258 AZOFICATION 



definite chemical reaction occurs between the phosphate and the 

 carbohydrate similar to that occurring in alcoholic fermentation. 



I. 2C 6 H, 2 O6 + 2R 2 HP0 4 -> 2CO 2 + 2H 2 O + C 6 HioO4(PO 4 R 2 ) 2 + 



2C 2 H e O 

 II. C 6 HioO4(PO 4 R 2 ) 2 + 2H 2 O -> C 6 Hi 2 O 6 + 2R 2 HPO 4 



The Azotobacter are able to utilize the phosphorus of di- and 

 tri-basic sodium and potassium phosphate and of dibasic calcium 

 phosphate. 



Mockeridge obtained an increase of 23 per cent, in nitrogen fixa- 

 tion with basic slag. There were two maxima, one with 0.4 per cent, 

 the other with 1.0 per cent. slag. This is attributed to the stimulat- 

 ing effect of the iron and manganese in the slag, the maximum effect 

 of one being produced at 0.4 per cent., the other at 1.0 per cent. 

 The tribasic calcium phosphate bone ash, iron, and aluminum 

 phosphate all serve only as difficultly available sources of phos- 

 phorus. Raw rock phosphate and bone meal fail entirely to furnish 

 enough available phosphorus for the development of Azotobacter. 



The addition of phosphorus to a soil often greatly increases azofi- 

 cation. 



Without With 



phosphorus. phosphorus. 



Treatment. mgm. mgm. 



No lime 0.6 0.9 



Lime 1.5 4.6 



Moreover, Christensen has found soils in which phosphorus is the 

 limiting element in Azotobacter growth. He entertains the hope that, 

 in view of the relationship between Azotobacter grow r th and lime and 

 phosphorus, it will become eventually possible by the determin- 

 ation of bacterial food requirements to secure a general expression 

 for the soil content of plant-food available to crops. He further 

 suggests that where a mannitol solution free from phosphorus 

 produces a vigorous growth of Azotobacter after inoculation with a 

 soil, it may be assumed that the soil is not deficient in available 

 phosphorus. Dzierzbicki notes that if soils are deficient in available 

 lime, phosphoric acid, or potash, nitrogen-fixing bacteria, such as 

 Azotobacter, are either entirely absent or present only in small 

 numbers. 



There is a definite relationship between the carbon and phos- 

 phorus content of a soil and the nitrogen assimilated. According 

 to Stoklasa, Azotobacter assimilates from 5.0 to 5.7 grains of free 

 nitrogen for every gram of phosphorus used. Although these 

 organisms are directly dependent upon a readily available supply 

 of phosphorus to promote growth, they do not change it into the 

 organic form as rapidly as do the ammonifying bacteria. 



Sulphur is required by the azofiers possibly for the formation of the 



