SOIL AIR AND SOIL TEMPERATURE lol 



A wet soil is always a cold soil, because it requires about 

 five times as much heat to raise the temperature of a pound 

 of water through one degree of temperature as it does to 

 heat a pound of dry soil to the same extent, and also because 

 when the water becomes warm it evaporates and in so doing 

 removes much heat from the soil. The evaporation of a 

 pound of water from a cubic foot of soil will reduce the tem- 

 perature of the soil about ten degrees Fahrenheit. Provision 

 for having the water drain away from the land in the spring 

 rather than evaporate will make a great difference in the 

 warmth of the soil. A dark soil absorbs more heat than a 

 light colored one. This is enough to make some practical 

 difference in a region having a short growing season. 



Land that slopes to the south absorbs more heat, in the 

 North Temperate zone, than does land having any other 

 slope, and the nearer the slope comes to making a right 

 angle with the sun's rays the more heat it will absorb. 

 An east or west slope receives more heat than does a north 

 slope. For this reason a north slope is especially favorable 

 for grass land, because grass is more injured by midsummer 

 heat than by lack of sunshine. 



196. Control of soil temperature. — As water is the 

 substance in the soil most difficult to heat, it is evident that 

 good drainage, that will remove the excess water derived 

 from melted snow and ice, is the most effective means of 

 warming land in the spring, in order that it shall be fitted 

 for planting. If water can pass out of the soil by under- 

 drainage it then becomes desirable to curtail evaporation, 

 and this may be done by surface tillage. Evaporation of 

 water removes, as we have seen, large quantities of heat. 

 If water can be removed in any other way much heat is 

 saved. In regions having hot spring days the loss by evapo- 

 ration may be so large that more water is removed than is 

 desirable and yet the soil may lack the necessary warmth. 



