CAPILLARY WATER 



209 



movement. It reduces the rapidity at first, but the water in the 

 mixture, as shown in column No. 2, passes Xo. 1 in six hours. In 

 the finer-grained soil the effect of organic matter is to not only 

 retard the movement from the first, hut to diminish the height, as 

 shown, by comparing Xos. 3 and 4, 5 and 0, and 7 and 8. A com- 

 parison of Xos. 9 and 10 shows the effect of the removal of organic 

 matter by cropping. Slow capillary movement is desirable in sur- 

 -face soils to prevent excessive loss of moisture by evaporation. The 

 subsurface and subsoil are better adapted for more rapid capillary 

 movement which brings the moisture up where roots in the surface 

 soil may obtain their supply. The peat is an excellent example of 

 very slow movement through a very porous soil. The limit was 

 reached in ten days. Figure 93 shows the effect of organic matter 

 on height of rise of water. 



Maximum Capillary Capacity or Moisture-holding Ca- 

 pacity of Soils. Soils possess varying powers of retaining moist- 

 ure- by capillarity due primarily to texture. The method of deter- 

 mining this has been devised by Hilgard and modified by Briggs. 

 A small cup five centimeters in diameter and one in height, 

 with the l)ottom made of very fine bolting cloth, is used. The soil 

 is settled slightly by jarring and stroked off level with the top of 

 the cup. It is then placed with the bottom in the water, and when 

 the soil has taken up the maximum amount of water, it is allowed 

 to drain for a few minutes, and the weight of the water determined 

 by comparing with the weights of the dry soil. This weight is des- 

 ignated as the water-holding capacity of the soil. This is much 

 higher than will be found under field conditions. The following 

 table shows the percentage of water held by capillarity and the total 

 water at saturation in some soils, all from Illinois except the last. 



Maximum Capillary and Maximum Water Cajmcity 9 



14 



