STEPPES, DESERTS, AND ALKALI LANDS. 611 



sufficient. In the hot summers of arid countries even more than 

 twice that depth may be necessary. In that case the alkali salts 

 left behind by evaporation will be diffused through so large a 

 mass of soil that no injury can ordinarily result. 



But experience proves that some alkali soils are, in their natu- 

 ral state, incapable of being reduced to a proper condition of 

 tilth ; and this, as well as the tendency of the obnoxious salts to 

 come to the surface more and more when land is irrigated, has 

 been made the subject of extensive investigations by the Califor- 

 nia Experiment Station, in order to determine the proper methods 

 for the permanent repression of these obstacles to cultivation. 



These investigations proved, as far back as 1880, that the cause 

 of difficult tillage in alkali lands is carbonate of soda (sal soda), the 

 presence of which is recognized by the blackish spots and rings 

 left on the soil when rain or irrigation water evaporates ; hence 

 the popular designation of " black " alkali, known to be specially 

 injurious and corrosive. It was also shown that the peculiar ill 

 effects of such alkali can be overcome by the use of sufficient 

 dressings of gypsum or land plaster, which acting in conjunction 

 with water transforms the corrosive sal soda into bland and rela- 

 tivety innocuous sulphate, or Glauber's salt. The latter, with more 

 or less of common salt, forms the bulk of the salts in the cases of 

 mild or " white " alkali, of which a much larger proportion is tol- 

 erated by all plants. Gypsum also has the effect of rendering in- 

 soluble the humus and phosphoric acid that had been dissolved 

 by the salsoda. 



But the rise of the alkali brought about by irrigation seemed 

 to indicate that an indefinite amount of these salts might lurk in 

 the depths of the soil ; and that as irrigation wets the land more 

 deeply than would the scanty natural rainfall, and correspond- 

 ingly increases the surface evaporation, permanent reclamation 

 of alkali lands seems difficult if not hopeless. 



To decide this question, at first examinations of the natural 

 bottom waters of such lands were made, which showed in most 

 cases saline contents not greater than those of many waters long 

 successfully used for irrigation. It then became important to 

 determine just to what depth the impregnation of salts actually 

 reaches. 



For this purpose borings were made at the Culture Experiment 

 Station near Tulare, Cal., samples being taken by means of a post- 

 hole auger of each successive three inches of soil, down to the 

 depth of two or four feet, as might be required. Each of these 

 (twelve to sixteen) samples was then separately leached and ana- 

 lyzed, determining both the total amounts of salts present and the 

 proportions of the three to five principal compounds. The results 

 of this work in four typical cases are embodied in the curve dia- 



