PHYSICAL PROPERTIES OF SOILS 2Q 



f 



sively investigated. Ordinarily crop yield is directly 

 proportional to and dependent upon the water supply. 

 The rainfall during the time of growth is frequently 

 less than the amount of water required for the produc- 

 tion of the crop. One inch of rainfall is equal to about 

 112 tons of water per acre. An average of two inches 

 per month during the three months of crop growth is 

 equivalent to only 675 tons, a large part of which is lost 

 by surface drainage and by evaporation. Hence it is 

 that the rainfall during an average growing season is 

 less than the amount of water required to produce 

 crops, and consequently the water stored up in the 

 subsoil must be drawn upon to a considerable extent. 

 Inasmuch as the soil's reserve supply of water is such 

 an important factor in crop production, it follows that 

 the capacity of the subsoil for storing up and supplying 

 water as needed is a matter of much importance, par- 

 ticularly since the power of the soil for absorbing and 

 retaining water may be influenced by cultivation and 

 manuring. Before discussing the influence of cultiva- 

 tion upon the soil water, the forms in which water is 

 in the soil should be studied. It is present in three 

 forms: (i) bottom water, (2) capillary water, and (3) 

 hydroscopic water. 



19. Bottom Water is that which stands in the soil at 

 a general level, and fills all the spaces between the soil 

 particles. Its distance from the surface can be told in 

 a general way by the depth of surface wells. Bottom 



