CHAPTER VII[ToC]
Soil Temperature
We learned that roots need heat for their growth and development. Now what is the relation of the different kinds of soil toward heat or what are their relative powers to absorb and hold heat?
Experiment.—Some days before this experiment, spread on a dry floor about a half bushel each of sand, clay and decayed leaf mould or black woods soil. Stir them occasionally till they are thoroughly dry. When they are dry place them separately in three boxes or large flower pots and keep dry. In three similar boxes or pots place wet sand, wet clay, and wet humus. Place a thermometer in each of the soils, placing the bulb between one and two inches below the surface ([Fig. 31]). Then place the soils out of doors where the sun can shine on them and leave them several days. If a rain should come up protect the dry soils. Observe and make a record of the temperatures of each soil several times a day. Chart the average of several days observations. Fig. 32 shows the averages of several days observations on a certain set of soils.
It will be noticed that the temperature of the soils increased until the early part of the afternoon and after that time they lost heat.
FIG. 31—SOIL TEMPERATURE EXPERIMENT.
Thermometer in pot of soil.[ToList]
HOW SOILS ARE WARMED
Experiment.—Hold your hand in bright sunlight or near a warm stove or radiator. Your hand is warmed by heat radiated from the sun or warm stove through the air to your body. In the same manner the rays of the sun heat the surface of the soil.