Chapter XII. 



FERTILIZERS. 



It is generally recognized that the great practical problem con- 

 fronting the soil chemist is the proper use of soil amendments or 

 fertilizers. The farmers of the United States now spend 

 annually for fertilizers upwards of $100,000,000. It is estimated 

 by various authorities that a large fraction, perhaps as much 

 as three- fourths, of the material represented by this expenditure 

 is misapplied for lack of intelligent direction. Yet all of this 

 enormous mass of fertilizers can be used to advantage. Great 

 as it is, it is relatively small beside the total which will, and 

 must, be used in a not distant future, with the growth and 

 development of intensive methods of cultivation consequent upon 

 the rapid settling of the country, the practical disappearance of 

 new lands and the increase in money value of the old lands. 

 The commercial importance of the problem, therefore, makes it 

 desirable that special emphasis should be given to fertilizers from 

 the point of view developed in the preceding chapters. It should 

 be recalled that the use of fertilizers constitutes one of the 

 three great general methods of soil control, and further that 

 while tillage methods, crop rotations, and fertilizer applications 

 can be used to supplement one another, no one of these methods 

 can be expected to take satisfactorily the place of another. 



Crop production is dependent upon a large number of factors. 

 Upon the rainfall, both as to the amount and distribution; upon 

 the sunlight, as to amount and distribution; upon the chemical 

 and physical properties of the soil; soil bacteria and other 

 biologic agents; enzymes in the soil; biological factors in the 

 plant, and probably many other things. Opinions do and will 

 continue to differ as to what these factors are, but at least every 

 one agrees that they are many. 



Attempting to formulate these factors develops fundamental 

 difficulties, since it is not positively known how far the variables 

 are dependent or independent, and we have no idea as to the 

 nature of the function or functions. The weight of existing 



