Misplaced Pages

#278721

97-403: Chrysopogon zizanioides , commonly known as vetiver and khus , is a perennial bunchgrass of the family Poaceae . Vetiver is most closely related to Sorghum while sharing many morphological characteristics with other fragrant grasses, such as lemongrass ( Cymbopogon citratus ), citronella ( Cymbopogon nardus , C. winterianus ), and palmarosa ( Cymbopogon martinii ). Vetiver

194-560: A gregarious habit and grows in tufts. Shoots growing from the underground crown make the plant frost and wildfire resistant, and allow it to survive heavy grazing pressure. The leaves can become up to 300 cm (10 ft) long and 8 mm ( 3 ⁄ 8  in) wide. The panicles are 15–30 cm (6–12 in) long and have whorled, 25–50 mm (1–2 in) long branches . The spikelets are in pairs, and there are three stamens . The plant stems are erect and stiff. They can survive deep water flow. Under clear water,

291-662: A porous phase that holds gases (the soil atmosphere) and water (the soil solution). Accordingly, soil is a 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 by way of 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

388-407: A dessert topping. Khus syrup does not need to be refrigerated, although khus flavored products may need to be. Vetiver is mainly cultivated for the fragrant essential oil distilled from its roots. In Cuddalore , farmers grow 400 hectares (1,000 acres) of vetiver for oil extraction with help of marudhamalai groups. In perfumery, the older French spelling, vetyver , is often used. Worldwide production

485-1137: A disc plough with special adjustment is used. Bunchgrass Many species have long roots that may reach 2 meters (6.6 ft) or more into the soil, which can aid slope stabilization, erosion control , and soil porosity for precipitation absorption. Also, their roots can reach moisture more deeply than other grasses and annual plants during seasonal or climatic droughts. The plants provide habitat and food for insects (including Lepidoptera ), birds, small animals and larger herbivores , and support beneficial soil mycorrhiza . The leaves supply material, such as for basket weaving , for indigenous peoples and contemporary artists . Tussock and bunch grasses occur in almost any habitat where other grasses are found, including: grasslands , savannas and prairies , wetlands and estuaries , riparian zones , shrublands and scrublands , woodlands and forests , montane and alpine zones, tundra and dunes , and deserts . In western North American wildfires , bunch grasses tend to smolder and not ignite into flames, unlike invasive species of annual grasses that contribute to

582-623: A dry bulk density (density of soil taking into account voids when dry) between 1.1 and 1.6 g/cm , though the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm . 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

679-454: A fire's spreading. Soil Soil , also commonly referred to as earth , is a mixture of organic matter , minerals , gases , liquids , 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 phase of minerals and organic matter (the soil matrix), as well as

776-403: A flavoring agent, usually as khus syrup. Khus syrup is made by adding khus essence to sugar, water and citric acid syrup. Khus essence is a dark green thick syrup made from the roots. It has a woody taste and a scent characteristic of khus. The syrup is used to flavor milkshakes and yogurt drinks like lassi , but can also be used in ice creams, in mixed beverages such as Shirley Temples , and as

873-451: 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 organisms per gram, whereas

970-658: A more floral quality and is considered of higher quality than the smokier oil from Java. In north India, oil is distilled from wild-growing vetiver. This oil is known as khus or khas , and in India is considered superior to the oil obtained from the cultivated variety. It is rarely found in commerce outside of India, as most of it is consumed within the country. Vetiver has been used in traditional medicine in South Asia (India, Pakistan, Sri Lanka), Southeast Asia (Malaysia, Indonesia, Thailand), and West Africa. Old Tamil literature mentions

1067-419: 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. Components of a silt loam soil by percent volume A typical soil

SECTION 10

#1732891178279

1164-549: A pH of 9, plant growth is reduced. High pH results in low micro-nutrient mobility, but water-soluble chelates of those nutrients can correct the deficit. Sodium can be reduced by the addition of gypsum (calcium sulphate) as calcium adheres to clay more tightly than does sodium causing sodium to be pushed into the soil water solution where it can be washed out by an abundance of water. There are acid-forming cations (e.g. hydronium, aluminium, iron) and there are base-forming cations (e.g. calcium, magnesium, sodium). The fraction of

