Bracken and Wood Ashes 



157 



CH. IX] 



The ashes of young plants are rich in potash and in 

 bjT^gone days a considerable amount used to be ex- 

 tracted from this source: unfortunately^ the percentage 

 falls off as the plant becomes older and larger so that 

 the amount of potash obtainable does not increase pro- 

 portionately to the growth. 





Fig. 32. Effect of potassic fertilisers on mangolds. 



(Barnfield, Rothamsted.) 



Left-hand heap Superphosphate and nitrogenous manure, no 



potassium salts. 



Right-hand heap Superphosphate, nitrogenous manure and 



potassium salts. 



The ash of young wood contains up to 35 per cent, of 

 potash, that of older wood about 15-25 per cent. All 

 dried vegetation loses potash on exposure to weather; 

 the ash obtained by burning brushwood, hedge trim- 

 mings, etc. contains only about 10 per cent, of potash, 

 and much of this is lost by the washing of the rain. 



