SOIL MOISTURE AND DRY FARMING 89 



as along the Canadian boundary in North Dakota and 

 Montana it is not more than half that amount. It is even 

 more imperative, therefore, that measures shall be taken 

 promptly and persistently to prevent the escape of soil 

 moisture in areas far south than in those far north. 



Prominent among the other influences that aid the 

 escape of soil moisture in the absence of preventive 

 measures are showers, especially those that fall fre- 

 quently and in small quantities. Water climbs upward 

 in the soil by capillary attraction. The more thin the 

 film of water that surrounds the soil grains the more 

 slowly does it move upward. Should the soil be dry, 

 the upward movement ceases. Should rain fall and 

 moisten the soil down to where soil moisture is .still 

 present, the upward movement begins again. Water 

 moves up to the surface and unchecked mingles with 

 the air. If this movement is not checked by stirring the 

 surface soil, much moisture will soon escape. Such stir- 

 ring of the soil is much more liable to be neglected after 

 light than after heavy rains, hence the hazard that light 

 showers will bring to dry farming in this way. 



Subsurface packing of the soil may also facilitate 

 the escape of soil moisture from below, since it facili- 

 tates the ascent of the same by making it possible for 

 it to climb more readily toward the surface than would 

 be possible in the absence of such packing. Any influ- 

 ence that will facilitate the ascent of soil moisture will 

 facilitate the escape of the same in the absence of hin- 

 dering influences. 



Weeds also pump water out of the soil in the proc- 

 ess of growth, hence the loss of moisture from this source 

 will be proportionate to the extent to which weeds are 

 allowed to grow. The same is true of useful plants in 

 their growth, but with the former, there is no compensa- 

 tion as with the latter. 



