SOILS. 



the average of a soil column of four feet. By calculating the 

 figures so obtained to an acre of ground, we can at least ap- 

 proximate the limits within or beyond which crops will suc- 

 ceed or perish. Applying this procedure to the cases repre- 

 sented in the diagrams (pp. 434, 452, chapter 22) and estimat- 

 ing the weight of the soil per acre-foot at 4,000,000 pounds, we 

 find in the land on which barley refused to grow the figures 

 32,470 and 43,660 pounds of total salts per acre, respectively 

 corresponding to 0.203 per cent, for the first figure (the second, 

 representing only the two surface feet, is not strictly compar- 

 able). For the land on which barley gave a full crop, we find 

 for the May sample 25, 550 pounds, equivalent to 0.159 per cent, 

 for the whole soil column of four feet. It thus appears that for 

 barley the limits of tolerance lie between the above two figures. 

 It should be noted that in this case a full crop of barley was 

 grown even when the alkali consisted of fully one-half of the 

 noxious carbonate of soda; proving that it is not necessary in 

 every case to neutralize the entire amount of that salt by means 

 of gypsum, which in the present case would have required 

 about g l / 2 tons of gypsum per acre a prohibitory expenditure. 

 Relative Injuriousness of the Several Salts. Of the three 

 sodium salts that usually constitute the bulk of " alkali," only 

 the carbonate of soda is susceptible of being materially changed 

 by any agent that can practically be applied to land. So far as 

 we know, the salt of sodium least injurious to ordinary vege- 

 tation is the sulfate, commonly called Glauber's salt, which 

 ordinarily forms the chief ingredient of " white '' alkali. 

 Thus barley is capable of resisting about five times more of the 

 sulfate than of the carbonate, and quite twice as much as of 

 common salt. Since the maximum percentage that can be re- 

 sisted by plants varies materially with the kind of soil, it is 

 difficult to give exact figures save with respect to particular 

 cases. For the sandy loam of the Tulare substation, Cali- 

 fornia, for instance, the maximum for cereals may be approxi- 

 mately stated to be one-tenth of i per cent, for salsoda : a 

 fourth of i per cent, for common salt ; and from forty-five to 

 fifty one-hundred ths of one per cent of Glauber's salt. For clay 

 soils the tolerance is in general markedly less, especially as re- 

 gards the salsoda; since in their case the injurious effect on the 



