26 THE OLIVER PLOW BOOK 



serving must be applied. The degree to which this 

 conservation must be practiced is determined solely by 

 the amount of moisture contained in the soil. In the 

 more humid districts it may be only necessary to adopt 

 a system for conserving the rains of summer and fall; 

 whereas, in the dryer territories it may be necessary to 

 practice a system of summer fallowing for an entire year 

 before enough moisture can be saved to insure a crop. 

 The big thing to remember is that moisture must be 

 present when the plants need it. 



Those farms underlaid with clay soils are easier to till 

 for conserving moisture for future use than those which 

 have an endless depth of sand or gravel. If the sub-soil 

 is of such a nature that it will not hold moisture within 

 the distance which capillary attraction operates, the 

 problems are extremely difficult and almost beyond 

 control unless the soil is kept chock full of humus at a 

 depth deep enough to prevent surface heat from evapor- 

 ating the moisture. 



