I 82 



SOIL CONDITIONS AND PLANT GROWTH 



TABLE LI. LOSSES OF NITROGEN FROM CULTIVATED SOILS, BROADBALK 

 WHEAT FIELD, ROTHAMSTED, FORTY-SEVEN YEARS, 1865-1912. 



Experiments of this kind have led to the conclusion that some 

 gaseous product is formed in addition to nitrates, and, as no 

 sufficient amount of ammonia can be detected, it is supposed 

 that gaseous nitrogen is given off. The conditions for this 

 decomposition appear to be copious aeration, such as is 

 produced by cultivation, and the presence of large quantities 

 of easily decomposable organic matter. Now these are 

 precisely the conditions of intense farming in old countries 

 and of pioneer farming in new lands, and the result is that the 

 reserves of soil and manurial nitrogen are everywhere being 

 depleted at an appalling rate. Fortunately there are recupera- 

 tive actions, but one of the most pressing problems at the 

 present time is to learn how to suppress this gaseous de- 

 composition and to direct the process wholly into the nitrate 

 channel. 



It is evident that there must be some recuperative agency 

 or the stock of soil nitrogen, which is never very great, would 

 long ago have disappeared in old countries. Experiment has 

 shown that soil gains nitrogen when it is allowed to remain 

 undisturbed and covered with unharvested vegetation as in 

 natural conditions. On the Broadbalk field a third plot 

 adjacent to the two already mentioned was in 1882 allowed 

 to go out of cultivation and has not been touched since ; it 



