172 



THE POTASSIC FERTILISERS 



[chap. 



whatever may be the explanation it is found in practice 

 that the growth of clover, etc., is very much promoted 

 by a free supply of potash, and this is very manifest 

 upon sands and gravelly soils usually poor in potash. 



This effect may be very strikingly seen when the 

 fertiliser is applied to grass land carrying a mixed 

 herbage, for the potash encourages the leguminous 

 plants until the aspect of the vegetation may be 

 entirely changed. On the Rothamsted grass land, 

 which is mown for hay every year, one plot gets a 

 complete mineral manure — phosphates and sulphates 

 of potash, soda, and magnesia ; the adjoining plot 

 receives the same phosphoric acid, magnesia, and soda, 

 but no potash, while a third plot gets the phosphates 

 alone. The Table XLVIII. shows the comparative 

 yield and the composition of the herbage by weight : — 



Table XLVIII.— Rothamsted Hay Crop, without and with 

 Potash. 



On the plots receiving a mineral manure including 

 potash half the vegetation now consists of leguminous 

 plants, but in the absence of potash the proportion is 