1261-731: A result of a trade-off between toxicity and requirement most nutrients are better available to plants at moderate pH, although most minerals are more soluble in acid soils. Soil organisms are hindered by high acidity, and most agricultural crops do best with mineral soils of pH 6.5 and organic soils of pH 5.5. Given that at low pH toxic metals (e.g. cadmium, zinc, lead) are positively charged as cations and organic pollutants are in non-ionic form, thus both made more available to organisms, it has been suggested that plants, animals and microbes commonly living in acid soils are pre-adapted to every kind of pollution, whether of natural or human origin. In high rainfall areas, soils tend to acidify as

1358-401: A result, layers (horizons) form in the soil profile. The alteration and movement of materials within a soil causes the formation of distinctive soil horizons . However, more recent definitions of soil embrace soils without any organic matter, such as those regoliths that formed on Mars and analogous conditions in planet Earth deserts. An example of the development of a soil would begin with

1455-412: A soil can be said to be developed, and can be described further in terms of color, porosity, consistency, reaction ( acidity ), etc. Water is a critical agent in soil development due to its involvement in the dissolution, precipitation, erosion, transport, and deposition of the materials of which a soil is composed. The mixture of water and dissolved or suspended materials that occupy the soil pore space

1552-399: A soil determines its ability to supply available plant nutrients and affects its physical properties and the health of its living population. In addition, a soil's chemistry also determines its corrosivity , stability, and ability to absorb pollutants and to filter water. It is the surface chemistry of mineral and organic colloids that determines soil's chemical properties. A colloid

1649-684: A technology of soil conservation and water quality management, is based on the use of the vetiver plant. The close-growing culms help to block surface water runoff . It slows the water flow and increases the amount absorbed by the soil (infiltration). It can withstand water velocity up to 5 metres per second (16 ft/s). Vetiver mulch increases water infiltration and reduces evaporation , thus protecting soil moisture under hot and dry conditions. The mulch also protects against splash erosion . In West African regions, such as Mali and Senegal, vetiver roots were traditionally used to reduce bacteria proliferation in water jugs and jars. In Indonesia,

1746-472: A valence of two, converts to (40 ÷ 2) × 1 milliequivalent = 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 leaching and decomposition, respectively, explains

1843-553: Is 0.04%, but in the soil pore space it may range from 10 to 100 times that level, thus potentially contributing to the inhibition of root respiration. Calcareous soils regulate CO 2 concentration by carbonate buffering , contrary to acid soils in which all CO 2 respired accumulates in the soil pore system. At extreme levels, CO 2 is toxic. This suggests a possible negative feedback control of soil CO 2 concentration through its inhibitory effects on root and microbial respiration (also called soil respiration ). In addition,

1940-421: Is a complex oil, containing over 150 identified components, typically: The oil is amber brown and viscous . Its odor is described as deep, sweet, woody, smoky, earthy, amber and balsam. The best quality oil is obtained from 18- to 24-month-old roots. The roots are dug up, cleaned, and then dried. Before distillation, the roots are chopped and soaked in water. The distillation process can take up to 24 hours. After

2037-603: Is a measure of the acidity or alkalinity of the soil. More precisely, it is a measure of hydronium concentration in an aqueous solution and ranges in values from 0 to 14 (acidic to basic) but practically speaking for soils, pH ranges from 3.5 to 9.5, as pH values beyond those extremes are toxic to life forms. At 25 °C an aqueous solution that has a pH of 3.5 has 10 moles H 3 O (hydronium ions) per litre of solution (and also 10 moles per litre OH ). A pH of 7, defined as neutral, has 10 moles of hydronium ions per litre of solution and also 10 moles of OH per litre; since

SECTION 20

#1732891178279

2134-509: Is a small, insoluble particle ranging in size from 1 nanometer to 1 micrometer , thus small enough to remain suspended by Brownian motion in a fluid medium without settling. Most soils contain organic colloidal particles called humus as well as the inorganic colloidal particles of clays . The very high specific surface area of colloids and their net electrical charges give soil its ability to hold and release ions . Negatively charged sites on colloids attract and release cations in what

2231-411: Is about 50% solids (45% mineral and 5% organic matter), and 50% voids (or pores) of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant (in the short term), while the percent soil water and gas content is considered highly variable whereby a rise in one is simultaneously balanced by a reduction in the other. The pore space allows for

2328-424: Is also a net sink of methane (CH 4 ) but a net producer of methane (a strong heat-absorbing greenhouse gas ) when soils are depleted of oxygen and subject to elevated temperatures. Soil atmosphere is also the seat of emissions of volatiles other than carbon and nitrogen oxides from various soil organisms, e.g. roots, bacteria, fungi, animals. These volatiles are used as chemical cues, making soil atmosphere

