8 



is also shown that when ammonium salts are absorbed by soil some 

 of the ammonia passes into a state of combination that is not broken 

 up on distillation with alkali, though the exact compound formed 

 was not identified. Only one or two parts per million of ammonia 

 are found in ordinary soils, rising in very rich garden soils to five or 

 six ; the ammonia being kept down to this limit by the nitrifying 

 organisms. Thus under field conditions the factor limiting the 

 formation of nitrates is really the preliminary ammonia-producing 

 process, and instead of the rate of nitrification, it is the rate of am- 

 monia production which determines the amount of nitrogen available 

 for the crop. 



E. J. Russell. " The Effect of Earthworms in Productiveness.'' 

 Journal of Agricultural Science. 1910. 3, 246. 



Earthworms have generally been credited with increasing the 

 productiveness of soil by decomposing the organic matter more 

 rapidly than could the micro-organisms unaided. Russell considers 

 that previous investigators have been misled by the nitrogen 

 introduced in the bodies of the earthworms themselves; for when 

 this is allowed for they seem to have no particular efiect on the 

 decomposition of organic matter and the production of nitrates. 

 They have, however, considerable effect as cultivators, loosening 

 and mulching the soil, and this may ultimately have an action 

 upon its fertility, though experimental demonstrations would be 

 difficult. 



