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Soil pH is an indication of the alkalinity or acidity of soil. It is based on the measurement of pH, which is based in turn on the activity of hydrogen ions (H⁺) in a water or salt solution. Image File history File links Broom_icon. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Technically, soil forms the pedosphere: the interface between the lithosphere (rocky part of the planet) and the biosphere, atmosphere, and hydrosphere. ... The correct title of this article is . ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... This article is about the electrically charged particle. ...

When in balance (pH 7) the soil is said to be neutral. The pH scale covers a continuum ranging from 0 (very acidic) to 14 (very alkaline or basic). It is however uncommon to find soils at either extreme of this range. Under many conditions soils tend to become more acid or alkaline over time if steps are not taken to maintain a balance. Acidity redirects here. ... The common (Arrhenius) definition of a base is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ...

(NOTE: Alkaline and basic are not interchangeable. However, aside from uncommon examples such as Ammonias, testing Alkaline and testing pH bring about similar results. The higher the Alkalinity, the greater the tendency towards a base.)

Soil pH is an important consideration for farmers and gardeners for several reasons, including the fact that many plants and soil life forms prefer either alkaline or acidic conditions, that some diseases tend to thrive when the soil is alkaline or acidic, and that the pH can affect the availability of nutrients in the soil. Soil life is a collective term for all the organisms living within the soil. ...

Nutrient availability in relation to soil pH

The majority of food crops prefer a neutral or slightly acidic soil. Some plants however prefer more acidic (e.g., potatoes, strawberries) or alkaline (brassicas) conditions. Species See text. ...

The above table gives a guide to the availability of several nutrients at various pH values Acidity redirects here. ... In chemistry, an alkali (from Arabic: al-qalyالقلوي, القالي ) is a basic, ionic salt of an alkali metal or alkali earth metal element. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... General Name, Symbol, Number phosphorus, P, 15 Chemical series nonmetals Group, Period, Block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Standard atomic weight 39. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... General Name, Symbol, Number boron, B, 5 Chemical series metalloids Group, Period, Block 13, 2, p Appearance black/brown Standard atomic weight 10. ... For other uses, see Copper (disambiguation). ... General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... General Name, Symbol, Number molybdenum, Mo, 42 Chemical series transition metals Group, Period, Block 6, 5, d Appearance gray metallic Standard atomic weight 95. ...

During the acidification process the decrease in pH results in a release of positively charged ions (cations) from the cation exchange surfaces (organic matter and clay minerals). In the short term acidification thus increases the concentration of potassium (K), magnesium (Mg), and calcium (Ca) in soil solution. Once the cation exchange surface has become depleted of these ions, however, the concentration in soil solution can be quite low and is largely determined by the weathering rate. The weathering rate in turn is dependent on such things as mineralogy (e.g. presence of easily weathered minerals), surface area (i.e. the soil texture), soil moisture (i.e. how large a fraction of the mineral surface area that is wet), pH, concentration of base cations such as Ca, Mg and K as well as concentration of Aluminium. The amount of plant available nutrients is a much more difficult issue than soil solution concentrations. The term plant available nutrients usually include pools other than soil solution but which are supposed to replenish soil solution pretty fast e.g. through cation exchange. One reason for including such pools is the plants capability of releasing organic acids which increase the total soil solution concentration of some cation nutrients that are important for the plant. General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Standard atomic weight 39. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... Soil texture triangle, showing the 12 major textural classes, and particle size scales. ...

It is thus important to realise that there exists no simple relation between soil solution concentration of Ca, Mg and K and reasonable pH-values. The reason for this is that Ca, Mg and K are base cations, i.e. cations of strong bases and strong bases are fully dissociated at the pH-ranges occurring in most natural waters. However, as the soil solution pH is dependent on mineral weathering and mineral weathering increase pH by releasing Ca, Mg and K a soil which is rich in easily weatherable minerals tends to have both a higher pH and higher soil solution concentration of Ca, Mg and K. On the other hand deposition of sulphate, nitrate and to some extent ammonia decrease pH of soil solution essentially without affecting Ca, Mg and K concentrations whereas deposition of sea salt increases Ca, Mg and K concentrations without having much of an effect on soil solution pH.

