CHAPTER XXVIII. 
MORE ABOUT FERTILIZERS. 
N the past we believed that fertilizers acted. 
as plant foods and that the substances to be 
applied must contain one or more of four 
elements which are probably the most important 
to the plant, namely: Nitrogen, phosphorus, 
potassium and calcium. Several other elements 
go to make up the plants; but these are con- 
sidered most difficult for the plant to secure 
from the soil and were therefore of the most 
importance for the farmer. 
Trials, by experimental work with different 
plants, soon showed that the forms of combina- 
tion of these elements make a great difference. 
For example, nitrogen is now applied either in 
the form of nitrate of soda and of potassium, 
which is called saltpetre, or in the form of sul- 
phate of ammonia; or, it may be applied as or- 
ganic matter in dried blood, tankage, hoof- and 
horn-meal and even muck. 
Both the nitrate and sulphate forms are readily 
dissolved, but the nitrate form is the one in 
which plants take up their nitrogen, so that either 
nitrate of soda or saltpetre is specially valuable 
for forcing a quick growth. The effect may be 
seen upon plants in a very few days after it is 
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