AND COLLEGE, PUSA, FOR 1914-15. 23 



days. Assuming a uniform rate of decomposition, the 

 whole of the green manure would be oxidized in about 95 

 days. There is, however, reason to suppose that the rate 

 would fall off as time went on, so that as an independent 

 test of the reliability of the equation, it may be considered 

 to support it very well. Again the calculated amount of 

 carbon dioxide production in soils in which nitrification 

 was in progress agreed very fairly with what was experi- 

 mentally determined under controlled conditions in the 

 laboratory. On the other hand calculations for the volumes 

 of oxygen diffusing into the soil yielded unexpectedly high 

 figures. One cannot go further with the matter at pre- 

 sent, but it is at least certain that the process is a much 

 more rapid one than is commonly supposed. 



The value of good cultivation of the surface soil has 

 been usually attributed to the fact that by stirring the soil, 

 gaseous interchange is suitably accelerated, carbon dioxide 

 is allowed to escape and oxygen to enter. It is often easy 

 to suggest an explanation which on paper bears the neces- 

 sary " hall-mark," but it is somewhat remarkable that 

 among the many who have accepted this explanation for 

 the advantage of good cultivation, none appears to have 

 considered that much deeper stratum of soil — several feet 

 in thickness — which is never disturbed by cultivating 

 implements but in which crop roots develop freely and 

 which it is equally necessary to aerate. If for efficient 

 gaseous interchange it is necessary to plough the top 6'', it 

 should be similarly necessary to plough the succeeding 

 several feet of soil ! So long as one is content to accept the 

 proved value of good cultivation without attempting to give 

 explanations for its advantage, the position is unassailable ; 

 but if one goes further and states that the explanation is 

 that thereby objectionable carbonic acid is released from 

 or valuable oxygen admitted into the soil, the premises are 

 very readily open to criticism. Even allowing Bucking- 

 ham's experimental work to have been a good deal in error, 

 the consideration of the cases which have been examined at 

 Pusa shows that, so far as aeration is concerned, the culti • 



