Experimental Plots at Rothamsted, from 1864 to 1883. 441 
in the 6600 lbs. of total produce obtained, in excess of that grown 
on plot 5, during the next 10 years — which produce would not 
contain more than 60 lbs. of nitrogen — could have its source in 
the salts of ammonia as such, except so far as a portion of the 
first crop was concerned. 
All the evidence, indeed, points to the residue of the crop 
itself as being the source of the unexhausted manure ; and it is 
quite certain that the very large amount of roots possessing 
considerable fertilising influence, which some of our rotation 
crops leave in the ground, have much to do with their value 
as restorative crops. In 1865 samples of soil taken from the 
various experimental plots were submitted to analyses, and the 
percentage of nitrogen in the first 9 inches of soil on plot 16 
was higher than on any other plot receiving artificial manures ; 
while, in 1881 — after 17 unmanured crops had been taken — 
when analyses of the soil were again made, it was found that 
the percentage of nitrogen was considerably reduced, and it was 
in fact not much higher than that on the unmanured plot. 
Farmyard Manure. 
From the commencement of the permanent wheat experiment, 
one plot has received annually 14 tons of ordinary farmyard- 
manure per acre. No attempt has been made to ascertain by 
means of chemical analysis the composition of the manure 
applied, for two reasons : (1) in the earlier years of the experi- 
ments, the importance of knowing the exact amount of the 
various ingredients applied to the soil was not well understood ; 
(2) later on, the want of success in a very careful attempt to 
ascertain the exact composition of some box dung at Woburn, 
satisfied us that it was better to trust to a composition derived 
from a variety of analyses of farmyard-manure, than to give the' 
composition derived from analyses in the accuracy of which we 
could feel no confidence. 
The following table gives the estimated amount of some of the 
more important ingredients supplied to the soil annually in 
14 tons of farmyard-manure, as also of the amount of ingre- 
dients supplied in artificial manure on plot 7 : — 
Table XXVIII. 
Dry organic 
M&tter. 
Xitrogen. 
Pho.sphate of 
Lime. 
Potasli. 
lbs. 
lbs. 
lbs. 
lbs. 
Duug, Plot 2 .. .. 
7526 
200 
155 
168 
Artificial, Plot 7 .. 
86 
140 
100 
2 o 2 
