380 
MESSES. J. B. LAWES AND J. H. G1LBEET ON THE EESIJLTS OF 
nitrogen would probably be gathered up before it finally passed beyond the reach of 
vegetation, than in the case of a single cereal crop grown year after year on the same 
land. For somewhat similar reasons it might indeed have been expected that, with 
the very varied herbage of grass-land, and possession of the soil by the roots of many 
descriptions of plant, the year round, a better result would have been obtained with 
the mixed herbage as compared with the cereal crops, than the evidence, as it stands, 
would show. That it was not so, may perhaps be taken to indicate that, in estimating 
the proportion of the nitrogen of the produce due to that supplied in the manure, it 
should not be assumed that as much was derived from natural sources as in the case 
of the unmanured produce, but more should be reckoned as derived from the manure. 
So much for the nitrogen. It will be of interest also to consider whether or not 
the most important mineral constituents of the manure are as slowly available to 
the crop. 
Of the amount of lime estimated to be supplied in the manure in the eight years, 
only about 12^ per cent, was obtained in the total produce of those years, about 9 per 
cent, in the next six, and little more than 4 per cent, in the last six years, making in 
all only about 25-| per cent, in the 20 years. Deducting the yield in the unmanured 
produce, however, there was an increase obtained representing only 3^ per cent, of the 
amount estimated to be supplied during the eight years, little more than 2 per cent, 
in the next six years, a small fraction of 1 per cent, in the second six, and not quite 
6 per cent, in the 20 years. 
Of the magnesia, a much larger proportion would appear to be taken up; that in 
the total produce (of the 20 years) amounting to nearly 70 per cent., and the estimated 
increased yield to about 21 per cent, of that supplied. 
Of the potass estimated to be supplied in the eight years, the produce of the period 
contained 44 per cent, as much, that of the next six years 22^ per cent, more, and 
that of the last six years 10ijr per cent, more; in all, 77 per cent. But the increased 
yield of potass represented only 30-g- per cent, during the eight years, scarcely 13 per 
cent, during the next six, and only 4-| per cent, during the last six years; in all, only 
about 48 per cent, of that supplied. This result, however, upon whichever basis taken, 
shows a great effect from the potass of the dung, though a much diminishing one in 
the later years. It is known that potass is, at any rate in moderately clayey soils, 
very little subject to loss by drainage; but it would appear that the unrecovered 
residue becomes so locked up (or distributed) as to be but slowly available to suc¬ 
ceeding crops. 
In the presence of an abundant supply of potass, there was even less soda taken up 
in the manured than in the unmanured crop, during the years of the application; 
though, during the subsequent years, there was some, but comparatively little, increase 
in the amount compared with that in the unmanured. 
Of phosphoric acid, a larger proportion of that supplied, though not so much as of 
the potass, would appear to be taken up. In the 20 years, about 57 per cent, of the 
