492 THE PRINCIPLES OF SOIL MANAGEMENT 



their death. Tillage in hot, dry weather is especially 

 effective in killing most weeds. They soon dry out from 

 lack of moisture. 



(2) Small-toothed implements which very thoroughly 

 stir the soil are more effective in killing small weeds 

 than are large shovels which may slide past the weed. 

 Thorough stirring of the soil is the essential point to 

 be aimed at. 



(3) Where weeds are beyond the reach of the culti- 

 vator, as in the row in maize that has reached a con- 





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. : l^0^$M ^SSMSS.^ 





Fig. 151. Terracing to prevent erosion of hillside. 



siderable size, they may often be killed by covering 

 with soil by use of large shovels. 



Shading by a rapid-growing leafy crop and spraying 

 with chemicals for some species are also effective aids 

 in weed control. 



349. Erosion. Erosion is often a serious menace to 

 the productiveness of the soil. It may result from two 

 causes: (1) The action of running water. (2) The action 

 of wind. The soil is removed and causes injury to the 

 productiveness of the land, first, by carrying away the 



