644 STATE BOARD OF AGRICULTURE. 



prevention of the cold currents of air from coming in contact with the 

 surface soil and thereby cooling it; second, the layer of dead vegetation, 

 and especially when it is quite thick, is porous and the spaces are filled 

 with air. This air being a very poor conductor of heat, does not trans- 

 mit very rapidly the heat of the soil to the air above, and as a result 

 the soil loses its heat less rapidly than if it were unprotected, l-^ven 

 in the summer time, the vegetation, though it is growing, acts as a 

 blanket, and prevents the loss of heat, as evidenced by the very unappre- 

 ciable variation that exists between the daily maximum and mininium 

 temperature. 



That the vegetation acts as a blanket and tends to prevent the loss 

 of heat from the soil was confirmed also by the following experiment: 

 A plot was covered with straw, and its fall of temperature was com- 

 pared with that of a plot which remained unprotected. The results 

 show that the uncovered soil froze at the depth of 7 inches on Decem- 

 ber 11, while that covered with straw froze on February 14th. On 

 certain very cold nights the ground covered with straw remained as 

 much as 10° F. warmer than the unprotected ground. 



What is true of the retarding effect of vegetation on the cooling of 

 the soil in the fall and winter applies also to its warming in the spring. 

 If the ground has a very thick layer of dead vegetation the slow rate 

 of warming will be evident. This does not necessarily mean, however, 

 that the soil will have a low daily average temperature because, while 

 the vegetation, which acts as a blanket, will prohibit a very high rise of 

 temperature during the day it will equally prevent a very low fall of 

 temperature during the night, and since the trend of the temperature is 

 upward, the sod land or tlie land covered with straw will have a higher 

 temperature during the early spring, especially during rapid alternation 

 of cold and warm days, than a bare and uncultivated soil, which on 

 account of its condition, permits greater and more nearly proportional 

 extremes of temperature. These facts find confirmation in the present 

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

 on the same day and the temperature of the former yjlot rose several 

 degrees higher than that of the latter, and also of the cultivated plot, 

 within the next few days, as has already been shown. TTufortunately the 

 thermographs were removed at this time (April) for repairs and conse- 

 quently it cannot be stated how long the temperature of the sod land 

 would have continued to be higher than that of the other plots and 

 es])ecially of the uncultivated plot. The uninterrupted i^ecords of the 

 second spring, however, sup])]y the data for this point and show that 

 the temperature of the sod plot remained above that of the other plots 

 until the beginning of ]\Iay, when the vegetation had grown consider- 

 ably. The second spring's results also show that the sod plot thawed 

 about the same time as the other plots and that its temperature rose 

 above that of the latter. Its average increase of temperature over the 

 cultivated plot was 1.82° F. and over Ihc luicultivatod ])lot 2.:>4° F.. for 

 the month of A])ril. Evidently the results of the second spring agree 

 very well with those of the preceding spring. 



The interesting question that suggests itself in connection with the 

 temperature of soils thickly covered with crops is whether the plants 

 themselves conduct heat into the soil, sinro the temperature of the latter 

 is far below that of the air. 



