THE PROBLEM OF TILLAGE 



supply of moisture for the seeds, but, of 

 course, it is also useful in crushing liunps 

 on soils which become cloddy. Great 

 care, however, must be taken not to roll 

 clayey soils when they are wet, as they 

 are liable to become cemented into hard 

 clods. In general it may be said that 

 rolling accomplishes three very useful 

 purposes: (a) it increases the water- 

 holding capacity of light soils, (b) it aids 

 the germination of seeds, and (c) crushes 

 the lumps in cloddy soils. 'A tendency 

 to-day, in America at least, is to restrict 

 the use of the roUer to light soils in order 

 to make the soil firm, and to use the im- 

 plement called the planker on heavy soils 

 where fining the soil is the end desired. 



Planking and Packing. 



The planker is made by bolting four 

 3-inch planks to two cross-pieces so as to 

 present the sharp edge of each plank to 

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