51 



IX 



and 



0U8 



* 



not to be expected that tlio amount found within such limits at any 

 given time would represent more than a fraction of that which would 

 be available, even within that range, during the long period of growth 

 of the clover crop. Then, the indications are that there is considerable 

 accumulation beyond the depth to which most of our examinations 

 apply. Still, it is difficult to suppose, with the evidence at command, 

 that the whole of ^he nitrogen which has to be accounted for, either 

 in the Melilotus, or in the clover and barley experiment, can be 

 attributed to that source. There remains the question whether the 

 roots of the plant do not take up nitrogen from the soil in other 

 states than as nitric acid. 



Finally in regard to the experiments with clover and barley, it is 

 admitted that the various results of soil examinations which have 

 been adduced do not conclusively show the source of the whole of 

 the nitrogen to have been the soil. It will, we think, nevertheless 

 be granted, that they do clearly point to the fact that at any rate 

 much of it is derived from that source ; whilst there is no evidence 

 whatever of an atmospheric source of more than the small amount of 

 combined nitrogen coming down in rain, and the minor aqueous 

 deposits, and the probably still smaller amount absorbed from the 

 atmosphere by the porous soil. 



Nitrogen in some of the Soils of the Ex;periviental Mixed Herbage Plots. 



The results next to be referred to will afford additional evidence of 

 the soil-source of the nitrogen of the Logurainosaj. 



In Table III it was shown that in the mixed herbage of permanent 

 grass land, without manure 33'0 pounds, and with a purely mineral 

 manure (including potash) 55-6 pounds of nitrogen were yielded per 

 acre per annum in the crop over a period of twenty years. Whence 

 comes the 22*6 pounds more nitrogen per acre per annum taken up 

 when the mineral manure was applied than without manure ? 



After twenty years of continuous experiment, samples of soil 

 were taken from three places on each plot, and in each case to the 

 depth of six times 9 inches, or 54 inches. The mean results of the 

 determinations of nitrogen in the surface soils of the unmanured 

 plot, and of the plot receiving a complex mineral manure (including 

 potash), are given in Table XVII which follows :— 



m-m 



