SPECIAL FARM TOPICS 279 



nating heights and hollows are difficult to reduce to an even grade. 

 Again, the land may be cut up by ravines, thereby increasing the 

 labor and cost of putting water upon it, or it may have too much or 

 too little slope. If land which is naturally smooth on the surface 

 and of the right slope costs $5 per acre to put in shape for irrigating, 

 hog-wallow land may cost $15. Thus it is evident that the cost of 

 preparing the surface is an important consideration in the first cost 

 of the land. Besides, some hog-wallow land is inferior in quality, 

 being frequently charged with injurious salts. (F. B. 263.) 



Irrigation Waters. The injurious effect of irrigation water is 

 due to the presence of such alkaline bases as soda, potash, ammonia. 

 These usually appear as sulphate of soda (Glauber's salt), and car- 

 bonate of soda (salsoda). Sulphate of potash, phosphate of soda, 

 nitrate of soda, and carbonate of ammonia rarely occur in under- 

 ground waters. Quantity considered, carbonate of soda is the most 

 injurious of the mineral elements, from an irrigation standpoint, 

 found in our water supply. This form of soda combines in many 

 cases with vegetable mould or humus forming a black compound 

 when dry, known as black alkali. (Tex. Bui. 43.) 



The best method of distributing alkaline accumulations is by 

 flooding, thereby lessening the concentration of the salts to an unin- 

 jurious degree. This may be done by growing crops upon affected 

 ground requiring irrigation by flooding, as alfalfa; or by using 

 (preferably) fresh river waters, where available, in sufficient amount 

 to effect the distribution or removal of salts. 



The rise of the alkali from the use of salty irrigating waters 

 may be controlled in large part, where practicable, by deep irriga- 

 tion, especially through subsoiler furrows. This method economizes 

 water by lessening surface evaporation, and at the same time hinders 

 the accumulation of salts at the surface. 



Deep and thorough cultivation must follow and supplement 

 deep irrigation, as this prevents the return of salts to the surface. 



(Ariz. Sta. Bui. 44.) 



Experience throughout the arid region is demonstrating that 

 the greatest danger to irrigated lands is lack of drainage. Water ap- 

 plied to crops raises the ground water, which brings with it the salts 

 dissolved from the soil ; capillarity brings this water to the surface, 

 where it evaporates, leaving the salts to accumulate until all vegeta- 

 tion is destroyed. The only insurance against this is proper drain- 

 age. The drainage conditions are therefore equally important with 

 the water supply and should be looked into with as much care. 

 When there is not good natural drainage it must be supplied arti- 

 ficially. This, usually, is as expensive as securing the water supply. 



(F. B. 263.) 



The sources of water supply and methods of use most frequently 

 available for a single farm include the following: Diversion of 

 perennial streams; development in dry stream beds; development 

 of springs; catchment from outcroppings of water-bearing strata; 

 tunneling to intercept such strata when deeply covered ; flowing 



