PHYSICAL PROPERTIES OF SOILS 47 



cooled, and if the heat for evaporation is all furnished 

 by the surrounding soil, it materially lowers the soil's 

 temperature and unfavorably affects crop growth. In 

 the early spring, drying winds may temporarily lower 

 the soil temperature by hastening evaporation. Much 

 heat is unnecessarily lost in evaporating excessive 

 amounts of water which should be removed by good 

 systems of drainage. 



41. Temperature of Drained and Undfained Land. 



The surface of well-drained land is usually several 

 degrees warmer than that of poorly drained land. Water 

 being a poor conductor of heat, it follows that soils 

 which are saturated are slow to warm up in the spring. 

 At a depth of 2 or 3 feet the difference in tempera- 

 ture between wet and dry soils is not marked. It is to 

 be observed that with proper systems of drainage the 

 surplus water is removed from the surface soil and 

 stored up in the subsoil for future use by the crop, and 

 at the same time the temperature of the surface soil is 

 raised, thus improving the conditions for growth. The 

 relation of drainage to the temperature and proper 

 supply of water for crop growth, receives too little con- 

 sideration in field practice. When the land is well 

 drained, and receives early cultivation, the conditions 

 are best. 



42. Color of Soils and Absorption of Heat. All dark- 

 colored soils have greater power of absorbing heat 



