TRANSFORMATION OF MINERALS IN THE SOIL 649 



Definite information is available on the transformation of a few of 

 the more important mineral elements by microorganisms; some of the 

 rarer elements, such as Ni and Co, 14 exist in the soil in small quantities 

 and probably play a role in the activities of microorganisms. A detailed 

 study of the transformation of sulfur in nature is given elsewhere 

 (p. 600). 



Nature of phosphorus compounds in the soil. Phosphorus undergoes 

 various changes in the soil as a result of activities of microorganisms. 

 When organic matter is mineralized, the phosphorus is liberated in the 

 form of inorganic salts; the latter may be reassimilated by the same or 

 by other microorganisms and synthesized into microbial protoplasm, 

 especially in the presence of available energy. Insoluble inorganic 

 phosphates may be made soluble, as a result of the action of the prod- 

 ucts of metabolism of microorganisms, including carbon dioxide and 

 the various organic and inorganic acids. Phosphorus compounds may 

 also be reduced by microorganisms. 15 



Phosphorus is present in normal soils in the form of inorganic and 

 organic compounds. The inorganic compounds include mono-, di-, 

 tri-, and tetra-phosphates of potassium, sodium, calcium, magnesium, 

 aluminum, iron and manganese. The organic compounds comprise 

 the phosphorus of plant and animal residues and that in the living or 

 dead protoplasm of microorganisms : these include various compounds, 

 such as nucleic acids, 16 lecithin 17 and phytin. 18 Phosphorus is usually 

 added to the soil in the form of superphosphates, insoluble tri- and tetra- 

 calcium phosphates, and organic forms, both in plant residues and in 

 organic fertilizers. When soluble phosphates, such as superphosphate, 

 are added to the soil, they interact with the hydroxides, carbonates, 

 silicates and tri-phosphates of calcium, magnesium, iron and aluminum 

 to give insoluble precipitated phosphates. Superphosphates were 

 found to change, in the presence of sufficient CaC0 3 in the soil, into 



14 Bertrand, G., and Mokradnatz, M. Sur la presence simultanee du nickel 

 et du cobalt dans la terre arable. Ann. Sci. Agron. 1921, 179-182. 



15 Rudakov. Viestnik Bakteriol. Agron. Sta. Moskau. No. 26. 1926. 



16 Shorey, E. Nucleic acid in soils. Science N. S., 35: 390. 1911; Biochem. 

 Bull., 1: 104. 1911; Some organic soil constituents. U. S. Dept. Agr., Bur. Soils, 

 Bui. 88. 1913. 



17 Stoklasa, J. Biochemischer Kreislauf des Phosphat-Ions im Boden. 

 Centrbl. Bakt. II, 29: 385-519. 1911. 



' 8 Auten, J. T. Organic phosphorus of soils. Soil Sci., 16: 281-294. 1923; 

 see also Aso, K. On organic compounds of phosphorus in soils. Bui. Coll. 

 Agr. Tokyo Imp. Univ., 6: 277-294. 1904. 



