for Twenty Years in succession on the same Land. 305 
straw and total produce, than over the first 6 years. It would 
be concluded, therefore, that the wheat plot was not unduly 
exhausted at the commencement ; and that the comparison 
between tlie two crops over the first 6 3'ears would, probably, 
be but little open to objection on the score of difference in pre- 
vious condition of the land. 
Taking first the produce per acre of the two crops, there is, as 
with the smaller quantity of ammonia-salts, considerably more 
barley-grain than wheat-grain ; but, on the other hand, less 
barley straw ; and an annual average of only 446 lbs. more 
total produce (corn and straw) of barley than of wheat, instead 
of nearly 1400 lbs., as when the smaller quantity of ammonia- 
salts was employed. This difference of result is doubtless due 
to the proportionally much less increase of barley for a given 
amount of ammonia in manure with the larger than with the 
smaller supply of ammonia-salts. The probability is that, in 
the case of the autumn-sowing for the wheat, the distribution, 
the state of combination, and the loss by drainage are such, that 
the quantity of the supplied nitrogen remaining available within 
a given range of soil when active growth commences in the 
spring is not excessive, and does not induce over luxuriance ; 
whereas, the same amount applied in the spring for the barley, 
being less subject to either rapid distribution or drainage, in- 
duces too much luxuriance, and, consequently, leads to the 
laying of the crop, and to reduced eventual productiveness. 
The less difference between the produce of wheat and of 
barley when the larger quantity of ammonia-salts is applied, is, 
therefore, due, in great measure, to a proportionally less effisct on 
the barley. Nevertheless, the fact of a less amount of produce 
per acre from a given amount of mineral manure and ammonia- 
salts applied in the autumn for wheat, than from the same 
amount applied in the spring for barley, is again clearly 
illustrated. 
If, however, the inci-ease of produce with ammonia over that 
without it be taken as the basis of illustration, the result is 
different. Thus, instead of an annual average of 446 lbs. more 
total produce (corn and straw together) of barley than of wheat, 
there is of increase of produce by the mineral manure and 400 lbs. 
of ammonia-salts over that by the mineral manure alone, less in 
the case of the barley than of the wheat. The average annual 
deficiency is 137 lbs. of corn, and 160 lbs. of straw, or 297 lbs. of 
total produce (corn and straw together). This difference is 
accounted for by the fact that there is an average of 743 lbs. 
more total produce of barley than of wheat by the mineral 
manure alone ; there is, therefore, so much more to be deducted 
from the produce by the mineral manure and the ammonia-salts 
