Some Principles Underlying the Use of Fertilizers 
* 
A. W. Blair. 
Mr . President, Ladies and Gentlemen : 
As one looks back over the reports of 
this society, he is struck with the great 
variety of opinions that have been ex¬ 
pressed with reference to the use of fer¬ 
tilizers for any given crop; and at first 
it might seem that we have made but lit¬ 
tle progress. On the other hand, we need 
not expect agreement of opinion; indeed 
in many cases there could not be such 
agreement. We must take into consid¬ 
eration the numerous types of soil, the 
difference in seasons and in methods of 
culture, and the personal equation. Be¬ 
cause A has used a certain formula or 
a certain brand of fertilizer with success 
and profit, it does not follow that B, 
working on a different type of soil or 
using different cultural methods, or with 
different moisture conditions, will have 
equal success with the same fertilizer. 
We cannot adopt certain formulas or 
certain materials and confidently say that 
they are good for all times and in all 
places. We may, however, get at some 
of the underlying principles which gov¬ 
ern the use of plant foods, and the man 
who does this will apply his fertilizers 
with more intelligence than the one who 
pays no heed to these principles. 
PLANT FOOD AND SOIL FERTILITY. 
We must learn that the terms plenty of 
fertilizer, and soil fertility, are not synon¬ 
ymous. Soil fertility refers to the crop- 
producing power of the soil, while the 
fertilizer is only one of several necessary 
conditions for crop production. There 
must be in addition, moisture, warmth, 
aeration, drainage, good texture, and the 
presence of bacteria in order that our 
soil may be productive. The crop-pro¬ 
ducing power of the soil constitutes its 
fertility. We are coming more and more 
to recognize the value of natural agen¬ 
cies in crop production and we must learn 
to so direct these natural agencies that 
they will be most potent for our benefit. 
Conditions must be made favorable for 
their activity. In the past we have per¬ 
haps relied too much upon the efficacy of 
commercial fertilizers without due regard 
to their effect upon the soil and upon 
other agencies that are at work, and in 
some instances we have entirely ignored 
other vital requirements of plant produc¬ 
tion. We have practiced constant culti¬ 
vation, and have as constantly applied 
commercial fertilizers until in some cases 
we have brought about unnatural condi¬ 
tions, and the result has been that we 
have had more than our share of dis¬ 
eases, insect pests and the like. I do not 
