if* REPORT OF THE AGRICULTURAL RESEARCH INSTITUTE 



conclude that they would apply to soils general- 

 ly in India. 

 (vi) The temperature of the soil near the surface, 

 (down to 3" or 4") is above the mean tempera- 

 ture for only about 8 hours and below it for 

 about 16 hours. 



(vii) The lag in temperature change is about 2 hours 

 at 3" deep and about 8 hours at 18" deep. 



(viii) A change in the specific heat and conductivity 

 of the soil due to change of proportion of water, 

 does not always affect the maxima and minima. 

 During the monsoon period when the soil con- 

 tains very much more water than during the 

 dry season, and when both its specific heat and 

 conductivity are consequently very much 

 greater, the relation between soil temperature 

 and air (shade) temperature remains substan- 

 tially unaltered. That a wet soil requires con- 

 siderably more heat to raise its temperature 

 1° C. than does a dry soil is of course well 

 understood, but apparently the period of ex- 

 posure is sufficiently great to allow the soil's 

 temperature to assume during the day or the 

 night the same relation to the air temperature 

 whether it is wet or dry ; the effect of increased 

 conductivity counterbalancing that of increased 

 specific heat. If, however, a heavy shower of 

 rain falls on the desiccated soil of the hot 

 weather, the conditions are different. Such 

 showers are accompanied by a marked fall of 

 air maximum temperature and the soil-maxi- 

 mum falls in a corresponding degree. But the 

 air humidity at this season rapidly falls after 

 such showers and evaporation of moisture from 

 the soil increases very greatly, causing a marked 

 change in the soil-minimum. 



(b) In cropped land. The effect of a covering crop on 

 the soil-temperature is naturally very marked, 



