclosing sediment or sedimentary rock. Examples include pyrite nodules in coal, a chert nodule in limestone, or a phosphorite nodule in marine shale.
Nodule, rounded mineral concretion that is distinct from, and may be separated from, the formation in which it occurs. Nodules commonly are elongate with a knobby irregular surface; they usually are oriented parallel to the bedding. Chert and flint often occur as dense and structureless nodules of
- The Editors of Encyclopaedia Britannica
Bacteroides can be discovered in the cytoplasm of plant cells by itself or in groups with peribacteroid members. Because of the presence of leghemoglobin, the energetic nodules are massive and pink, with well-developed and organized tissue. When the nodule dies, stationary-phase rhizobia are launched into the soil.
Jun 11, 2004 · Soil is one of the last great scientific frontiers (Science, 11 June, 2004) and the rhizosphere is the most active portion of that frontier in which biogeochemical processes influence a host of ...
- O Horizon –
- A Horizon –
- E Horizon –
- B Horizon –
- C Horizon –
- R Horizon –
‘O’ is for organic. This layer is the uppermost layer of the soil rich in organic matter, such as the remains of plants and dead animals. Due to high organic content, this layer is typically black brown or dark brown. The O horizon is thin in some soil, thick in some others, or absent in the rest.
Found below the O horizon, it has a dark brown color as it contains the maximum organic matter of the soil. The A horizon or topsoil is thus also called the humus layer. The topsoil is the region of intense biological activity and has the most nutrients. Insects, earthworms, centipedes, bacteria, fungi, and other animals are found inside this layer...
This layer consists of nutrients leached from O and A horizons and is thus called the eluviations layer. Leaching of clay, minerals, and organic matter leavesthis layer with a high concentration of sand, slit particles, quartz, and other resistant materials. E horizon is absent in most soils but is more common in forested areas.
Mostly found below the topsoil is another layer called the subsoil or horizon B. It is lighter in color than the topsoil due to lower humus content. However, it is comparatively more rigid and compact than the topsoil. This layer has less organic content but is rich in minerals that are leached down from the topsoil. The subsoil is the region of de...
Also known as regolith or saprolite, it lies just below the subsoil. It is called the parent rock because all the upper layers developed from this layer. C horizon is devoid of any organic matter and is made of broken-up bedrocks, making it hard. Plantroots do not penetrate this layer. This layer is a transition between the inner layer of earth and...
Found beneath all the layers, it consists of un-weathered igneous, sedimentary, and metamorphic rocks. It is highly compact. Granite, basalt, quartzite, sandstone, and limestone make up the bedrock.
Mar 8, 2018 · Legumes are able to form a symbiotic relationship with nitrogen-fixing soil bacteria called rhizobia. The result of this symbiosis is to form nodules on the plant root, within which the bacteria can convert atmospheric nitrogen into ammonia that can be used by the plant.
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Jan 1, 2013 · Soil bacteria collectively called rhizobia establish a unique beneficial interaction with most legumes and a few nonleguminous plants in the family of Ulmaceae (Parasponia sp.). This endosymbiosis between rhizobia and the host plant leads to the formation of...
