BULLETIN OF THE 



No. 149 



Contribution from the Bureau of Soils, Milton Whitney, Chief. 

 December 11, 1914. 



THE USE OF RADIOACTIVE SUBSTANCES AS 

 FERTILIZERS. 



By Wiixiam H. Ross, 

 Scientist m 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, 

 plrysical, or biological condition of the soil, and generally in 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 to 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 



Note. — This bulletin discusses the fertilizer value of radioactive materials ; it is suit- 

 able for distribution in any part of the United States. 

 58972°— 14 



