180 
On Rape-dust. 
In illustration of its particular value as a manure for grain 
crops, I need only refer to its common use for such crops in 
many parts of England. A ride in the neighbourliood of We- 
theri»y will convince the most sceptical of its efficacy, if they ob- 
serve the crops produced on many soils by the application of from 
8 to IG bushels per acre. 
The quick effect of rape-dust upon the growing crop, and its 
speedy escape from the soil, are matters which the experience of 
every farmer will have taught him. 
From this view of the elements of rape-dust, and of its general 
operation, we deduce the following practical conclusions to regu- 
late its application with respect to corn : — 
1st. That rape-dust, being so beneficial to the growth of grain 
in general, is most marked in its effects upon thin, jjoor soils. 
2nd. That it does not operate so well in a dry season as in a 
moist one. 
ord. That it is most certain in its effects upon the winter-sown 
wheat crops ; but, in favourable seasons, most remunerative on 
the spring crops. 
4th. That it answers best on strong soils for the wheat crop. 
5th, That it is not judicious to apply large quantities at one 
time. 
6th. That it is necessary, after using rape-dust for several rota- 
tions, to apply a dressing of saline and earthy matters. 
These are matters of fact, as well as of reason. The explanation 
we would offer is — 
1st. That the marked effect of rape-dust upon thin, poor soils, 
is to be attributed to the general deficiency of these soils in the 
vegetable and animal matters necessary to supply the plant with 
carbonic acid and ammonia ; which matters rape-dust, as we have 
shown, contains. Again, these soils often possess a large share 
of the mineral constituents of plants, in which matters rape-dust 
is deficient. So that the capabilities of the manure are adapted 
to the wants of the soil. 
2nd. That it does not act so well in a droughty as in a moist 
season is not strange.* No manure can operate well — no crop 
southerns in this point, we must not, however, be vain of our know- 
ledge ; for the writer at the same time says, " as another instance of the 
local prevalence of manures, woollen rags may be cited, lohicli arc the 
only hand-tillage familiarly known to farmers in my own neijjhbour- 
hood. Mr. Haimam states, '20,000 tons of rags are said to be used 
annually by the farmers of Kent, Sussex, Oxford, and Berkshire.' " — 
The Author. 
* The rule applies to guano and gypsum ; thus we are told that the 
natives of Peru irrigate the soil after an application of guano. As to 
