120 The Duration of the Action of Manures. 
soil. The phosphates do, however, undergo change, and by 
combination with the bases in the soil pass into compounds 
which are more insoluble and but slightly available to the crop, 
the character of the change depending upon the composition of 
the soil. Some, at any rate, of the unused phosphoric acid is 
thus put out of action, and the whole must be counted as of 
less value, pound for pound, than in the original manure. 
Potash behaves very similarly to phosphoric acid, though it is 
rather more soluble and subject to loss by drainage. 
As the problem could not be solved by theoretical con- 
siderations, it was resolved at Rothamsted to subject it to actual 
trial, and the Little Hoos Field, in 1904, was set aside for that 
purpose. In view of the smallness of some of the effects the 
experiment has hardly yet lasted long enough for accurate 
results ; the main trend is, however, sufficiently indicated to 
permit of certain general conclusions being drawn. The 
experiment took the following form : for each manure five 
plots were set aside — one was a check plot, which at no time 
received the manure under investigation. Of the other plots, 
one received the manure in 1904, but remained unmanured in 
1905, 6, and 7 ; a second plot was manured in 1906, but not in 
1907 ; the third in 1907. Thus in 1907, by which year the 
experiment was in full swing, there was a plot that had been 
manured in that vear, another that had been manured in the 
V 
previous year ; a third two years previously ; and a fourth 
three years previously. In 1908 it was considered that the 
manure applied in 1904 to the first plot had been exhausted by 
the four crops grown with it, and the manuring was renewed 
on that plot ; on the second plot it was renewed in 1909, and 
so on ; the result being that in any year after 1907 there was a 
crop grown on some plot with the manure ; on a second plot 
with the residue of the manure after one crop had been taken ; 
on a third with the residue after two crops ; and on a fourth 
with the residue after three crops ; while there was a further 
check plot that had never received the manure. The Table on 
the following page will show more exactly the arrangement. 
The field was farmed on a rotation of alternating corn and 
roots — swedes, barley, mangolds, wheat ; clover being omitted 
because it would introduce nitrogen. In the field there were 
eight sets of five plots; five for nitrogenous manures — dung made 
from roots and hay only, cake fed dung, shoddy (wmol waste), 
Peruvian guano, rape dust, and three for phosphatic manures — 
bone meal, superphosphate, and basic slag. Once during each 
rotation a dressing of superphosphate and sulphate of potash 
was applied equally to all the nitrogen plots ; similarly for the 
corn crops a dressing of sulphate of ammonia was given alike 
to all the phosphatic plots. It will be noticed that for each 
