OVER-IRRIGATION AND ALKALI 



383 



the impervious layer is often sufficient to improve the 

 drainage and to send the obnoxious standing water down- 

 ward. It has also been proposed that water-logged lands 

 may be drained by pumping, the pumped water to be 

 lifted to reclaim lands yet without water. Drainage water 

 of the right composition, that is, free from alkali, can 

 well be so used, especially in view of the fact that the 

 next great development in irrigation, so far as sources of 

 water are concerned, will be the use of subsoil water by 

 pumping. In Europe, the practice of pumping water for 

 the purpose of reliev- 

 ing the land from ex- 

 cessive moisture and 

 of using the pumped 

 water, prevails largely. 



Without question, 

 underdrainage will 

 become an established 

 practice in the irriga- 

 tion region as it is in 

 the humid region. 

 The excellent drainage investigations of the Office of 

 Experiment Stations of the United States Department 

 of Agriculture have collected a great deal of information 

 concerning the right methods of draining irrigated lands. 



229. Alkali defined. Soluble substances are being 

 continuously formed in all soils from the progressive 

 decomposition of the soil particles. Under high rainfall 

 most of these soluble materials are washed into the country 

 drainage, and finally into the ocean. It has been suggested 

 that the salinity of the ocean is at least in part due to the 

 accumulation of salts lost by soils. Under low rainfall, 

 which penetrates only a few feet of soil, the soluble 



FIG. 112. Drainage of irrigated lands by inter- 

 cepting drains. 



