140 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



Capillary Action. If the water-table of the soil is so low that 

 capillary action cannot raise water to the plant roots, it has no 

 effect upon the plant. If it is within such distance that water 

 can be raised to the soil's surface, the water raised by capillarity 

 will tend to replace the water lost by evaporation and transpira- 

 tion. The extent to which this replacement takes place depends 

 upon the relative rates of evaporation and transpiration, and the 

 rate of capillary action. 



King 1 studied the amount of water which can be brought up- 

 ward by capillary action, using cylinders 4 feet high and one foot 

 in diameter, which could be supplied with water from below. The 

 cylinder was partly filled with water, soil dropped in and stirred, 

 and the operation repeated until the cylinder was filled. The water 

 level was then lowered to one foot below the surface, and main- 

 tained at this point, while the surface of the cylinder was exposed 

 for eight days to a strong current of air, and the quantity of water 

 evaporated determined. The evaporation was determined for 

 depths of i, 2, 3, and 4 feet of the water-table. At the depth of 

 4 feet, the average evaporation from a fine sand and a clay loam 

 was 0.9 pounds per day and square foot. In order for this 

 experiment to be complete, it would be necessary to prove that 

 this quantity of water passed upward from the water-table. The 

 evaporation of the water may have been due, in part, to the 

 natural drying of the soil, although it decreased as the water-table 

 was lowered. In Wisconsin, crops in this soil suffer considerably 

 from drought, though the water-table is only five feet from the 

 surface, showing that in the natural condition the soil is able to 

 raise but little water even a distance of five feet. 



The effect of capillary action in bringing up water is also shown 

 by the Rothamsted drain gauges. The shallow one is 20 inches 

 deep, the deeper one 40 inches. On an average of twenty-five 

 years, the annual evaporation from the deeper gauge is only 0.6 

 inches greater than from the shallow ; this probably represents the 

 quantity of water brought to the surface from below the depth of 

 20 inches. 



1 Report Wisconsin Station 1889-1890. 