When interpreting soil solution pH values it is essential to take into account the method by which pH has been measured. Depending on whether or not the water has been equilibrated with ambient CO₂ pressure or not the pH reported from the same site may be either high or low. This is simply because the carbon dioxide pressure deep down in the soil might be 10–20 times higher than the ambient pressure due to decomposition of organic material. The higher carbon dioxide pressure result in more carbonic acid and hence a lower pH. Furthermore, soil solution can be extracted from the soil in many ways, e.g. by lysimeters, zero-tension lysimeters, centrifugation, extraction with CaCl₂, overhead shaking of soil sample with added water, etc. The CaCl₂ extraction method do not give the actual soil solution pH but rather a mix between soil solution pH and what is easily available e.g. through cation exchange. Also when mixing soil samples with water and using overhead shakers (or similar) the result is a mix between actual soil solution and cation exchange, although the hope is that the extracted water will be similar to the actual soil solution in most respects. If centrifugation or pressurised lysimeters are used, care must be taken that the extracted water do not include water that is not readily available (think wilting point and crystal water). Naturally, taking a sample introduces a disturbance of the system, which can e.g. result in a change in nutrient uptake and decomposition rates (e.g. due to cutting of fine roots when placing the lysimeter). A lysimeter is a measuring device which can be used to measure the amount of actual evapotranspiration which is released from an area of woodland. ...

Many nutrient cations such as zinc (Zn²⁺), aluminium (Al³⁺), iron (Fe²⁺), copper (Cu²⁺), cobalt (Co²⁺), and manganese (Mn²⁺) are soluble and available for uptake by plants below pH 5.0, although their availability can be excessive and thus toxic in more acidic conditions. In more alkaline conditions they are less available, and symptoms of nutrient deficiency may result, including thin plant stems, yellowing (chlorosis) or mottling of leaves, and slow or stunted growth. General Name, Symbol, Number zinc, Zn, 30 Chemical series transition metals Group, Period, Block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ... General Name, symbol, number aluminium, Al, 13 Chemical series poor metals Group, period, block 13, 3, p Appearance silvery Standard atomic weight 26. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... For other uses, see Copper (disambiguation). ... For other uses, see Cobalt (disambiguation). ... General Name, Symbol, Number manganese, Mn, 25 Chemical series transition metals Group, Period, Block 7, 4, d Appearance silvery metallic Standard atomic weight 54. ... In botany, Chlorosis is a condition in which plant foliage produces insufficient chlorophyll. ...

pH levels also affect the complex interactions among soil chemicals. Phosphorus (P) for example requires a pH between 6.0 and 7.0 and becomes chemically immobile outside this range, forming insoluble compounds with iron (Fe) and aluminium (Al) in acid soils and with calcium (Ca) in calcareous soils.

Soils and acidity

Under conditions in which rainfall exceeds evapotranspiration (leaching) during most of the year, the basic soil cations (Ca, Mg, K) are gradually depleted and replaced with cations held in colloidal soil reserves, leading to soil acidity. Clay soils often contain Fe and hydroxy Al, which affect the retention and availability of fertilizer cations and anions in acidic soils. A cation is an ion with positive charge. ... An anion is an ion with negative charge. ...

Soil acidification may also occur by addition of hydrogen, due to decomposition of organic matter, acid-forming fertilizers, and exchange of basic cations for H⁺ by the roots.

Soil acidity is reduced by volatilization and denitrification of nitrogen. Under flooded conditions, the soil pH value increases. In addition, the following nitrate fertilizers -- calcium nitrate, magnesium nitrate, potassium nitrate and sodium nitrate -- also increase the soil pH value. Volatilisation is the process whereby a dissolved sample is vaporised. ... This does not cite its references or sources. ... An electrostatic potential map of the nitrate ion. ... Calcium nitrate, also called Norgessalpeter (Norwegian saltpeter) and Kalksalpeter, is a soluble salt with the formula Ca(NO3)2. ... Magnesium nitrate is a hygroscopic salt with the formula Mg(NO3)2. ... R-phrases   S-phrases   Supplementary data page Structure and properties n, εr, etc. ... Made of Porn and sex things Inhalation respiratory irritation Skin May cause irritation. ...

Some alkaline soils have Calcium in the form of limestone that is not chemically available to plants. In this case sulfuric acid or Sulfur may be added to reclaim the soil. Sulfuric (or sulphuric) acid, H2SO4, is a strong mineral acid. ... General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ...

Factors affecting soil pH

The pH value of a soil is influenced by the kinds of parent materials from which the soil was formed. Soils developed from basic rocks generally have higher pH values than those formed from acid rocks.

Rainfall also affects soil pH. Water passing through the soil leaches basic nutrients such as calcium and magnesium from the soil. They are replaced by acidic elements such as aluminum and iron. For this reason, soils formed under high rainfall conditions are more acidic than those formed under arid (dry) conditions.

Human distractions like pollution alter the pH of soil. Researches have also revealed that soil pH is affected by the vehicular and ongoing traffic. This largely hampers the soil pH and in turn the primary productivity by compacting the soil and decreasing its friability.

