234 THE PRINCIPLES OF SOIL MANAGEMENT 



where it maintains a fairly constant supply of water to 

 those crops which may be growing on the surface. 

 The ground water is so near the surface in some stream 

 bottoms, lake shores, etc., that this condition prevails. 

 Soils ordinarily poor in their moisture relations become 

 highly satisfactory in such cases. Sandy land is almost 

 ideal in its crop relations, so far as moisture goes, under 

 such conditions. 



In a limited way it has been attempted to irrigate 

 the soil from beneath the surface by forming under- 

 ground channels of porous pipe, properly graded, into 

 which irrigation water may be turned, which should 

 diffuse through the soil by percolation and capillarity. 



In some situations, as lawns, truck and fruit gardens, 

 it may be possible to install a drainage system of tile, 

 which may also serve as a means of irrigation. 



The system has a number of advantages, which in 

 ordinary practice are more than offset by its disad- 

 vantages. Its advantages may be summarized as fol- 

 lows: (1) It is very economical of water. (2) In alkali 

 soil it greatly reduces the surface accumulation of 

 alkali. (3) It insures deep rooting of the crop. (4) It 

 avoids waste land. (5) It avoids injury to the physical 

 condition of the soil. (6) Involves very little super- 

 vision in the application of water. (7) Possibility of 

 the use of the system for drainage purposes. 



Its disadvantages are: (1) The strong tendency of 

 roots to enter and clog the pipes. (2) The slow diffusion 

 of water by capillarity in dry soil. (3) The expense 

 involved in the installation of a system of pipes ade- 

 quate to irrigate most soils. 



