472 Report of Experiments on the Growth of Wheat. 
Plot 4, unmanured for the 12 years only, and manured for 7 years 
previously with superphosphate of lime and ammonia-salts, and 
for 1 year with the ashes of farmyard dung (supplying- very much 
more phosphoric acid than was removed in the crops, and con- 
siderably more of nitrogen and of every mineral constituent than 
was removed in the increase of the crops), gave an annual average 
during the subsequent 12 years of nearly 1^ bushel of dressed 
corn, and a little straw also, more than either plot 3 or plot 20. 
Rearing this difference in mind, we shall see that the result 
accords very well with that of the other unmanured plots ; and, as 
shown more in detail in Section II., usefully indicates the limit 
of effect on immediately succeeding crops of an unexhausted 
residue from previous manuring. It is worthy of remark, how- 
ever, that the produce of this plot had nearly as high a pro- 
portion of corn to straw as that of any in the entire series ; being 
only surpassed on this point by that of plots 0 and 5, on which, 
as on plot 4, phosphoric acid would be present in large pro- 
portion relatively to other constituents, when compared with the 
condition of other plots in this respect. 
An average annual produce of wheat, amounting to from 15 to 
10 bushels of corn, and from' 15 to 16 cwts. of straw, without 
manure of any kind, is looked upon by many as an extraordinary 
yield, and as indicating a somewhat unusual quality of land. There 
is no doubt that it bears a higher proportion than might be ex- 
pected, to the produce obtained, even under rotation with periodical 
manuring, in a large majority of cases where land is badly farmed, 
and deficient range and aeration of soil, luxuriant weeds, and 
defective manuring, have all their share in the miserable result. 
The experimental land, though kept extremely clean, was not, 
however, ploughed more deeply than in the ordinary practice of 
the farm ; and, there can be little doiabt, that a large proportion of 
those soils of the country which are recognised as possessing 
average wheat-producing qualities, would yield very similar 
results, if kept equally clean and otherwise as well cultivated ; 
whilst some would, under like conditions, produce much more, 
though, many light soils probably much less. 
Average Annual Produce hij Farmyard Manure. 
The average annual produce by farmyard manure over the last 
12 years was 35$ bushels of dressed corn, and 3869 lbs. or about 
34£ cwts. of straw ; equal to an average annual increase over the 
produce of plot 3 of nearly 20 bushels of corn, and nearly 20 cwts. 
or 1 ton of straw. 
As has been already pointed out (see Table XXIII. and com- 
ments thereon), whilst the average annual produce without 
manure was nearly the same during the earlier and the later 
