144 Points in the Composition of Soils. 



Next, that determinations of the amounts of nitrogen as nitrate 

 in soils of known history as to manuring and cropping, and to 

 a considerable depth, show that the amount of nitrogen in the soil 

 in that form is much less after the growth of a crop than under 

 corresponding conditions without a crop. It was hence concluded 

 that nitrogen had been taken up by the plant as nitrate. In 

 the case of gramineous crops and some others, the evidence 

 points to the conclusion that most, if not the whole, of the 

 nitrogen is taken up from the soil. It is also clear that some, 

 at any rate, of the nitrogen of Leguminosse has the same source 

 and the results are in favour of the supposition that in some of 

 the cases the whole of it might be so accounted for. Still it is 

 admitted that, in other cases, this seems doubtful. 



The conditions and the results of a large number of new experi- 

 ments are next described. It is found that there is very much 

 more nitrogen as nitrate, in the soils and subsoils down to the 

 depth of 108 inches, where leguminous than where gramineous 

 plants have grown. The results point to the conclusion that under 

 the influence of leguminous growth and crop residue, especially 

 in the case of strong and deep-rooted plants, the conditions are 

 more favourable for the development and distribution of the 

 nitrifying organism ; and if this view be confirmed, an important 

 6tep would be gained towards the more complete explanation of the 

 sources of the nitrogen of the Leguminosse, which assimilate 

 a very large quantity of nitrogen, including, as above supposed, 

 the nitrification of the nitrogen of the subsoil, which may thus 

 become the source of the nitrogen of such crops. An alternative 

 obviously is that the plants might still take up nitrogen from the 

 subsoil, but as organic nitrogen and not as nitrate. There is 

 however no direct experimental evidence in favour of such a view, 

 whilst some physiological considerations, which are discussed, 

 seem to be against it. Again, results show that the soil and 

 subsoil contain less nitrogen as nitrate after the growth of good 

 crops of Vicia sativa than where the more shallow-rooted Trifo- 

 liurn repens fails to grow. This is further evidence that the 

 Leguminosae take up nitrogen as nitrate ; and in the experiments 

 in question the deficiency of nitric nitrogen in the soil and subsoil 

 of the Vicia sativa plots, compared with the amount of those of 

 the TrifoUum repens plot to the depth examined, is sufficient to 





