THE FORMS OF SOIL WATER 217 



(see Fig. 31) from Buckingham 1 makes clear not only 

 the influence of texture on capillary water, but also the 

 distribution of water in a capillary column. 



The final mean water content of these soils was 10, 

 15, and 20 per cent, respectively, for the fine sand, the 

 sandy loam, and the clay; showing that as the texture 

 becomes finer, the greater is the average capillary content 

 even after allowing for the differences in hygroscopic 

 moisture. 



145. Effect of structure on the amount of capillary 

 moisture. The structure of the soil, or, in other words, 

 the arrangement of the particles, will become a factor in 

 capillary capacity in so far as it affects the amount of 

 effective capillary surface. Any arrangement of parti- 

 cles that will increase the number of angles of contact will 

 evidently increase the amount of capillary water. The 

 compacting of a loose soil will increase the possible capil- 

 lary moisture until all the interstitial space becomes 

 capillary in its nature; further compacting will then 

 cause a marked decrease. The granulation of a clay soil, 

 by producing a crumb structure and by actually increas- 

 ing the effective surface exposure, tends to increase its 

 water-holding capacity. At the same time the compacting 

 of a sand, by increasing not only the actual effective sur- 

 face, but also the number of angles possible for capillary 

 concentration, will cause a rise in the capillary capacity 

 of that soil. 



In a study of this kind it is very evident' that the aver- 

 age data of a long column should be considered, since 

 the percentage of moisture at any one point is not in- 

 dicative of the true capillary capacity of a soil. Such 



1 Buckingham, E. Studies on the Movement of Soil 

 Moisture. U. S. D. A., Bur. Soils, Bui. 38, p. 32. 1907. 



