324 SOILS; PROPERTIES and management 



The daily and hourly temperature of the air and the 



soil may be fairly constant or rather variable, according 

 to conditions. On days of sunshine, however, consis- 

 tent, changes may be expected. The air temperature rises 



from morning until about two o'clock, when the maxi- 

 mum is reached. It then falls rapidly. The soil, how- 

 ever, does not reach it maximum temperature until 

 later in the afternoon, due to the lagging so apparent in 



soil temperature changes. This lagging is greater in 



the lower layers than at the surface. The following data, 1 

 iaken on a bright day on May L'ti in Germany, illustrate 

 the ordinary differences that may be expected in soil 

 and air temperat nres : — 



HoUBLI Ti;\ii'i;i(\Tn(KS takia in Ckumany ON May '-'<'.. I 

 ON A Loam Son- at l-l\< ii Di 



1 Wollny, E. tJnterauchungen iiber don Kinfluss der 

 Pflanzendeoke und di-v Beschattung auf <li<- PhyrikoUsohen 

 Eigenjohaften <l<-s Bodens. Foriofeu a. d, Geb. 'I. A^ri.-Physik, 

 Band <>, Seite l«>7 -266. 1885. 