2425-556: 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

2522-464: Is assumed acid-forming cations). Base saturation is almost in direct proportion to pH (it increases with increasing pH). It is of use in calculating the amount of lime needed to neutralise an acid soil (lime requirement). The amount of lime needed to neutralize a soil must take account of the amount of acid forming ions on the colloids (exchangeable acidity), not just those in the soil water solution (free acidity). The addition of enough lime to neutralize

2619-414: Is called the pedosphere . The pedosphere interfaces with the lithosphere , the hydrosphere , the atmosphere , and the biosphere . Soil has four important functions : 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

2716-401: Is called the soil solution. Since soil water is never pure water, but contains hundreds of dissolved organic and mineral substances, it may be more accurately called the soil solution. Water is central to the dissolution , precipitation and leaching of minerals from the soil profile . Finally, water affects the type of vegetation that grows in a soil, which in turn affects the development of

2813-421: Is dependent on the type of parent material , the processes that modify those parent materials, and the soil-forming factors that influence those processes. The biological influences on soil properties are strongest near the surface, though the geochemical influences on soil properties increase with depth. Mature soil profiles typically include three basic master horizons: A, B, and C. The solum normally includes

2910-459: Is derived from the Tamil வெட்டிவேர் ( veṭṭivēr ) meaning 'root that is dug up', via French vétyver . In Northern India it is also called [khus] Error: {{Lang}}: invalid parameter: |script= ( help ) ('grass', not to be confused with [khus khus] Error: {{Lang}}: invalid parameter: |script= ( help ) , which refers to poppy seed ). During the reign of Harshavardhan , Kannauj became

3007-427: Is done by using insecticides and by appropriate cultural management: hedges are cut to 3 cm above ground at the end of the growing season. In general, vetiver is tolerant to herbicides and pesticides. Harvest of mature plants is performed mechanically or manually. A machine uproots the mature stock 20–25 cm (8–10 in) below ground. To avoid damaging the plant crown, a single-blade mouldboard plough or

Chrysopogon zizanioides - Misplaced Pages Continue

3104-565: Is estimated at about 250 tonnes per annum. Vetiver is used widely in perfumes for its excellent fixative properties. It is contained in 90% of Western perfumes. Vetiver is a more common ingredient in fragrances for men; some notable examples include Dior's Eau Sauvage , Guerlain Vétiver, M. Vétiver by Une Nuit à Bali, Zizan by Ormonde Jayne , Vétiver by L'Occitane en Provence , Encre Noire by Lalique or Vetiver Root by Korres. Indonesia , China , and Haiti are major producers. Vetiver processing

3201-468: Is grown for many purposes. The plant helps to stabilise soil and protects it against erosion , but it can also protect fields against pests and weeds . Vetiver has favourable qualities for animal feed . From the roots, oil is extracted and used for cosmetics , aromatherapy , herbal skincare and ayurvedic soap. Its fibrous properties make it useful for handicrafts , ropes and more. Vetiver has been used to produce perfumes, creams and soaps. It

3298-401: Is induced. Capillary action is responsible for moving groundwater from wet regions of the soil to dry areas. Subirrigation designs (e.g., wicking beds , sub-irrigated planters ) rely on capillarity to supply water to plant roots. Capillary action can result in an evaporative concentration of salts, causing land degradation through salination . Soil moisture measurement —measuring

3395-531: Is likely home to 59 ± 15% of the species on Earth. Enchytraeidae (worms) have the greatest percentage of species in soil (98.6%), followed by fungi (90%), plants (85.5%), and termites ( Isoptera ) (84.2%). Many other groups of animals have substantial fractions of species living in soil, e.g. about 30% of insects , and close to 50% of arachnids . While most vertebrates live above ground (ignoring aquatic species), many species are fossorial , that is, they live in soil, such as most blind snakes . The chemistry of

3492-477: Is more advanced. Most plant nutrients, with the exception of nitrogen , originate from the minerals that make up the soil parent material. Some nitrogen originates from rain as dilute nitric acid and ammonia , but most of the nitrogen is available in soils as a result of nitrogen fixation by bacteria . Once in the soil-plant system, most nutrients are recycled through living organisms, plant and microbial residues (soil organic matter), mineral-bound forms, and

