•108 Report of Experiments on the Growth of Wheat. 
increase when in the latter year they were used alone), continued 
to increase the effect of ammonia-salts afterwards annually applied 
for 13 consecutive years. 
6. A given amount of ammonia -salts gave very different 
amounts of increase, according to the supply of available mineral 
constituents within the soil ; giving very much more when 
mineral manures were applied in the same, than in the preceding 
year, notwithstanding that, in the latter case, there could be no 
deficiency, though doubtless less favourable condition and dis- 
tribution of the mineral constituents. 
7. The same mineral manures which were very effective when 
supplied with ammonia-salts, gave very little increase of pro- 
duce when used alone year after year for 12 years, although 
following an excess of ammonia-salts applied in preceding years i-; 
and they gave very little more when they were applied every year 
succeeding an excess of ammonia-salts applied in the immediately 
preceding year. 
8. The unexhausted residue from previous mineral manuring, 
though it served as an effective reserve against exhaustion, had 
little or no effect in increasing the growth of wheat without 
the aid of available nitrogen provided within the soil. An 
unexhausted residue from previous nitrogenous manuring had 
also but little influence upon the immediately succeeding crops, 
even when aided by the application of mineral manures. 
The bearing of the facts adduced in this Section, upon the 
question of the probable influence on the mineral wealth of our 
soils, of the use of artificial nitrogenous manures, under the cir- 
cumstances, and in the degree, in which they are generally em- 
ployed in the ordinary course of agriculture in this country, will 
be considered further on, when the whole of the experimental 
evidence which it is proposed to bring forward in the present 
Report is before the reader. 
With regard to the bearing of the results on the subject of the 
next Section, it is obvious that the degree and limit of effect of 
the unexhausted residue of previous manuring, whether nitrogen- 
ous or mineral, are such that, if the circumstances of the different 
plots are duly considered, there will be little danger of misinter- 
preting the results obtained on the application of the different 
manures year after year on the same plot during the last 12 
years. 
IT I. Average annual results over the last 1 2 years. 
Subject to such reservations as the facts already adduced sug- 
gest, and to others which will be referred to in the course of the 
discussion, attention may now be directed to the average annual 
