4 Tin AliiKisjthi'n of the Soil 



attributable to ditt'ereuces iu composition of the soil^ especiall}- the 

 distribution of organic matter, organisms, plant roots and passages 

 such as cracks, burrows of earthworms, etc. ; to daily changes in tempera- 

 ture and moisture content of the soil, or to any cause that would 

 facilitate interchange between the soil air and the atmosphere. These 

 local and daily fluctuations lie between relatively narrow limits, and 

 bv taking a mean of a number of samples it is not difficult to arrive 

 at a value that approximately expresses the composition of the soil air 

 at the time. Some of these values are given in Taljle II. 



Table II. Mean composition of soil air from various 

 Rothanisled plots. Percentage by volume. 



The column labelled nitrogen is simply the residual gas after the 

 carbon dioxide and oxygen have been removed in the analytical process 

 and it includes other gases just as in the case of atmospheric air. Sir 

 James Uewar kindly examined some of the samples for hydrogen, but 

 found only quantities of the same order as in the atmosphere, while 

 our own tests have failed to reveal appreciable quantities either of 



' We arc here u.sing the word to denote the whole of the surface .soil complex: solid 

 matter, »-ater, air spaces, etc. It is unfortunate that no .soil chemist has j-et had the 

 couraRe to coin a word to express this meaning;. The word ".soil" is ambiicruous, as it 

 means also the actual solid nuitter. 



