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i 
USE OF RADIOACTIVE SUBSTANCES AS FERTILIZERS. 11 
reference to any material which when added to the soil brings about 
an increase in the growth of crops. If radioactive manure really 
acts in the way described, it could then be properly called a fer- 
tilizer; and, further, if its function is to give to the plant additional 
power to consume plant food, its effect should be noticed when 
added to the soil alone as well as when mixed with a standard 
fertilizer. 
Field tests with radioactive mineral from still another source 
have been made by Ewart,! Melbourne University. These tests were 
made in two different places, in each of which there were selected 
a series of four plots. In the case of the first series each plot had 
an area of one-third acre. Plot 1 received 50 pounds of superphos- 
phate per acre; plot 2, 50 pounds of superphosphate and 50 pounds 
of finely ground radioactive mineral per acre; plot 3, 50 pounds of 
radioactive mineral per acre; and plot 4 was unmanured. The plots 
used in the second series had an area of approximately one-fourth 
acre, and the same applications were made in this case as in the first, 
with the exception that 59-pound portions of the materials were used 
instead of 50-pound portions. From the yields obtained it was con- 
cluded that “there is no evidence to indicate any beneficial action 
of the radioactive mineral upon the growth and germination of 
wheat, when quantities which could be used in agricultural practice 
are employed. Any stimulating action which it might exercise when 
first applied, seems, if anything, to be converted into an injurious 
action when in prolonged contact. There is nothing, therefore, in 
these results to show that radioactive mineral is of the least benefit 
to wheat when applied in the same manner as manure.” 
CATALYTIC FERTILIZERS. 
In addition to the experiments which have been described on the use 
of the radio-elements as fertilizers, many tests have also been made 
during the last few years of the action on plants of still other ele- 
ments which are not recognized as essential to the growth of plants. 
Among the different elements which have been studied in this way 
may be mentioned copper, nickel, zinc, and lead. These elements are 
of rare occurrence in the soil, and are ordinarily recognized as plant 
poisons, but quite remarkable benefits have been obtained by the 
application to the soil of a very small quantity of a soluble salt 
of these elements. Plants so treated are said to have been stimu- 
jated, and because of the small amount of the material necessary to 
produce noticeable results, these compounds when used in this way 
are spoken of as “ catalytic fertilizers.” 
1J. Dept. Agr., Victoria, 10, 417 (1912). 