Application of fertilizers containing ammonium or urea speeds up the rate at which acidity develops. The decomposition of organic matter also adds to soil acidity.

Soil life and pH

A pH level of around 6.3-6.8 is also the optimum range preferred by most soil bacteria, although fungi, molds, and anaerobic bacteria have a broader tolerance and tend to multiply at lower pH values. Therefore, more acidic soils tend to be susceptible to souring and putrefaction, rather than undergoing the sweet decay processes associated the decay of organic matter, immeasurably benefitting the soil, also prefer these near-neutral conditions. Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... Organic matter (or organic material) is matter which has come from a recently living organism; is capable of decay, or the product of decay; or is composed of organic compounds. ...

pH and plant diseases

Many plant diseases are caused or exacerbated by extremes of pH, sometimes because this makes essential nutrients unavailable to crops or because the soil itself is unhealthy (see above). For example, chlorosis of leaf vegetables and potato scab occur in overly alkaline conditions, and acidic soils can cause clubroot in brassicas. In botany, Chlorosis is a condition in which plant foliage produces insufficient chlorophyll. ...

Determining pH

PH is not constant in soil or water, but varies on a seasonal or even daily basis due to factors such as rainfall, biological growth within the soil, and temperature changes. Rather, a map of the pH level is a mosaic, varying according to soil crumb structure, on the surface of colloids, and at microsites. The pH also exhibits vertical gradients, tending to be more acidic in surface mulches and alkaline where evaporation, wormcasts, and capillary action draw bases up to the soil surface. It also varies on a macro level depending on factors such as slope, rocks, and vegetation type. Therefore the pH should be measured regularly and at various points within the land in question.

Methods of determining pH include:

• Observation of predominant flora. Calcifuge plants (those that prefer an acidic soil) include Erica, Rhododendron and nearly all other Ericaceae species, many Betula (birch), Digitalis (foxgloves), gorse, and Scots Pine. Calcicole (lime loving) plants include Fraxinus (Ash), Honeysuckle (Lonicera), Buddleia, Cornus spp (dogwoods), Lilac(Syringa) and Clematis spp.
• Observation of symptoms that might indicate acidic or alkaline conditions, such as occurrence of the plant diseases mentioned above or salinisation of alkaline soils. The house hydrangea (Hydrangea macrophylla) produces pink flowers at pH values of 6.8 or higher, and blue flowers at pH 6.0 or below.
• Use of an inexpensive pH testing kit based on barium sulfate in powdered form, wherein a small sample of soil is mixed with water which changes colour according to the acidity/alkalinity.
• Use of litmus paper. A small sample of soil is mixed with distilled water, into which a strip of litmus paper is inserted. If the soil is acid the paper turns red, if alkaline, blue.
• Use of a commercially available electronic pH meter, in which a rod is inserted into moistened soil and measures the concentration of hydrogen ions.

For other uses, see Erika. ... Subgenera Azaleastrum Candidastrum Hymenanthes Mumeazalea Pentanthera (Azaleas) Rhododendron Therorhodion Tsutsusi (Azaleas) Vireya Source: RBG, Edinburgh Rhododendron (from the Greek: rhodos, rose, and dendron, tree) is a genus of flowering plants in the family Ericaceae. ... Genera See text The plant Family Ericaceae (Heath Family) or ericaceous plants are mostly lime-hating or calcifuge plants that thrive in acid soils. ... Species Many species; see text and classification Birch is the name of any tree of the genus Betula, in the family Betulaceae, closely related to the beech/oak family, Fagaceae. ... Species Digitalis ferruginea Digitalis grandiflora Digitalis lanata Digitalis lutea Digitalis obscura Digitalis purpurea Digitalis is a genus of about 20 species of herbaceous biennials, perennials and shrubs in the foxglove family Scrophulariaceae. ... Species Ulex argenteus Ulex boivinii Ulex borgiae Ulex cantabricus Ulex densus Ulex europaeus - Common Gorse Ulex gallii - Dwarf Furze or Furse Ulex genistoides Ulex micranthus Ulex minor - Dwarf Gorse Ulex parviflorus Ref: ILDIS Version 6. ... Binomial name L. Image:Scotspine map. ... Species Many, see text. ... Species See text - Selected Species Honeysuckles (genus Lonicera; syn. ... Subgenera Cornus Benthamidia Swida The Dogwoods comprise a group of 30-50 species of deciduous woody plants (shrubs and trees) in the family Cornaceae, divided into one to nine genera or subgenera (depending on botanical interpretation). ... Look up lilac in Wiktionary, the free dictionary. ... Species See text. ... This article or section does not cite its references or sources. ... The term litmus test can be literal or metaphorical. ... The term litmus test can be literal or metaphorical. ... A pH meter is an electronic instrument used to measure the pH (acidity or basicity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances, such as cheese). ...

