274 ELEMENTS OF AGRICULTURE 



around; it provides for cash crops and crops to feed; it 

 prevents total failure when one crop fails. All these 

 advantages may be had when each of the several crops 

 grows on the same field continuously. 



245. Advantages of Crop-Rotation. The rotation of 

 crops (1) helps to control weeds, insects and fungi; (2) it 

 provides for keeping up the humus supply on each field; 

 (3) it may provide for the growth of grass and legumes 

 on each field; (4) it often saves labor; (5) it keeps the 

 'land occupied with plants a greater part of the time; 

 (6) it allows the alternation of deep- and shallow-rooted 

 crops; (7) it may provide for a balanced removal of plant- 

 food; (8) it is possible that toxic substances may be de- 

 stroyed; (9) it systematizes farming. 



(1) Nearly every crop is accompanied by certain kinds 

 of weeds that are able to grow with it. The weeds that 

 thrive in small grain are usually quite different from those 

 that thrive in meadows. If small grain is grown continu- 

 ously, the land is likely to become very weedy. These 

 particular weeds are likely to be easily killed by cultiva- 

 tion. Wild oats are a serious pest in the grain fields in 

 Minnesota, but if crop-rotation is practiced they readily 

 disappear. Such weeds as daisies may be bad in hay land, 

 but are not serious in corn. The opposite is true of pig- 

 weeds. 



Similarly, there are many diseases and insects that 

 live on one crop but that, are not harmful to another. 

 The soil may become infested with potato-scab or corn- 

 root-worm, but crop-rotation will check either. 



(2) If crops are not rotated, those fields that are con- 

 stantly in tilled crops will have their humus supply ex- 



