64 DRY-FARMING 
regions of limited rainfall. The annual rainfall, 
which is approximately constant, penetrates from 
year to year very nearly. to the same depth. Some 
of the lime found so abundantly in arid soils is dis- 
solved and worked down yearly to the lower limit of 
the rainfall and left there to enter into combination 
with other soil ingredients. Continued 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 
only 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 clayey hardpan. A hard- 
pan formed in such a manner is frequently 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 proper 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 
