EXPERIMENT STATION BULLETINS. 691 



ever, it is the thin layer of dry soil formed at the surface that plays the 

 leading role rather than the entire tilled layer. 



Again in such abnormal soil as peat heat conductivity might predomi- 

 nate and cause a slightly greater cooling at the upper one or two inch 

 depths than in the mineral soils. 



The radiating power of the various types of soil was also investigated. 

 It was discovered that color had no effect upon radiation, which is con- 

 trary to the popular belief, — but it had a tremendous influence upon the 

 absorption of the solar energy. The various classes of soil radiated 

 slightly differently when in the dry condition, about the same and slightly 

 more when well moistened and that a dry surface or mulch reduced 

 somewhat the amount of radiation. In the dry state sand exhibited the 

 highest radiating power, followed in order by gravel, clay, loam, and 

 peat, respectively. The water, however, manifested far greater radiating 

 capacity than any soil either in the dry or moist condition. The deduc- 

 tion was made that as far as radiation is concerned all the diverse classes 

 of soil lose heat practically to the same extent and that the difference iu 

 minimum temperature that is noted in them in the morning or during a 

 period of sudden cold weather is attributed to the difference in their 

 total specific heat. 



It was discovered that a high concentration of soil solution tended to 

 raise the soil temperature during the insolation by reducing the amount 

 of evaporation and that during the winter it diminished the lowering 

 of the freezing point and hastened the rate of thawing. 



The study on the effect of decomposition of manure on the temperature 

 of soil showed that large applications of this material in the fresh state 

 could raise the soil temperature appreciably, but considering the small 

 amounts that are commonly applied to the soil under field conditions 

 and that a rather high temperature is required for the decomposition 

 process, it was concluded that the amount of heat gained by the soil from 

 this source is absolutely insignificant. 



The field studies on the effect of cultivation, noncultivation, and sod 

 upon soil temperatures indicated that during the winter the temperature 

 of the soil under these three cultural conditions was about the same with 

 a slightly higher degree in favor of the sod. In the spring all the soils 

 thawed practically simultaneously and maintained identical average tem- 

 perature until the vegetation in the sod plot commenced to grow when 

 its temperature began to be lower than that of the other plots, and con- 

 tinued to be smaller until in the fall when the order was reversed. The 

 temperature of the cultivated and uncultivated plots was the same 

 throughout the year except during the spring and summer months when 

 the uncultivated plot had a slightly higher average temperature than the 

 cultivated. 



The results from the investigation on the influence of organic matter 

 on the soil temperature showed that those soils containing 1.8, 2.01, 

 3.32, 5.47j and 6.95% of organic matter thawed practically simultaneously 

 and peat several days later. After complete thawing, however, the peat 

 and the soil containing the least percentage of organic matter and which 

 had a white surface, reached and maintained an appreciably lower aver- 

 age temperature than the other soils throughout the spring and summer 

 months up until in the fall and then this difference disappeared and 



