810 STATE BOARD OF AGRICULTURE. 



peratnre Avas perceptibly influenced. Since the heat traveled in both 

 opposite directions, then a lateral palh of 20 feet was kept warm, but 

 the degree of waraith, of course, decreased inversely wilh the distance. 



As already stated, these temperature records were taken at 3-inch 

 depth. At a lower depth, the magnitude of temperature would be greater 

 at the respective distances. 



It will be readily realized that the foregoing data are of considerable 

 practical importance. 



CONCLUSIONS. 



The soil temperature has been studied at this Station for four years. 

 The results of the investigation for the first year have already been pub- 

 lished in a previous report. In the present report there are presented 

 the data obtained in the following three years and the general conclusion 

 that might be deducted from the entire investigation. 



The number of factors influencing the temperature of soil is very great. 

 These factors may be divided into two main groups, (1) the intnnsic, 

 and (2) the extei*nal. The intrinsic factors are those contained by the 

 soil and include the specific heat, heat conductivity, radiation, water 

 content, evaporation of water, concentration of soil solution, topographic 

 position, condition of surface, etc. The external factors comprise the 

 metereological elements and include the air temperature, sunshine, wind 

 velocity, barometric pressure, rainfall, etc. The temperature of soil, 

 therefore, is controlled by and is the resultant of these intrinsic and ex- 

 ternal factors. Part of these factors of both groups favor a high soil 

 temperature and part a low, and whichever class predominates de- 

 termines the degree of soil temperature at any time. 



The intrinsic factors play a passive and the external an active role. In 

 other words the intrinsic factors tend to remain passive but are acted 

 npon by the external factors. Hence, the degree of soil temperature is 

 almost wholly controlled by the external factors and especially the air 

 temperature, but modified by the intrinsic factors. Inequality in tem- 

 perature, therefore, in the different kinds of soil during the same day will 

 depend upon the intrinsic factors but variation in temperature in any 

 soil in succeeding days or seasons will depend upon the external factors. 



All soils possess practically the same intrinsic factors but in different 

 degree. Witness, for example, the great disproportionality between sand 

 and peat. Indeed these soils possess most of the intrinsic factors in 

 opposite degree. Thus for example, peat has black color, low heat 

 conductivity, a high water-holding capacity, etc. These same properties 

 exist in sand in almost exactly the opposite degree. Hence a law of com- 

 pensation intervenes. 



This unparallelism of the various intrinsic factors in the different 

 kinds of soil tends to give the latter an equal degree of average tem- 

 perature. In other words each type of soil possesses the various intrin- 

 sic factors in a compensating or neutralizing degree and consequently 



