20 AGRICULTURE FOR COMMON SCHOOLS 



water. Free water is not only of little use to the plants, but 

 instead it carries away particles of rich soil when it runs off 

 the surface, or dissolved plant food when it escapes in drains. 



Capillary Movement of Water. — In most soils there is 

 a point more or less distant, usually six to thirty feet, from the 

 surface where the spaces between the soil grains are filled 

 with water, that is, the soil is saturated. This is called the 

 standing water or water table, and it extends beneath the sur- 

 face at variable depths as a sheet of water. It is this water 

 table that we drill or dig into when, in putting down a well, 

 we say we have struck a "vein'^ of water. The water table 

 follows the general outline of the surface soil and has its high 

 and low places just like the land. 



When the soil near the surface begins to get dry, water 

 creeps up over the particles of soil in the subsoil toward the 

 surface and tends to renew the water there. This is called 

 capillary movement. The cause of the loss at the surface is 

 the drying action of the wind and sun called evaporation, and 

 the loss by evaporation from the leaves of plants called trans- 

 piration. Now the water rarely moves up fast enough to keep 

 up the supply at the surface, so that the ground gets quite dry 

 after a time, but by cultivation we can help to keep up the 

 supply. We shall explain this presently. 



Capillary movement takes place differently in different 

 kinds of soil. In coarse grained soils like sandy soils it moves 

 faster, but not through so great a distance. A clay or loam 

 subsoil is the best to supply moisture to crops in dry seasons, 

 because in such soils the capillary water will move through 

 a greater distance than in any other soils. This is because the 

 grains in these soils are quite small and the films on their 

 surfaces are comparatively strong. These films make a strong 



