TIIK HKOADHALk WHKAT SOILS. 
109 
is correct, a very much larger quantity of phosphoric acid in the 
form of dung must have descended into the subsoil than has been 
the case on the plats manured with superphosphate. Even if we 
allow some considerable margin in the estimate, it still appears that 
then* musl have been a considerable descent. Unfortunately the 
■•regularity in the mineral composition of the subsoils, to which ref- 
erence has already been made, makes it impracticable to trace the 
descent quantitatively as far as total phosphoric acid is concerned. 
The descent, nevertheless, is qualitatively seen in the increase of 
Rtric-acid-soluble phosphoric acid in both the second and third 
depth*. Of the excess of total phosphoric acid (as compared with 
plat 3) actually found arrested in the firsl 9 inches, considerably 
more than half exists in the eitric-acid-soluble state, forming a large 
reserve of phosphoric fertility. This reserve, as we have seen, is far 
from being confined to the surface soil, though much of the phos- 
phoric acid which must be supposed to have descended into the sub- 
soil has evidently assumed a less available form. 
This greater descent of phosphoric acid into the subsoil in the case 
of the dunged plats, as compared with the artificially fertilized plats, 
is a point of much interest The reason for it may be a merely chemi- 
L*al one. We have Seen that in the case of platfi 5 and 7, where alka- 
line salts have been Liberally applied, these have markedly influenced 
be condition of the phosphoric acid as compared with that on the 
■atson which do alkaline salts were used; and the saline matters of 
the dun- may have had some similar effect It also seems just possi- 
ble t hat ea rt h worms may play a part in the distribution of the con- 
stituents of the dung, by devouring it and conveying it downward. 
In t he case of plat i\u which had been dunged for only nine years 
at the time at which the last soil samples were taken, the total excess 
ft phosphoric acid over plat actually found by analysis is 1,186 
pounds per acre, whereas the estimated excess should only be 592 
pounds; but the excess found in a citric-acid-soluble condition is 604 
pounds in the firsl 9 inches, pounds in the second :» inches, and 19 
pounds in the third !) inches, a total excess of i'>,T2 pounds per acre as 
Bmpared with plat :>. 
The calculated excess of course involves not only the supposition 
that the dung was on the average of uniform composition, but also 
Re supposition that the soils were uniform to begin with, and there 
is no evidence to show that such was actually the case. 
Viewing the figures broadly it is at any rate evident that much less 
3f the dun- phosphates applied to this plat during the nine years 
have reverted to the insoluble condition than in the case of the older 
lung accumulations on plat 2b. The influence of the dung on the 
available phosphoric acid of the subsoil is also much less marked 
than in the case of the plat dunged for fifty years; nevertheless it is 
apparent. 
