244 
Report of Experiments with different Manures 
elated with a liberal provision of the necessary mineral consti- 
tuents. Such at any rate is the result, on the assumption that 
as much of the nitrogen of the produce as was in excess of that 
obtained loithout manure, is to be attributed to that which was 
artifcialbj supplied. When, liowever, the same nitrogenous 
manures were employed without the aid of mineral manures, 
only about half as much of the supplied nitrogen appeared to be 
recovered in the immediate increase. There was, moreover, little 
more than half as much of the supplied nitrogen estimated as 
recovered, if, when mineral and nitrogenous manures were used 
together, the yield of nitrogen by the mineral manures alone, 
instead of that without manure, were assumed to represent the 
amount obtained from natural sources. But, even thougli the larger 
amount may more nearly represent the actual proportion of the 
supplied nitrogen which was recovered in the increase when 
mineral manures were also used, it will be, at the same time, 
obvious that, in a certain practical sense, the only qain of nitro- 
gen in produce by the addition of it to mineral manures, is 
that amount beyond what would have been obtained by the 
mineral manures alone. 
On other occasions it has been shown, that, in the growth of 
full crops of either lolieat or harley by the direct application 
of nitrogenous manures, little more than 40 per cent, of the sup- 
plied nitrogen could be estimated as recovered in the immediate 
increase obtained. It might perhaps be anticipated, that the 
result would be difiFerent in the case of the hay-crop. Not only 
are but few of the plants composing it fully ripe at the time of 
being cut, but their roots have a much more complete possession 
of the whole area of the superficial layers of soil. So lar as the 
experiments have yet extended, the hay-crop does not appear to 
return in its immediate increase, a larger proportion of the sup- 
plied nitrogen compared with wheat or barley, than might 
perhaps with reason be attributed to the more extended distri- 
bution of the feeders of the crop on a given area of land. 
It appears, then, from the evidence as 3et at command, that 
in the case of the grass-ci'op, as in that of the ripened cereal 
grains, a considerable proportion of the expensive constituent — 
nitrogen — which may be supplied in manure, has to be reckoned 
as unrecovered in either the immediate or the closely-succeeding 
increase of crop. 
The possible explanations of this loss »)f nitrogen — real or 
apparent as the case may be — are numerous ; but they are more 
or less within the reach of careful and extended exj)erimental 
inquiry. It may be supposed — that a portion of the unrecovered 
amount of nitrogen is, in some form, drained away and lost? — that 
the supplied nitrogenous compound is transformed in the soil, 
