Agricultural Chemistry. 
443 
But can the increase of produce of plot 10a over the unmanured 
plot be attributed to the efficacy of the mineral constituents 
supplied in the first year, in the sense in which Baron Liebig 
attributes efficacy to soluble mineral manures ; namely, as in- 
creasing the assimilation of nitrogen from atmospheric sources ? 
Diagram I. shows that the minerals alone (superphosphate of 
lime and silicate of potass), which were employed in 1844, gave 
only 77 lbs. more produce than the unmanured plot. 
In 1845, a liberal supply of ammonia salts alone, to this plot 
10, on which soluble minerals alone had given scarcely any 
increase in the previous year, increased the produce over that of 
the unmanured plot by more than 2000 lbs. 
In the third year (1846), this plot 10 was divided into two 
equal portions. One half (10a) again received ammoniacal 
salts alone, and the other (lOi) no manure at all. 
Now surely, if the soluble minerals supplied in the first year, 
are to have so much of the credit of the increase of crop during the 
seven years, and if, with " a sufficient supply of the mineral food 
of plants," . . . the ammonia required for their development will 
be furnished by the atmosphere," surely, upon these suppositions, 
we ought to get some increase of produce over the continuously 
unmanured plot, on plot IQb, in this third year (1846) ; when, 
having had, but two years previously, this supposed very efficient 
supply of minerals, it is now left unmanured. The fact is, how- 
ever, that in 1846 the continuously unmanured plot gave 2720 lbs. 
of total produce, and plot \0b only 2671 lbs. ! — though lOa, 
where ammonia salts were again applied, gave 4094 lbs. ! The 
result is, then, that plot 10Z», with minerals in 1844, ammonia in 
1845, and no manure at all in 1846, gave even rather less pro- 
duce than plot 3 (the continuously unmanured plot), which had 
had no supply of minerals at all. How, we would ask, are these 
facts consistent with attributing the increased produce during the 
seven years on plot 10a " to the one only constant value which ope- 
rated" in the experiments — "that is, to the total sum of the avail- 
able or soluble nutritive mineral constituents present in the 
soil " ? The obvious truth is, that however liberal the supply of 
minerals in the soil, they were utterly incompetent to yield 
any agriculturally adequate increase of produce of wheat, unless 
accompanied by an artificial supply of available nitrogen within 
the soil ; and this being so, we would ask, Was not the produce 
*' rather proportional to the supply of ammonia " ? 
In 1847, plots 10a and 10b both received equal amounts of 
ammonia-salts alone, and gave neaily identical amounts of pro- 
duce, and half as much again as the unmanured plot. 
In 1848, the produce of the unmanured plot was 2664 lbs. ; 
that of 10a, with ammoniacal salts only, for the fourth year, 
