2 ALUNITE AND KELP AS POTASH FERTILIZERS. 



In the experiments made to test the effect of this mineral on the 

 soil both the raw and the ignited alunite were used. The sample of 

 raw aluiMte, containing 10 per cent of potash (K 2 O), was finely 

 ground. The ignited alunite was also thoroughly pulverized. It con- 

 tained 14.7 per cent K 2 O. These minerals were applied to soil in 

 such quantities as to add 25, 50, 100, 200, and 500 pounds of potash 

 (K 2 O) per acre. Equivalent amounts of potash as potassium sul- 

 phate and potassium chloride, the soluble potash salts, were included 

 in the experiment in order to compare the efficiency of the potash- 

 carrying mineral, alunite, with the pure soluble potash salts. 



Cameron and his associates are making a thorough investigation 

 of the kelps of the Pacific coast and conclude that they are at present 

 the most promising source of potash in the United States. 1 That 

 kelps have value as a fertilizer has long been known. Seaweed has 

 been used locally as a fertilizer on the Pacific coast, in New England, 

 and in European countries. It is stated that the giant kelps of the 

 Pacific coast, namely, Nereocystis luetkeana and Macrocystis pyrifera, 

 are essentially different from the Atlantic kelps and those of Japan 

 in that the potash content is higher and the iodine content lower. 

 The dry kelps from the Pacific coast contain 30 per cent or more 

 potassium chloride as an average of a large number of samples. 



The effect of the kelp on soil was tested. The kelp used was dry 

 and powdered. It contained 19.8 per cent of potash (K 2 O). It was 

 applied to soil in amounts sufficient to add 25, 50, 100, 200, and 500 

 pounds of potash (K 2 O) per acre. This experiment was carried on 

 at the same time as the experiments with alunite, and the fertilizing 

 action of the two substances was compared with potassium sulphate 

 and potassium chloride. 



CULTURAL METHOD. 



The effect of these potash fertilizers in soils was tested by growing 

 wheat plants in the treated soil in paraffined wire pots. The wire- 

 pot method for testing the efficiency of fertilizers and the fertilizer 

 requirement of so ; ls is described fully in Circular No. 18 of th : s bureau. 

 The soil was we : ghed into pans, 3 pounds to each pan. The soil in 

 one pan received no fertilizer and was used as a control. To each of 

 the other pans the fertilizer to be tested was added. To the different 

 pans of soil we*3 added raw alunite, ignited alunite, kelp, potassium 

 sulphate, and potassium chloride, each in quantities of 25, 50, 100, 

 200, and 500 pounds of KjO per acre, based on an acre half-foot of 

 soil weighing 2,000,000 pounds. 



' Cameron, Frank K., and others: Fertilizer Resources of the United States, 8. Doc. No. 190, 62d Cong., 

 2d sess., 1912. Further investigations are now in progress. 

 ICir. 761 



