82 DRY LAND FARMING 



greatest extent practicable. This, of course, can only 

 be accomplished by keeping the soil sufficiently open 

 to admit of the downward passage of all the water that 

 falls, and by not cropping so frequently as to completely 

 exhaust the supply. 



Capillary water is the thin film that surrounds and 

 adheres to each soil grain. It is the outcome of the at- 

 traction between soil grains and water which is always 

 present. Because of the almost infinite number of the 

 soil grains, an average soil may hold a large amount of 

 capillary water. As the fineness of the soil grains in- 

 creases, it is manifest that the capacity of the soil to 

 hold capillary water will increase. Thus it is that the 

 capacity of clay loams to hold capillary water is much 

 greater than that of sandy loams. King is authority for 

 the statement that the largest amount of water that can 

 be held in clay loams varies from 22.67 to 18.16 per cent., 

 in sandy loams from 17.65 to 10.67 per cent., and in 

 humus soils from 44.72 to 21.29 per cent. 



The movement of capillary water in the soil is up- 

 ward when it moves. It climbs thus on the principle 

 that oil climbs up through the pore spaces of a lamp 

 wick when the lamp is lighted. The supply of oil that 

 renews the flame is thus maintained until the oil is con- 

 sumed, when the flame must cease. Capillary water is 

 thus drawn upon as the supply above becomes exhausted. 

 It may be drawn up in two ways : first, to supply water 

 removed from the surface by evaporation, and, second, to 

 renew the supply called for by plants in process of 

 growth. If evaporation should virtually cease, as it does 

 frequently in winter in the absence of plant growth, the 

 movement of capillary water would practically cease 

 for the time being. The movement of water in the soil 

 may be thus summarized: (1) It enters the soil in the 

 form of rain or melted snow. (2) It moves downward 

 in the soil as gravitational water until it is converted 



