226 SOILS: PROPERTIES AND MANAGEMENT 



ing the capillary limits as to the height of rise in dry and 

 moist Michigan soils, found this limit much greater where 

 the soil was damp. This vertical rise from a water table 

 was almost three times greater, on the average, in the soil 

 in which the films were originally thicker. Briggs and 

 Lapham l found this ratio in Sea Island soil to be as high 

 as four and one-half ; while Wollny 2 has shown sand with 

 9.5 per cent of moisture to raise moisture from a water 

 table one-half higher in six days than did the same sand 

 dry. It is evident, therefore, that a soil with a thick 

 capillary film will carry moisture faster than one with a 

 thinner film, and also will raise the moisture higher when 

 the final film adjustment has taken place. 



In an air-dry soil it is obvious that before capillarity 

 may take place a thicker film than has already existed 

 must be established. This is often difficult because of the 

 presence of oily materials deposited on the surface of the 

 particles during the process of drying out. Such a condi- 

 tion probably accounts, at least partially, for the differ- 

 ence in total rise of capillary water in a dry and in a moist 

 soil, since, theoretically, if time enough were given for 

 adjustment, the total height should be the same in both 

 columns. This resistance of dry soil to the resumption 

 of a capillary film is made use of in soil mulches, where a 

 dry surface layer of the soil checks evaporation by imped- 

 ing capillary rise. It is also obvious that in a study of the 

 rate and height of capillary movement and the factors 

 affecting it, moist columns should be used, as this is a 



1 Briggs, L. J., and Lapham, M. H. Capillary Studies. 

 U. S. D. A., Bur. Soils, Bui. 19, p. 26. 1902. 



2 Wollny, E. Untersuchungen iiber die Kapillare Leitung 

 des Wassers im Boden. Forsch. a. d. Gebiete d. Agri.-Physik, 

 Band 7, Seite 269-308. 1884. 



