SOIL WATER 83 



of most cultivated crops rarely go more than five 

 feet deep, hence a soil in which the water table is 

 from four to six feet below the surface is apt to be 

 most abundantly supplied with film water. When 

 wet land is tile drained, the level of the water table 

 is reduced from four to six feet deep, depending 

 upon the depth at which the drains are laid below 

 tne surface. The chief reason why wet lands are 

 so valuable after being under-drained is that the 

 water table is lowered only to the point where it can 

 most easily supply the soil above with film moisture ; 

 while in lands that need no under-drainage the 

 water table may be thirty feet deep instead of six. 



HOW TO INCREASE THE WATER-HOLDING CAPACITY 



OF SOILS 



Fortunately for the farmer he can do much to in- 

 crease the amount of film water that some soils can 

 hold, and thereby increase their productiveness. The 

 farmer who irrigates should be interested in the sub- 

 ject as much as the farmer who depends upon natural 

 rainfall to supply his crops with water; it is tedious 

 and expensive to irrigate frequently, and he should 

 know how to increase the capacity of his soil to hold 

 water so that fewer irrigations will be needed. 



Under-drainage is the most efficient means of im- 

 proving a soil in which the water table is always so 

 close to the surface that the soil is too wet for farm 

 crops; or which is very wet in winter and very dry 

 in summer. Deep plowing, harrowing, cultivating 

 and other tillage operations also do much to deepen 

 the soil and enlarge the reservoir, because the more 

 a soil is pulverised the more water it will hold. 

 The addition of humus to a soil in the form of farm 

 manure, muck or a green manure, has a very 



