20G THE PRINCIPLES OF SOIL MANAGEMENT 



the other hand, the pulverized clay has so great hygro- 

 scopic and capillary power that its efficiency as a mulch 

 may be readily destroyed by natural climate and soil 

 conditions of common occurrence. It is therefore more 



Fig. 65. An example of clean, thorough tillage, and the maintenance of an 



effective "dust mulch." 



difficult to maintain a dust mulch of clay than of sand. 

 The strong natural mulching tendency of sand may be 

 seen on sand-dunes, where, although the surface is dry 

 and hot, moisture may be exposed by the toe of one's 

 boot at any season. 



A perfectly dry dust mulch need not be very deep, to 





