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1 lie Duration of the Action of Manures. 
the first year of application less than one-half of its total effect. 
Doubtless we should include in the same category all manures 
made from hair, fur, skin, silk, hoofs, horns, &c. ; and probably 
also the nitrogen compounds of bones. 
Very different are the results yielded by Peruvian guano 
and rape dust. For both these manures the return in the first 
season is high ; they are well-knoAvn, indeed, as active and 
effective nitrogenous fertilisers ; but the experiments show 
that they leave no residue possessing any value for succeeding 
crops. Owing to the limited number of experiments, too much 
stress cannot be laid on the actual figures obtained — there is a 
possible error of 5 per cent, or so, and, moreover, some evidence 
exists that the check-plot figure, = 100, is somewhat too high 
for the plots in the guano and rape dust series, which are in 
consequence rated too low. Plowever, we shall be justified in 
concluding that the nitrogenous residue from Peruvian guano 
or rape cake after a crop has been taken will give less than 
10 per cent, increase in the second crop, and after that will be 
completely exhausted. (It should be noted that this statement 
applies to the nitrogenous part only of these manures, not to 
the phosphates they contain.) Now, the nitrogen compounds 
in question are, in the guano, ammonium compounds, uric 
acid and its derivatives, and -some proteins; in the rape 
cake, almost entirely proteins ; and it is a point of great 
importance in this connection thus to find that proteins are as 
active and as temporary in their action as ammonium com- 
pounds. Such a result is indeed intelligible, for the true 
proteins are readily and completely digestible, are equally 
easily attacked by bacteria, and pass thereby into ammonia and 
kindred bodies with great rapidity. Wb have other evidence 
from the Rothamsted experiments that the nitrogen in rape cake 
is» pound for pound, very nearly as immediately effective as the 
nitrogen in ammonium salts. The proteins thus fall into line 
Avith nitrates, ammonia, urea, &c., as compounds which produce 
all their effect in the season of their application, and leave little 
appreciable residue behind, in contrast to the collagens (the in- 
soluble nitrogen compounds of wool, skin, bone, &c.) and the 
indigestible residues of food. With this distinction in mind we 
can roughly estimate the residual value of the nitrogen in other 
fertilisers in cakes and seed residues it will be present in the 
form of protein ; in fish guanos it will be mainly protein ; in 
meat guanos protein and collagen; the latter predominating’ the 
pooiei the manure becomes, and the more it approximates to 
bone meal. Though these conclusions are based on experi- 
ments on the Rothamsted soil alone, it is one that Avould usually 
be considered retentive of manure, being both heavy and cool 
fairly supplied with rain but not waterlogged. 
