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Topsoil is the upper, outermost layer of
soil Soil is a mixture In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, comp ...

soil
, usually the top . It has the highest concentration of
organic matter Organic matter, organic material, or natural organic matter refers to the large source of Carbon compounds, carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compo ...
and
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
s and is where most of the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
's
biological Biology is the natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowl ...

biological
soil activity occurs. Topsoil is composed of mineral particles, organic matter, water, and air. Organic matter varies in quantity on different soils. The strength of soil structure decreases with the presence of
organic matter Organic matter, organic material, or natural organic matter refers to the large source of Carbon compounds, carbon-based compounds found within natural and engineered, terrestrial, and aquatic environments. It is matter composed of organic compo ...
, creating weak bearing capacities. Organic matter condenses and settles in different ways under certain conditions, such as roadbeds and foundations. The structure becomes affected once the soil is dehydrated. Dehydrated topsoil volume substantially decreases and may suffer
wind erosion Wind is the flow of gases on a large scale. On the surface of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continent ...
.


Importance

There is generally a high concentration of roots in this layer as plants obtain much of their vital
nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and t ...
s here. Accurate depth of the topsoil layer is measured as the depth of the surface to the first densely packed soil layer known as
subsoil Subsoil is the layer of soil under the topsoil Topsoil is the upper, outermost layer of soil Soil (often stylized as SOiL) is an American rock band that was formed in Chicago (''City in a Garden''); I Will , image_map ...
.


Classification

In soil classification systems, topsoil is known as the "O Horizon or A Horizon," therefore, it is the very top layer. Commercially available topsoil (manufactured or naturally occurring) in the United Kingdom should be classified to British Standard BS 3882 with the current version dated 2015. The standard has several classifications of topsoil with the final classification requiring material to meet certain threshold criteria such as nutrient content, extractable phytotoxic elements, particle size distribution, organic matter content, carbon:nitrogen ratio, electrical conductivity, loss on ignition, pH, chemical and physical contamination. The topsoil should be sampled in accordance with the British Standard and European Norm BS EN 12579:2013 Soil improvers and growing media - Sampling. During construction of garden areas for housing plots the topsoil should be underlain by a layer of suitably certified subsoil that conforms to the British Standard BS 8601:2013 Specification for subsoil and requirements for use. It is always recommended that for construction projects that topsoil is placed in accordance with the DEFRA report Construction Code of Practice for the Sustainable Use of Soils on Construction Sites


Evaluation

When starting a gardening project, it is crucial to check whether or not the soil has proper soil pH levels and suitable nutrient levels for the types of vegetation to be grown. Different types of plants vary in their nutrient needs and preferred soil conditions, and many are strongly adapted to particular conditions. However, some general guidelines for "desired levels of Topsoil nutrients" have been made, broadly suitable for many plants. The two common types of Topsoil are Bulk and Bagged Topsoil. The following table illustrates major differences between the two. Alternatively the British Standard relates to other working values: This is for a multipurpose grade and certain levels can alter with regard to
soil pH Soil pH is a measure of the acidity An acid is a molecule or ion capable of donating a proton (hydrogen ion H+) (a Brønsted–Lowry acid–base theory, Brønsted–Lowry acid), or, alternatively, capable of forming a covalent bond with an ...
. Other uses specified in the standard that allows for a variety of uses in different and specific scenarios includes: Acidic, Calcareous, Low Fertility, Low Fertility Acidic and Low Fertility Calcareous. These uses are limited to specific site scenarios and acceptance should be on a case-by-case basis for construction projects.


Carbon to nitrogen ratio

Topsoil is the primary resource for plants to grow and crops to thrive and the main two parameters for this are carbon and nitrogen. The nitrogen provides energy and carbon is a tissue builder and plants require them in a range of ratios to enable suitable growth. An optimum figure for topsoil in the UK is a C:N ratio of less than 20:1. This ensures that the soil has a suitable energy reserve as well as tissue building material to enable the plants to thrive. A sawdust typically has a carbonaceous base and this a high C:N ratio (in the order of c. 400:1) while an alfalfa hay has a low carbonaceous content and can typically have a C:N ratio in the order of 12:1.


