. Means of Controlling Soil Temperature. 221 



In the table above are given the observed differences 

 in temperature of a well drained sandy loam and an ad- 

 jacent black marsh soil, not well drained, the observa- 

 tions being taken simultaneously and the differences in 

 temperature being due largely to differences in the rate of 

 evaporation in the two cases. 



MEANS OF CONTROLLING SOIL TEMPERATURE. 



269. Effect of Rolling on Soil Temperature. In the spring 

 of the year, when the soil is naturally cold, the first effect 

 of rolling is to cause the soil to warm deeply at a more 

 rapid rate, and Fig. 62 shows how strong this influence 

 may be. In extreme cases the soil temperature, at 1.5 

 inches below the surface, has been found as much as 10 F. 

 higher than on entirely similar and adjacent ground, not 

 rolled, and 6.5 at 3 inches below the surface. This dif- 

 ference is due to the better conducting power of the soil, 

 on account of its firmer texture, and is in spite of the loss 

 of heat due to greater evaporation which takes place from 

 the rolled surface. 



FIG. 62. Showing the effect of rolling on soil temperature. 



The average difference in temperature of soil on eight 

 Wisconsin farms, at the season when oats were germinat- 

 ing, was found to be as given in the table below: 



