404 Decomposition of Organic Matter in Soil 



Prior to May and after the crop is removed the COg fluctuates in 

 much the same way as the bacterial numbers. 



The ordinary quantities of nitrate, CO^, and bacteria 

 'present in soils. 



Our results enable us to draw up the following Table, which will 

 probably be found helpful to teachers and others in visualising the 

 conditions in the soil. The figures are derived from a consideration of 

 all our results; they do not include abnormal extremes, but give a 

 fair idea of the usual conditions on a heavy arable loam : 



* Running on occasions up to 1-8. 



% Occasionally up to 2-5. 



t Occasionally up to 2-3. 



Effect of ploughing on bacterial activity. 



We took observations before and after ploughing but they throw 

 less light than might have been expected on the effect of this iniportant 

 operation on the biochemical processes in the soil : we do not therefore 

 propose to discuss them in detail. 



The ploughing of the summer fallows was followed by a fall in 

 bacterial numbers, while the autumn ploughing of the cropped land 

 was followed by a rise. It is possible that the phenomena are related, 

 but we prefer to leave the matter open for the present. 



There was a distinct accumulation of nitrates on some of the plots 

 after ploughing, but as a rule this happened so long afterwards as to 

 make it uncertain whether there is any casual connection. Where the 

 rise was pronounced it had usually followed an earher rise in bacterial 

 numbers with which it might at least equally probably be associated. 



