36 



FLOODING AND DRAINAGE. 



This is the one true and permanent method of reclamation if thor- 

 oughly carried out. As the salts composing alkali are easily soluble 

 in water, except the black alkali which can be made so by the use 

 of gypsum, the remedy is to dissolve them and draw them off. 



To do this, the land to be reclaimed is carefully treated with 

 gypsum, if it contains black alkali, then flooded and drained by sub- 

 drainage. At the lower end of the piece of land there should be a 

 drainage ditch sufficiently deep to collect the seepage waters. If the 

 land is a large tract, other sub-drains should be dug at convenient 

 intervals but all leading to the main drainage canal. The water rim 

 on the field is allowed to drain out through the soil from below. Af- 

 ter this, the laud is flooded and the operation repeated until the soil 

 has been thoroughly leached. 



The success of the reclamation will depend on the thoroughness of 

 the work; if the soil is only partly washed, enough alkali may still 

 exist to hinder the proper growing of cane. Simply running water on 

 the soil and allowing it to stand without subsequent drainage will 

 only make matters worse because when the water has evaporated the 

 salts absorbed from the under strata will be found accumulated at 

 the surface. Allowing the water to pass over the surface and then off 

 into a ditch is not effective; some of the alkalies are washed away, it 

 is true, but those below still remain. Thorough flooding and thor- 

 ough drainage are all -important. 



The time required for complete reclamation will depend on the lo- 

 cation of the land relative to the great valley drainage system, the 

 character and quantity of salts present, and the rapidity with which 

 the water drains through the ground. If, after flooding'and drying, 

 no trace of a crust is to be found, it is pretty sure evidence that the 

 work is complete. 



Tile drains are advantageous but in Peru where the natural drain- 

 age is so good there is less need for this additional expense. 



IRRIGATING CANE GROWING ON ALKALI AREAS. 



Tin's has been spoken of indirectly in other places but a few points 

 may be added here. 



The best way is, of course, to reclaim first and irrigate according 

 to the usual methods. It often happens, however, that there is not 

 enough water for thorough washing, or that the cane already grow- 

 ing would not bear the addition of so much water, or that there are 



