VALUE OF POTASH 105 



produces but little increase of crop except when used with 

 nitrate of soda ; the average increase of crop due to superphos- 

 phate on Series A, AC, and C, where ammonia or rape cake is 

 the source of nitrogen, is only one ton per acre, whereas the 

 average increase it causes where nitrate of soda is used 

 amounts to 5*1 tons per acre. This latter result demonstrates 

 that phosphoric acid is necessary for the proper development 

 of the mangold plant, but that in the absence of alkaline salts 

 on the ammonia and rape cake plots it cannot exercise any 

 sensible influence. 



The great increase of crop comes as a rule when potash is 

 added to the superphosphate : the crop on the plots receiving 

 ammonium-salts rises from 7 '04 to 14*08 tons per acre; with 

 rape cake the rise is from 1078 to 19 '28 tons per acre ; with 

 rape cake and ammonium-salts the increase is from 9 '68 to 

 23*42 tons per acre. Only with nitrate of soda as the source of 

 nitrogen is there no increase for the addition of potash, the 

 crop being practically equal on the two plots 6 and 5, with and 

 without potash. The necessity of potash for the mangold crop 

 is still more strikingly seen in the seasons of large crop : where 

 no potash is supplied in the manure the plant has to get as 

 much as it can from the reserves of potash contained in the 

 soil, and, as it is difficult to accelerate this process, the crop on 

 these plots cannot make nearly such good use of favourable 

 conditions for growth as the crops which have a large amount 

 of potash at command. For example, in 1900 the addition of 

 potash to superphosphate and ammonium-salts raised the crop 

 from 12*0 to 28*2 tons per acre, and on the plots receiving rape 

 cake and ammonium-salts the rise was from 14*9 to 37'5 tons 

 per acre. 



A further inspection of the diagram shows that the addition 

 of magnesium sulphate and salt to the plots receiving potash 

 and superphosphate, as represented by the last columns in the 

 figure, brings about a further small but perceptible increase of 

 crop, and the increase is proportionately more for the larger 

 crops. The most probable cause is that the 400 Ib. of soluble 



