Report of Experiments on the Growth of Wheat. 453 
over, in a season of inferior grain-producing quality, gave in the 
year of the application an increase of about 13f bushels of dressed 
corn, and 1494 lbs. or rather more than 13J cwts. of straw. This 
amount of increase would, however, carry off only about one- 
fourth of the nitrogen supplied. Yet the total increase obtained 
without further manure during the 7 succeeding years, was only 
H- bushel of dressed corn, and 388 lbs., or about 3-J cwts., of 
straw. Here again, then, the residue of the previous nitrogenous 
manuring was but very slowly, and very partially, recovered in 
the succeeding crops. 
It may, of course, be alleged against this experiment, that 
the want of effect of the residue of the previous nitrogenous 
manuring was due to the exhaustion of mineral constituents. 
The experiment next considered is less open to this objection. 
Plot 5 was variously, but liberally, manured during the first 
8 years of the experiments. During that period, considerably 
more nitrogen, more than twice as much potass and phosphoric 
acid, and probably more of every other mineral constituent, 
except silica, had been applied in the manures than was taken 
off in the total produce ; and very much more, therefore, than 
was contained in the increase of produce. In each of the 12 
succeeding years, a mixed mineral manure, supplying liberally 
potass, soda, magnesia, lime, sulphuric acid, and phosphoric 
acid (but no silica), was applied. Table XXV. (over leaf) shows 
the results obtained during these 12 years. 
It is seen that the total increase obtained during 12 years by 
the annual use of a liberal mixed mineral manure, succeeding 8 
years of accumulation of nitrogen and mineral constituents, was 
only about 35^- bushels of dressed corn, and 2827 lbs., or about 
25J cwts. of straw ; equal to an average annual increase of less 
than 3 bushels of dressed corn, and little more than 2 cwts. of 
straw. 
The question arises — is this amount of increase due to the 
mineral manures applied during the 12 years of its production, 
or is the whole, or part of it, to be attributed to the previous 
accumulation? Doubtless part is due to previous accumulation, 
and part only to the direct effect of the newly-supplied mineral 
manure in enabling the plant to avail itself more fully of the 
natural supplies of the soil and season. Even were nearly the 
whole attributable to accumulation of nitrogen previously sup- 
plied, the amount is very small compared with that from direct 
nitrogenous manure. In fact, the limit of the effect of the unex- 
hausted residue from the nitrogenous manuring of the earlier years 
is seen to be such, that it is obvious the average results of the 
different manures over the last 12 years, may, in most cases, be 
