622 EXPERIMENT STATION RECORD. [Vol.35 



covered with growing vegetation. . . . Immediately upon the commencement of 

 growth of the vegetation the temperature of the sod or grass land became 

 decidedly lower than that of the cultivated and uncultivated soil. The maxi- 

 mum difference [was] reached in June and July, when the sod soil at the 7-in. 

 depth, for instance, [was] about 6° colder than the bare soils. This difference, 

 however, [became] smaller and smaller, so that by September it entirely disai)- 

 peared, and by October the order [was] reversed ; the bare plats [became] 

 colder and the sod warmer. The latter continued to have a higher temperature 

 throughout the fall and winter months. . . . 



" In exceptionally cold weather the soil covered with vegetation and a layer 

 of snow had 25° higher temperature than a bare soil at 3-in. depth. Certain 

 topogi'aphic positions have a marked controlling influence upon the soil temper- 

 ature. A southern exposure had about 2° higher average temperature than a 

 northern during the spring and summer months, but during the fall and winter 

 months both locations were equally warm. The soil temperature at a river 

 bank was far below that of the south and north slope during the spring and 

 summer months, but slightly higher during the fall and winter months. The 

 marked influence of the slant of the surface with respect to the position of the 

 sun on the soil temperature is manifested on a cultivated soil with very lumpy 

 and uneven surface. The sides of the lumps or dead furrows facing the sun 

 in the morning had a higher temperature than those shaded." 



Fundamental interrelationships between certain soluble salts and soil 

 colloids, L. T. Sharp (Univ. Cal. Pubs. Agr. Sci., 1 (1916), No. 10, pp. 291-SS9, 

 figs. 3). — It was found in cylinder experiments that clay loam soil, exposed to 

 natural conditions and to which surface applications of solutions of sodium 

 chlorid, sulphate, and carbonate had been made, became very impervious to 

 water, diflicult to cultivate, and manifested the characteristics of a high degree 

 of diffusion. Laboratory studies showed that the salts had moved downward 

 into the lower layers of soil and that only the surface soil was affected. 



" The deflocculated condition resulting from adding certain salts to and 

 subsequently washing them from soils can be reproduced in the laboratory. 

 The deflocculation of soils [so] treated ... is intimately associated with the 

 leaching of the NaCl and Na-SOi down into the lower layers of soil by water. 

 In the case of NaiCOa the leaching process is not so essential for the diffusion 

 of the soil colloids. The addition of NaCl, Na2S04, and NasCOs to the soil when 

 followed with applications of water was particularly effective in diminishing 

 the rate of percolation through the soil so treated. NaCl and NajSOi in con- 

 stant contact with the soil increased the rate of percolation, except when a com- 

 paratively dilute solution of NaCl was slowly passed through the soil for a 

 considerable period of time. 



"The soil treated with NaCl, NaOH, NaaCOa and other salts, followed by 

 leaching with water, yields a suspension in water containing approximately ten 

 times as much solid matter as the same soil washed with water only. A real 

 diffusion in such salt-treated soils seems evident. The soil once diffused by 

 washing out added NaCl requires considerably more salt to completely flocculate 

 it, than does the water-washed soil. Likewise the injured physical condition 

 of such soils is not readily repaired by a second addition of NaCl. 



" The portion of the organic matter of the soil known as humus has little 

 or no connection with the appearance of diffusion in salt-treated, water-washed 

 soils. The diffusion in soils treated as described above seems to be closely asso- 

 ciated with the direct addition of sodium to or with the absorption of sodium 

 by the soil, thereby producing a new silicate complex of a colloidal character in 

 the soil . . . [which] is formed simultaneously with the interchange of ions 

 occurring between the salt and the soil. The washing process serves, in the case 



