174 



NATURE AND PROPERTIES OF SOILS 



data, obtained in the laboratory of the Department of Soil 

 Technology, Cornell University : 



Table XXXII 



EFFECT OF MOISTURE ON RATE AND HEIGHT OF CAPILLARY RISE 

 FROM A WATER-TABLE THROUGH AIR-DRY SOIL 



It is seen that the movement in sand is rapid, one-half of 

 the total rise being attained in one hour. The maximum 

 height is reached in about three days. The silt loam in this 

 case seems to be of just about the proper textural condition 

 for a fairly rapid rise, yet it exerts enough capillary pull to 

 attain a good distance above the water-table. The friction 

 in the clay is greater, however, and this results in a slower 

 rate. 



Structure has already been shown to affect capillary capac- 

 ity by its influence on the angle interstices and the closeness 

 of the contacts. Evidently, therefore, it may alter both the 

 rate and the height of capillary rise. The loosening of a clay 

 soil or the compacting of a sandy soil will lessen the effective 

 film friction, while at the same time it may strengthen the 

 capillary pull resulting in a faster and a higher capillary flow 

 of water. What may be the best structural condition of any 

 soil in which this result is realized to its highest degree can 

 not be predicted exactly. In general, however, this point is 

 approached when the soil is in the best physical condition for 

 crop growth. Tillage operations, tile drainage, and the addi- 

 tion of lime and organic matter operate toward this result by 

 their granulating tendencies; while rolling, by compacting a 



