1916] SOILS FERTILIZERS. 621 



the peat. Whenever rapid and sudden changes of air temperature occurred the 

 sand and gravel warmed and cooled the fastest, followed by clay, loam, and 

 peat, respectively. The equilibrium [was] quickly reestablished. The degree 

 of amplitude was greatest in sand and gi-avel, somewhat smaller in loam and 

 clay, and least in peat. The highest fluctuation occurred in summer and the 

 lowest in winter. The maximum temperature was approximately the same for 

 all types of soil, after complete thawing had taken place, but the minimum 

 varied somewhat ; it was lowest in sand and gravel, slightly higher in clay and 

 loam, and highest in peat. . . . 



" When the same types of soil were not covered with a thin layer of sand but 

 their natural surface was allowed to be exposed to the atmosphere . . . their 

 average temperature . . . was about the same during the fall and winter 

 months, but varied somewhat during the spring and summer months. During 

 the latter seasons the sand and gravel [had] the highest average temperature, 

 the clay and loam slightly lower, and peat the lowest. ... In the spring the 

 peat [did] not thaw and its temperature [did] not approach that of the mineral 

 soils after complete thawing as rapidly as when its surface was covered with 

 the thin layer of sand. Besides the average temperature the order of the 

 maximum and minimum temperature [was reversed] in the various types of 

 soil under the to'O surface conditions. . . . 



" The average air temperature was lower than that of any soil at the 2-, 4-, 

 6-, 12-, and 18-in. depths, throughout the year. . . . The maximum tempera- 

 ture of all the soils at i-in. depth was about 30° F. higher during hot and clear 

 days than that of the air at an elevation of 4 ft. The minimum temperature of 

 all the soils except peat, however, immediately at the surface was only about 

 1 or 2° higher, as a monthly average, than that of the air at a height of 4 ft. 

 . . . Unless the various soils were frozen they always had a gradient of tem- 

 perature at their adjacent depths [which], however, reversed itself between day 

 and night during the warm part of the year to the depth that the diurnal- 

 nocturnal amplitude of oscillation of temperature extended. . . . 



" The rate at which the maximum and minimum temperature waves traveled 

 through any particular soil tended to follow approximately a mathematical law. 

 . . . Thus, the lag of the maximum and minimum epochs tended to be approxi- 

 mately proportional to the depth in all the different types of soil. 



" The decrease of the diurnal-nocturnal amplitude of temperature with the 

 increase in depth also followed a mathematical law in all the diverse types of 

 soil and the geometric progression law. . . . The diurnal-nocturnal amplitude 

 of oscillation of temperature decreased in geometric progression as the depth 

 increased in arithmetric progression, in all the different types of soil. 



" The four years' data obtained on the temperature of sand to which was 

 added different percentages of organic matter (peat) showed that during the 

 fall and winter months all these soils had approximately the same degree of 

 average temperature, but in the spring and summer months it varied somewhat. 

 During the latter months the sand which received no organic matter and had a 

 white colored surface and the peat had about the same and lower average tem- 

 perature than the other soils which were treated with various percentages of 

 peat. . . . The amplitude of temperature at the 3- and 5-in. depths was high, 

 but approximately of equal degree in all the treated and untreated soils, but 

 comparatively low in the peat. . . . 



" The uncultivated soil had practically the same or only a few tenths of a 

 degree higher temperature during the spring months than the cultivated and 

 only about 1° higher during the summer months. During the fall and winter 

 months there was hardly any difference. There did exist, however, a very 

 marked difference in average temperature between the two bare soils and one 



