94 SOIL WATER AND ITS RELATION TO SOIL FERTILITY 



of surface per unit volume to which water films can cling. A fine 

 sand, on the other hand, can hold a larger percentage of capillary 

 water because there is a much larger amount of surface over which 

 water films can form. 



A black silt loam or clay loam containing much organic matter 

 and being crummy in structure can hold a large amount of capil- 



<W' 



^u-. -^m^ 



m 



mm 



wm?y . 



FIG. 38. Checks and cracks aid entrance of water into the soil, and facilitate perco- 

 lation of water through it. Silt loams, clay loams and clays check and crack when they 

 dry out. 



lary water, for three reasons: (1) its fine texture affords much 

 surface for water films; (2) the organic matter has a high- water 

 absorptive capacity, and (3) the crumbs contain pore spaces, 

 many of which may become filled with water. 



Peat holds the greatest amount of water per unit weight. 



Movements of Water in Soil. There are three important move- 

 ments of soil water percolation, seepage and capillary rise of water. 



Percolation is the passing of free or gravitational water straight 

 down through the soil (Fig. 38). This movement takes place 

 through the pore spaces in between the soil particles or crumbs. 



