146 DRY-FARMING 



exists in any cultivated soil. In fact, the soil-water 

 film may be viewed as being in a state of trembling 

 activity, tending to place itself in full equilibrium 

 with the surrounding contending forces which, them- 

 selves, constantly change. Were it not that the 

 water film held closely around the soil particles is 

 possessed of extreme mobility, it would not be 

 possible to meet the demands of the plants upon 

 the water at comparatively great distances. Even 

 as it is, it frecjuently happens that when crops are 

 planted too thickly on dry-farms, the soil-moisture 

 cannot move cjuickly enough to the absorbing 

 roots to maintain plant growth, and crop failure 

 results. Incidentally, this points to planting that 

 shall l)e proportional to the moisture contained by 

 the s(.)il. See Chapter XL 



As the temperature rises in sfiring, Avith a decrease 

 in the relative humidity, and an increase in direct 

 sunshine, evaj^oration from the soil surface increases 

 greatly. However, as the topsoil becomes drier, 

 that is, as the water film becomes thinner, there is 

 an attempt at readjustment, and water moves up- 

 ward to take the place of that lost b}" evaporation. 

 As this continues throughout the season, the moisture 

 stored eight or ten feet or more below the surface 

 is gradually brought to the top and evaporated, and 

 thus lost to plant use. 



