SOILS FEETILIZEKS. 619 



" The stndy on radiation showed that color had no effect upon radiation, which 

 is contrary to the common belief, but it had upon absorption; that the different 

 types of soil tended to radiate differently when dry. about the same and more 

 when well moistened and in their natural condition, and that a dry surface or 

 mulch reduced the radiation. In the dry state sand exhibited the highest radiat- 

 ing power, followed by gravel, clay, loam, and peat, respectively. The water, 

 however, had by far the highest radiation capacity of any soil either in the drj' 

 or moist state. 



"When the temperature of the different types of soil (all covered with a 

 thin layer of the same kind of soil in order to eliminate the factor of color and 

 other factors) was studied under field conditions, it was found that they all 

 cooled and froze about the same time in the upper 6 in., but in the spring they 

 thawed and warmed up at different rates. This was attributed to their differ- 

 ent specific heats and to the downward and upward trend of air temperature 

 in the faD and spring respectively. The gravel and sand thawed first, followed 

 by clay 1 day later, loam 2 days later, and peat 10 days later. The tempera- 

 ture of the first two soils rose very rapidly after thawing, while that of the 

 others rose very slowly. AVhen the lower depths of the latter soils had thawed, 

 however, their temperature rose also quite rapidly and finally reached the same 

 degree of magnitude as in the former or lighter soils, and all continued to have 

 almost the same temperature from then on throughout the summer, autumn, 

 and winter. 



" This equal degree of warmth of all the diflferent types of soil during the 

 warm part of the year and especially during the summer season was believed 

 to be due largely to the thin layer of the same kind of soil with which they 

 were all covered. This thin layer of soil tended to equalize the amount of 

 heat that penetrated into these different kinds of soils by eliminating the dif- 

 ferences of their color and by equalizing, to a large extent, the amount and 

 rate of evaporation of their moisture. . . . 



" Of aU the different types of soil, sand showed the greatest amplitude and 

 was followed by gravel, clay, loam, and peat, respectively. The greatest 

 monthly fluctuation for all soils occurred in June and the least in February. 



" The different meteorological elements played a great part in the tempera- 

 ture of the soils, but on account of the complexity of their behavior it was difla- 

 cult to trace the direct influence of all of them. . . . 



" The results from the investigation on the effect of organic matter on soil 

 temperature showed that the rate of thawing was about proportional to the 

 amount of organic matter present, but that after thawing the temperature of 

 the soils containing 2.01, 3.32, 5.47, and 6.95 per cent organic matter was higher 

 throughout the summer than the temperature of the white sand and of the 

 peat. The temperature of these last two soils was about the same during 

 the warmer part of the year, but during the cold seasons the peat had a higher 

 temperature. The magnitude of the amplitude of all these soils behaved in 

 the same order as the average temperature. 



" The conditions of cultivation, noncultivation. and sod had a very distinct 

 effect upon the soil temperature. During the winter all three plats had about 

 the same temperature with a small difference in favor of the sod. In the 

 spring the sod and uncultivated plats thawed first and the cultivated plat 

 about one day later, at the 7-in. depth. The temperature of the sod plat rose 

 several degrees above that of the other two plats and continued to be in 

 excess until the plants had made a considerable grovrth, and then it dropped 

 below that of the two bare plats, and remained so throughout the summer 

 months, but when the cold period came the order was reversed, the temperature 

 of the bare plats fell below that of the sod plat and continued to be lower 



