On Agricultural Chemistry. 



27 



impunity continuously exhaust our soils in the growth of corn by 

 its means ; but, on the contrary, fully admit that under such a 

 course our mineral supply would soon become deficient. This is 

 not the condition of British agriculture, and it is not for such 

 circumstances, therefore, that we have at present to provide. 



But to recur to the summary table. We see that notwithstand- 

 ing in the two cases there was an equal and very liberal supply of 

 minerals in 18a and 18^, we have with the cessation of am- 

 moniacal supply in the latter, in 1846, a produce 10 bushels less 

 than in the former, where the ammoniacal salts were continued. 

 The produce of 18Z>, indeed, with the minerals only, is 3i bushels 

 of corn and about 380 lbs. of straw more in 1846 than on the 

 unmanured plot ; but this exhaustion, by means of a liberal pro- 

 vision of minerals, seems to have been not without its effect upon 

 the succeeding crop; for although, in 1847, Plots 18<2 and 18^ 

 are equal, both in mineral and ammoniacal manure, we have in 

 the latter — which we have just seen gave 3 bushels increase 

 under mineral only, in 1846 — 3 bushels less in 1847 than 18a. 

 The straw, however, of 18Z> is about 300 lbs. heavier than that 

 of ISa. 



We may here observe that the production of straw, as well as 

 that of grain, would seem to be intimately connected with the ex- 

 penditure of nitrogen derived through the roots of the plant, and 

 had we time to consider the question more fully on this occasion, 

 we should not have dwelt so exclusively on the production of corn 

 alone as we have done. We may, however, remark, that the pro- 

 duction of a heavy crop of straw in a wet season is probably, from 

 the cause alluded to, a very dearly purchased produce. 



We have already said that, excepting in the first two seasons, 

 the mineral manures of \7h were exactly the same as those of 

 18a and 18&, and although we have seen that the minerals of 

 these plots have rendered the ammoniacal supply more effective 

 than it was on 10a without the minerals, yet we observe that 

 when, in 1847 and 1848, we give to 17 h an additional quantity 

 of ammoniacal salt, the produce is increased beyond that of 18a 

 and ISZ*. Thus we have in 1847, with an increased amount of 

 ammoniacal salt on 11 h, 3^ bushels more dressed corn and about 

 400 lbs. more straw than on 18a with its equal supply of minerals : 

 and again, we have in 1848, on 17 h, two bushels more dressed 

 corn and 400 lbs. more straw than on 18a. It is clear then that 

 the minerals supplied, which have been throughout much more 

 than equivalent to those taken off in the increased produce, were 

 only available so long as there was a liberal provision of nitrogen 

 in the soil; and that when this artificially supplied nitrogen was 

 exhausted, the minerals remained inactive and useless. We have, 

 then, in the very cases where minerals gave an increased produce. 



