Report of Experiments on the Growth of Wheat. 487 
cwts. of commercial muriate of ammonia, in about 2 J cwts. of 
genuine Peruvian guano, or .in rather more than 2\ cwts. of 
nitrate of soda. These amounts are more than are usually em- 
ployed in common practice for the wheat crop ; and most prac- 
tical men would consider double these quantities to be'very heavy, 
if not excessive dressings. 
In bringing to hear upon the question under consideration 
the additional experimental evidence now at command, we shall 
assume, therefore, that the results obtained by the use, per acre, 
of 50 or 100 lbs. of ammonia (or their equivalent of nitrogen 
as nitrate) most nearly represent those which may be expected in 
ordinary practice ; and further, that the results obtained by these 
amounts in the cases where the mineral constituents (unless silica) 
are not in relative defect, are also such as are most likely to be ob- 
tained in ordinary farm practice. Accordingly, we adopt for our 
purpose, the results obtained on plots 6 with 200 lbs., and on 
plots 7 with 400 lbs. of ammonia- salts (containing, respectively, 
50 and 100 lbs. of ammonia) in each case used in conjunction 
with the mixed mineral manure ; and these will be taken as 
the standards by which to compare the effects of larger amounts 
of ammonia with the same mineral manure, or the same amounts 
of ammonia under less favourable conditions as to the supply of 
mineral constituents. 
It will be observed, that, almost uniformly, rather less ammonia 
was required to produce 60 lbs. increase of corn on the average 
of the last 6, as compared with the first 6 of the last 12 years. 
It will, perhaps, be said that the apparently better effect during 
the later years is in reality due to the unexhausted residue of the 
supplies in the earlier years. Evidence enough has been adduced 
showing the limit of the effect of such unexhausted residue ; and, 
whilst admitting that a portion of the difference in favour of the 
later years may be attributed to previous accumulation, there 
can be no doubt, as has been shown, that the last 6 seasons were 
themselves more favourable than the preceding 6, and that to 
this cause a considerable portion of the difference is really due. 
Subject, then, to some correction on the score of accumulation, 
the average result over the 12 years may doubtless be taken as 
pretty closely representing the average effect of a given amount of 
ammonia, according to the amount of it employed, and to the 
favourable or unfavourable condition of the soil in regard to 
the supply of mineral constituents. 
When 50 lbs. of ammonia per acre were annually applied in 
conjunction with a complex mineral manure, excluding silica 
(plot 6), the average annual result was, that 4"86 lbs. of ammonia 
were required to produce 60 lbs. increase of corn, with its equi- 
valent of straw. This amount of ammonia, as has been said, 
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