Price of Wheat, dter 40 Harvest-Years, 1852-3 to 1891 - 2 . 85 
The Unmanured Plot . — There can be no doubt that the 
produce of this plot has gradually declined ; and, independently 
of the evidence of diminishing produce, analyses of the soil, at 
different periods, show that there has been a gradual diminution 
in the amount of nitrogen in it. But, owing to the great 
fluctuations in the amount of produce from year to year depen- 
dent on season, it is by no means easy to estimate the decline 
due to exhaustion of the soil, as distinguished from variations 
due to the seasons. 
In the first place it is difficult to say what figure should be 
adopted as the standard produce of the plot by which to compare 
the yield from year to year. The whole field was manured with 
farmyard dung in 1839, and then grew turnips (fed on the land), 
barley, peas, wheat, and oats, before the commencemeut of the 
experiments in 1843-4. The plot then grew eight crops of 
wheat without manure, to 1850-1, before the commencement 
of the period to which our present estimates refer. Although, 
at the conclusion of the five-course rotation since manuring 
above described, the land would doubtless be, in an agricultural 
sense, so far exhausted as to require re-manuring, there can be 
no doubt that there would nevertheless be some accumulation 
due to comparatively recent manuring and cropping. It would 
be supposed, however, that the growth of wheat for eight years 
in succession without manure would remove most, if not all, 
accumulation which could be attributed to comparatively recent 
treatment. Indeed, there can be little doubt that the land 
would suffer more or less exhaustion during those eight years ; 
but, as serving to counteract the tendency to decline in yield 
from exhaustion during that period, it happened that, taken 
together, those eight seasons were of more than average pro- 
ductiveness. 
Upon the whole, therefore, it was, in 1880, considered that 
the average produce of those eight years, which was 17 bushels 
per acre, at 01 lb. per bushel, might be taken fairly to represent 
the standard produce of the unmanured land, independently of 
material exhaustion. Adopting this as the standard, we en- 
deavoured to estimate whether, or to what extent, there had been 
decline in yield during the twenty-eight years, due to exhaustion, 
independently of variations due to season. To this end we 
first endeavoured to calculate what should be the produce in 
each year subsequent to the first eight, provided there were no 
decline from exhaustion, but only variation from season. As- 
suming that, if there were no exhaustion, it would each year 
fluctuate from the standard under the influence of season in the 
same proportion as the fluctuation of the adopted average yield 
