100 SOIL WATER AND ITS RELATION TO SOIL FERTILITY 



such as coarse sand or gravel During a dry period the main source 

 of moisture that crops can draw on is the capillary water stored 

 in the shallow surface stratum, since no water is supplied to the 

 seed bed by capillarity from lower depths. Furthermore, roots 

 extending into a gravelly subsoil can secure but little moisture. 

 In contrast to this, a silty clay subsoil, for example, furnishes much 

 water to the seed bed, and to the deep roots extending down into it. 

 Moreover, a seed bed underlaid by* a fine textured subsoil can hold 

 more capillary water than if the subsoil were sand or gi^avel. 

 In buying a farm it is important to examine into the nature of 

 the subsoil to ascertain whether or not it can furnish the seed bed 

 with any capillary water and supply the deep roots with sufficient 

 moisture; and whether or not it can permit percolation sufficient 

 at least to favor proper drainage. 



MOISTURE CONSERVATION AND CONTROL, WITH SPECIAL REFERENCE 



TO HUMID FARMING 



The loss of water from rainfall may occur by running off the 

 surface of the soil, by percolating through it, a.nd by evaporating 

 from it. Roughly speaking, only about twenty-five to thirty per 

 cent of the rainfall in a humid climate is used by crops — the rest 

 is lost (Fig. 43). Moistm-e conservation and control consists 

 (a) in preventing surface run-off as much as possible; (6) in increas- 

 ing water-holding capacity of soils; (c) in aiding capillary rise of 

 soil moisture; (d) in lessening the loss by evaporation either from 

 the soil or through weeds; (e) in draining wet lands, and (/) in 

 supplying water through irrigation. 



How Run-off May be Lessened. — Loss of rainfall through 

 surface run-off may be much lessened by aiding soils to catch or 

 trap water. This may be accomplished in several ways: (a) by 

 fall plowing; (b) deep hillside plowing; (c) by loosening up any 

 hard and compact soil and subsoil; (d) by plowing at right angles 

 to the slope or hillside, and (e) by terracing. Any one of these 

 methods permits more of the rainfall to soak into the ground, and 

 that which is not stored or retained by the soil passes on down and 

 away. In some sections, and especially on hillsides, the storage 

 of water by the soil during late fall, winter and early spring, or at 

 any other time, is greatly hindered, because no provision is made 

 whereby soils can catch the rainfall. Any other method whereby 

 soils may be aided in ''trapping" and storing water from rainfall 

 is worthy of consideration. 



