542 Journal of Agricultural Research voi. x, No. n 



nesium. In this paper the term will be used to include all the wiater- 

 soluble salts of the soil, whether organic or inorganic. 



The alkali tolerance of the plant varies widely. For instance, a plant 

 may thrive in a saturated solution of gypsum and be killed by i part per 

 million of copper, or even by lesser amounts of some of the more toxic 

 organic salts. The accumulation of alkali in the soil, therefore, in suf- 

 ficient amounts to make agriculture impossible does not necessarily 

 mean the accumulation of the salts of sodium, calcium, and magnesium. 



In 1892, Dorsey (3)^ estimated that about 847,000 acres of the irrigated 

 land in the United States had already been lost by alkali accumulation. 

 He placed a value of $50 an acre on this land, and calculated a loss of 

 $42,000,000 on account of alkali accumulation. A valuation of $50 an 

 acre seems reasonable, as this would hardly pay for the average recla- 

 mation and water right. This was 14 years ago and the evil has been 

 increasing year by year since that time; $100,000,000 would probably 

 not now cover the loss sustained by alkali during our brief experience in 

 irrigation agriculture. 



The loss of land by alkali accumulation might well be divided into two 

 distinct classes: The first, or greatest loss, generally occurs when the 

 soils are first brought under irrigation. Water is applied to the soils 

 on the benches or higher levels, usually in excessive amounts, and this 

 dissolves out the salts that have accumulated in the soil while in a 

 desert condition. The water, carrying with it the salt, gradually finds 

 its way to the lower levels and to the lower drainage basins, and upon 

 evaporation leaves the dissolved salts on, or near, the surface. These 

 salts are ordinarily largely sodium chlorid, sodium sulphate, sodium 

 carbonate, and sodium bicarbonate This seepage takes place when 

 there is an abundance of water and drainage from the higher to the lower 

 levels, and it is probably responsible for 90 per cent of the loss that has 

 been sustained in the irrigation projects of the United States up to date. 



The alkali accumulation, v^'hich might be considered as secondary, is 

 much slower and takes place upon the bench lands, as well as upon the 

 lower levels, and also upon many areas where there is a limited amount 

 of irrigation water, and no drainage or seepage. This phase of alkali 

 accumulation will be taken up later. 



FORMATION OF " BLACK ALKALI " 



In the arid and semiarid regions of the West, where alkali conditions 

 abound, the presence of calcium carbonate, or carbonate of lime, is so 

 common that it has been termed by Dr. Hilgard "a standing character- 

 istic" of alkali soil. In a great many cases, although the carbonate is 

 not in evidence upon the surface of the soil, it may be found from a few 

 inches to a few feet below the surface, acting as a cementing material 

 in the troublesome hardpan. This hardpan usually occurs at the lower 



1 Reference is made by number to " Literature cited," p. 589. 



