8o CHEMICAL FERTILIZERS 



9 milligrammes of nitrogen were fixed for each gramme of 

 sugar decomposed. The nature of the carbo-hydrate pre- 

 sented to the organism is important. With xylose, a sugar 

 obtained from straw, lactose and galactose obtained from 

 milk, maltose and dextrin obtained from starch, and sucrose 

 from cane or beet, the best results were obtained ; other 

 compounds also produced some fixation of nitrogen, but starch 

 was rather inefficient. Much, however, depended upon the 

 presence of calcium carbonate and other substances. The 

 organism appears to have no power to utilize oxalic acid. 

 Ivittle is known of the chemistry of these changes and it is 

 not known what becomes of the sugar. The only obvious 

 product is carbon dioxide, fatty acids being formed only in 

 small quantities. The nitrogen is found partly in compounds 

 dissolved in the liquids, but mostly in the bacterial mass. 

 It seems probable that the nitrogen is used chiefly by the 

 bacteria for their own protoplasm. The organisms are 

 extremely active, i gramme weight evolving 1*3 grammes 

 of carbon dioxide in 24 hours. An adequate supply 

 of phosphates is essential, any deficiency limiting the 

 amount of fixation. Traces of nitrogen compounds are 

 helpful in the early stages, but larger quantities reduce the 

 amount of fixation, and may themselves suffer some change ; 

 for example, sodium nitrate is partially reduced to nitrite 

 and ammonia. Algi can work in symbiosis with these 

 organisms. In experiments extending over a considerable 

 length of time, it was found that the fixation of nitrogen 

 was much more rapid during the earlier stages than during 

 the later stages. If the soil temperature falls as low as 7 C. 

 nitrogen fixation ceases. Experiments in the laboratory 

 and in the field show that azotobacter fixes nitrogen, provided 

 it can obtain a sufficient amount of carbohydrate, and so 

 long as the temperature is within certain limits. Where 

 the soil is naturally deficient in some of the conditions 

 necessary for nitrogen fixation, the application of appropriate 

 fertilizers enables the azotobacter to carry out its function 

 where otherwise it might fail to do so. The greater part of 

 the nitrogen fixation in the soil is carried out by bacteria 