3589-435: Is planted in long, straight rows across the slope for easy mechanical harvesting . The soil should be wet. Trenches are 15–20 cm (6–8 in) deep. A modified seedling planter or mechanical transplanter can plant large numbers of vetiver slips in the nursery. Flowering and nonflowering varieties are used for cultivation. Sandy loam nursery beds ensure easy harvest and minimal damage to plant crowns and roots. Open space

3686-485: Is recommended, because shading slows growth. Overhead irrigation is recommended for the first few months after planting. More mature plants prefer flood irrigation. Weed control may be needed during establishment phase, by using atrazine after planting. To control termites that attack dead material, hexachlorobenzene , also known as benzene hexachloride-BCH, can be applied to the vetiver hedge. Brown spot seems to have no effect on vetiver growth. Black rust in India

3783-409: Is referred to as cation exchange . Cation-exchange capacity is the amount of exchangeable cations per unit weight of dry soil and is expressed in terms of milliequivalents of positively charged ions per 100 grams of soil (or centimoles of positive charge per kilogram of soil; cmol c /kg ). Similarly, positively charged sites on colloids can attract and release anions in the soil, giving

3880-402: Is to add vetiver cooler perfume or even pure khus attar to the tank. Another advantage is that vetiver padding does not catch fire as easily as dry wood shavings. Mats made by weaving vetiver roots and binding them with ropes or cords are used in India to cool rooms in a house during summer. The mats are typically hung in a doorway and kept moist by spraying with water periodically; they cool

3977-428: Is used for its antiseptic properties to treat acne and sores. Several aspects of vetiver make it an excellent erosion control plant in warmer climates. Vetiver's roots grow almost exclusively downward, 2–4 m (7–13 ft), which is deeper than some tree roots. This makes vetiver an excellent stabilizing hedge for stream banks, terraces and rice paddies , and protects soil from sheet erosion . The roots bind to

Chrysopogon zizanioides - Misplaced Pages Continue

4074-540: Is very little organic material. Basaltic minerals commonly weather relatively quickly, according to the Goldich dissolution series . The plants are supported by the porous rock as it is filled with nutrient-bearing water that carries minerals dissolved from the rocks. Crevasses and pockets, local topography of the rocks, would hold fine materials and harbour plant roots. The developing plant roots are associated with mineral-weathering mycorrhizal fungi that assist in breaking up

4171-475: Is vetiver-specific and does not cross-infect other plants. In China, stemborers ( Chilo spp.) have been recognised, but they seem to die once they get into the stems. Further, vetiver is affected by Didymella andropogonis on leaves, Didymosphaeria andropogonis on dead culms, Lulworthia medusa on culms and Ophiosphaerella herpotricha . Only in Malaysia, whiteflies seem to be a problem. Pest management

4268-478: Is widely cultivated in tropical regions. The major vetiver producers include Haiti , India , Indonesia , and Réunion (part of the Mascarene Islands , east of Madagascar). The most commonly used commercial genotypes of vetiver are sterile , and because vetiver propagates itself by small offsets instead of underground stolons , these genotypes are noninvasive and can easily be controlled by cultivation of

4365-490: The aeration of the soil and the ability of water to infiltrate and to be held within the soil. Soil water content can be measured as volume or weight . Soil moisture levels, in order of decreasing water content, are saturation, field capacity , wilting point , air dry, and oven dry. Field capacity describes a drained wet soil at the point water content reaches equilibrium with gravity. Irrigating soil above field capacity risks percolation losses. Wilting point describes

4462-561: The humus form ), the copedon (in intermediary position, where most weathering of minerals takes place) and the lithopedon (in contact with the subsoil). The soil texture is determined by the relative proportions of the individual particles of sand , silt , and clay that make up the soil. The interaction of the individual mineral particles with organic matter, water, gases via biotic and abiotic processes causes those particles to flocculate (stick together) to form aggregates or peds . Where these aggregates can be identified,

4559-425: The mineralogy of those particles can strongly modify those properties. The mineralogy of the finest soil particles, clay, is especially important. Large numbers of microbes , animals , plants and fungi are living in soil. However, biodiversity in soil is much harder to study as most of this life is invisible, hence estimates about soil biodiversity have been unsatisfactory. A recent study suggested that soil

