114 Journal of Agricultural Research vo1.x,no.3 



below the surface may contribute large amounts of water * * * for 

 the use of vegetation at the surface." He (21) also found that the loss 

 of moisture due to evaporation at the surface of columns of moist soil 

 caused capillarity to act through a depth of 10 feet in 10 days. 



From his studies with long columns of soil, King (20, 21) decided that 

 the water in moist soils tends to distribute itself with the most moisture 

 at the bottom of the column and the least above, regardless of the pre- 

 vious distribution. 



The work of Briggs (4) and Briggs and Lapham (5), on the other 

 hand, indicates that the final distribution leaves the most moisture 

 nearest the source of supply and the least farthest away. They believe 

 the movement to be due to the difference in the cur\^ature of the soil- 

 moisture films. The resistance of this film to a tangential shearing 

 stress prevents an excessive thinning of the film, thereby checking the 

 tendency for an equal distribution of water applied at a given point. 



The irrigation experiments of Loughridge (24) and Widtsoe and 

 McLaughlin (32) show that most of the soil moisture is found nearest 

 the source of supply, no matter in what direction the movement takes 

 place. The latter investigators (32, p. 268) also found that "when 

 water is abstracted from a soil the loss is felt to every depth reached by 

 the soil augers." 



That considerable movement of water takes place in moist soil was 

 demonstrated by Alway and Clark (2), who found that loss of water 

 from the surface of soil having but 12 per cent of moisture was felt to a 

 depth of 3 feet. Lynde and Bates (25) and Lynde and Dupre (26) think 

 that osmosis may cause a considerable movement of soil moisture. 



It has been demonstrated by Bouyoucos (3) that a change in tempera- 

 ture will occasion a large movement of moisture in unsaturated soil. 



Burr (7) found that very little moisture was brought to plant roots by 

 capillarity. Away from a source of soil water, in a soil partially dry, 

 capillary movement was not detected. 



FORCES ACTING ON SOIL MOISTURE 



That discordant results in soil-moisture investigations should be found 

 is not strange when it is remembered how complex is the soil itself and 

 how many are the forces acting on soil moisture. 



Bouyoucos (3) has pointed out that soils have a great attractive and 

 adhesive force for water. The moisture equivalents found by Briggs 

 and McLane (6) give an idea of the magnitude of these forces. As has 

 been stated, osmosis may play an important part in the movement of 

 soil moisture. 



Viscosity, concentration of soil solution, surface tension, and moisture- 

 film curvature are all important in soil-moisture movement, according to 

 Briggs (4) and Briggs and Lapham (5). 



