VI.] POTASH MOST EFFECTIVE IN DR Y SEASONS 175 



inferred from the fact that its effect upon the yield is 

 always most pronounced in dry seasons. 



Referring again to Table XXXIV., it will be seen 

 that in the dry season of 1893, the yield of barley 

 (grown also with ammonium salts and superphosphate) 

 was increased by a dressing of potash from i8-i to 30-8 

 bushels per acre, whereas in the wet season of 1894 the 

 increase was only from 34-9 to 41-4 bushels per acre. 



Similarly with the wheat (Table XXXV., p. 139), 

 in the wet season the application of potash only 

 increased the yield of grain from ii-i to i6-o bushels, 

 and the weight from 54-6 to 57-8 lb. per bushel ; whereas 

 in the dry season the yield was increased from 77 to 

 16-4 bushels (more than double), while the weight was 

 raised from 56-4 to 62-6 lb. per bushel. That the bad 

 results in the dry year were due to a premature ripen- 

 ing of the plant, which was deferred by the potash, is 

 seen from the fact that with potash the ratio of grain 

 to straw was 98, whereas without potash it only reached 

 67-3, in which case the migration of materials from the 

 straw to the grain is clearly incomplete. But though 

 in such cases of grain crops the use of potash prolongs 

 the development of the plant and defers maturity, 

 apparently an opposite effect is produced upon root 

 crops. On the Rothamsted field, for example, where 

 potash is used, the mangold leaves will begin to turn 

 yellow and fall, indicating that the plant has finished 

 its season's growth, long before any such appearance 

 is seen on the potash-starved plots alongside, where 

 a tuft of dark green and apparently growing leaves 

 persists until the plant is cut off by the frosts. Similar 

 appearances, though in a less pronounced degree, can 

 be seen on ordinary crops in light soils, whenever a 

 strip has been left to show the action of potash in the 

 manure. 



