Experimental Plots at Rothamsted, from 1864 to 1883. 433 
It will be observed that in 1848, when 10 B received 
mineral manures as well as salts of ammonia, the produce 
was 25| bushels per acre, as against 19^ bushels per acre on 
plot 10 a, which received the same salts of ammonia without 
minerals. On the other hand, when 10 b, in 1850, received 
minerals alone, the produce was only 18 bushels per acre as 
against 27 bushels obtained on 10 a, which was manured with 
salts of ammonia only. 
Turning now to the period of 8 years each, it will be seen 
that in every case the produce of 10 B was larger than that of 
10 A ; the difference is however a declining one, being in the 
first 8 years not quite 5 bushels per acre per annum, in the 
last 5 years 1^ bushels per acre, and over the whole period not 
quite 3 bushels per acre per annum. 
It is well known that the drainage-water that comes from 
cultivated fields contains but a very small amount of potash, 
and frequently no phosphoric acid ; we have no difficulty, there- 
fore, in tracing the increased produce obtained by lO B over 
10 a to the minerals applied to the former in 1848 and 1850. 
The potash and phosphoric acid applied to both 10 A and 
10 B must have been removed in the crops many years ago, but 
the much greater amount which 10 B received in the earlier 
years of the experiment must have caused the resources of the 
soil to be more largely drawn upon by the crops upon plot 10 A, 
than by those upon plot 10 B. 
These large applications of potash and phosphoric acid — 
although applied in the form of soluble compounds — appear to 
enter into very fixed combinations, somewhat similar to those 
already existing in the soil : and in this respect they differ 
altogether from compounds of ammonia and nitric acid, as the 
latter appear to be either destroyed or washed away, unless they 
are fixed in vegetation, while the former are fixed by the soil 
itself, and are only taken out of it by means of vegetation. 
Plots 17 and 18, 
In the last experiment it was shown that potash and phos- 
phoric acid were producing an influence upon the wheat crop 
33 years after their application. 
In the experiment to which we are now about to refer we have 
to trace the unexhausted residue of another substance perfectly 
soluble in water. On plots 17 and 18 the mineral manures 
and the salts of ammonia are never used together. When 
plot 17 receives minerals, plot 18 receives salts of ammonia ; 
and when plot 18 receives minerals, plot 17 receives salts of 
ammonia. During the 32 years of the experiment each plot 
