524 SOILS: PROPERTIES AND MANAGEMENT 



known as unleached wood ashes contains from 5 to 6 per 

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

 cent of hme. Leached wood ashes contain about 1 per cent 

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

 per cent of lime. They contain the potassium in the form 

 of a carbonate, which is alkaUne in its reaction and in large 

 amount may be injurious to seeds. They are beneficial 

 to acid soils through the action of both the potassimu and 

 calcium salts. The lime is valuable for the other effects it 

 has on the properties of the soil. (See pars. 454-457.) 



443. Insoluble potassium fertilizers. — Insoluble forms 

 of potassium, existing 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 investigators, but have, in the 

 main,, given little encouragement for the successful use of 

 this material. An insoluble form of potassium is not 

 given any value in the rating of a fertilizer based on the 

 results of its analysis. 



SULFUR AND SULFATES AS FERTILIZERS 



The use of these substances as a means of increasing 

 plant growth when applied to soils has recently received 

 revived attention. The use of free sulfiu* has been in- 

 vestigated to some extent in Prance and Germany. There 

 have been suggested three ways in which it may be bene- 

 ficial to plants (1) as a direct stimulant; (2) by its in- 

 fluence on the activities of microorganisms; (3) as a 

 source of plant-food, which might otherwise be deficient. 



444. The use of free sulfur, — BouUanger^ added 

 flowers of sulfur to a soil at the rate of 23 parts to a million 



^ Boullanger, E. Action du soufre en fleur sur la vegetation. 

 Compt. Rend. Acad. Sei. Paris, T. 154, pp. 36^370. 1912. 



