EXPERIMENTS ON THE MIXED HERBAGE OF PERMANENT MEADOW. 371 
as much removed in the total produce of the 20 years, as had been supplied during the 
eight years. But obviously we must not assume that the whole of the nitrogen of the 
crops was derived from the manure. It would be nearer the truth to deduct the amount 
obtained in the unmanured produce, and to suppose only the so reckoned increase to be 
due to the manure. But, inasmuch as the manured produce contained considerably 
more gramineous herbage, which would probably depend largely on the artificial supply 
of nitrogen, and, further, as it contained upon the whole less total leguminous 
herbage, which would depend more on natural sources, it is probable that the manured 
produce might derive less nitrogen from such sources than the unmanured, especially 
in the presence of the presumably more readily available supply by the manure. Still, 
it is doubtless a nearer approximation to the truth to assume that only so much of 
the nitrogen of the manured produce as was in excess of that of the unmanured was 
derived from the nitrogen of the manure. Beckoned in this way, only 10’4 per cent, 
of the estimated supplied nitrogen was recovered as increased yield during the eight 
years of the application, only 6 per cent, more during the next six years, and only 1 ‘7 
per cent, during the second six years since the application ; making, in all, a recovery 
as increase during the 20 years, of about 18'1 per cent, of that supplied in the first 
eight years. 
Thus, on the supposition that the whole of the nitrogen of the produce was derived 
from the manure, there would still remain, at the end of the 20 years, about 41 per 
cent, of the 1600 lbs., or about 658 lbs., not accounted for. But on the supposition 
that only the increase above that in the unmanured produce was derived from the 
manure, which is doubtless at any rate much nearer the truth, there would remain 
unaccounted for, at the end of the 20 years, 81'9 per cent, of the nitrogen supplied— 
that is, about 1315 lbs. ; and yet, during the last six years of the 20 less than 2 per 
cent, of the original amount supplied was recovered as increase. The prospect of 
recovering the whole, or even a considerable proportion, would thus seem, to say the 
least, extremely remote. 
The question arises—whether this large amount of unrecovered supplied nitrogen does 
remain in the soil, and in such a condition of combination, and distribution, as to be 
available to succeeding crops \ or whether some of it be not lost by drainage, or in 
other ways, and the remainder so locked up, or distributed, as to be so slowly recover¬ 
able, if ever, that it can be reckoned of scarcely appreciable practical value ? 
Samples of the soils of all the experimental grass-plots were taken in February and 
March, 1876—that is, after the experiments had been in progress for 20 years, and 
before the next growing season had commenced. Table XXI. shows, for the un¬ 
manured plot (3), and for the plot (2) manured for eight years with farmyard manure, 
and then unmanured for 12 years— 
(1) The calculated average amounts of soil, free from stones, and free from moisture 
expelled at 100° C., in pounds per acre, for each layer of nine inches down to a depth 
of 54 inches ; 
3 b 2 
