for Twenty Years in succession on the same Land. 
289 
Is the less result with mineral manures on wheat than on barley 
due to the dilution and distribution of the autumn-sown manures 
by the winter rains, and to their having acquired a comparatively 
insoluble condition, resulting in a less active root-development in 
the upper, and more highly nitrogenous layers of the soil, when 
growth commences in the spring ? Is there, consequently, a more 
rapid exhaustion of the accumulated nitrogen within the soil by 
the barley than by the wheat ? Or, does the pipe-draining of the 
wheat-field render the drainage the more free, and so cause a 
greater washing out of nitrogenous compounds in the winter ; 
even from the plots where none are artificially applied ? It is at 
any rate consistent with the supposition that there is a more rapid 
exhaustion of the nitrogen accumulated within the soil, by the 
barley than by the wheat, when each is grown without nitrogenous 
manure, that, according to calculation it appears probable that, 
both without manure, and with purely mineral manure, the 
barley has carried off more nitrogen from a given area than the 
wheat, whilst it has, under both conditions, declined more rapidly 
in annual produce of corn, and without manure in total produce 
also. 
The general result with the purely mineral manures is — that 
superphosphate of lime gave more increase of barley than a 
mixture of salts of potass, soda, and magnesia ; that neither 
the one nor the other, nor the mixture of all, sufficed to raise the 
produce to anything like a fair crop ; and that, with either, the crop 
fell off considerably over the later years. Nevertheless, boththe pro- 
duce and the increase of barley by the mixed mineral manure were 
considerably greater than those of wheat by the same manure. It 
may be concluded that the exhaustion which the soil undoubtedly 
suffered, was not connected with a relative deficiency of any of 
the constituents which these mineral manures supplied. The 
results next to be considered will show in what the exhaustion 
really did consist. 
Average Annual Produce by Ammonia-salts alone, or Nitrate 
of Soda alone. 
Of the four experiments under this head, the first to be noticed 
are those on — 
Plot 1 A with 200 lbs. of ammonia-salts per acre per annum, 
for 20 years, 1852-1871. 
Plot 1 N with 275 lbs. nitrate of soda per acre per annum, for 
19 years, 1853-1871. 
200 lbs. of ammonia salts and 275 lbs. of nitrate of soda, are esti- 
mated to supply the same amount of nitrogen, namely 41 lbs. = 
50 lbs. of ammonia. But it must be noted that the plot subsequently 