Altering soil pH

The aim when attempting to adjust soil acidity is not so much to neutralise the pH as to replace lost cation nutrients, particularly calcium. This can be achieved by adding limestone to the soil, which is available in various forms:-1...

• Agricultural lime (ground limestone or chalk). These are natural forms of calcium carbonate which are extracted in the UK from areas such as the Mendips and Salisbury Plain. This is probably the cheapest form of lime for gardening and agricultural use and can be applied at any time of the year. These forms are slow reacting, thus their effect on soil fertility and plant growth is steady and long lasting. Ground lime should be applied to clay and heavy soils at a rate of about 500 to 1,000 g/m² (1 to 2 lb/yd² or 4,500 to 9,000 lb/ac).
• Quicklime and slaked lime. The former is produced by burning rock limestone in kilns. It is highly caustic and cannot be applied directly to the soil. Quicklime reacts with water to produce slaked, or hydrated, lime, thus quicklime is spread around agricultural land in heaps to absorb rain and atmospheric moisture and form slaked lime, which is then spread on the soil. Quicklime should be applied to heavy clays at a rate of about 400 to 500 g/m² (0.75 to 1 lb/yd² or 3,600 to 4,500 lb/ac), hydrated lime at 250 to 500 g/m² (0.5 to 1 lb/yd²). However, quicklime and hydrated lime are very fast acting and are not suitable for inclusion in an organic system. Their use is prohibited under the standards of both The Soil Association and the Henry Doubleday Research Association.
• Calcium sulfate, also known as gypsum can not be used to amend soil acidity. It is a common myth that gypsum effects soil acidity.^[1]

Unattributable commenter "... thi[s] is totally wrong don't believe in this." removed from citation. I'm sorry, mystery commenter, but this is how science works. You are free to believe or disbelieve anything you wish. However, demonstrated facts are just that. If you disagree so strongly with the above conclusions, please conduct your own experiments that show the above article to be untrue. Please do not interfere with others who seek knowledge gained by the scientific method. Agricultural lime is a soil additive made from pulverized limestone or chalk. ... Categories: Stub | Somerset ... This article is about the plateau in southern England; Salisbury Plain is also an area on South Georgia Island. ... Soil fertility is the characteristic of soil that supports abundant plant life. ... The Soil Association is the main umbrella group in the UK for organic farmers. ... The Henry Doubleday Research Association (HDRA) is a UK organisation dedicated to researching and promoting organic gardening, farming and food. ... It has been suggested that Selenite be merged into this article or section. ... A soil amendment is any of a class of materials which are used to adjust the soil for increased fertility. ...

The pH of an alkaline soil is lowered by adding sulfur, iron sulfate or aluminum sulfate, although these tend to be expensive, and the effects short term. Urea, urea phosphate, ammonium nitrate, ammonium phosphates, ammonium sulfate and monopotassium phosphate also lower soil pH. General Name, Symbol, Number sulfur, S, 16 Chemical series nonmetals Group, Period, Block 16, 3, p Appearance lemon yellow Standard atomic weight 32. ... General Name, symbol, number iron, Fe, 26 Chemical series transition metals Group, period, block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... In inorganic chemistry, a sulfate (IUPAC-recommended spelling; also sulphate in British English) is a salt of sulfuric acid. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... In inorganic chemistry, a sulfate (IUPAC-recommended spelling; also sulphate in British English) is a salt of sulfuric acid. ... Urea is an organic compound with the chemical formula (NH2)2CO. Urea is also known as carbamide, especially in the recommended International Nonproprietary Names (rINN) in use in Europe. ... Urea phosphate is an organic compound of carbon, hydrogen, nitrogen, oxygen and phosphorus. ... This article or section does not cite its references or sources. ... Ammonium phosphate. ... Ammonium sulphate, [NH4]2[SO4] contains 21% nitrogen as ammonia and 24% sulfur as sulfate. ... Monopotassium phosphate (also potassium dihydrogen phosphate, KDP, or monobasic potassium phosphate, MKP) -- KH2PO4 -- is a soluble salt which is used as a fertilizer, a food additive and a fungicide. ...

References

1. ^ Smith, C. J.; Peoples, M. B. Keerthisinghe, G. James, T. R. (1994). "Effect of surface applications of lime, gypsum and phosphogypsum on the alleviating of surface and subsurface acidity in a soil under pasture". Australian Journal of Soil Research 32 (5): 995-1008. ISSN 0004-9573. 

See also

• Acid sulfate soil
• Cation Exchange Capacity
• Organic gardening
• Soil conservation