THE SOIL AND WATER 139 



If the water-table is only a few inches beneath the surface, we 

 have a swamp or bog; at one and a half to three feet in depth, 

 we ha\e a wet soil in which some plants, especially grasses, may 

 flourish. A depth of four to eight feet is favorable to agricultural 

 conditions, though in many regions the water-table is much lower 

 than this. 



In general, agricultural plants are injured if their roots are im- 

 mersed for any length of time in the ground water, though many 

 plants may send down roots to this water. 



Gains of Water by the Soil. The chief ways in which the soil 

 may gain water are by rainfall and irrigation. In addition, ground 

 water may be brought up to within reach of the plant roots 

 by capillary action. 



Regions having more than 20 inches rainfall are said to have 

 a humid climate. The character of the rainfall must be con- 

 sidered as well as the total quantity. If it is heavy 

 and infrequent, a large proportion of the water will 

 run off on the surface and the region may possess more 

 characteristics of an arid climate than a region with a moderate 

 rainfall well distributed. 



The amount of water gained from rain depends upon the 

 nature and the extent of the rainfall, the drainage, etc. A heavy, 

 rapid rainfall may saturate the surface and flow off without any 

 large quantity sinking into the soil. A slight rain may decrease 

 the water content of the soil by establishing such capillary connec- 

 tion between surface soil and lower layers, as to bring water to 

 the surface which is lost by evaporation. 



If the surface of the soil is compact, the rain may flow off 

 instead of penetrating the soil; but if the soil is loose, it will 

 absorb considerable quantities of rain. ' One method of prevent- 

 ing the washing of hilly land consists in deep plowing or subsoil 

 plowing, so that the water will sink into the soil instead of run- 

 ning off. In regions of slight rainfall, where it is desirable to 

 save all the rain, the subsoil is stirred, and packed ; this increases 

 the capillarity of the soil and its power of holding water. These 

 are the methods of dry farming. 1 

 1 See Dry Farming, by Widstoe. 



