Issued April 10, 1913. 



United States Department of Agriculture, 



BUREAU OF SOILS CIRCULAR No. 76. 

 MILTON WHITNEY, Chief of Bureau. 



U. S. DEPARTMENT OP AGRICULTURE, 



Washington, D. C., January 25, 191,1. 



Star I have the honor to transmit herewith the manuscript of a report covering 

 investigations of alunite and kelp as potash fertilizers, by J. J. Skinner and A. M. 

 Jackson, of this bureau, and to recommend that this article be published as Circular 

 No. 76 of the Bureau of Soils. 



Respectfully, MILTON WHITNEY, 



Chief of Bureau. 

 Hon. JAMES WILSON, 



Secretary of Agriculture. 



ALUNITE AND KELP AS POTASH FERTILIZERS. 



By J. J. SKINNER and A. M. JACKSON, 

 Scientists in Soil Fertility Investigations. 



The investigations by this bureau of the fertilizer resources of the 

 United States has led to suggestions from time to tune of the use of 

 certain minerals and of kelp as potash fertilizers. The use of these 

 substances as sources of potash salts is described in other publica- 

 tions. In this paper are given the results of several experiments 

 showing the effect of the mineral alunite and of kelp on soils. 



Alunite has been described in a circular by Waggaman l as a double 

 sulphate of potassium and aluminum which, on heating, first gives off 

 water and sulphur trioxide, leaving a residue consisting largely of 

 potash alum, and on further heating at a higher temperature decom- 

 poses with an evolution of the oxides of sulphur, leaving the final 

 residue composed chiefly of potassium sulphate and alumina. Wag- 

 gaman suggested that it might be more practicable from an economic 

 standpoint to use ignited alunite directly as a fertilizer than to 

 leach the potassium sulphate from the residue. He found that a 

 large amount of water is required to free entirely the ignited residue 

 from soluble salts and that the subsequent evaporation is tedious 

 and expensive. 



1 Alunite as a source of potash. Cir. No. 70, Bureau of Soils, U. 8. Dept. Agr. (1912). 

 77329 Clr. 7613 



