606 
Rotation of Crops. 
7,626 lb. in 1863 ; and lastly, on tbe mixed manure plot, only 
2,478 lb. in 1879, but 8,837 lb. in 1863. 
Tbe cases cited are those of tbe most extreme fluctuations 
due to season ; but a glance at tbe columns will show that there 
were very considerable variations in other years, under each 
condition as to manuring, or other treatment ; whilst the 
amounts of the variations differ more or less under the different 
soil conditions. It will be obvious, therefore, that if we would 
fairly compare with one another the effects of the varying con- 
ditions, it is important to take the average results of a sufficient 
number of years to eliminate the influence of the varying 
seasons. Most of our illustrations will, therefore, be drawn 
from the average results over the eight years of wheat in the 
second to the ninth courses ; but some reference will also be 
made to the averages for the tenth and eleventh courses. 
Let us first compare ■ the average amounts of produce of 
grain under the three main conditions as to manuring, 
excluding, however, those obtained on the portion of the un- 
manured plot where the roots were fed on the land, and where 
beans or clover were grown in the third year of each course ; 
as the crops, especially of the barley and of the wheat, were 
somewhat adversely affected by a dell on one side of the plot, 
the surface soil being in consequence comparatively shallow. 
The figures show that, on the three portions, the produce ranged, 
without manure, from 26 to 284 bushels ; with superphos- 
phate from 284 to 31f ; and with the mixed manure from 304 
to 33£ bushels. Or, taking the amounts of total produce 
(grain and straw together), the range of amounts is — without 
manure from 4,407 to 4,976 lb. ; with superphosphate from 
4,841. to 5,658 lb. ; and with the mixed manure from 5,808 to 
5,932 lb. There is, therefore, both in grain and in total 
pi’oduce of the fourth crop of the course, an obvious difference, 
but certainly less than might have been expected, due to the 
varying conditions as to manuring in the first year, sepa- 
rated from the fourth by the growth and removal of the inter- 
mediate crops. 
Next, comparing the effects on the fourth crop — the wheat — 
of the removal of the first — the turnips — or the retention of 
them, or of most of their constituents, on the land, it is seen 
that without manure, under which conditions there were prac- 
tically no roots grown, the difference of result from removal or 
otherwise is quite immaterial, and is probably accidental. 
With superphosphate alone, and more roots grown, the nitro- 
gen of which was doubtless obtained from previous accumula- 
tions within the soil, the removal or the retention on the 
