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hence, must be furnished if satisfactory yields are 
to be obtained. 
How to furnish these elements — in what forms; 
at what time; and in what quantity — are problems, 
which, like the poor, we have always with us. 
That fertilizers pay is attested every year on 
nearly every farm and with most emphatic proofs. 
That they are often, if not usually, employed 
without the attention due their importance is also 
certainly true. 
The judicious use of fertilizers demands that 
every farmer make not only a study of sources and 
relative values, but also a study of his own soil and 
crop conditions. Fertilizers show their greatest 
profit where the farmer practices thorough prep- 
paration of land and careful tillage. Here it is, too, 
that they can be used in greatest quantities with 
most economical results. 
NITROGEN 
Nitrogen is the most costly element of plant food 
that we buy, and for this reason its production by 
means of home-made manures and legumes should 
be carefully considered. 
Four-fifths of the atmosphere is made of nitro- 
gen, but unfortunately this atmospheric nitrogen is 
in a form not available for plant use. There is a 
compensating influence, however, in the fact that 
nitrifying bacteria seek out the leguminous crops, 
and on their roots store up nitrogen in small 
tubercles, ready for use by the growing plant. 
SOURCES OF NITROGEN 
In commercial forms and factory-mixed ferti- 
