Transfoniuitioii ot Pliospliorus 237 



Niiclooprotcins contain 7-9 per cent i^hosphorus and 13-14 per 

 cent nitrogen. When attacked by microorganisms, they give rise to 

 phosplioric acid, sngar, pnrine, and pyrimi(Hne bases. These com- 

 pounds are decomposed further by a variety of bacteria and fungi. 

 Certain bacteria, designated as the Niicleohacter group, have been 

 found to l)e specifically concerned in the decomposition of nucleins, 

 through the nucleic acid stage, into phosphoric acid. 



A number of other organic phosphorus compounds, notably inosite 

 monophosphate (C(;H,;;Oi,P), which is found in wheat bran, are 

 commonly added to the soil. Their decomposition is similar to the 

 transformation of phytin and nucleic acids. 



The insoluble phosphates added to the soil are subject to the 

 activities of microorganisms largely in an indirect manner. The 

 \arious organic and inorganic acids produced by microorganisms 

 interact with the insoluble phosphates, giving rise to soluble com- 

 pounds. This is illustrated bv the following reactions: 



Ca3(P04)2 + ^2HX()3 = ^>raHP04 -f ( alXOs), 



Ca3(P04)2 + 4HX()3 = Ca(H2P()4)2 + '2Ca(N03)2 



ra3(P()4)2 + H2SO4 = ^2CaHP04 + ("aS04 



The relation between sulfur oxidation and phosphate solubilization 

 is brought out in Fig. 95. 



Gerretsen presented evidence that the intake of phosphorus by 

 plants from basic slag is markedly improved by the activity of soil 

 microbes. The solvent action of the soil microorganisms on insoluble 

 phosphates was obtained with the aid of glass plates, covered with 

 an agar film, in which calcium phosphate was precipitated, and 

 buried aslant in the culture vessels. Clear solubilization zones were 

 observed in distinct spots, especially underneath root tips and young 

 branches. In sterile cultures these solubilization zones were absent, 

 proving that the solvent action of the roots was negligible. When 

 the roots excrete organic substances with a low C : N quotient, there 

 is a possibility that phosphates may be precipitated by microbio- 

 logical activity. 



hi the decomposition of organic matter by microorganisms, usually 

 not all the phosphorus is liberated as phosphate, a certain amount 

 being assimilated by the organisms for the synthesis of fresh cell 

 material. When the organic complexes contain little or no phos- 

 phorus, the bacteria and fungi are able to remove from the soil some 



