420 
Clover as a Preparatory Crop for Wheat. 
richer in nitrog^cn after clovcr-seetl tlian after clover mown twice 
for hay ; or as it may be expressed : — In 1 lb. of ammonia there 
were 3592^ more of ammonia in the land where clover-seed 
was grown than where other clover was made entirely into hay ; 
or the former part of the same field produced rather more than 
half the total quantity of nitrogen yielded by the latter. 
Reasons are given in the beginning of this paper which it 
is hoped will have convinced the reader that the fertility of 
land is not so much measured by the amount of ash-constituents 
of plants which it contains, as by the amount of nitrogen which, 
together with an excess of such ash-constituents, it contains in 
an available form. It has been shown likewise that the removal 
from the soil of a large amount of mineral matter in a good 
clover-crop, in conformity with many direct field experiments, 
is not likely in any degree to affect the wheat-crop, and that the 
yield of wheat on soils under ordinary cultivation, according to 
the experience of many farmers, and the direct [and numerous 
experiments of ^lessrs. Lawes and Gilbert, rises or falls, other 
circumstances being equal, with the supply of available nitro- 
genous food which is given to the wheat. This being the case, 
we cannot doubt that the benefits arising from the growth of 
clover to the succeeding wheat are mainly due to the fact that 
an immense amount of nitrogenous food accumulates in the 
soil during the growth of clover. 
This accumulation of nitrogenous plant-food, specially useful 
to cereal crops, is, as shown in the preceding experiments, 
much greater when clover is ^rown for seed than when it is 
made into hay. This affords an intelligible explanation of a fact 
long observed by good practical men, although denied by others 
who decline to accept their experience as resting on trustworthy 
evidence, because, as they say, land cannot become more fertile 
when a crop is grown upon it for seed which is carried off, than 
when that crop is cut down and the produce consumed on the 
land. The chemical points brought forward in the course of 
this inquiry show plainly that mere speculations as to what can 
take place in a soil and what not, do not much advance the true 
theory of certain agricultural practices. It is only by carefully 
investigating subjects like the one under consideration that 
positive proofs are given showing the correctness of intelligent 
observers in the fields. Many years ago I made a great many 
experiments relative to the chemistry of farmyard-manure, and 
then showed, amongst other particulars, that manure, spread at 
once on the land, need not there and then be ploughed in, inas- 
much as neither a broiling sun nor a sweeping and drying wind 
will cause the slightest loss of ammonia, and that, therefore, the 
old-fashioned farmer who carts his manure on the land as soon 
