HUMUS AND ITS NITROGEN CONTENTS. 
179 
gives a " Hilgard ratio" of 6.13, and plat 5 (minerals without nitrogen 
for fifty years) gives <i.43, while the richest and most fertile plat, 
namely, plat 2b (dunged for fifty years) gives almost the same ratio, 
namely, 6.38. 
It would seem, therefore, that although the ratio on which Professor 
Hilgard lays stress may serve as an index to initial nitrogenous fer- 
tility in soils comparatively newly brought under cultivation, it does 
not afford a means of differentiating between a Btarved and a fertile 
soil in the ease of long-cultivated land such a^ we have at Rothamsted. 
As regards the wheat soils, the quantity of soluble organic matter 
is greatest, as we should expect, on the continuously dunged plat, 
2b, in which the proportion appears to have increased from 0.96 per 
cent to 1 .7 ( X> per cent between 1st;;) and ISli.'J; hut it must be remem- 
bered that the I860 sample was thirty years old when examined, and 
ma\ possibly have Undergone some decomposition or alteration. 
Next to the dunged plat comes the rape-cake plat, L9, with L. 04 per 
cent of soluble organic matter. In the other plats the variations lie 
between <».7;>i percent and 0.!»1 percent. 
The last column of the table expresses the soluble nitrogen as per- 
centage of the total nitrogen of the soil, and it will be seen that the 
variations all lie within the range 47.11 per cent to 58.47 per cent. 
In fact, it may be broadly said thai the soluble nitrogen all through 
follows pretty closely the total nitrogen, and in the case of the arable 
land is about one-half of it. It' we take the plat s that differ most 
widely in their treatment, we find 51.76 per cent of the total nitrogen 
to be soluble in dilute soda in t he case of t he permanently unmanured 
plat. No. ">. and ^-2.')'-) per cent, or almost the Same proportion, in the 
case of the continuously dunged and richest plat, 2b. Of the chemic- 
ally manured plats, plat l<»a, continuously dressed witb ammonium 
salts without minerals, shows 50.19 percent, and plat L3, dressed with 
phosphates ami potassium salts as well as ammonium salts, gives 
53.33 per cent . 
It would seem, therefore, that as far as the Broad balk wheat held 
concerned the determination of soluble nitrogen in the manner 
described does not give us any more information as to potential fer- 
tility than would be derived merely from the determination of the 
total nitrogen. 
In the Rothamsted garden soil (clover plats) the proportion is also 
nearly 50 per cent, ranging from 41.21 per cent to 53.03 per cent, but 
in the park and meadow land it ranges from 62.27 per cent to 66.80 
per cent, there being, therefore, a distinctly higher proportion of 
soda-soluble nitrogen than occurs in the arable land. 
It is worth noting that in the garden clover soil as the percentage 
of total nitrogen diminishes the percentage of soluble nitrogen in that 
total also diminishes. 
In the very rich .Manitoba soil the proportion of soluble nitrogen is 
only 37 per cent of the total nitrogen. 
