ion 

 ate 





47 



Table XV. 

 Nitrogen as Nitric Acid. 



Thus the melilotus had not only exhausted the water, but the nitric 

 acid of the soil, at each depth very much more than the white clover 

 had done ; and the difference is very marked, and increases, at the 

 lower depths. It is seen that in the case of the white clover soil there 

 is a diminishing amount of nitric acid from the first to the third depth, 

 and then an increasing quantity to the sixth depth. There was, in 

 fact, about the same total amount found in the three lower as in the 

 three upper layers. It may fairly be supposed that there is greater 

 concentration lower still, and that the exhausting action of the melilotua 

 extended beyond the depth examined. 



There is here direct evidence that the soil is the source of at 

 any rate some of the excess of nitrogen of the melilotus over that in 

 the white clover. The quantity, and the distribution, of nitric acid 

 in the soil at any one time are so dependent on temporary conditions, 

 that it would be fallacious to attempt to estimate from the figures as 

 they stand the exact amount which the melilotus has taken up more 

 than the white clover. Then it is obvious that the action extended 

 below the depth examined ; and it is a question whether, with the 

 greater disintegration, and greater aeration, nitrification would not be 

 favoured in the lower depths, and if so the supply would be in a sense 

 cumulative. Lastly, it may be that the deeply and widely distributed 

 m.elilotus roots have the capacity of taking up nitrogen from the soil 

 in other forms than as nitric acid. 



\*..J^ 



