THE POTASSIUM GROUP OF FERTILIZERS 39 



deflocculated, and, therefore, to interfere with bacteria 

 or plant life. Such refuse materials as contain cyanides 

 will require a fairly lengthy period to enable the poisonous 

 cyanogen compounds to be rendered harmless and converted 

 into useful nitrates. It may be taken as a general rule that 

 potash manures should be applied early. Potash is not 

 fixed in the soil with quite the same completeness as phos- 

 phate, but in a parallel calculation to that given in the 

 section dealing with phosphatic manures it has been found 

 at Rothamsted that something like about three-quarters of 

 the potash can be accounted for, the remainder having 

 presumably been lost in the drainage during fifty odd years. 

 The need for potash manures is not as great as for phosphates 

 or nitrogen. Cla}^ soils contain a sufficient amount of potash 

 for most crops. It is only on the light and sandy soils that 

 potash manure is absolutely essential. The really most 

 important member of the group of potassium fertilizers is, 

 however, farmyard manure. The recent effort to utilize 

 blast furnace dust promises a valuable addition to home 

 potash production. 



REFERENCES TO SECTION III 



Cresswell, " Possible Sources of Potash," Journ. Soc. Chem. Ind., April, 

 * f 9i5, P- 387- 



Russell, " How can Crops be Grown without Potash ? " Journ. Board 

 of Agric., 1915-16, p. 393. 



Voelcker, " Absorption of Potash by Soils of known Composition," 

 Journ. Roy. Agric. Soc., 25, n. 



Schreiner, " The Absorption of Potassium by Soils," Journ. Phys. Chem., 

 1906, p. 361. 



Cranfield, "A New Source of Potash," Journ. Board of Agric., 1917-18, 

 p. 526. 



