{"id":294,"date":"2019-03-09T04:52:04","date_gmt":"2019-03-09T04:52:04","guid":{"rendered":"http:\/\/esp10.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=294"},"modified":"2019-04-22T09:14:16","modified_gmt":"2019-04-22T09:14:16","slug":"294","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/esp10\/chapter\/294\/","title":{"rendered":"Chemical properties of soil"},"content":{"raw":"
\"epgp<\/a>\r\n<\/span><\/div>\r\n \r\n\r\n \r\n\r\n27.1 Introduction<\/strong>\r\n\r\n \r\n

Soil chemistry is the collaboration of various chemical components that exists among soil particles as well as in the soil solution the water sustained by soil. The chemical reactions that occur in soil are highly complicated, but their understanding will better help in managing turf and ornamentals. Soils act as storehouses for plant nutrients. Many nutrients, such as calcium and magnesium, may be supplied to plants entirely from reserves retained in the soil. Others like potassium are added regularly to soils as fertilizer with the purpose of being withdrawn when needed by crops. The relative capability of soils to store one particular group of nutrients, the cations, is referred to as cation exchange capacity<\/em> or CEC. Soils are composed of a mixture of sand, silt, clay and organic matter. Both the clay and organic matter particles have a net negative charge. These negatively charged soil particles will attract and hold positively-charged particles, much like the opposite poles of a magnet attract each other. By the same demonstration, they will repel other negatively-charged particles, similarly as like poles of a magnet repel each other.<\/p>\r\n \r\n\r\n27.2 Cation Exchange Capacity<\/strong>\r\n\r\n \r\n

Most chemical interactions occurring in soil on colloidal surfaces are because of their charged surfaces. Colloids have charged surfaces because of their chemical make-up and large surface area, which attract, \u2018ions\u2019 (charged particles) present in the soil solution. Depending on the ionic charge, size and concentration in the soil, ions can be sorbed by the colloid surface or exchanged with other ions and released to the soil solution. (Fig 27.1)<\/p>\r\n\"\"<\/a>\r\n\r\ncomplex 27.3 Factors affecting Cation Exchange Capacity<\/strong>\r\n\r\n \r\n

Soil <\/strong><\/a>texture: <\/strong>The negatively charged clay colloids attract positively charged cations and retain them. Therefore, the cation exchange capacity of soils rises with rise in percentage of clay content.<\/p>\r\n\u00a0<\/strong>\r\n

Clay soils with high CEC can hold large quantity of cations and reduces the loss of cations by leaching. Sandy soils, with low CEC, hold lesser amount of cations and thus cations are evacuated from soil <\/a>by leaching (Fig 27.2).<\/p>\r\n \r\n

Soil <\/strong><\/a>organic matter: <\/strong>High organic matter content increases the CEC. The CEC of clay<\/p>\r\n

\u00a0<\/strong><\/p>\r\n

minerals varies from 10 to 150 [cmol (p+) kg-1] whereas that of organic matter ranges from 200 to 400 [cmol (p+) kg-1].<\/p>\r\n\u00a0<\/strong>\r\n

Nature of clay minerals: <\/strong>The CEC and specific area of the clay minerals are in the order: smectite > fine mica > kaolinite. Thus the CEC of a soil <\/a>dominated by smectite type of clay minerals is much higher than kaolinite type dominated soils<\/p>\r\n \r\n

Soil <\/strong><\/a>Reaction: <\/strong>As the pH is increased, the hydrogen held by the organic colloids and silicate clays (Kaolinite) becomes ionized and replaceable. The net result is enhancement of negative charge on the colloids and in turn an increase in CEC.<\/p>\r\n \r\n\r\n27.4 Importance of Cation Exchange<\/strong>\r\n\r\n \r\n\r\n \r\n

Cation exchange is an important parameter in determination of soil <\/a>fertility, soil <\/a>acidity and basicity that results in altering soil <\/a>physical properties as well as in mechanism for purifying or altering percolating waters.<\/p>\r\n \r\n

Plant nutrients like calcium, magnesium, and potassium are supplied to plants in large amount from exchangeable forms.<\/p>\r\n \r\n