342 Report of Experiments on t/ie Groictli of Barleij. 
nitrate of sotla. It is further worthy of remark, that there is a 
general consistency between these results relating to the drainage 
from the dunged plot, and those obtained by Dr. Voelcker ; for, 
in one case examined by him, the amount of nitrogen as nitrates, 
&c., also ranged somewhat below that in the drainage from 
Plot 6, and in the other not much above it. 
In regard to wheat, therefore, it has been experimentally 
established, that, even when a comparatively moderate amount of 
ammonia-salts was applied as manure, only about one-third of the 
nitrogen so supplied was recovered in the increase of the crop ; 
that the unexhausted residue, if any, was but very slowly, and 
very, partially recovered as increased yield in succeeding years ; 
that, nevertheless, there was an accumulation within the soil 
itself, of some of the nitrogen not at first recovered in increase ; 
but that there was a loss by drainage which increased almost in 
proportion to the amount of nitrogen supplied in the manure. 
The question arises — whether the whole of the supplied nitrogen 
which is not recovered in the crop either remains in the soil, or 
is lost by drainage? Owing to the difficulty of determining 
with certainty, either the total amount of nitrogen retained by 
the soil within the reach of the roots, the proportion of the total 
rain passing beyond their reach, or the average composition of 
the drainage, absolute proof on this point is not at command. 
The following illustration will nevertheless be useful. 
Of the total nitrogen supplied to the wheat plot No. 7, 
during the 20 years, 1852— 1S71, it may be assumed that about 
33 per cent, was recovered in the increase of crop, leaving 67 per 
cent, to be otherwise accounted for. The determinations of 
nitrogen made in the samples of soil collected in 1865 are ob- 
viously not strictly applicable to the present calculation ; but from 
them it may perhaps be concluded that approximately one-third, 
or possibly more, of the nitrogen not recovered in the increase 
of crop, remains accumulated within the soil to the depth of 
the 27 inches examined. This would leave say 44 per cent, of the 
82 lbs. of nitrogen annually applied as manure, or, in other words, 
an average of 36 lbs. of nitrogen, *o be annually accounted for by 
drainage or otherwise. Now, there can be no doubt that by far 
the larger proportion, though not the whole, of the drainage takes 
place during the autumn and winter months; and taking the 
mean of Dr. Voelcker's three determinations of nitric-acid in the 
winter drainage from this plot, the amount of nitrogen so found in 
it is 2 "16 parts for 100,00U of water. As 1 inch of rain is equal 
to a fall of 226,263 lbs. (about 101 tons) of water per acre, every 
inch passing as drainage beyond the reach of the roots, and con- 
taining 1 part of nitrogen per 100,000, would carry with it 2^ 
(2'26) lbs. of nitrogen per acre ; and 2'16 parts per 100,000 
