312 Report of Experiments on the Groicth of Barley. 
another ; but, so far as can be judged, a given amount of nitrogen 
as nitrate of soda has yielded more produce than the same 
amount as ammonia-salts, and especially so in dry seasons. 
This is probably due to the greater solubility of the nitrate, or 
its products of decomposition, to their action on the subsoil, 
disintegrating it, and rendering it more porous ; thus affording 
more surface for the absorption and retention of moisture and 
manure, and greater permeability to the roots, rendering the 
plants less dependent on the fall of rain during growth. 
12. By the annual application of rape-cake, whether without 
or with the addition of mineral manures, more barley than the 
average crop of the country has been obtained ; but, in propor- 
tion to the nitrogen it contained, less than by ammonia-salts or 
nitrate of soda. The mineral constituents of the rape-cake 
no doubt aid in renderins: effective the nitrogen associated with 
them, though its effects are doubtless mainly dependent on the 
amount of nitrogen rendered available by the decomposition of 
its nitrogenous organic matter ; but the nitrogen of such matter 
IS much less rapidly available than that of ammonia-salts or 
nitrates. 
13. Over 20 years or more, in succession, ammonia-salts, or 
nitrate of soda, with mineral manure (without silica), have 
yielded considerably more of both wheat and barley than the 
average crops of the country, and more also than either farm- 
yard manure or rape-cake. It is obvious, therefore, that the 
return to the soil of carbonaceous organic matter as manure is 
unessential, so far as the successful growth of either of these 
crops is concerned. 
Section III. — Amount of Ammonia in Manure (or its 
EQUIVALENT OF NiTROGEN IN OTHER FORMS) REQUIRED TO 
YIELD A GIVEN INCREASE OF GrAIN (AND ITS RROPORTION 
OF Straw). 
Comparison of the produce obtained by the different manures 
has shown — that carbonaceous organic matter, supplied so largely 
in farmyard manure and rape-cake, is at any rate not essential 
as manure for either wheat or barley ; that mineral manures alone 
will not yield fair crops of either ; that nitrogenous manures 
give much more produce than mineral manures alone ; and that 
the mixture of nitrogenous and mineral manures will give full 
crops for many years in succession. In other words — the supply 
by manure of matter yielding by decomposition carbonic acid, 
and other carbon compounds, within the soil, has little or no 
effect ; mineral manures alone will not enable the growing plant 
to obtain sufficient nitrogen from the soil or the atmosphere ; 
when nitrogen in an available form was liberally provided, the 
