2 BULLETIN 149, XT, S. DEPARTMENT OF AGRICULTURE. 



elements — nitrogen, potassium, phosphorus, and calcium. These ele- 

 ments are therefore spoken of as fertilizing elements. 



It is further recognized that in a very general way the value of a 

 material is proportional to the percentage of the fertilizing con- 

 stituent or constituents present in soluble form. Because of its wide 

 distribution, calcium can usually be obtained locally, and consequently 

 it does not enter into the fertilizer trade in the same sense as the other 

 fertilizing elements. To each of the three remaining elements is given 

 by common consent and as a trade practice a definite value per unit, 

 which varies with the form in which the element occurs; the price 

 set on a standard fertilizer, while thus in a sense an arbitrary one, 

 is nevertheless determined in a scientific way by multiplying the 

 percentages of the constituents present by their prices per unit and 

 adding the products. 



If nitrogen, potash, and phosphoric acid are absent, the fertilizing 

 value of the material as calculated in this way will be zero; and no 

 material, with the exception of certain calcium compounds, as lime 

 and gypsum, that does not contain one or more of the constituents 

 referred to is recognized at present by agricultural scientists as hav- 

 ing commercial value as a fertilizing agent for general farming. 



Notwithstanding these facts there have frequently been placed on 

 the market from time to time various so-called fertilizers which con- 

 tain little or none of the recognized fertilizing elements even in an 

 insoluble form. As a rule these materials consist simply of ground 

 rock, usually of volcanic origin, from various sources, and for which 

 an arbitrary price is asked out of all proportion to the value of 

 the small amount of the fertilizing elements which may be present. 

 Some of these materials, although exploited to quite an extent in 

 the past, have later fallen into disfavor and are now no longer used 

 by anyone, but others of more recent development are still being 

 placed on the market under different trade names. One of these new 

 materials, which is known as " radioactive manure," consists of low- 

 grade uranium-radium ores or ores from which the uranium has 

 been extracted, and it is claimed to bring about by virtue of its 

 radioactivity phenomenal increase in crop yields when mixed with 

 barnyard manure and applied to the soil. Within the past few 

 years the use of this material as a fertilizer has been quite extensively 

 advertised in various parts of the world, and accounts have been 

 given in various scientific publications of numerous results which 

 have been obtained in pot and field tests using radioactive material 

 from different sources. 



The object of this bulletin is to give a review of these results and 

 likewise an explanation of the property of radioactivity, in order 

 that a conclusion may be reached as to the value of applying radio- 

 active material to the soil. 



