for Tittenty Years in succession on the same Land. 3(57 
required to produce 1 bushel increase of barley, and its straw. 
But whilst an avera<^e bushel of wheat may be reckoned to 
weigh 61 lbs., and its average proportion of straw 105 lbs., an 
average bushel of barley will weigh only 52 lbs., and its straw 
only ()3 lbs. Hence, whilst it required 5 lbs. of ammonia in 
manure to yield 61 lbs. of wheat-grain, and 105 lbs. of straw = 
166 lbs. of total produce, it only requires from 2 to 2J lbs. to yield 
52 lbs. of barley-grain and 63 lbs. of straw = 115 lbs. of total 
produce. In other words, for the production of 100 lbs. in- 
crease of total produce of wheat, it required 3 lbs., and for the 
production of 100 lbs. increase of barley (containing a larger 
proportion of grain, but about the same amount of nitrogen) it 
required only from about IJ to 2 lbs. of ammonia in manure. 
That is to say, it required much more ammonia to yield a given 
amount of increase when applied in the autumn for wheat, than 
when in the spring for barley. 
The following questions obviously suggest themselves : — 
What proportion of the nitrogen supplied in manure will pro- 
bably, on the average, be recovered in the increase of the crop 
for which it is applied ? 
Will the at first unrecovered amount have any marked effect 
on the immediately or early succeeding crops ? 
Will there be any residue retained by the soil and the subsoil, 
in such a state of combination, and distribution, as only to be 
yielded up, if ever, in the course of a long series of years ? 
Will there be any drained away and lost ? 
Lastly, will the answers arrived at on these points, in regard 
to wheat or to barley, be equally applicable to both crops? 
With regard to the proportion of the nitrogen of artificial 
manures recovered in the increase of crop obtained by their 
use, in former papers it has been estimated, taking the average 
over a comparatively limited number of years, that about 40 
per cent, was recovered in the increase of wheat, of barley, and 
of meadow-hay indifferently. But, by the aid , of numerous new 
determinations of nitrogen in the produce of wheat for twenty 
years, of barley for twenty years, and of oats for three years, it now 
appears that, with the same mixed mineral manure in each case, 
and the same amount of ammonia-salts applied in the autumn 
for wheat, and in the spring for barley and for oats, rather less 
than one-third of the supplied nitrogen has been recovered in 
the increase of the wheat, but nearly one-half in that of the 
barley and the oats. When, however, there were applied, even 
for wheat, the same mineral manure and nitrate of soda, the 
latter sown in the spring, a not much less proportion of its 
nitrogen was recovered in the increase of the crop, than in the 
case of the ammonia-salts applied for barley in the spring, or of the 
ammonia-salts or nitrate of soda applied for oats in the spring. 
