* 
2 BULLETIN 149, U. S. DEPARTMENT OF AGRICULTURE. 
elements—nitrogen, potassium, phosphorus, and calcium. These ele- 
ments are therefore spoken of as fertilizing elements. i 
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 
fertilizingelements. 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 calclum 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 radic- 
active material to the soil. : 
