192 J. H. Gilbert — Points in connection with 'Vegetation. 



of soda, was either recovered in the increase of crop, or may be 

 accounted for by determinable accumulation within the soil, or 

 by loss by drainage. 



In ordinary agriculture, the amounts of soluble nitrogenous 

 manures applied would generally be much less than in some of 

 these special experiments ; and the losses by drainage would 

 from that cause alone be proportionately less than that shown 

 above. Much, obviously, would also depend upon the charac- 

 ter of the soil and of the subsoil. Again, in an ordinary rota- 

 tion of crops, more of the supplied nitrogen would probably be 

 gathered up before it reached the lower layers, than in the case 

 of a cereal crop grown year after year on the same land. It 

 may be safely concluded, however, that whenever cereals were 

 grown, a material proportion of the nitrogen specially applied 

 to, or existing in the soil, which would be available to other 

 crops, would not be so to them; but would in the first instance 

 accumulate in the surface soil, and gradually pass into the lower 

 layers in the form of nitrates, to be eventually lost by drainage 

 if not arrested by some other crop. 



The question obviously arises, whether we have not here a 

 source of some at least of the nitrogen available to leguminous 

 or to other plants having possession by their roots of a greater 

 range of subsoil than the Gr.-miiiieae. We have evidence enough 

 that although wheat and barley send roots down very deep into 

 the subsoil, and pump up moisture from the deeper layers, they 

 nevertheless derive much of their nitrogen within the surface 

 soil. If the Leguminosse do not so readily do so. or at any rate 

 naturally depend more upon the nitrogen in the lower layers 

 for a considerable proportion of that which thev require, and 

 moreover are able to avail themselves of the residue from the 

 manuring for other crops, what is the nature of the problem 

 that we may have to solve to elucidate this point? 



By way of illustration it mav be mentioned that, supposing 

 a leguminous crop to acquire 100 lbs. of nitrogen per acre from 

 a layer of subsoil three feet in thickness weighing approxi- 

 mately 10,000,000 lbs. (exclusive of stones ami water) this 

 would represent only O01 per cent of nitrogen so acquired in 

 such subsoil; 200 lbs. of nitrogen per acre so available would 

 represent -002 percent, and soon. Now, even supposing that 

 the nitrogen existed in the subsoil in such a condition as to be 

 converted into ammonia in the process of combustion with soda- 

 lime, the difference between onesulw.il containing this, or even 



nit of nitrogen, more than another could not with 



certainty be determined by that process; for, in taking say 1$ 



or 20 grams of the subsoil for combustion the difference be- 



onscoald not be expected to be 



less than some units in the third decimal place (per cent); that 