4656-548: The murti of Lord Nataraja (Shiva) in Hindu temples. It is a favourite offering to Ganesha . Vetiver oil has been used in an effort to track where mosquitoes live during dry seasons in Sub-Saharan Africa. Mosquitoes were tagged with strings soaked in vetiver oil then released. Dogs trained to track the scent, not native to Africa, found the marked mosquitoes in such places as holes in trees and in old termite mounds . Vetiver

4753-448: The A and B horizons. The living component of the soil is largely confined to the solum, and is generally more prominent in the A horizon. It has been suggested that the pedon , a column of soil extending vertically from the surface to the underlying parent material and large enough to show the characteristics of all its horizons, could be subdivided in the humipedon (the living part, where most soil organisms are dwelling, corresponding to

4850-406: The acronym CROPT. The physical properties of soils, in order of decreasing importance for ecosystem services such as crop production , are texture , structure , bulk density , porosity , consistency, temperature , colour and resistivity . Soil texture is determined by the relative proportion of the three kinds of soil mineral particles, called soil separates: sand , silt , and clay . At

4947-446: The addition of any more hydronium ions or aluminum hydroxyl cations drives the pH even lower (more acidic) as the soil has been left with no buffering capacity. In areas of extreme rainfall and high temperatures, the clay and humus may be washed out, further reducing the buffering capacity of the soil. In low rainfall areas, unleached calcium pushes pH to 8.5 and with the addition of exchangeable sodium, soils may reach pH 10. Beyond

SECTION 50

#1732891178279

5044-452: The apparent sterility of tropical soils. Live plant roots also have some CEC, linked to their specific surface area. Anion exchange capacity is the soil's ability to remove anions (such as nitrate , phosphate ) from the soil water solution and sequester those for later exchange as the plant roots release carbonate anions to the soil water solution. Those colloids which have low CEC tend to have some AEC. Amorphous and sesquioxide clays have

5141-437: 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. 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

5238-426: The basic cations are forced off the soil colloids by the mass action of hydronium ions from usual or unusual rain acidity against those attached to the colloids. High rainfall rates can then wash the nutrients out, leaving the soil inhabited only by those organisms which are particularly efficient to uptake nutrients in very acid conditions, like in tropical rainforests . Once the colloids are saturated with H 3 O ,

5335-541: The biggest centre for aromatic trade and for the first time, a vetiver tax was introduced. Vetiver grows to 150 centimetres (5 ft) high and forms clumps as wide, and under favorable conditions, the erect culms can reach 3 m (9.8 ft) in height. The stems are tall and the leaves are long, thin, and rather rigid. The flowers are brownish-purple. Unlike most grasses, which form horizontally, spreading mat-like root systems, vetiver's roots grow downward 2–4 m (7–13 ft) in depth. The vetiver bunch grass has

5432-511: The distillate separates into the essential oil and hydrosol , the oil is skimmed off and allowed to age for a few months to allow some undesirable notes formed during distillation to dissipate. Like patchouli and sandalwood essential oils, vetiver's odor develops and improves with aging. The oil's characteristics can vary significantly depending on where the grass is grown and the climate and soil conditions. The oil distilled in Haiti and Réunion has

5529-436: The dry limit for growing plants. During growing season, soil moisture is unaffected by functional groups or specie richness. Available water capacity is the amount of water held in a soil profile available to plants. As water content drops, plants have to work against increasing forces of adhesion and sorptivity to withdraw water. Irrigation scheduling avoids moisture stress by replenishing depleted water before stress

5626-519: 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 . Soil is a major component of the Earth 's ecosystem . The world's ecosystems are impacted in far-reaching ways by

5723-419: The highest AEC, followed by the iron oxides. Levels of AEC are much lower than for CEC, because of the generally higher rate of positively (versus negatively) charged surfaces on soil colloids, to the exception of variable-charge soils. Phosphates tend to be held at anion exchange sites. Iron and aluminum hydroxide clays are able to exchange their hydroxide anions (OH ) for other anions. The order reflecting

5820-632: The infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction , a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile that consists of two or more layers, referred to as soil horizons. These differ in one or more properties such as in their texture , structure , density , porosity, consistency, temperature, color, and reactivity . The horizons differ greatly in thickness and generally lack sharp boundaries; their development

5917-466: The largest producer in the world. The plant extracts vetiver oil by steam distillation. Another major operation in the field is the one owned by the Boucard family. Réunion is considered to produce the highest quality vetiver oil, called "bourbon vetiver", with the next favorable being Haiti and then Java. The United States , Europe , India , and Japan are the main consumers. Vetiver oil, or khus oil,

