320 SOILS: PROPERTIES AND MANAGEMENT 



Wollny found also that the soil temperature on the 

 southward slopes varied according to the time of year. 

 For example, the southeasterly inclination was highest 

 in the early season, the southerly slope during mid-season, 

 and the southwesterly slope during the fall. A southeast- 

 erly slope is usually preferred by gardeners. Orchardists 

 also pay strict attention to aspect, as it often is a factor 

 in susceptibility to sun scald and other diseases. 



King, in comparing a red clay with a southerly slope 

 of 18° to that on a level on July 21, obtained the follow- 

 ing results : — 



It is apparent immediately that the influence of slope 

 is not confined to the surface, but, owing to conduction 

 and convection, is felt to a considerable depth. Slope, 

 therefore, together with moisture control, becomes a 

 dominant factor in the heat relations of a soil. This is 

 particularly true with specialized crops, with which the 

 early w r arming of the soil is important. A normally early 

 soil may become late because of exposure, or a naturally 

 late soil may become earlier due to an inclination south- 

 ward. Slope many times is a dominant factor in the 

 adaptation of crop to soil. 



227. Heat supply and its effects. — The direct heat 

 supply is without doubt the controlling factor in soil 



