CROPPING SYSTEMS , 405 



tinuously. However, the fact that plants use foods in 

 different proportions may be of some importance. 



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

 off certain substances through its roots that are injurious 

 to the plant, but that may not harm another crop. If the 

 theory is true, it furnishes another reason for rotation. 



(9) Crop rotation systematizes farming. It makes 

 farming less complex rather than more so. It may re- 

 quire considerable study to get a rotation established, 

 because the fields may need to be rearranged, and one of 

 the new fields may have several kinds of crops to be 

 adjusted. Usually a cropping system simplifies the farm 

 layout and reduces the number of fields on the farm. See 

 Figures 88 and 89. 



249. Characteristics of a good cropping system. 

 There are a number of things that a crop rotation should 

 provide if possible : 



(1) The area of each crop should be nearly the same year 

 after year, unless there is a definite reason for changing it. 



(2) The rotation ought ordinarily to provide an abun- 

 dance of roughage and pasture for the number of animals 

 kept. The cost of handling such bulky .products as hay, 

 straw, silage, and roots is too great if these are bought 

 from other regions. 



(3) It is very desirable that the rotation include one 

 tilled crop for the elimination of weeds. 



(4) It is very desirable that the rotation include a sod. 

 A sod is favorable for the fixation of nitrogen and the 

 increase of the humus supply. If the sod includes clover 

 or alfalfa, the fixation of nitrogen is further favored by the 

 legume. 



(5) The rotation and feeding system should in some way 

 provide for keeping up the organic matter of the soil. 



