ALKALI SOILS. 



433 



It is thus that the luxuriant vegetation of the San Joaquin 

 plains, dotted with occasional alkali spots, is maintained ; the 

 spots themselves being almost always depressions in which 

 the rain water may gather, and where, in consequence of the in- 

 creased evaporation, the noxious salts have risen to the surface 

 and render impossible all but the most resistant saline growth ; 

 particularly when, in consequence of maceration and fermenta- 

 tion in the soil, the formation of carbonate of soda has caused 

 the surface to sink and become almost water-tight. 



Upward Translocation from Irrigation. Fig. 65 shows the 

 corresponding profile of the same soil after several years' irri- 

 gation. The upward movement of the salts is clearly seen by 

 comparison with the previous figure ; and the surface soil has 

 become so charged with salts that the seeds of culture plants 

 refuse to germinate. 



Ten feet from this bare alkali ground, on which barley had 

 refused to grow, a crop of barley four feet high was harvested 

 the same year, without irrigation. Investigation proved that 

 here the condition of the soil was intermediate between the two 

 preceding diagrams. The irrigation water had dissolved the 

 alkali of the subsoil, and the more abundant evaporation had 

 brought it nearer the surface; but the shading by the barley 

 crop and the evaporation of the moisture through its roots 

 and leaves had prevented the salts from reaching the surface 

 in such amounts as to injure the crop, although the tendency to 

 rise was clearly shown. By the use of gypsum, moreover, the 

 injuriousness of the alkali had been somewhat diminished. 



The same season, grain crops were almost a failure on alkali- 

 free land in the same region ; and in connection with this result 

 it should be noted as a general fact that alkali lands always re- 

 tain a certain amount of moisture perceptible to the hand dur- 

 ing the dry season, and that ////.v moisture can be utilized b\ 

 crops; so that at times when crops fail on non-alkaline land, 

 good ones are obtained where a slight taint of alknli exists in 

 the soil. Actual determinations showed that while a sample of 

 alkali soil containing .54% of salts absorbed 12.3' ' f of moisture 

 from moist air. the same soil when leached absorbed only 2.5' r 

 a figure corresponding to that of sandy upland loams. 



Alkali in Sand\ Lands. In rery sandy lands, and particu- 

 larly when the alkali is " white " only, the tendency to accumu- 

 ' 28 



