X.] 



FERTILISERS REQUIRED BY BARLEY 



279 



from 46-1 to 45-6 bushels per acre. Evidently the soil 

 was able to supply all the requirements of the plant for 

 potash, despite the large amounts which the crop 

 removes. In the latter years of the experiment this 

 stock of available potash in the soil had become some- 

 what depleted, so that the omission of potash from the 

 fertiliser reduced the yield from 36-3 to 28-0 bushels per 

 acre. The exhausted soil in these latter years causes the 



Table LXXXVI. — Average Yield of Barley Grain (Hoos 

 Field, Rothamsted). 



Plot. 



Manuring. 



4A 



3A 



2A 



lA 

 4O 



lO 



Complete Fertiliser — Nitrogen, Phosphoric 



Acid, Potash 



Phosphoric Acid omitted — Nitrogen and 



Potash 



Potash omitted — Nitrogen and Phosphoric 



Acid 



Nitrogen only ...... 



Nitrogen omitted — Phosphoric Acid and 



Potash 



Unmanured ...... 



crop to respond to the constituents of the fertiliser only 

 when they are all present together ; taken singly, they 

 increase the yield but little, and the omission of any one 

 of them reduces the crop almost to the minimum pro- 

 duced on the unmanured plot. The soil has thus become 

 but a small factor in the nutrition of the crop, whereas, 

 as regards potash, it was a very large one at the begin- 

 ning of the experiment, and the defect of Liebig's theory 

 was to neglect it entirely. 



These differences in the manurial requirements of 

 wheat and barley, differences which would not be 



