814 STATE BOARD OF AGRICULTURE. 



cold. Both of these chisses of waves penetrated the soils in gradual 

 increase of intensities of temperature. 



The rate at which the maximum and niininium temperature waves 

 traveled through an,y particular soil tended to follow apj)r()ximately a 

 mathematical law. This law may be stated thus: The lag of the maxi- 

 mum and minimum epochs tended to be approximately 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 indeed the geometric progression laAV. This law may 

 be stated as follows: The diurnal-nocturnal amplitude of oscillation of 

 temperature decreased in geometric progression as the depth increased 

 in ai-ithmetric progression, in all the different types of soil. 



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

 was added ditferent 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 S])ring 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 a\erage temperature than the other 

 soils which were treated with various percentages of peat. 



In the spring all the treated and untreated mineral soils would thaw 

 first and approximately at the same time, the peat, however, would thaw- 

 last and several days later. 



The amplitude of temperature at the 3 and 5-inch depths was high but 

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

 comparatively low in the peat. 



The higher average temperature of the sand to which was added various 

 quantities of peat during the spring months after thawing, and in the 

 summer months, over the sand which received no peat and had white- 

 colored surface, and the peat, goes to prove that the white color reflected 

 so much of the solar energy that it kept the temperature of white sand 

 low in spite of the many other intrinsic factors which are favorable for 

 a high temperature. On the other hand a large amount of evaporation 

 of water predominated over the high heat absorptive power of the black 

 color and consequently kept the temperature of the peat also low. Soils, 

 however, possessing these properties in medium degree maintained a 

 higher average temperature dnring the same periods. 



The general belief that there exists a large difference in temperature 

 between a cultivated and uncultivated soil is much exaggerated. The 

 observations conducted for four years show that the uncultivated soil 

 had practically the same or only a few tenths of a degree higher tem- 

 perature during the spring months than the cultivated, and only about 

 1°F 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 tem- 

 perature between thse two bare soils and one covered with growing 

 vegetation. The data show that immediately upon the commencement 

 of growth of the vegetation the temperature of the sod or grass land 

 w-ould become decidedly lower than that of the cultivated and unculti- 

 vated soil. The maximum difference would be reached in June and July 

 when the sod soil at the 7-inch depth for instance would be about 6°F 



