Report of Experiments on the Growth of Wheat. 4G5 
with that of tlic preceding 6, it is found that, whilst 10a has given 
\\ bushel of dressed corn and 180 lbs. of straw, 10/; has given 
\\_ bushel of dressed corn and 304 lbs. of straw, less over the 
later than over the earlier period. 
Over the whole 19 years, plot 10a, with its larger amount of 
ammonia-salts and less supply of mineral constituents, gave 
38^- bushels of dressed corn, and 4205 lbs., or about 37^ cwts., of 
straw less than 10ft — equal to an average annual deficiency of 2 
bushels of dressed corn, and nearly 2 cwts. of straw. 
Here, then, is an obvious case of exhaustion of available 
mineral constituents relatively to the available supply of nitrogen, 
and also a very marked effect from the unexhausted residue of the 
mineral manures applied in the earlier years. 
It would be inappropriate to go into detail as to the compara- 
tive exhaustion of the two plots in respect to individual mineral 
constituents without adducing the results of analysis relating to 
the subject. But it may be stated generally, that the average 
percentage of mineral matter is considerably lower in the pro- 
duce of plot 10a, than in that of plot 3 without manure ; and 
further, that in the ash of the grain the proportion of phosphoric 
acid, and in that of the straw the proportion of the silica more 
particularly, is becoming reduced. During these 19 years, how- 
ever, there have been removed from the plot as much phosphoric 
acid as would suffice for more than 50 years, as much potass as 
would suffice for more than 100 years, and as much silica as 
would suffice for more than 500 years of ordinary rotation, where 
only corn and meat are sold, and the due proportion of the home- 
manures are periodically returned to the land ; whilst the first 
five crops of the twenty would remove about as much phosphoric 
acid, and the first three about as much potass, as was supplied 
in the first year of the experiments.* 5 Under such very un- 
usual treatment, it is ' certainly not surprising that the annually 
available mineral constituents of the soil should prove to be 
insufficient. 
Diagram II. (facing p. 461), further illustrates the point in 
epiestion. There are there shown, side by side, the bushels of 
dressed corn per acre, in each of the last 12 years of the experi- 
ments, on plots 3, 5, 17, 18, 10a, 10ft, and 7 ; and the further 
* Baron Liebig tells his readers that we applied in the first year as much soluble 
phosphoric acid as would be contained in about 1750 lbs. of guano. The fact 
is. that the total phosphoric acid applied would be contained in about one-half 
that amount of Peruvian guano of average composition. He also misrepresents 
our conclusions ; and so, as in other instances, by the aid of his own mis- 
statements, makes a point for ridicule where he cannot controvert. (Einlcitung 
r.nd 'Natural Laws of Husbandry,' pi 300, and context,) 
