342 THE PRINCIPLES OF SOIL MANAGEMENT 



There are a number of other Stassfurt salts, consisting 

 of mixtures of potassium, sodium and magnesium in 

 the form of chlorides and sulfates. They are not so 

 widely used for fertilizers as are those mentioned above. 



207. Wood ashes. For some time after the use of 

 fertilizers became an important farm practice, wood 

 ashes constituted a large portion of the supply of potas- 

 sium. They also contain a considerable quantity of lime 

 and a small amount of phosphorus. The product known 

 as unleached wood ashes contains 5 to 6 per cent of pot- 

 ash, 2 per cent of phosphoric acid, and 30 per cent of 

 lime. Leached wood ashes contain about one per cent of 

 potash, 1^ per cent of phosphoric acid, and 28 to 29 per 

 cent of lime. The}^ contain the potassium in the form of a 

 carbonate, which is alkaline in its reaction, and may be 

 injurious to seeds when in large amount. They are 

 beneficial to acid soils through the action of both the 

 potassium and calcium salts. The lime is valuable for the 

 other effects it has on the properties of the soil. (See 

 page 348.) 



208. Insoluble potassium fertilizers. Insoluble 

 forms of potassium, occurring in many rocks, usually 

 in the form of a silicate, are not regarded as having 

 any manurial value. Experiments with finely ground 

 feldspar have been conducted by a number of experi- 

 menters, but have, in the main, given little encourage- 

 ment for the successful use of this material. An insoluble 

 form of potassium is not given any value in the rating 

 of a fertilizer, based upon the results of its analysis. 



209. Fertilizer practice. The purchase and use of 

 commercial fertilizers is an art that requires some 



