S22 = 556 Influence of Chemical Discoveries 071 ' j 
potash-salts having given unsatisfactory results, but no doul 
there are other farms where it would be necessary to add potas 
in some form or other to the manuring agents employed if th 
whole produce were sold off land which naturally contains potas 
in more limited quantities than Mr. Prout's. 
CHAPTEE III. 
Manures. 
Altogether, then, our knowledge of the agricultural cap; 
bilities of the various classes of soils found in England has bee 
greatly extended during the last fifteen years, and, in const 
quence, a general improvement has taken place in the cultivj 
tion of the land. Furthermore, the recent achievements by agr: 
cultural chemists, who have studied experimentally questior 
relating to the exhaustion of soils, and the means of incrcasin 
their productiveness, have had the effect of breaking down, in 
great measure, the rigid adherence to farm covenants prescribin 
a strict observance of certain rotations of crops, regulations as t 
the sale of produce, &c., and have rendered the cultivator of tb 
land more independent in pursuing the course of cropping, systei 
of manuring, and general farm-management, which local cor 
siderations and actual experience have pointed out to yield t 
him the best economical return without permanently injurin 
the land. 
Of all the constituents of soils, none affects so much the 
productive powers as nitrogen, in a condition in which it . 
available for the use of plants, and none is so rapidly remove 
from the land than available nitrogen, by the production of cor 
and other crops, by drainage, and by other yet unexplaine 
causes. 
In a certain sense, it is the available nitrogen which main! 
imparts condition to the land, or imparts to it an acquired fe 
tility, which may be described as " good condition," and whic 
it rapidly loses again if the supply of suitable nitrogenous manui 
is withheld for a few years. Speaking with reservation, it may I 
said, on the other hand, that the standard of natural produce, ( 
the permanent fertility of different soils, mainly depends upo 
the larger or smaller quantities of available phosphoric acii 
potash, lime, and other of the more important ash-constituents i 
plants, which exist in an available form in a given area an 
depth of land. Unquestionably, nitrogen in the shape of ammi 
nia-salts, or as nitrates or nitrogenous organic matters readil 
entering into decomposition and furnishing nitrates as ultima 
