for Twenty Years in succession on the same Land. 361 
was practically left fallow for the barley ; whilst, from the 
superphosphated plot, the quantity removed would considerably 
exhaust the land,* Again (omitting- the first year), the produce 
after the removal of the full-manured and larger crops of turnips 
was uniformly, and on the average, very much higher than after 
the removed superphosphated turnips, and also generally, and 
on the average, higher than after the unmanured turnips. This 
larger produce of barley after the removal of the larger crops of 
turnips grown by the mixed manure, is doubtless due to the fact 
that there would still be a considerable residue of the manure 
left within the soil. 
It has already been shown, both by the results of the growth 
of barley year after year on the same land, and by those of its 
growth after the removal of a series of mineral-manured turnip- 
crops, that a liberal supply of mineral constituents alone is 
insufficient to secure a fair crop of barley. In both sets of expe- 
riments it was also shown that the further addition of nitrogenous 
manure raised the produce to a maximum. It might safely be 
concluded, therefore, that the larger produce of barley after the 
full manured, than after the superphosphated or the unmanured 
turnips in rotation, was not attributable to any residue of mineral 
constituents alone which would be left after the removal of the 
highly manured roots ; and that the larger produce after the un- 
manured than after the superphosphated turnips was not due to 
a less exhaustion or greater accumulation of available mineral 
constituents where the smaller crop of turnips was removed. 
But other evidence is not wanting to confirm the conclusion 
that the higher produce of barley after the unmanured than after 
the superphosphated turnips in rotation, and the higher produce 
still after the full-manured than after the unmanured turnips, 
were each due, in great part, to an accumulation of available 
nitrogen within the soil for the barley. Thus, it is estimated 
that, from the superphosphated plot, which yielded the smallest 
produce of barley, the turnips would probably, on the average 
of the five seasons in which they grew, remove about 50 lbs, of 
nitrogen per acre, or more than would be supplied in 200 lbs. 
ammonia-salts. From the unmanured plot they would remove 
only from one-fourth to one-third as much ; and much less than 
would be contained in the increased produce of a corn-crop that 
would result from the fallowing of the land ; so that, presumably, 
there would remain a considerable available store for the barley. 
From the mixed-manured plot, again, though the turnip-crop 
of the first course most probably removed considerably more 
* The larger produce of barley on the superphosphated than on the unmanured 
plot in 1869 is only apparently an exception; for, as has been stated, the turnips 
failed in 1868, and there was, therefore, nothing removed from either plot in that 
year. 
