330 University of California Publications in Agricultural Sciences [Vol. 1 



filtrate takes on a rich, dark brown color, not unlike the usual 

 NH4OH humus extract. Frequently the soil when dry is covered 

 with a thin layer of hard, black, organic matter. Indeed the re- 

 semblance between the NaCl + H.O soil, the water in contact 

 Avith it, or its percolate, and the natural alkali soils and the water 

 bathing their particles, is so striking as to deceive even those 

 experienced in the handling of ' ' black alkali ' ' soils. 



The increased solubility of the organic matter in the salt- 

 treated, water-washed soils, as indicated by the increased depth 

 of the brown color, cannot be due to the presence of the NaCl 

 as a chemical entity, for the color does not appear until after 

 some of the salt has been removed from the soil by washing. There 

 can be no doubt that the NaNOg by means of an interchange of 

 ions with the organic salts of calcium or magnesium does affect a 

 greater solubility of organic matter, but this solubility may be 

 greatly increased if the added salt is washed from the soil. This 

 fact may be of assistance in accounting for the color of the nitre 

 spots. 



In agreement with Van Bemmelen°- and Warington,'^^ we have 

 also noted the appearance of tluff.y, flocculent colloids passing 

 through the filter paper, when the added salt is practically 

 washed from the soil. These colloids coagulate when in contact 

 with the filtrate containing the soluble salts from the soil. 



One other point which has not received prior attention. Init 

 which seems of sufficient importance to be mentioned at this 

 time, is the fact that all of the salt need not be washed from the 

 soil to produce the effects noted. In another series of experiments, 

 which will be reported in detail later, 3200 cc. of a 1.5 per cent 

 solution of NaCl (which was intended to represent the strength 

 of the soil solution when 0.3 per cent of NaCl is added to the soil 

 under optimum water conditions) was passed through 1 (iOO grams 

 of Davis soil. The soil was affected to a greater extent than a 

 soil receiving a similar quantity of NaCl, namely 4.8 grams, or 

 than a third soil receiving a similar quantity of NaCl, which in 

 addition was leached with 3200 cc. of water. The injury to the 

 first soil was greater than to the other soils despite the fact that 



52 Lac. cit. 



53 Loc. cit. 



