MAINTENANCE OF YIELD WITHOUT MANURE 193 



a comparison between the crops on the unmanured and the 

 completely manured plot for the four courses from 1852-1867, 

 the five courses from 1884-1903, and the two courses from 

 1904-1911, from which an idea can be obtained of how far 



80 



Swedes. 



Barley. 



Manured Plots 

 =100. 



I 



Clover 

 (or Beans) 



Four Courses 

 (1852-67). 



I 



Five Courses 

 (1884-1903). 



Unmanured Plots. 



FIG. 41. Crops Grown in Rotation. Relative Yield on Manured and Unmanured Plots 

 in the earlier and later years of the Experiment. 



each crop has been affected during the whole fifty-nine years 

 of the experiment by the continued absence of manure. The 

 same results are shown graphically in Fig. 41. 



Since 1884 (Table LXVI.) the crop of Swedes on the 

 unmanured plots has averaged only 15'0 cwt. per acre, and the 

 Toots have lost the appearance of Swedes, becoming tap-roots 



N 



