28 



The Atmofipfien of the Soil 



Thus the soil conditions are still not entirely comparable but on 

 the whole they are more so than on Hoos field. The percentages of 

 CO, in the soil air were: 



Ma\ \r< ' May 25 June 10 I June 12 June 13 | July 7 



Fallow portion 

 Cropped portion 



0-22 

 0-61 



0-32 

 0-32 



0-17 

 0-35 



0-36 

 0-48 



036 

 0-42 



0-30 

 0-48 



July 27 



0-35 

 0-30 



Now the crop was considerable (30-4 bushels per acre), yet the increase 

 in CO, over that in the fallow plot is not only no greater than in Hoos 

 field but it is not usually (except on May 15) much larger than the 

 error of experiment. Hence it appears that the effect of the growing 

 crop in increasing the amount of COg in the soil air is not great. 



We can make the comparison in a different way so as to reduce in 

 another direction the differences in physical state between the plots. 

 The Broadbalk dunged and unmanured cropped plots both receive 

 similar cultivations and treatment apart from manuring: both are 

 equally exposed to the consolidating effect of the weather though the 

 unmanured land does actually become the more closely packed. The 

 dunged land possesses a large quantity of organic matter and carries 

 a dense crop, both conditions favourable for a high percentage of COj 

 in soil air, yet as a matter of fact this high percentage is not obtained, 

 and in summer when one would expect the maximum differences from 

 the unmanured plot there is practically no difference at all^. 



' On the following occasions the unmanured plot gave a higher COj content than the 

 dunged plot in Broadbalk field : 



