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XXI. — Experiments with different Top-Dressings upon Wlieat. 
By Dr. Augustus Voelcker. 
There is no lack of experiments made with guano, nitrate of 
soda, soot, shoddy, gas-water, and other nitrogenized substances, 
which are occasionally used as top-dressings upon wheat. Ex- 
perience has shown that all these manures may be used, with 
more or less advantage, for the wheat-crop ; and that, generally 
speaking, they are the more effective the more nitrogen they 
contain. Thus Peruvian guano or nitrate of soda, which are both 
very rich in nitrogen, are justly considered more powerful wheat- 
manures than soot or shoddy — two materials much poorer in this 
element. Whilst I consider the relative proportions of nitrogen 
in different fertilizers, intended to be used for wheat or other 
cereal crops, to be an important element in estimating the com- 
parative commercial and agricultural value of artificial manures, 
such as Peruvian guano, nitrate of soda, or sulphate of ammonia, 
I am of opinion that the form or state of combination in which 
the nitrogen is contained in the manure materially affects its 
efficacy. Any one who has tried side by side nitrate of soda, 
Peruvian guano, and shoddy, must have felt surprised at the 
different degree of rapidity with which the effects of these three 
fertilizers are rendered perceptible in the field. I have noticed 
more than once that, under favourable circumstances, tl)e effects 
of nitrate of soda became visible in the course of three or four 
days in the darker green colour and more luxuriant appearance 
of the young wheat, whilst it took eight or ten days in the case 
of guano to produce a similar effect. On wheat dressed with 
shoddy no apparent effect was produced even after the lapse oi 
four or six weeks. So slow is the action of the latter that a 
superficial observer might well doubt the efficacy of shoddy as a 
wheat-manure, for it often produces no visible improvement in 
the wheat-crop, and it is only after threshing out the corn that it 
can be ascertained that shoddy has had some effect upon the 
yield of corn. These examples appear to indicate that nitrogen 
in the shape of nitric acid has a different practical value from 
that which it possesses in the shape of ammonia, and that it has 
again another value in the form of nitrogenized organic matter. 
It must be confessed that our knowledge of the comparative 
e!|fficacy of nitrogen, in its various states of combination, is 
extremely limited, inasmuch as we scarcely possess any suffi- 
ciently accurate and trustworthy comparative field experiments 
■which are calculated to throw light on this subject. As yet the 
sure foundation on which an explicit opinion as to the relative 
merits of nitrogen — in the shape of nitric acid, ammonia, or or- 
ganic matter — can be given, is altogether wanting. It is true the 