SECTION 60

#1732891178279

6014-537: The leaves, so that they instead fall to the ground and die. Vetiver's essential oil has anti-fungal properties against Rhizoctonia solani . As a mulch , vetiver is used for weed control in coffee , cocoa and tea plantations. It builds a barrier in the form of a thick mat . When the mulch breaks down, soil organic matter is built up and additional crop nutrients become available. Vetiver extracts can repel termites . However, vetiver grass alone, unlike its extracts, cannot be used to repel termites. Unless

6111-429: The negatively charged colloids resist being washed downward by water and are out of reach of plant roots, thereby preserving the soil fertility in areas of moderate rainfall and low temperatures. There is a hierarchy in the process of cation exchange on colloids, as cations differ in the strength of adsorption by the colloid and hence their ability to replace one another ( ion exchange ). If present in equal amounts in

6208-412: The negatively-charged soil colloid exchange sites (CEC) that are occupied by base-forming cations is called base saturation . If a soil has a CEC of 20 meq and 5 meq are aluminium and hydronium cations (acid-forming), the remainder of positions on the colloids ( 20 − 5 = 15 meq ) are assumed occupied by base-forming cations, so that the base saturation is 15 ÷ 20 × 100% = 75% (the compliment 25%

6305-419: The next larger scale, soil structures called peds or more commonly soil aggregates are created from the soil separates when iron oxides , carbonates , clay, silica and humus , coat particles and cause them to adhere into larger, relatively stable secondary structures. Soil bulk density , when determined at standardized moisture conditions, is an estimate of soil compaction . Soil porosity consists of

6402-472: The ocean has no more than 10 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

6499-635: The other cations more weakly bound to colloids are pushed into solution as hydrogen ions occupy exchange sites ( protonation ). A low pH may cause the hydrogen of hydroxyl groups to be pulled into solution, leaving charged sites on the colloid available to be occupied by other cations. This ionisation of hydroxy groups on the surface of soil colloids creates what is described as pH-dependent surface charges. Unlike permanent charges developed by isomorphous substitution , pH-dependent charges are variable and increase with increasing pH. Freed cations can be made available to plants but are also prone to be leached from

6596-428: The passing air, as well as emitting a fresh aroma. In the hot summer months in India, sometimes a muslin sachet of vetiver roots is tossed into the earthen pot that keeps a household's drinking water cool. Like a bouquet garni , the bundle lends distinctive flavor and aroma to the water. Khus -scented syrups are also sold. A recent study found the plant is capable of growing in fuel-contaminated soil. In addition,

6693-479: The plant can survive up to two months. The root system of vetiver is finely structured and very strong. It can grow 3–4 m (10–13 ft) deep within the first year. Vetiver has neither stolons nor rhizomes . Because of all these characteristics, the vetiver plant is highly drought-tolerant and can help to protect soil against sheet erosion . In case of sediment deposition , new roots can grow out of buried nodes . Originally from India , C. zizanioides

6790-492: The plant roots release hydrogen ions to the solution. CEC is the amount of exchangeable hydrogen cation (H ) that will combine with 100 grams dry weight of soil and whose measure is one milliequivalents per 100 grams of soil (1 meq/100 g). Hydrogen ions have a single charge and one-thousandth of a gram 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

6887-486: The porous lava, and by these means organic matter and a finer mineral soil accumulate with time. Such initial stages of soil development have been described on volcanoes, inselbergs, and glacial moraines. How soil formation proceeds is influenced by at least five classic factors that are intertwined in the evolution of a soil: parent material, climate, topography (relief), organisms, and time. When reordered to climate, relief, organisms, parent material, and time, they form

6984-414: 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

7081-414: The rate of diffusion of gases into and out of soil. Platy soil structure and soil compaction (low porosity) impede gas flow, and a deficiency of oxygen may encourage anaerobic bacteria to reduce (strip oxygen) from nitrate NO 3 to the gases N 2 , N 2 O, and NO, which are then lost to the atmosphere, thereby depleting the soil of nitrogen, a detrimental process called denitrification . Aerated soil

7178-399: The roots are damaged, the anti-termite chemicals, such as nootkatone , are not released. The leaves of vetiver are a useful byproduct to feed cattle , goats , sheep and horses . The nutritional content depends on season , growth stage and soil fertility . Under most climates, nutritional values and yields are best if vetiver is cut every 1–3 months . Vetiver (khus) is also used as

