Report of Experiments on the Growth of Wheat. 451 
during- the 7 years of its application, a total increase of about G9^ 
bushels of dressed corn, and 7821 lbs. of straw; or an average 
annual increase of nearly 10 bushels of dressed corn, and 1118 
lbs., or about half a ton of straw. These amounts would re- 
move from the land only about one-third of the nitrogen, and 
one-seventh of the phosphoric acid supplied in the manure ; to 
say nothing of the phosphoric acid, and all other mineral consti- 
tuents, supplied in the first year of the experiments (1843-4) in 
the form of the ashes of farmyard-dung. Yet the total amount 
of increase obtained during the next 12 years, due to the large 
residue from the previous manuring, was only Yl\ bushels of 
corn, and 843 lbs. of straw, or of corn about one-fourth and of 
straw about one-ninth as much as that yielded during the seven 
years of the application of the phosphate and ammonia. The 
average annual increase over the 12 years amounted to less than 
\\ bushel of dressed corn and to 70 lbs. of straw. 
This experiment was arranged for the purpose of determining 
whether during the later years there would be a less produce 
than on the continuously unmanured plot, indicating exhaustion 
of the available alkalies and silica during the 7 years of forcing 
by the application of other constituents to their exclusion ; or 
whether there would be an increase, due to the accumulation in 
the soil of nitrogen and phosphoric acid, in which case it might 
be concluded that there was, as yet, no deficiency of available 
alkalies and silica in the soil, relatively to the annually available 
supplies of nitrogen from natural sources. The latter proved to 
be the case. In fact, there is no doubt that the farmyard manure 
ashes applied in the first year, would supply at any rate consi- 
derably more potass than was removed by the increased produce 
during the next 7 years. It will perhaps be objected, that the 
increase would have been much greater, both during and after 
the 7 years, had fresh supplies of alkalies been provided. Under 
the conditions of the experiment, such as they were, however, 
the unexhausted residue of previous manuring was obviously 
very slowly available in succeeding seasons. 
Again, to a portion of the experimental plot 3, from which 
12 unmanured crops of wheat had been taken — a kind of treat- 
ment which it has been alleged by Baron Liebig would bring 
our soil into such a condition of exhaustion of available mineral 
constituents that it would yield no increase on the application of 
ammonia-salts alone — a dressing of these salts was applied in the 
13th season, and then 7 crops were taken without further manure, 
in order to trace the degree or limit of the effect of the unex- 
hausted residue of nitrogen supplied. The results are given in 
the following Table (XXIV.) :— 
