Tillage to Modify Soil Texture. 233 



283, Why Good Tilth and Good Tillage Are Important. 



It is clear from the rounded form of the granules of soil 

 shown in Fig. 70, that when they are massed together with- 

 out being crushed a very large amount of unoccupied space 

 must exist ; this unoccupied space in a soil is needed for the 

 movement of air and of water; for the spreading out of 

 the root fibers and root hairs, and for the home of micro- 

 organisms which develop the available nitrogen used by all 

 the higher plants. 



If the granules are too large and too loosely packed the 

 soil lets the rains fall through it too freely and does not 

 bring it back rapidly enough by capillarity to meet the 

 needs of crops. If the granules are too small and too close 

 then the water moves too slowly, too much is retained by 

 capillarity and there is too little air. If the granules are 

 bound together too strongly, the soil is too hard and the 

 roots are unable to set it aside in making their advance and 

 this lack of freedom reduces the yield. 



284. How Texture and Tilth Are Developed. The soil 



particles are drawn together into the rounded granules by 

 the tension of the soil water in the same way that water 

 forms itself into spheres when sprinkled on a dust covered 

 floor. As long as there are large open spaces in the soil not 

 filled with water the water is all the time drawing itself to- 

 gether, tending to form spheres, and in this system of pulls 

 the soil particles become involved and are drawn together 

 also. As the water is lost by evaporation and the salts dis- 

 solved become too strong to remain in solution they are de- 

 posited upon and between the grains and granules tending 

 to cement them together. 



2.85. Difference Between Soil and Potter's Clay. When 

 the granules of a fine soil are all broken down and separated 

 into their ultimate grains we have the puddled condition so 

 fatal to crops, but the one the potter strives to secure to 

 make his wares close in texture and strong. In the pud- 

 dled soil and potter's clay enough of the granules have been 



