PRINCIPLES GOVERNING TILLAGE 137 



because of its adaptability to the soil in which it is to be used. 

 It should be remembered that every good implement is designed 

 to do a certain kind of work, and, in most cases, in a particular way ; 

 and each one is built with certain adjustments so that it can be 

 regulated to meet varying conditions. 



The " How " of Tillage Depends Upon the ** Why."~When the 

 specific objects of tillage are kept in mind, and the principles 

 governing the methods of tillage are clearly understood, there can 

 be little difficulty in deciding upon the kinds and types of machines 

 to use, and when best to operate them. 



The Objects of Tillage. — The objects of tillage are: to loosen 

 and pulverize the soil, to deepen the seed bed, to crush lumps and 

 break crusts, to turn under coarse litter and vegetation, to com- 

 pact the seed bed, to kill weeds, to enable soils to catch and thus 

 store more moisture, to conserve soil moisture, and to mix fertil- 

 izers and other materials into the soil. Two or more of these 

 objects may be accomplished in one operation. 



Principles Governing Tillage. — Some of the principles govern- 

 ing tillage may be stated as follows: 



(a) A mellow and firm seed bed is necessary to favor ger- 

 mination, and to enable young plants to develop good, strong 

 root systems. 



(b) The liberation of plant-food elements through the action 

 of organisms and other agencies is favored when soils are well 

 aerated. Aside from drainage, tillage promotes the exchange of 

 air in soils. 



(c) The fact that capillary water in soils rises from soil particle 

 to soil particle makes it necessary that the soil particles within 

 the seed bed and between the seed bed and the subsoil be in close 

 contact with each other (Chapter V). 



(d) Since soil moistxn-e readily evaporates when the surface 

 soil is firm and compact, it is essential that a soil mulch be developed, 

 wherever necessary and practicable, to check or lessen this loss of 

 moisture (Chapter VIII). 



(e) Heavy, compa'ct soils can be made to trap and thus store 

 more moisture when they are loosened, plowed or subsoiled. 



(/) The natural, crummy structure of the heavier soils may 

 be easily destroyed when they are worked too wet. This creates 

 a 'Spuddled'' condition which is unfavorable to plant growth. 



(g) Weeds should be destroyed. 



In the following paragraphs these objects and principles are 



