550 STATE BOARD OF AGRICULTURE. 



their dillerent specific beats: the light soils with the smallest heat 

 capacity cooled the most and the heavier soils with the largest capacity 

 for heat the least. The average between the maximnm and minimum 

 temperature ought to give the same temi>eralure lor all the soils. That 

 is just what has been obtained. 



The temperature of the peat during the sununer months is very inter- 

 esting and deserves special attention. This material has not only the 

 greatest water holding eajjacity of any other soil, but also the ability 

 to absorb considerable moisture from the air, and on account of the 

 slow but continuous evaporation of the water the temperature of this 

 soil is kept low or much lower than that of other soils, as will be shown 

 in a subsequent experiment, but when it is covered with a thin layer 

 sand, as was done in the present experiment, its temperature is higher 

 that that of the other dilTerent types of soil. A thin top dressing of 

 sand, therefore, ai)pears to increase the temperature of jieat soils. This 

 seems to be true also with the other heavy soils. 



It would seem, then, from this study, that the greatest difference 

 in temperature between the different types of soil exists in the early 

 spring during thawing and inmiediately afterwards. Perhaps this is 

 the most important period of the year from the practical or agricul- 

 tural ])oint of view, and especially where planting in the spring has 

 to be done very early, because at this season small differences in the 

 temperature will make great differences in the rate of germination of 

 seed and in the rate of growth of plants. The differences in the present 

 case are quite appreciable. As has already been mentioned, the gravelly 

 and sandy soils not only thawed first followed by clay 1 day later, 

 loam 2 days later, and peat 10 days later, but the temperature of the 

 former soils rose immediately about 10° or more above that of the 

 other soils. It took the clay soil 11 days to attain the same tempera- 

 ture as the light soils, the loam 12 days and the peat 32 days. Since 

 this difference in the rate of thawing and rising of temperature in the 

 various soil types is largely due to their different water content, and 

 hence to the sjjecific heat of water, the conclusion is irresistable that 

 water is the most predominal controlling agent of soil temperature at 

 this j)eriod and is of disadvantage. This disadvantage, however, becomes 

 an advantage during the rapid fall of the air temperature in the cold 

 parts of the year. 



Special attention might also be called to the thawing of the 18-inch 

 depth of peat 7 days before the 12-inch. This is intt^resting because it 

 tends to confirm the general theory that the soil receives in the winter 

 some heat from the interior of the earth. 



EFFECT OF THE METEOROLOGICAL ELEMENTS ON THE SOIL TEMPERATURE. 



So far the temperature of the different types of soil has been con- 

 sidered as affected or controlled by the difference of their intrinsic or 

 soil factors. It will now be well to consider the temperature of these 

 soils in relation to the external or meteorological elements which are 

 air temperature, sunshine, wind pressure, precipitation, dew point, 

 cloudiness, etc. These meteorological elements are very complex as to 

 their behavior and make it very difficult to see the influence of all of 



