SOIL MOISTURE AND DRY F4.RMJMO 101 



ture a crop. This result is almost certain to follow 

 when grain crops are grown every year in the semi-arid 

 country. The amount of moisture in the soil and also 

 in the subsoil are not enough to properly mature a 

 grain crop in a dry year, and the outcome is that the 

 crop fails. The moisture that has been used in growing 

 it is therefore lost. Under such conditions subsoil mois- 

 ture is drawn upon to no good purpose. 



A reserve of moisture in the subsoil is so important 

 that its presence or absence may make the difference 

 between success and failure in the growing of crops. In 

 areas with an average rainfall of less than 15 inches, ex- 

 periment has shown that enough of reserve moisture 

 cannot be maintained in the soil to produce good crops 

 when small grains are grown upon the soil every year. 

 In a dry year they may promise well for a time, but be- 

 fore they reach full maturity they fail. Experiments 

 conducted by the Montana experiment station extending 

 over a period of five years have shown that more grain 

 can be obtained in a series of years by alternate crop- 

 ping and alternate summer-fallowing of the land than 

 by growing on it annual crops of small grains. Such a 

 process of tillage maintains a reserve of moisture in the 

 soil and this reserve carries a crop through safely in a 

 time of drought that but for its presence might abso- 

 lutely fail. 



In order to maintain this reserve of soil moisture, 

 therefore, the bare-fallow must be occasionally intro- 

 duced where such introduction is practicable. It may 

 not be practicable in all instances, as where, for instance, 

 soils are so light as to drift with the wind. In lieu of 

 the summer-fallow a cultivated crop may answer the 

 purpose, but not quite so well, as the cultivated crop 

 makes drafts upon the soil moisture in the process of its 

 growth. The timeliness of the cultivation and the depth 

 of the same to effect these ends is greatly significant. 



