24 



LAND DRAINAGE 



which must be kept at a minimum. Few farmers, how- 

 ever, obtain this service from water. 



TABLE V 



In the fourth column of the table are shown the yields 

 of the several crops that should be obtained from eight 

 inches of rainfall under the same conditions of efficiency. 



36. Conditions of water. Water may exist in the 

 soil in any one of three conditions; as gravitational, 

 as capillary, and as hygroscopic water. 



37. Gravitational water. That water in the soil 

 which, if opportunity be given it, will flow downward 

 or away through the soil because of its own weight, is 

 gravitational water. Its tendency is to flow directly 

 downward. Obstructions and restrictions of various 

 kinds will turn it out of its course and cause it to flow 

 in other directions even upward, as is seen in a boiling 

 spring (the stream of water rising out of the ground - 

 not from heat). Water which in the soil would be grav- 



