OBJECTS OF TILLAGE 467 



pronounced in its effects, as well as complex in its 

 modes of operation, that it is given a separate treatment. 



332. Objects of tillage. Tillage rests upon three 

 primary objects. These are: (1) Modification of the 

 texture and structure of the soil. (2) Disposal of rubbish 

 or other coarse material on the surface, and the incor- 

 poration of manures and fertilizers in the soil. (3) To de- 

 posit seeds and plants in the soil in position for growth. 



The most prominent of these objects is the modifi- 

 cation of the soil structure. 

 No perceptible change in the 

 soil texture can be effected but 

 through changes in structure, 

 by which it is made either 

 more open *or more compact. 

 Thereby the retention and fig. 128. Heel plate for regukt- 

 movement of moisture is ing the width at the heel. 



affected, aeration is altered, the absorption and reten- 

 tion of heat is influenced, the growth of organisms 

 is either promoted or retarded; through all of these the 

 composition of the soil solution is affected and, lastly, 

 the penetration of plant roots is influenced. The crea- 

 tion of a soil mulch is simply a change in the structure 

 of the soil at such time and in such manner as will 

 prevent evaporation of moisture. For this reason, it 

 is essential to appreciate the relation of soil structure to 

 movement of moisture in managing the mulch. In fine- 

 textured soils, where the granular or crumbly structure 

 is most desired, tillage may have an important influ- 

 ence on the promotion or destruction of these granules. 

 As has been pointed out (page 105), any treatment 



