vi.l SOIL POTASH RENDERED SOLUBLE BY SODA 171 



senting the attack of the soda salt upon the insoluble 

 potash in the soil, but it will be seen that the potash thus 

 present in the crop by no means came up to the quantity 

 removed by the crops on 6A and 6N, where an excess of 

 potash had been applied in the manure. Since, also, the 

 sum of the two alkalis, potash and soda together, in 



Table XLVII.— Potash and Soda contained in 

 Mangolds. Rothamsted, 1900. 



the crops on 5N, 6 A, and 6N is nearly the same, it may 

 be concluded that on 6A and 6N the plant was taking 

 up a much greater amount of potash than it needed, 

 due to the excess of this constituent in the soil and 

 manure. 



Next to their effect upon carbohydrate-making 

 crops, the most striking action of potassic manures is 

 their value in promoting the growth of clover and all 

 leguminous crops. The function of potash here may be 

 still that of prom^tinga^milatiDn, because the bacteria 

 which fix mtrogenin the nodules on the roots of the 

 leguminous plants must be supplied with carbohydrate 

 by the plant in order to obtain, by its oxidation, the 

 energy requisite for the fixation of nitrogen. There is 

 evidence to show that the fixation of nitrogen by these 

 organisms is promoted by a supply of carbohydrate ; but 



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