On the Valuation of Unexhausted Manures. 
7 
growing plant. When, however, nitrate of soda is applied, its 
great solubility, and the much less power of the soil for the 
absorption of it, or of its products of decomposition, than for 
that of ammonia, render it more liable still to loss by drainage 
if heavy rain should follow soon after sowing. 
Although the nitrogen of manures is thus found to be very 
liable to loss by drainage, direct experiments show that the two 
important mineral constituents — phosphoric acid and potass — are 
much less liable to such loss. 
Thus, Dr. Voelcker's analyses of the drainage-waters showed 
them to contain very little of either phosphoric acid or potass ; 
and analyses of the soils themselves, made by Hermann von 
Liebig, son of the late Baron Liebig, showed that they con- 
tained considerably more of both phosphoric acid and potass — 
especially in the upper layers — the greater had been the supplies 
of them by manure. Experiments in the field further showed 
that these substances, though remaining dormant and ineffective 
in the soil in the absence of a sufficient supply of nitrogen, 
become effective even for twenty years or more, after their 
application, if nitrogen in an available form be also provided 
within the soil. 
Of the three constituents of manures — nitrogen, phospho7'ic 
acid, and potass — which, in the sense that by the production and 
sale of corn and meat they are the most likely to become rela- 
tively deficient, are the most important constituents of manures 
generally, it is then proved, that the nitrogen is, at any rate 
Avhen applied to ammonia-salts or nitrate of soda, very liable to 
loss by drainage, whilst the phosphoric acid and potass are, in a 
much greater degree, retained by the soil. 
When farmyard-manure is employed, or other manures con- 
taining a large quantity of nitrogenous organic matter are 
used, the result is not quite so simple. For example, in farm- 
yard-manure a portion of the nitrogen exists as ready-formed 
ammonia, but a large proportion becomes only very gradually 
converted into ammonia as the nitrosrenous organic matter 
decomposes in the soil. Indeed, owing to the slow decom- 
position of dung, and the tardiness with which a large pro- 
portion of its nitrogen becomes available for the use of the 
growing crop, three or four times more nitrogen in the form of 
dung, than in active artificial manures, must be applied to 
produce the same effect upon the immediately succeeding crop. 
How slow is the perfect decomposition of dung in the soil, 
and how slowly a large proportion of its nitrogen becomes 
available for the use of growing crops, is strikingly illustrated 
in the following facts : 
In the experiments at Rothamsted on permanent grass-land, one 
