Report of Experiments on (he Growth of lllicat. 489 
to have contained only a moderate proportion of nitrogen, the 
amount expended for the production of a given quantity of 
increase corresponded to considerably more ammonia than was 
required when nitrogen equal to 50, or even 100 lbs., of ammonia 
was employed as ammonia-salts, or nitrate of soda, in conjunction 
with the mixed mineral manure, notwithstanding that the latter 
contained no silica, a constituent so liberally provided in the 
farmyard manure. It would appear, therefore, that the practical 
results have not yet been materially affected for want of available 
silica where the mixed mineral manure was employed. There 
is, however, evidence in our analytical results that silica has 
become relatively deficient where it has not been supplied in the 
manure. 
Very striking indeed, then, is the difference of effect upon the 
immediate increase, of a given amount of nitrogen in manure, 
whether used as ammonia-salts or nitrate, according to the 
available supply of mineral constituents within the soil ; and 
with the overwhelming evidence before him, which such a com- 
prehensive summary of experimental results on the point affords, 
the practical man will not fail to see that he not only very in- 
juriously further reduces his immediately available supply of 
mineral constituents, but also pays very dearly for his increase, 
if he seek to obtain it by means of purely nitrogenous manures, 
when his soil is already unduly exhausted of mineral consti- 
tuents. 
Equally, if not more, striking, is the difference of effect of a 
given amount of ammonia in one season as compared with 
another. Where the mineral condition is the most defective, 
there the result of a given amount of ammonia is the most 
reduced below the average in a bad season. Leaving the reader 
to the study of all such abnormal cases in the records given in 
the Table, it will be sufficient here to direct attention to the 
great difference of effect according to season even under the more 
favourable conditions as to the amount of ammonia employed, 
and as to the associated supply of mineral constituents. 
The results of plot 6, where only 50 lbs. of ammonia were 
applied each year, and always in conjunction with the mixed 
mineral manure, will well illustrate the point in question. 
Whilst, taking the average of the 12 years, it required 4 - 86 lbs. 
of ammonia in manure to yield 60 lbs. of increase of corn and 
its proportion of straw, in the remarkably productive season of 
1803 it required only 2"42 lbs., but in 1853, 7\L3 lbs., in 1860, 
8 - 85 lbs., and in 1852, 1245 lbs. The amount of produce was, 
indeed, lower in 1853 than in 1852 ; but as the deficiency was 
very much greater with the mineral manure alone (upon the 
produce of which the increase is calculated) than where the 
