CHAPTER V 



Potassic Manures in General 



The Occurrence and Functions of Potash in 

 the Soil. 



Setting aside farmyard manure, in which in any 

 case there is a great loss of potash — often more than 

 half — the restoration of potash taken from the soil 

 or the supplying of natural deficiencies was only 

 accomplished for a long time past by the application 

 of wood ashes, seaweed ash, burnt weeds, and salts 

 obtained from the French Midi and nitre beds. Peat 

 ash contains practically no potash. 



The sources were quite insufficient either to make 

 good deficiencies caused by the crops sold, or the 

 losses in the manure ; also a part of the potash 

 derived from them is still required in the manu- 

 facture of glass, soft soap, and gunpowder. 



There is a lack of potash therefore in the 

 majority of soils, and in some — those very acid and 

 peaty for example — there may even be none at all. 

 We shall see how these acid soils dissolve the 

 potash : in the absence of lime the humus cannot 

 retain it and it is carried off by the rain water. 

 Such soils therefore require potash as well as lime, 



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