818 = 552 Influence of Chemical Discoveries on 
Effect of dif- 
ferent ma- 
both corn and straw, than the annual application of 14 tons 
farmyard-manure per acre. 
The Table on page 551 embraces some of the most instructi 
results of experiments on the continuous growth of wheat a 
barley. 
It will be seen from the preceding Table that mineral manur 
and notably superphosphate, had a better effect upon barley th 
upon wheat ; further, that in combination with minerals nitr; 
of soda produced a larger increase, both in corn and straw, tb 
minerals combined with salts of ammonia. This agrees w 
with the general experience of the British farmer, who derr 
much advantage from the use of a mixture of nitrate of soda a 
superphosphate as a manure for barley ; whilst for wheat, gro 
on good clay-soils, a top-dressing of nitrate of soda alone p 
duces as large an increase as a mixture of nitrate with sup 
phosphate. On light soils, comparatively poor in availai 
potash and phosphoric acid, it would not be safe to rely upon 
exclusive use of nitrate of soda or of salts of ammonia for p - 
ducing a succession of remunerative corn-crops. Even on hee • 
land it is desirable to add phosphates to the nitrogen(j 
manures, for although the phosphoric acid in most soils is ; 
nearly so rapidly removed in the growing crops or by drain; 
as available nitrogen is, yet as a rule, phosphoric acid is ' 
sparingly distributed in the soil to withstand without injury i 
continuous removal of these important fertilising elements ii . 
succession of corn-crops, top-dressed solely with nitrate of s( i 
and salts of ammonia. 
Messrs. Lawes and Gilbert's experiments clearly prove ; 
advantage of combining mineral with nitrogenous manures ; 1 1 
they show that by the use of such mixed manures the fertilit} f 
the land may be preserved, and better crops often be grown tl i - 
with farmyard-manure. 
Modifications One of the most important advantages of such a system f 
" in™ ^rd° manuring consists in the freedom of action which it gives to J 
ticiais. occupier of land, enabling him to dispense with any recogni I 
system of rotation of crops, and under favourable circumstance; ) 
grow a succession of corn-crops with greater advantage tl i 
by slavishly following the ordinary course of cropping of 
district. 
These experiments have also had a marked influence upon ( 
extended use of nitrate of soda as a top-tlressing for corn-cnj 
They further have induced farmers to grow barley more frequen 
than formerly on heavy land, and in some instances they bj 
led to the adoption of the system of selling, year by year, 
whole or nearly the whole of the growing crops, and of rcstoil 
an equivalent of plant-food in the form of portable fertilisers 
