504 



STATE BOARD OF AGRICULTURE. 



TABLE -.—COMPARISON OF HEAT CONDUCTIVITY OF NATURAL SOILS UNDER FIELD 



AND LABOR.'VTORY CONDITIONS. 



This table not only shxiws the close agreement in the order of the heat 

 conductivity of Ihe different types of soil as measured in their natural 

 state under field and laboratory conditions, but also the more important 

 fact that the magnitude in both cases is very much the same, except in 

 peat in which case there is quite a disagreement. 



It must be stated here that these different types of soil under field 

 conditions were all covered Avith a very thin laver of a sandy soil so 

 as to eliminate the factor of color. This layer of soil incidently per- 

 formed several other functions, such as the prevention of formation of 

 cracks on the top of the clay and loam soils, the tendency for equalizing 

 Ihe rate of eva])oration among the different soils, etc. As a result, the 

 heat conduction values obtained both under laboratory and field condi- 

 tions approach more closely to the true heat conducting power of these 

 soils. If these different soil types were not covered with the thin 

 layer of the sandy soil the clay and loam would crack on the surface 

 and these cracks would increase the rate of air diffusion and thereby 

 decrease the difference in magnitude of conducting power between the 

 sand and gravel and the clay and the loam. 



In connection with the observations made on the heat conductivity 

 of the different types of soil under field conditions, might be mentioned 

 the similar studies made on cultivated, uncultivated and sod land. As 

 will be stated later, the original object of this experiment was to as- 

 certain the effect of these whollv different soil managements on the 

 soil temperature. The temperature of. these plots was taken by means 

 of thermographs, the bulbs of which were placed at two different 

 depths, 7 inches and 20 inches respectively. The results obtained are 

 summnrized below. The figures show Ihe number of hours required for 

 the heat to arrive at the 7" depth, as indicated by the rise of 

 the temperature, from the time the air temperature began to ascend. 



TABLE 8.— HEAT CONDUCTIVITY OF FIELD SOILS UNDER CULTIVATED, UNCULTIVATED 



AND SOD CONDITIONS. 



Date. 



July 27 



Aupust 5 . . . . 

 August 26. . . 

 August 27. . . 

 September 23 . 



Depth. 



Unculti- 

 vated. 



4.0 hrs. 

 4.0 hrs. 

 3.30 hrs. 

 4 hrs. 

 3.30 hrs. 



Culti- 

 vated. 



5.0 hrs. 

 5.0 hrs. 

 5.0 hrs. 

 5.0 hrs. 

 4.30 hrs. 



Sod. 



hrs. 

 30 hrs. 

 hrs. 

 30 hrs. 

 bia. 



It will be ^ccu in every observation that the uncultivated ground al- 

 lowed the heat to pass through it fastest and was followed in order by 



