64 DRY-FARMING 



regions of limited rainfall. The annual rainfall, 

 which is approximately constant, penetrates from 

 year to year very nearly to tlae same depth. Some 

 of the lime found so abundantly in arid soils is dis- 

 solved and worked down }'early to the lower limit of 

 the rainfall and left there to enter into combination 

 with other soil ingredients. C(.)ntinued through long 

 periods of time this results in the formation of a 

 layer of calcareous material at the average depth to 

 which the rainfall has penetrated the soil. Not 

 onl}' is the lime thus carried down, but the finer 

 particles are carried down in like manner. Espe- 

 cially where the soil is poor in lime is the clay worked 

 down to form a somewhat claj'C}^ hardpan. A hard- 

 j3an formed in such a manner is freciuently a serious 

 obstacle to the downward movement of the roots, 

 and also prevents the annual precipitation from 

 moving down far enough to be beyond the influence 

 of the sunshine and winds. It is fortunate, how- 

 ever, that in the great majority of instances this 

 hardpan gradually disappears under the influence of 

 proper methods of dry-farm tillage. Deep plowing 

 and ]5roper tillage, which allow the rain waters to 

 penetrate the soil, gradually break up and destroy 

 the hardpan, even when it is 10 feet below the sur- 

 face. Nevertheless, the farmer should make sure 

 whether or not the hardpan does exist in the soil 

 and plan his methods accordingly. If a hardpan 

 is present, the land must be fallowed more carefully 



