276 



ELEMENTS OF AGRICULTURE 



PASTURE 

 24 71 A. 



OATS 

 19.13 A 



BARLEY 

 14 70 A. 



OATS 

 19 04 A 



CORN 

 12 86 A. 



FIG. 142. 



Fields on a 160-acre farm in 

 Minnesota 



increased yields result- 

 ing from crop-rotation 

 will cause the removal 

 of more of each kind 

 of plant-food than will 

 be taken from the field 

 by the smaller yields 

 that are secured if any 

 one crop is grown con- 

 tinuously. However, 

 the fact that different 

 plants do use the plant- 

 food in different pro- 

 portions may be of some importance. 



(8) It is thought by some persons that each plant 

 gives off certain substances through its roots that are 

 toxic, or poisonous, to that plant, but that may not be 

 harmful to some other 



crop. This theory has 

 not yet been accepted 

 by all investigators. 



(9) Crop -rotation 

 systematizes farming. 

 It does not make farm- 

 ing more complex or 

 make more fields, as 

 some have supposed. 

 Thought is required in 

 getting the system es- 

 tablished. The farm 

 mav need to be re- 



Flo. 143. Same farm as Fig. 142, with the 

 fields arranged fora five-year rotation (Minne- 

 sota Bulletin No. 109.) 