7275-463: The roots of vetiver are widely used in the production of fragrant mats. In the Philippines and India, the roots are woven to make fragrant-smelling fans called "sandal root fans". Vetiver can be used for crop protection. It attracts the stem borer ( Chilo partellus ), which lays its eggs preferentially on vetiver but whose larvae cannot thrive there, as the plant's hairiness prevents their moving onto

7372-442: The seat of interaction networks playing a decisive role in the stability, dynamics and evolution of soil ecosystems. Biogenic soil volatile organic compounds are exchanged with the aboveground atmosphere, in which they are just 1–2 orders of magnitude lower than those from aboveground vegetation. Humans can get some idea of the soil atmosphere through the well-known 'after-the-rain' scent, when infiltering rainwater flushes out

7469-441: The soil anion exchange capacity. The cation exchange, that takes place between colloids and soil water, buffers (moderates) soil pH, alters soil structure, and purifies percolating water by adsorbing cations of all types, both useful and harmful. The negative or positive charges on colloid particles make them able to hold cations or anions, respectively, to their surfaces. The charges result from four sources. Cations held to

7566-459: The soil at the boundary of the hedge. However, care must be taken, because fertile genotypes of vetiver have become invasive. Almost all vetiver grown worldwide is vegetatively propagated ; bioengineering has shown them as essentially the same nonfertile cultigen by DNA profiling . In the United States the cultivar is named 'Sunshine,' after the town of Sunshine, Louisiana . Vetiver grass

7663-538: The soil by volatilisation (loss to the atmosphere as gases) or leaching. Soil is said to be formed when organic matter has accumulated and colloids are washed downward, leaving deposits of clay, humus , iron oxide , carbonate , and gypsum , producing a distinct layer called the B horizon. This is a somewhat arbitrary definition as mixtures of sand, silt, clay and humus will support biological and agricultural activity before that time. These constituents are moved from one level to another by water and animal activity. As

7760-420: The soil solution composition (attenuate changes in the soil solution) as soils wet up or dry out, as plants take up nutrients, as salts are leached, or as acids or alkalis are added. Plant nutrient availability is affected by soil pH , which is a measure of the hydrogen ion activity in the soil solution. Soil pH is a function of many soil forming factors, and is generally lower (more acidic) where weathering

7857-402: The soil solution. Both living soil organisms (microbes, animals and plant roots) and soil organic matter are of critical importance to this recycling, and thereby to soil formation and soil fertility . Microbial soil enzymes may release nutrients from minerals or organic matter for use by plants and other microorganisms, sequester (incorporate) them into living cells, or cause their loss from

7954-473: The soil voids are saturated with water vapour, at least until the point of maximal hygroscopicity , beyond which a vapour-pressure deficit occurs in the soil pore space. Adequate porosity is necessary, not just to allow the penetration of water, but also to allow gases to diffuse in and out. Movement of gases is by diffusion from high concentrations to lower, the diffusion coefficient decreasing with soil compaction . Oxygen from above atmosphere diffuses in

8051-430: The soil water solution will be insufficient to change the pH, as the acid forming cations stored on the soil colloids will tend to restore the original pH condition as they are pushed off those colloids by the calcium of the added lime. The resistance of soil to change in pH, as a result of the addition of acid or basic material, is a measure of the buffering capacity of a soil and (for a particular soil type) increases as

8148-433: The soil water solution: Al replaces H replaces Ca replaces Mg replaces K same as NH 4 replaces Na If one cation is added in large amounts, it may replace the others by the sheer force of its numbers. This is called law of mass action . This is largely what occurs with the addition of cationic fertilisers ( potash , lime ). As the soil solution becomes more acidic (low pH , meaning an abundance of H ),

8245-462: The soil where it is consumed and levels of carbon dioxide in excess of above atmosphere diffuse out with other gases (including greenhouse gases ) as well as water. Soil texture and structure strongly affect soil porosity and gas diffusion. It is the total pore space ( porosity ) of soil, not the pore size, and the degree of pore interconnection (or conversely pore sealing), together with water content, air turbulence and temperature, that determine

8342-502: The soil, a complex feedback which is exemplified in the dynamics of banded vegetation patterns in semi-arid regions. Soils supply plants with nutrients , most of which are held in place by particles of clay and organic matter ( colloids ) The nutrients may be adsorbed on clay mineral surfaces, bound within clay minerals ( absorbed ), or bound within organic compounds as part of the living organisms or dead soil organic matter. These bound nutrients interact with soil water to buffer

