Physical Properties of Soil
Soil Temperature
The main source of heat energy for soil is solar radiation, which determines the thermal regime of soil and growth of plants. Soil temperature is an important physical property that regulates life processes of soil biota including plants. Soil temperature may affect plant growth through its effects on many physical, chemical, and biological processes of the soil and physiological processes of plants. Soil temperature is critical to growers because it affects seed germination and root growth, as well as water and nutrient availability and biological activity. Each plant species has a range of proper temperatures for germination, with a minimum below which seed does not germinate, an optimum for best and most rapid germination, and an upper range. Above that, seeds may fail to germinate, die, or enter a dormant state. In field growing, soil temperature determines planting date. Cool-season plants such as peas that can germinate in cool soil can be planted early in the spring, while warmer season crops must be planted later. Root growth also depends on soil temperature, with species-specific responses.
Conditions Affecting Soil Temperature
The temperature a soil attains depends on (a) heat supply—how much heat reaches the soil surface and (b) dissipation of heat—what happens to that heat within the soil mass. The amount of solar radiation that a soil receives, absorbs, and transmits depends on a number of conditions.
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