Agricultural Chemistry. 
445 
an increase over tlic unmanuretl plot of 1G78 lbs ; and plot 10Z», 
with nine years of ammoniacal salts and two years of minerals, 
gave an annual average of 4642 lbs. of total produce, and of 
1786 lbs. of increase. That is to say, plot lOh has only given 
during these eleven years, an annual increase of 108 lbs. more 
total produce than plot lOct, although during this period it re- 
ceived considerably more than ten times as much of all the 
more important mineral constituents, except silica, as Avould be 
contained in the total increase in the eleven years, of \0h over 
10a! In fact, all that this mineral supply has done, has been 
to render efficient that amount of ammonia, which was added 
in excess of the annually available supply of minerals from the 
soil itself. 
But in Diagram II. (p. 439), we have even a more striking 
answer still, to the assertion that in our experiments the whole 
produce is proportional " to the total sum of the available or 
soluble nutritive mineral constitiients present in the soil." The pro- 
duce of two plots (17 and 18) is here compared with that of the 
continuously unmanured plot. The results extend over a period 
of six years, namely, 1850 to 1855 inclusive. As before, the 
unmanured space is without shading ; mineral manures are re- 
presented by horizontal shading, ammonia-salts only by perpen- 
dicular shading, and the mixture of both minerals and ammonia 
by dotted shading. 
It should be mentioned, that the plots (17 and 18) had, pre- 
viously to 1850, been manured somewhat similarly since the 
commencement of the experiment in 1844. They had generally 
received a liberal supply of minerals and of nitrogenous matter 
also; plot 17 having had upon the whole rather more nitrogen 
supplied to it than plot 18. 
In 1850, both plots (17 and 18) received a large amount both 
of soluble minerals and of ammonia-salts, and they each gave 
nearly a ton and a half more produce than the unmanured plot ; 
though plot 17, which had been rather the most higlily manured 
throughout the previous years, gave rather m.ore produce than 
plot 18. 
In 1851, plot 17 received the same amount of minerals and 
ammonia as previously, and gave 2905 lbs. of increased produce. 
Plot 18 received no minerals, but the same amount of ammonia 
as plot 17, and the result is nearly as much increase, that is, 
2864 lbs. instead of 2905 lbs. 
In 1852, plot 17, which had minerals and ammonia the year 
before, has now only ammonia; and plot 18, which had am- 
monia only in the previous year, has now only minerals. The 
result is, that the ammonia plot (17) gives 5418 lbs. of produce, 
VOL. XVI. 2 G 