Commercial application

A variety of soil mixtures are sold
commercially Commerce is the exchange of goods and services, especially on a large scale. Etymology The English-language word ''commerce'' has been derived from the Latin word ''commercium'', from ''com'' ("together") and ''merx'' ("merchandise"). History ...

commercially
as topsoil, usually for use in improving
garden A garden is a planned space, usually outdoors, set aside for the cultivation, display, and enjoyment of plants and other forms of nature. The single feature identifying even the wildest wild garden A wildlife garden (or wild garden) is an Biophy ...

garden
s and
lawn A lawn is an area of soil-covered land planted with grass Poaceae () or Gramineae () is a large and nearly ubiquitous family In , family (from la, familia) is a of people related either by (by recognized birth) or (by mar ...

lawn
s, e.g.
container garden Container gardening or pot gardening/farming is the practice of growing plants, including edible plants, exclusively in containers instead of planting them in the ground. A container in gardening is a small, enclosed and usually portable object ...
s,
potting soil Potting soil, also known as potting mix or miracle soil, is a medium in which to grow plants, herbs and vegetables in a pot or other durable container. The first recorded use of the term is from an 1861 issue of the ''American Agriculturist''. I ...

potting soil
and
peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation Vegetation is an assemblage of species and the they provide. It is a general term, without specific reference to particular , life forms, structure, ...
. Another important yet not commonly known use for topsoil is for proper surface grading near residential buildings such as homes. "The ground around the home should slope down six inches for the first ten feet away from the home. This can often be done by adding topsoil (not sand or gravel)."


Erosion

A major environmental concern known as topsoil
erosion In earth science Earth science or geoscience includes all fields of natural science Natural science is a branch of science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific ...

erosion
occurs when the topsoil layer is blown or washed away. Without topsoil, little plant life is possible. The estimated annual costs of public and environmental health losses related to soil erosion exceed $45 billion. Conventional agriculture encourages the depletion of topsoil because the soil must be plowed and replanted each year. Sustainable techniques attempt to slow erosion through the use of
cover crops Cover or covers may refer to: Packaging * Another name for a lid * Cover (philately), generic term for envelope or package * Album cover, the front of the packaging * Book cover or magazine cover * CD and DVD cover, CD and DVD packaging * Smar ...
in order to build organic matter in the soil. The United States alone loses almost 3 tons of topsoil per acre per year. This is of great ecological concern as one inch of topsoil can take between 500 and 1,000 years to form naturally. Based on 2014 trends, the world has about 60 years of topsoil left.


Conservation


See also

* Agricultural wastewater *
Desertification Desertification is a type of land degradation Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or distu ...
*
Dust bowl The Dust Bowl was a period of severe dust storm A dust storm, also called a sandstorm, is a meteorological phenomenon common in arid A region is arid when it is characterized by a severe lack of available water, to the extent o ...
*
Erosion control Erosion control is the practice of preventing or controlling wind or water erosion In earth science, erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved ...
*
No-till farming No-till farming (also known as zero tillage or direct drilling) is an agricultural technique for growing crops or pasture without disturbing the soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Irel ...
*
Sustainable agriculture Sustainable agriculture is farming Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise tren ...

Sustainable agriculture
*
Waterway degradation Water pollution is the contamination of water bodies ( Lysefjord) in Norway Norway ( nb, ; nn, ; se, Norga; smj, Vuodna; sma, Nöörje), officially the Kingdom of Norway, is a Nordic countries, Nordic country in Northern Europe ...


References


Further reading


The lowdown on topsoil: It's disappearing
*


External links


USDA Electronic Field Office Technical Guide
- Detailed soil conservation guides tailored to individual states/counties {{Authority control Soil Horticulture Soil improvers Lawn care Types of soil