r68 



THE POT AS SIC FERTILISERS 



fCHAP. 



The Rothamsted results with barley are less striking, 

 because of the large amount of potash originally in the 

 soil; it is only during the later years, as has already 

 been explained, that any deficiency of potash has been 

 manifest on the plots that do not receive this fertiliser. 

 Still, as shown in the following table (XLIV.), which 

 gives average results for the fourteen years 1889-1902, 

 the use of potash has increased both the weight per 

 bushel and the weight of the individual grains : — 



The effect of potash manuring on the production of a 

 carbohydrate, in this case sugar, is most manifest on the 

 mangold crop. If Nos. 4 and 5 of the Rothamsted 

 mangold plots which receive the same supply of nitrogen 

 and phosphoric acid are compared, it will be found that 

 in a good year they produce approximately the same 

 weight of leaf; indeed, the similarity would be still closer 

 if the comparison were made when the leaves were in 

 full activity, and not at the end of the growing season. 

 One plot (4), however, receives a dressing of potash 

 salts, but not the other (5), and the plot with potash 

 produces nearly two and a half times the weight ot 

 roots grown upon the other plot without potash. Now 

 the difference in dry weight is almost wholly due to sugar 

 and other carbohydrates, which were manufactured in 

 the leaf and then passed on to the root for storage ; yet 



