SOIL TEMPERATURE 6 I 



sorbed more heat, but they also held more water, 

 and, therefore, lost more heat by evaporation. 



Of the dry soils, then, the humus averaged warm- 

 est, because, on account of its dark color, it absorbed 

 heat more readily than the others. The dry clay 

 was warmer than the sand on account of its color 

 and compact texture. Of the wet soils the sand 

 was the warmest, because, on account of its holding 

 less moisture, less heat was required to raise its 

 temperature and there was less cooling by evapora- 

 tion, while the other soils, although they absorbed 

 more heat than the sand, lost more on account of 

 greater evaporation, due to their holding more 

 moisture. Why are sandy soils called \varm soils 

 and clay soils said to be cold? 



How may we check losses of heat from the soil? 



If we make a mulch on the surface of the soil 

 evaporation will be checked and therefore loss of 

 heat by evaporation will be checked also. The 

 mulch will also, check the conduction of heat from 

 the lower soil to the surface and therefore check 

 loss of heat by radiation from the surface. 



VALUE OF ORGANIC MATTER 



Figure 33 illustrates a simple way to show the 

 value of organic matter in the soil. The boxes are 

 about twelve inches square and ten inches deep. 

 They were filled with a clay subsoil taken from the 

 second foot below the surface of the field. To the 

 second box was added sufficient commercial fer- 



