SOIL HEAT FLUX

Authors: Sauer, Thomas; HORTON, ROBERT - IOWA STATE UNIVERSITY

Submitted to: Micrometeorological Measurements in Agricultural Systems
Publication Type: Book / Chapter
Publication Acceptance Date: 6/4/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soil temperature has a strong impact on biological and chemical processes in the soil like residue decomposition and nutrient availability. Most crops also have a range of soil and air temperatures in which they grow best. The amount of heat that enters or leaves the soil is called the soil heat flux. Soil heat flux has been measured in many soils and for many crops. Four methods have been developed to measure soil heat flux but the plate method is by far the most popular. Specially-designed, calibrated plates are placed in the soil along with soil temperature sensors to determine soil heat flux. The advantage or the flux plate method is that it is simple. However, care must be taken to avoid errors with this method. Other methods and estimation techniques are available and are also discussed. This research highlights the limitations of the available methods for measuring soil heat flux and should help scientists improve the accuracy of their soil heat flux measurements.

Technical Abstract: Climatic conditions on the earth's surface are in part a function of varying physical position (elevation, latitude, and aspect) and the influence of large-scale meteorological forces such as air and ocean currents. Properties of the surface soil layer including color, water content, texture, and density affect the partitioning of incident radiation and how much energy is used to evaporate water, warm the air above the ground, or warm the soil. The amount of thermal energy that moves through an area of soil in a unit of time is the soil heat flux or heat flux density. The ability of a soil to conduct heat determines how fast its temperature changes during a day or between seasons. Soil temperature is a key factor affecting the rate of chemical and biological processes in the soil essential to plant growth. Soil heat flux is important in micrometeorology because it effectively couples energy transfer processes at the surface (surface energy balance) with energy transfer processes in the soil (soil thermal regime). Four methods, flux plate, calorimetric, gradient, and combination, are presented for the measurement of soil heat flux. Recommended procedures, advantages, and limitations are discussed for each method. The flux plate method is simple to employ and is currently the most commonly used technique. Nonetheless, there are important factors to consider to ensure that accurate data are obtained with this method. Techniques to estimate soil heat flux in the absence of direct measurements are also discussed.