If the soil is open and porous, warm air and warm rains can enter
readily and carry heat to the lower soil.

You have noticed how a pile of stable manure steams in cold weather.
You doubtless know that manure from the horse stable is often used to
furnish heat for hotbeds and for sweet potato beds.

Now the heat which warms the manure and sends the steam out of it, and
warms the hotbed and sweet potato bed, is produced by the decaying or
rotting of the manure. More or less heat is produced by the decay of
all kinds of organic matter. So if the soil is well supplied with
organic matter, the decay of this material will add somewhat to the
warmth of the soil.


HOW SOILS LOSE HEAT

Wet one of your fingers and hold your hand up in the air. The wet
finger will feel colder than the others and will gradually become dry.
This is because some of the heat of your finger is being used to dry
up the water or change it into a vapor, or in other words to evaporate
it.

In the same manner a wet soil loses heat by the evaporation of water
from its surface.

=Experiment.=--Heat an iron rod, take it from the fire and hold it
near your face or hand. You will feel the heat without touching the
rod. The heat is radiated from the rod through the air to your body
and the rod gradually cools. In the same way the soil may lose its