676 STATE BOARD OV AGRICULTURE. 



and all continued to have almost the same temperature from then on 

 throughout the summer, autumn and winter. 



This equal degree of warmth of all these different types of soil dur- 

 ing the warm part of the year and especially during the summer sea- 

 son, was believed to be due largely to the thin layer of the same kind 

 of soil with which thev were all covered. This thin laver of soil tended 

 to equalize the amount of heat that penetrated into these different kinds 

 of soils by eliminating the differences of their color and by equalizing, 

 to a large extent, the amount and rate of evaporation of their moisture. 

 If it had not been for this external layer of soil these different soil 

 types would have taken in unequal amounts of heat and consequently 

 their temperature would have been different. This point, however, is 

 now under investigation. 



Of all these different types of soil, sand showed the greatest ampli- 

 tude and was followed by gravel, clay, loam, and peat, respectively. 

 The greatest monthly fluctuation for all soils occurred in June and the 

 least in February. 



The different meteorological elements played a great part in the tem- 

 perature of these soils, but on account of the complexity of their be- 

 havior it was difficult to trace the direct influence of all of them. The 

 influence of the most important ones w^as discussed in detail. 



The results from the investigation on the effect of organic matter on 

 soils temperature showed that the rate of thawing was about propor- 

 tional to the amount of organic matter present, but that after thaw- 

 ing the temperature of the soils containing 2.01, 3.32, 5.47 and 6.95% 

 organic matter was higher throughout the summer than the temperature 

 of the white sand and of the peat. The temperature of these last two 

 soils was about the same during the warmer part of the year, but during 

 the cold seasons the peat had a higher temperature. The magnitude 

 of the amplitude of all these soils behaved in the same order as the aver- 

 age temperature. 



The conditions of cultivation, noncultivation and sod had a verv dis- 

 tinct effect upon the soil temperature. During the winter all three 

 plots had about the same temperature with a small difference in favor 

 of the sod. In the spring the sod and uncultivated plots thawed first 

 and the cultivated plot about one day later, at the 7 inches depth. The 

 temperature of the sod plot rose several degrees above that of the other 

 two plots and continued to be in excess until the plants had made a 

 considerable growth, and then it dropped below that of the two bare 

 plots, and remained so throughout the summer months, but when the 

 cold period came the order was reversed, — the temperature of the bare 

 plots fell below that of the sod plot and continued to be lower through- 

 out the second winter. The temperature of the cultivated j)lot rose slight- 

 ly higher than that of the uncultivated, after thawing, and continued to 

 be slightly higher during the early part of the spring season or up to 

 about the middle of May, and then the uncultivated ])lot became the 

 warmer and remained so throughout the whole summer. Diu'ing the fall 

 both plots had about the same temperature with a slight difference in fa- 

 vor of the uncultivated plot. The difference in temperature between these 

 two plots was explained upon the following general fads: (1) Different 

 rate of evaporation; (2) different rate of heat conductivity; (3) differ- 