8439-414: The soil, possibly making the soil less fertile. Plants are able to excrete H into the soil through the synthesis of organic acids and by that means, change the pH of the soil near the root and push cations off the colloids, thus making those available to the plant. Cation exchange capacity is the soil's ability to remove cations from the soil water solution and sequester those to be exchanged later as

8536-503: The soil, therefore it can not dislodge. Vetiver has been used to stabilize railway cuttings/embankments in geologically challenging situations in an attempt to prevent mudslides and rockfalls, such as the Konkan railway in western India. The plant also penetrates and loosens compacted soils . Vetiver was advocated for erosion control in Thailand by the late King Bhumibol . The Vetiver System ,

8633-409: The strength of anion adhesion is as follows: The amount of exchangeable anions is of a magnitude of tenths to a few milliequivalents per 100 g dry soil. As pH rises, there are relatively more hydroxyls, which will displace anions from the colloids and force them into solution and out of storage; hence AEC decreases with increasing pH (alkalinity). Soil reactivity is expressed in terms of pH and

8730-451: The study discovered the plant is also able to clean the soil, so in the end, the soil is almost fuel-free. Vetiver grass is used as roof thatch (it lasts longer than other materials) and in mud brick -making for housing construction (such bricks have lower thermal conductivity). It is also made into strings and ropes , and grown as an ornamental plant (for the light purple flowers ). Garlands made of vetiver grass are used to adorn

8827-491: The two concentrations are equal, they are said to neutralise each other. A pH of 9.5 has 10 moles hydronium ions per litre of solution (and also 10 moles per litre OH ). A pH of 3.5 has one million times more hydronium ions per litre than a solution with pH of 9.5 ( 9.5 − 3.5 = 6 or 10 ) and is more acidic. The effect of pH on a soil is to remove from the soil or to make available certain ions. Soils with high acidity tend to have toxic amounts of aluminium and manganese . As

8924-516: The use of vetiver for medical purposes. In the Indian Subcontinent, khus (vetiver roots) is often used to replace the straw or wood shaving pads in evaporative coolers . When cool water runs for months over wood shavings in evaporative cooler padding, they tend to accumulate algae , bacteria and other microorganisms. This causes the cooler to emit a fishy or seaweed smell. Vetiver root padding counteracts this odor. A cheaper alternative

9021-473: The void part of the soil volume and is occupied by gases or water. Soil consistency is the ability of soil materials to stick together. Soil temperature and colour are self-defining. Resistivity refers to the resistance to conduction of electric currents and affects the rate of corrosion of metal and concrete structures which are buried in soil. These properties vary through the depth of a soil profile, i.e. through soil horizons . Most of these properties determine

9118-553: The water content of the soil, as can be expressed in terms of volume or weight—can be based on in situ probes (e.g., capacitance probes , neutron probes ), or remote sensing methods. Soil moisture measurement is an important factor in determining changes in soil activity. The atmosphere of soil, or soil gas , is very different from the atmosphere above. The consumption of oxygen by microbes and plant roots, and their release of carbon dioxide, decreases oxygen and increases carbon dioxide concentration. Atmospheric CO 2 concentration

9215-461: The weathering of lava flow bedrock, which would produce the purely mineral-based parent material from which the soil texture forms. Soil development would proceed most rapidly from bare rock of recent flows in a warm climate, under heavy and frequent rainfall. Under such conditions, plants (in a first stage nitrogen-fixing lichens and cyanobacteria then epilithic higher plants ) become established very quickly on basaltic lava, even though there

9312-476: The whole soil atmosphere after a drought period, or when soil is excavated, a bulk property attributed in a reductionist manner to particular biochemical compounds such as petrichor or geosmin . Soil particles can be classified by their chemical composition ( mineralogy ) as well as their size. The particle size distribution of a soil, its texture, determines many of the properties of that soil, in particular hydraulic conductivity and water potential , but

9409-432: Was introduced to Haiti in the 1940s by Frenchman Lucien Ganot. In 1958, Franck Léger established a plant on the grounds of his father Demetrius Léger's alcohol distillery. The plant was taken over in 1984 by Franck's son, Pierre Léger, who expanded the size of the plant to 44 atmospheric stills, each built to handle one metric ton of vetiver roots. Total production increased in ten years from 20 to 60 tonnes annually, making it

#278721