18 DRY LAND FARMING 



on and near the surface ; (2) to the depth to which it has 

 been stirred by the implements of tillage, and (3) to the 

 measures taken to arrest precipitation that is violent 

 in character. When the soil is thus treated in semi- 

 arid areas, there should be an accumulation of moisture 

 up to a certain limit. The determination of that .limit will 

 depend upon such influences as the amount of the normal 

 precipitation, the extent to which measures have been 

 adopted for conserving the moisture, and to the extent 

 to which the soil moisture is .drawn upon by the crops 

 that are grown. The increase of the moisture content 

 in the soil and subsoil is clearly shown in a comparison 

 made of soils in the semi-arid areas that have never 

 been tilled and similar soils adjacent that have been 

 tilled judiciously for a term of years. The increase of 

 moisture in the latter is marked. The methods of con- 

 serving moisture are given in chapters VII and VIII. 



The deep stirring of the soil and subsoil not only 

 admits the moisture more readily, but it increases the 

 holding capacity of the soil. When moisture falls it 

 descends quickly in the spaces between the particles of 

 soil in the cultivated section of the same, and but slowly 

 in the undisturbed subsoil, that is, when the subsoil is 

 naturally dense. If the soil' has not been stirred at all, 

 much of the precipitation that falls on such soils in semi- 

 arid areas runs away over the surface. When stirred, 

 the moisture enters the soil quickly as far as it has been 

 stirred. In such instances the holding capacity of these 

 soils is soon met, hence any excess of moisture falling 

 at such a time runs away over the surface. Increase, 

 therefore, in the depth to which the soil has been stirred 

 within a comparatively recent period, means increase in 

 the capacity of the soil to receive moisture. For the dis- 

 cussion on the deep stirring of the soil, see pp. 129, 133. 



The object sought in compressing the soil is to 

 prevent the escape of moisture from land that has been 



