Experimental Plots at Rothamsted, from 1864 to 1883. 437 
increases the amount of wheat by between 8 and 9 bushels 
over the whole period ; the minerals alone yielding 15^ bushels, 
the 43 lbs. of nitrogen 24| bushels, and the 86 lbs. of nitrogen, 
32J bushels per acre. 
Comparing the four periods of 8 years with each other, it 
will be seen that the minerals alone, during the last period of 
8 years gave 6J bushels per acre less than during the first 
period ; while the 43 lbs. of nitrogen yielded between 7 and 8 
bushels per acre, and the 86 lbs. of nitrogen yielded 7^ bushels 
per acre less than during the first period. The reduction there- 
fore would appear to be due to some cause which equally affected 
the three crops. 
The addition of another 43 lbs. of nitrogen, by the applica- 
tion of 129 lbs. of the substance, proved far less effective than 
the previous additions, as instead of being from 8 to 9 bushels, 
the increase was only 3^ bushels per acre ; the average of 
the whole period of 32 years being, for the highest manure — 
where the 129 lbs. of ammonia was applied — 3G|^ bushels per 
acre, and where 86 lbs. of nitrogen was applied, 32f bushels 
per acre. 
The total increase obtained by this large amount of nitrogen 
— in excess of the produce obtained by the mineral manures 
alone — amounted only to 21 bushels per acre per annum; it is 
therefore quite evident that in this experiment the nitrogen 
applied was in excess of the quantity which could be utilised 
by the crop ; and even in the best season of growth, 1863, when 
the crop which received 86 lbs. of nitrogen yielded 53^ bushels 
per acre, the crop receiving 129 lbs. only yielded 2 bushels 
more ! 
The average yield of wheat in Great Britain is estimated by 
us at 28 bushels, and by others at 30 bushels per acre. The 
crop obtained by 86 lbs. of nitrogen appears to have quite reached, 
if it has not exceeded the profitable limit of growth ; and it 
is only a rise in the price of wheat — and not lower prices — that 
could justify the outlay in manure which would be required 
to grow a larger crop. We have abundant evidence that a 
considerable amount of the nitrogen of the salts of ammonia 
has been converted into nitric acid during the autumn and 
washed into the drains during the winter. At the time of the 
application of the nitrate of soda in the spring, the plots receiv- 
ing the ammonia had lost more or less nitrogen, and until 1877 
the relative crop-producing power of nitrogen as ammonia, and 
as nitric acid in the form of nitrate of soda, was not carried out 
on equal terms. Since 1877, plot 7 A and B has received its 
dressing of salts of ammonia in the spring, while we have 
