430 



SOILS. 



after irrigation, 1 are shown in the annexed diagrams; in which 

 the kind and amount of salts is shown for every three inches of 

 vertical depth, down to four feet, by curves whose extension 

 from left to right indicate the several percentages, while the 

 outer curved line gives the total of salts for each of the several 

 depths. 



Fig. 63 represents the condition of the salts in an " alkali spot" as 

 found at the end of the dry season at the Tulare substation, California. 

 The soil was sampled to the depth of two feet at intervals of three 

 inches each. It is easy to see that at this time the bulk of the salts 

 was accumulated within the first six inches from the surface, while 

 lower down the soil contained so little that few culture plants would be 

 hurt by them. 



How Native Plants Lire. Fig. 64 represents similarly the state of 

 things in a natural soil alongside of the alkali spot, but in which the 

 native vegetation of brilliant flowers develops annually without any 

 hindrance from alkali. Samples were taken from this spot in March, 

 near the end of the wet, and in September, near the end of the dry 

 season, and each series fully analyzed. There was scarcely a noticeable 

 difference in the results obtained. It is seen in the figure that down to 

 the depth of 15 inches there was practically no alkali found (0.035%), 

 and it was within these 15 inches of soil that the native plants mostly 

 had their roots and developed their annual growth. Hut from that 

 level downward the alkali rapidly increased, and reached a maximum 

 (0.529%), at about 33 inches ; decreasing rapidly thence until, at the 

 end of the fourth foot in depth, there was not more alkali than within 

 the first foot from the surface. In other \\ords, the bulk of the salts 

 had accumulated at the greatest depth to which the annual rainfall 

 (7 inches) ever reaches, forming there a sheet of tough, intractable clay- 

 hardpan. The shallow-rooted native plants germinated their seeds freely 

 on the alkali-free surface; their roots kept above the strongly-charged 

 subsoil, and through them and the stems ; .ml foliage all the soil mois- 

 ture was evaporated by the time the plants died. Thus no alkali was 

 brought up from below by evaporation. The seeds shed would remain 

 uninjured, and would again germinate the coming season. 



1 IFilgard and Loughridge, Bulletin X<>. uS. California Experiment Station; Re- 

 port California Kxperiment Station. ^94-95, p. 37 ; Bulletin No. 30, Office of 

 Experiment Stations; Wollny's Forsch. Geb. Agr. I'hys., 1896. 



