Alkali and Seepage Problems 99 



water. As most of the salts in this class of land 

 are contained in the top layers of the soil often in 

 the first six inches the furrow system of watering 

 is not of much use in leaching the salts into the 

 drainage pipes, as by this method of watering the 

 top of the soil only receives such moisture as soaks 

 upward out of the furrows. 



Where the sprinkler system of watering is in- 

 stalled the leaching of a piece of ground, whether 

 of a level or of an undulating nature, is a compara- 

 tively simple matter, as the whole of the surface of 

 the land can- be heavily soaked with water. Where 

 sprinkler irrigation is not available the land has to 

 be graded into level checks and then given a heavy 

 flooding of water. By this means a large proportion 

 of the soluble salts will be leached into the drainage 

 pipes. 



CULTIVATION. 



As has been previously pointed out in Chapter X, 

 one of the most effective ways of preventing the 

 rise of injurious salts to the surface of the ground is 

 by means of deep ploughing and cultivation. Cul- 

 tivation destroys the capillary tubes through which 

 the salt-impregnated water finds its way to the top 

 layers of the soil, where, through the 4 evaporation of 

 the water, the salt is deposited. 



The deeper, then, that the land is cultivated the 

 thicker is the blanket of loose, dry soil mulch shield- 

 ing the moister soil beneath, and the farther from 

 the surface of the ground is the salt kept from 

 rising. Cultivation should be most frequent and 

 thorough during the hottest months of the year, and 

 to be effective should not be less than six inches 

 in depth. 



SEEPAGE. 



Seepage has already been defined as the concen- 

 tration of drainage waters at or near the surface of 



