QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
105 
In a field where the leguminous crop, beans, had been grown 25 years out of 32, 
with mineral but without nitrogenous manure, and had yielded less than average 
agricultural crops, the percentage of nitrogen in the surface soil w'as also greatly 
reduced. 
In another field, where the leguminous crop, red-clover, had been sown 12 times in 
30 years, the clover failed many times, the yield of nitrogen in the crops very greatly 
diminished, and the percentage of nitrogen in the surface soil was greatly reduced. 
Again, in a rich garden soil, where red clover has been grown for more than thirty 
consecutive years, and has yielded throughout good, but gradually much diminishing 
crops, it was found, after the first 22 years, that the nitrogen in the surface soil had 
been reduced from 0'5095 to 0'3634 per cent., calculated on the soil dried at 100° G. 
Even in an actual course of rotation, of turnips, barley, clover or beans, and wheat, 
with mineral, but without nitrogenous manure, the percentage of nitrogen in the 
surface soil has been much reduced ; whilst in a parallel rotation in which fallow 
takes the place of the clover or beans, the reduction is still greater. 
Thus, in all the cases cited, including gramineous, cruciferous, chenopodiaceous, and 
even leguminous crops, and a rotation of crops, when each has been grown for many 
years in succession without nitrogenous manure, and has yielded comparatively small 
and declining amounts of nitrogen in the crops, there has, coincidently, been a 
considerable reduction in the amount of nitrogen in the surface soil. There has, in 
fact, not been compensation from the free nitrogen of the air, or at any rate not at all 
in amount corresponding to the annual losses. 
Lastly, grass land which, under the influence of a full mineral manure, including 
potash, but without any supply of nitrogen for more than thirty years, has grown 
crops containing large amounts of comparatively superficially rooting leguminous 
herbage, succeeded by increased amounts of gramineous herbage, bas, under those 
conditions, yielded about the same amount of nitrogen per acre as M. Berthelot 
assumes to be the average produce of a meadow; but it has done so only with 
coincident great reduction in the nitrogen of the surface soil. 
Whether, therefore, we consider the facts of agriculture generally, or confine 
attention to special cases under known experimental conditions, the evidence does not 
favour the supposition that a balance is maintained by the restoration of nitrogen 
from the large store of it existing in the free state in the atmosphere. Further, our 
original soil-supplies of nitrogen are, as a rule, due to the accumulations by natural 
vegetation, wdth little or no removal, over long periods of time ; or, as in the case of 
many deep subsoils, the nitrogen is largely due to vegetable and animal remains, 
intermixed with the mineral deposits. The agricultural production of the present age 
is, in fact, so far as its nitrogen is concerned, mainly dependent on previous accumula¬ 
tions ; and as in the case of the use of coal for fuel there is not coincident and cor¬ 
responding restoration, so in that of the use or waste of the combined nitrogen of the 
MDCCCLXXXIX.—B. P 
