The Soil and Soil Water 



33 



W. T. SKilling 



FIG. 21. Capillary action under different conditions. 



If a dry stone is partly immersed in water, the 

 moisture will be seen to creep up a little way above 

 the water level. (Exps. n, 12, 13.) If a brick is set 

 on end in a shallow pan of water, the water will in 

 time draw to the top. Because the brick is porous, 

 water can go up through the many capillary spaces 

 within it much better than it can rise on the outside of a 

 stone. Similarly, the small spaces in fine-grained soil 

 like clay draw up and hold considerable water, and the 

 larger spaces in coarse-grained soil like sand remain 

 empty. So sand will not hold nearly so much water as 

 clay. 



A most important water-holding constituent of the 

 soil is humus. This partly decayed matter not only 

 holds water on its surface and in the small spaces be- 



Examples 



of 



capillarity 



What 

 happens to 

 water in 

 clay and in 

 sand 



How humus 

 holds water 



