236 Transformation of Mineral Substances 



3. Soluble inorganic phosphates, like those of sodium, potassium, 

 calcium, and magnesium, are added to the soil in fertilizer materials 

 and in plant and animal residues. 



Among the organic phosphorus compounds which find their way 

 into the soil, lecithin, nucleic acids, and phytin occupy a prominent 

 place. 



Lecithin contains 9.39 per cent Pi-O.-,, 1.6 per cent N, and 65.36 

 per cent C. It contains two fatty acid radicals, such as pahnitic 

 and stearic or oleic acids, as shown by the following structural 

 formula: 



CHo OR 



CH OR^ 



I /OH 



CHoOPO< /(CHgjg + ,SHo() 



\0-(CH9).,\< 



\0H 



Lecithin 



CHoOH 



= CHOH 



I /OH /(CH3)3 



CHoO P0< + ROH + RK)H + (( H,).,OH X< 



^OH \0H 



( Uyccro- I'atty acids Choline 



phosphoric acid 



Nucleic acids are found abundantK' in the microbial cell substance. 

 In their decomposition, some of the groups are broken down more 

 readily than others. In the presence of readily available sources of 

 carbon and nitrogen, various bacteria and fungi are capable of break- 

 ing down both lecithin and nucleic acids and liberating the phos- 

 phorus as phosphate. As much as 66 per cent of the lecithin phos- 

 phorus was transformed into soluble phosphate in 60 days. The rest 

 of the phosphorus was assimilated by the bacteria for the synthesis 

 of cell material. 



Phytin is a hexaphosphate, which occurs abundantly in plant ma- 

 terials, notably in the seeds. It contains about 26 per cent phosphorus 

 in the form of phytic acid. C(;Ho4027P,;. This compound is acted 

 upon by fungi and bacteria by means of an enzyme, designated as 

 "phytase," with the result that the organic phosphorus is transformed 

 into phosphate: 



C6H24O27P6 + «02 = 6H3PO4 + 6CO2 + 3H2O 



