Report of Experiments on the Growth of Wheat. 477 
manure, with all its supply of silica, and organic matter yielding 
carbon, both of which were entirely absent in the artificial 
manures. To this point further reference will be made. 
Average Annual Produce by 400 lbs. of Ammonia- Salts per Acre, 
alone, in alternation with the Mixed Mineral Manure, and in 
combination with different descriptions of Mineral Manure. 
Throughout the preceding series the same mixed mineral 
manure was always used, but in conjunction with varying amounts 
of ammonia-salts. In the series now to be considered, a fixed 
quantity of ammonia-salts (400 lbs. per acre per annum) was 
employed throughout, but under varying conditions as to the 
supply of mineral constituents. 
The results of this series which stand first in order in the Table, 
those of plots 17 and 18, where the ammonia-salts were used in 
alternation with the mixed mineral manure, have been so fully 
discussed in Section II. (pp. 457-8 and 466-7) that it is only 
necessary here to recall attention to the fact, that under these con- 
ditions the 400 lbs. of ammonia-salts gave an average annual in- 
crease of scarcely 14J- bushels of dressed corn, and only 1858 lbs. 
= 16J cwts. of straw, more than the mineral manure alone ; whilst 
the same amount of ammonia-salts, used in conjunction with the 
mineral manure, as on plots 7, gave an increase of nearly 18 
bushels of dressed corn, and 2315 lbs. = 20f cwts. of straw. 
It has also already been shown how much less was the effect of 
400 lbs. of ammonia-salts when used for 19 years without mineral 
manure, as on plot 10a, or for 13 years only, as on plot 10b, 
than when they were used in conjunction, or even in immediate 
alternation, with the mixed mineral manure. 
The results next in order, those of plots 11, 12, 13, and 14, 
show in an interesting manner the more or less diminished effect 
when the mineral manure was less complete than the so-called 
"mixed mineral manure" employed on plots 17, 18 and 7, and 
occasionally on plot lQb. 
During the first 8 years of the 20, that is, during the 8 imme- 
diately preceding the 12 the average produce of which is now 
under consideration, plots 11, 12, 13, and 14, all received in 
manure from 2^ to 3 times as much phosphoric acid as was taken 
off in the crops, and all much about the same excess. Of potass, 
all four plots yielded much about the same amount in their 
produce ; but whilst plot 11 received no direct supply in manure 
(only a small quantity in rapecake), plots 12, 13, and 14, each 
received from two to three times as much as was removed from 
them ; the accumulation being somewhat the greatest on plot 13. 
During the last 12 years, in addition to the 400 lbs. of am- 
monia-salts per acre per annum, plots 11 have had superphosphate 
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