SOIL STRUCTURE 197 



for successful plowing is relatively narrow. The ability 

 to detect when this zone has been reached in a clay soil 

 is one of the essentials of successful soil management. 

 Another essential is the effective widening of such a 

 zone by granulation operations. The optimum mois- 

 ture condition for tillage is also the optimum condition 

 for plant growth — a happy coincident, since by regu- 

 lating the moisture content for plant development condi- 

 tions are rendered most favorable for all soil activities. 

 It is thus possible to realize that criterion in all soil physi- 

 cal operations, a maximum tilth. . 



