SiGe TIN OF THE 
y 
USDEPARTNENT OFAGRCULTURE © se 
No. 149 
Contribution from the Bureau of Soils, Milton Whitney, Chief. 
December 1}1, 1914. 
THE USE OF RADIOACTIVE SUBSTANCES AS 
FERTILIZERS. 
By WituiAM H. Ross, 
Scientist in Soil Laboratory Investigations. 
INTRODUCTION. 
A fertilizer may be conveniently defined as any commercial mate- 
rial which, when added to a soil that has been brought into suitable 
condition for the growth of plants, produces an increased yield in 
crop production. In producing this result a fertilizer may act in 
various ways, bringing about an improvement in the chemical, 
physical, or biological condition of the soil, and generally m all of 
these. An improvement in all these three classes of soil conditions 
may also be brought about by other farm operations, as by tillage, 
green manuring, and the rotation of crops. To what extent these 
latter operations should be supplemented, or even in a measure re- 
placed, by the use of fertilizers so as to lead to the most profitable 
returns, is a matter which has given rise to a great. deal of contro- 
versy, and there still remain considerable differences of opinion on 
the subject. This is due in a large measure to the fact that the 
results obtained from experiments carried on locally and under 
special conditions of farming are often quoted as applying to the 
whole country, and toe conditions of farming of an entirely different 
type. It is quite evident, however, that any set rules governing the 
use of fertilizers in farm practice are only applicable when all con- 
ditions of soil fertility, climate, cultivation, and crop production are 
about the same. Fertilizers must therefore be used differently under 
different conditions, and it is universally admitted that when in- 
telligently applied, where the conditions warrant it, the use of the 
proper fertilizer brings profitable returns. 
_ A great many forms of fertilizers are used, but all those com- 
mercial products which are recognized as of value in the fertilizer 
trade have the common feature of containing one or more of the 
Noty.—tThis bulletin discusses the fertilizer value of radioactive materials; it is suit- 
able for distribution in any part of the United States. 
58972°—14 
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