1916] Sharp : Soluble Salts and Soil Colloids 335 



probably insufficient to promote normal growth. At least this 

 condition is suggested by the moisture equivalents of the defloe- 

 culated NaCl 4- HoO soil as determined with the centrifugal 

 machine developed by Briggs. In addition to the low availability 

 of the moisture in such soils as an inhibiting factor, the rate of 

 movement of water through such soils must also be considered 

 in its relation to the growth of plants. From all appearances, it 

 seems justifiable to predict that the movement of water through 

 the highly diffused soils is so slow as to fail to resupply the area 

 occupied by the roots from the more moist soil layers lying 

 adjacent to the root area. 



The observed effects of washing salts from soils may also have 

 some bearing upon fertilizer practices and the results on crop 

 plants secured therefrom. The salts used as fertilizers undoubt- 

 edly effect certain modifications of the physical condition of 

 soils. It is also true that the washing out from the soil of at 

 least some of these salts brings a far greater change in the 

 physical properties of the soil than that accompanying the ap- 

 plication of the salts. Probably no instance with respect to this 

 feature, as a phase of soil management, is so patent as that con- 

 cerning the use of NaNOg. HalP" comments upon the inadvis- 

 ability of applying this material under certain conditions be- 

 cause of the deflocculating effect of the alkalinity due to residual 

 sodium carbonate. Warington"^ also notes the deflocculating 

 effect of NaNOg and refers to it as being particularly noticeable 

 after heavy rains. More recently McGeorge"'' has observed a 

 marked retardation of percolation through Hawaiian soils receiv- 

 ing applications of NaNOg, but attributes this effect to some 

 reaction between the added salt and the organic matter of the 

 soil. Undoubtedly the application of NaNOg to soils under cer- 

 tain circumstances has resulted in a deterioration of the physical 

 condition of the soil, although the NaNOg, as a salt, is in itself 

 a flocculating agent. 



The writer has produced marked deflocculation in the Davis 

 soil b}^ applying NaNOg and subsequently washing the soluble 



67 The Soil, p. 252, 1910. 



68 Loc. cit. 



69 Hawaiian Agric. Exper. Sta, Bull. 35, 1914. 



