26 FIELD OPERATIONS OF THE BUREAU OF ROILS, 1903. 



the "normal salt.'' Hence the matter of drainage becomes doubly 

 imporant in areas in which the comparatively harmless bicarbonate of 

 sodium prevails. 



In the Gila ValW area the subsoils of the heavier types carry in the 

 aggregate great quantities of the alkali salts. Fortunately, however, 

 natural drainage is good and the practice of excessive irrigation is less 

 frequent than in many western areas. The water table lies at such 

 depths under the greater portion of the area that the movement of salts 

 upward takes place only to a limited extent. The accumulation of the 

 alkali salts upon the surface results for the most part from evapora- 

 tion of irrigating water carrying in solution the salts derived from 

 percolation of the upper portion of the soil section. The water table 

 plays but little or no part in the accumulation. 



RECLAMATION OF ALKALI LAND. 



There is always a tendency in irrigated districts to use a greater 

 quantity of water than is actually necessary. This excess, unless car- 

 ried away through efficient natural or artificial drainage channels, 

 sooner or later results in raising the water table. At the present time 

 but little of the irrigated lands of the valley are in need of drainage. 

 Should future irrigation result in raising the water table, however, as 

 is likely, trouble will ensue, especially in the heavier soils. When 

 the water approaches within 6 feet or less of the surface the limit of 

 safety is reached and provision should at once be made for carrying 

 away the excess of water. Tile or open drains at intervals of one- 

 eighth or one-fourth mile will assist greatly in keeping the water table 

 below the danger line. 



Among the most prominent methods proposed for reclaiming alkali 

 lands may be mentioned the removal of the crust by scraping, the 

 application of chemical correctives, the growing of alkali-resistant 

 crops, and drainage. Of these only the last mentioned is thoroughly 

 effective, since it is the onhy method which removes the cause of the 

 trouble. Some of the other methods may, however, be used with good 

 results in connection with drainage. 



The removal of the alkali salts by scraping the surface calls for 

 much labor and must be constantly repeated, an}- good that may result 

 being merely temporary. This method need receive little serious 

 consideration. 



The application of gypsum is practiced with beneficial results in 

 soils where there occurs an excess of sodium carbonate or "black 

 alkali.' 1 In this case chemical reaction takes place, and the injurious 

 carbonate salt is changed into the less injurious "white alkali." This 

 method alone does not remove the cause or permanently improve the 

 land, and it is but a question of time until the white alkali itself will 

 accumulate in sufficient quantities to be destructive of plant life. 



