666 SOILS: PROPERTIES AND MANAOEMl 



farmer. The optimum moisture content for plowing b 

 indicated by that moist state in which a mass of the soil, 

 when pressed in the hand, will adhere without puddling 

 but may be readily broken up without injury to the 

 intimate soil structure. This is a much more critical 

 stage for fine-textured soils than for coarse-textured ones. 

 Sandy soils are not greatly altered by plowing when out 

 of optimum moisture condition. On the other hand, if 

 a clay is plowed when it is saturated with water, it will 

 be thoroughly puddled and will dry out into a hard, lumpy 

 condition. Such a structure requires a considerablr time 

 to remedy. 



571. Types of plows (Fig. 68). — There are two gen- 

 eral types of turning plows, the common moldboard plow 

 and the disk plow. Their mode of action is quite dif- 

 ferent, although, so far as the soil is concerned, the result 

 is much the same. The moldboard plow seems to have 

 a wider application than the disk plow, but both have 

 a particular sphere of usefulness. 



The disk plow is essentially a large revolving disk 

 set at such an angle that it cuts off and inverts the soil, 

 at the same time pulverizing it fairly effectively after 

 the manner of the moldboard plow. One advantage 

 claimed for the disk plow is its lighter draft for the same 

 amount of work done, due to its having rolling friction in 

 the soil instead of sliding friction. In practice it appears 

 to be especially effective on very dry, hard soil and in 

 turning and covering rubbish. 



For any given texture of soil and any given soil condi- 

 tion, there is a type of plow, a shape of moldboard, and 

 a depth of furrow slice, that will give the best results. 

 This fact is to be kept constantly in mind in plowing soil. 

 Sod land requires a different shape of plow from fallow 



