6i2 POPULAR SCIENCE MONTHLY. 



grams below, whicli show the facts more plainly than would fig- 

 ures ; the vertical line to the left representing the soil depth (in 

 feet and inches), while on the horizontal lines the percentages of 

 salts in the soil are entered at intervals representing two, or four 

 one-hundredths of one per cent each. The area within the curve 

 generated by connecting the points of actual observation repre- 

 sents, of course, the total of each ingredient indicated. 



Diagram No. 1 represents the natural condition, the soil being 

 at the time covered with the native spring growth of bright flow- 

 ers. No alkali salts are seen on the surface at this point at any 

 season. 



It will be noted that the alkali salts are almost wholly accumu- 

 lated between the depths of twenty and forty inches. Both above 

 and below these limits impregnation is not strong enough to inter- 

 fere with vegetable growth of any kind ; witlihi them, the sub- 

 soil is hardened into a sheet of hard pan, which not only prevents 

 the passage of roots by its resistance, but would corrode them by 

 contact with a mixture of salts containing up to ninety-four per 

 cent of carbonate of soda. But as the native vegetation is mostly 

 shallow-rooted and annual, this does not interfere with its welfare. 

 The moisture imparted to the land by the scanty rainfall (about 

 seven inches) evaporates through the roots and leaves of this 

 vegetation during its growing period ; when it dies off it leaves 

 the ground completely dry, so that no rise of the salts to the sur- 

 face by evaporation can take place during the season, and the 

 seeds dropped can germinate when the rainy season comes, with- 

 out injury from alkali. 



Diagram No. 3 shows, on the other hand, what happens when 

 irrigation is practiced on this land (or when the water rises from 

 below by seepage from leaky ditches), and the ground is left hare. 

 The abundant water then dissolves the alkali salts in the subsoil 

 hardpan ; and evaporation continuing through the whole year, 

 the entire salts are in the course of a few seasons carried upward 

 nearer to the surface. Diagram 3 shows the state of things under 

 these conditions at the same date as Diagram 1 (May 3, 1895) ; 

 No. 4, a and h, shows the condition existing near the surface at the 

 end of the dry season, in September or October. It will be seen 

 that at that time the salts have accumulated so near the surface 

 that by taking the soil away to the depth of six inches, from five 

 sixths to seven eighths of the total mass of salts would be re- 

 moved, leaving the land with no more than almost any crop can 

 easily resist. 



Diagram 2, a and h, shows the state of the irrigated land when 

 sown to barley, it being understood that these samples were taken 

 within ten feet of No. 3. A glance reveals that we have here a 

 case intermediate between Nos. 1 and 3. The upward movement of 



