286 Report of Experimeata on the Growth of Bar let/. 
Over the whole period, the average annual produce by super- 
phosphate of lime alone, is 25 bushels of dressed corn, and 13^ 
cwts. of straw ; by the mixed alkali-salts alone, 22i bushels of 
dressed corn, and 12| cwts. of straw; and by the two manures 
together, 27tV bushels of corn, and 14^ cwts. of straw. The unma- 
nured produce being 21 bushels of corn, and 12 cwts. of straw, 
the average annual increase is, by the superphosphate alone, 4^ 
bushels of corn, and 1 J cwts. of straw ; by the mixed alkali-salts, 
1^ bushel of corn, and ] cwt. of straw ; and by the mixture of 
the two, 6^ bushels of corn, and 2^ cwts. of straw. 
Neither of these purely mineral manures has, then, sufficed 
to yield anything like a fair crop of barley. The mixed alkali- 
salts alone have given scarcely any increase at all. It was, 
therefore, not in an available supply of potass, soda, or magnesia, 
that the soil was rendered relatively deficient, either by the 
previous ordinary cropping, or by the continuous growth of 
barley. Superphosphate of lime alone gave but little, though 
still notably more increase than the mixed alkali-salts. It would 
appear, therefore, that there was, within the range of the roots, a 
greater relative deficiency of available phosphoric acid than of 
available alkalies. The mixture of the two manures, again, gave 
slightly more increase than either, or than both, used separately. 
The explanation of the effects of these mineral manures, and 
of the great falling off in the produce, not only by them, but 
without manure, probably is, that in each case the produce 
has been limited by the supply of available nitrogen accumulated 
within the soil, whether from previous cultivation, manuring, and 
cropping, or by annual deposition and absorption ; and that, with 
the increased supplies of available mineral matter near the sur- 
face, root-development has been more or less increased, possession 
thus acquired of a greater range of soil, and, with this, access 
obtained to more of its stored-up nitrogen. On this view, the 
condition" of the soil, as distinguished from its normal or 
natural fertility, is at any rate so far as available nitrogen is con- 
cerned, being gradually worked out by the growth of the crop, 
whether without manure, or with the purely mineral manures ; 
and it remains to be seen whether or not the point of normal 
annual produce has yet been reached. 
There are two other plots receiving annually mineral manure 
alone; namely 5 O, and M; the full particulars of which will be 
found in the Appendix Tables. Thev are much smaller, and at 
the opposite end of the field from the other mineral-manured 
plots, and the results seem not altogether comparable with those 
of the latter, though there is less reason to suppose that they are 
not so with one another. Plot 5 O has received annually super- 
