The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

102 ECONOMIC GEOLOGY 4 per cent. of coarse sand. Clay is “ heavy,” as it is hard to work, and is often left as grassland ; it shrinks during droughts and the cracks tear across the plant roots; and clay breaks into rough clods which are difficult to cultivate. Lime makes a clay soil looser and more tractable. Soir Composition—Chemical analysis of soil determines its supply of plant foods. The four chief elements which plants obtain from the soil are nitrogen, calcium, phos- phorus, and potassium.! Calcium is usually present in the soil as carbonate, but may be added as gypsum, the sulphate. Its chief functions are to coagulate colloidal clay, and to neutralize the acids and thus cure ** sourness.” Phosphorus is used by plants as phosphoric acid, P,0;, and average English soils have about 1 per cent. or up to '2 per cent. of it, with about a third more in the soil than in the subsoil. The prairie soils of the United States have a similar excess. Thus in Illinois the average percentage of phosphorus is ‘161 per cent. in the uppermost inch; -149 per cent. for the depth of 2-3 inches; :143 per cent. for 4-6 inches and +127 per cent. for 7-12 inches (Alway and Rost, Soil Science, ii, 1916, p. 495). The Australian soils are poor in phosphorus—the average of many clay soils of Victoria is only -047 per cent.—and it is often lower in the soil than the subsoil; this abnormal feature is probably due to the absence of ordinary mammals, whose litter of bones and dung in other continents have enriched the soil with phosphate. Potassium, in the form of potash (K,0), is an essential plant food and prevents some diseases. It is usually derived in soils from potash felspar. The other -essential inorganic elements of soil are mag- nesia—which is injurious if in excess of the lime as in some basic igneous rocks that yield surprisingly poor soil—iron, aluminium, chloride, and sulphur. Chlorine is chiefly present as sodium chloride, which is present in all soils ; most crops can tolerate +25 per cent. in the soil, while the vegetation of salt marshes is adapted to a high percentage. Sodium carbonate is very injurious except in small amounts. Few plants withstand more than one part in 1000, and owing to it much land has been ruined bv ill-managed irrigation. 1 For the effect of the different constituents on plant growth, see Sir E. J. Russell, Soil Conditions and Plant Growth, 5th ed., 1026.

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