The Duration of the Action of Manures. 123 
for both kinds contain about the same percentage of nitrogen 
combined in an insoluble form. 
This is exactly what should be expected from the fact that 
the nitrogen compounds in the cake, being almost wholly 
digestible, are excreted as urea, which changes rapidly into 
ammonia ; thus the effect of cake feeding is to enrich the 
dung in ammonia and other active compounds of nitrogen, 
but not particularly in those more slowly acting insoluble 
compounds which come from the litter and the undigested 
portions of the food. From numerous other experiments we 
learn that ammonia and such compounds are only of value as 
manures for the crops to which they are applied, or to a much 
smaller degree to the succeeding crops ; hence the effect of 
the cake feeding is pronounced in the first year, much less in 
the succeeding year, and then nil. After the second year the 
slowly acting nitrogen compounds that were derived from the 
straw and the undigested residues of the food are still coming 
into action, and continue to do so for many years before they 
are exhausted, but these effects, as they arise less from the cake 
feeding than from the other constituents of the manure, become 
alike for both kinds of dung. The general conclusion that we 
can draw is that cake feeding only adds fertility to the land for 
the first two crops grown with the manure. 
2. Other Nitrogenous Manures. 
Table III. — Yield from various nitrogenous manures over 
a period of four years. 
YIELD.— Total produce (unmanured plot = 100) 
Year of 
application 
1 year old 
residue 
2 year old 
residue 
3 year old 
residue 
Mean of 9 
Mean of 8 
Mean of 7 
Mean of 6 
Shoddy .... 
139-7 
125-2 
116-1 
106-7 
Peruvian Guano . 
150-0 
101-0 
96'5 
98-4 
Rape Dust .... 
136-2 
100-4 
100-0 
94-4 
The results obtained with the wool-waste, Peruvian guano, 
and rape dust are set out in. Table III. A marked contrast 
exists between the first and the two latter of these manures. 
The shoddy or wool-waste evidently contains compounds of 
nitrogen subject to comparatively slow decay, so that its effect 
in the second and succeeding years is considerable, there being 
a distihct increase indicated in the fourth crop grown with the 
manure. Indeed the values yielded by shoddy compare veiy 
closely with those obtained with farmyard manure made from 
roots and hay only. It is a persistent manure that exerts in 
