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, 1 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- 

 lated, 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." 



ij. Dept. Agr., Victoria, 10, 417 (1912). 



