Abstract
A method of obtaining continuous records are discussed.
The relations between surface and subβsurface temperatures are briefly considered, and then, in more detail, the interβdependence of soil surface and air temperatures is examined. At all seasons the soil temperature is in phase with solar radiation whereas the maximum air temperature is delayed; for air maxima below 52Β° F. the daily range of soil surface temperature is approximately the same as that of the air temperature. Above this threshold the soil surface maximum increases twice as rapidly as the air maximum. Using this value of the air maximum, 5244F., to divide the year into two seasons, it is found that the winter and summer periods so separated are the same as those previously obtained form the criterion:βSeasonal evaporation is equal to or less than that from an open water surface. Interest is primarily centred on the summer season, in which the soil surface temperature exceeds that of the air for a considerable part of the day, and for a rainless summer period of t days an anticipated relation of the form Ξ£E=at1/n, where n=3, a is a constant and Ξ£E=the total evaporation, is confirmed from the Rothamsted records.
The effect of the diurnal oscillation of surface temperature on germinating seed is briefly discussed.