soil, temperature, importance
All soil reactions such as plant growth go through a wide range in temperature. Direct solar radiation is the chief source of heat to solls. Difference in texture, structure and organic matter determine the moisture capacity of soils and influence their ability to absorb and transmit heat. Dry soils, with air in pores, have higher resistance to heat transfer than moist soils. Water is a better heat conductor than air. Heat usually moves from the surface downward as atmospheric temperature increases and from lower soil layers upward as it decreases. Changes in soil temperature are less variable than changes for atmospheric temperatures. Difference in temperature of oils for the same degree of latitude is caused by variations in colour, moisture content and vegetative colour. Organic matter increases the amount of soil water and soils get a darker colour. Only when the surface becomes dry, soil gets a lighter colour. Wet soils are cold and it is difficult to warm them up in spring. A bare soil heats more quickly and has a higher temperature in summer - than a soil protected by vegetation. The vegetation acts as an insulator, reducing absorption and loss of heat through radiation. When soil is protected by vegetation, leaves or snow, heat is retained better and the soil remains warmer during the winter. Control of soil temperature is a matter of soil moisture content. Excess water must be removed, if possibly, by drainage. This will reduce evaporation, conserve heat and lower specific heat thus decreasing the heat necessary to raise the soil temperature.
