12 
SIR J. B. LAWES AND PROFESSOR J. H. GILBERT O^T THE 
for nitrification, and with its deeper roots, would each year the more exhaust the 
nitric nitrogen especially of the lower layers. Hence, notwithstanding the much 
lower yield of nitrogen in the Melilotus than in the Trifolium reipens crop in 1885, 
the lower layers of the Melilotus soil contained less nitric acid than those of the 
Trifolium 'j-ejjens soil. There can, indeed, be no doubt, that the Melilotus derived at 
any rate much of its nitrogen fi’oin nitric acid, either within the actual range of its 
roots, or within the range of their action in causing the passage upwards of water 
with its dissolved contents. Still, the figures show,' that with the comparatively 
limited growth in the recent years, there remained per acre about 56 lbs. of nitrogen 
as nitric acid in the 6 lower depths of the Melilotus soil. 
But by far the most striking results in the Table are those relating to the Medicago 
sativa (lucerne) soil, and to the comparison betw’een the amounts of nitric nitrogen in 
the soil of the shallow rooting and weakly growing Trifolium repens and those in the 
soil of the very deep and strong rooted, and very free growing lucerne. 
Table III. shows that the estimated yields of nitrogen per acre in the lucerne were 
in the 6 years, 1880-1885, respectively as follows :—28 lbs., 28 lbs.. Ill lbs., 143 lbs., 
337 lbs., and 233 lbs. That is to say, with the increasing root range, and consequently 
increased command of the stores of the soil and subsoil, the yield of nitrogen in the 
crop increased from 28 lbs. in the first and second years, to 337 in the fifth year ; 
declining, however, somewhat in the sixth year, 1885, and it did so still further in 1886. 
It is seen that under these circumstances of very large yields of nitrogen in the crops, 
there is, at every one of the twelve depths, less, and at most very much less nitrogen 
as nitric acid remainino' in the soil than where so much less nitrogen had been removed 
in the Trifolium repens crops. The difference is distinct even in the upper layers, but 
it is very striking in the lower depths. Thus, there is, on the average, not one-twelfth 
as much nitric nitrogen in the lower ten depths of the deep rooting and high nitrogen- 
yielding Jiech’mpo sot wet soil, as in those of the shallow rooting and comparatively low 
nitrogen-yielding Trifolium repens soil. Indeed, the nitric acid is nearly exhausted 
in the deep rooting Medicago sativa plot; there remaining, to the total depth of 
9 feet, only about 17 lbs. of nitric nitrogen against more than 100 lbs. to the same 
depth in the Trifolium repens soil. The total deficiency of nitric nitrogen in the 
Medicago as compared wdth the Trifolium rep)ens soil, is seen to be 85’69 lbs. 
according to one set of determinations, and 83‘94 lbs. according to the other. 
As already said, we cannot know what was the stock of nitric nitrogen in the soil 
at the commencement of the growth of the season, or the amount formed during the 
growing period. But with so much more Medicago growth for several previous years, it 
seems reasonable to assume that there would be much more nitrogenous crop-residue 
for nitrification than in the case of the Trifolium repens plot. 
But even supposing, for the sake of illustration, that each year’s growth would 
leave crop-residue yielding an amount of nitrogen as nitric acid for the next crop, or 
succeeding crops, approximately equal to the amount which had been removed in the 
