464 NATUEE AND PROPERTIES OF SOILS 



of potash. The chief impurity is common salt. Some of the 

 potash salts produced in this country carry boron, which is 

 extremely toxic to plants. Such is not generally true of the 

 German and French products. 



Potassium chloride and potassium sulfate when added to 

 the soil are immediately soluble, being held in the soil solu- 

 tion or absorbed either physically or chemically by the col- 

 loidal complexes. Due to the selective absorption of the soil 

 for the potassium ion and the fact that plants absorb more of 

 this ion than of the acid radical, an acid residue tends to re- 

 sult from the use of such fertilizers. Some means, such as the 

 use of lime, should be employed to counteract this tendency. 



261. Other sources of potash.^ — For some time after the 

 use of fertilizers became an important farm practice, wood- 

 ashes were the source of most of the potash. They also con- 

 tain a considerable quantity of lime and a small amount of 

 phosphorus. The product known as unleached wood-ashes 

 contains from 5 to 6 per cent, of potash, 2 per cent, of phos- 

 phoric acid, and 30 per cent, of calcium oxide. Leached wood- 

 ashes contain about 1 per cent, of potash, l^^ per cent, of phos- 

 phoric acid, and from 28 to 29 per cent, of lime in the form 

 of the hydroxide and carbonate. Unleached ashes carry the 

 oxide, hydroxide, and carbonate forms of calcium. Ashes 

 contain the potassium in the form of a carbonate, (K2CO3), 

 which is alkaline in its reaction and in large amounts may be 

 injurious to seeds. Otherwise this form of potash is very de- 

 sirable, since no acid residue is left in the soil by its use. 



* Young, G. J., Potash Salts and Other Salines in the Great Basin; 

 IT. S. Bept. Agr., Bui. 61^ 1914. 



Waggaman, W. H., and Cnllen, J. A., The Meccvery of Potash from 

 Alwiite; U. S. Dept. Agr., Bui. 415, 1916. 



Hirst, C. T., and Carter^ E. Gr., Some Sources of Potassium; Utah 

 Agr. Exp. Sta., Circ. 22, 1916. 



Waggaman, W. H., The Production and Pertiliser Value of CitriC' 

 Soluble Phosphoric Acid and Potash; U. S. jDep.t. Agr., Bui. 143, 

 1914. 



Boss, W. H., et atf The JKecovery of Potash as a By -Product in the 

 Cement Industry; U. S. Dept. Agn, Bui. 572, 1917. 



