340 THE STUDY OF PLANT COMMUNITIES ' Chapter XII 



Much advance has been made in cultural practice. Contour 

 plowing, in which cultivation follows lines of equal elevation, is 

 becoming steadily more common. In many areas, strip-cropping 

 is an additional control, in which clean-cultivated crops are 

 planted between strips of cover crops, such as legumes, which 

 retard runoff and hold soil. A further necessity on contoured 



FlG. 182. Aerial view showing strip-cropping of terraces that follow con- 

 tours. Erosion is checked, much water is retained, and what runs off is di- 

 rected to a sodded runaway channel. Such elaborate operations may require 

 co-operation of several landowners. In this instance, two farms are involved. 

 — U. S. Soil Conservation Service. 



slopes may be terraces, which are ridges so placed that they catch 

 and hold water in a channel behind themselves and thus check 

 runoff and cause water to soak in. In special instances, deep fur- 

 rows are maintained (listing) in which water and snow are held 

 and crops are planted in the bottom of these troughs. Basin listing 

 is done on some soils with special machinery that shapes these 

 troughs with cross dams at regular intervals further to reduce 

 runoff. It has been shown that wind erosion can be reduced by 



