Alkali, or Alkaline, soils are clay soils with high pH (greater than 8.5), a poor soil structure and a low infiltration capacity. Often they have a hard calcareous layer at 0.5 to 1 metre depth. Alkali soils owe their unfavorable physico-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and difficult to clarify/settle. They derive their name from the alkali metal group of elements, to which sodium belongs, and which can induce basicity. Sometimes these soils are also referred to as alkaline sodic soils. Alkaline soils are basic, but not all basic soils are alkaline. The causes of soil alkalinity can be natural or man-made: The natural cause is the presence of soil minerals producing sodium carbonate (Na2CO3) and sodium bicarbonate (NaHCO3) upon weathering. Coal-fired boilers / power plants, when using coal or lignite rich in limestone, produce ash containing calcium oxide. CaO readily dissolves in water to form slaked lime, Ca(OH)2, and carried by rain water to rivers / irrigation water. Lime softening process precipitates Ca2+ and Mg2+ ions / removes hardness in the water and also converts sodium bicarbonates in river water into sodium carbonate. Sodium carbonates (washing soda) further reacts with the remaining Ca2+ and Mg2+ in the water to remove / precipitate the total hardness. Also water-soluble sodium salts present in the ash enhance the sodium content in water. The global coal consumption in the world was 7.7 billion tons in the year 2011. Thus river water is made devoid of Ca2+ and Mg2+ ions and enhanced Na+ by coal-fired boilers. Many sodium salts are used in industrial and domestic applications such as sodium carbonate, sodium bicarbonate (baking soda), sodium sulphate, sodium hydroxide (caustic soda), sodium hypochlorite (bleaching powder), etc. in huge quantities. These salts are mainly produced from sodium chloride (common salt). All the sodium in these salts enter into the river / ground water during their production process or consumption enhancing water sodicity.

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Concepts associés (16)
PH du sol
droite|vignette|343x343px| Variation globale du pH du sol. Rouge = sol acide. Jaune = sol neutre. Bleu = sol alcalin. Noir = pas de données. Le pH du sol est une mesure de l'acidité ou de la basicité (alcalinité) d'un sol. Le pH est défini comme le logarithme négatif (base 10) de l'activité des ions hydronium ( ou, plus précisément, ) dans une solution. Dans les sols, il est mesuré dans une boue de sol mélangée à de l'eau (ou une solution saline, telle que 0,01 M CaCl2), et se situe normalement entre 3 et 10, 7 étant neutre.
Environmental effects of irrigation
The environmental effects of irrigation relate to the changes in quantity and quality of soil and water as a result of irrigation and the subsequent effects on natural and social conditions in river basins and downstream of an irrigation scheme. The effects stem from the altered hydrological conditions caused by the installation and operation of the irrigation scheme. Amongst some of these problems is depletion of underground aquifers through overdrafting.
Index of soil-related articles
This is an index of articles relating to soil. Acid sulfate soil Acrisol Active layer Agricultural soil science Akadama Albeluvisols Alfisols Alkali soil Andisols Angle of repose Antigo (soil) Anthrosol Aridisols Atriplex Australian Society of Soil Science Incorporated - Baer's law Bama (soil) Barren vegetation Base-richness Bay mud Bearing capacity Bentonite Berkshire (soil) Bevameter Biochar Biogeology Blandford (soil) Blue goo Bog Brickearth Brown earth Brown podzolic Calca
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