150 BACTERIA AND SOIL FERTILITY 



bacteria may compete with the higher plant for the limited supply 

 of available nitrogen of the soil. This latter appears to be the 

 correct explanation as legumes which are not dependent upon 

 soil nitrogen if properly inoculated are not retarded by carbohy- 

 drates. 



The effect produced by the application of carbohydrate also 

 varies with the season. If applied to the soil in the spring when 

 the soil temperature is low and when other bacteria are more active 

 than Azotobactefy the results are that they rapidly multiply and 

 compete with the higher plants for the limited available plant 

 food. If, however, the carbohydrates are applied in the autumn 

 directly after the removal of the crop when the soil is warm, 

 Azotohacter are active with the result that sujSScient nitrogen is 

 fixed to produce an increased crop the following season. 



Many workers have noted either no effect or even a detrimen- 

 tal effect when soils are treated with the carbohydrates and then in- 

 oculated with Azotobacter. This may be due in a great measure 

 to any or all of the following factors: (i) absence of a suitable 

 environment, such ^ temperature, moisture, aeration, food, and 

 alkalinity; (2) absence of a suitable host from which Azotobacter 

 may obtain part of its carbon; and (3) injurious effects due to the 

 decomposition products of the carbohydrate added. 



There is considerable interest in the work of Bottomley who 

 uses bacterized peat or humos-en. The bacterizins: process con- 

 sists of three stages: (i) treatment of peat with a culture solution 

 of the special "humating" bacteria and an incubation of it at 

 constant temperature for a week or ten days during which pe- 

 riod soluble humates are formed; (a) destruction of the humat- 

 ing bacteria by sterilization with live steam; and (3) treatment 



organisms — A. chroococcum and B, radicicola — and an incuba- 

 tion at 20° C. for a few days, after which it is ready for use. 



Theoretically, there is much in this process which recommends 

 it, for there is no abrupt change in environmental conditions for 

 the organism added, as would be the case when added from lab- 

 oratory cultures. Moreover, they are added in enormous quanti- 



