210 



SOIL PHYSICS AND MANAGEMENT 



Amount of Water Moved by Capillarity. The many experi- 

 ments made indicate the movement of large amounts of water by 

 surface tension. King used a fine sand taken from the subsoil and 

 a clay loam in cylinders four feet high, each with a section equiva- 

 lent to one square foot. The soils were completely saturated and 

 the cylinders were placed so that the water level was one foot below 

 the surface. A strong current of air was passed over the surface 

 for eight days and the evaporation determined. The same thing 

 was done with the water level at two, three, and four feet below the 

 surface. 



Water Evaporated Daily Per Square Foot with the Water Level at Different 

 Distances Below the Surface 10 



These results show that the amount of water raised four feet 

 was equivalent to one inch of rain in five and one-half days. From 

 such experiments the impression is given that capillarity is the 

 great factor in bringing water to the crop. It does play a large part, 

 but the conditions in the above experiment were much more favor- 

 able than are ordinarily found in the field. The water rose from a 

 free-water surface and the artificial breeze increased evaporation 

 enormously. Capillary movement is extremely slow through clay 

 loam, and it is very likely that the water evaporated from that soil 

 when the water table was 36 or 48 inches below the surface was not 

 obtained from the water table, but from the reserve in the soil. It 

 takes more than eight days, as seen in the table, page 207, for water 

 to be carried 48 inches or even 36 inches in height. The results are 

 without doubt much higher than would be obtained under normal 

 field conditions. In regard to capillary movement, Rotmistrov, 11 

 of Russia, says, "As regards the mechanical raising of water, how- 

 ever, by capillary action, it may be assumed that the limit from 

 which water can make its way upward lies much higher than the 

 limit accessible to roots. All the data at my command regarding 

 moisture in the soil of the Odessa experimental field point only to 

 one conclusion, namely, that water percolating beyond a depth of 

 40 to 50 centimeters (16 to 20 inches) does not return to the surface 

 except by way of roots." 



