

BACTERIA AND SOIL FERTILITY 



into ammonia depends upon the moisture in the soil medium. The 

 average of numerous results obtained were as follows: 



Per cent Water- 



Per cent Am- 



Per cent Water- 



Per cent Am- 



holding Capacity 



monia Produced 



holding Capacity 



monia Produced 



10 



2 



60 



100 



20 



8 



70 



78 



30 



32 



80 



57 



40 



68 



90 



49 



50 



B5 



100 



45 



The soil which contains water to the extent of 60 per cent of 

 its water-holding capacity produces more ammonia than does soil 

 having any other water content. It has been our experience with 

 all soils tested that this is the case irrespective of the physical 

 nature of the soil. In other words, soils as unlike as clay' and 

 sand are at their optimum condition for ammonifi cation when 

 they contain 60 per cent of water. 



Nitrification. — But how about the speed with which the am- 

 monia is transformed into nitric acid? Is this dependent upon 

 the water supply? This is answered by the following results: 



Per cent Water- 

 holding Capacity 



Per cent Nitric 

 Acid Formed 



Per cent Water- 

 holding Capacity 



Per cent Nitric 

 Acid Formed 



10 



ao 



30 

 40 



50 



• 



II 



17 



31 

 62 



85 



60 

 70 

 80 



90 



100 

 40 



9 







Here also the greatest activity goes on in soil which is at 60 

 per cent of its water holding capacity. If the water content 

 greatly exceeds this, the speed of the reaction is materially re- 

 tarded. Moreover, an excessive quantity of water is more detri- 

 mental than is insufficient water. Under optimum conditions 



